The reaction of the pyrophosphate ion with the antitumour complex [{CuL(CH 3COO)} 2] (HL=2-formylpyridine thiosemicarbazone) and the single-crystal X-ray structure of [(CuL) 4P 2O 7]· nH 2O

Abstract

The preparation of the complex [(CuL) 4P 2O 7]· nH 2O (HL=2-formylpyridine thiosemicarbazone; n=9–12) from the reaction of Na 4P 2O 7 with [{CuL(CH 3COO)} 2] is described. The complex has been characterized by a variety of physiochemical techniques and its crystal and molecular structure determined. Crystals of [(CuL) 4P 2O 7]· nH 2O are monoclinic, space group C2/ c, with a=29.074(6), b=28.021(3), c=13.374(3) Å, β=102.93(2)° and Z=8. The complex is tetranuclear, containing four CuL + moieties linked by a bridging P 2O 7 4− anion. Each copper atom is in an approximately square pyramidal environment. The equatorial positions are occupied by a pyrophosphate oxygen, a pyridine nitrogen, an imine nitrogen and a thioamide sulfur, the latter three from the same L ligand. A weakly bound S atom from an adjacent L ligand, is in an axial position, thus completing the coordination sphere. Each tetranuclear [(CuL) 4P 2O 7] molecule may be considered as a pair of dinuclear (CuL +) 2 units linked by a P 2O 7 4− anion. Each dinuclear unit is further linked by the axial CuS bonds. The pyrophosphate ion, which displays a staggered conformation, plays an important role in the hydrogen bonding network involving phosphate oxygens, the thioamide and amine nitrogens of L, and the watet molecules in the structure. The variable temperature magnetic susceptibility of [(CuL) 4P 2O 7]· nH 2O is compared with that of [{CuL(CH 3COO)} 2] and in both cases the results are interpreted in terms of very weak antiferromagnetic coupling between the copper atoms. In the case of the pyrophosphate complex, the fact that the structure contains dinuclear (CuL +) 2 units linked in pairs required that an interaction between the dinuclear units as well as the intramolecular J value be included to fit the magnetic data.