X-ray structures versus NMR signals in pentacoordinate [PtX2(η2-CH2=CH2)(Me2phen)] (X = Cl, Br, I) complexes

The single crystal X-ray structure of the pentacoordinate complex [PtBr2(eta(2)-CH2=CH2)(Me(2)phen)], Me(2)phen = 2,9-dimethyl-1,10-phenanthroline, is here reported for the first time. Comparison of the complete series of [PtX2(eta(2)-CH2=CH2)(Me(2)phen)] (X = Cl, Br, I) X-ray structures shows a very low variability of the bond lengths and angles, in the trigonal equatorial plane (where eta(2)-olefin and Me(2)phen are bound), on varying the coordinated axial halogens. In first approximation, this suggests describing as independents and not interacting the two subsystems constituted by the metal bonds with axial (X-Pt-X) and equatorial ligands (Me(2)phen-Pt-eta(2)-ethene). This means that the electric charge donated to the metal, by the axial ligands, cannot substantially modify the bonds of the metal with the ligands in the trigonal equatorial plane. The H-1, C-13, N-15 and Pt-195 NMR chemical shifts variations, studied as a function of the ionic radius of the axial halides are here discussed. The NMR data strongly suggest the existence of electric pseudo-ring currents circulating around the Pt-X axes and modulated by the ionic radius of the coordinated halides. (C) 2015 Elsevier B.V. All rights reserved.