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

A new nanocrystalline inorganic−organic hybrid compound, VO(C 6 H 5 COO) 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(C 6 H 5 COO) 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) Å, β = 92.145(6) °, space group C 2, and Z = 4. The inorganic part of the structure can be regarded as staggered V−V−V chains, formed of corner-sharing VO 6 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(C 6 H 5 COO) 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 1D nature of the compound. The magnetic susceptibility and X-band EPR measurements shows that the magnetic properties of VO(C 6 H 5 COO) 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(C 6 H 5 COO) 2 . Such calculations allowed explaining the yellow-green color of the powder and the one-dimensional character of the magnetic structure.