Synthesis, structure and magnetic characterization of dinuclear copper(II) complexes bridged by bicompartmental phenolate

The reaction of Cu(II) salts with the bicompartmental 2,6-bis[bis(2-pyridylmethyl) aminomethyl]-4-chlorophenol (L-Cl-OH) ligand afforded four new dinuclear bridged phenoxido Cu(II) complexes. Three doubly bridged complexes namely [Cu-2(mu-L-Cl-O)(mu-X)](ClO4)(2) (1: X = OH-, 3: X = O2P(OC6H5)(2)(-)) and 2: [Cu-2(mu-L-Cl-O)(mu-pz)(ClO4)]ClO4 (2) where pz = pyrazolyl anion, and one singly bridged-phenoxido, [Cu-2(mu-L-Cl-O)(dca)(2)]PF6 center dot 2CH(3)CN (4.2CH(3)CN) (dca = dicyanamide anion). A complex similar to 4 was also obtained with 2,6-bis[bis(2-pyridylmethyl) aminomethyl]-4-methylphenol (L-Me-OH), [Cu-2(mu-L-Me-O)(dca)(2)] PF6 center dot 2CH(3)CN (5.2CH(3)CN) where in both cases dca are acting as terminal monodentate ligands. The complexes were structurally characterized by various spectroscopic techniques (IR, UV-VIS and ESI-MS) and by single crystal crystallography. Magnetic susceptibility measurements at variable temperature revealed strong to very strong antiferromagnetic coupling (AF) in the doubly bridged complexes 1-3 and very weak AF interaction in the dicyanamido compounds 4 and 5. The DFT calculations for the coupling constants, J were in agreement with the experimentally observed behavior. The trend in magnetic properties was attributed to the strength of overlap between the orbitals (d(x2-y2)/d(x2-y2) vs. d(z2)/d(x2-y2) vs. d(z2)/d(z2)) resulting from trigonal bipyramidal (TBP) or square pyramidal (SP) geometries.