Coα‐(1H‐Imidazolyl)‐Coβ‐methylcob(III)amide: Model for Protein‐Bound Corrinoid Cofactors

Coα‐(1H‐Imidazol‐1‐yl)‐Coβ‐methylcob(III)amide ( 4 ) was synthesized by methylation with methyl iodide of (1H‐imidazol‐1‐yl)cob(I)amide, obtained by electrochemical reduction of Coα‐(1H‐imidazol‐1‐yl)‐Coβ‐cyanocob(III)amide ( 5 ). The spectroscopic data and a single‐crystal X‐ray structure analysis indicated 4 to exhibit a base‐on constitution in solution and in the crystal. The crucial lengths of the axial Co−N and Co−CH₃ bonds also emerged from the crystallographic data and were found to be smaller by 0.1 and 0.02 Å, respectively, than those in methylcob(III)alamin ( 2 ). The data of 4 support the view, that the `long' axial Co−N bonds as determined by X‐ray crystallography for the B<sub>12</sub>‐dependent methionine synthase, for methylmalonyl‐CoA mutase, and for glutamate mutase represent stretched Co−N bonds. The thermodynamic effect (the `trans influence') of the 1H‐imidazole base in 4 on the organometallic reactivity of this model for protein‐bound organometallic B₁₂ cofactors was examined by studying Me‐group‐transfer equilibria in aqueous solution and using (5′,6′‐dimethyl‐1H‐benzimidazol‐1‐yl)cobamides (cobalamins) as reaction partners (Schemes 2 – 5, Table). In comparison with methylcob(III)alamin ( 2 ), 4 was found to be destabilized for an abstraction of the Co‐bound Me group by a Co^III electrophile. In contrast, the abstraction of the Co‐bound Me group by a radical(oid) Co^II species was not significantly influenced thermodynamically by the exchange of the nucleotide base. Likewise, exploratory Me‐group‐transfer experiments with Me−Co^III and nucleophilic Co^I corrinoids at pH 6.8 provided an apparent equilibrium constant near unity. However, this finding also was consistent with partial protonation of the imidazolylcob(I)amide at pH 6.8, suggesting an interesting pH dependence of the Megroup‐transfer equilibrium near neutral pH. Therefore, the replacement of the 5′,6′‐dimethyl‐1H‐benzimidazole base by an 1H‐imidazole moiety, as observed in methyl transferases and in C‐skeleton mutases, does not by itself strongly alter the inherent reactivity of the B₁₂ cofactors in the crucial homolytic and nucleophilic‐heterolytic reactions involving the organometallic bond, but may help to enhance the control of the organometallic reactivity by protonation/deprotonation of the axial base.     

Homocoenzyme B12 and Bishomocoenzyme B12: Covalent Structural Mimics for Homolyzed,Enzyme‐Bound Coenzyme B12

Efficient electrochemical syntheses of “homocoenzyme B₁₂” ( 2 , Co_β‐(5′‐deoxy‐5′‐adenosyl‐methyl)‐cob(III )alamin) and “bishomocoenzyme B₁₂” ( 3 , Co_β‐[2‐(5′‐deoxy‐5′‐adenosyl)‐ethyl]‐cob(III )alamin) are reported here. These syntheses have provided crystalline samples of 2 and 3 in 94 and 77 % yield, respectively. In addition, in‐depth investigations of the structures of 2 and 3 in solution were carried out and a high‐resolution crystal structure of 2 was obtained. The two homologues of coenzyme B₁₂ ( 2 and 3 ) are suggested to function as covalent structural mimics of the hypothetical enzyme‐bound “activated” (that is, “stretched” or even homolytically cleaved) states of the B₁₂ cofactor. From crude molecular models, the crucial distances from the corrin‐bound cobalt center to the C5′ atom of the (homo)adenosine moieties in 2 and 3 were estimated to be about 3.0 and 4.4 Å, respectively. These values are roughly the same as those found in the two “activated” forms of coenzyme B₁₂ in the crystal structure of glutamate mutase. Indeed, in the crystal structure of 2 , the cobalt center was observed to be at a distance of 2.99 Å from the C5′ atom of the homoadenosine moiety and the latter was found to be present in the unusual syn conformation. In solution, the organometallic moieties of 2 and 3 were shown to be rather flexible and to be considerably more dynamic than the equivalent group in coenzyme B₁₂. The homoadenosine moiety of 2 was indicated to occur in both the syn and the anti conformations.     

