Assembly And Properties Of Polyoxometalates-based Transition Metal Functional Complexes Constructed From Bis-pyridyl-bis-amide Ligands

In this paper, twelve polyoxometalates(POMs)–based metal-organic complexes constructed from bis–pyridyl–bis–amide major ligands have been hydrothermally synthesized and structurally characterized by IR, TG, powder X-ray diffraction and single crystal X–ray diffractions. The electrochemical and photocatalytic properties of these complexes have been studied as well.1. The classical Anderson–type POM anions were used as inorganic building units to assemble with Cu ions and flexible bis–pyridyl–bis–amide ligands(3–dpye= N, N’–bis(3–pyridinecarboxamide)–1,2–ethane, 3–dpyp= N,N’–bis(3–pyridinecarboxamide)–1.3–propane) under hydrothermal conditions, resulting in three new POM–based complexes. The influences of the spacer lengh of the flexible ligands and the coordination modes of the POMs on the structures of these complexes have been investigated. H{Cu(3–dpye)0.5[Cr Mo6(OH)6O18](H2O)}·0.5(3–dpye)(1) {Cu2(3–dpyp)2[Cr Mo6(OH)5O19](H2O)2}·2H2O(2) [Cu3(3–dpyp)2(Te Mo6O24)(H2O8]·4H2O(3) Complex 1 is a one–dimensional(1D) infinite belt–like chain, which is constructed from Anderson-type POM and semi-rigid bis–pyridyl–bis–amide ligands. Complex 2 displays a 3D POM–based metal–organic framework containing metal–organic left– and right–handed helical chains, which have never been reported. Complex 3 exhibits a 3D [Te Mo6O24]6– polyoxoanions–based metal–organic framework. The results indicate that the ligand lengh and coordination modes of the POMs show great effect on the structures of these complexes. Complexes 1-3 exhibit remarkable photocatalytic activities for the degradation of methylene blue(MB) under UV and visible light irradiation. 3 also shows good electrocatalytic activity toward the reduction of nitrite and hydrogen peroxide. II2. By using CuII ions and semi-rigid bis–pyridyl–bis–amide ligands(3–dpp = N,N’-bis(3-pyridinecarboxamide)-piperazine and 4–dpp = N,N’-bis(4-pyridinecarboxamide)-piperazine) to modify classical Keggin–, Anderson–type POMs and [K2Mo8O28]6– polyoxoanions, six POM–based complexes have been hydrothermally synthesized. H{Cu2(μ2–OH)2(3–dpp) [Cr Mo6(OH)6O18]}·4H2O)(4) {Cu2(4–dpp) [Cr MoVI5MoV(OH)6O18](H2O)4}·4H2O(5)[Cu2(3–dpp)2(PMoVI11MoVO40)(H2O)2]·2H2O(6) [Cu2(3–dpp)2(PWVI11WVO40)(H2O)6]·H2O(7) [Cu2(3–dpp)2(Si W12O40)(H2O)6]·H2O(8) [Cu2(3–dpp)2(H2K2Mo8O28)(H2O)2](9) Complex 4 is a 3D Anderson–type POM–based metal–organic framework, in which the amide group of the bis–pyridyl–bis–amide ligand is uncoordinated, while complex 5 also shows a 3D Anderson–type POM–based metal–organic framework, in which the amide group of the bis–pyridyl–bis–amide ligand is coordinated. Complex 6 is a 2D metal–organic architecture based on the Keggin–type [PMoVI11MoVO40]4– anions and quadrate Cu2(3-dpp)2 loops. Complexes 7 and 8 display 1D infinite chains, which are also constructed from quadrate Cu2(3-dpp)2 loops and Keggin polyoxoanions. Complex 9 exhibits a 3D metal–organic framework derived from the newly–reported [K2Mo8O28]6– polyoxoanions and quadrate Cu2(3-dpp)2 loops. The coordination modes of ligands and the structural characteristic of POMs have great effect on the final structures of these complexes. Complexes 6-9 show electrocatalytic properties in the reduction process of H2O2, nitrite and bromote. Complexes 4, 5 and 8 show high photocatalytic activity toward MB degradation under UV and visible light irradiation. Complexes 6, 7 and 9 show obvious photocatalytic activity toward MB degradation only under UV irradiation.3. By introducing the flexible bis–pyridyl–bis–amide ligands(3–dpyb = N,N’-bis(3-pyridinecarboxamide)-1,4-butane, 3–dpyh = N,N’-bis(3-pyridinecarboxamide)-1,6-hexane) and phenanthroline(phen) as mixed ligands into Cu–POM systems, three POM–based complexes were synthesized under hydrothermal conditions. [Cu2(Si W12O40)(3–dpye)(phen)2(H2O)]·3H2O(10) [Cu2(Si W12O40)(3–dpyb)(phen)2(H2O)4](11) [Cu2(Si W12O40)(3–dpyh)(phen)(H2O)4]·6H2O(12) Complex 10 exhibits a 2D network, in which [Si W12O40]4–(Si W12) anions act as tetradentate linkages. Complex 11 is a 0D structure containing a dinuclear complex cation Cu2(3-dpyb)(phen)2(H2O)4]4+ and a discrete Si W12 anion. Complex 12 shows a 1D chain structure, in which the Si W12 anions as bidentate linkages bridge the adjacent complex cations [Cu2(3–dpyh)(phen)2(H2O)4]4+. The ligand lengh shows great effect on the structures of these complexes. In addition, the introduction of the secondary ligand plays an important role in tuning the structures of the title complexes.Compelxes 10-12 show good electrocatalytic activity toward the reduction of nitrite and H2O2, and possess good photocatalytic activity and stability for the photodegradation of MB under UV irrdiation,...