View source for Nickel compounds

{{short description|Any chemical compound having at least one nickel atom}}
'''Nickel compounds''' are chemical compounds containing the element [[nickel]] which is a member of the [[group 10 element|group 10]] of the [[periodic table]]. Most compounds in the group have an [[oxidation state]] of +2. Nickel is classified as a [[transition metal]] with nickel(II) having much chemical behaviour in common with iron(II) and cobalt(II). Many salts of nickel(II) are [[isomorphous]] with salts of [[magnesium]] due to the [[ionic radii]] of the cations being almost the same. Nickel forms many [[coordination complex]]es. [[Nickel tetracarbonyl]] was the first pure metal carbonyl produced, and is unusual in its volatility. [[Metalloprotein]]s containing nickel are found in biological systems.

Nickel forms simple binary compounds with non metals including [[halogens]], [[chalcogenides]], and [[pnictides]]. Nickel ions can act as a cation in salts with many acids, including common [[oxoacid]]s. Salts of the hexaaqua ion (Ni{{hydrate|6}}<sup>2+</sup>) are especially well known. Many double salts containing nickel with another cation are known. There are organic acid salts. Nickel can be part of a negatively charged ion (anion) making what is called a nickellate. Numerous quaternary compounds (with four elements) of nickel have been studied for [[superconductivity]] properties, as nickel is adjacent to copper and iron in the periodic table can form compounds with the same structure as the [[high-temperature superconductor]]s that are known.

==Colour==
Most of the common [[Salt (chemistry)|salts]] of nickel are green due to the presence of hexaaquanickel(II) ion, Ni(H<sub>2</sub>O)<sub>6</sub><sup>2+</sup>.

==Geometry==
Nickel atoms can connect to surrounding atoms or ligands in a variety of ways. Six coordinated nickel is the most common and is [[octahedral]], but this can be distorted if ligands are not equivalent. For four coordinate nickel arrangements can be square planar, or [[tetrahedral]]. Five coordinated nickel is rarer.

==Magnetism==
Some nickel compounds are [[ferromagnetic]] at sufficiently low temperatures. In order to show magnetic properties the nickel atoms have to be close enough together in the solid structure.

==Binary compounds==
A binary compound of nickel contains one other element. Substances that contain only nickel atoms are not actually compounds.

In a [[noble gas matrix]], nickel can form [[Dimer (chemistry)|dimers]], a molecule with two nickel atoms: Ni<sub>2</sub>.<ref name=barrett/> Ni<sub>2</sub> has a bonding energy of 2.07±0.01&nbsp;eV. For Ni<sub>2</sub><sup>+</sup> the bond energy is around 3.3&nbsp;eV. Nickel dimers and other clusters can also be formed in a gas and plasma phase by shooting a powerful laser at a nickel rod in cold helium gas.<ref name=lian91>{{cite journal |last1=Lian |first1=Li |last2=Su |first2=C.-X. |last3=Armentrout |first3=P.B. 
|title=The bond energy of <math chem>\ce{Ni^{+2}}</math>
|journal=Chemical Physics Letters 
|date=May 1991 |volume=180 |issue=3 |pages=168–172 |doi=10.1016/0009-2614(91)87135-X|bibcode=1991CPL...180..168L }}</ref>

===Oxides===
Nickel oxides include [[Nickel(II) oxide]] and [[Nickel(III) oxide]].

===Hydroxides===
Nickel hydroxides are used in [[nickel–cadmium battery|nickel–cadmium]] and [[Nickel–metal hydride battery|Nickel–metal hydride]] batteries.
Nickel(II) hydroxide Ni(OH)<sub>2</sub>, the main hydroxide of nickel is coloured apple green. It is known as the mineral [[theophrastite]].
[[Nickel oxide hydroxide|β-NiO(OH)]] is a black powder with nickel in the +3 oxidation state. It can be made by oxidising [[nickel nitrate]] in a cold alkaline solution with [[bromine]]. A [[Mixed valency|mixed oxidation state]] hydroxide Ni<sub>3</sub>O<sub>2</sub>(OH)<sub>4</sub> is made if oxidation happens in a hot alkaline solution. A Ni<sup>4+</sup> hydroxide: nickel peroxide hydrate NiO<sub>2</sub>{{hydrate}}, can be made by oxidising with alkaline peroxide. It is black, and unstable and oxidises water.

===Halides===
[[File:Nickel(II)-chloride-hexahydrate-sample.jpg|thumb|right|nickel chloride hexahydrate]]
[[Nickel(II) fluoride]] NiF<sub>2</sub> is yellow, crystallising in the [[rutile structure]] and can form a [[Water of crystallization|trihydrate]], NiF<sub>2</sub>·3H<sub>2</sub>O.<ref name=mellor>{{cite book |last1=Mellor |first1=J. W. |chapter=Nickel 
|title=A COMPREHENSIVE TREATISE ON INORGANIC AND THEORETICAL CHEMISTRY VOLUME XV Ni Ru, Rh Pd, Os, Ir 
|chapter-url=https://archive.org/details/b2980789x_0015/ |access-date=17 January 2019 
|date=1946}}</ref> A tetrahydrate also exists.<ref name="CRC"/>

[[Nickel chloride]] NiCl<sub>2</sub> is yellow, crystallising in the [[cadmium chloride]] structure. It can form a hexahydrate, NiCl<sub>2</sub>·6H<sub>2</sub>O, a tetrahydrate NiCl<sub>2</sub>·4H<sub>2</sub>O over 29&nbsp;°C and a dihydrate, NiCl<sub>2</sub>·2H<sub>2</sub>O over 64&nbsp;°C.<ref name=mellor/> Ammine complexes like [[hexaamminenickel chloride]] also exist.

[[Nickel bromide]] NiBr<sub>2</sub> is yellow, also crystallising in the cadmium chloride structure. It can form a hexahydrate, NiBr<sub>2</sub>·6H<sub>2</sub>O.<ref name=mellor/> Crystallisation above 29° forms a trihydrate NiBr<sub>2</sub>·3H<sub>2</sub>O, and a dihydrate NiBr<sub>2</sub>·2H<sub>2</sub>O.<ref name=nicholls>Nicholls p1126-1127</ref> Nonahydrate, NiBr<sub>2</sub>·9H<sub>2</sub>O can crystallise from water below 2&nbsp;°C.<ref name=mellor/> Nickelous hexammine bromide Ni(NH<sub>3</sub>)<sub>6</sub>Br<sub>2</sub>is violet or blue. It is soluble in boiling aqueous [[ammonia]], but is insoluble in cold.<ref name=mellor/> Diammine, monoammine, and dihydrazine nickel bromides also exist.<ref name=mellor/>

With four bromide atoms, nickel(II) forms a series of salts called [[tetrabromonickelates]].

[[Nickel iodide]] NiI<sub>2</sub> is black, also crystallising in the cadmium chloride structure. It can form a green hexahydrate, NiI<sub>2</sub>·6H<sub>2</sub>O.<ref name=mellor/> Nickel iodide has a brown diammine NiI<sub>2</sub>•2NH<sub>3</sub> and a bluish-violet hexammine NiI<sub>2</sub>•6NH<sub>3</sub>.<ref name=mellor/>

[[Nickel(III) fluoride]] NiF<sub>3</sub>

[[Nickel(IV) fluoride]] NiF<sub>4</sub>

===Chalcogenides===
[[File:Millerite-Quartz-232902.jpg|thumb|right|needles of Halls Gap Millerite]]
By reacting nickel with [[chalcogen]]s, [[nickel sulfide]], [[nickel selenide]], and [[nickel telluride]] are formed.
There are numerous sulfides: Ni<sub>1.5</sub>S, Ni<sub>17</sub>S<sub>18</sub>, Ni<sub>3</sub>S<sub>2</sub> ([[heazlewoodite]]), Ni<sub>3</sub>S<sub>4</sub> ([[polydymite]]), Ni<sub>9</sub>S<sub>8</sub> ([[godlevskite]]), NiS ([[millerite]]) and two other NiS forms, NiS<sub>2</sub> ([[vaesite]]) in pyrite structure. Black nickel tetrasulfide NiS<sub>4</sub> is formed from [[ammonium polysulfide]] and nickel in water solution. Mixed and double sulfides of nickel also exist. Nickel with [[selenium]] forms several compounds Ni<sub>1−x</sub>Se 0≤x≤0.15, Ni<sub>2</sub>Se<sub>3</sub>, NiSe<sub>2</sub> also known as a mineral [[penroseite]].

