Nickel compounds
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Nickel compounds are chemical compounds containing the element
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
which is a member of the
group 10 Group 10, numbered by current IUPAC style, is the group of chemical elements in the periodic table that consists of nickel (Ni), palladium (Pd), platinum (Pt), and darmstadtium (Ds). All are d-block transition metals. All known isotopes of d ...
of the
periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
. Most compounds in the group have an
oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
of +2. Nickel is classified as a
transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
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 Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
due to the
ionic radii Ionic radius, ''r''ion, is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation ...
of the cations being almost the same. Nickel forms many
coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. M ...
es. Nickel tetracarbonyl was the first pure metal carbonyl produced, and is unusual in its volatility.
Metalloprotein Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins (out of ~20,000) contain zinc-binding protein domains al ...
s containing nickel are found in biological systems. Nickel forms simple binary compounds with non metals including
halogens The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group i ...
, chalcogenides, and
pnictides A pnictogen ( or ; from grc, πνῑ́γω "to choke" and -gen, "generator") is any of the chemical elements in group 15 of the periodic table. Group 15 is also known as the nitrogen group or nitrogen family. Group 15 consists of the ele ...
. Nickel ions can act as a cation in salts with many acids, including common
oxoacid An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce ...
s. Salts of the hexaaqua ion (Ni2+) 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 quarternary compounds (with four elements) of nickel have been studied for
superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...
properties, as nickel is adjacent to copper and iron in the periodic table can form compounds with the same structure as the high-temperature superconductors that are known.


Colour

Most of the common
salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...
of nickel are green due to the presence of hexaaquanickel(II) ion, Ni(H2O)62+.


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 In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...
, but this can be distorted if ligands are not equivalent. For four coordinate nickel arrangements can be square planar, or
tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
. Five coordinated nickel is rarer.


Magnetism

Some nickel compounds are
ferromagnetic Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...
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 Matrix isolation is an experimental technique used in chemistry and physics. It generally involves a material being trapped within an unreactive matrix. A ''host'' matrix is a continuous solid phase in which ''guest'' particles (atoms, molecules, ...
, nickel can form dimers, a molecule with two nickel atoms: Ni2. Ni2 has a bonding energy of 2.07±0.01 eV. For Ni2+ the bond energy is around 3.3 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.


Oxides

Nickel oxides include Nickel(II) oxide and
Nickel(III) oxide Nickel (III) oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subf ...
.


Hydroxides

Nickel hydroxides are used in nickel–cadmium and Nickel–metal hydride batteries. Nickel(II) hydroxide Ni(OH)2, the main hydroxide of nickel is coloured apple green. It is known as the mineral
theophrastite Nickel(II) hydroxide is the inorganic compound with the formula Ni(OH)2. It is an apple-green solid that dissolves with decomposition in ammonia and amines and is attacked by acids. It is electroactive, being converted to the Ni(III) oxy-hydroxi ...
. β-NiO(OH) is a black powder with nickel in the +3 oxidation state. It can be made by oxidising
nickel nitrate Nickel nitrate is the inorganic compound Ni(NO3)2 or any hydrate thereof. The anhydrous form is not commonly encountered, thus "nickel nitrate" usually refers to nickel(II) nitrate hexahydrate. The formula for this species is written in two way ...
in a cold alkaline solution with
bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
. A mixed oxidation state hydroxide Ni3O2(OH)4 is made if oxidation happens in a hot alkaline solution. A Ni4+ hydroxide: nickel peroxide hydrate NiO2, can be made by oxidising with alkaline peroxide. It is black, and unstable and oxidises water.


