Experimental and TDDFT Characterization of the Light-Induced Cluster-to-Iron Charge Transfer in the (Ferrocenylethynyl)-Substituted Trinuclear Platinum Derivative [Pt3(μ-PBut2)3(CO)2(Ct≡C-Fc)]+

The reaction between Pt3(μ-PBut 2)3(CO)2Cl (2) and ethynylferrocene, in the presence of catalytic amounts of CuI, gives Pt3(μ-PBut 2)3(CO)2CtCFc (1), characterized by X-ray crystallography and representing a rare example of the σ-coordination of an alkynyl moiety to a cluster unit. In a dichloromethane (CH2Cl2) solution, compound 1 undergoes three consecutive one-electron oxidations, the first of which is assigned to the ferrocene centered FeII/FeIII redox couple. Spectroelectrochemistry, carried out on a solution of 1, shows the presence of a broad band in the near-IR region, growing after the electrochemical oxidation, preliminarily associated with a metal-to-metal charge transfer toward the FeIII ion of the ferrocenium unit. Density functional theory (DFT) has been employed to analyze the groundand excited-state properties of 1 and 1+, both in the gas phase and in a CH2Cl2 solution. Vertical excitation energies have been computed by the B3LYP hybrid functional in the framework of the time-dependent DFT approach, and the polarizable continuum model has been used to assess the solvent effect. Our results show that taking into account the medium effects together with the choice of an appropriate molecular model is crucial to correctly reproducing the excitation spectra of such compounds. Indeed, the nature of the substituents on P atoms has been revealed to have a key role in the quality of the calculated spectra.