Synthesis, crystal structure, magnetic properties, and cyclic voltammetry of the unsymmetric (mu-oxalato)-[N,N ',N '',N '''-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane]dicobalt(II) perchlorate trihydrate

A new dinuclear cobalt(II) complex, [Co-2(ox)tpmc](ClO4)(2). 3H(2)O, (tpmc = N,N',N ",N"'-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane, ox(2-) = oxalate ion), has been synthesized and its crystal structure solv ed by single crystal X-ray diffraction studies. It crystallizes in the mono clinic system, space group P2(1),with a = 9.7858(8) Angstrom, b = 21.455(2) Angstrom, c = 21.241(2) Angstrom, beta = 100.069(8)degrees, V = 4391.0(8) Angstrom(3), Z = 4, R = 0.083, Rw = 0.086. Its Structure consists of two di nuclear, crystallographically unique molecules in which the oxalate ion bri dges two cobalt(II) ions unsymmetrically. Each cobalt is hexacoordinated wi th four macrocyclic nitrogens and two oxygens in an octahedral arrangement of an "exo" coordination of a macrocyclic ligand. The third oxygen is simul taneously bonded to both cobalt ions and the last one remains uncoordinated , which is the unique way of oxalato ion coordination. Intramolecular antif erromagnetic coupling between the two cobalt(II) ions is observed and yield ed J = -9.3 cm(-1), g(parallel to) = 5.64 and g(perpendicular to) =-1.21. T he variable temperature (4.2 - 292 K) magnetic susceptibility measurements are interpreted on the basis of the spin Hamiltonian H = 25/9JS(A)S(B) + go beta Hz(S-AZ + S-BZ). Cyclic voltammetry suggests that the complex is elec trochemically stable up to the potential of the cobalt reduction.