Energetic and topological analyses of the oxidation reaction between Mo(n) (n = 1, 2) and N2O

The interaction between molybdenum, atom, and dimer, with nitrous oxide has been investigated using density functional theory. The analysis of the potential energy surfaces for both reactions has revealed that a single molybdenum atom can activate the N--O bond of N2O requiring a small activation energy. However, the presence of several intersystem crossings between three different spin states, namely, septet, quintet and triplet states, seems to be the major constraint to the Mo + N2O reaction. Contrarily, the low-lying excited states (triplet and quintet) do not participate in the reaction between the molybdenum dimer and N2O. The latter reaction fully evolves on the singlet spin surface. Three different regions have been distinguished along the pathway: formation of an adduct complex, formation of an inserted compound, and the N2 detachment. The connection between the two first regions has been characterized by the formation of a special complex in which the N--O bond is so weakened that it could be considered as a first step in the insertion process. It has been shown that the topological changes along the pathways provide a clear explanation for the geometrical changes that occur along the reaction pathway. In summary, the detachment of the N2 molecule is found to be kinetically an effective process for both reactions, owing to the high exothermicity and consequently to the high internal energy of the insertion intermediates. However, in the case of Mo atom, the reaction should be a slow process due to the presence of spin-forbidden transitions. These results fully agree with previous experimental works.     

ChemInform Abstract: From 1∞ [(UO2)2O(MoO4)4]6‐ to 1∞ [(UO2)2(MoO4)3(MoO5)] 6‐ Infinite Chains in A6U2Mo4O21 (A: Na,K, Rb,Cs) Compounds: Synthesis and Crystal Structure of Cs6 [(UO2)2(MoO4)3(MoO5)] .

Single crystals of the title compound are obtained from a melt of U₃O₈, MoO₃, and excess Cs₂CO₃ (Pt crucible, 950 °C, 12 h, cooling rate 5 °C/h).     

ChemInform Abstract: Computational Study of Analogues of the Uranyl Ion Containing the —N=U=N— Unit: Density Functional Theory Calculations on UO22+, UON+, UN2, UO(NPH3)3+, U(NPH3)24+, [UCl4{NPR3}2] (R: H,Me), and [UOCl4{NP(C6H5)3}]‐

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Catalytic behavior of a polynuclear Mg-Mo complex and nitrogenase active site (FeMoco) isolated from the enzyme in reactions with C2H2, N2, and CO: A comparative study

In order to identify common and distinctive features in the catalytic behavior of natural and artificial nitrogen-fixation clusters, the kinetics of the catalytic reduction of C₂H₂ in the presence of Mg-Mo-cluster (1) was investigated and compared with the kinetics of acetylene reduction catalyzed by the cluster FeMoco (2) isolated from the enzyme nitrogenase we studied previously. The reactions were conducted in the presence of Zn/Hg and Eu/Hg as reducing agents and PhSH and C₆F₅SH as proton donors, i.e., under the same conditions as had been used in the case of 2. Both polynuclear Mg-Mo-complex and the europium amalgam-reduced FeMoco have multiple interdependent binding sites for substrates and/or inhibitors. Carbon monoxide inhibits the acetylene reduction much less efficiently in systems with cluster 1 than in systems with cluster 2, although the type of inhibition is mixed in both systems: CO binds to multiple sites of the cluster and affects both C₂H₂ complexation to the reduced cluster and decomposition of the catalyst-substrate complex to give the products. Unlike isolated FeMoco, the Mg-Mo-cluster efficiently catalyzes the reduction of molecular nitrogen. The reaction is greatly inhibited by acetylene, while no inhibiting effect of N₂ is observed in acetylene reduction, as was found earlier for a system with the natural cluster as the catalyst. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 766–774, May, 2006.     

