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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. [ABSTRACT FROM AUTHOR]

Heterodinuclear complexes [Cr(bpy)2(H2O)(μ-O)Ta(C2O4)3]2·3.5H2O (1) and [H2(terpy)][Cr(terpy)(C2O4)(μ-O)Ta(C2O4)3]·0.5H2C2O4·2.5H2O (2) (bpy = 2,2′-bipyridine; terpy = 2,2′:6′,2′′-terpyridine) have been synthesised through a reaction of a tris(oxalate)oxotantalate(v) anion and a complex chromium(iii) cation with corresponding aromatic N-donor ligands. These are the first examples of a Cr–O–Ta bridge in molecular compounds, and the first report of heterodinuclear complexes prepared from a tris(oxalate)oxotantalate(v) anion as a building block. Structural analysis of both compounds revealed that TaV in pentagonal bipyramid geometry is connected through a slightly bent μ-O bridge to CrIII having a distorted octahedral environment. The geometry optimization performed with density functional theory (DFT) calculations gave very good agreement with the experimentally obtained structure of 1. Room temperature solid state UV-Vis spectra were recorded for both compounds and compared to those of starting reagents, in order to test for possible new electronic transitions attributed to the metal-to-metal charge transfer between CrIII and TaV through the oxo-bridge. Infrared (IR) spectroscopy supported with DFT calculations was used to assign vibrational modes to all spectral features, especially those coming from the molecular μ-oxo bridge. Temperature dependence of magnetic properties of 1 and 2 were probed with magnetic susceptibility measurements on a SQUID magnetometer. Additionally, zero-field splitting parameters were determined from electron paramagnetic resonance (EPR) spectra of compound 1 and experimentally obtained values were confirmed by DFT calculations. [ABSTRACT FROM AUTHOR]