Nickel(II) acetylacetonate

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Nickel(II) acetylacetonate
Other names

Ni(acac)2, nickel acac

Identifiers
CAS number 3264-82-2 YesY
PubChem 273707
Properties
Molecular formula C10H14NiO4 or C30H42Ni3O12 (trimer)
Molar mass 256.91 g/mol
Appearance dark green
Density 1.455 g/cm3
Melting point 229.5 °C (decomposes)
Boiling point decomposes
Solubility in water H2O
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Nickel(II) acetylacetonate is a coordination complex with the formula [Ni(acac)2]3, where acac is the anion C5H7O2- derived from deprotonation of acetylacetone, . It is a dark green paramagnetic solid that is soluble in organic solvents such as toluene. It reacts with water to give the blue-green diaquo complex Ni(acac)2(H2O)2.[1]

Structure and properties

Anhydrous nickel(II) acetylacetonate exists as molecules of Ni3(acac)6. This structure is not cyclic; the three nickel atoms are approximately collinear and each pair of them is bridged by two μ2 oxygen atoms. Each nickel atom has tetragonally distorted octahedral geometry, caused by the difference in the length of the Ni-O bonds between the bridging and non-bridging oxygens.[2] Ni3(acac)6 molecules are almost centrosymmetric, despite the non-centrosymmetric point group of the cis-Ni(acac)2 "monomers," which is uncommon.[3] The trimeric structure allows all nickel centers to achieve an octahedral coordination. The trimer is only formed if intramolecular sharing of oxygen centers between pairs of nickel centers occurs.

When bound to bulkier analogues of acetylacetonate ligand, steric hindrance favors formation of the mononickel derivatives. This behavior is observed for the derivative of 3-methylacetylacetonate.[4]

Dihydrate

As in the anhydrous form, the Ni(II) centres occupy octahedral coordination sites. The coordination sphere is provided by two bidentate acetylacetonate (acac) ligands and two aquo ligands. Ni(acac)2(H2O)2 exists as cis and trans isomers.[5] The trans isomer is preferred over the cis isomer (which was only found when pyridine N-oxide was used as the solvent).[6] 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).[7]

Trans and cis isomers of [Ni(acac)2X2] where X is a coordinating molecule

Synthesis

Bis(2,4-pentanedionato)nickel(II) is prepared by treating nickel nitrate with acetylacetone in the presence of base. The product is the blue-green diaquo complex Ni(CH3COCHCOCH3)2(H2O)2.[8]

Ni(NO3)2 + 2 CH3COCH2COCH3 + 2 H2O + 2 NaOH → Ni(CH3COCHCOCH3)2(H2O)2 + 2 NaNO3

This complex can be dehydrated using a Dean-Stark trap by azeotropic distillation:[8]

3 Ni(CH3COCHCOCH3)2(H2O)2 → [Ni(CH3COCHCOCH3)2]3 + 6 H2O

Subliming Ni(acac)2(H2O)2 at 170–210 °C under reduced pressure (0.2-0.4 mmHg) also gives the anhydrous form.[3]

Reactions

The anhydrous complex reacts with a range of Lewis bases to give monomeric adducts:

[Ni(CH3COCHCOCH3)2]3 + 6 L → 3 Ni(CH3COCHCOCH3)2L2

Ni(acac)2(H2O)2 reacts quickly in high yield at a methine positions, producing diamides from isocyanates. Related reactions occur with diethyl azodicarboxylate and dimethyl acetylenedicarboxylate:

Ni(acac)2(H2O)2 + 2 PhNCO → Ni(O2C5Me2C(O)NHPh)2 + 2 H2O

The trimer condenses with N,N-dimethylaminoethanol to imino derivatives.[9]

3 [Ni(acac)2]3 + 6 Me2NCH2CH2OH → 3 [Ni(acac)2(OCH2CH2NMe2)] + 3 H2

Applications

The anhydrous complex is the precursor to nickel-based catalysts such as nickel bis(cyclooctadiene).

[Ni(acac)2]3 is a precursor for the deposition of NiO thin film on conductive glass substrates using solution-gel techniques.[9]

References

  1. ↑ R. C. Mehrotram, R. Bohra, D.P. Gaur (1987). Metal ß-Diketones And Allied Derivatives. 
  2. ↑ 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. 
  3. ↑ 3.0 3.1 G. J. Bullen, R. Mason & P. Pauling. (1965). "The crystal and Molecular Structure of Bis(acetylacetonato)nickel (II)". Inorganic Chemistry 4 (4): 456–462. doi:10.1021/ic50026a005. 
  4. ↑ 1. A. Döhring, R. Goddard, P. W. Jolly, C. Krüger, V. R. Polyakov, "Monomer-Trimer Isomerism in 3-Substituted Pentane-2,4-dione Derivatives of Nickel(II)", Inorg. Chemistry 1997, 36, 177-183. doi:10.1021/ic960441c
  5. ↑ 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. 
  6. ↑ B. N. Figgis, M. A. Hitchman (2000). Ligand Field Theory and its Application. 
  7. ↑ O. Metin, L. T. Yildirim & S. Ozkar (2007). "Synthesis, characterization and crystal structure of bis(acetylacetonato)dimethanolnickel(II)". Inorganic Chemistry 10 (9): 1121–1123. doi:10.1016/j.inoche.2007.06.011. 
  8. ↑ 8.0 8.1 J. W. Wielandt, D. Ruckerbauer "Bis(1,5-cyclooctadiene)nickel(0)" Inorganic Syntheses 2010, vol. 35, p. 120. doi:10.1002/9780470651568.ch6
  9. ↑ 9.0 9.1 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 (9): 2329–2334. doi:10.1039/b103288g. 
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