Tight‐binding molecular dynamics simulation of Si?H bond dissociation in silicon clusters

New model of Si? H bond dissociation is proposed and tested in the cluster Si₁₀H₁₆ by the simulation approach that combines classic molecular dynamics method and the self‐consistent tight‐binding electronic and total energy calculation one. It is shown that the monohydride Si? H bond is unstable with respect to silicon dangling bond and bend‐bridge Si? H? Si bond formation when this cluster traps the single positive charge and that hydrogen migrates through a path involving rather rotation around the Si? Si bond than the center of this bond (the bond‐centered position). These results can be useful for understanding hydrogen‐related phenomena at surfaces, interfaces, and internal voids of various hydrogenated silicon systems: electronic devices, silicon solar cells, and nanocrystalline and porous silicon. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 351–359, 2003     

A role of non-hydrogen framework vibrational modes in formation of ferroelectric properties of H-bonded K3H(SO4)2-like materials

An effect of molecular vibrational modes within the dimers [O₃AO–(H/D)OAO₃]³⁻ on behavior of H-bond protons or deuterons is studied theoretically for H-bonded antiferroelectrics and quantum paraelectrics of the M₃(H/D)(AO₄)₂ family (M=alkali metal, A=S, Se). The ‘heavy’ reorganization modes in D-species of this family and both reorganization and promoting modes in corresponding H-analogues are examined. It is shown that the analysis with due regard for the reorganization modes results in insignificant decreasing of the effective tunneling frequency of light nuclei. Hence the reasonable estimations of the critical temperature of the low-temperature phase transition in M₃D(AO₄)₂ materials are available only with additional corrections related to potential profiles of a deuteron. It is noted that in the limits of the proposed model the promoting mode in the case of H-species can favor, in principle, the increasing as well as the decreasing of effective proton level splitting.     

Diazoalkanes in the Reactions with Dialkyl (Thio)-Phosphites

Abstract

The photochemical, thermo-catalytical and thermal reactions of diazoalkanes with dialkyl (thio)phosphites were studied.

Thus, the photolysis of dimethyldiazomalonate and methyl-diazoacetate with dialkyl(thio)phosphites gives P-H insertion products only upon triplet-sensitized conditions (i), whereas diphenyldiazomethane gives P-H insertion products upon direct photolysis as well (ii). The investigation of 31 the reaction mechanism is based on CIDNP ³¹P method. The catalytical reactions (iii) are a convenient method of preparing (thio)phosphonates.     

Stereochemically controlled synthesis of unsaturated acids via diphenylphosphinoyl (Ph2PO) -ketoacids

Acylation of phosphine oxide anions with derivatives of cyclic anhydrides or oxidative cleavage of cyclic allyl phosphine oxides gives Ph₂PO-ketoacids: reduction, separation of diastereoisomers, and completion of the Horner-Wittig reaction gives single isomers ($\text{E}$) or ($\text{Z}$) of unsaturated acids.     

Synthesis of 5,10,15,20-tetra[6' -nitro-1,3,3-trimethylspiro- (indolino-2,2' -2H-chromen-5-yl)]porphyrin and its metal complexes

A new 5,10,15,20-tetrasubstituted porphyrin containing four 6’-nitro-1,3,3-trimethylspiro(indolino-2,2’-2H-chromene) substituents and its complexes with Zn²⁺ and Cu²⁺ ions were prepared and characterized by physicochemical methods of analysis.     

Cyclic Voltammetry and the Impedance of Electrodes Modified by Indium(III) Hexacyanoferrate Films

The results of studying indium(III) hexacyanoferrate films by the cyclic voltammetry and faradaic impedance methods are presented. It is shown that the synthesis from solutions with different contents of potassium salts leads to the appearance of films with different electrochemical properties. The impedance spectra exhibit semicircles corresponding to the Randles circuit and portions of the Warburg dependence. Parameters of the equivalent circuit corresponding to the obtained spectra are determined.     

Two new polymorphs of 4‐(N,N‐dimethyl­amino)­benzoic acid

Two new polymorphs of 4‐(N,N‐dimethyl­amino)­benzoic acid, C₉H₁₁NO₂, resulting from the attempted cocrystallization in ethanol of 4‐(N,N‐dimethyl­amino)­benzoic acid and a mixture of 3‐(N,N‐dimethyl­amino)­benzoic acid and 3‐(3‐pyrid­yl)‐2‐pyridone producing one polymorph, and a mixture of 3‐(N,N‐dimethyl­amino)­benzoic acid and 5‐meth­oxy‐3,3′‐bipyridine producing the second polymorph, have been crystallographically characterized. The primary inter­molecular O—H⋯O hydrogen bonds generate a dimeric acid–acid motif that is present in all three polymorphs.