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

The triazolate-assisted asymmetric dinuclear oxovanadium(IV) citrate [V 2 O 2 (cit)(Hdatrz) 3 ]·5H 2 O (1, H 4 cit = citric acid, Hdatrz = 1 H -1,2,4-triazole-3,5-diamine) and its additive salt [V 2 O 2 (cit)(Hdatrz) 3 ][V 2 O 2 (cit) 2 ] ½ ·2H 2 datrz·9.5H 2 O (2) and the polymerized hexanuclear product [V 6 O 6 (μ 3 -O) 2 (cit) 2 (Hdatrz) 4 ]·4H 2 O (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 [V 3 O 6 (μ 2 -OH)(μ 3 -O)(Hdatrz) 2 ]·4.5H 2 O (4) has also been isolated as a quasi -intermediate product of 3 without the coordination of citrate. Intriguingly, an octanuclear mixed-valence oxovanadium(V/IV) citrate K 2 {[VIV/V2O 2 (cit)(Hdatrz)(datrz)] 2 [VIV2O 2 (cit)(Hdatrz)(datrz)] 2 }·27.5H 2 O (5) has been obtained with different vanadium units, where dinuclear mixed-ligands and mixed-valence oxovanadium(IV/V) citrates [VIV/V2O 2 (cit)(Hdatrz)(datrz)] (5a) and [VIV2O 2 (cit)(Hdatrz)(datrz)] (5b) have been trapped. Citrate adopts a μ 2 -η 1 :η 1 :η 1 :η 2 coordination mode in 1, 2 and 5, while a μ 3 -η 1 :η 1 :η 1 :η 2 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 3 -η 1 :η 1 :η 1 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 2 and CO 2 over gases N 2 , H 2 , and CH 4 .