Synthesis, structure, and magnetic properties of a new chloro-bridged dimer [Cu2(dpt)2Cl2]Cl2 with an unusual structure and ferromagnetic coupling

The complexes [Cu-2(dpt)(2)Cl-2]X-2 (dpt = dipropylenetriamine; X = Cl, 1; X-2 = (Cl)(BPh4), 2) have been prepared and their magnetic properties studied. The crystal structure of complex 1 has been solved. The compound belongs to the C2/c space group with Z = 4, a = 17.201(2) Angstrom, b = 10.873(2) Angstrom, c = 11.835(2) Angstrom, and beta = 99.720(10)degrees. The geometry about each copper approximates that of a distorted square pyramid. The three N-atoms of the dpt ligand and one of the Cl bridging ligands form the base of the pyramid while the other chloro bridging ligand occupies the axial site. The two pyramids share a base-to-apex edge with the basal planes being perpendicular, an arrangement which had not been previously observed far this type of dimers. The chloro counterions are responsible for interdimer interactions through hydrogen bonding forming chains of dimers throughout the lattice. Magnetic susceptibility data show a ferromagnetic coupling between the two Cu(II) centers (J = 42.94 cm(-1) for 1 and J = 13.89 cm(-1) for 2). Dimer-dimer interaction and ZFS have been considered with the J' parameter (1, J' = -3.92 cm(-1); 2, J' = -2.9 cm(-1)). Extended Huckel calculations on complex 1 clearly reveal that the intradimer magnetic interaction only takes place through the basal chloro bridging ligand (with a CuCl(1)Cu angle of 91.4 degrees) which in turn is consistent with the observed ferromagnetic coupling.