I. Bhattacharyya

Chemistry of a family of semiquinone monochelates of carbonyl ruthenium(II) generated by reacting quinones with hydridic species

Abstract The reactions of [Ru(H)(Cl)(CO)(PPh3)3] with 3,5-di-tert-butyl-o-benzoquinone (dbq) and 3,4,5,6-tetrachloro-o-benzoquinone (tcq) have afforded the corresponding semiquinone complexes [RuII(dbsq)(Cl)(CO)(PPh3)2] and [RuII(tcsq)(Cl)(CO)(PPh3)2], respectively. The reaction of [Ru(H)2(CO)(PPh3)3] with tcq has furnished [RuII(tcsq)(H)(CO)(PPh3)2]. Structure determination of [Ru(dbsq)(Cl)(CO)(PPh3)2] has revealed that it is a model semiquinonoid chelate with two equal CO lengths ( 1.291(6) and 1.296(6) A). The complexes are one-electron paramagnetic (∼1.85μB) and their EPR spectra in fluid media display a triplet structure (g∼2.00) due to superhyperfine coupling with two trans-31P atoms (Aiso∼17 G). The stretching frequency of the CO ligand increases by 20 cm−1 in going from [Ru(dbsq)(Cl)(CO)(PPh3)2] to [Ru(tcsq)(Cl)(CO)(PPh3)2] consistent with electron withdrawal by chloro substituents. For the same reason the E1/2 values of the cyclic voltammetric quinone/semiquinone and semiquinone/catechol couples undergo a shift of ∼500 mV to higher potentials between [Ru(dbsq)(Cl)(CO)(PPh3)2] and [Ru(tcsq)(Cl)(CO)(PPh3)2].

Structure, stability and energetics of ionic arsenic–water complexes

The structure, stability and energetics of ionic arsenic–water complexes [As3+–nH2O (n = 1–5) and As5+–nH2O (n = 3–5)] have been studied in detail using the MP2 method. Both the trivalent and pentavalent ionic states of arsenic were considered. The change in binding energy of the complexes with increasing number of water molecules was investigated. For both complexes involving trivalent and pentavalent arsenic, highly intense modes are observed in the high-frequency region. The structure and symmetry of the complexes with increasing number of water molecules is discussed. The charge transfer in these complexes is illustrated with the help of the natural electron configuration. Both donation and back-donation processes involving the orbitals of oxygen and arsenic are analysed to explain the charge transfer.

Dissociation and thermochemistry of methylsilanitrile and silylsilanitrile: implications for the chemistry of silicon in interstellar medium

Dissociation and thermochemistry of CH3SiN and SiH3SiN have been studied in detail using high level quantum chemical methods. The enthalpy of formation of these molecules at 0 K and 298.15 K are predicted by G3 and G3//B3LYP methods using an atomization scheme. The bond dissociation energy and energy barrier for the dissociation pathways are estimated at 0 K and the most energetically favourable dissociation products are predicted for the thermal decomposition reactions of the species in the gas phase. Finally, the enthalpy of dissociation for the most energetically favourable channel is calculated at 298.15 K. Among the four dissociation channels of CH3SiN, the most energetically favourable is SiN(2∑+) + CH3( ) having dissociation energy 57.4 kcal/mol. For SiH3SiN, dissociation channel SiN(2∑+) + SiH3( ) is the most energetically favourable, and its dissociation energy is about 1.4 kcal/mol higher than that of CH3SiN. The most energetically favourable dissociation channels may be a potential source of SiN radical in the interstellar medium.