Synthesis, crystal structure and magnetic properties of the cobalt(II) chain [Co(bipym)(H2O)2](NO3)2 and the dinuclear compounds [Co2(bipym)3(H2O)4](NO3)4•2H2O and [Co2(bipym)3(H2O)2(SO4)2]•12H2O

Three new cobalt(II) complexes of formula [Co(bipym)(H(2)O)(2)](NO(3))(2) (1), [Co(2)(bipym)(3)(H(2)O)(4)](NO(3))(4) . 2H(2)O (2) and [Co(2)(bipym)(3)(H(2)O)(2)(SO(4))(2)]. 12H(2)O (3) (bipym = 2,2'-bipyrimidine) have been synthesized and characterized by single-crystal X-ray diffraction. The structure of 1 consists of cationic chains of cobalt(II) ions bridged by bis(chelating) bipym whereas those of 2 and 3 are made up of dinuclear entities containing both chelating and bis(chelating) bipym ligands. The metal atom in this family is bound to four bipym nitrogen atoms belonging to two bipym groups (1-3) and to two cis oxygen atoms belonging either to water molecules (1 and 2) or to water and monodentate sulfate (3), to build a distorted CoN(4)O(2) octahedral environment. A crystallographically imposed inversion center is located halfway between the tyro pyrimidyl rings of the bridging bipym. The metal-metal separation across bridging bipym varies between 5.736(2) and 5.808(2) Angstrom. The study of the magnetic properties of 1-3 in the temperature range 2.5-290 K reveals the occurrence of antiferromagnetic coupling with susceptibility maxima at 18 (1), 14 (2) and 13.5 K (3). Fits of the magnetic data through the Lines and Ising models were carried out and the results compared and discussed.