Halides

Nickel(II) fluoride NiF2 is yellow, crystallising in the rutile structure and can form a trihydrate, NiF2·3H2O. A tetrahydrate also exists.
Nickel chloride Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl2. The anhydrous salt is yellow, but the more familiar hydrate NiCl2·6H2O is green. Nickel(II) chloride, in various forms, is the most important source of nickel for che ...
NiCl2 is yellow, crystallising in the
cadmium chloride Cadmium chloride is a white crystalline compound of cadmium and chloride, with the formula CdCl2. This salt is a hygroscopic solid that is highly soluble in water and slightly soluble in alcohol. The crystal structure of cadmium chloride (describ ...
structure. It can form a hexahydrate, NiCl2·6H2O, a tetrahydrate NiCl2·4H2O over 29 °C and a dihydrate, NiCl2·2H2O over 64 °C. Ammine complexes like
hexaamminenickel chloride Hexaamminenickel chloride is the chemical compound with the formula i(NH3)6l2. It is the chloride salt of the metal ammine complex i(NH3)6sup>2+. The cation features six ammonia (called ammines in coordination chemistry) ligands attached to the ...
also exist. Nickel bromide NiBr2 is yellow, also crystallising in the cadmium chloride structure. It can form a hexahydrate, NiBr2·6H2O. Crystallisation above 29° forms a trihydrate NiBr2·3H2O, and a dihydrate NiBr2·2H2O.Nicholls p1126-1127 Nonahydrate, NiBr2·9H2O can crystallise from water below 2 °C. Nickelous hexammine bromide Ni(NH3)6Br2is violet or blue. It is soluble in boiling aqueous
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
, but is insoluble in cold. Diammine, monoammine, and dihydrazine nickel bromides also exist. With four bromide atoms nickel(II) forms a series of salts called tetrabromonickelates. Nickel iodide NiI2 is black, also crystallising in the cadmium chloride structure. It can form a green hexahydrate, NiI2·6H2O. Nickel iodide has a brown diammine NiI2•2NH3 and a bluish-violet hexammine NiI2•6NH3. Nickel(III) fluoride NiF3 Nickel(IV) fluoride NiF4


Chalcogenides

By reacting nickel with
chalcogen The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
s,
nickel sulfide Nickel sulfide is any inorganic compound with the formula NiSx. They range in color from bronze (Ni3S2) to black (NiS2). The nickel sulfide with simplest stoichiometry is NiS, also known as the mineral millerite. From the economic perspective, ...
, nickel selenide, and nickel telluride are formed. There are numerous sulfides: Ni1.5S, Ni17S18, Ni3S2 (
heazlewoodite Heazlewoodite, Ni3S2, is a rare sulfur-poor nickel sulfide mineral found in serpentinitized dunite. It occurs as disseminations and masses of opaque, metallic light bronze to brassy yellow grains which crystallize in the trigonal crystal system. ...
), Ni3S4 (
polydymite Polydymite, Ni2+Ni23+S4, is a supergene thiospinel sulfide mineral associated with the weathering of primary pentlandite nickel sulfide. Polydymite crystallises in the isometric system, with a hardness of 4.5 to 5.5 and a specific gravity of abo ...
), Ni9S8 ( godlevskite), NiS (
millerite Millerite is a nickel sulfide mineral, Ni S. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates. It can be distinguished from pentlandite by crystal habit, its duller colour, and general la ...
) and two other NiS forms, NiS2 (
vaesite Vaesite ( Ni S2) is a mineral found together with cattierite in the Democratic Republic of Congo. It is named after Johannes F. Vaes, a Belgian mineralologist. It is part of the pyrite group The pyrite group of minerals is a set of cubic crystal ...
) in pyrite structure. Black nickel tetrasulfide NiS4 is formed from ammonium polysulfide and nickel in water solution. Mixed and double sulfides of nickel also exist. Nickel with
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
forms several compounds Ni1−xSe 0≤x≤0.15, Ni2Se3, NiSe2 also known as a mineral
penroseite Penroseite is a rare selenide mineral with formula (Ni,Co,Cu)Se2. It has a gray-steel color and black streak with a hardness of 3. It is an isometric mineral, 2/m. Penroseite was first discovered in 1925 in a Bolivian rhyolite. It was named for ...
. Nickel forms two different
polonide A polonide is a chemical compound of the radioactive element polonium with any element less electronegative than polonium. Polonides are usually prepared by a direct reaction between the elements at temperatures of around 300–400 °C... They a ...
s by heating nickel and
polonium Polonium is a chemical element with the symbol Po and atomic number 84. Polonium is a chalcogen. A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character ...
together: NiPo and NiPo2.


