BINUCLEAR PLATINUM(II) TRIAZOLOPYRIMIDINE BRIDGED COMPLEXES - PREPARATION, CRYSTAL-STRUCTURE, NMR-SPECTROSCOPY, AND AB-INITIO MO INVESTIGATION ON THE BONDING NATURE OF THE PT(II)CENTER-DOT-CENTER-DOT-CENTER-DOT-PT(II) INTERACTION IN THE MODEL-COMPOUND (PT-2[NHCHN(C(CH2)(CH3))](4))

A condensation reaction between two cis-[PtCl2(Hmtpo)(2)] (where Hmtpo = 7-H-5-methyl-7-oxo[1,2,4]triazolo[1,5a]pyrimidine) molecules takes place in neutral aqueous media, giving [Pt2Cu-mtpo)(4)]. 4H(2)O (1). T he X-ray structure of the recrystallization product of 1 in DMSO:EtOH (1:1) (DMSO =, dimethyl sulfoxide), namely, [Pt2Cu-mtpo)(4)]. 2DMSO (2 ) has been determined. Compound 2 crystallizes in the orthorhombic spa ce group Pbcn with unit cell dimensions a = 14.207(3) Angstrom, b = 15 .187(3) Angstrom, c = 17.165(3) Angstrom, and Z = 4. The molecular str ucture shows that the two Pt atoms are bridged by four mtpo ligands. T hus, it presents two face to face PtN4 units with a Pt ... Pt 2.744(2) Angstrom separation. Compound 1 has also been characterized by H-1 an d Pt-195 NMR. The very short Pt(II)... Pt(II) contact suggests an inte raction between the two metal centers, supported by the great deshield ing observed for the platinum nuclei in the Pt-195 NMR spectrum (delta = -2005 ppm) compared to a Pt(II) in a typical N-4 environment. In or der to make an approach to the possible bonding nature of the Pt(II) P t(II) interaction, a theoretical analysis has been performed on the ba sis of the properties of the electronic charge density distribution, d erived from ab initio MO calculations for the model compound {Pt-2[NHC HN(C(CH2)(CH3))]4} using RHF/LANL2DZ and B3LYP/LANL2DZ wave functions; both take into account relativistic effects and the second electronic correlation also. A significant directional interaction between the t wo metal centers has been found. Thus, a bond critical point appears b etween the two platinum nuclei, with a density of charge rho(b) = 0.05 6, e . bohr(-3), which is half of that found for the platinum nitrogen bond. Moreover, a value of the energy density, E(d)(r(b)) < 0 (E(d)(r ) = -0.0175 hartree . bohr(-3)), at this point, shows the bonding natu re of the interaction.