Assembly and photocatalysis of two novel 3D Anderson-type polyoxometalate-based metal-organic frameworks constructed from isomeric bis(pyridylformyl)piperazine ligands

摘要

Two novel Anderson-type polyoxometalates (POMs)-based metal-organic frameworks (MOFs), namely, H{Cu_2(μ_2-OH)_2L~1[CrMo_6(OH)_6O_(18)]}·4H_2O (1), {Cu_2L~2[CrMo~(VI)_5Mo~V(OH)_6O_(18)](H_2O)4}·4H_2O (2) (L~1 = N,N'-bis(3-pyridinecarboxamide)-piperazine, L~2 = N,N'-bis(4-pyridinecarboxamide)-piperazine), are hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex 1, the hexadentate [CrMo_6(OH)6O_(18)]~(3-) polyoxoanion bridges the CuII ions to generate a 2D Cu-POM inorganic layer, which is further extended by the μ_2-bridging L1 ligands (via ligation of pyridyl nitrogen atoms) to form a 3D MOF with a 4,6-connected {4~4·6~(10)·8}{4~4·6~2} topology. Complex 2 is also a 3D POM-based MOF exhibiting a {4~2·8~4} topology, which is constructed from the quadridentate [CrMo~(VI)_5Mo~V(OH)_6O_(18)]~(4-) polyoxoanions and μ_4-bridging L~2 ligands (via ligation of pyridyl nitrogen and carbonyl oxygen atoms). The different coordination modes of POM polyanions and the isomeric bis(pyridylformyl)piperazine ligands play key roles in the construction of the title complexes. In addition, the photocatalytic activities of the title complexes on the degradation of methylene blue (MB) under UV, visible light and sunlight irradiation have been investigated in detail.