- Nickel(II) acetylacetonate
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Nickel(II) acetylacetonate 
Other namesNi(acac)2, nickel acacIdentifiers CAS number 3264-82-2 Properties Molecular formula C10H14NiO4 or C30H42Ni3O12 (trimer) Molar mass 256.91 Appearance dark green Density 1.455 g/cm3 Melting point 229.5 °C (dec.)
Boiling point 227.0 °C (dec.)
Solubility in water H2O 
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)Infobox references Nickel(II) acetylacetonate is a coordination complex with the formula [Ni(acac)2]3. This dark green solid reacts with water to give the dihydrate Ni(acac)2·2H2O.
Structure: Ni(II), bonded to two bidentate acetylacetonate (acac) ligands. Acac is a β-diketone that forms one oxygen-nickel covalent bond with the metal centre, and one oxygen-nickel coordinated bond. The Ni-O bonds are equivalent. It exists in two different configurations, one of which is its monomeric dihydrate, with two water ligands. Dehydration gives a trimer, [Ni(acac)2]3. Geometry at Ni is octahedral in both anhydrous and dihydrate.
Contents
Structure and properties
The nickels in Ni(acac)2 have tetragonally distorted octahedral geometry, caused by the difference in the length of the Ni-O bonds of bridging oxygens, and non-bridging oxygens.[1] Ni(acac)2 has a trinuclear structure that contains two nickel-nickel bonds. The trimeric structure of the compound is the smallest unit in which all nickel centers can obtain an octahedral coordination. The trimer is only formed if intramolecular sharing of oxygen centers between pairs of nickel centers occurs. For bulkier ligands, trimeric structures would not be precluded by steric hindrance.[2] The molecules are almost centrosymmetric, despite the noncentrosymmetric space group of the host, which is uncommon.[3]
Trans and cis isomers of [N(iacac)2X2] where X is a coordinating molecule
Ni(acac)2·2H2O also exhibits a tetragonally distorted octahedral geometry by coordinating to two additional solvent molecules, resulting in two isomers in the cis and trans form (Fig 1.).[4] The trans isomer is preferred over the cis isomer (which was only found when pyridine N-oxide was used as the solvent.[5] In the trans isomer, the X group occupies the axial position, forming Ni-O bonds in ethanol solvents. These axial bonds are greater in length (2.1000Å) than the equatorial Ni-O bonds (2.0085 Å and 1.9961Å).[6]
Synthesis
Bis(2,4-pentanedionato)nickel(II) is prepared by reacting nickel chloride with acetylacetone, yielding a blue-green hydrate Ni(CH3COCHCOCH3)2·2H2O. A range of solvents may be used in the reaction, depending on which of the isomers (trans or cis) of the hydrate is desired. Subliming Ni(acac)2·2H2O at 170-210 °C under reduced pressure (0.2-0.4 mmHg) gives the anhydrous form.[3]
- NiCl2 + 2CH3COCH2COCH3 + 2H2O → Ni(CH3COCHCOCH3)2·2H2O + 2HCl
- 3Ni(CH3COCHCOCH3)2·2H2O → [Ni(CH3COCHCOCH3)2]3 + 6H2O
Reactions
Ni(acac)2·2H2O reacts quickly, with a high yield at a methine position, producing diamides from isocyanates. Related reactions occur with diethyl azodicarboxylate and dimethyl acetylenedicarboxylate.
- Ni(acac)2·2H2O + 2PhNCO → Ni(O2C5Me2C(O)NHPh)2 + 2H2O
One reaction involving the trimer occurs when [Ni(acac)2]3 is reacted with N,N-dimethylaminoethanol, which has the ability to coordinate through oxygen and nitrogen donors.[7]
- 3[Ni(acac)2]3 + 6Me2NCH2CH2OH → 3[Ni(acac)2(OCH2CH2NMe2)] + 3H2
Applications
[Ni(acac)2]3 is used as a precursor for the deposition of NiO thin film on conductive glass substrates using solution-gel techniques. Ni(acac)2·2H2O is unsuitable for this reaction because its solubility in alcohol at room temperature is limited.[7]
References
- ^ R. C. Mehrotram, R. Bohra, D.P. Gaur (1987). Metal ß-Diketones And Allied Derivatives.
- ^ G. J. Bullen, R. Mason & P. Pauling (1961). "Octahedral Co-ordination of Nickel in Nickel(II) Bisacetylacetone". Nature 4761 (4761): 291–292. doi:10.1038/189291a0.
- ^ a b G. J. Bullen, R. Mason & P. Pauling. (1965). "The crystal and Molecular Structure of Bis(acetylacetonato)nickel (II)". Inorganic Chemistry 4: 456–462. doi:10.1021/ic50026a005.
- ^ M. Kudrat-E-Zahan, Y. Nishida & H. Sakiyama (2010). "Identification of cis/trans isomers of bis(acetylacetonato)nickel(II) complexes in solution based on electronic spectra". Inorganica Chimica Acta 363: 168–172. doi:10.1016/j.ica.2009.09.011.
- ^ B. N. Figgis, M. A. Hitchman (2000). Ligand Field Theory and its Application.
- ^ O. Metin, L. T. Yildirim & S. Ozkar (2007). "Synthesis, characterization and crystal structure of bis(acetylacetonato)dimethanolnickel(II)". Inorganic Chemistry 10: 1121–1123. doi:10.1016/j.inoche.2007.06.011.
- ^ a b Paul A. Williams, Anthony C. Jones, Jamie F. Bickley, Alexander Steiner, Hywel O. Davies, Timothy J. Leedham, Susan A. Impey, Joanne Garcia, Stephen Allen, Aline Rougier and Alexandra Blyr (2001). "Synthesis and crystal structures of dimethylaminoethanol adducts of Ni(II) acetate and Ni(II) acetylacetonate. Precursors for the sol–gel deposition of electrochromic nickel oxide thin films". Journal of Materials Chemistry 11: 2329–2334. doi:10.1039/b103288g.
Categories:- Nickel compounds
- Acetylacetonate complexes
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