Pnictides

Non-stoichiometric compounds of nickel with
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
,
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
and
antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...
exist, and some are found in nature. One interstitial
nitride In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...
has formula Ni3N (hexagonal P6322, Z = 2, a = 4.6224 Å and c = 4.3059 Å). In a
solid nitrogen Solid nitrogen is a number of solid forms of the element nitrogen, first observed in 1884. Solid nitrogen is mainly the subject of academic research, but low-temperature, low-pressure solid nitrogen is a substantial component of bodies in the ou ...
matrix, nickel atoms combine with nitrogen molecules to yield Ni(N2)4. Nickel phosphide Ni2P has density 7.33 and melts at 1100 °C. The mineral
Nickelskutterudite Named after Skuterudåsen, a hill in Modum, Norway, skutterudite is a cobalt arsenide mineral containing variable amounts of nickel and iron substituting for cobalt with the ideal formula CoAs3. Some references give the arsenic a variable formula ...
has formula NiAs2-3,
nickeline Nickeline or niccolite is a mineral consisting primarily of nickel arsenide (NiAs). The naturally-occurring mineral contains roughly 43.9% nickel and 56.1% arsenic by mass, but composition of the mineral may vary slightly. Small quantities of ...
has formula NiAs and
breithauptite Breithauptite is a nickel antimonide mineral with the simple formula NiSb. Breithauptite is a metallic opaque copper-red mineral crystallizing in the hexagonal - dihexagonal dipyramidal crystal system. It is typically massive to reniform in habit, ...
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 g/cm3. NiAsS
gersdorffite Gersdorffite is a nickel arsenic sulfide mineral with formula NiAsS. It crystallizes in the isometric system showing diploidal symmetry. It occurs as euhedral to massive opaque, metallic grey-black to silver white forms. Gersdorffite belongs to ...
, and NiSbS
ullmannite Ullmannite is a nickel antimony sulfide mineral with formula: NiSbS. Considerable substitution occurs with cobalt and iron in the nickel site along with bismuth and arsenic in the antimony site. A solid solution series exists with the high c ...
, NiAsSe Jolliffeite are pnictide/chalcogenide compounds that occur as minerals.


Other

Nickel also forms
carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of t ...
s and
boride A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some bo ...
s. Nickel borides include forms Ni2B (a green/black solid), NiB, Ni3B, ''o''-Ni4B3 and ''m''-Ni4B3. Nickel hydride NiH is only stable under
high pressure In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. By ''high pressure'' is usually meant pressures of th ...
s of
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
.
Nickel silicide Nickel silicides include several intermetallic compounds of nickel and silicon. Nickel silicides are important in microelectronics as they form at junctions of nickel and silicon. Additionally thin layers of nickel silicides may have applicati ...
s include Ni3Si, Ni31Si12, Ni2Si, Ni3Si2, NiSi and NiSi2. Nickel silicides are used in
microelectronics Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre- ...
.


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 emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an electron making a transition from a high energy state to a lower energy state. The photon energy of ...
. The nickel monohalides are well studied.


Alloys

Compounds of nickel with other metals can be called
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
s. The substances with fixed composition include
nickel aluminide Nickel aluminide typically refers to the one of the two most widely used compounds, Ni3Al or NiAl, however is generally any aluminide from the Ni-Al system. These alloys are widely used due to their corrosion resistance, low-density and easy product ...
(NiAl) melting at 1638° with hexagonal structure. NiY, NiY3, Ni3Y, Ni4Y, NiGd3, BaNi2Ge2 changes structure from orthorhombic to tetragonal around 480 °C. This is a ternary intermetallic compound. Others include BaNiSn3 and the superconductors SrNi2Ge2, SrNi2P2, SrNi2As2, BaNi2P2, BaNi2As2.


Simple salts


Oxo acid salts

Important nickel oxo acid salts include
nickel(II) sulfate Nickel(II) sulfate, or just nickel sulfate, usually refers to the inorganic compound with the formula NiSO4(H2O)6. This highly soluble blue green coloured salt is a common source of the Ni2+ ion for electroplating. Approximately 40,000 tonnes wer ...
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. 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 °C. The heptahydrate crystallises from water below 31.5 above this blue hexhydrate forms, and above 53.3 the green form. 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 Nickel nitrate is the inorganic compound Ni(NO3)2 or any hydrate thereof. The anhydrous form is not commonly encountered, thus "nickel nitrate" usually refers to nickel(II) nitrate hexahydrate. The formula for this species is written in two way ...
, and nickel phosphate


