Ferromagnetic Exchange in Bichloride Bridged Cu(II) Chains: Magnetostructural Correlations between Ordered and Disordered Systems

The synthesis, structure, magnetic properties, and theoretical analysis of a new phase of dichloro(2-thlaro-3-methylpyridine)copper(II) (2) and its isomorphous analogue dichloro(2bromo-3-methylpyridine)copper(II) (3) are reported. Both complexes crystallize in the orthorhombic space group Pbca and present square pyramidal Cu(II) ions bridged into chains by chloride ions with each,copper(II)-bearing a single pyridine ligand. Variable temperature magnetic Susceptibility measurements were well fit by a uniform one-dimensional ferromagnetic chain model with,2) J = 69.0(7) K, C = 0.487 emu-K/mol-Oe; 3, J = 73.9(4) K, C = 0.463 emu-K/mol-Oe = Hamiltonian). The experimental J-values were confirmed-via theOretical calculations. Comparison to a known disordered polymorph of dichloro(2-chloro-3-inethylpyridine)copper(II), 1, shows marked differences as there are significant antiferromagnetic next-nearest neighbor interactions, in 1 in addition to randomness induced by the disorder which provide a distinctly different magnetic response. The differences in magnetic behavior are attributed principally to the structural difference in the Cu(II) coordination sphere, 1 being significantly closer to trigonal-bipyramidal, whose difference changes both the nearest and next-nearest neighbor interactions.