Nickel(II) acetylacetonate

Nickel(II) acetylacetonate
Ball-and-stick model of the nickel(II) acetylacetonate complex
Names
Other names
Ni(acac)2, nickel acac
Identifiers
3264-82-2 YesY
ECHA InfoCard 100.019.887
PubChem 5359853
Properties
C10H14NiO4 or C30H42Ni3O12 (trimer)
Molar mass 256.91 g/mol
Appearance dark green
Density 1.455 g/cm3
Melting point 229.5 °C (445.1 °F; 502.6 K) (decomposes)
Boiling point decomposes
H2O
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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 cleaves with bases such as N,N-dimethylaminoethanol and TMEDA.[9]

[Ni(acac)2]3 + 3 chel → 3 [Ni(acac)2(chel)]

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 sol-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. 1 2 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. 1 2 Wielandt, J. W.; Ruckerbauer, D. (2010). "Bis(1,5-cyclooctadiene)nickel(0)". Inorganic Syntheses. 35: 120. doi:10.1002/9780470651568.ch6.
  9. 1 2 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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