Synthesis of cubane-type Ni(ii) complexes from pyridyl-alcohol ligands; their single-molecule magnet behaviour

Abstract

The reactions of NiCl₂·2H₂O or [NiCl₂(DME)] (DME = dimethoxyethane) with 2-methyl-1-(pyridin-2-yl)propan-2-ol (HL) and 2-(pyridin-2-yl)ethanol (HL_Et), in a 1 : 1 ratio, afforded the tetranuclear, cubane-type clusters [Ni(μ₃-Cl)Cl(HL)]₄ (3) and [Ni(μ₃-Cl)Cl(HL_Et)]₄ (4), respectively. These are tetramers of the hypothetical mononuclear formula-isomers [NiCl₂(HL)] and [NiCl₂(HL_Et)], respectively, and represent rare examples of structurally characterized cubane-like transition metal dihalogenide complexes. The 2 : 1 reactions between HL or HL_Et and [NiCl₂(DME)] yielded, instead, the mononuclear [NiCl₂(HL)₂] (1) and the dinuclear complex [Ni(μ-Cl)(HL_Et)₂]₂Cl₂ (2), respectively. The reaction of 3 with NaOH afforded selectively the cubane-type cluster [Ni(μ₃-OH)Cl(HL)]₄ (5) which differs only in the nature of the capping anions (Cl vs. OH, respectively). The magnetic properties of the unusual tetranuclear cubanes 3 and 5 have been investigated and revealed in both cases single-molecule magnet (SMM) behaviour.