Structural Characterization of a Nanocrystalline Inorganic-Organic Hybrid with Fiberlike Morphology and One-Dimensional Antiferromagnetic Properties

A new nanocrystalline inorganic-organic hybrid compound, VO(C6H5COO)(2) has been synthesized under solvothermal conditions by reacting vanadium(V) oxytriisopropoxide with benzoic acid in toluene. A detailed investigation of the composition, structure and properties Of VO(C6H5COO)(2) using chemical and thermal analysis, synchrotron X-ray powder diffraction, electron microscopy techniques including SEM, TEM and SAED, spectroscopy techniques like XPS, EDX and FTIR, SQUID magnetometry and EPR is carefully described. Due to the low-crystallinity of the final material, its crystal structure has been solved from synchrotron X-ray powder diffraction data by combining a direct space global optimization technique and DFT geometry optimization and subsequently refined by the constraint Rietveld method. The compound crystallizes in the monoclinic system with a = 20.652(3), b = 6.798(1), c = 9.954(1) angstrom, beta = 92.145(6)degrees, space group C2, and Z = 4. The inorganic part of the structure can be regarded as staggered V-V-V chains, formed of corner-sharing VO6 octahedra, running along the monoclinic b-axis. A strong V-O bond alternation along the chain was evidenced by the DFT geometry optimization. The organic part is based on two crystallographically independent singly ionized benzoate moieties linked to vanadium atoms through a bidentate bridging mode. The morphology of VO(C6H5COO)(2) exhibits long nanofibers, which further consist of smaller individual nanofibers aligned in parallel to the growth direction along the b-axis, as expected from the ID nature of the compound. The magnetic susceptibility and X-band EPR measurements shows that the magnetic properties Of VO(C6H5COO)(2) can be described by a S = 1/2 linear antiferromagnetic chain model with the isotropic interaction between nearest neighbors and an estimated magnetic spin exchange parameter of J = -189 K. DFT calculations have also been carried out to simulate the optical response and to estimate the magnetic spin exchange related to VO (C6H5COO)(2). Such calculations allowed explaining the yellow-green color of the powder and the one-dimensional character of the magnetic structure.