Evidence for nonpolar alignment of [NbOF5]2- anions in Cd(pyridine)4NbOF5 chains

A new phase of Cd(py)(4)NbOF5 (py = pyridine) (A) is a rare example of a mixed metal oxide fluoride in an ordered linear chain structure. This phase is of particular interest because it is a polymorph of a previously reported Cd(PY)(4)NbOF5 phase (B) that crystallizes in disordered linear chains. The ordered polymorph A contains two distinct Cd2+ Sites: one which is coordinated to the oxide ligands from two [NbOF5](2-) units, and another that is coordinated to two trans fluoride ligands. As a result, the structure of polymorph A features nonpolar linear chains with locally ordered of the inherent electronic differences between oxide and fluoride ligands. The stabilization provided by pi-stacking interactions between pyridine ligands on neighboring chains, as well as the effects of reactant stoichiometry on the general structure of the products in the CdO center dot 1/2Nb(2)O(5)/(HF)(x)center dot py/H2O system, is also discussed. Crystal data for the ordered Cd(PY)(4)NbOF5 polymorph: monoclinic space group P2(1)/c (No. 14) with a = 14.097(l) angstrom, b = 16.353(l) angstrom, c = 10.4380(9) angstrom, = beta 95.569(2)degrees, and Z = 4.