Hydrothermal syntheses, crystal structures and characterizations of two new metal-fluorides based on niobium and tantalum

Two novel metal-fluorides [H2N(C2H4)2NH2][NbOF5](1) and [H2N(C2H4)2NH2][TaF7](2) have been obtained by a two-step hydrothermal method and characterized by elemental analysis, IR, PXRD, EDS, TG analysis and single-crystal X-ray diffraction. X-ray diffraction reveals that both compounds exhibit the supramolecular architectures through the electrostatic interactions and hydrogen bonding interactions between protonated piperazine and anions. In the [NbOF5]2− of compound 1, the Nb atom moves from the center of the octahedron toward the oxide atom to form a short Nb=O bond and long terminal Nb–F bond. In compound 2, the Ta atom can be described as a pentagonal bipyramidal geometry coordinated by seven fluorine atoms. Furthermore, the UV spectra in solid state of compounds 1 and 2 have also been discussed, which shows both of them have strong absorption bands.