Nitridorhenium(V) Complexes with 1,3‐Dialkyl‐4,5‐dimethylimidazole‐2‐ylidenes

The nitridorhenium(V) complexes [ReNCl₂(PR₂Ph)₃] (R = Me, Et) react with the N‐heterocyclic carbenes (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐5‐ylidene (L^Et) or 1,3,4,5‐tetramethylimidazole‐2‐ylidene (L^Me) in absolutely dry THF under complete replacement of the equatorial coordination sphere. The resulting [ReNCl(L^R)₄]⁺ complexes (L^R = L^Me, L^Et) are moderately stable as solids and in solution, but decompose in hot methanol under formation of [ReO₂(L^R)₄]⁺ complexes. With 1,3‐diisopropyl‐4,5‐dimethylimidazole‐5‐ylidene (L^i‐Pr), the loss of the nitrido ligand and the formation of a dioxo species is more rapid and no nitridorhenium intermediate could be isolated. The Re‐C bond lengths in [ReNCl(L^Et)₄]Cl of approximately 2.195Å are relatively long and indicate mainly σ‐bonding in the electron‐deficient d² system under study. The hydrolysis of the nitrido complexes proceeds via the formation of [ReO₃N]^2? anions as could be verified by the isolation and structural characterization of the intermediates [{ReN(PMe₂Ph)₃}{ReO₃N}]₂ and [{ReN(OH₂)(L^Et)₂}₂O][ReO₃N].     

Coordination compounds based on the cluster anion [Re4Te4(CN)12]4− and Zn2+ cation

Three new coordination compounds [{Zn(H₂O)₂} {Zn(H₂O)₄} Re₄Te₄(CN)₁₂] (1), [Zn(en)₂(NH₃)₂][{Zn(en)(NH₃)₂} Re₄Te₄(CN)₁₂]·H₂O (2), and [{Zn₂(dien)₃} Re₄Te₄(CN)₁₂]· ·₆H₂O (3) (dien is diethylenetriamine) were prepared by reactions of aqueous solutions of the tetrahedral cluster rhenium tellurocyanide complex K₄[Re₄Te₄(CN)₁₂]· 5H₂O with zinc dichloride in the presence of ammonia, ethylenediamine, and diethylenetriamine, respectively. Complex 1 has a three-dimensional structure with two types of the Zn atoms; complex 2 is ionic with the polymeric chain anion; complex 3 has a molecular structure. The structures of complexes 1–3 were determined by single-crystal X-ray diffraction analysis. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 718–721, April, 2006.     

Terahertz time-domain and Raman spectroscopy of the sulfur-containing peptide dimers: Low-frequency markers of disulfide bridges

The terahertz time-domain and Raman spectra of sulfur-containing cystein-based peptides in the region of the low-frequency infrared vibrations have been measured at room temperature. The low-frequency bands that can be assigned to the S–S bridges are observed. The vibrational modes found in molecular crystalline materials should be described as phonon modes with strong coupling to the intra molecular vibrations.     

New Type of Neutral Binuclear Spin-Crossover Complex of Iron(III) with Twist of Two Disulfide Bridges as a Product of Electrochemical Oxidation of [FeIII(5Cl-thsa)2]− Anions

As a result of the electrochemical oxidation process, the [Fe^III(5Cl-thsa)₂]⁻ spin-crossover (SCO) anion with N₂S₂O₂ coordination sphere transforms into N₄O₂-coordinated Fe^III SCO neutral binuclear complex 2 with twist of two disulfide bridges. Each dimeric complex is a binuclear double-stranded helicate with similar chirality of both Fe centers. The crystal structure of the complex 2 ⋅ 3H₂O at 100 K has a monoclinic C2/c space group and contains large cavities (about 21.5 % of the unit cell volume) half-filled by 3 water molecules per one dimer. The N₄O₂ coordination of iron(III) with two oxygen atoms (−O⁻) of phenoxy groups, two imine-type (−N_im=) nitrogen atoms of azomethine groups, one amidrazone-type (=N_amidH) nitrogen atom and one ionized terminal group (−N_ionizH) of nitrogen has not been observed in CCDC so far. The oxidation state of the iron atoms in the dimeric complex was confirmed by ⁵⁷Fe Mössbauer spectroscopy on 90 % enriched ⁵⁷Fe sample. Mössbauer spectra and dc magnetic measurements demonstrated the partial HS-HS→LS-LS SCO in the 185–225 K temperature range. The details of the structure of complex 2 and the features of its magnetic properties were refined by theoretical analysis based on DFT calculations. The B3LYP* functional correctly predicting the energy of the spin-crossover process was revealed.     

