COPPER AND BISMUTH COMPLEXES CONTAINING DIPYRIDYL GEM-DIOLATO LIGANDS : BIIII2(2-PY)2CO(OH)2(O2CCF3)4(THF)2, CUII(2-PY)2CO(OH)2(HO2CCH3)2 AND CUII4(2- PY)2CO(OH)2(O2CCH3)6(H2O)2, A FERROMAGNETICALLY COUPLED TETRANUCLEAR COPPER (II) CHAIN