Asymmetric dinuclear, hexanuclear and octanuclear oxovanadium citrates with triazolates: novel mixed-ligands and mixed-valence complexes.

The triazolate-assisted asymmetric dinuclear oxovanadium(IV) citrate [VO(cit)(Hdatrz)]·5HO (1, Hcit = citric acid, Hdatrz = 1-1,2,4-triazole-3,5-diamine) and its additive salt [VO(cit)(Hdatrz)][VO(cit)]·2Hdatrz·9.5HO (2) and the polymerized hexanuclear product [VO(μ-O)(cit)(Hdatrz)]·4HO (3) have been isolated at different temperatures, respectively. Adduct 2 shows strong evidence for the conversion of a symmetric dinuclear oxovanadium(IV) citrate to a mixed-ligand asymmetric oxovanadium(IV) citrate. Moreover, a fully oxidized trinuclear vanadium(V) species [VO(μ-OH)(μ-O)(Hdatrz)]·4.5HO (4) has also been isolated as a -intermediate product of 3 without the coordination of citrate. Intriguingly, an octanuclear mixed-valence oxovanadium(V/IV) citrate K{[VIV/V2O(cit)(Hdatrz)(datrz)][VIV2O(cit)(Hdatrz)(datrz)]}·27.5HO (5) has been obtained with different vanadium units, where dinuclear mixed-ligands and mixed-valence oxovanadium(IV/V) citrates [VIV/V2O(cit)(Hdatrz)(datrz)] (5a) and [VIV2O(cit)(Hdatrz)(datrz)] (5b) have been trapped. Citrate adopts a μ-η:η:η:η coordination mode in 1, 2 and 5, while a μ-η:η:η:η fashion has been observed in 3. Unlike 1-4, complex 5 contains both protonated and deprotonated triazolates simultaneously, where four triazolates further coordinate in a μ-η:η:η manner to construct an octanuclear unit. These different structural features in 1-5 are dominated by flexible multidentate citrates and protonated/deprotonated triazolates, showing their synergistic effects. Furthermore, 1 exhibits a rectangular channel, showing preferential adsorption of O and CO over gases N, H, and CH.