The syntheses and structures of a series of polyoxometalate-based metal-organic arsonates constructed from a dual-ligand strategy with organic arsenic acids and N-donor ligands

Abstract

Seven polyoxometalate (POM)-based metal-organic arsenates, namely, [Ni(H2O)3(bipy)]2(Mo6O18)(L1)2·4H2O (POMAs-1), [Zn(H2O)2(bipy)]2(Mo6O18)(L1)2·4H2O (POMAs-2), [Cd(H2O)2(bipy)]2(Mo6O18)(L1)2·4H2O (POMAs-3), [Ni(phen)2]2(Mo6O18)(L1)2·2H2O (POMAs-4), [Cd(H2O)(phen)2]2(Mo12O34)(L1)4·H2O (POMAs-5), (Mo12O34)(L2)2∙H4(bipy)2·3H2O (POMAs-6), H2(Mo6O19)(L2)(HAsO4) ∙H4(bipy)2·4H2O (POMAs-7) (H2L1 = phenylarsonic acid, C6H5AsO3H2, PhAsO3H2; H2L2 = 3-NO2-4-OH-C6H3-AsO3H2; phen = 1,10-phenanthroline; bipy = 4,4′-bipyridine), have been successfully synthesized under similar hydrothermal conditions. Single-crystal X-ray diffraction analyses reveal that three types of polyoxoanions were obtained in the seven compounds, containing α-octamolybdate-type {(Mo6O18)(L1)2}4− in POMAs-1–4, very large molydoarsonate cluster {(Mo12O34)(L1)4}4− and {(Mo12O34)(L2)4}4− polyoxoanions in POMAs-5–6, and a totally new {(Mo6O19)(L2)(HAsO4)}6− cluster in POMAs-7. In POMAs-1–5, transition metal-organic unit built by metal centers and N-donor ligands as counter cations balance the charge of target structure, however, in POMAs-6–7, transition metal ions do not coordinate to the framework of polyoxoanion. In this work, the effects of metal cations and organic ligand containing N-donor ligands and organic arsenic ligands on target POM clusters were presented clearly and discussed in detail.