Nickel forms two different [[polonide]]s by heating nickel and [[polonium]] together: NiPo and NiPo<sub>2</sub>.<ref>{{cite book |last1=Meyer |first1=R. J. 
|title=Gmelins Handbuch Der Anorganischen Chemie - Nickel: Teil B — Lieferung 2. Verbindungen bis Nickel-Polonium 
|date=1974 |publisher=Springer-Verlag |location=Berlin |isbn=9783662133026 |page=764 
|chapter-url=https://books.google.com/books?id=0lGyBgAAQBAJ&pg=PA764 |language=de |chapter=Nickel und Polonium}}</ref>

===Pnictides===
[[File:Nickeline.jpg|thumb | right|The nickel arsenide [[nickeline]]]]
[[Non-stoichiometric]] compounds of nickel with [[phosphorus]], [[arsenic]] and [[antimony]] exist, and some are found in nature. One interstitial [[nitride]] has formula Ni<sub>3</sub>N (hexagonal P6322, Z = 2, a = 4.6224 Å and c = 4.3059 Å).<ref>{{cite journal |last1=Leineweber |first1=Andreas |last2=Jacobs |first2=Herbert |last3=Hull |first3=Steve 
|title=Ordering of Nitrogen in Nickel Nitride <math chem>\ce{Ni3N}</math> Determined by Neutron Diffraction 
|journal=Inorganic Chemistry 
|date=November 2001 |volume=40 |issue=23 |pages=5818–5822 |doi=10.1021/ic0104860|pmid=11681891 }}</ref>
In a [[solid nitrogen]] matrix, nickel atoms combine with [[nitrogen molecule]]s to yield Ni(N<sub>2</sub>)<sub>4</sub>.<ref name=barrett>{{cite journal |last1=Barrett |first1=Paul H. |last2=Montano |first2=P. A. 
|title=Proposed iron–nitrogen molecule produced in a solid nitrogen matrix 
|journal=Journal of the Chemical Society, Faraday Transactions 2 
|date=1977 |volume=73 |issue=3 |pages=378–383 |doi=10.1039/F29777300378}}</ref>

[[Nickel phosphide]] Ni<sub>2</sub>P has density 7.33 and melts at 1100&nbsp;°C.<ref name="CRC"/>

The mineral [[Nickelskutterudite]] has formula NiAs<sub>2-3</sub>, [[nickeline]] has formula NiAs and [[breithauptite]] has formula NiSb. NiAs melts at 967° and has density 7.77. NiSb melts at 1174°. It has the highest density of a nickel compound at 8.74&nbsp;g/cm<sup>3</sup>.<ref name="CRC"/>

NiAsS [[gersdorffite]], and NiSbS [[ullmannite]], NiAsSe [[Jolliffeite]] are pnictide/chalcogenide compounds that occur as minerals.

===Other===
Nickel also forms [[carbide]]s and [[boride]]s. [[nickel boride (disambiguation)|Nickel borides]] include forms Ni<sub>2</sub>B (a green/black solid), NiB, Ni<sub>3</sub>B, ''o''-Ni<sub>4</sub>B<sub>3</sub> and ''m''-Ni<sub>4</sub>B<sub>3</sub>.<ref name="Encyclopedia">{{cite book
 | title=Encyclopedia of Inorganic Chemistry
 | chapter=Boron: Inorganic Chemistry
 | author1=Robert A. Scott
 | publisher=Wiley
 | year=2011
 | isbn=9780470862100
 | page=401
}}</ref>

[[Nickel hydride]] NiH is only stable under [[high pressure]]s of [[hydrogen]].

[[Nickel silicide]]s include Ni<sub>3</sub>Si,<ref>{{cite journal |last1=Itahara |first1=Hiroshi |last2=Simanullang |first2=Wiyanti F. |last3=Takahashi |first3=Naoko |last4=Kosaka |first4=Satoru |last5=Furukawa |first5=Shinya |title=Na-Melt Synthesis of Fine Ni3Si Powders as a Hydrogenation Catalyst |journal=Inorganic Chemistry |volume=58 |issue=9 |pages=5406–5409 |date=15 April 2019 |doi=10.1021/acs.inorgchem.9b00521 |pmid=30983337 |s2cid=115204460 |issn=0020-1669|url=https://figshare.com/articles/Na-Melt_Synthesis_of_Fine_Ni_sub_3_sub_Si_Powders_as_a_Hydrogenation_Catalyst/7993316 }}</ref> Ni<sub>31</sub>Si<sub>12</sub>, Ni<sub>2</sub>Si, Ni<sub>3</sub>Si<sub>2</sub>, NiSi and NiSi<sub>2</sub>.<ref>{{cite journal |last1=Dahal |first1=Ashutosh |last2=Gunasekera |first2=Jagath |last3=Harringer |first3=Leland |last4=Singh |first4=Deepak K. |last5=Singh |first5=David J. |title=Metallic nickel silicides: Experiments and theory for NiSi and first principles calculations for other phases |journal=Journal of Alloys and Compounds |date=July 2016 |volume=672 |pages=110–116 |doi=10.1016/j.jallcom.2016.02.133 |url=https://ws680.nist.gov/publication/get_pdf.cfm?pub_id=920134|arxiv=1602.05840 |s2cid=55434466 }}</ref> Nickel silicides are used in [[microelectronics]].

===Diatomic molecules===
Hot nickel vapour reacting with other atoms in the gas phase can produce molecules consisting of two atoms. These can be studied by their [[emission spectrum]]. The nickel monohalides are well studied.<ref>{{cite book |last1=Hauffe1 |first1=Karl |last2=Puschmann |first2=Herbert 
|title=Corrosion Handbook |pages=NA |chapter=A26 nickel |date=2008 |doi=10.1002/9783527610433.chb203030 |publisher=Wiley|isbn=978-3527610433 }}</ref><ref name=muzangwa>{{cite journal |last1=Muzangwa |first1=L.G. |last2=Ayles |first2=V.L. |last3=Nyambo |first3=S. |last4=Reid |first4=S.A. 
|title=Probing the electronic structure of the nickel monohalides: Spectroscopy of the low-lying electronic states of NiBr and NiCl 
|journal=Journal of Molecular Spectroscopy |date=September 2011 |volume=269 |issue=1 |pages=36–40 |doi=10.1016/j.jms.2011.04.012|bibcode=2011JMoSp.269...36M }}</ref><ref>{{cite journal |last1=Reddy |first1=S Paddi |last2=Rao |first2=P Tiruvenganna |title=The Band Spectra of NiCl and NiBr in the Visible |journal=Proceedings of the Physical Society |date=1 February 1960 |volume=75 |issue=2 |pages=275–279 |doi=10.1088/0370-1328/75/2/314|bibcode=1960PPS....75..275R }}</ref><ref>{{cite journal |last1=Kant |first1=Arthur |title=Mass-Spectrometric Studies of the Gaseous Systems Au-Ni, Au-Co, and Au-Fe, and Dissociation Energies of AuNi, AuCo, and AuFe 
|journal=Journal of Chemical Physics |date=1968 |volume=49 |issue=11 |pages=5144–5146 |doi=10.1063/1.1670012|bibcode=1968JChPh..49.5144K }}</ref><ref>{{cite journal |last1=Krishnamurty |first1=V. G. |title=The Complex Band Spectrum of Nickel Bromide (NiBr) |journal=Indian Journal of Physics |publisher=Indian Association for the Cultivation of Science |date=16 April 1952 |volume=26 |page=429|hdl=10821/1696 |url=http://hdl.handle.net/10821/1696|issn=0973-1458}}</ref>

==Alloys==
{{Further|Alloy 601}}
Compounds of nickel with other metals can be called [[alloy]]s. The substances with fixed composition include [[nickel aluminide]] (NiAl) melting at 1638° with [[Hexagonal crystal system|hexagonal structure]].<ref name="CRC">{{cite book |editor1-last=Haynes |editor1-first=W. M. 
|title=CRC Handbook of Chemistry and Physics 
|date=2014 |isbn=9781482208672 |pages=4–77–4–78 |publisher=CRC Press 
|edition=95}}</ref>
NiY, NiY<sub>3</sub>, Ni<sub>3</sub>Y, Ni<sub>4</sub>Y, NiGd<sub>3</sub>,<ref>{{cite web 
|title=Кристаллические структуры соединений Ni 
|url=http://www.kipt.kharkov.ua/kipt_sites/isspmst/crystal/ni/ni15.html |website=www.kipt.kharkov.ua}}</ref>

