Nickel(II) complexes of 3-alkylacetylacetones

Abstract

Nickel(11) complexes have been prepared from 3-alkylacetylacetones, LH = CH₃COCHRCOCH₃ (R = Me, Et, Bu, and CH₂Ph). The anhydrous complexes, NiL₂, are red and diamagnetic in the solid state and dissolve in toluene to give equilibrium mixtures of monomeric, low-spin and trimeric, high-spin species. Equilibrium constants have been obtained for the low-spin-high-spin equilibrium when R = Et or CH₂Ph. Reaction with pyridine in toluene solution gives the adducts NiL₂ py₂, probably with Ni₂L₄ py as an intermediate. The relative stabilities of the low-spin and high-spin forms of NiL₂ are shown to depend not only on steric factors, but also on electronic factors related to the acid dissociation constants of the ligands, LH.