Application in the cyclohexane oxidation of a scorpionate oxovanadium(IV) complex: synthesis,structure, and properties of VO(C5H7O2)(BC9H7N6I3)

An oxovanadium(IV) complex, VO(C₅H₇O₂)(BC₉H₇N₆I₃), derived from hydrotris(4-iodinpyrazolyl)borate was designed and synthesized at room temperature in methanol. The complex was characterized by elemental analysis, IR spectra, UV-Vis spectroscopy, and single-crystal X-ray diffraction. The structural analysis shows that the vanadium(IV) center possesses a distorted-octahedral geometry with a N₃O₃ core, containing a tridentate hydrotris(4-iodinpyrazolyl)borate with nitrogen as three donors. The complex is the first structurally characterized example of a vanadium(IV) complex with hydrotris(4-iodinpyrazolyl)borate. It was used as a catalyst for cyclohexane oxidation under mild conditions and the effects of a variety of factors such as amount of acid and H₂O₂, the kind of solvent, as well as temperatures were evaluated; the maximum turnover number value reaches 321.     

Progress in the understanding of drug-receptor interactions, part 2: experimental and theoretical electrostatic moments and interaction energies of an angiotensin II receptor antagonist (C30H30N6(O)3S)

A combined experimental and theoretical charge density study of an angiotensin II receptor antagonist (1) is presented focusing on electrostatic properties such as atomic charges, molecular electric moments up to the fourth rank and energies of the intermolecular interactions, to gain an insight into the physical nature of the drug-receptor interaction. Electrostatic properties were derived from both the experimental electron density (multipole refinement of X-ray data collected at T=17 K) and the ab initio wavefunction (single molecule and fully periodic calculations at the DFT level). The relevance of SO and SN intramolecular interactions on the activity of 1 is highlighted by using both the crystal and gas-phase geometries and their electrostatic nature is documented by means of QTAIM atomic charges. The derived electrostatic properties are consistent with a nearly spherical electron density distribution, characterised by an intermingling of electropositive and -negative zones rather than by a unique electrophilic region opposed to a nucleophilic area. This makes the first molecular moment scarcely significant and ill-determined, whereas the second moment is large, significant and highly reliable. A comparison between experimental and theoretical components of the third electric moment shows a few discrepancies, whereas the agreement for the fourth electric moment is excellent. The most favourable intermolecular bond is show to be an NHN hydrogen bond with an energy of about 50 kJ mol(-1). Key pharmacophoric features responsible for attractive electrostatic interactions include CHX hydrogen bonds. It is shown that methyl and methylene groups, known to be essential for the biological activity of the drug, provide a significant energetic contribution to the total binding energy. Dispersive interactions are important at the thiophene and at both the phenyl fragments. The experimental estimates of the electrostatic contribution to the intermolecular interaction energies of six molecular pairs, obtained by a new model proposed by Spackman, predict the correct relative electrostatic energies with no exceptions.     

Investigation of the Hydrolysis Stability of Triazine Tricarboxylate in the Presence of Transition Metal(II) Ions and Synthesis and Crystal Structure of the Alkaline Earth Triazine Tricarboxylates M3[C3N3(CO2)3]2·12H2O (M = Sr,Ba)

The stability against hydrolysis of triazine tricarboxylate (TTC) in the presence of divalent transition metal and alkaline earth ions was investigated by means of X‐ray diffraction and FTIR spectroscopy. Depending on the size of the cation either formation of the respective triazine tricarboxylate salts or hydrolysis of TTC yielding oxalate was observed. The hydrolysis of TTC induced by transition metal ions could be explained in analogy to the hydrolysis of triazine tris(2‐pyrimidyl) as a result of ring tension caused by the coordination of these ions. By the reaction of potassium triazine tricarboxylate with alkaline earth salts in aqueous solution the alkaline earth triazine tricarboxylates M₃[C₃N₃(CO₂)₃]₂ · 12H₂O (M = Sr, Ba) were obtained and analyzed by single‐crystal X‐ray diffraction. The isotypic salts represent the first examples of alkaline earth triazine tricarboxylates and the first TTC salts comprising solely divalent cations.