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Static solid state NMR investigation of niobium cluster [Nb6Br12(H2O)6][HgBr4]•12H2O

Niobium chemistry has attracted growing attention, especially in the field of catalysis, due to its unique iono-covalent coordination properties[1]. Between halides significant part of research is devoted to the edge-bridged clusters [(Nb6Xi12)La6] (Xi = Cl, Br, La = Cl−, Br−, H2O, etc.), which can exist in several oxidation states. However, only limited number of studies reports solid state 93Nb NMR data for niobium[2], without data for cluster compounds. We have chosen the bromide cluster [Nb6Br12(H2O)6][HgBr4]·12H2O to obtain referent ssNMR data for [Nb6Br12(H2O)6]2+ cluster unit. The sample was prepared by the literature procedure as small crystals of known structure[3]. Static 93Nb NMR measurements have been done on powdered samples in several fields up two 12 T. In addition, zero field NQR measurements of 93Nb, 79Br and 81Br have provided precise EFG parameters. In order to test the applicability of the GIPAW-DFT calculation methods for this class of materials, the independent computations were carried out using version 4.3 of CASTEP-NMR [4]. Very good agreement between experimentally determined and calculated NMR parameters was achieved for quadrupole coupling constant Cq and asymmetry parameter η. Fair agreement was achieved for shielding anisotropy and asymmetry.

solid state NMR; niobium

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