Isolated Mixed-Valence Iron Vanadium Malate and Its Metal Hydrates (M = Fe²⁺, Cu²⁺, Zn²⁺) with Reversible and Irreversible Adsorptions for Oxygen

Abstract

Isolated octanuclear iron–vanadium malate (NH4)3(CH3NH3)3[FeIII 2VIV 2VV 4O11(mal)6]·7.5H2O (1; H3mal = malic acid) and its family of metal hydrates M′3n [MII(H2O)2]1.5n [FeIII 2VIV 2VV 4O11(mal)6] n ·xnH2O (2 or 2-Fe, M′ = NH4 +, M = Fe, x = 7.5; 3 or 3-Cu, M′ = K+, M = Cu, x = 10; 4 or 4-Zn, M′ = K+, M = Zn, x = 6.5) have been obtained by self-assembly in water. The cluster anion [Fe2V6O11(mal)6]6– (1a) shows an interesting iron bicapped-triangular-prismatic structure, which is bridged by M2+ hydrates (M = Fe, Cu, Zn) to construct isostructural metal organic frameworks (MOFs) 2–4. The mixed-valence vanadium systems in 1–4 were determined by theoretical bond valence calculations (BVS) and charge balance. The magnetic susceptibilities are further elucidated as high spin for Fe3+ in 1a and bridging Fe2+ in 2-Fe, respectively. A strong ferromagnetic interaction was also observed for 2-Fe at 3 K. 2-Fe, 3-Cu, and 4-Zn have similar hydrophilic channels with diameters of 6.8, 6.5, and 6.6 Å, respectively, which show obvious affinity for O2 in comparison with no adsorption of N2, H2, CO2, and CH4 at room temperature under different pressures. Moreover, 2-Fe and 4-Zn exhibit irreversible O2 absorptions, which may be attributed to charge transfer between O2 and open metal sites (OMSs) formed during vacuum heating pretreatment. UV–vis and EPR spectra show a change in electronic structure of 2-Fe after O2 adsorption. The reversible adsorption observed in 3-Cu suggests a weak interaction between O2 and Cu2+ due to the Jahn–Teller effect. The properties of gas adsorption provide an insight into the performances of small molecules in the channels constructed by synthetic octanuclear model compounds, which are related to the interactions between the gas substrate and the heterometal cluster in biology.

Octa- and Tetradecanuclear Mixed-Valent Vanadium(III/IV) Malates with Triazoles: Gas Adsorptions, Chiral Interface Recognition, and In Situ Decarboxylation

“…However, the valencies of the V2 atom in 1 and V2 and V3 atoms in 2 and 3 in {V 6 O 5 } cores are ambiguous between +3 and +4, indicating that these vanadium centers have some degree of mixed-valence states with strong electron delocalization, which is similar to previously reported mixed-valent vanadium clusters. 14,34 BVS calculations for μ 2 −O and μ 3 −O atoms in 1−3 show that they are all in O 2− states (Table S5). Charge balance considerations indicate the assignments of the six vanadium centers in {V 6 O 5 } cores are V III 2 V IV 4 in 1, V III 3 V IV 3 in 2, and V III 1 V IV 5 in 3A, respectively.…”

“…Previously, we reported a racemic heterometallic iron−vanadium malate cluster. 14 On the other hand, since the spontaneous resolution of sodium ammonium tartrates was first discovered and separated mechanically by Pasteur in 1848, 15 spontaneous resolution upon crystallization becomes an effective approach to obtain chiral metal clusters. Nevertheless, only 5−10% of racemates can undergo spontaneous resolution, while more than 90% of them crystallize as racemic compounds.…”

“…Studies of chemical syntheses of FeV-co analogues could help to gain insight into the relationships between the structures and functions of cofactors. Previously, we reported a racemic heterometallic iron–vanadium malate cluster . Here, we successfully construct a pair of enantiomeric mixed-valent vanadium­(III/IV) model clusters [Δ-V III 4 V IV 4 O 5 ( R -mal) 6 (Hdatrz) 6 ]·44.5H 2 O (Δ R - 1 ) and [Λ-V III 4 V IV 4 O 5 ( S -mal) 6 (Hdatrz) 6 ]·38.5H 2 O (Λ S - 1 ).…”

Binuclear, tetranuclear and hexadecanuclear thio-oxomolybdenum(v/iv) glycolates with selective adsorptions of gases

“…The small values correspond to the micropores that existed in 4. 46,47 In order to further illustrate the gas adsorption characteristics of 4, we have carried out CO 2 adsorption experiments for 4 at different temperatures (298 and 308 K) under atmospheric pressure. As shown in Fig.…”

Successive constructions of regular tetra-, hexa- and octanuclear microporous polyoxovanadates(iii) for gas adsorption

“…S9, † the results show negligible N 2 sorption for 1, 2 and 4, which should be ascribed to their small pore sizes. 35,50 The Brunauer-Emmett-Teller (BET) surface areas of 1, 2 and 4 are 0.2534, 0.3293 and 0.4734 m 2 g −1 , respectively. Owing to the existence of diversified microchannels in POMOFs 1, 2 and 4, their gas storage capabilities have been further investigated by using some common smallmolecular gases like CO 2 , O 2 , H 2 , CH 4 and N 2 at 298 K, respectively.…”