大跨悬索桥三维非平稳耦合抖振分析

基于Priestley(1967)演变功率谱模型，并采用Lin和Yang(1983)的建议，建立了脉动风速的非平稳功率谱模型。依据此模型，采用三维有限元法，建立了大跨桥梁非平稳耦合抖振运动方程。然后，将虚拟激励法和精细时程积分法相结合，建立了求解桥梁三维非平稳耦合抖振运动方程的快速算法。以某大跨悬索桥为例，分析了该桥的非平稳耦合抖振响应，并与平稳耦合抖振响应进行了比较。计算结果表明：随着脉动风速平稳部分持时的增大，非平稳抖振分析结果逐渐收敛于平稳抖振分析结果；但若脉动风速的平稳部分持时较短，非平稳抖振分析结果将低于平稳抖振分析结果。     

Two Pseudopolymorphic Star‐Shaped Tetranuclear Co3+ Compounds with Disulfide Anions Exhibiting Two Different Connection Modes and Promising Photocatalytic Properties

The compound [Co₄(C₆H₁₄N₂)₄(μ₄‐S₂)₂(μ₂‐S₂)₄] ( I ) and the pseudo‐polymorph [Co₄(C₆H₁₄N₂)₄(μ₄‐S₂)₂(μ₂‐S₂)₄] ? 4 H₂O ( II ) were obtained under solvothermal conditions (C₆H₁₄N₂=trans‐1,2‐diaminocyclohexane). The structures feature S₂^2? ions exhibiting two different coordination modes. Terminal S₂^2? entities join two Co³⁺ centres in a μ₂ fashion, whereas the central S₂^2? groups connect four Co³⁺ cations in a μ₄‐ coordination mode. Compound II can be transformed into compound I by heat and storage over P₂O₅ and storing compound I in humid air yields in the formation of compound II . The intermolecular interactions investigated through Hirshfeld surface analysis reveal that besides S???H bonding close contacts are associated with relatively weak H???H interactions. A detailed DFT analysis of the bonding situation explains the long S?S bonds in the μ₄‐bridging S₂^2? units and the short bonds for the S₂^2? moieties in the μ₂‐connecting mode. Photocatalytic hydrogen evolution experiments demonstrate the potential of compound II as catalyst.     

Secondary Binding Interactions in a Synthetic Receptor for Trimethyllysine

We have systematically studied how secondary interactions with neighboring lysine (Lys) and arginine (Arg) residues influence the binding and selectivity of the synthetic receptor A₂N for trimethyllysine (Kme₃). Multiple secondary binding sites on A₂N are formed by carboxylates rigidly positioned over aromatic rings, a motif that has been shown to stabilize salt bridges. We varied the spacing between Kme_X (X=0, 3) and an ancillary Lys or Arg and measured binding by isothermal titration calorimetry (ITC). These studies revealed that both neighboring residues improve the binding of A₂N to Kme_X by approximately 1 kcal mol^?1, with little influence of the spacing. Nonetheless, the improvement in affinity caused by Arg is enthalpically driven, while for Lys it is entropically driven, suggesting different mechanisms by which the residues interact with the secondary binding site.     

Rational Design of Heterodimeric Protein using Domain Swapping for Myoglobin

Protein design is a useful method to create novel artificial proteins. A rational approach to design a heterodimeric protein using domain swapping for horse myoglobin (Mb) was developed. As confirmed by X‐ray crystallographic analysis, a heterodimeric Mb with two different active sites was produced efficiently from two surface mutants of Mb, in which the charges of two amino acids involved in the dimer salt bridges were reversed in each mutant individually, with the active site of one mutant modified. This study shows that the method of constructing heterodimeric Mb with domain swapping is useful for designing artificial multiheme proteins.     

The Lewis basicity of nitrido complexes. Theoretical investigation of the structure and bonding of Cl2 (PH3)3ReN–X (X = BH3, BCl3, BBr3, AlH3, AlCl3, AlBr3, GaH3, GaCl3, GaBr3, O, S, Se, Te)

Quantum chemical calculations using gradient-corrected density functional theory (B3LYP) and ab initio methods at the MP2 level are reported for the geometries and bond energies of the nitrido complexes Cl₂ (PH₃)₃ReN–X (X = BH₃, BCl₃, BBr₃, AlH₃, AlCl₃, AlBr₃, GaH₃, GaCl₃, GaBr₃, O, S, Se, Te). The theoretical geometries are in excellent agreement with experimental values of related complexes which have larger phosphine ligands. The parent nitrido complex Cl₂(PH₃)₃ReN is a very strong Lewis base. The calculated bond dissociation energy of Cl₂(PH₃)₃ReN–AlCl₃ is D _e = 43.7 kcal/mol, which is nearly as high as the bond energy of Me₃N–AlCl₃. The donor-acceptor bonds of the other Cl₂(PH₃)₃ReN–AY₃ complexes are also very strong. Even stronger N–X bonds are predicted for most of the nitrido-chalcogen complexes, which exhibit the trend X = O ≫ S > Se > Te. Analysis of the electronic structure shows that the parent compound Cl₂(PH₃)₃ReN has a Re–N triple bond. The Re–N σ bond is clearly polarized towards nitrogen, while the two π bonds are nearly nonpolar. The Re–N σ and π bonds become more polarized toward nitrogen when a Lewis acid or a chalcogen atom is attached. Bonding in AY₃ complexes should be described as Cl₂(PH₃)₃ReE≡N→AY₃, while the chalcogen complexes should be written with double bonds Cl₂(PH₃)₃Re=N=X. The charge-decomposition analysis indicates that the nitrogen-chalcogen bonds of the heavier chalcogen complexes with X = S, Se, Te can also be interpreted as donor-acceptor bonds between the nitrido complex acting as a Lewis base and the chalcogen atom with an empty p(σ) orbital acting as a Lewis acid. The nitrido oxo complex Cl₂(PH₃)₃ Re=N=O has a covalent N–O double bond. Received: 27 July 1998 / Accepted: 26 October 1998 / Published online: 16 March 1999