Structure of Tetraammonium Pentamolybdodiselenite Trihydrate

Abstract

2(NH₄)₂O·₂SeO₂.₅MoO₃·3H₂O was proved to be (NH₄)₄Se₂Mo₅O₂₁·3H₂O being isomorphous to (NH₄)₄S2Mo₅O₂₁·3H₂O. The structural difference between the two analogous heteropoly compounds is limited around the O atoms bonded to the heteroatoms. The distances of Se-Oranging from 1.67 to 1.73A are greater than those of S-0 of S₂Mo₅O₂₁^4- anion by 0.14. -0.20A. Mo-O bond lengths agree well with the corresponding ones found in the analogous structure, except for the shortened distances between Mo and O atoms bonded to the heteroatoms. There are short contacts which may be hydrogen bonds within 3.2A among NH₄⁺, H₂O and Se₂Mo₅O₂₁^4-. The hydrogen-bond acceptors in the anion are mainly terminal 0atoms. This intermolecular interaction is thought to act upon the deformation of the heteropolyanion molecule.