Glycolato and R,S-lactato imidazole molybdenum(iv) complexes [Mo3SO3(glyc)2(im)5]·im·H2O (1), Na2[Mo3SO3(R,S-lact)3(im)3]·10H2O (2), and [Mo6O10(R,S-lact)2(im)10]·16H2O (3) have been isolated and characterized (H2glyc = glycolic acid, H2lact = lactic acid, im = imidazole). α-Alkoxy coordination with molybdenum [Mo-Oα-alkoxy 1.993(7)av Å] in 1 and 2 showed obvious differences to their counterpart with α-hydroxy coordination [MoIV3S4(PPh3)3(Hlact)2(lact)] [2.204(4)av Å] as shown in M. N. Sokolov, S. A. Adonin, A. V. Virovets, P. A. Abramov, C. Vicent, R. Llusar and V. P. Fedin, Inorg. Chim. Acta, 2013, 395, 11-18. This was also true for the 36 reported structures of FeMo-cofactors in the RCSB protein data bank (Mo-Oav 2.272 Å), which can serve as indirect evidence for the protonation of homocitrate in FeMo-co. The C-OHα-hydroxy bonds were longer than the short C-Oα-alkoxy bonds. Trinuclear Mo3SO3 cores were stabilized by imidazoles and/or α-hydroxycarboxylates, whereas only two glycolates were present in 1. α-Hydroxycarboxylates in 1 and 2 acted as bidentate ligands of Mo(iv) atoms through α-alkoxy and α-carboxy groups, while the imidazoles coordinated monodentately with nitrogen atoms. The lactates in 3 coordinated with Mo(iv) atoms through two oxygen atoms of α-carboxy groups, leaving the α-hydroxy group free. Furthermore, novel hexanuclear oxomolybdenum(v) malate Na6[(Mo2O4)3(mal)4]·5H2O (4) was also isolated (H3mal = malic acid). Solid-state and solution 13C NMR resonances of carbon atoms in α-alkoxy groups appeared in a high-field region (71.6, 77.4 ppm), indicating that α-alkoxy groups were easy to protonate.

A similar pair of protonated and deprotonated mononuclear oxidovanadium glycolates [VO(Hglyc)(phen)(H2O)]Cl·2H2O (1) and [VO(glyc)(bpy)(H2O)] (2) and a mixed-(de)protonated oxidovanadium triglycolate (NH4)2[VO(Hglyc)2(glyc)]·H2O (3) were isolated and examined. The ≡C–O(H) (≡C–OH or ≡C–O) groups coordinated to vanadium were spectroscopically and structurally identified. The glycolate in 1 features a bidentate chelation through protonated α-hydroxy and α-carboxy groups, whereas the glycolate in 2 coordinates through deprotonated α-alkoxy and α-carboxy groups. The glycolates in 3 coordinate to vanadium through α-alkoxy or α-hydroxy and α-carboxy groups, and thus has both protonated ≡C–OH and deprotonated ≡C–O bonds simultaneously. Structural investigations revealed that the longer protonated V–Oα-hydroxy bonds [2.234(2) Å and 2.244(2) Å] in 1 and 3 are close to those of FeV-co 2.17 Å1 (FeMo-co 2.17 Å2), while deprotonated V–Oα-alkoxy bonds [2, 1.930(2); 3, 1.927(2) Å] were obviously shorter. This shows a similar elongated trend as the Mo–O distances in the previously reported deprotonated vs. protonated molybdenum lactates,3 and these vanadium and molybdenum complexes have the same local V/Mo-homocitrate structures as those of FeV/Mo-cos of nitrogenases. The IR spectra of these oxidovanadium and the previously synthesized molybdenum complexes including different substituted ≡C–O(H) model compounds show red-shifts for ≡C–OH vs. ≡C–O alternation, which further assign the two IR bands of extracted FeMo-co at 1084 and 1031 cm−1 to ≡C–O and ≡C–OH vibrations respectively. Although the structural data or IR spectra for some of the previously synthesized Mo/V complexes and extracted FeMo-co were measured earlier, this is the first time that the ≡C–O(H) coordinated peaks are assigned. The overall structural and IR results well suggest the co-existence of homocitrates coordinated with α-alkoxy (deprotonated) and α-hydroxy (protonated) groups in the extracted FeMo-co.

Iron valences of 129 P-clusters from FeMo/V proteins were analyzed using a bond valence method, supposing the existence of Fe3+ in a generally considered all-ferrous PN cluster in solution with excess reducing agent.

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.

Dimeric mixed-valence vanadium (IV/V) glycolates and lactates with N-heterocycle ligands, (4) and (NH 4 ) 2 [V 2 O 3 (bpy) 2 (R,S-lact) 2 ]Cl·H 2 O (5), have been isolated in a wide pH range from weak acidic to alkaline solutions (H 2 glyc = glycolic acid, H 2 lact = lactic acid, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine). The glycolates and lactates in 1 and 2 [a]

Water-soluble wheel-like icosanuclear peroxotitanate K 16 1) chelated by tartrate has been successfully isolated. As the largest peroxotitanate reported, {Ti 20 } features 20 (hydro)peroxo groups with three kinds of coordination modes in μ-η 1 :η 2 , μ-η 2 :η 2 , and η 2 fashions. The cluster is stable in solution and solid states. It has been tested for the catalytic oxidations of methyl phenyl sulfide and pyridine with hydrogen peroxide, respectively, which shows reversible elimination and the addition of peroxo groups. This provides a rare example of wellcharacterized titanium peroxide for homogeneous catalysis and mechanism research.

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Anion zinc-based metal-organic framework [HDMA]2n[Zn2n(DMA)2n(1,4-BDC)3n]•2nDMF•6nH2O (1, DMF = N,N-dimethylformamide, 1,4-H2BDC = 1,4-benzenedicarboxylic acid, DMA = dimethylamine) with open-channels has been used as a luminescence sensor for Cd2+detection, which was obtained...