Bond-valence analyses of the crystal structures of FeMo/V cofactors in FeMo/V proteins

The bond-valence method has been used for valence calculations of FeMo/V cofactors in FeMo/V proteins using 51 crystallographic data sets of FeMo/V proteins from the Protein Data Bank. The calculations show molybdenum(III) to be present in MoFe7S9C(Cys)(HHis)[R-(H)homocit] (where H4homocit is homocitric acid, HCys is cysteine and HHis is histidine) in FeMo cofactors, while vanadium(III) with a more reduced iron complement is obtained for FeV cofactors. Using an error analysis of the calculated valences, it was found that in FeMo cofactors Fe1, Fe6 and Fe7 can be unambiguously assigned as iron(III), while Fe2, Fe3, Fe4 and Fe5 show different degrees of mixed valences for the individual Fe atoms. For the FeV cofactors in PDB entry 5n6y, Fe4, Fe5 and Fe6 correspond to iron(II), iron(II) and iron(III), respectively, while Fe1, Fe2, Fe3 and Fe7 exhibit strongly mixed valences. Special situations such as CO-bound and selenium-substituted FeMo cofactors and O(N)H-bridged FeV cofactors are also discussed and suggest rearrangement of the electron configuration on the substitution of the bridging S atoms.

Synthesis, detailed geometric analysis and bond-valence method evaluation of the strength of π-arene bonding of two isotypic cationic prehnitene tin(II) complexes: [{1,2,3,4-(CH3)4C6H2}2Sn2Cl2][MCl4]2 (M = Al and Ga)

From solutions of prehnitene and the ternary halides (SnCl)[MCl4] (M = Al, Ga) in chlorobenzene, the new cationic SnII–π-arene complexes catena-poly[[chloridoaluminate(III)]-tri-μ-chlorido-4′:1κ2 Cl,1:2κ4 Cl-[(η6-1,2,3,4-tetramethylbenzene)tin(II)]-di-μ-chlorido-2:3κ4 Cl-[(η6-1,2,3,4-tetramethylbenzene)tin(II)]-di-μ-chlorido-3:4κ4 Cl-[chloridoaluminate(III)]-μ-chlorido-4:1′κ2 Cl], [Al2Sn2Cl10(C10H14)2] n , (1) and catena-poly[[chloridogallate(III)]-tri-μ-chlorido-4′:1κ2 Cl,1:2κ4 Cl-[(η6-1,2,3,4-tetramethylbenzene)tin(II)]-di-μ-chlorido-2:3κ4 Cl-[(η6-1,2,3,4-tetramethylbenzene)tin(II)]-di-μ-chlorido-3:4κ4 Cl-[chloridogallate(III)]-μ-chlorido-4:1′κ2 Cl], [Ga2Sn2Cl10(C10H14)2] n , (2), were isolated. In these first main-group metal–prehnitene complexes, the distorted η6 arene π-bonding to the tin atoms of the Sn2Cl2 2+ moieties in the centre of [{1,2,3,4-(CH3)4C6H2}2Sn2Cl2][MCl4]2 repeating units (site symmetry \overline{1}) is characterized by: (i) a significant ring slippage of ca 0.4 Å indicated by the dispersion of Sn—C distances [1: 2.881 (2)–3.216 (2) Å; 2: 2.891 (3)–3.214 (3) Å]; (ii) the non-methyl-substituted arene C atoms positioned closest to the SnII central atom; (iii) a pronounced tilt of the plane of the arene ligand against the plane of the central (Sn2Cl2)2+ four-membered ring species [1: 15.59 (11)°, 2: 15.69 (9)°]; (iv) metal–arene bonding of medium strength as illustrated by application of the bond-valence method in an indirect manner, defining the π-arene bonding interaction of the SnII central atoms as s(SnII—arene) = 2 − Σs(SnII—Cl), that gives s(SnII—arene) = 0.37 and 0.38 valence units for the aluminate and the gallate, respectively, indicating that comparatively strong main-group metal–arene bonding is present and in line with the expectation that [AlCl4]− is the slightly weaker coordinating anion as compared to [GaCl4]−.

A new structure family of oxide-ion conductors Ca0.8Y2.4Sn0.8O6 discovered by a combined technique of the bond-valence method and experiments

Mg3TeO6-type Ca0.8Y2.4Sn0.8O6 was found as a new structure family of oxide-ion conductors by BVE calculations followed by experiments.