Crystal building chemistry of vanadium, niobium and tungsten oxide fluoride anions

The metal-oxygen bonds of the [NbOF5]2-, [WO2F4]2- and [VOF5] 2- anions exhibit electronic distortions similar to those observed in the [NbO6/2]- octahedra in LiNbO3 . The nonlinear optical susceptibilities of the Nb-O and the W-O bonds are some of the largest known for inorganic species. The electronic effects and, in certain cases, the bond network cause the out-of-center distortions in octahedral d0 transition metal oxide fluoride anions. The primary electronic distortion is independent of the extended structure and is due to significant overlap between filled oxide p-orbitals and vacant cation d-orbitals The degree to which the inherent primary distortion can be modified by smaller, secondary distortions caused by interactions with the bond network could be discerned based on the three bond network contacts to the anion in [HNC6H6OH] 2[Cu(NC5H5)4(NbOF5) 2]. Similarly, the [WO2F4]2- anion is ordered in [HNC6H6OH]2[Cu(py) 4(WO2F4)2] because three separate contacts to the anion are possible with the 5-hydroxy-2-methylpyridinium cation. The third contact, which is necessary to order the anion, is to the moderately nucleophilic fluoride trans to the uncoordinated oxide.;The two coordinating nitrogens and two hydrogen bonding NH groups of the bidentate ligand biimidazole (N4C6H6) in Cu(N4C6H6)(H2O)NbOF5 lead to the formation of two-dimensional layers with a nucleophilic fluoride top surface and a hydrogen bond donating bottom surface that pack into the polar space group, Pna21. Individual [NbOF 5]2- anions align in the two-dimensional layers formed from parallel one-dimensional chains and ensure that the Nb-O bonds assemble along the polar 21 screw axis.;Exploration of the CuO,VOX/HF·py/H2O/pyridine system uncovered four different anions: [VOFS]2-, [VOF 4]-, [VOF4]2-, and [V2O3F7]3-. In [pyH]2 [Cu(py)4(VOF5)2], the ordered [VOF 5]2- anion was observed to direct coordination through cis fluoride ligands, while the analogous Group 5 anions [NbOF 5]2- and [TaOF5]2- direct coordination through their trans oxide and fluoride ligands. This change in structure directing properties results from a lengthened metaloxide bond and the decreasing electronegativity of the transition metal down Group 5. In the noncentrosymmetric Cu(py)4VOF4, the square pyramidal geometry of the [VOF4]2- groups causes the anions to align in layers with nucleophilic oxide top surfaces and bottoms with cavities created by the empty coordination sites of the anion.