BaNi<sub>2</sub>Ge<sub>2</sub> changes structure from orthorhombic to tetragonal around 480&nbsp;°C.<ref name=banige>{{cite journal |last1=Hlukhyy |first1=Viktor |last2=Trots |first2=Dmytro |last3=Fässler |first3=Thomas F. 
|title=First-Order Phase Transition in BaNi2Ge2 and the Influence of the Valence Electron Count on Distortion of the <math chem>\ce{ThCr2 Si2}</math> Structure Type 
|journal=Inorganic Chemistry |volume=56 |issue=3 |pages=1173–1185 
|date=13 January 2017 |doi=10.1021/acs.inorgchem.6b02190|pmid=28085271 }}</ref> This is a ternary intermetallic compound. Others include BaNiSn<sub>3</sub> and the superconductors SrNi<sub>2</sub>Ge<sub>2</sub>, SrNi<sub>2</sub>P<sub>2</sub>, SrNi<sub>2</sub>As<sub>2</sub>, BaNi<sub>2</sub>P<sub>2</sub>, BaNi<sub>2</sub>As<sub>2</sub>.<ref name=banige/>

==Simple salts==

===Oxo acid salts===
{{main|Nickel oxo acid salts}}
[[File:Annabergite-20960.jpg|thumb|right|alt=bright green crystals in two clusters on a white and grey rock|Mint green Annabergite, a nickel arsenite]]
Important nickel oxo acid salts include [[nickel(II) sulfate]] can crystallise with six water molecules yielding [[Retgersite]] or with seven making [[Morenosite]] which is isomorphic to Epsom salts. These contain the hexaquanickel(II) ion.<ref name=caw>{{cite book 
|title=Advanced Inorganic Chemistry: A Comprehensive Treatise 
|author=Cotton and Wilkinson |year=1966 |pages=878–893 |publisher=John Wiley & Sons}}</ref>
There is also an anhydrous form, a dihydrate and a tetrahydrate, the last two crystallised from [[sulfuric acid]]. The hexahydrate has two forms, a blue tetragonal form, and a green monoclinic form, with a transition temperature around 53&nbsp;°C.<ref>Mellor pp462-465</ref> The heptahydrate crystallises from water below 31.5 above this blue hexhydrate forms, and above 53.3 the green form.<ref>Mellor p 466-467</ref> Heating nickel sulfate dehydrates it, and then 700° it loses sulfur trioxide, sulfur dioxide and oxygen. Other important nickel compounds in this class are [[nickel carbonate]], [[nickel nitrate]], and [[nickel phosphate]]

===Fluoro acid salts===
Nickel tetrafluoroborate, Ni(BF<sub>4</sub>)<sub>2</sub>{{hydrate|6}} is very soluble in water, alcohol and acetonitrile. It is prepared by dissolving [[nickel carbonate]] in [[tetrafluoroboric acid]].<ref>{{cite journal |last1=O'Brien |first1=James F. |last2=Reynolds |first2=Warren Lind 
|title=Nuclear magnetic resonance study of cobalt and nickel tetrafluoroborates 
|journal=Inorganic Chemistry 
|date=November 1967 |volume=6 |issue=11 |pages=2110–2111 |doi=10.1021/ic50057a041}}</ref><ref>{{cite journal |last1=Ryss |first1=A. I. |last2=Radchenko |first2=I. V. 
|title=X-ray study of aqueous solutions of nickel tetrafluoroborate 
|journal=Journal of Structural Chemistry 
|date=1966 |volume=6 |issue=4 |pages=489–492 |doi=10.1007/BF00744813|s2cid=96193596 }}</ref> Nickel tetrafluoroberyllate NiBeF<sub>4</sub>•''x''H<sub>2</sub>O, can be hydrated with six or seven water molecules.<ref>{{cite journal |last1=Rây |first1=Nirmalendu Nath 
|title=Fluoberyllate und ihre Analogie mit den Sulfaten. II. Fluoberyllate einiger zweiwertiger Metalle 
|journal=Zeitschrift für anorganische und allgemeine Chemie 
|date=20 April 1932 |volume=205 |issue=3 |pages=257–267 |doi=10.1002/zaac.19322050307}}</ref>
Both nickel [[hexafluorostannate]] <math chem>\ce{NiSnF6.6H2O}</math> and nickel [[fluorosilicate]] <math chem>\ce{NiSiF6.6H2O}</math> crystallise in the trigonal system.<ref>{{cite journal |last1=Karnezos |first1=M. |last2=Friedberg |first2=S. A. 
|title=FERROMAGNETISM IN <math chem>\ce{NiSnF6.6H2O}</math> AND <math chem>\ce{NiSiF6.6H2O}</math>
|journal=Le Journal de Physique Colloques 
|date=August 1978 |volume=39 |issue=C6 |pages=C6–814–C6–815 |doi=10.1051/jphyscol:19786362 
|url=https://hal.archives-ouvertes.fr/jpa-00217826/document |access-date=14 May 2016}}</ref> Nickel hexafluorogermanate NiGeF<sub>6</sub> has a rosy-tan colour and a hexagonal crystal with a = 5.241&nbsp;Å unit cell volume is 92.9&nbsp;Å<sup>3</sup>. It is formed in the reaction with GeF<sub>4</sub> and K<sub>2</sub>NiF<sub>6</sub>.<ref name=Chacon/> Nickel fuorotitanate <math chem>\ce{NiTiF6.6H2O}</math> crystallises in hexagonal green crystals. It can be made by dissolving nickel carbonate, and titanium dioxide in hydrofluoric acid. The crystal dimensions are a = 9.54, c = 9.91 density = 2.09 (measure 2.03).<ref>{{cite journal |last1=Davidovich |first1=R. L. |last2=Kaidalova |first2=T. A. |last3=Levchishina |first3=T. F. 
|title=X-ray diffraction data for some divalent metal fluorotitanates 
|journal=Journal of Structural Chemistry 
|date=1971 |volume=12 |issue=1 |pages=166–168 |doi=10.1007/BF00744565|bibcode=1971JStCh..12..166D |s2cid=95953256 }}</ref>

Ni(AsF<sub>6</sub>)<sub>2</sub>, Ni(SbF<sub>6</sub>)<sub>2</sub>, Ni(BiF<sub>6</sub>)<sub>2</sub> are made by reacting the hexafluoro acid with NiF<sub>2</sub> in [[hydrofluoric acid]].<ref name=Chacon>{{cite web |last1=Chacon |first1=Lisa Carine 
|title=The Synthesis, Characterization and Reactivity of High Oxidation State Nickel Fluorides 
|url=https://publications.lbl.gov/islandora/object/ir%3A112067/datastream/PDF/download/citation.pdf |publisher=University of California |access-date=27 April 2016 |location=Berkeley California 
|date=December 1997}}</ref> They all have hexagonal crystal structure, resembling the similar salts of the other first row transition metals.<ref name=Chacon/> For Ni(AsF<sub>6</sub>)<sub>2</sub> a = 4.98, c = 26.59, and V = 571, formula weight Z=3.<ref name=Chacon/> Ni(SbF<sub>6</sub>)<sub>2</sub> is yellow with a = 5.16Å, c = 27.90Å Z = 3. The structure resembles LiSbF<sub>6</sub>, but with every second metal along the c axis missing.<ref>{{cite journal |last1=Christe |first1=Karl O. |last2=Wilson |first2=William W. |last3=Bougon |first3=Roland A. |last4=Charpin |first4=Pierrette 
|title=Preparation and characterization of <math chem>\ce{Ni(SbF6)2}</math>
|journal=Journal of Fluorine Chemistry 
|date=January 1987 |volume=34 |issue=3–4 |pages=287–298 |doi=10.1016/S0022-1139(00)85173-8}}</ref>

Others include the green fluorohafnate NiHfF<sub>6</sub>{{hydrate|6}}, and Ni<sub>2</sub>HfF<sub>8</sub>{{hydrate|12}},<ref>{{cite journal |last1=Davidovich |first1=R. L. |last2=Buslaev |first2=Yu. A. |last3=Levchishina |first3=T. F. 
|title=Synthesis of some new fluorohafnate complexes 
|journal=Bulletin of the Academy of Sciences of the USSR Division of Chemical Science 
|date=March 1968 |volume=17 |issue=3 |pages=676 |doi=10.1007/BF00911649}}</ref> NiZrF<sub>6</sub>{{hydrate|6}}<ref>{{cite journal |last1=Karnezos |first1=M. |last2=Meier |first2=D. |last3=Friedberg |first3=S. A. 
|title=Magnetic ordering in <math chem>\ce{NiZrF6.6H2O}</math>
|journal=AIP Conference Proceedings 
|date=9–12 December 1975 |volume=29 |page=505 |doi=10.1063/1.30416|bibcode=1976AIPC...29..505K }}</ref>

