Divalent transition metal complexes of the anionic form of 4,7-dihydro-1,2,4-triazolo [1,5-a]pyrimidine-7-one:: crystal structure of the zinc(II) compound

Several complexes of the ligand 4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine-7-one (7HtpO) in its anionic form (7tpO(-)) with divalent metals (the complete first series from Mn to Zn plus Cd) have been synthesized and characterized by means of analytical techniques (elemental analysis, thermogravimetry and differential scanning calorimetry), spectral methods (IR and electronic spectroscopy), magnetic measurements (77-290 K) and EPR in the case of the Cu compound. All compounds display a M(7tPO)(2) (.) nH(2)O stoichiometry. The crystal structure of [Zn(7tPO)(2)(H2O)(4)]. 2H(2)O has been solved by single crystal X-ray diffraction. In this compound, the ligand 7tpO- binds the metal ion through the N atom in position 3 and four water molecules complete the slightly distorted octahedral environment with the Zn atom occupying an inversion center. For all other compounds except Cu, infrared data suggest that the ligand binds in a similar fashion whereas visible spectroscopy and magnetic measurements point to octahedral geometry. On the other hand, magnetic and EPR measurements of the copper compound indicate that it is dinuclear with an antiferromagnetic coupling constant 2J = -87.8 cm(-1) and a zero-field splitting parameter D = 0.168 cm(-1). (C) 2003 Elsevier Ltd. All rights reserved.