2,2'-BIPYRIMIDINE (BIPYM)-BRIDGED DINUCLEAR COMPLEXES .4. SYNTHESIS, CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF [CO2(H2O)8(BIPYM)][NO3]4, [CO2(H2O)8(BIPYM)][SO4]2.2H2O AND [CO2(BIPYM)3(NCS)4]

Three new dinuclear cobalt(II) complexes [Co2(H2O)8(bipym)][NO3]4 1, (Co2(H2O)8(bipym)]-[SO4]2.2H2O 2 and [Co2(bipym)3(NCS)4] 3 (bipym = 2,2'-bipyrimidine) have been synthesised and their crystal structures determined by X-ray diffraction methods. Crystals of 1 and 3 are triclinic, space group P1BAR, Z = 1 with a = 7.511 (1), b = 8.844(2), c = 9.514(1) angstrom, alpha = 79.67(1), beta = 88.54(1) and gamma = 82.46(1)-degrees for 1 and a = 9.045(2), b = 9.149(2), c = 11.621 (2) angstrom, alpha = 74.73(2), beta = 80.67(2) and gamma = 61.17(1)-degrees for 3. Crystals of 2 are monoclinic, space group P2(1)/c with a = 8.115(1), b = 11.596(2), c = 11.823(3) angstrom, beta = 91.57(2)-degrees and Z = 2. The structures of 1 and 2 are made up of dinuclear cations [Co2(H2O)8(bipym)]4+ with nitrate counter ions for 1 and water of crystallization and sulfate groups for 2. The structure of 3 consists of dimeric neutral [Co2(bipym)3(NCS)4] units. Bipyrimidine bridges the cobalt atoms in this series of complexes in a bis(chelating) fashion and a crystallographically imposed inversion centre is located halfway between its two pyrimidyl rings. It is present also as a terminal ligand in 3. The two equivalent cobalt atoms of 1 and 2 are each bound to four water oxygens and two cis nitrogens of bipym in a slightly distorted octahedral environment. Each cobalt atom in 3 is bound to six nitrogen atoms belonging to two thiocyanate groups in cis position and to two bipym ligands, one terminal and the other bridging. The intramolecular metal-metal separation varies between 5.761(1) and 5.942(2) angstrom. The magnetic properties of 1-3 have been investigated in the temperature range 4.2-300 K. They all exhibit antiferromagnetic exchange with susceptibility maxima at 13.0-16.4 K. Fits of the magnetic data through the Lines model and the simpler Ising spin-only formalism are compared.