Outer and inner coordination sphere chemistry of polyazacyclophane platinum(II) complexes. Crystal structure of [PtBr4]2(H4L1) · H2O (L1 = 2,6,9,13-tetraaza[14]paracyclophane)

Abstract

The interaction of PtCl42− with the new azaparacyclophane 2,5,8,11-tetraaza[12]paracyclophane (L2) has been studied by 1H, 13C and 195Pt NMR spectroscopy. Three different complexes are detected as a function of pH, all of them presenting cis-arrangement of nitrogen donors and chloride anions. In the first one, formed at acidic pH, the central nitrogen atoms of the macrocyclic are coordinating to Pt(II) while the benzylic nitrogens remain protonated. Deprotonation of these nitrogens brings about a reorganisation of the complex, and the platinum is then coordinated by one benzylic nitrogen and the consecutive nitrogen in the macrocycle. This process can be monitored by NMR. Finally, addition of a second mol of PtCl42− for each mole of L2 causes, most likely, the formation of a binuclear complex in which the tetrammine chain behaves as two ethylenediamine subunits. The crystal structure of the adduct [PtBr4]2[H4L1] has been solved by X-ray diffraction analysis (space group P21/c, a = 8.092(2), b = 16.049(2), c = 21.783(3) Å, α = 90.00(1), β = 100.34(2), γ = 90.00(1), Z = 4, R1 = 0.0528, wR2 = 0.1612). The compound is held together mainly through coulombic interactions between the charged polyammonium groups of the macrocycle and the PtBr42− anions aswell as through an extensive hydrogen bond network in which participate the bromides of the two PtBr42− anions and a lattice water molecule.