X-ray structures versus NMR signals in pentacoordinate [PtX2(η2-CH2CH2)(Me2phen)] (X = Cl, Br, I) complexes

• The single crystal X-ray structure of [PtBr2(η2-CH2CH2)(Me2phen)] is reported.
• The existence of electric pseudo-ring currents circulating in halogen ligands is demonstrated.
• Low electronic influence of axial on equatorial ligands in pentacoordinate complexes.

The single crystal X-ray structure of the pentacoordinate complex [PtBr2(η2-CH2CH2)(Me2phen)], Me2phen = 2,9-dimethyl-1,10-phenanthroline, is here reported for the first time. Comparison of the complete series of [PtX2(η2-CH2CH2)(Me2phen)] (X = Cl, Br, I) X-ray structures shows a very low variability of the bond lengths and angles, in the trigonal equatorial plane (where η2-olefin and Me2phen 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 (Me2phen–Pt–η2-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 1H, 13C, 15N and 195Pt 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.

The X-ray structure of pentacoordinate [PtX2(η2-CH2CH2)(Me2phen)] (X = Br), Me2phen = 2,9-dimethyl-1,10-phenanthroline, (left picture) is here compared with analogue structures (X = Cl, I). NMR chemical shifts variations, in such pentacoordinate species suggest the presence of electric pseudo-ring currents in the axial X− ligands, out of the trigonal plane (circle in the right picture).Figure optionsDownload as PowerPoint slide