Structure-dependent electrochemical behavior of thienylplatinum(II) complexes of N,N-heterocycles

trans-[Pt(MeCN)(PPh3)(2)(2-thienyl)]BF4 (1) serves as a convenient precursor to bifunctional mononuclear trans[Pt(PPh3)(2)(eta(1)-N-N)(2-thienyl)]BF4 [N-N = pyrazine (2); 2-chloropyrazine, (3)] and dinuclear trans, trans-[Pt-2(PPh3)(4)(mu-N-N)(2-thienyl)(2)](BF4)(2) [(N-N = 4,4'-bipyridine (4); 4,4'-vinylenedipyridine (5)] complexes. The nuclear selectivity is conveniently controlled by the choice of the heterocyclic ligands or spacers. Both structural types 3 and 5 were confirmed by single-crystal X-ray crystallographic analyses. Their solution identities were established by positive-ion Electrospray Mass Spectrometry (ESMS). The electroactivities of these complexes were studied by cyclic voltammetry (CV). Continuous CV scans of 4 and 5 revealed variations in the redox waves with the number of scans. While the initial oxidative scan exhibited only a broad, irreversible wave, further cycling showed the growth of two additional redox couples up to about the tenth cycle. The peak currents of these redox couples began to decay with prolonged potential cycling beyond the tenth cycle. These findings are consistent with the formation of electroactive oligomers/polymers, and this conclusion is supported by visible thin film formation on the electrodes. In contrast, the mononuclear complexes (2 and 3) do not show such behavior. The films formed were further studied by repetitive potential cycling and XPS. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).