Reaction of MoCl3(THF)3 with [Me2Si{NLi(Dipp)}2]2 (Dipp = 2,6-i-PrC6H3) afforded a triply bonded dimolybdenum complex 1,2-Mo2Cl2[Me2Si(NDipp)2]2 1, spanned by two Me2Si[N(Dipp)]2 ligands, thus resulting in a syn conformation. The air- and moisture-sensitive compound 1 was characterized by NMR spectroscopic, elemental, and single-crystal X-ray crystallographic analysis. Reduction of 1 by Na/Hg yielded the quadruply bonded dimeric complex Mo2[Me2Si(NDipp)2]2 2, which was also characterized by the aforementioned analytical methods. The Mo-Mo bond was determined to be 2.1784(12) A, which is considered a long quadruple bond. In addition, density functional theory (DFT) computations on compound 2 provided insight into the intriguing Mo-Mo quadruple bond.

The theoretical spectra of electroluminescent polymers are studied with time-dependent density functional theories, followed by a systematic scheme with a symmetry restriction to extrapolate the absorption and emission corresponding to infinite chains avoiding periodic boundary conditions. Application to poly(p-phenylene vinylene) (PPV) and the derivatives has been attempted, and the hybrid B3LYP is concluded to be the most suitable functional for computation. The theoretical excitation energies of PPV by B3LYP/6-31G*//B3LYP/STO-3G and B3LYP/6-311G* are 2.107 and 2.027 eV, respectively. With optimization performed by single-excited configuration interaction, the emission spectroscopy can be estimated. By our scheme, the Stokes shift of PPV is calculated to be 0.223 eV, which corresponds to approximately 62 nm in the spectral region.

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S-sulfhydration is generally anticipated to proceed through the transfer of the SH group (Nu-SH···(-)S-R → Nu(-)···HS-S-R). The other route involves the sulfur atom (S(0)) transfer between two sulfhydryl anions (Nu-S(-)···(-)S-R → Nu(-)···(-)S-S-R) and is considered electrostatically unfavorable. Mercaptopyruvate sulfurtransferase (MST, PDB code: 4JGT ) catalyzes sulfur transfer from mercaptopyruvate to sulfur acceptors, and the first step of the reaction is the formation of cysteine (Cys248) persulfide via S-sulfhydration. Mechanistic studies on S-sulfhydration in MST using QM/MM methods show that the sulfur atom transfer initialized by the deprotonation of the Ser250/His74/Asp63 triad is kinetically preferred to the SH-promoted sulfur transfer. The calculated barrier of approximately 16 kcal mol(-1) for the S(0) transfer agrees well with experimental results. The electrostatic repulsion during the S(0) transfer can be sophisticatedly reduced by the aid of the Cys248-Gly249-Ser250-Gly251-Val252-Thr253 (CGSGVT) loop. Electrostatic potentials and frontier orbitals are also analyzed for the persulfide anion surrounded by the loop. The sulfur atom transfer which is seldom regarded possible is therefore facilitated with the assistance of the triad and the loop in the enzyme.

Take five: A unique quintuply bonded dimolybdenum complex [Mo(2)(μ-Li){μ-HC(N-2,6-Et(2)C(6)H(3))(2)}(3)] (see picture) was synthesized and characterized. The Mo-Mo interaction includes an unexpected bridging Li(+) ion. Calculations indicate the bridging Li(+) ion does not perturb the Mo-Mo bond length (2.0612(4) Å), but results in a relatively small effective Mo-Mo bond order of 3.67.