===Chloroacid salts===
Nickel tetrachloroiodate Ni(ICl<sub>4</sub>)<sub>2</sub> can be made by reacting iodine with nickel chloride and chlorine gas. It consists of green needles.<ref>{{cite journal |last1=Weinland |first1=R. F. |last2=Schlegelmilch |first2=Fr. 
|title=Über Doppelsalze des Jodtrichlorids mit Chloriden zweiwertiger Metalle 
|journal=Zeitschrift für anorganische Chemie 
|date=7 March 1902 |volume=30 |issue=1 |pages=134–143 |doi=10.1002/zaac.19020300109|url=https://zenodo.org/record/1428094 }}</ref>

===Nitrogen anion salts===
[[Nickel cyanide]] tetrahydrate Ni(CN)<sub>2</sub>{{hydrate|4}} is insoluble in water, but dissolves in aqueous ammonia.<ref name="CRC"/> It forms double salts with interesting structures.<ref name="hibble">{{cite journal |last1=Hibble |first1=Simon J. |last2=Chippindale |first2=Ann M. |last3=Pohl |first3=Alexander H. |last4=Hannon |first4=Alex C. 
|title=Surprises from a Simple Material—The Structure and Properties of Nickel Cyanide 
|journal=Angewandte Chemie International Edition 
|date=17 September 2007 |volume=46 |issue=37 |pages=7116–7118 |doi=10.1002/anie.200701246 |pmid=17683027}}</ref>

Nickel azide Ni(N<sub>3</sub>)<sub>2</sub> is a sensitive explosive. It can be made by treating nickel carbonate with [[hydrazoic acid]]. Acetone causes the precipitation of the hydrous solid salt, which is green. At 490K it slowly decomposes to nitrogen and nickel metal powder, losing a half of the nitrogen in four hours.<ref>{{cite journal |last1=Sood |first1=R. K. |last2=Nya |first2=A. E. |last3=Etim |first3=E. S. 
|title=Thermal decomposition of nickel azide 
|journal=Journal of Thermal Analysis 
|date=December 1981 |volume=22 |issue=2 |pages=231–237 |doi=10.1007/BF01915269|s2cid=95478362 }}</ref> Nickel azide is complexed by one azo group when dissolved in water, but in other solvents, the nickel atom can have up to four azo groups attached.<ref>{{cite journal |last1=Abu-Eittah |first1=R. |last2=Elmakabaty |first2=S. 
|title=Spectra of Nickel(II)-Azide Complexes in Organic Solvents 
|journal=Bulletin of the Chemical Society of Japan 
|date=1973 |volume=46 |issue=11 |pages=3427–3431 |doi=10.1246/bcsj.46.3427|doi-access=free }}</ref> Nickel azide forms a dihydrate: Ni(N<sub>3</sub>)<sub>2</sub>{{hydrate|2}} and a basic salt called nickel hydroxy azide Ni(OH)N<sub>3</sub>.<ref>{{cite journal |last1=IROM |first1=I I 
|title=Photolysis of nickel hydroxy azide. 
|journal=Global Journal of Pure and Applied Sciences 
|date=1 January 2001 |volume=7 |issue=1 |pages=73–80 |doi=10.4314/gjpas.v7i1.16208|doi-access=free }}</ref>

Nickel amide, Ni(NH<sub>2</sub>)<sub>2</sub> is a deep red compound that contains Ni<sub>6</sub> clusters surrounded by 12 NH<sub>2</sub> groups.<ref>{{cite journal |last1=Tenten |first1=A. |last2=Jacobs |first2=H. 
|title=Isolierte <math chem>\ce{Ni6(NH2)12}</math>-Einheiten in Nickel(II)-Amid 
|journal=Journal of the Less Common Metals 
|date=June 1991 |volume=170 |issue=1 |pages=145–159 |doi=10.1016/0022-5088(91)90060-H}}</ref> Nickel amide also forms a series of double salts. Other homoleptic nickel amides derived by substituting the hydrogen atoms are Ni[N(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>]<sub>2</sub> (diphenyl) and boryl amides Ni[NBMes<sub>2</sub>Mes]<sub>2</sub> and Ni[NBMes<sub>2</sub>C<sub>6</sub>H<sub>5</sub>]<sub>2</sub>.<ref>{{cite book |last1=Lappert |first1=Michael 
|title=Metal amide chemistry 
|url=https://archive.org/details/metalamidechemis00lapp |url-access=limited |date=2009 |publisher=Wiley |location=Chichester, U.K. |isbn=9780470721841 |pages=[https://archive.org/details/metalamidechemis00lapp/page/n183 172]–173}}</ref>

===Organic acid salts===
{{main|Nickel organic acid salts}}
Nickel forms many known salts with organic acids. In many of these the ionised organic acid acts as a ligand.

==Double salts==

{{Main article|Nickel double salts}}

Nickel is one of the metals that can form [[Tutton's salts]]. The singly charged ion can be any of the full range of potassium, rubidium, cesium, ammonium (<chem>NH4</chem>), or thallium.<ref name="Wang2008">{{cite journal |last=Wang |first=Xia  |author2=Xinxin Zhuang  |author3=Genbo Su  |author4=Youping He |year=2008 
|title=A new ultraviolet filter: <math chem>\ce{Rb2Ni(SO4)2.6H2O}</math> (RNSH) single crystal 
|journal=Optical Materials |volume=31 |issue=2 |pages=233–236 |issn=0925-3467 |doi=10.1016/j.optmat.2008.03.020 
|url=http://ir.fjirsm.ac.cn/bitstream/350002/5857/1/Wang-2008-A%20new%20ultraviolet%20fi.pdf|bibcode=2008OptMa..31..233W  }}</ref> As a mineral the ammonium nickel salt, (NH<sub>4</sub>)<sub>2</sub>Ni(SO<sub>4</sub>)<sub>2</sub>{{hydrate|6}}, can be called nickelboussingaultite.<ref>{{cite web 
|title=Nickelboussingaultite: Nickelboussingaultite mineral information and data. 
|url=http://www.mindat.org/min-2896.html |website=www.mindat.org |access-date=3 May 2016}}</ref> With sodium, the double sulfate is nickelblödite Na<sub>2</sub>Ni(SO<sub>4</sub>)<sub>2</sub>{{hydrate|4}} from the [[blödite family]]. Nickel can be substituted by other divalent metals of similar sized to make mixtures that crystallise in the same form.<ref>{{cite web 
|title=Nickelblödite: Nickelblödite mineral information and data. 
|url=http://www.mindat.org/min-2890.html |website=www.mindat.org |access-date=4 May 2016}}</ref>

Nickel forms double salts with Tutton's salt structure with [[tetrafluoroberyllate]] with the range of cations of ammonia,<ref>{{cite journal |last1=Montgomery |first1=H. 
|title=Diammonium nickel bis(tetrafluoroberyllate)hexahydrate 
|journal=Acta Crystallographica Section B  
|date=15 September 1980 |volume=36 |issue=9 |pages=2121–2123 |doi=10.1107/S0567740880008060|doi-access=free |bibcode=1980AcCrB..36.2121M 
}}</ref> potassium, rubidium, cesium,<ref>{{cite journal |last1=Rây |first1=Nirmalendunath 
|title=Fluoberyllate und ihre Analogie mit Sulfaten. IV. Doppelsalze mit Rubidium- und Cäsiumfluoberyllaten 
|journal=Zeitschrift für anorganische und allgemeine Chemie 
|date=18 April 1936 |volume=227 |issue=1 |pages=32–36 |language=de |doi=10.1002/zaac.19362270105}}</ref> and thallium.<ref>{{cite journal |last1=Bose |first1=A. |last2=Mitra |first2=S. C. |last3=Datta |first3=S. K. 
|title=The Behaviour of the Paramagnetic Ions in the Single Crystals of Some Similarly Constituted Salts of the Iron Group of Elements. II. Hydrated NiFormula Salts 
|journal=Proceedings of the Royal Society A  
|date=11 November 1958 |volume=248 |issue=1253 |pages=153–168 |doi=10.1098/rspa.1958.0236|bibcode=1958RSPSA.248..153B |s2cid=98423115 }}</ref>

Anhydrous salts of the formula M<sub>2</sub>Ni<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>, which can be termed metal nickel trisulfates, belong to the family of [[langbeinites]]. The known salts include (NH<sub>4</sub>)<sub>2</sub>Ni<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>, K<sub>2</sub>Ni<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> and Rb<sub>2</sub>Ni<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>, and those of Tl and Cs are predicted to exist.