The Cofactor of Tetrachloroethene Reductive Dehalogenase of Dehalospirillum multivorans Is Norpseudo‐B12, a New Type of a Natural Corrinoid

The corrinoid cofactor of the tetrachloroethene reductive dehalogenase of Dehalospirillum multivorans was isolated in its Coβ‐cyano form. This cofactor represents the main corrinoid found in D. multivorans cells. Analysis of the isolated cyano‐corrinoid by a combination of HPLC and UV/VIS‐absorbance spectroscopy revealed it to be nonidentical to a variety of known natural B₁₂ derivatives. From high‐resolution mass‐spectrometric analysis, the molecular formula of the corrinoid isolated from D. multivorans could be deduced as C₅₈H₈₁CoN₁₇O₁₄P. The sample of the novel corrinoid from D. multivorans was further analyzed by UV/VIS, CD, and one‐ and two‐dimensional ¹H‐, ¹³C‐, and ¹⁵N‐NMR spectroscopy, which indicated its structure to be closely related to that of pseudovitamin B₁₂ (Coβ‐cyano‐7″‐adeninylcobamide). By the same means, the corrinoid could be shown to differ from pseudovitamin B₁₂ only by the lack of the methyl group attached to carbon 176, and, therefore, it was named norpseudovitamin B₁₂ (or, more precisely, 176‐norpseudovitamin B₁₂). Norpseudovitamin B₁₂ represents the first example of a ‘complete’ B₁₂‐cofactor that lacks one of the methyl groups of the cobamide moiety, indicating that the B₁₂‐biosynthetic pathway in D. multivorans differs from that of other organisms. X‐Ray crystal‐structures were determined for norpseudovitamin B₁₂ from D. multivorans and the analogues pseudovitamin B₁₂ and factor A (Coβ‐cyano‐7″‐[2‐methyl]adeninylcobamide). These first accurate crystal structures of complete corrinoids with an adeninyl pseudonucleotide confirmed the expected coordination properties around Co and corroborated the close conformational similarity of the nucleotide moieties of norpseudovitamin B₁₂ and its two homologues.     

[1,1,2,2‐(CO)4‐1,2‐μ‐(CO)‐4,11‐(SMe2)2‐closo‐1,2‐Co2B10H8]

The title compound, 1,1,2,2‐tetra­carbonyl‐1,2‐μ‐carbonyl‐4,11‐di­methyl­sulfido‐closo‐1,2‐dicobaltadodecaborane, [Co₂(C₄H₂₀B₁₀S₂)(CO)₅], has a closo 12‐vertex {1,2‐Co₂B₁₀H₈} structure with SMe₂ ligands at the exo‐4‐ and 11‐positions. The cluster displays close structural similarities to the SEt₂ analogue.     

White Light Emissive DyIII Single‐Molecule Magnets Sensitized by Diamagnetic [CoIII(CN)6]3− Linkers

The self‐assembly of Dy^III–3‐hydroxypyridine (3‐OHpy) complexes with hexacyanidocobaltate(III) anions in water produces cyanido‐bridged {[Dy^III(3‐OHpy)₂(H₂O)₄] [Co^III(CN)₆]}?H₂O ( 1 ) chains. They reveal a single‐molecule magnet (SMM) behavior with a large zero direct current (dc) field energy barrier, ΔE=266(12) cm^?1 (≈385 K), originating from the single‐ion property of eight‐coordinated Dy^III of an elongated dodecahedral geometry, which are embedded with diamagnetic [Co^III(CN)₆]^3? ions into zig‐zag coordination chains. The SMM character is enhanced by the external dc magnetic field, which results in the ΔE of 320(23) cm^?1 (≈460 K) at H_dc=1 kOe, and the opening of a butterfly hysteresis loop below 6 K. Complex 1 exhibits white Dy^III‐based emission realized by energy transfer from Co^III and 3‐OHpy to Dy^III. Low temperature emission spectra were correlated with SMM property giving the estimation of the zero field ΔE. 1 is a unique example of bifunctional magneto‐luminescent material combining white emission and slow magnetic relaxation with a large energy barrier, both controlled by rich structural and electronic interplay between Dy^III, 3‐OHpy, and [Co^III(CN)₆]^3?.     