Fluoro acid salts

Nickel tetrafluoroborate, Ni(BF4)2 is very soluble in water, alcohol and acetonitrile. It is prepared by dissolving nickel carbonate in
tetrafluoroboric acid Fluoroboric acid or tetrafluoroboric acid (archaically, fluoboric acid) is an inorganic compound with the chemical formula +BF4−], where H+ represents the solvated proton. The solvent can be any suitably Lewis-basic entity. For instance, in w ...
. Nickel tetrafluoroberyllate NiBeF4•''x''H2O, can be hydrated with six or seven water molecules. Both nickel hexafluorostannate \ce and nickel fluorosilicate \ce crystallise in the trigonal system. Nickel hexafluorogermanate NiGeF6 has a rosy-tan colour and a hexagonal crystal with a = 5.241 Å unit cell volume is 92.9 Å3. It is formed in the reaction with GeF4 and K2NiF6. Nickel fuorotitanate \ce 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). Ni(AsF6)2, Ni(SbF6)2, Ni(BiF6)2 are made by reacting the hexafluoro acid with NiF2 in
hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepres ...
. They all have hexagonal crystal structure, resembling the similar salts of the other first row transition metals. For Ni(AsF6)2 a = 4.98, c = 26.59, and V = 571, formula weight Z=3. Ni(SbF6)2 is yellow with a = 5.16Å, c = 27.90Å Z = 3. The structure resembles LiSbF6, but with every second metal along the c axis missing. Others include the green fluorohafnate NiHfF6, and Ni2HfF8, NiZrF6


Chloroacid salts

Nickel tetrachloroiodate Ni(ICl4)2 can be made by reacting iodine with nickel chloride and chlorine gas. It consists of green needles.


Nitrogen anion salts

Nickel cyanide tetrahydrate Ni(CN)2 is insoluble in water, but dissolves in aqueous ammonia. It forms double salts with interesting structures. Nickel azide Ni(N3)2 is a sensitive explosive. It can be made by treating nickel carbonate with
hydrazoic acid Hydrazoic acid, also known as hydrogen azide or azoimide, This also contains a detailed description of the contemporaneous production process. is a compound with the chemical formula . It is a colorless, volatile, and explosive liquid at room tem ...
. 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. 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. Nickel azide forms a dihydrate: Ni(N3)2 and a basic salt called nickel hydroxy azide Ni(OH)N3. Nickel amide, Ni(NH2)2 is a deep red compound that contains Ni6 clusters surrounded by 12 NH2 groups. Nickel amide also forms a series of double salts. Other homoleptic nickel amides derived by substituting the hydrogen atoms are Ni (C6H5)2sub>2 (diphenyl) and boryl amides Ni BMes2Messub>2 and Ni BMes2C6H5sub>2.


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

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 (NH4), or thallium. As a mineral the ammonium nickel salt, (NH4)2Ni(SO4)2, can be called nickelboussingaultite. With sodium, the double sulfate is nickelblödite Na2Ni(SO4)2 from the blödite family. Nickel can be substituted by other divalent metals of similar sized to make mixtures that crystallise in the same form. Nickel forms double salts with Tutton's salt structure with tetrafluoroberyllate with the range of cations of ammonia, potassium, rubidium, cesium, and thallium. Anhydrous salts of the formula M2Ni2(SO4)3, which can be termed metal nickel trisulfates, belong to the family of langbeinites. The known salts include (NH4)2Ni2(SO4)3, K2Ni2(SO4)3 and Rb2Ni2(SO4)3, and those of Tl and Cs are predicted to exist. Some minerals are double salts, for example Nickelzippeite Ni2(UO2)6(SO4)3(OH)10 · 16H2O which is isomorphic to cobaltzippeite, magnesiozippeite and zinczippeite, part of the zippeite group. Double hydrides of nickel exist, such as Mg2NiH4.


Ternary chalcogenides

Nickel forms a series of double nickel oxides with other elements, which may be termed "nickelates". There are also many well defined double compounds with sulfur, selenium and tellurium.


Ternary pnictides

Ternary pnictides that contain nickel are metallic and include MgNi2Bi4, SrNi2P2, SrNi2As2, BaNi2P2, and BaNi2As2.


Ternary halides

Nickel can form anions and salts with halogens including the hexafluoronickelates, and tetrafluoronickelates,
tetrachloronickelate Tetrachloronickelate is the metal complex with the formula iCl4sup>2−. Salts of the complex are available with a variety of cations, but a common one is tetraethylammonium. When concentrated lithium chloride and nickel chloride solution in ...
s, tetrabromonickelates and tetraiodonickelates. The subiodide Bi12Ni4I3 is also known.