Some minerals are double salts, for example [[Nickelzippeite]] Ni<sub>2</sub>(UO<sub>2</sub>)<sub>6</sub>(SO<sub>4</sub>)<sub>3</sub>(OH)<sub>10</sub> · 16H<sub>2</sub>O which is isomorphic to [[cobaltzippeite]], [[magnesiozippeite]] and [[zinczippeite]], part of the [[zippeite]] group.<ref>{{cite web 
|title=Nickelzippeite: Nickelzippeite mineral information and data. 
|url=http://www.mindat.org/min-2898.html |website=www.mindat.org |access-date=10 May 2016}}</ref>

Double hydrides of nickel exist, such as Mg<sub>2</sub>NiH<sub>4</sub>.<ref>{{cite journal |last1=Reilly |first1=James J. |last2=Wiswall |first2=Richard H. 
|title=Reaction of hydrogen with alloys of magnesium and nickel and the formation of <math chem>\ce{Mg2NiH4}</math>
|journal=Inorganic Chemistry 
|date=November 1968 |volume=7 |issue=11 |pages=2254–2256 |doi=10.1021/ic50069a016}}</ref>

===Ternary chalcogenides===
Nickel forms a [[oxonickelates|series of double nickel oxides]] with other elements, which may be termed "nickelates". There are also many well defined [[Nickel ternary chalcogenides|double compounds with sulfur, selenium and tellurium]].

===Ternary pnictides===
Ternary pnictides that contain nickel are metallic and include MgNi<sub>2</sub>Bi<sub>4</sub>,<ref name=Hertz>{{cite journal |last1=Hertz |first1=Mary B. |last2=Baumbach |first2=Ryan E. |last3=Latturner |first3=Susan E. |title=Flux Synthesis of MgNi2Bi4 and Its Structural Relationship to NiBi3 |journal=Inorganic Chemistry |date=15 January 2020 |doi=10.1021/acs.inorgchem.9b03196 |volume=59 |issue=6 |pages=3452–3458|pmid=31939654 |s2cid=210814692 }}</ref> SrNi<sub>2</sub>P<sub>2</sub>, SrNi<sub>2</sub>As<sub>2</sub>, BaNi<sub>2</sub>P<sub>2</sub>, and BaNi<sub>2</sub>As<sub>2</sub>.<ref name=banige/>

===Ternary halides===
Nickel can form anions and salts with halogens including the [[hexafluoronickelate]]s, and [[tetrafluoronickelate]]s, [[tetrachloronickelate]]s, [[tetrabromonickelate]]s and [[tetraiodonickelate]]s. The subiodide Bi<sub>12</sub>Ni<sub>4</sub>I<sub>3</sub> is also known.<ref name=Hertz/>

===Polyoxometallates===
Nickel can enter into metal oxygen clusters with other high oxidation state elements to form [[polyoxometalate]]s.  These may stabilize higher oxidation states of nickel, or show catalytic properties.

Nonamolybdonickelate(IV), [NiMo<sub>9</sub>O<sub>32</sub>]<sup>6−</sup> can oxidize aromatic hydrocarbons to alcohols.<ref>{{cite journal |last1=Bhattacharya |first1=Santanu |last2=Saha |first2=Basudeb |last3=Dutta |first3=Amitava |last4=Banerjee |first4=Pradyot 
|title=Electron transfer reactions of nickel(III) and nickel(IV) complexes 
|journal=Coordination Chemistry Reviews 
|date=March 1998 |volume=170 |issue=1 |pages=47–74 |doi=10.1016/S0010-8545(98)00065-4}}</ref>

There is a dark brown heptamolybdonickelate(IV) potassium salt, K<sub>2</sub>H<sub>8</sub>NiMo<sub>7</sub>O<sub>28</sub>·6H<sub>2</sub>O.<ref>{{cite journal|last1=Roy|first1=Ajoy|last2=Chaudhury|first2=Muktimoy
|title=A New Series of Heptamolybdonickelate(IV) and Manganate(IV). Investigation of the Unusual Magnetic and Electronic Spectral Behavior of the Nickel(IV) Compound
|journal=Bulletin of the Chemical Society of Japan
|date=September 1983|volume=56|issue=9|pages=2827–2830|doi=10.1246/bcsj.56.2827}}</ref>

13-Vanadonickelate(IV) compounds such as K<sub>7</sub>NiV<sub>13</sub>O<sub>38</sub>{{hydrate|16}} with black octahedral crystals exist. It can be made from isopolyvanadate, with nickel(II) oxidised by peroxydisulfate at a pH around 4.<ref>{{cite book|editor1-last=Parshall|editor1-first=George W.|isbn=0070485216|author1 = George B. Kauffman|author2 = Russell Fuller|author3 = James Felser|author4 = Charles M. Flynn Jr.|author5 = Michael T. Pope
|chapter=13-Vanadomanganate(IV) and Nickelate(IV) |title=Inorganic Syntheses
|date=1974|volume=15|pages=103–110|doi=10.1002/9780470132463.ch24}}</ref>
Nickel(IV) heteropolyniobates such as the dark maroon Na<sub>12</sub>NiNb<sub>12</sub>O<sub>38</sub>{{hydrate|21}} are also known.<ref>{{cite journal|last1=Flynn|first1=Charles M.|last2=Stucky|first2=Galen D.
|title=Heteropolyniobate complexes of manganese(IV) and nickel(IV)
|journal=Inorganic Chemistry
|date=February 1969|volume=8|issue=2|pages=332–334|doi=10.1021/ic50072a029}}</ref> An alternate orange red hydrate perhaps with 44 water molecules also exists. With nickel-II (tetramethylammonium)<sub>6</sub>[H<sub>3</sub>NiNb<sub>9</sub>O<sub>28</sub>{{hydrate|17}} forms a green salt that is very soluble in water, but hardly soluble in ethanol.<ref>{{cite journal|last1=Son|first1=Jung-Ho|last2=Ohlin|first2=C. André|last3=Casey|first3=William H.
|title=Highly soluble iron- and nickel-substituted decaniobates with tetramethylammonium countercations
|journal=Dalton Transactions
|date=2013|volume=42|issue=21|pages=7529–33|doi=10.1039/C3DT50887K|pmid=23588819|doi-access=free}}</ref>

H<sub>43</sub>K<sub>14</sub>Na<sub>6</sub>Nb<sub>32</sub> Ni<sub>10</sub>O<sub>183</sub> is a nickel-cation-bridged polyoxoniobate which crystallizes in the monoclinic system with cell dimensions a=15.140 b=24.824 c=25.190&nbsp;Å and β=103.469 and two formulas per unit cell.<ref>{{cite journal|last1=Liang|first1=Zhijie|last2=Zhang|first2=Dongdi|last3=Wang|first3=Haiying|last4=Ma|first4=Pengtao|last5=Yang|first5=Zongfei|last6=Niu|first6=Jingyang|last7=Wang|first7=Jingping
|title=The <math chem>\ce{{Ni10Nb32}}</math> aggregate: a perspective on isopolyniobates as ligands
|journal=Dalton Trans.
|date=2016|volume=45|issue=41|pages=16173–16176|doi=10.1039/C6DT02575G|pmid=27711767}}</ref>

Na<sub>8</sub>Li<sub>12</sub>[Ni<sub>2</sub>(P<sub>2</sub>W<sub>15</sub>O<sub>56</sub>)<sub>2</sub>]{{hydrate|74}} forms a sandwich structure, and Na<sub>4</sub>Li<sub>5</sub>[Ni<sub>3</sub>(OH)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>P<sub>2</sub>W<sub>16</sub>O<sub>59</sub>]{{hydrate|48}} is a Wells-Dawson polyoxometalate.<ref>{{cite journal|last1=Guo|first1=Weiwei|last2=Lv|first2=Hongjin|last3=Bacsa|first3=John|last4=Gao|first4=Yuanzhe|last5=Lee|first5=Je Seong|last6=Hill|first6=Craig L.
|title=Syntheses, Structural Characterization, and Catalytic Properties of Di- and Trinickel Polyoxometalates
|journal=Inorganic Chemistry
|date=19 January 2016|volume=55|issue=2|pages=461–466|doi=10.1021/acs.inorgchem.5b01935|pmid=26479899}}</ref>

