Syntheses, Crystal Structures And Characterizations Of Inorganic/Organic Hybrid Polyoxomolybdates

Six polyoxomolybdate crystals were prepared by means of hydrothermal techniques on the basis of organic amine molecules, carboxylic acids and polyoxometalate anions. They were determined structurally by X–ray single crystal diffraction and characterized by elemental analysis, IR and TG–DTA.1. Two new polyoxomolybdate crystals, [(C₆H₄NO₂)Mo₂O₅OH] (1) and [Co(H₂O)(dpa)MoO₄] (2) were synthesized. The structure of crystal (1) consists of {MoO₆} octahedra and pyridine?4?carboxylic ligands. {MoO₆} octahedra share their adjacent equatorial edges with adjacent octahedra, forming a new 1D ribbon-like molybdenum oxide framework. Pyridine?4?carboxylic ligands are coordinated to the molybdenum sites and project up and down along the chain alternately as bidentate ligands. The structure of crystal (2) consists of a one-dimensional ladder?like chain constructed of {Co(H₂O)(dpa)}²⁺ subunits, linked by corner-sharing {MoO₄}^2- tetrahedrons. The dpa ligands are coordinated to the cobalt sites and project along the chain alternately. There exists intermolecular hydrogen bonding between N–H and O–Mo. These hydrogen-bonding andπ…πstacking interactions of pyridine rings between neighboring chains hold one-dimensional chains together into two-dimensional layer.2. Two new polyoxomolybdate crystals containing {Mo8O26} cluster, [Co(2,2–bpy)2]2{γ–Mo8O26} (3) and [(dpaH)4(α–Mo8O26)] (4), were synthesized. The structure of crystal (3) consists of a novel 1D ribbon constructed from characteristicγ–[Mo₈O₂₆]^4- anions and [Co(2,2–bpy)2]2+ subunits. Eachγ?[Mo₈O₂₆]^4- cluster bridges four {CoN4O2} octahedra units by the terminal oxygen atoms. The structure of crystal (4) consists of a characteristicα–[Mo₈O₂₆]^4- anion and four protonated dpaH ligands as charge-compensating cations. It is noteworthy that there exist extended intermolecular hydrogen bonding between the nitrogen atoms of the protonated dpaH ligands and the terminal or bridging oxygen atoms of molybdenum atoms in theα-[Mo₈O₂₆]^4- anions, these overall hydrogen bonding connect the cations and the anions together to form the 3D network structure. 3. Two new Keggin structure polyoxomolybdate crystals of [Cu₂(dpa)₃]₂[PV₂Mo₁₂O₄₂] (5) and [Co(dpa)₂(H₂O)]₂[PV₆Mo₈O₄₂]{dpaH} (6) were synthesized. The structure of crystal (5) is constructed from {VO5} bicapped [PV₂Mo₁2O₄₂]^4- anions and [Cu₂(dpa)₃]²⁺ cations. Cu complex cations are cooridinated with three nitrogen atoms from two dpa ligands, forming plane–trigonal geometry. Two Cu subunits are linked with a dpa ligand to form a binuclear Cu complex cation. The structure of crystal (6) consists of neutral {Co(dpa)₂(H₂O)}₂·{PV₆Mo₈O₄₂} clusters and disordered dpaH molecules. The [Co(dpa)₂(H₂O)]2·[PV₆Mo₈O₄₂] cluster is constructed from a mixed-metal bicapped Pseudo-Keggin cluster [PV₆Mo₈O₄₂]^6- covalently bonded to two [Co(dpa)₂(H₂O)]³⁺ units via two terminal oxygen atoms.