Dodekahydro‐closo‐dodekaborate der schweren Erdalkalimetalle aus wäßriger Lösung: Ca(H2O)7[B12H12] · H2O,Sr(H2O)8[B12H12] und Ba(H2O)6[B12H12]

Dodecahydro‐ closo ‐dodecaborates of the Heavy Alkaline‐Earth Metals from Aqueous Solution: Ca(H₂O)₇[B₁₂H₁₂] · H₂O, Sr(H₂O)₈[B₁₂H₁₂], and Ba(H₂O)₆[B₁₂H₁₂] The crystalline hydrates of the heavy alkaline earth metal dodecahydro‐closo‐dodecaborates (M[B₁₂H₁₂] · n H₂O, n = 6–8; M = Ca, Sr, Ba) are easily accessible by reaction of an aqueous (H₃O)₂[B₁₂H₁₂] solution with an alkaline earth metal carbonate (MCO₃). By isothermic evaporation of the respective aqueous solution we obtained colourless single crystals which are characterized by X‐ray diffraction at room temperature. The three compounds Ca(H₂O)₇[B₁₂H₁₂] · H₂O (orthorhombic, P2₁2₁2₁; a = 1161.19(7), b = 1229.63(8), c = 1232.24(8) pm; Z = 4), Sr(H₂O)₈[B₁₂H₁₂] (trigonal, R3; a = 1012.71(6), c = 1462.94(9) pm; Z = 3) and Ba(H₂O)₆[B₁₂H₁₂] (orthorhombic, Cmcm; a = 1189.26(7) pm, b = 919.23(5) pm, c = 1403.54(9) pm; Z = 4) are neither formula‐equal nor isostructural. The structure of Sr(H₂O)₈[B₁₂H₁₂] is best described as a NaCl‐type arrangement, Ba(H₂O)₆[B₁₂H₁₂] rather forms a layer‐like and Ca(H₂O)₇[B₁₂H₁₂] · H₂O a channel‐like structure. In first sphere the alkaline earth metal cations Ca²⁺ and Sr²⁺ are coordinated by just seven and eight oxygen atoms from the surrounding water molecules, respectively. A direct coordinative influence of the quasi‐icosahedral [B₁₂H₁₂]^2– cluster anions becomes noticeable only for the Ba²⁺ cations (CN = 12) in Ba(H₂O)₆[B₁₂H₁₂]. The dehydratation of the alkaline earth metal dodecahydro‐closo‐dodecaborate hydrates has been shown to take place in several steps. Thermal treatment leads to the anhydrous compounds Ca[B₁₂H₁₂], Sr[B₁₂H₁₂] and Ba[B₁₂H₁₂] at 224, 164 and 116 °C, respectively.     

Cyano‐bridged extended heteronuclear supramolecular architectures with hexacyano­cobalt(III) as building blocks

The cyano‐bridged heteronuclear coordination polymer poly[tris[(5,12‐dimethyl‐7,14‐diphenyl‐1,4,8,11‐tetraazacyclo­tetra­deca‐4,11‐diene)copper(II)]‐hexa‐μ‐cyano‐bis[tricyano­cobalt(III)] di­methyl­formamide solvate trihydrate], {[Cu₃Co₂(CN)₁₂(C₂₄H₃₂N₄)₃]·C₃H₇NO·3H₂O}_n, was synthesized by the assembly reaction of [CuL]²⁺ (L is 5,12‐dimethyl‐7,14‐di­phenyl‐1,4,8,11‐tetraazacyclotetradeca‐4,11‐diene) and [Co(CN)₆]³⁻ in a dimethyl­formamide–water solution. The structure consists of neutral cyano‐bridged Cu₃Co₂ units with the unique Co atom in a general position and all three Cu atoms on independent inversion centres. Each [Co(CN)₆]³⁻ ion connects three Cu^II ions via three cyano groups to form a novel cyano‐bridged two‐dimensional stair‐shaped‐layer structure. The water and dimethyl­formamide molecules are situated in the inter‐fragment spaces.     

