Countercomplementarity and strong ferromagnetic coupling in a linear mixedmu-acetato, mu-hydroxo trinuclear copper(II) complex. Synthesis, structure, magnetic properties, EPR, and theoretical studies

The structural and magnetic data of the trinuclear compound [Cu-3(L)(2)(CH3 COO)(2)(OH)(2)(dmf)(2)] (HL = N-(2-methylpyridyl)toluensulfonylamide) are r eported. The compound crystallizes in the monoclinic system, space group P2 (1)/n (no. 14), with a = 11.6482(6) Angstrom, b = 13.5772(6) Angstrom, c = 13.5306(7) Angstrom, alpha = 90 degrees, beta = 92.859(5)degrees, gamma = 9 0 degrees, and Z = 2. The three copper atoms form an exact linear arrangeme nt. Neighboring coppers are connected by a hydroxo bridge and a bidentate s yn-syn carboxylato group. The coordination spheres of the terminal copper a toms are square pyramidal with a dmf molecule as the apical ligand. The cen tral copper has a regular square planar geometry. The mixed bridging by a h ydroxide oxygen atom and a bidentate carboxylato group leads to a noncoplan arity of the adjacent basal coordination planes with a dihedral angle of 51 .96(9)degrees. Susceptibility measurements (2-300 K) reveal a strong ferrom agnetic coupling, J = 93(6) cm(-1), in the mixed-bridged moiety leading to a quartet ground state that is confirmed by the EPR spectra. The ferromagne tic exchange coupling is discussed using DFT calculations on model compound s that have shown a countercomplementary effect of the hydroxo and acetate bridges.