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-chloro-3-methylpyridine)­copper­(II) (2) and its isomorphous analogue dichloro­(2-bromo-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 (H = −JΣSi·Sj Hamiltonian). The experimental J-values were confirmed via theoretical calculations. Comparison to a known disordered polymorph of dichloro­(2-chloro-3-methylpyridine)­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.