SYNTHESES, CRYSTAL-STRUCTURES AND ELECTRONIC-PROPERTIES OF [CU(BIPYM)(C5O5)(H2O)2].H2O AND [CU2(BIPYM)(C5O5)2-(H2O)2].4H2O (BIPYM = 2,2'-BIPYRIMIDINE)

Two new complexes [Cu(bipym)(C5O5)(H2O)2].H2O 1 and [Cu2(bipym)(C5O5)2(H2O)2].4H2O 2 [bipym = 2,2'-bipyrimidine and C5O52- = dianion of croconic acid (4,5-dihydroxycyclopent-4-ene-1,2,3-trione)] have been synthesised and characterized by spectroscopic and X-ray diffraction methods. Crystals of 1 and 2 are triclinic, space group P1BAR, with a = 6.604(1), b = 9.491 (1), c = 12.019(1) angstrom, alpha = 88.37(l ), beta = 79.77(l ), gamma = 86.08(l)-degrees and Z = 2 for 1, and a = 6.638(l), b = 8.765(2), c = 10.093(2) angstrom, alpha = 95.96(2), beta = 93.11(2), gamma = 91.73(2)-degrees and Z = 1 for 2. Compound 1 consists of mononuclear [Cu(bipym)(C5O5) (H2O)2] units in which the copper atom shows a slightly distorted elongated octahedral co-ordination with two bipym nitrogens and two croconate oxygens forming the equatorial plane, and two water molecules in the axial positions. The structure of compound 2 is made up of centrosymmetric bipym-bridged dinuclear [CU2(bipym)(C5O5)2(H2O)2] units in which the copper atom exhibits a slightly distorted square-pyramidal co-ordination, with two bipym nitrogens and two croconate oxygens defining the equatorial plane whereas a water molecule occupies the axial position. In addition, the second axial position is occupied by a water molecule at a distance of close to 3 angstrom. The intradimer metal-metal separation is 5.384 angstrom. The croconate group acts as a bidentate ligand in both complexes whereas bipym adopts the chelating and bis(chelating) co-ordination modes in 1 and 2, respectively. The temperature dependence of the magnetic susceptibility of 2 reveals the occurrence of a relatively strong intramolecular antiferromagnetic coupling, J (singlet-triplet energy gap) = -160 cm-1. This value is compared with those of related compounds on the basis of structural data and theoretical calculations.