Polyoxometallates

Nickel can enter into metal oxygen clusters with other high oxidation state elements to form
polyoxometalate In chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are ...
s. These may stabilize higher oxidation states of nickel, or show catalytic properties. Nonamolybdonickelate(IV), iMo9O32sup>6− can oxidize aromatic hydrocarbons to alcohols. There is a dark brown heptamolybdonickelate(IV) potassium salt, K2H8NiMo7O28·6H2O. 13-Vanadonickelate(IV) compounds such as K7NiV13O38 with black octahedral crystals exist. It can be made from isopolyvanadate, with nickel(II) oxidised by peroxydisulfate at a pH around 4. Nickel(IV) heteropolyniobates such as the dark maroon Na12NiNb12O38 are also known. An alternate orange red hydrate perhaps with 44 water molecules also exists. With nickel-II (tetramethylammonium)6[H3NiNb9O28 forms a green salt that is very soluble in water, but hardly soluble in ethanol. H43K14Na6Nb32 Ni10O183 is a nickel-cation-bridged polyoxoniobate which crystallizes in the monoclinic system with cell dimensions a=15.140 b=24.824 c=25.190 Å and β=103.469 and two formulas per unit cell. Na8Li12[Ni2(P2W15O56)2] forms a sandwich structure, and Na4Li5[Ni3(OH)3(H2O)3P2W16O59] is a Wells-Dawson polyoxometalate.


Acidic salts

Nickel hydrofluoride, H5NiF7·6H2O is made by using excess hydrofluoric acid solution on nickel carbonate. It is deep green.


Basic salts

Nickel oxyfluoride Ni4F4O(OH)2 is green. Nickelous enneaoxydiiodide 9NiO•Nil2 forms when solutions of nickel iodide are exposed to air and evaporated.


Complexes

Simple complexes of nickel include hexaquonickel(II), yellow tetracyanonickelate i(CN)4sup>2−, red pentacyanonickelate i(CN)5sup>3− only found in solution, i(SCN)4sup>2− and i(SCN)6sup>4−. Halo- complexes include iCl4sup>2−, iF4sup>2−, iF6sup>4−, iCl2(H2O)4 i(NH3)4(H2O)2sup>2+, i(NH3)6sup>2+, i(en)3)sup>2+. Some complexes have fivefold coordination. N H2CH2NMe2 (tris(N,N-dimethyl-2-aminoethyl)amine); P(o-C6H4SMe)3; P(CH2CH2CH2AsMe2)3. Other ligands for octahedral coordination include PPh3, PPh2Me and
thiourea Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the ''thio-'' prefix); however, the properties of urea a ...
. Nickel tetrahedral complexes are often bright blue and 20 times or more intensely coloured than the octahedral complexes. The ligands can include selections of neutral
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s,
arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications ...
s, arsine oxides,
phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
s or
phosphine oxide Phosphine oxides are phosphorus compounds with the formula OPX3. When X = alkyl or aryl, these are organophosphine oxides. Triphenylphosphine oxide is an example. An inorganic phosphine oxide is phosphoryl chloride (POCl3). Structure and bondi ...
s and halogens. 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 Ni4H4 shape in its core.
Nickel bis(dimethylglyoximate) Nickel bis(dimethylglyoximate) is the coordination complex with the formula Ni NC(CH3)C(CH3)NOHsub>2. The compound is a bright red solid. It achieved prominence for its use in the qualitative analysis of nickel. Structure The geometry of the n ...
, an insoluble red solid is important for
gravimetric analysis Gravimetric analysis describes a set of methods used in analytical chemistry for the quantitative determination of an analyte (the ion being analyzed) based on its mass. The principle of this type of analysis is that once an ion's mass has been ...
.


