Targeted synthesis of a CrIII–O–VV core oxo- bridged complex: spectroscopic, magnetic and electrical properties

The synthesis and the structural, spectroscopic, thermal, magnetic and electrical properties of a new heterodinuclear [Cr(bpy)2(H2O)(μ-O)V(C2O4)2]2·9H2O (1) complex, which contains terminal and unsupported oxo- bridge CrIII–O–VV, isolated for the first time in a molecular compound, are reported. Oxo- bridged metal units as functional intramolecular motifs exhibit interesting properties in complexes, and the discovery of new combinations of metals with different electronic configurations and redox potentials is important for the design of new materials. The reaction for the preparation of 1, involving an aqueous solution of CrIII precursor [Cr(bpy)2(H2O)2]3+ cations and VV precursor [VO2(C2O4)2]3− anions, was monitored by UV/vis spectroscopy. New absorbance bands in the 400–600 nm region can be recognized in the electronic spectrum of 1 that could originate from metal- to-metal charge transfer (MMCT). The assignment of MMCT was further supported by ATR spectroscopy under visible light irradiation. Upon exposure to visible light, a change in the intensities and positions of the absorptions bands related to vibrations of the oxo- bridged Cr–O–V moiety is observed. X-band ESR spectroscopy and magnetic susceptibility measurements point to paramagnetic behaviour of 1. The electrical response of complex 1 was studied by impedance measurements over a temperature range of −90 to 50 °C, revealing its semiconducting nature and the absence of a dielectric anomaly.