==Acidic salts==
Nickel hydrofluoride, H<sub>5</sub>NiF<sub>7</sub>·6H<sub>2</sub>O is made by using excess hydrofluoric acid solution on nickel carbonate. It is deep green.<ref name=mellor/>

==Basic salts==
Nickel oxyfluoride Ni<sub>4</sub>F<sub>4</sub>O(OH)<sub>2</sub> is green.<ref name=mellor/>

Nickelous enneaoxydiiodide 9NiO•Nil<sub>2</sub>{{hydrate|15}} forms when solutions of nickel iodide are exposed to air and evaporated.<ref name=mellor/>

==Complexes==
[[File:Potassium tetracyanonickelate.jpg|thumb|right|150px|Sample of potassium tetracyanonickelate hydrate]]
Simple complexes of nickel include hexaquonickel(II), yellow [[tetracyanonickelate]] [Ni(CN)<sub>4</sub>]<sup>2−</sup>, red pentacyanonickelate [Ni(CN)<sub>5</sub>]<sup>3−</sup> only found in solution, [Ni(SCN)<sub>4</sub>]<sup>2−</sup> and [Ni(SCN)<sub>6</sub>]<sup>4−</sup>. Halo- complexes include [NiCl<sub>4</sub>]<sup>2−</sup>, [NiF<sub>4</sub>]<sup>2−</sup>, [NiF<sub>6</sub>]<sup>4−</sup>, [NiCl<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>] [Ni(NH<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>2+</sup>, [Ni(NH<sub>3</sub>)<sub>6</sub>]<sup>2+</sup>, [Ni(en)<sub>3</sub>)]<sup>2+</sup>.<ref name=caw/> Some complexes have fivefold coordination. <chem>N[CH2CH2NMe2]3</chem> (tris(N,N-dimethyl-2-aminoethyl)amine); P(o-C<sub>6</sub>H<sub>4</sub>SMe)<sub>3</sub>; P(CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>AsMe<sub>2</sub>)<sub>3</sub>.<ref name=caw/>

Other ligands for octahedral coordination include [[Triphenylphosphine|PPh<sub>3</sub>]], [[methyldiphenylphosphine|PPh<sub>2</sub>Me]] and [[thiourea]].<ref name=caw/>

Nickel tetrahedral complexes are often bright blue and 20 times or more intensely coloured than the octahedral complexes.<ref name=caw/> The ligands can include selections of neutral [[amine]]s, [[arsine]]s, [[arsine oxide]]s, [[phosphine]]s or [[phosphine oxide]]s and halogens.<ref name=caw/>

Several nickel atoms can cluster together in a compound with other elements to produce nickel cluster complexes. One example where nickel atoms form a square pyramid is a nickel hydride cluster complexed by [[triphenyl phosphine]] ligands and bonding a hydrogen atom on each edge. Another example has a square planar Ni<sub>4</sub>H<sub>4</sub> shape in its core.<ref>{{cite journal|last1=Shoshani|first1=Manar M.|last2=Beck|first2=Robert|last3=Wang|first3=Xiaoping|last4=McLaughlin|first4=Matthew J.|last5=Johnson|first5=Samuel A.
|title=Synthesis of Surface-Analogue Square-Planar Tetranuclear Nickel Hydride Clusters and Bonding to μ4-NR, -O and -BH Ligands
|journal=Inorganic Chemistry
|date=15 November 2017|volume=57|issue=5|pages=2438–2446|doi=10.1021/acs.inorgchem.7b02546|pmid=29140692}}</ref>

[[Nickel bis(dimethylglyoximate)]], an insoluble red solid is important for [[gravimetric analysis]].

==Biological molecules==
[[File:NiSOD active site.png|thumb|right|Active site of [[Nickel superoxide dismutase]]]] 
[[Cofactor F430]] contains nickel in a tetrapyrrole derivative, and is used in the production of methane. Some [[hydrogenase]] enzymes contain a nickel-iron cluster as an active site in which the nickel atom is held in place by [[cysteine]] or [[selenocysteine]].<ref>{{cite journal |last1=Greening |first1=C. |last2=Berney |first2=M. |last3=Hards |first3=K. |last4=Cook |first4=G. M. |last5=Conrad |first5=R. 
|title=A soil actinobacterium scavenges atmospheric <math chem>\ce{H2}</math> using two membrane-associated, oxygen-dependent [NiFe] hydrogenases 
|journal=Proceedings of the National Academy of Sciences 
|date=3 March 2014 |volume=111 |issue=11 |pages=4257–4261 |doi=10.1073/pnas.1320586111|pmid=24591586 |bibcode=2014PNAS..111.4257G |pmc=3964045 |doi-access=free }}</ref> Plant [[urease]]s contain a bis-μ-hydroxo dimeric nickel cluster.<ref name="karplus">{{cite journal  | vauthors=Karplus PA, Pearson MA, Hausinger RP  | year=1997  | title=70 years of crystalline urease: What have we learned?  | journal=Accounts of Chemical Research  | volume=30  | issue=8 | pages=330–337 | doi=10.1021/ar960022j}}</ref> [[CO-methylating acetyl-CoA synthase]] contains two active nickel atoms, one is held in a square planar coordination by two cysteine and two amide groups, and the other nickel is held by three sulfur atoms. It is used to catalyse the reduction of carbon monoxide to [[acetyl-CoA]].<ref>{{cite journal |last1=EVANS |first1=D 
|title=Chemistry relating to the nickel enzymes CODH and ACS 
|journal=Coordination Chemistry Reviews 
|date=August 2005 |volume=249 |issue=15–16 |pages=1582–1595 |doi=10.1016/j.ccr.2004.09.012}}</ref>

[[Nickel superoxide dismutase]] (or Ni-SOD) from ''[[Streptomyces]]'' contains six nickel atoms. The nickel holding is done by a "nickel binding hook" which as the amino acid pattern '''H<sub>2</sub>N'''-'''His'''-'''Cys'''-X-X-Pro-'''Cys'''-Gly-X-Tyr-rest of protein, where the bold bits are ligands for the nickel atom.<ref>{{cite journal |last1=Wuerges |first1=J. |last2=Lee |first2=J.-W. |last3=Yim |first3=Y.-I. |last4=Yim |first4=H.-S. |last5=Kang |first5=S.-O. |last6=Carugo |first6=K. D. 
|title=Crystal structure of nickel-containing superoxide dismutase reveals another type of active site 
|journal=Proceedings of the National Academy of Sciences 
|date=1 June 2004 |volume=101 |issue=23 |pages=8569–8574 |doi=10.1073/pnas.0308514101|bibcode=2004PNAS..101.8569W |pmid=15173586 |pmc=423235 |doi-access=free }}</ref>

[[Nickel transporter]] proteins exist to move nickel atoms in the cell. in ''[[E. coli]]'' these are termed ''Nik''A, ''Nik''B, ''Nik''C, ''Nik''D, ''Nik''E. In order to come through a cell membrane a [[nickel permease]] protein is used. In ''[[Alcaligenes eutrophus]]'' the gene for this is ''hox''N.<ref>{{cite book |last1=Cammack |first1=Richard |last2=Vliet |first2=Pieter |editor1-last=Reedijk |editor1-first=Jan |editor2-last=Bouwman |editor2-first=Elisabeth 
|title=Bioinorganic Catalysis 
|date=1999 |publisher=Marcel Dekker |location=New York |isbn=0-8247-0241-7 |chapter=Catalysis by Nickel in Biological Systems |page=233 |edition=2 
|chapter-url=https://books.google.com/books?id=FVAxjWo4LbAC&pg=PA233}}</ref>

==Organometallics==
{{main|Organonickel}}
Well known nickel organometalic (or [[organonickel]]) compounds include [[Nickelocene]], [[bis(cyclooctadiene)nickel(0)]] and [[nickel tetracarbonyl]].<ref name="Jolly2">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1975 |volume=2 |publisher=Academic Press |location=New York |isbn=0-12-388402-0}}</ref>

