Articles written in Journal of Chemical Sciences

    • Isolobal analogy between trivalent boron and divalent silicon

      Eluvathingal D Jemmis Bharatam V Prasad PV A Prasad Seiji Tsuzuki Kazutoshi Tanabe

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      Singlet organosilylenes with a lone pair and an emptyp orbital are isolobal to trivalent borane if a B-H is equated to the lone pair on Si. Using this analogy, a particular isomer of CSi2H2 (24) is predicted to be a stable structure. MNDO calculations on24 and many of its possible isomers suggest that24 is at global minimum on the potential energy surface of CSi2H2.Ab initio calculations using a, minimal STO-3G basis set, on some selected structures also support these results.

    • Structural variations in aromatic 2𝜋-electron three-membered rings of the main group elements

      Dibyendu Mallick Eluvathingal D Jemmis

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      Structural variations of different 2𝜋-aromatic three-membered ring systems of main group elements, especially group 14 and 13 elements as compared to the classical description of cyclopropenyl cation has been reviewed in this article. The structures of heavier analogues as well as group 13 analogues of cyclopropenyl cation showed an emergence of dramatic structural patterns which do not conform to the generalnorms of carbon chemistry. Isolobal analogies between the main group fragments have been efficiently used to explain the peculiarities observed in these three-membered ring systems.

    • Computational design of Oligo-sulfuranes


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      We studied the effect of electronegativity perturbation on the isolobal behavior of tetra-coordinate hypervalent compounds of S (sulfuranes, SL₄, L is any atom or group which can provide one electron for S-L bonding). Though formally the fragment SL₄ obtained from SL6 is an isolobal equivalent of CH₂, a qualitative molecular orbital study shows that only SF₂H₂ with equatorial F atoms is a practical isolobal substitute for CH₂ and can form oligomers, (SF₂H₂)₂, (14), (SF₂H₂)₃, (15) and (SF₂H₂)₄, (16) analogous to ethylene, cyclopropane and cyclobutane, respectively. DFT computations at the B2PLYP/6-311++g(d,p), MP2/ aug-ccpVTZ and B3LYP/6-311++g(d,p) levels confirm these structures to be minima on the PES. The skeletal S-S bonds in these structures are formed solely by the bonding combination of anti-bonding fragment orbitals of SF₂H₂. In contrast, per-fluorination, the usual way to stabilize hypervalent structures, is found to have an opposite effect here. Calculations at the same levels show (SF₄)₂, (SF₄)₃, and (SF₄)₄ not to be minima. The highly stable HOMO of SF₄ fragment and large HOMO-LUMO gap makes SF₄ a stable entity, preventing it from oligomerization. Out of the various isomers of SFnH₄−n, n = 0-4, only SF₂H₂ with equatorial F atoms can form oligomeric sulfuranes. Substitution of F by heavier analogs of the group did not lead to any stable oligomers.

    • The dynamic behavior of the exohedral transition metal complexes of B₄₀ : η⁶- and η⁷-B₄₀Cr(CO) ₃ and Cr(CO) ₃η⁷-B₄η₀-Cr(CO) ₃


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      The dynamic nature of the exohedral η⁶- and the η⁷-complexes of B₄₀ with Cr(CO) ₃ has been explored using density functional theory. The ab initio molecular dynamic simulations were performed at 1200 K to investigate the fluxionality of the heptagonal and hexagonal faces of exohedral B40 complexes. Our computations show that the coordination of the B40 faces with Cr(CO) ₃ fragment reduces its fluxionality to a limited extent. The activation barrier for the inter-conversion of the heptagonal and hexagonal rings in (CO)₃Cr(η⁶-B₄₀) complex is around 15.2 kcal/mol whereas in the (CO)₃ Cr(η⁷-B₄₀) complex, it is slightly higher at around 19.7 kcal/mol. The coordination with another Cr(CO)₃ fragment is found to be equally exergonic, with a barrier for interconversion of 21.5 kcal/mol. The HOMO-LUMO gap is almost similar as the mono-metallated complexes. The di-metallated complexes also show a dynamical behavior of the six and seven membered rings at 1200 K.

    • Designing M-bond (X-M...Y, M 5 transition metal): r-hole and radial density distribution


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      Following the ubiquitous H-bond, there is a growing interest in weak non-covalent interactions involving other elements, viz., the Z-bonds (X-Z...Y, Z = halogens, chalcogens, etc.). Although almost all the main group elements can act as Z bond donors, the search for a similar role for transition metals in X-M...Y,(M = transition metal) interaction, called the Metal-bond, is still in its infancy. This article summarizes our attempts to understand the participation of transition metal elements as electron acceptors in a weak interaction with electron-rich species Y. Cambridge Structural Database analysis revealed that except Group 11and 12 transition metal complexes (Type-II), electron-saturated (18 electron) metal complexes having partly filled d orbitals (Group 3–10; Type-I) hesitate to form Metal-bonds. This is attributed to the partial r-hole screening by core electron density and diminished stabilization from charge polarization in Type I complexes. We also show that Type-I complexes could be forced to form Metal-bonds by employing extreme ligand conditions, thereby opening new areas of research where Metal-bonds can act as emerging non-covalent interaction in designing supramolecular architectures

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