pH-Dependent Assembly of Reduced Polyoxomolybdenum Phosphates Modified by MnII

Abstract

Three reduced polyoxomolybdenum(v) phosphates modified by MnII: (Hen)(H2en){Mn(H2O)[Mn0.5Mo6(HPO4)3(PO4)(OH)3O12]}·2H2O (1) (en = ethylenediamine), (en)(Hen)4{Mn(H2O)[MnMo12(H2PO4)3(HPO4)4(PO4)(OH)6O24]}·3.5H2O (2), and [H7(en)Mn2.5P4Mo6O31(H2O)3]·2.5H2O (3) were synthesized through the hydrothermal reaction at different pH values. Compound 1 exhibits a 3-D framework; each basic [Mn(P4Mo6O31)2] unit coordinates with eight MnII ions. Compound 2 contains two kinds of [Mn(P4Mo6O31)2] basic units, which are linked by MnII ions to form a 2-D network. For compound 3, each basic [Mn(P4Mo6O31)2] unit is modified by 12 MnII ions and exhibits a 3-D framework. It was established that the pH of the reaction and the amount of ethanediamine play very important roles in the assembly of polyoxometalate-based compounds. The pH value determines the electron density of polyoxometalate and the degree of en protonation, which affect the coordination ability of polyoxometalates and result in different structures. Compounds 1–3 display weak antiferromagnetic coupling.