Synthesis, Crystal Structure And Properties Of Sandwich-type Polyoxometalates Modified By Different Terminal Ligands

Polyoxometalates (POMs), a kind of metal-oxygen clusters, have attracted many interests in recent years. The transition metal substituted POMs developed rapidly, that's not only because of their structural varieties, but also their potential applications, such as analytical science, materials science, catalysis, medicine, and so on. The sandwich-type polyoxometalates (STPs) are a largest subfamily of them which receive much attention in application and fundamental research. This could be ascribed to the variety of the metallic cluster and the heteroatom, as well as their large molar mass, high negative charge and multi-magnetism center.In this paper, two new poly-nuclear transition metal cluster sandwich-type heteropolytungstates were obtained by adopting different tri-vacant Keggin POMs by conventional aqueous synthesis method at different pHs.1. Sandwich-type polyoxometalate in which coordination water molecules were replaced by organic ligands: Na₁₀(HC₃H₄N₂){[Na(H₂O)][Mn(C₃H₄N₂)]₃[SbW₉O₃₃]₂}·20H₂O (1)Compound 1 is a sandwich-type heteropolytungstate consisting of two tri-vacant Keggin units [SbW9], a tri-nuclear manganese (II) cluster, four imidazole (im) molecules and eleven sodium atoms. Every manganese atom coordinates with one im molecule. The sodium atoms connect the polyanions to form a 2D layer structure through O–Na–O bonds. The magnetic investigation indicates that the existence of the weak antiferromagnetic interaction in the sandwiched three-nuclear [Mn(C3H4N2)]3 cluster.2. Sandwich-type polyoxometalate in which coordination water molecules were not replaced by organic ligands: (C₄H₇N₂)₁₀[Mn₄(H₂O)₂(PW₉O₃₄₂] (2)Compound 2 is composed of a tetra-nuclear manganese (II) cluster, two tri-vacant Keggin units [PW9] and ten 2-methylimidazole (mim) molecules. Four manganese atoms form a tetra-metal cluster M4-(H₂O)₂ in inerratic parallelogram type in the same plane. Ten free protonated mim molecules connected the polyanions to form a 3D supramolecular framework through hydrogen bondings.Both the compounds are determined by single crystal structure X-ray diffraction and characterized by IR spectra, TG, elemental analyses and XRD. Meanwhile, the magnetic behaviors of compound 1 were also studied.