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Nickel(II) hydroxide
Names
	IUPAC name Nickel(II) hydroxide
	Other names Nickel hydroxide, Theophrastite
Identifiers
CAS Number	12054-48-7 ; 36897-37-7 (monohydrate) ;
3D model (JSmol)	Interactive image;
ChemSpider	55452 ;
ECHA InfoCard	100.031.813
EC Number	235-008-5;
PubChem CID	61534;
RTECS number	QR648000;
UNII	L8UW92NW6J ;
CompTox Dashboard (EPA)	DTXSID90274011 ;
	InChI InChI=1S/Ni.2H2O/h;21H2/q+2;;/p-2 Key: BFDHFSHZJLFAMC-UHFFFAOYSA-L ; InChI=1/Ni.2H2O/h;21H2/q+2;;/p-2 Key: BFDHFSHZJLFAMC-NUQVWONBAJ;
	SMILES [Ni+2].[OH-].[OH-];
Properties
Chemical formula	Ni(OH)2
Molar mass	92.724 g/mol (anhydrous) ; 110.72 g/mol (monohydrate)
Appearance	green crystals
Density	4.10 g/cm3
Melting point	230 °C (446 °F; 503 K) (anhydrous, decomposes)
Solubility in water	0.0015 g/L
Solubility product (Ksp)	5.48×10−16
Magnetic susceptibility (χ)	+4500.0·10−6 cm3/mol
Structure
Crystal structure	hexagonal, hP3
Space group	P3m1, No. 164
Lattice constant	a = 0.3117 nm, b = 0.3117 nm, c = 0.4595 nm α = 90°, β = 90°, γ = 120°
Thermochemistry
Std molar; entropy (S⦵298)	79 J·mol−1·K−1
Std enthalpy of; formation (ΔfH⦵298)	−538 kJ·mol−1
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H315, H317, H332, H334, H341, H350, H360, H372
Precautionary statements	P201, P260, P280, P284, P405, P501
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	1515 mg/kg (oral, rat)
Safety data sheet (SDS)	External SDS
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Nickel(II) hydroxide is the inorganic compound with the formula Ni(OH)₂. It is a lime-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-hydroxide, leading to widespread applications in rechargeable batteries.^[6]

Properties

Nickel(II) hydroxide has two well-characterized polymorphs, α and β. The α structure consists of Ni(OH)₂ layers with intercalated anions or water.^[7]^[8] The β form adopts a hexagonal close-packed structure of Ni²⁺ and OH⁻ ions.^[7]^[8] In the presence of water, the α polymorph typically recrystallizes to the β form.^[7]^[9] In addition to the α and β polymorphs, several γ nickel hydroxides have been described, distinguished by crystal structures with much larger inter-sheet distances.^[7]

The mineral form of Ni(OH)₂, theophrastite, was first identified in the Vermion region of northern Greece, in 1980. It is found naturally as a translucent emerald-green crystal formed in thin sheets near the boundaries of idocrase or chlorite crystals.^[10] A nickel-magnesium variant of the mineral, (Ni,Mg)(OH)₂ had been previously discovered at Hagdale on the island of Unst in Scotland.^[11]

Reactions

Nickel(II) hydroxide is frequently used in electrical car batteries.^[8] Specifically, Ni(OH)₂ readily oxidizes to nickel oxyhydroxide, NiOOH, in combination with a reduction reaction, often of a metal hydride (reaction 1 and 2).^[12]^[13]

Reaction 1 Ni(OH)₂ + OH⁻ → NiO(OH) + H₂O + e⁻

Reaction 2 M + H₂O + e⁻ → MH + OH⁻

Net Reaction (in H₂O) Ni(OH)₂ + M → NiOOH + MH

Of the two polymorphs, α-Ni(OH)₂ has a higher theoretical capacity and thus is generally considered to be preferable in electrochemical applications. However, it transforms to β-Ni(OH)₂ in alkaline solutions, leading to many investigations into the possibility of stabilized α-Ni(OH)₂ electrodes for industrial applications.^[9]

Synthesis

The synthesis entails treating aqueous solutions of nickel(II) salts with potassium hydroxide. When the same reaction is conducted in the presence of bromine, the product is Ni₃O₂(OH)₄.^[14]

Toxicity

The Ni²⁺ ion is a carcinogen when inhaled.

References

^ CRC Handbook of Chemistry and Physics (84 ed.). CRC press. 2003. pp. 4–71. ISBN 0849304849.
^ John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.
^ Enoki, Toshiaki; Tsujikawa, Ikuji (1975). "Magnetic Behaviours of a Random Magnet, Ni_pMg_(1-p)(OH₂)". Journal of the Physical Society of Japan. 39 (2): 317. Bibcode:1975JPSJ...39..317E. doi:10.1143/JPSJ.39.317.
^ ^a ^b Zumdahl, Steven S. (2009). Chemical Principles (6 ed.). Houghton Mifflin Company. p. A22. ISBN 978-0-618-94690-7.
^ "Nickel Hydroxide". American Elements. Retrieved 2018-08-30.
^ Chen, J.; Bradhurst, D.H.; Dou, S.X.; Liu, H.K. (1999). "Nickel Hydroxide as an Active Material for the Positive Electrode in Rechargeable Alkaline Batteries". Journal of the Electrochemical Society. 146 (10): 3606–3612. Bibcode:1999JElS..146.3606C. doi:10.1149/1.1392522. S2CID 33058220.
^ ^a ^b ^c ^d Oliva, P.; Leonardi, J.; Laurent, J.F. (1982). "Review of the structure and the electrochemistry of nickel hydroxides and oxy-hydroxides". Journal of Power Sources. 8 (2): 229–255. Bibcode:1982JPS.....8..229O. doi:10.1016/0378-7753(82)80057-8.
^ ^a ^b ^c Jeevanandam, P.; Koltypin, Y.; Gedanken, A. (2001). "Synthesis of Nanosized α-Nickel Hydroxide by a Sonochemical Method". Nano Letters. 1 (5): 263–266. Bibcode:2001NanoL...1..263J. doi:10.1021/nl010003p.
^ ^a ^b Shukla, A.K.; Kumar, V.G.; Munichandriah, N. (1994). "Stabilized α-Ni(OH)₂ as Electrode Material for Alkaline Secondary Cells". Journal of the Electrochemical Society. 141 (11): 2956–2959. Bibcode:1994JElS..141.2956V. doi:10.1149/1.2059264.
^ Marcopoulos, T.; Economou, M. (1980). "Theophrastite, Ni(OH)₂, a new mineral from northern Greece" (PDF). American Mineralogist. 66: 1020–1021.
^ Livingston, A.; Bish, D. L. (1982). "On the new mineral theophrastite, a nickel hydroxide, from Unst, Shetland, Scotland" (PDF). Mineralogical Magazine. 46 (338): 1. Bibcode:1982MinM...46....1L. doi:10.1180/minmag.1982.046.338.01. S2CID 8381523.
^ Ovshinsky, S.R.; Fetcenko, M.A.; Ross, J. (1993). "A nickel metal hydride battery for electric vehicles". Science. 260 (5105): 176–181. Bibcode:1993Sci...260..176O. doi:10.1126/science.260.5105.176. PMID 17807176. S2CID 9523468.
^ Young, Kwo (2016). Nickel Metal Hydride Batteries. MDPI. doi:10.3390/books978-3-03842-303-4. ISBN 978-3-03842-303-4.
^ O. Glemser (1963). "Nickel (II) Hydroxide and Nickel (II,III) Hydroxide". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2. New York: Academic Press. p. 1549-1551.