Géométrie moléculaire tétraédrique

En chimie, la géométrie moléculaire tétraédrique est la géométrie des molécules où un atome central, noté A, est lié à quatre atomes, notés X, aux sommets d'un tétraèdre régulier (ou presque régulier). Ces composés appartiennent à la classe AX4E0 selon la théorie VSEPR. Les angles de liaison sont de \arccos\left(-\tfrac13\right) ≈ 109,47° (double de l'angle dit « magique ») lorsque tous les substituants sont les mêmes, comme dans le cas du méthane (CH4). Les tétraèdres parfaitement symétriques appartiennent au groupe ponctuel de symétrie Td, mais la plupart des molécules tétraédriques ne possèdent pas une si forte symétrie. Les molécules tétraédriques peuvent être chirales. Cette géométrie est proche de la géométrie moléculaire pyramidale trigonale (AX3E1), où la place de l'un des substituants est tenue par un doublet non liant. Dans cette géométrie les angles de liaison sont inférieurs à 109,5°, par exemple 107° dans le cas de l'ammoniac. Cette légère contraction résu

Structural elucidation and antibacterial activity of new dialkylstannyl- and chlorodialkylstannyl(IV) 3,4-dihydroisoquinoline-2-(1H)-carbodithioate

In extension with growing concern to develop new antimicrobial organometallic drugs, an attempt has been made to synthesize five new antimicrobial organotin(IV) carbodithioates with general formula, Me2SnClL (1), Me2SnL2 (2), Et2SnClL (3), Et2SnL2 (4), Bu2SnClL (5), Bu2SnL2 (6), (where L = Sodium 3,4-dihydroisoquinoline-2-(1H)-carbodithioate). Compounds have been synthesized by refluxing organotin(IV) chlorides with ligand in dry toluene for 7-8 h. Compound 1, 3 and 5 exhibited Penta coordination, while 2, 4 and 6 showed hexacoordination in solid state, as evident from the difference obtained between symmetric and asymmetric CSS stretches in IR spectra. Solid-state structures of 1 was further attested by single crystal analysis as distorted trigonal bipyramidal geometry. H-1-, C-13- and Sn-119- NMR spectroscopy was used to assess the geometry of the compounds in solution state. It was observed that 1, 3, 4 and 5 completely dissociated in solution and showed tetrahedral geometry, whereas 2 and 6 exhibit pentacoordinate geometry after partial dissociation in solution. The pronounced activity was observed for all the compounds against five different strains of bacteria. (C) 2021 Elsevier B.V. All rights reserved.

ELSEVIER2021

Synthesis and structural elucidation of bioactive triorganotin (IV) derivatives of sodium deoxycholate

Rosario Scopelliti

Trimethyl (1), tributyl (2), and triphenyl tin (3) derivatives of sodium (R)-4-((3R, 5R, 8R, 9S, 10S, 12S, 13R, 14S, 17R)-3,12-dihydroxy-10,13-dimethyl-hexadecahydro-1H-cyclopenta[a] phenanthren-17-yl)pentanoate (sodium deoxycholate) were synthesized by refluxing sodium deoxycholate with the corresponding triorganotin(IV) chloride in 1 : 1M ratio. All the three compounds were characterized by elemental analysis, infrared spectroscopy, H-1, C-13, Sn-119 NMR, and X-ray diffraction studies. From FT-IR spectra,Delta nu values proposed bridging or chelating behavior of the ligand. The three compounds gave a trigonal bipyramidal geometry in the solid state and tetrahedral geometry in solution. Single crystal of 1 showed polymeric trigonal bipyramidal geometry. Synthesized compounds obtained were screened for their antimicrobial and antitumor activities against A2780 cell line. Results revealed that only 2 showed significant antibacterial activity. However, all the three compounds exhibited promising antifungal and anticancer activities.

Taylor & Francis Ltd2014

Properties of Ir4 clusters in the gas phase and on oxide substrates

Vladan Stevanovic

Results of a theoretical study on the properties of Ir4 clusters in the gas–phase and on oxide surfaces are presented. The work is based on density functional theory (DFT) within the generalized gradient approximation (GGA) and ultrasoft pseudopotentials. Properties of a small particle such as Ir4 cluster are entirely determined by its geometry. The already known result that the most stable form of Ir4 in the gas–phase is the square structure which is significantly more stable than the butterfly and tetrahedron is confirmed. This result is in contradiction with experiments which indicate that the oxide supported Ir4 adopts a tetrahedral configuration. It is shown in this thesis that the chemical environment has a strong influence on the relative stability of Ir4 clusters. On MgO(100) surface, the square isomer remains the most stable Ir4 structure, well separated in energy from the other two. Moreover, the tetrahedron is heavily distorted by the interaction with the surface oxygen. Presence of point defects (neutral and charged O vacancies) affects the energy ordering making tetrahedron and square very close in energy, but the structural distortion of the tetrahedron is even bigger and the predicted data do not correspond to experiments. On TiO2(110) the tetrahedron and square structures become degenerate and the butterfly becomes the least stable isomer. Moreover, structural distortions are very small, in agreement with experimental data. It is shown that the TiO2 surface influences the relative stability of the three isomers through a particularly strong electrostatic field. Interactions of Ir4 with H, C and O atoms as well as with CO molecules have been studied. Adsorption of a single C atom strongly influences the relative stability of the three isomers. Upon C adsorption, the butterfly becomes the most stable gas–phase isomer while on both surfaces the tetrahedron is the most probable structure. Adsorption of a single H or O atom does not produce the same effect. The interaction with CO molecules is also important given the experimental procedure used for producing supported Ir4 clusters. It is shown that on MgO(100), CO dissociation is as probable as the competing process CO desorption justifying the presence of carbon adatoms on Ir4 clusters which brings theoretical predictions in better agreement with experimental data.

EPFL2009

Properties of Ir4 clusters in the gas phase and on oxide substrates

Vladan Stevanovic

EPFL2009