Determination of charge transfer in molybdenum complexes of 7,7,8,8-tetracyano-p-quinodimethane with vibrational spectroscopy

Abstract

Abstract The influence of charge transfer on the vibrational lines of three new molybdenum TCNQ complexes [MoO(dtc)3](TCNQ) 1a, [Mo(dtc)4](TCNQ) 2a, and [Mo(dtc)4](TCNQ)2 3a is reported (dtc=Et2NCS2). It is shown that Raman scattering is able to probe the charge state of TCNQ entities in these complexes. Infrared spectra are discussed and compared to Raman spectra. Electronic polarization of the TCNQ moieties and reduction of TCNQ° in TCNQ•− is found for all complexes. The estimated charge transferred when reduction occurs is one electron onto the TCNQ molecule whereas it is about 0.2–0.3 electron onto nitrile groups. The formation of monomers and dimers of TCNQ in these complexes is discussed in relation with specific Raman lines found in reference compounds such as TCNQ salts of alkali. These new Raman data suggest to us that TCNQ moieties form mainly dimers and monomers in complexes 1a and 2a, respectively.