Structure and property of a Cu(II) compound bearing isopolyanion and flexible triol ligand

Abstract

The investigations of the organic-inorganic hybrid materials attract widely attentions in recent years due to their applications in many fields, such as medicine, magnetism and catalysis. As one of the important types of inorganic components, polyoxometalates (POMs) bear the features of various compositions, rich structures and tunable charges, and play key roles in the construction of hybrid materials. Since the first [Mo7O24]6- polyanion was synthesized and its structure was confirmed by single-crystal X-ray analysis, many different kinds of cations, including inorganic and organic ions, were introduced to this system. While the studies of this type of polyanion with coordination compounds are still rarely, especially for transition metal ions and oxygenated ligands. As our ongoing study in the field of POM-containing compounds, we succeeded in obtaining an organic-inorganic hybrid based on [Mo7O24]6- polyanion in aqueous solution with CuSO4·5H2O, (NH4)6Mo7O24·4H2O and a triol ligand as staring materials. The formula of the obtained compound was determined as (NH4)2[CuL(H2O)]2MO7O24∙3H2O, L=(HOCH2)3CNH(CH2)3NHC(CH2OH)3 ( 1 ) through X-ray analysis, elemental analysis, IR spectrum and TG analysis. Single-crystal X-ray analysis reveals that compound 1 belongs to the monoclinic system with the space group of P 21. The unit cell parameters is a =10.778(2) A, b =21.391(3) A, c =11.596(3) A, α =90°, β =96.82(1)°, γ =90°, V =2654.4(9) A3, Z =2, and the final R 1 is 0.0155. In the crystal structure of compound 1 , Cu2+ cation is in a six-coordination environment and combines with ligand L in the unsymmetrical chelate coordination manner, where two triol groups provide one and two O atoms respectively and the other three positions are occupied by two N atoms and one O atom from water molecule. The [CuL(H2O)]2+ subunit connects with [Mo7O24]6- polyanion through the strong O−H∙∙∙O and N−H∙∙∙O hydrogen bonds to form a supramolecular two-dimensional network. TG curve shows that compound 1 has a good thermal stability until 160°C. The behavior of temperature dependence magnetic susceptibility of compound 1 in the range of 2−300 K expresses a strong antiferromagnetic property. In this work, the flexibility of the ligand plays a key role and provides the possibility for the formation of the unsymmetrical chelate coordination style of Cu2+. In addition, the high charge number of polyanion is an important factor for the construction of the two-dimensional network through providing more interactive sites.