Orientational order of [VOF5]2− and [NbOF5]2− polar units in chains

The generation of polarity in the solid state necessitates ordered, polar basic-building units (BBUs). This paper examines the evolution of ordered BBUs of 1D chains constructed of early transition metals (ETMs) and late transition metals. The cause of polar distortion orientation is illustrated with subtle alterations in the heterotypic structures of one previously reported compound (CuNbOF5(H2O)2(pyz)3) and three new hybrid materials, presented here: CuNbOF5(H2O)4(pyz)2 (1), CuVOF5(H2O)4(pyz)2 (2) and CuVOF5(H2O)2(pyz)3 (3) (pyz=pyrazine). In contrast to the [NbOF5]2− octahedra of CuNbOF5(H2O)2(pyz)3 and compound (1) that have oxide ligands within the 1D BBUs, the [VOF5]2− octahedra of compounds (2) and (3) contain disordered oxide ligands perpendicular to the chains. To create polar 1D BBUs in the solid state, one must have an understanding of how to direct distortions. We demonstrate that the choice of specific polar BBUs within a distinct environment is necessary for orientational order of the ETM anions.

Graphical abstractThe orientational order of [VOF5]2− and [NbOF5]2− polar anions in chains and its influence on noncentrosymmetry are discussed on the basis of the three new hybrid compounds composed of linear chains: (CuVOF5(H2O)4(pyz)2, CuNbOF5(H2O)4(pyz)2 and CuVOF5(H2O)2(pyz)3). Orientational order of the distortion of the early transition metal can be achieved by subtle modifications of the anisotropy in the anionic environment and a proper choice of the polar anion.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Three new hybrid compounds were characterized by single-crystal XRD. ► [VOF5]2− and [NbOF5]2− anions differ in the nucleophilicities of the ligands. ► The order of the anion is controlled by increasing the anisotropy of its environment.