Influence of pendant 2-[1,2,4]triazol-4-yl-ethylamine and symmetrical bis(pyrazol) ligands on dimensional extension of POM-based compounds

Abstract

Through utilizing pendant 2-[1,2,4]triazol-4-yl-ethylamine (tea) and two kinds of bis(pyrazol) ligand, five new polyoxometalate (POM)-based compounds [Cu₃K₂(tea)₂(OH)₄(H₂Mo₈O₂₇)] (1), [Ag(tea)(β-H₂Mo₈O₂₆)_0.5] (2), [Ag(tea)(H₂O)(γ-H₂Mo₈O₂₆)_0.5] (3), [Cu(H₂bdpm)(β-Mo₈O₂₆)_0.5] (4) and [Ag₂(Hbhpe)(θ-Mo₈O₂₆)_0.5] (5) (H₂bdpm = 1,1′-bis(3,5-dimethyl-1H-pyrazol-4-yl)methane, H₂bhpe = 1,2-bis(1H-pyrazolate)ethane) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. In compound 1, three Cu^II are fused by two tea and two OH⁻ moieties to form a tri-nuclear cluster [Cu₃(tea)₂(OH)₂]⁴⁺. The Mo₈ anions link each other through sharing terminal O atoms to build an Mo-chain. The tri-nuclear clusters are further connected by an Mo-chain and K⁺ ions to form a 3D framework. In compound 2, two Ag⁺ ions are fused by two tea ligands to construct a bi-nuclear subunit, which are linked by β-Mo₈ anions alternately to form a 1D chain. In compound 3, there exists a bi-nuclear Ag⁺ cluster [Ag₂(tea)₂]²⁺. The γ-Mo₈ anions link bi-nuclear Ag⁺ clusters alternately and a 1D chain is constructed. Furthermore, each [Ag₂(tea)₂]²⁺ offers two additional N donors to connect two anions through Mo–N bonds. In compound 4, two 1D zigzag Cu–H₂bdpm chains cover one 1D inorganic Mo-chain up and down to build a “hamburger-like” chain. The adjacent hamburger chains share the same Cu atoms to build a 2D structure. In compound 5, there exists a bi-nuclear [Ag₂(Hbhpe)₂]²⁺ cycle and a tetra-nuclear [Ag₄(Hbhpe)₄]⁴⁺ cycle. The bi-nuclear cycles and tetra-nuclear cycles alternately connect to form 1D metal–organic chains, which are further linked by θ-Mo₈ anions to construct a 2D layer. The electrochemical and photocatalytic properties of compounds 1–5 are studied.