Crystal structure and spin-doublet electron spin resonance of a magnetically coupled di(mu-phenoxo)-copper(II)nickel(II) complex

The complex [CuNiL][ClO4](2) . H2O (S-Ni = 1) of a dinucleating macrocycle H(2)L, 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 P2(1)2(1)2(1) with Z = 4, a = 15.62(1), b = 16.49(1) and c = 14.75(1) Angstrom. Crystallographic refinement converged with R = 0.060 and R' = 0.048 for 2958 reflections having I > 3.00 sigma(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) Angstrom. 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 = -2JS(1)S(2)) and shows an axial ESR feature with g(parallel to) = 2.16, g(perpendicular to) = 2.27 and A(parallel to) = 64 x 10(-4) cm(-1) (in frozen dmf at 78 K), attributable to a spin-doublet ground state. The relations g(perpendicular to) > g(parallel to) and A(parallel to) = -1/3A(Cu){A(Cu) 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 d(z2) character comprising d(z2)(Cu) and d(z2)(Ni).