Nickel tetracarbonyl was the first discovered organonickel compound. It was discovered that carbon monoxide corroded a nickel reaction chamber valve. And then that the gas coloured a bunsen burner flame green, and then that a nickel mirror condensed from heating the gas. The [[Mond process]] was thus inspired to purify nickel.<ref name="jolly1-1">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1974 |publisher=Academic Press |location=New York |isbn=0-12-388401-2 |volume=1 |pages=1–9}}</ref> The nickel tetracarbonyl molecule is tetrahedral, with a bond length for nickel to carbon of 1.82&nbsp;Å.<ref name="jolly1-1"/>
Nickel tetracarbonyl easily starts breaking apart over 36° forming Ni(CO)<sub>3</sub>, Ni(CO)<sub>2</sub>, and Ni.<ref name="jolly1-1"/> Ni(CO) and NiC appear in mass spectroscopy of nickel carbonyl.<ref name="jolly1-1"/>

There are several nickel carbonyl cluster anions formed by reduction from nickel carbonyl. These are [Ni<sub>2</sub>(CO)<sub>5</sub>]<sup>2−</sup>, dark red [Ni<sub>3</sub>(CO)<sub>8</sub>]<sup>2−</sup>, [Ni<sub>4</sub>(CO)<sub>9</sub>]<sup>2−</sup>, [Ni<sub>5</sub>(CO)<sub>9</sub>]<sup>2−</sup>, [Ni<sub>6</sub>(CO)<sub>12</sub>]<sup>2−</sup>. Salts such as Cd[Ni<sub>4</sub>(CO)<sub>9</sub>] and Li<sub>2</sub>[Ni<sub>3</sub>(CO)<sub>8</sub>]•5acetone can be crystallised.<ref name="jolly1-20">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1974 |publisher=Academic Press |location=New York |isbn=0-12-388401-2 |volume=1 |pages=20–22}}</ref>

Mixed cluster carbonyl anions like [Cr<sub>2</sub>Ni<sub>3</sub>(CO)<sub>16</sub>]<sup>2−</sup>, [Mo<sub>2</sub>Ni<sub>3</sub>(CO)<sub>16</sub>]<sup>2−</sup> and [W<sub>2</sub>Ni<sub>3</sub>(CO)<sub>16</sub>]<sup>2−</sup> [Mo<Ni<sub>4</sub>(CO)<sub>14</sub>]<sup>2−</sup> can form salts with bulky cations like tetraethylammonium. The brown [NiCo<sub>3</sub>(CO)<sub>11</sub>]<sup>−</sup> changes to red [Ni<sub>2</sub>Co<sub>4</sub>(CO)<sub>14</sub>]<sup>2−</sup>.<ref name="jolly1-23">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1974 |publisher=Academic Press |location=New York |isbn=0-12-388401-2 |volume=1 |pages=23–24}}</ref>

With oxygen or air the explosive Ni(CO)<sub>3</sub>O<sub>2</sub> can be formed from nickel carbonyl.<ref name="jolly1-16">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1974 |publisher=Academic Press |location=New York |isbn=0-12-388401-2 |volume=1 |pages=16}}</ref>

Yet other ligands can substitute for carbon monoxide in nickel carbonyl. These lewis base ligands include triphenylphosphine, triphenoxyphosphine, trimethoxyphosphine, tributylphosphine, triethoxyphosphine, triethylisonitrolphosphine, triphenylarsine, and triphenylstibine.

Nickel forms dark blue planar complexes with [[1,2-Diimino-3,5-cyclohexadiene]] or [[bisacetylbisaniline]] [(C<sub>6</sub>H<sub>5</sub>N-C(CH<sub>3</sub>)=)<sub>2</sub>]<sub>2</sub>Ni. Another planar bis compound of nickel is formed with phenylazothioformamide C<sub>6</sub>H<sub>5</sub>N=NC(S)NR<sub>2</sub>, and dithizone C<sub>6</sub>H<sub>5</sub>N=NC(S)NHNHC<sub>6</sub>H<sub>5</sub>.<ref name="jolly1-19">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1974 |publisher=Academic Press |location=New York |isbn=0-12-388401-2 |volume=1 |pages=19}}</ref> [[tetrasulfur tetranitride]] when reduced with nickel carbonyl makes Ni[N<sub>2</sub>S<sub>2</sub>H]<sub>2</sub> also coloured dark violet.<ref name="jolly1-19"/>

One [[nickellabenzene]] is known where nickel substitutes for carbon in benzene. At nickel the plane of the molecule is bent, however the connection to the ring has aromatic character.<ref>{{cite book |last1=Wright |first1=L. James 
|title=Metallabenzenes: An Expert View 
|date=2017 |publisher=John Wiley & Sons |isbn=9781119068099 |page=97 
|url=https://books.google.com/books?id=wrcuDwAAQBAJ&pg=PA97 |language=en}}</ref> A hexavalent nickel complex, Ni(BeCp)<sub>6</sub>, has been synthesized, and aromaticity has also been calculated to contribute to its stability.<ref>{{Cite journal |last=Boronski |first=Josef T. |last2=Crumpton |first2=Agamemnon E. |last3=Aldridge |first3=Simon |date=2024-12-12 |title=A Crystalline NiX6 Complex |url=https://pubs.acs.org/doi/10.1021/jacs.4c12125 |journal=Journal of the American Chemical Society |doi=10.1021/jacs.4c12125 |issn=0002-7863|pmc=11673578 }}</ref> 

===Alkoxy compounds===
Nickel ''tert''-butoxide Ni[OC(CH<sub>3</sub>)<sub>3</sub>]<sub>2</sub> is coloured violet. It is formed in the reaction of di-''tert''-butylperoxide with nickel carbonyl.<ref name="jolly1-1"/>

Nickel dimethoxide is coloured green.<ref>{{cite book |last1=Bradley] |first1=D.C.  
|title=Alkoxo and aryloxo derivatives of metals 
|date=2001 |publisher=Academic Press |location=San Diego |isbn=0-12-124140-8 |page=97}}</ref> 
There are also nickel chloride methoxides with formulae: NiClOMe, Ni<sub>3</sub>Cl<sub>2</sub>(OMe)<sub>4</sub> and Ni<sub>3</sub>Cl(OMe)<sub>5</sub> in which Nickel and oxygen appear to form a [[cubane-type cluster]].<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |page=[https://archive.org/details/alkoxoaryloxoder00brad/page/n101 100]}}</ref>

Other alkoxy compounds known for nickel include nickel dipropoxide, nickel di-isopropoxide, nickel ''tert''-amyloxide, and nickel di-''tert''-hexanoxide.<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |page=[https://archive.org/details/alkoxoaryloxoder00brad/page/n12 11]}}</ref> These can be formed by crystallising nickel chloride from the corresponding alcohol, which forms an adduct. This is then heated with a base.<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |page=[https://archive.org/details/alkoxoaryloxoder00brad/page/n20 19]}}</ref> Nickel(II) alkoxy compounds are polymeric and non-volatile.<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |page=[https://archive.org/details/alkoxoaryloxoder00brad/page/n69 68]}}</ref>

[[Ziegler catalysis]] uses nickel as a catalyst. In addition it uses diethylaluminum ethoxide, phenylacetylene and [[triethylaluminium]] It converts [[ethylene]] into [[1-butene]]. It can dimerise [[propylene]]. The catalyst, when combined with optically active phosphines, can produce optically active dimers. An intermediate formed is tris(ethylene)nickel.(CH<sub>2</sub>=CH<sub>2</sub>)<sub>3</sub>Ni in which the ethylene molecules connect to the nickel atom side on.<ref name="Jolly2-3">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1975 |volume=2 |publisher=Academic Press |location=New York |isbn=0-12-388402-0 |page=3}}</ref>

Homoletptic bimetallic alkoxides have two different metals, and the same alkoxy group. They include Ni[(μ&minus;OMe)<sub>3</sub>AlOMe]<sub>2</sub>, Ni[Al(OBu<sup>t</sup>)<sub>4</sub>]<sub>2</sub> (nickel tetra-''tert''-butoxyaluminate) and Ni[Al(OPr<sup>i</sup>)<sub>4</sub>]<sub>2</sub>. (nickel tetra-isopropoxyaluminate a pink liquid)<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |page=[https://archive.org/details/alkoxoaryloxoder00brad/page/n208 208]}}</ref> Potassium hexaisoproxynoibate and tantalate can react with nickel chloride to make Ni[Nb(OPr<sup>i</sup>)<sub>6</sub>]<sub>2</sub> and Ni[Ta(OPr<sup>i</sup>)<sub>6</sub>]<sub>2</sub>. Ni[Zr<sub>2</sub>(OPr<sup>i</sup>)<sub>9</sub>]<sub>2</sub> The bimetallic alkoxides are volatile and can dissolve in organic solvents.<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |pages=[https://archive.org/details/alkoxoaryloxoder00brad/page/n185 185]–192}}</ref> A trimetallic one exists [Zr<sub>2</sub>(OPr<sup>i</sup>)<sub>9</sub>]Ni[Al(OPr<sup>i</sup>)<sub>4</sub>].<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |pages=[https://archive.org/details/alkoxoaryloxoder00brad/page/n215 215]–216}}</ref> NiGe(OBu<sup>t</sup>)<sub>8</sub>], NiSn(OBu<sup>t</sup>)<sub>8</sub>] and NiPb(OBu<sup>t</sup>)<sub>8</sub>] are tricyclic. [Ni<sub>2</sub>(μ3&minus;OEt)<sub>2</sub>(μ&minus;OEt)<sub>8</sub>Sb<sub>4</sub>(OEt)<sub>6</sub>]

Heteroleptic bitmetallic ethoxides have more than one variety of alkoxy group, e.g. Ni[(μ&minus;OPr<sup>i</sup>)(μ&minus;OBu<sup>t</sup>)Al(OBu<sup>t</sup>)<sub>2</sub>]<sub>2</sub> which is a purple solid.