Synthesis,Characterization, and Crystal Structures of [N(CH3)4]2[B12H12] and [N(CH3)4]2[B12H12] · CH3CN

Bis(tetramethylammonium) dodecahydrododecaborate, [(CH₃)₄N]₂[B₁₂H₁₂], and bis(tetramethylammonium) dodecahydrododecaborate acetonitrile, [(CH₃)₄N]₂[B₁₂H₁₂] · CH₃CN, were synthesized and characterized via Infrared, ¹H and ¹¹B NMR spectroscopy. [(CH₃)₄N]₂[B₁₂H₁₂] crystallizes isopunctual to the alkali metal dodecaborates. The crystal structure of [(CH₃)₄N]₂[B₁₂H₁₂] · CH₃CN was determined from single crystal data and refined in the orthorhombic crystal system (Pcmn, no. 62, a = 898.68(8), b = 1312.85(9) c = 1994.5(1) pm, R(|F| , 4σ) = 5.9%, wR(F²) = 18.3%). Here, the geometry of the dodecaborate anion is that of an almost ideal icosahedron, less distorted than most other dodecaborates known. By low‐temperature Guinier‐Simon diffractometry phase transitions were detected for [(CH₃)₄N]₂[B₁₂H₁₂] and [(CH₃)₄N]₂[B₁₂H₁₂] · CH₃CN at –70 and –15 °C, respectively.     

Die Struktur der Hydrate von Co3[Co(CN)6]2 und Cd3[Co(CN)6]2

The crystal structures of Co₃[Co(CN)₆]₂, 12 H₂O (a, = 10.210 ± 0.005 Å) and Cd₃[Co(CN)₆]₂, 12 H₂O (a = 10.590 ± 0.005 Å) have been determined by X-ray powder methods. According to the measured density the unit cell contains 1 1/3 formula units with 4 Co²⁺ (Cd²⁺) in 4a, 2 2/3 Co³⁺ in 4b, 16 C and 16 N in 24e, 8 H₂O_I near 24e, (96k) and 8 H₂O_II near 8 _c (192 l). Structure factor calculations based on the space group O_h⁵ - F m 3 m lead to the following final values of the reliability index R: 0.038 (Co₃[Co(CN)₆]₂, 12 H₂O) and 0.037 (Cd₃[Co(CN)₆]₂, 12 H₂O). The interatomic distances for the cobaltous compound (in parentheses for the cadmium compound) are: Co³⁺-C: 1.88 Å (1.89); C-N: 1.15 Å (1.17); Co²⁺-N: 2.08 Å (2.24); Co²⁺-O_I: 2.10 Å (2.27); shortest O_I-H-O_II-bonds: 2.89 Å (2.82). Co³⁺ is octahedrally coordinated by six carbon atoms, the divalent metal ion by four nitrogen atoms and two water molecules. The two different metal ions are connected by M²⁺-N-C-Co³-bonds to a threedimensional network. The infrared and electronic spectra are shown to be in agreement with the results of the structure analyses of these compounds. The observed positions of the OH-stretching vibrations lead to a hydrogenbond-length of 2.8–2.95 Å.     

ChemInform Abstract: Stability of B12(CN)122‐: Implications for Lithium and Magnesium Ion Batteries.

DFT calculations are used to calculate the binding energies of the second electron of the closo‐borane B₁₂H₁₂^2‐ and B₁₂(CN)₁₂^2‐.     

Zu den Kristallstrukturen der Übergangsmetall(II)‐Dodekahydro‐closo‐Dodekaborat‐Hydrate Cu(H2O)5,5[B12H12]·2,5 H2O und Zn(H2O)6[B12H12]·6 H2O

