Int. J. Mol. Sci., Volume 4, Issue 6 (June 2003) – 6 articles , Pages 312-407

The theoretical method of determination of absolute atomic size, discussed in Int. J. Mol. Sci. 2002, 3, 87-113, is exploited to calculate absolute radii of the ions whose experimental radii are published by Shanon. The computed radii are found to reproduce the expected periodic variation of size in periods and in groups and nicely reproduce the d-block and f-block contractions in the respective series. It is pointed out that experimental radii of d and f block transition metal ions make erroneous and misleading representation of the size behaviour of the respective series. A detailed comparative study of the crystal radii vis-à-vis the theoretical radii is reported. A rationale of the double hump curve of the experimental radii of 3 d-block transition metal ions is put forward in terms of the crystal field theory and Jahn-Teller distortion. The theoretical radii are exploited to calculate the diamagnetic susceptibility, polarizability and chemical hardness of the ions and compared with available experimental data. The fact of good agreement between the experimental and computed global hardness of ions and correct demonstration of d-block and f-block contraction by the computed radii are used as benchmark to test the validity of the values of the computed theoretical radii of the ions as their representative sizes. It is concluded that the theoretically computed radii of ions are visualizable size representation of ions and can be used as their absolute radii at the respective oxidation states. Full article

Comparative reactivities of three diaqua(tetraamine)Co(III) complexes towards hydrolysis of 4-nitrophenyl phosphate was undertaken. The results were contrasted with prussian blue promoted hydrolysis of 4-nitrophenyl phosphate. The tetraamineCobalt(III) complexes accelerated the hydrolytic reaction to varying degrees with the following reactivity order. [(tn)2Co(OH2)2]3+ < [(trpn)Co(OH2)2]3+ < [(tme)2Co(OH2)2]3+ [ tn = trimethylenediamine; tme = 1,1,2,2-tetramethyl-1,2-diaminoethane; trpn = tris(3- aminopropyl)amine].These observations are attributed to the active aquo-hydroxo forms of the tetraamineCobalt(III) complexes. The hydrolysis rate for prussian blue promoted hydrolysis was comparable to that obtained for [(tme)2Co(OH2)2]3+. The mixed valence bimetallic centers of prussian blue aid in substrate binding and organizing the nitrophenyl phosphate for effective intramolecular nucleophilic attack by coordinated hydroxide or water. Full article

Two series of compounds, one comprising of 2-(2′-hydroxyphenyl)benzoxazole (HBO), 2-(2′-hydroxyphenyl)benzimidazole (HBI), 2-(2′-hydroxyphenyl)benzothiazole (HBT), and the other of 2-(2′-hydroxyphenyl)oxazole (HPO), 2-(2′-hydroxyphenyl)imidazole (HPI) and 2-(2′-hydroxyphenyl)thiazole (HPT) are susceptible to ground state rotamerization as well as excited state intramolecular proton transfer (ESIPT) reactions. Some of these compounds show experimental evidence of the existence of two ground state conformers. Out of these two one undergoes ESIPT reaction leading to the formation of the tautomer. The two photophysical processes, in combination, result in the production of a number of fluorescence bands each one of which corresponding to a particular species. Semiempirical AM1-SCI calculations have been performed to rationalize the photophysical behaviour of the compounds. The calculations suggest that for the first series of compounds, two rotational isomers are present in the ground state of HBO and HBI while HBT has a single conformer under similar circumstances. For the molecules of the other series existence of rotamers depends very much on the polarity of the environment. The potential energy curves (PEC) for the ESIPT process in different electronic states of the molecules have been generated theoretically. The simulated PECs reveal that for all these systems the IPT reaction is unfavourable in the ground state but feasible, both kinetically and thermodynamically, in the S₁ as well as T₁ states. Full article

Three systems, isobutyric acid – water (I–W), “(I-W) + 5 10^-4 M (KCl)” and “(IW) + 5 10^-3 M (KCl)”, have been studied by measuring the electrical conductivity σ (Ω^-1cm^-1) along the coexistence curve in a single phase, as a function of the variations temperature T and composition X in acid. The coefficient σ is a temperature dependent parameter for ions, increasing as temperature is elevated. Contrary to the visconty, the electrical conductivity does not show any anomaly in the critical region. Full article

“Maghnite” a montmorillonite sheet silicate clay, exchanged with protons to produce “H-Maghnite” is an efficient catalyst for polymerization of many vinylic and heterocyclic monomers (Belbachir, M. U.S. Patent. 066969.0101 –2001). The structure compositions of both “Maghnite” and “H-Maghnite” have been developed. This catalyst was used for the polycondensation of the tetrahydrofuran with phthalic anhydride. The polymerization was performed under suitable conditions at temperature (40°C), in presence of acetic anhydride. Experiments revealed that polymerization induced by “H-Maghnite”, proceed in bulk and the conversion increases with increasing “H-Maghnite” proportion. Full article