Oxoalkoxides contain extra oxygen in addition to the alcohol. With only nickel, none are known, but with antimony an octanuclear molecule exists [Ni<sub>5</sub>Sb<sub>3</sub>(μ4&minus;O)<sub>2</sub>(μ3&minus;OEt)<sub>3</sub>(&minus;OEt)<sub>9</sub>(OEt)<sub>3</sub>(EtOH)<sub>4</sub>].<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |pages=[https://archive.org/details/alkoxoaryloxoder00brad/page/n432 432]–433}}</ref>

===Aryloxy compounds===
There are many nickel compounds with the formula template Ni(OAr)XL<sub>2</sub> and Ni(OAr)<sub>2</sub>L<sub>2</sub>. L is a ligand with phosphorus or nitrogen atoms. OAr is a phenol group or O- attached to an aromatic ring. Often an extra molecule of the phenol is hydrogen bonded to the oxygen attached to nickel.<ref>{{cite book |last1=Bradley |first1=Don C. |last2=Mehrotra |first2=R. C. |last3=Rothwell |first3=Ian |last4=Sin |first4=A. 
|title=Alkoxo and aryloxo derivatives of metals 
|url=https://archive.org/details/alkoxoaryloxoder00brad |url-access=limited |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-124140-7 |pages=[https://archive.org/details/alkoxoaryloxoder00brad/page/n618 619]–621}}</ref>

===μ-bonded molecules===
Others include [[cyclododecatriene]] nickel and [[Trans,trans,trans-(1,5,9-Cyclododecatriene)nickel(0)|''t''-Ni(cdt)]].

===Sulfur rings===

Nickel bis-dithiobenzoate can form a violet coloured sodium salt.<ref name="jolly1-1"/>

Two bisperfluoromethyl-l,2-dithietene molecules react with nickel carbonyl to make a double ring compound with nickel linked to four sulfur atoms. This contains four trifluoromethyl groups and is dark purple. Instead of this methyl or phenyl can substitute. These can be made by substituted acetylenes with sulfur on nickel carbonyl, or on nickel sulfide. Bis-diphenyldithiene nickel has a planar structure<ref name="jolly1-18">{{cite book |last1=Jolly |first1=P. W. |last2=Wilke |first2=G. 
|title=The organic chemistry of nickel 
|date=1974 |publisher=Academic Press |location=New York |isbn=0-12-388401-2 |volume=1 |pages=18–19}}</ref>

===Nickel chalcogen cluster compound===

A hexameric compound [Ni(SR)<sub>2</sub>]<sub>6</sub> is produced in the reaction of nickel carbonyl with [[dialkyl sulfide]]s (RSR).<ref name="jolly1-18"/>

Nickel can be part of a cubane-type cluster with iron and [[chalcogen]]s. The metal atoms are arranged in a tetrahedron shape, with the sulfur or selenium making up another tetrahedron that combines to make a cube. For example, the [NiFe<sub>3</sub>S<sub>4</sub>(PPh<sub>3</sub>)(SEt)<sub>3</sub>]<sup>2−</sup> is a dianion that has a tetraethyl ammonium salt. Similar ion clusters are [NiFe<sub>3</sub>Se<sub>4</sub>(PPh<sub>3</sub>)(SEt)<sub>3</sub>]<sup>2−</sup> and [NiFe<sub>3</sub>Se<sub>4</sub>(SEt)<sub>4</sub>]<sup>3−</sup>.<ref>{{cite journal |last1=Ciurli |first1=Stefano |last2=Ross |first2=Paul K. |last3=Scott |first3=Michael J. |last4=Yu |first4=Shi Bao |last5=Holm |first5=R. H. 
|title=Synthetic nickel-containing heterometal cubane-type clusters with <math chem>\ce{NiFe3Q4}</math> cores (Q=sulfur, selenium) 
|journal=Journal of the American Chemical Society 
|date=June 1992 |volume=114 |issue=13 |pages=5415–5423 |doi=10.1021/ja00039a063}}</ref> In the natural world cube shaped metal sulfur clusters can have sulfur atoms that are part of [[cysteine]].

[Ni<sub>4</sub>Se<sub>23</sub>]<sup>4−</sup> has a cube with Ni{{sup|IV}}<sub>4</sub>Se<sub>4</sub> at its core, and then the nickel atoms are bridge across the cube faces by five Se<sub>3</sub> chains and one Se<sup>4</sup> chain. It is formed as a tetraethylammonium salt, from Li<sub>2</sub>Se, Se, NEt<sub>4</sub>Cl and nickel dixanthate in [[dimethylformamide]] as a solvent. This reaction also produces (NEt<sub>4</sub>)<sub>2</sub>Ni(Se<sub>4</sub>)<sub>2</sub>.<ref>{{cite journal |last1=McConnachie |first1=Jonathan M. |last2=Ansari |first2=Mohammad A. |last3=Ibers |first3=James A. 
|title=Synthesis and characterization of nickel chalcogenide <math chem>\ce{[Ni4Se4(Se3)5(Se4)]4}</math>- anion, a Ni(IV) cubane species 
|journal=Journal of the American Chemical Society 
|date=August 1991 |volume=113 |issue=18 |pages=7078–7079 |doi=10.1021/ja00018a079}}</ref>

===Nitrosyl compounds===

When liquid nickel carbonyl is dissolved in liquid hydrogen chloride, it can react with [[nitrosyl chloride]] to form a dimer Ni(NOCl)<sub>2</sub>. This then decomposes to Ni(NO)Cl<sub>2</sub>, which is polymeric.<ref name="jolly1-1"/>

Nickel carbonyl reacting with [[nitric oxide]] yields blue coloured mononitrosyl nickel NiNO. With cyclohexane as well, pale blue Ni(NO<sub>2</sub>)NO is produced with nitrous oxide as a side product. With cyclopentadiene as well, π-C<sub>5</sub>H<sub>5</sub>NiNO is produced.<ref name="jolly1-1"/>

== See also ==
* [[:Category:Nickel compounds]]
* [[Nickel(IV) organometallic complex]]

==References==
{{Reflist|30em}}

==Sources==

*{{cite book |last1=Mellor |first1=J. W. |chapter=Nickel 
|title=A COMPREHENSIVE TREATISE ON INORGANIC AND THEORETICAL CHEMISTRY VOLUME XV Ni Ru, Rh Pd, Os, Ir 
|chapter-url=http://tera-3.ul.cs.cmu.edu/NASD/01cf394d-c0ee-4090-918f-a8413fe96bee/China/disk6/73/51-150/31005548/HTML/00000414.htm |archive-url=https://web.archive.org/web/20170207113127/http://tera-3.ul.cs.cmu.edu/NASD/01cf394d-c0ee-4090-918f-a8413fe96bee/China/disk6/73/51-150/31005548/HTML/00000414.htm |url-status=dead |archive-date=2017-02-07 |access-date=31 May 2016 
|date=May 1936 }} (pages accessible by changing number on url)
*{{cite book |last1=Nichols |first1=David 
|title=The chemistry of iron, cobalt and nickel 
|date=1975 |publisher=Pergamon Press |location=Oxford |isbn=0080188737}}

{{Nickel compounds}}
{{Chemical compounds by element}}
{{Authority control}}

[[Category:Nickel compounds| ]]
[[Category:Chemical compounds by element|N]]