Oxidovanadium(v) coordination compounds based on 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbohydrazide: from discrete to polymeric assemblies

Abstract

The reaction of NH₄VO₃ or VO(acac)₂ with 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbohydrazide (H₄L) has led to the formation of new homometallic dinuclear and tetranuclear V(V) coordination compounds, namely (NH₄)₂[(VO₂)₂(L)]·2H₂O (1) and [(VO₂)(VO)(EtO)(HL)]₂·2EtOH (2). The introduction of alkali metal cations (Na⁺ and Cs⁺) into the reaction resulted in the formation of the heterometallic hexanuclear [Na₂(H₂O)₄][(VO₂)₄(HL)₂]·16H₂O compound 3 and the {[Cs₂(H₂O)₂][(VO₂)₂(L)]}_n coordination polymer 4. Their composition and structure were determined by IR, ¹H and ¹³C NMR spectroscopy, and ESI-MS spectrometry. Single-crystal X-ray diffraction analysis of 1 reveals that the hexadentate L⁴⁻ ligand coordinates to two V(V) atoms via an ONN and an ONO donor set, resulting in the formation of a dinuclear vanadium-based complex dianion, [(VO₂)₂(L)]²⁻. The charge is compensated by two NH₄⁺ cations. In 2, two dinuclear vanadium-based [(VO₂)(VO)(EtO)(HL)] entities, each containing the hexadentate Schiff base ligand HL³⁻, which utilizes a set of donor atoms in a manner analogous to that in 1, are bridged through oxido (V–O–V) bonds into a tetranuclear cluster. In compound 3, the hexadentate HL³⁻ utilizes additional donor atoms to bind sodium cations to two [(VO₂)₂(HL)]⁻ moieties. The [Na₂(H₂O)₄]²⁺ cations are sandwiched by the oxygen atoms of the methoxy groups of the HL³⁻ ligands and the oxide atoms of the VO₂ core resulting in the formation of a hexanuclear cluster in 3. The structure of compound 4 is based on the mutually linked clusters containing monomeric [(VO₂)₂(L)]²⁻ moieties and water-alkali chains {[Cs₂(H₂O)₂]}_n to form a 3D coordination framework.