Electrostatic vs Electronic interactions within oxidized multinuclear Pt(bipyridine)(dithiolene) complexes

Bi- and trimetallic platinum(bipyridine)(dithiolene) complexes involving different organic linkers between the redox active platinum(dithiolene) moieties have been synthesized and studied by electrochemistry and spectroelectrochemistry. Cyclic voltammetry experiments carried out on these multinuclear complexes in dichloromethane using [NBu4][PF6] as the supporting salt show only one oxidation process involving the metallacycles. Nevertheless, spectro-electrochemical studies, carried out under the same conditions, show a different evolution of the spectra during oxidation depending on the position of the metallacycles on the phenyl ring. For instance, only the 1,3-disubtituted (Pt21,3-P) and 1,3,5-trisubstituted (Pt31,3,5-P) complexes show the growth of an absorption band in the NIR region upon oxidation while it was not observed for the other complexes. In contrast, electrochemical studies carried out using the poorly coordinating supporting electrolyte, [Na][B(C6H4(CF3)2)4], indicate sequential oxidation of the redox centers with ΔE values varying according to the nature of the bridge and the distance between metal centers. For all the investigated multinuclear complexes, spectro-electrochemical experiments performed in the presence of [Na][B(C6H4(CF3)2)4] show an absorption band in the NIR region consistent with appreciable electrostatic effects and charge delocalization in the mixed valent intermediates.