On the Crystal Structures of the Transition‐Metal(II) Dodecahydro‐closo‐Dodecaborate Hydrates Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O and Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O By neutralization of an aqueous solution of the free acid (H₃O)₂[B₁₂H₁₂] with basic copper(II) carbonate or zinc carbonate, blue lath‐shaped single crystals of the octahydrate Cu[B₁₂H₁₂]·8 H₂O (≡ Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O) and colourless face‐rich single crystals of the dodecahydrate Zn[B₁₂H₁₂]·12 H₂O (≡ Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O) could be isolated after isothermic evaporation. Copper(II) dodecahydro‐closo‐dodecaborate octahydrate crystallizes at room temperature in the monoclinic system with the non‐centrosymmetric space group Pm (Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O: a = 768.23(5), b = 1434.48(9), c = 777.31(5) pm, β = 90.894(6)°; Z = 2), whereas zinc dodecahydro‐closo‐dodecaborate dodecahydrate crystallizes cubic in the likewise non‐centrosymmetric space group F23 (Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O: a = 1637.43(9) pm; Z = 8). The crystal structure of Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O can be described as a monoclinic distortion variant of the CsCl‐type arrangement. As characteristic feature the formation of isolated [Cu₂(H₂O)₁₁]⁴⁺ units as a condensate of two corner‐linked Jahn‐Teller distorted [Cu(H₂O)₆]²⁺ octahedra via an oxygen atom of crystal water can be considered. Since “zeolitic” water of hydratation is also present, obviously both classical H–O^δ?···^+δH–O and non‐classical B–H^δ?···^+δH–O hydrogen bonds play a significant role for the stabilization of the structure. A direct coordinative influence of the quasi‐icosahedral [B₁₂H₁₂]^2? anions on the Cu²⁺ cations has not been determined. The zinc compound Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O crystallizes in a NaTl‐type related structure. Two crystallographically different [Zn(H₂O)₆]²⁺ octahedra are present, which only differ in their relative orientation within the packing of the [B₁₂H₁₂]^2? anions. The stabilization of the crystal structure takes place mainly via H–O^δ?···^+δH–O hydrogen bonds, since again the hydrogen atoms of the [B₁₂H₁₂]^2? anions have no direct coordinative influence on the Zn²⁺ cations.     

Measurement of the Binding of Adenosylcobalamin to Glutamate Mutase by Fluorescence Spectroscopy

Fluorescence spectroscopy is a fast, highly sensitive technique for investigating protein‐ligand interactions. Intrinsic protein fluorescence is usually occurred by exciting the proteins with 280‐295 nm ultraviolet light, and the light emission is observed approximately between 330‐350 nm. No emission light between 330‐350 nm can be observed when adenosylcobalamin (AdoCbl) is excited at 282 nm. The binding of AdoCbl to glutamate mutase was therefore investigated by fluorescence spectroscopy in this study. Our results show that direct measurement for determining the K_d of AdoCbl by fluorescence spectroscopy leads to significant errors. Here we report the source of error and a corrected method for measuring the binding of coenzyme B₁₂ to glutamate mutase using fluorescence spectroscopy.     

Substituent‐Stabilized Organic Dianions in the Gas Phase and Their Potential Use as Electrolytes in Lithium‐Ion Batteries

Using density functional theory and a hybrid exchange‐correlation functional, a systematic study of the stability and electronic structure of neutral and multiply charged organic molecules, B_nC_6?nX₆ (n=0, 1, 2; X=H, F, CN) and B_nC_5?nX₅ (n=0, 1; X=H, F, CN) is performed. The results show that in addition to the aromaticity of the molecules, substituents play an important role in stabilizing the organic dianion complexes. In particular, it is demonstrated that CN groups are responsible for the stability of organic dianions as it has recently been found to be the case in B‐cage compounds such as B₁₂(CN)₁₂^2? and CB₁₁(CN)₁₂^2?. It is also shown that the stable organic dianions B₂C₄(CN)₆^2? and BC₄(CN)₅^2? might be halogen‐free electrolytes in Li‐ion batteries.     

Partial Synthesis of CoαCoβ-Dicyano-176-Norcobinamide

Summary. Recent interest in norvitamin B₁₂-derivatives, homologues of complete vitamin B₁₂-derivatives, lacking the methyl group at carbon 176, stems from the identification of the corrinoid cofactor of the tetrachloroethene reductive dehalogenase of Sulfurospirillum multivorans as 176-nor-pseudovitamin B₁₂. Here we report the partial synthesis of the corrinoid Co_αCo_β-dicyano-176-norcobinamide by condensation of cobyric acid and 2-aminoethanol. In addition, the partial synthesis of crystalline Co_α-aquo-Co_β-cyanocobyric acid by acid catalyzed hydrolysis of vitamin B₁₂ is detailed, improving the method and the isolation procedure worked out earlier by Bernhauer et al. The solution structure of Co_αCo_β-dicyano-176-norcobinamide was studied by spectroscopy and was compared with that of the homologue Co_αCo_β-dicyanocobinamide. The title compound, Co_αCo_β-dicyano-176-norcobinamide, represents the dicyano-form of a potential biosynthetic precursor of the 176-nor-B₁₂-derivatives, such as 176-nor-pseudovitamin B₁₂.     

