Syntheses, Crystal Structures And Characterizations Of Transition-Metal Complexes Based On Polyoxovanadate Building Units

In recent years, the assembly of transition-metal complexes based on polyoxometalate blocks is of great interest owing to not only the intriguing structural chemistry but also the potential applications in catalysis, medicine and materials etc. Combining with molecular design and self–assembly, four novel complexes were prepared by means of hydrothermal techniques on the basis of organic amine molecules and polyoxovanadate anions.1. [Cu(dpaH)V₂O₆]2. [Cu(dpaH)V₃O_8.5]3. [{Cu(dpaH)₂}2V₄O₁₂]4. {Co(2,2'-bipy)3}2V₄O₁₂·11H2OThey were determined structurally by X–ray single crystal diffraction and characterized by elemental analysis, FI–IR and TG.Complexes 1 and 2 were both 2D structures. The former consists of helical {VO3}nn- chains bridged through [Cu(dpaH)]²⁺ fragments into 2D layered structure and the latter exhibits a layered structure constructed from {V₃O_8.5}^2- layers inlaid with [Cu(dpaH)]²⁺ subunits. The {V₃O_8.5}^2- layers consist of ribbon-like chains of edge-sharing {VO5} square pyramids bridged through {V2O7} fragments.Two novel discrete complexes 3 and 4 are both consist of a cyclic {V₄O₁₂}^4- anion. Complex 3 and [{Cu(dpaH)₂}₂V₄O₁₂] 5 are isomeric. The {V₄O₁₂}^4- anions adopt boat-like and chair-like configurations respectively, and are coordinated to each Cu(II) ions through a single terminal oxygen atom of two cross vanadium sites. Moreover, complexes 3 and 5 exhibit cis- and trans-configurations, respectively. In crystal 4, there are electrostatic interactions between the Co(2,2'–bipy)₃²⁺ cations and the [V₄O₁₂]^4- anions. The [V₄O₁₂]^4- anions exhibit a chair-like configuration.