The key role of -CH3 steric hindrance in bis-(pyrazolyl) ligand on polyoxometalate-based compounds

Through using two kinds of bis(pyrazolyl) ligands, four polyoxometalate (POM)-based compounds were hydrothermally synthesized and structurally characterized, [Ag-3(Hbhpe)(2)(H2O)(H2PMo12O40)] center dot H2O (1), [Ag(H(2)bdpm)(2)(H2PW12O40)]center dot 4H(2)O (2), [Ag-6(H(2)bdpm)(6)((HPW8W4O40)-W-VI-O-V)]center dot 2H(2)O (3) and [Ag-4(H(2)bdpm)(4)-(H2P2W18O62)]center dot 3H(2)O (4) (H(2)bhpe = 1,2-bis(1-H-pyrazolate)ethane, H(2)bdpm = 1,1'-bis(3,5-dimethyl-1H-pyrazolate)methane). In compound 1, the Ag-Hbhpe subunit is a 2D layer containing large penta-membered cycles and small tri-nuclear Ag-i clusters. The Keggin anions covalently float on the large cycles. In compound 2, the Keggin anions are fused by [Ag(H(2)bdpm) (2)](+) subunits to form a 1D chain. Compound 3 contains hexa-membered metal-organic cycles, which are further linked by Keggin anions to build a 1D chain. Adjacent chains share the Ag-i ions to construct a 3D framework of 3. Compound 4 exhibits a wavy double-track chain structure, with the Wells-Dawson anions covalently suspended up and down this chain. The steric hindrance of -CH3 groups in H(2)bdpm leads to the formation of mononuclear Ag-i subunits in 2-4. The influence of -CH3 steric hindrance in bis(pyrazolyl) ligands on the structures of 1-4 is discussed. The electrochemical and photocatalytic properties of the title compounds have been studied.