Partial Synthesis of CoαCoβ-Dicyano-176-Norcobinamide

Recent interest in norvitamin B₁₂-derivatives, homologues of complete vitamin B₁₂-derivatives, lacking the methyl group at carbon 176, stems from the identification of the corrinoid cofactor of the tetrachloroethene reductive dehalogenase of Sulfurospirillum multivorans as 176-nor-pseudovitamin B₁₂. Here we report the partial synthesis of the corrinoid Co_αCo_β-dicyano-176-norcobinamide by condensation of cobyric acid and 2-aminoethanol. In addition, the partial synthesis of crystalline Co_α-aquo-Co_β-cyanocobyric acid by acid catalyzed hydrolysis of vitamin B₁₂ is detailed, improving the method and the isolation procedure worked out earlier by Bernhauer et al. The solution structure of Co_αCo_β-dicyano-176-norcobinamide was studied by spectroscopy and was compared with that of the homologue Co_αCo_β-dicyanocobinamide. The title compound, Co_αCo_β-dicyano-176-norcobinamide, represents the dicyano-form of a potential biosynthetic precursor of the 176-nor-B₁₂-derivatives, such as 176-nor-pseudovitamin B₁₂.     

TiO2‐assisted Photocatalytic Degradation of Vitamin B12 in Aqueous Solution:Influencing Factors,Kinetics, and Reaction Investigations

The photodegradation (λ=365 nm) of the biomolecule vitamin B₁₂, catalyzed by the photocatalyst TiO₂ nanoparticles (NPs), has been investigated in aqueous suspension. The photodegradation process of vitamin B₁₂ has been monitored by means of electronic absorption (Abs), Fourier‐transform infrared (FT‐IR), and resonance Raman (RR) spectroscopies, respectively. The results show that only under UV illumination in the presence of TiO₂ is there effective degradation, and the photocatalytic degradation of vitamin B₁₂ is strongly influenced by the amount of TiO₂ NPs, the pH, and the initial concentration of vitamin B₁₂. The photocatalytic reaction kinetics of vitamin B₁₂ conforms to a Langmuir‐Hinshelwood isotherm model. Changes involving the three structural units of the carbon‐metal bond C–Co, the organic corrin macrocycle combined with the benzimidazole nucleotide, and the inorganic CN in the vitamin B₁₂ molecule during the photocatalytic degradation are also discussed.     

Stability of B12(CN)122−: Implications for Lithium and Magnesium Ion Batteries

Multiply charged negative ions are seldom stable in the gas phase. Electrostatic repulsion leads either to autodetachment of electrons or fragmentation of the parent ion. With a binding energy of the second electron at 0.9 eV, B₁₂H₁₂^2? is a classic example of a stable dianion. It is shown here that ligand substitution can lead to unusually stable multiply charged anions. For example, dodecacyanododecaborate, B₁₂(CN)₁₂^2?, created by substituting H by CN is found to be highly stable with the second electron bound by 5.3 eV, which is six times larger than that in the B₁₂H₁₂^2?. Equally important is the observation that CB₁₁(CN)₁₂^2?, which contains one electron more than needed to satisfy the Wade‐Mingos rule, is also stable with its second electron bound by 1.1 eV, while CB₁₁H₁₂^2? is unstable. The ability to stabilize multiply charged anions in the gas phase by ligand manipulation opens a new door for multiply charged species with potential applications as halogen‐free electrolytes in ion batteries.     

Synthese,Kristallstruktur und thermischer Abbau von Mg(H2O)6[B12H12] · 6 H2O

Synthesis, Crystal Structure, and Thermal Decomposition of Mg(H₂O)₆[B₁₂H₁₂] · 6 H₂O By reaction of an aqueous solution of the free acid (H₃O)₂[B₁₂H₁₂] with MgCO₃ and subsequent isothermic evaporation of the resulting solution to dryness, colourless, bead‐shaped single crystals of the dodecahydrate of magnesium dodecahydro closo‐dodecaborate Mg(H₂O)₆[B₁₂H₁₂] · 6 H₂O (cubic, F4₁32; a = 1643.21(9) pm, Z = 8) emerge. The crystal structure is best described as a NaTl‐type arrangement in which the centers of gravity of the quasi‐icosahedral [B₁₂H₁₂]^2— anions (d(B—B) = 178—180 pm, d(B—H) = 109 pm) occupy the positions of Tl^— while the Mg²⁺ cations occupy the Na⁺ positions. A direct coordinative influence of the [B₁₂H₁₂]^2— units at the Mg²⁺ cations is however not noticeable. The latter are octahedrally coordinated by six water molecules forming isolated hexaaqua complex cations [Mg(H₂O)₆]²⁺ (d(Mg—O) = 206 pm, 6×). In addition, six “zeolitic” water molecules are located in the crystal structure for the formation of a strong O—H^δ+···^δ—O‐hydrogen bridge‐bonding system. The evidence of weak B—H^δ—···^δ+H—O‐hydrogen bonds between water molecules and anionic [B₁₂H₁₂]^2— clusters is also considered. Investigations on the dodecahydrate Mg[B₁₂H₁₂] · 12 H₂O (≡ Mg(H₂O)₆[B₁₂H₁₂] · 6 H₂O) by DTA/TG measurements showed that its dehydration takes place in two steps within a temperature range of 71 and 76 °C as well as at 202 °C, respectively. Thermal treatment eventually leads to the anhydrous magnesium dodecahydro closo‐dodecaborate Mg[B₁₂H₁₂].     

