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By comparisons of N2 and isoelectronic substrate CO bound FeMo-cofactors (FeMo-cos) in nitrogenases, we have used a classical bond valence method to calculate the oxidation states of the iron and molybdenum atoms in FeMo-cos. For single N2- and CO-bound FeMo-cos that have the same charge in iron counterparts, Fe1/7 can be unambiguously assigned to Fe(III), while Fe3/4/5 show different degrees of mixed valences related to the individual iron atoms in FeMo-cos. The only difference is the valence of binding sites Fe2 and Fe6, where N2-bound FeMo-co in 6UG0 shows +3 and +2, respectively, while the opposite is observed in the CO-bound FeMo-cos in 4TKV. For double CO- and N2-bound FeMo-cos with different coordination modes, the N2-bound species in 6UG0 performs a similar oxidation state and more electron-localized than those of CO-bound species in 7JRF. Calculations also show an unprecedented Mo(II) in N2-bound FeMo-cos with monodentate homocitrate, while they show Mo(III) in CO-bound and other high resolution nitrogenases. Bond comparisons imply that monodentate homocitrate and unreasonable long Mo–O distances are attributed to the low valence of Mo(II) in N2-bound FeMo-cos. [ABSTRACT FROM AUTHOR]

Reactions of carbon dioxide with lanthanide ethylenediaminetetraacetates M[Ln(EDTA)(H2O)3]·5H2O (M = NH4, Na or K; Ln = La or Ce) result in the formation of highly water-soluble lanthanide carbonates with ethylenediaminetetraacetates (NH4)5[La3(CO3)(EDTA)3(H2O)3]·12H2O (1), Na8[Ln2(CO3)3(EDTA)2]·17.5H2O (Ln = La, 2; Ce, 3), and K5[Ln3(CO3)(EDTA)3(H2O)3]·13.5H2O (Ln = La, 4; Ce, 5; H4EDTA = ethylenediaminetetraacetic acid) in dimethylformamide–water solution, which have been fully characterized. The main structures of these five complexes are all based on the [Ln(EDTA)]− unit, where carbonates participate due to coordination in μ1:η2(O,O) and μ2:η2(O,O′):η2(O,O′) fashion. The reactions of lanthanum ethylenediaminetetraacetate with CO2 have been monitored via13C NMR measurements. Furthermore, the calcined products of 1 and 2 are used for the oxidative coupling reaction of methane (OCM). The results demonstrate the good catalytic performances of La2O3 or La2O2CO3 from 1 and a mixture of La2O2CO3 and Na2CO3 from 2. The coordination modes of the lanthanide carbonates in precursors 1 and 2 may provide a model for the interaction of lanthanide carbonates, which is useful for the OCM reaction. [ABSTRACT FROM AUTHOR]

Monomeric oxidovanadium(IV) citrate and malate, [VO(H2cit)(Him‐py)] ⋅ H2O (1) and [VO(R,S‐Hmal)(Him‐py)] (2), and an additive of mixed‐valence oxidovanadium(IV/V) (1H‐imidazol‐2‐yl)pyridine [V2O2(μ2‐O)(glyc)(Him‐py)2(im‐py)] ⋅ [VO2(Him‐py)(im‐py)] ⋅ 9.5H2O (3) [Him‐py=2‐(1H‐imidazol‐2‐yl)pyridine, H4cit=citric acid, R,S‐H3mal=R,S‐malic acid, H2glyc=glycolic acid] have been isolated from the reactions of vanadyl sulfate with α‐hydroxycarboxylate (citrate, malate, and glycolate) and 2‐(1H‐imidazol‐2‐yl)pyridine in acidic solutions, respectively. The citrate or malate chelates to vanadium atom tridentately through α‐hydroxy, α‐carboxy and β‐carboxy groups that different with bidentate glycolate, while the other β‐carboxy acidic group of citrate in 1 remains uncoordinated and participates in strong hydrogen bonds with water molecules. Further substitution of 2‐(1H‐imidazol‐2‐yl)pyridine for citrate in 1 results in the formation of [VO2(Him‐py)(im‐py)]3 ⋅ 4.5H2O (4) in basic solution. With comparable chelation, 1 shares a similar V−Oα‐hydroxy distance [2.214(2) Å] with that observed in FeV‐cofactor [2.156av Å],[1] where a protonated model is suggested for the local chelated environment of FeV‐cofactor in citrate‐substituted V‐nitrogenase variant. Interestingly, 2D porous structure of additive 3 features two types of irregular microchannels with diameters of 16.6 and 6.4 Å, respectively, which can adsorb CO2 and O2 for 9.28 and 29.68 mg/g at 29.89 bar, respectively, while little or no adsorption for H2, N2, and CH4. [ABSTRACT FROM AUTHOR]