SYNTHESES, CRYSTAL-STRUCTURES AND MAGNETIC-PROPERTIES OF ONE-, 2- AND3-DIMENSIONAL 2,2'-BIPYRIMIDINE-CONTAINING COPPER(II) COMPLEXES

Three new copper(II) complexes of formula [Cu(bipym)(H2O)(2)][NO3](2) . H2O 1, [Cu(bipym)(Cr2O7)] 2 and [Cu(bipym)(SO4)]. H2O 3 (bipym = 2,2 '-bipyrimidine) have been synthesized and characterized by single-crys tal X-ray diffraction. Compound 1 loses water very easily transforming into [Cu(bipym)][NO3](2) 1'. The structure of 1 consists of zigzag ch ains of bipym-bridged copper(II) ions with unco-ordinated nitrate anio ns and co-ordinated and crystallization water molecules, whereas the s tructures of 2 and 3 are made up of bipym-bridged copper(II) chains wh ich are connected through bis(monodentate)-dichromate (2) and -sulfate (3) groups to yield sheet-like (2) and three-dimensional (3) polymers . The copper atom in compounds 1-3 exhibits a distorted elongated-octa hedral co-ordination. In 1, it is linked to two bis(chelating) bipym g roups and two water molecules in cis positions. The equatorial positio ns of the octahedron are occupied by three bipym-nitrogen atoms and a water-oxygen, while the axial ones are filled by the remaining bipym-n itrogen and the second aqua ligand. The equatorial mean planes of two adjacent copper(II) ions within the chains are mutually perpendicular. In 2, two different bis(chelating) bipym groups alternate regularly w ithin the chain. The four nitrogen atoms of one of them build the equa torial positions of two neighbouring octahedra and the two remaining e quatorial sites around each metal atom are filled by an oxygen atom of the dichromate group and a nitrogen atom of the second bipym. The two trans axial positions are occupied by another nitrogen atom of the se cond bipym and an oxygen atom of the dichromate anion. The two adjacen t equatorial copper(II) mean planes through this second bridging bipym in 2 are mutually parallel. Two adjacent crystallographically indepen dent metal atoms alternate regularly within the bipym-bridged copper(I I) chain in 3. Their equatorial plane is built by three nitrogen atoms from bipym and one oxygen atom from a sulfate anion, whereas the axia l positions are filled by the remaining bipym nitrogen atom and an oxy gen atom from another sulfate anion. The equatorial mean planes of adj acent copper(II) ions within the bipym-bridged chain of 3 are mutually perpendicular as in 1. The metal-metal separations across bridging bi pym are 5.646(1) Angstrom in 1, 5.486(2) and 5.765(2) Angstrom in 2 an d 5.648(1) and 5.715(1) Angstrom in 3, values which are close to that through bridging dichromate [5.774(1) Angstrom in 2] but shorter than those through bridging sulfate [6.464(2) and 6.417(2) Angstrom in 3]. Variable-temperature magnetic susceptibility measurements reveal that bridging bipym is able to mediate relatively strong (1' and 2) and wea k (1 and 3) antiferromagnetic couplings. The magnitude of the exchange coupling in this series is analyzed and discussed in the light of the complexes structural patterns.