Syntheses, Structures, and Electrochemistry of Polynuclear CuI, AgI, and PtII Complexes Bearing Ferrocenyl Group

Three polynuclear complexes, [PtII2(dppm)2(μ-η1:η1-HCCFc)Cl2] (1), [AgI3(dppm)3(μ3-η1-C⋮CFc)]·2CF3SO3 (2·2CF3SO3), and [CuI3(dppm)3(μ3-η1-C⋮CFc)2]·PF6 (3·PF6), were synthesized and characterized using single-crystal X-ray diffraction, UV−vis spectroscopy, and voltammetry (dppm = bis(diphenylphosphino)methane; Fc = ferrocenyl). Compound 1 is an A-frame complex in which two PtII ions are bridged by two dppm and one ethynylferrocene. Both 2·2CF3SO3 and 3·PF6 are composed of trimetallic AgI3 and CuI3 cores bridged by three dppm and capped with one and two ferrocenylacetylides, respectively. All complexes exhibit reversible Fc oxidation in their cyclic voltammograms (CV), ranging from −48 ± 10 to 235 ± 10 mV vs Ag/AgNO3 (0.1 M). The reduction potential difference between silver and copper complexes is mostly due to intramoleuclar electrostatic interactions. A weak intervalence charge-transfer transition at 1250 nm arising from the mixed-valence 32+ is observed in the solution near-infrared absorption spectrum of a mixture of 3·PF6 and ferrocenium hexafluorophosphate (Cp2FePF6). Cyclic and differential pulse volatmmograms of 3·PF6 show two reversible Fc oxidations separated by 110 ± 14 mV, giving a comproportionation constant Kc of 77 ± 30. The stability of the mixed-valence complex 32+ arises mainly from the reduction of electrostatic repulsion and statistical distribution.