Bio molecules

Cofactor F430 F430 is the cofactor (sometimes called the coenzyme) of the enzyme methyl coenzyme M reductase (MCR). MCR catalyzes the reaction that releases methane in the final step of methanogenesis: : + HS–CoB → + CoB–S–S–CoM It is found ...
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 Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, some ...
or
selenocysteine Selenocysteine (symbol Sec or U, in older publications also as Se-Cys) is the 21st proteinogenic amino acid. Selenoproteins contain selenocysteine residues. Selenocysteine is an analogue of the more common cysteine with selenium in place of the ...
. Plant
urease Ureases (), functionally, belong to the superfamily of amidohydrolases and phosphotriesterases. Ureases are found in numerous bacteria, fungi, algae, plants, and some invertebrates, as well as in soils, as a soil enzyme. They are nickel-contai ...
s contain a bis-μ-hydroxo dimeric nickel cluster.
CO-methylating acetyl-CoA synthase Acetyl-CoA synthase (ACS), not to be confused with Acetyl-CoA synthetase or Acetate-CoA ligase (ADP forming), is a nickel-containing enzyme involved in the metabolic processes of cells. Together with Carbon monoxide dehydrogenase (CODH), it forms ...
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 Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for ...
. Nickel superoxide dismutase (or Ni-SOD) from ''
Streptomyces ''Streptomyces'' is the largest genus of Actinomycetota and the type genus of the family Streptomycetaceae. Over 500 species of ''Streptomyces'' bacteria have been described. As with the other Actinomycetota, streptomycetes are gram-positiv ...
'' contains six nickel atoms. The nickel holding is done by a "nickel binding hook" which as the amino acid pattern H2N-His-Cys-X-X-Pro-Cys-Gly-X-Tyr-rest of protein, where the bold bits are ligands for the nickel atom. 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 ''Cupriavidus metallidurans'' is a non-spore-forming, Gram-negative bacterium which is adapted to survive several forms of heavy metal stress. As a model and industrial system It is an ideal subject to study heavy metal disturbance of cell ...
'' the gene for this is ''hox''N.


Organometallics

Well known nickel organometalic (or organonickel) compounds include
Nickelocene Nickelocene is the organonickel compound with the formula Ni( ''η''5-C5H5)2. Also known as bis(cyclopentadienyl)nickel or NiCp2, this bright green paramagnetic solid is of enduring academic interest, although it does not yet have any known prac ...
,
bis(cyclooctadiene)nickel(0) Bis(cyclooctadiene)nickel(0) is the organonickel compound with the formula Ni(C8H12)2, also written Ni(cod)2. It is a diamagnetic coordination complex featuring tetrahedral nickel(0) bound to the alkene groups in two 1,5-cyclooctadiene ligands. Thi ...
and nickel tetracarbonyl. 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. The nickel tetracarbonyl molecule is tetrahedral, with a bond length for nickel to carbon of 1.82 Å. Nickel tetracarbonyl easily starts breaking apart over 36° forming Ni(CO)3, Ni(CO)2, and Ni. Ni(CO) and NiC appear in mass spectroscopy of nickel carbonyl. There are several nickel carbonyl cluster anions formed by reduction from nickel carbonyl. These are i2(CO)5sup>2−, dark red i3(CO)8sup>2−, i4(CO)9sup>2−, i5(CO)9sup>2−, i6(CO)12sup>2−. Salts such as Cd i4(CO)9and Li2 i3(CO)85acetone can be crystallised. Mixed cluster carbonyl anions like r2Ni3(CO)16sup>2−, o2Ni3(CO)16sup>2− and 2Ni3(CO)16sup>2− o4(CO)14sup>2− can form salts with bulky cations like tetraethylammonium. The brown iCo3(CO)11sup>− changes to red i2Co4(CO)14sup>2−. With oxygen or air the explosive Ni(CO)3O2 can be formed from nickel carbonyl. 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 C6H5N-C(CH3)=)2sub>2Ni. Another planar bis compound of nickel is formed with phenylazothioformamide C6H5N=NC(S)NR2, and dithizone C6H5N=NC(S)NHNHC6H5.
tetrasulfur tetranitride Tetrasulfur tetranitride is an inorganic compound with the formula . This gold-poppy coloured solid is the most important binary sulfur nitride, which are compounds that contain only the elements sulfur and nitrogen. It is a precursor to many S-N ...
when reduced with nickel carbonyl makes Ni 2S2Hsub>2 also coloured dark violet. 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.


