SYNTHESIS, CRYSTAL-STRUCTURE, AND MAGNETIC-PROPERTIES OF (MU-BIPYRIMIDINE)(CYANATO)COPPER(II) AND (MU-BIPYRIMIDINE)(THIOCYANATO)COPPER(II) COMPLEXES

The synthesis, structure, and spectroscopic and magnetic properties of three 2,2'-bipyrimidine (C8H6N4, bpm)-containing copper(II) complexes of formula [Cu2(bpm)(NCO)4]n (1), [Cu(bpm)(NCS)2]n (2) and [Cu2(bpm)(NCS)4]n (3) are reported. Compounds 1 and 2 crystallize in the monoclinic system, space group C2/c and Z = 4, with a = 19.486(1) angstrom, b = 7.527(1) angstrom, c = 15.252(1) angstrom, beta = 137.8(2)-degrees, and V = 1530.7(7) angstrom3 for 1 and a = 11.543(1) angstrom, b = 13.948(2) angstrom, c = 7.818(1) angstrom, beta = 93.26(1)-degrees, and V = 1256.7(3) angstrom3 for 2, whereas compound 3 is orthorhombic, space group Fddd, with a = 12.811 (1) angstrom, b = 22.473(1) angstrom, c = 24.259(1) angstrom, Z = 16, and V = 6983.9(7) angstrom3. The copper environment in 1-3 is distorted octahedral. The structure of 1 consists of a 2D-array of copper(II) ions bridged by bis-bidentate bpm ligands and end-on and end to end cyanato groups. The structure of 2 is made up of 1D-chains of f Cu(bpm)]2+units linked by thiocyanato groups which act as asymmetrical end to end bridges. The structure of 3 consists of a 3D-network of copper(II) ions bridged by bis-bidentate bpm ligands and bis-unidentate end to end thiocyanato groups. The three compounds exhibit antiferromagnetic coupling, which is very weak in 2 (J = -0.6 cm-1, H = -J SIGMA S(i).S(i+1)) and strong in 1 and 3 (singlet-triplet energy gaps of -199 and -230 cm-1, respectively). The efficiency of the bpm bridge in undergoing antiferromagnetic coupling between copper(II) ions which are separated by more than 5.5 angstrom is at the origin of the strong coupling observed in this series as revealed by a simple orbital model.