Crystal structure and spin-doublet electron spin resonance of a magnetically coupled di(µ-phenoxo)-copper(II)nickel(II) complex
Abstract
The complex [CuNiL][ClO4]2·H2O (SNi= 1) of a dinucleating macrocycle H2L, derived from the [2: 1 : 1] condensation of 2,6-diformyl-4-methylphenol, 1,2-diaminoethane and 1,4-diaminobutane, has been obtained. The efflorescent dimethylformamide (dmf) adduct [CuNiL][ClO4]2·H2O·2dmf crystallizes in the orthorhombic crystal system, space group P212121 with Z= 4, a= 15.62(1), b= 16.49(1) and c= 14.75(1)Å. Crystallographic refinement converged with R= 0.060 and R′= 0.048 for 2958 reflections having I > 3.00σ(I). The structure comprises [CuNiL(dmf)(H2O)]2+ where the two metal ions are bridged by the endogenous phenolic oxygens of the macrocycle and Cu ⋯ Ni is 3.038(2)Å. The Cu resides at a N2O2 site with an ethylene lateral chain and assumes an essentially planar geometry, the Ni at a site with a tetramethylene lateral chain and a pseudo-octahedral geometry having dmf and water molecules at the axial sites. The complex [CuNiL][ClO4]2·H2O exhibits a strong antiferromagnetic spin exchange (J=–90 cm–1 based on H=–2JS1S2) and shows an axial ESR feature with g∥= 2.16, g⊥= 2.27 and A∥= 64 × 10–4 cm–1(in frozen dmf at 78 K), attributable to a spin-doublet ground state. The relations g⊥ > g∥ and A∥=–⅓ACu{ACu is the hyperfine coupling constant of the analogous [CuZnL][ClO4]2·H2O} demonstrate that one unpaired electron of the spin-coupled complex resides in the molecular orbital of dz2 character comprising dz2(Cu) and dz2(Ni).