Alkoxy compounds

Nickel ''tert''-butoxide Ni C(CH3)3sub>2 is coloured violet. It is formed in the reaction of di-''tert''-butylperoxide with nickel carbonyl. Nickel dimethoxide is coloured green. There are also nickel chloride methoxides with formulae: NiClOMe, Ni3Cl2(OMe)4 and Ni3Cl(OMe)5 in which Nickel and oxygen appear to form a
cubane-type cluster A cubane-type cluster is an arrangement of atoms in a molecular structure that forms a cube. In the idealized case, the eight vertices are symmetry equivalent and the species has Oh symmetry. Such a structure is illustrated by the hydrocarbon ...
. Other alkoxy compounds known for nickel include nickel dipropoxide, nickel di-isopropoxide, nickel ''tert''-amyloxide, and nickel di-''tert''-hexanoxide. These can be formed by crystallising nickel chloride from the corresponding alcohol, which forms an adduct. This is then heated with a base. Nickel(II) alkoxy compounds are polymeric and non-volatile. Ziegler catalysis uses nickel as a catalyst. In addition it uses diethylaluminum ethoxide, phenylacetylene and
triethylaluminium Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industrially ...
It converts
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...
into
1-butene 1-Butene (or 1-Butylene) is the organic compound with the formula CH3CH2CH=CH2. It is a colorless gas that is easily condensed to give a colorless liquid. It is classified as a linear alpha-olefin. It is one of the isomers of butene (butylene). ...
. It can dimerise
propylene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petro ...
. The catalyst, when combined with optically active phosphines, can produce optically active dimers. An intermediate formed is tris(ethylene)nickel.(CH2=CH2)3Ni in which the ethylene molecules connect to the nickel atom side on. Homoletptic bimetallic alkoxides have two different metals, and the same alkoxy group. They include Ni μ−OMe)3AlOMesub>2, Ni l(OBut)4sub>2 (nickel tetra-''tert''-butoxyaluminate) and Ni l(OPri)4sub>2. (nickel tetra-isopropoxyaluminate a pink liquid) Potassium hexaisoproxynoibate and tantalate can react with nickel chloride to make Ni b(OPri)6sub>2 and Ni a(OPri)6sub>2. Ni r2(OPri)9sub>2 The bimetallic alkoxides are volatile and can dissolve in organic solvents. A trimetallic one exists r2(OPri)9i l(OPri)4 NiGe(OBut)8], NiSn(OBut)8] and NiPb(OBut)8] are tricyclic. i2(μ3−OEt)2(μ−OEt)8Sb4(OEt)6 Heteroleptic bitmetallic ethoxides have more than one variety of alkoxy group, e.g. Ni μ−OPri)(μ−OBut)Al(OBut)2sub>2 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 i5Sb3(μ4−O)2(μ3−OEt)3(−OEt)9(OEt)3(EtOH)4


Aryloxy compounds

There are many nickel compounds with the formula template Ni(OAr)XL2 and Ni(OAr)2L2. 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.


μ-bonded molecules

Others include cyclododecatriene nickel and ''t''-Ni(cdt).


Sulfur rings

Nickel bis-dithiobenzoate can form a violet coloured sodium salt. 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


Nickel chalcogen cluster compound

A hexameric compound i(SR)2sub>6 is produced in the reaction of nickel carbonyl with dialkyl sulfides (RSR). Nickel can be part of a cubane-type cluster with iron and
chalcogen The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
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 iFe3S4(PPh3)(SEt)3sup>2− is a dianion that has a tetraethyl ammonium salt. Similar ion clusters are iFe3Se4(PPh3)(SEt)3sup>2− and iFe3Se4(SEt)4sup>3−. In the natural world cube shaped metal sulfur clusters can have sulfur atoms that are part of
cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, some ...
. i4Se23sup>4− has a cube with Ni4Se4 at its core, and then the nickel atoms are bridge across the cube faces by five Se3 chains and one Se4 chain. It is formed as a tetraethylammonium salt, from Li2Se, Se, NEt4Cl and nickel dixanthate in
dimethylformamide Dimethylformamide is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the majo ...
as a solvent. This reaction also produces (NEt4)2Ni(Se4)2.


Nitrosyl compounds

When liquid nickel carbonyl is dissolved in liquid hydrogen chloride, it can react with
nitrosyl chloride Nitrosyl chloride is the chemical compound with the formula NOCl. It is a yellow gas that is commonly encountered as a component of aqua regia, a mixture of 3 parts concentrated hydrochloric acid and 1 part of concentrated nitric acid. It is a ...
to form a dimer Ni(NOCl)2. This then decomposes to Ni(NO)Cl2, which is polymeric. Nickel carbonyl reacting with
nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ...
yields blue coloured mononitrosyl nickel NiNO. With cyclohexane as well, pale blue Ni(NO2)NO is produced with nitrous oxide as a side product. With cyclopentadiene as well, π-C5H5NiNO is produced.


See also

* Nickel(IV) organometallic complex


References


Sources

* (pages accessible by changing number on url) * {{Chemical compounds by element N