New 3-D polyoxovanadoborate architectures based on [V12B18O60]16− clusters

Abstract

Three new 3-D polyoxovanadoborates {[Cu(dien)(H₂O)]₃V₁₂B₁₈O₅₄(OH)₆(H₂O)}·4H₃O·5.5H₂O (1, dien = diethylenetriamine), {[Cd(H₂O)₂]₃V₁₂B₁₈O₅₄(OH)₆(H₂O)}·4H₃O·9.5H₂O (2) and {[Na(H₂O)₃]₄Na₂V₁₂B₁₈O₅₆(OH)₄(H₂O)}(H₃dien)₂ (3) have been hydrothermally synthesized and structurally characterized. Compounds 1–3 contain vanadoborate cluster [V₁₂B₁₈O₆₀] constructed by two hexameric oxovanadate units [V₆O₉] and one puckered [B₁₈O₄₂] ring via sharing O atoms. The vanadoborate cage [V₁₂B₁₈O₆₀] can present different degrees of protonation, namely [V₁₂B₁₈O₆₀H₆]¹⁰⁻ for 1 and 2, [V₁₂B₁₈O₆₀H₄]¹²⁻ for 3. The clusters [V₁₂B₁₈O₆₀H₆]¹⁰⁻ in 1 are connected by complex cations [Cu(dien)(H₂O)]²⁺ into a new 3-D framework via all terminal O atoms of square-pyramidal [VO₅] groups, while the clusters [V₁₂B₁₈O₆₀H₆]¹⁰⁻/[V₁₂B₁₈O₆₀H₄]¹²⁻ in 2 and 3 are linked with [Cd(H₂O)₂]²⁺ groups/the combination of [Na(H₂O)₃]⁺ and Na⁺ ions to give another two types of new 3-D frameworks via O atoms of [BO_x] (x = 3, 4) polyhedra, respectively. Magnetic measurements illustrate that compounds 1 and 2 have antiferromagnetic exchange interactions between metal centers. The theoretical band structure of 2 has been also studied.