Formation and Structure of an Anionic Ruthenaborane Compound:[Et4N][(PPh3)2ClRuB12H12]

在研究RuCl2(PPh3)3 和 closo-B10H102- 在乙醇中的反应时,意外分离得到一个阴离子型的钌硼烷化合物[Et4N][(PPh3)2ClRuB12H12], 并且经过红外光谱和单晶X射线衍射分析确证. 在其结构中,闭式B12H122-配体与Ru(II)中心通过三个B-H-Ru三中心-二电子键结合. 分析原因应是在通过文献方法制备闭式B10H102-时的少量副产物闭式B12H122-在反应体系中与RuCl2(PPh3)3反应而生成了标题化合物. 根据硼烷簇合物的电子计数规则, 标题化合物也可以看成是含有2n (n为簇顶点数)个骨架电子的pileo型簇合物, 具有加帽(capped)的闭式多面体骨架构型. 这是第一个阴离子型的含有闭式B12H122- 的钌化合物.     

A Robust One‐Compartment Fuel Cell with a Polynuclear Cyanide Complex as a Cathode for Utilizing H2O2 as a Sustainable Fuel at Ambient Conditions

A robust one‐compartment H₂O₂ fuel cell, which operates without membranes at room temperature, has been constructed by using a series of polynuclear cyanide complexes that contain Fe, Co, Mn, and Cr as cathodes, in sharp contrast to conventional H₂ and MeOH fuel cells, which require membranes and high temperatures. A high open‐circuit potential of 0.68 V was achieved by using Fe₃[{Co^III(CN)₆}₂] on a carbon cloth as the cathode and a Ni mesh as the anode of a H₂O₂ fuel cell by using an aqueous solution of H₂O₂ (0.30 M , pH 3) with a maximum power density of 0.45 mW cm^?2. The open‐circuit potential and maximum power density of the H₂O₂ fuel cell were further increased to 0.78 V and 1.2 mW cm^?2, respectively, by operation under these conditions at pH 1. No catalytic activity of Co₃[{Co^III(CN)₆}₂] and Co₃[{Fe^III(CN)₆}₂] towards H₂O₂ reduction suggests that the N‐bound Fe ions are active species for H₂O₂ reduction. H₂O₂ fuel cells that used Fe₃[{Mn^III(CN)₆}₂] and Fe₃[{Cr^III(CN)₆}₂] as the cathode exhibited lower performance compared with that using Fe₃[{Co^III(CN)₆}₂] as a cathode, because ligand isomerization of Fe₃[{M^III(CN)₆}₂] into (FeM₂)[{Fe^II(CN)₆}₂] (M=Cr or Mn) occurred to form inactive Fe? C bonds under ambient conditions, whereas no ligand isomerization of Fe₃[{Co^III(CN)₆}₂] occurred under the same reaction conditions. The importance of stable Fe²⁺? N bonds was further indicated by the high performance of the H₂O₂ fuel cells with Fe₃[{Ir^III(CN)₆}₂] and Fe₃[{Rh^III(CN)₆}₂], which also contained stable Fe²⁺? N bonds. The stable Fe²⁺? N bonds in Fe₃[{Co^III(CN)₆}₂], which lead to high activity for the electrocatalytic reduction of H₂O₂, allow Fe₃[{Co^III(CN)₆}₂] to act as a superior cathode in one‐compartment H₂O₂ fuel cells.