Tetrahedral molecular geometry

About: Tetrahedral molecular geometry is a research topic. Over the lifetime, 1795 publications have been published within this topic receiving 30706 citations.

Bent Chemical Bonds: Present theories and experimental results concerning electrons in some specific molecules are discussed.

Abstract: The obvious and not original conclusion is that the results obtained from considerations of sp3 hybridization in the substituted methanes breaks down as soon as all of the bonding atoms are not equivalent. Indeed, the concept of sp3 localized carbon hybrids may be invalid even for tetrahedral molecules like CCl4 where the result of tetrahedral angles may be inferred from a naive hard sphere model. In other words the electrons in CCl4 have a more delocalized molecular quality than the apparently more localized atomic quality in CH4. This result implies that perhaps a Hartree-Fock treatment of the outer valence electrons in the substituted methanes (frozen inner atomic shells) might give a fairly good description of the electron distribution. On the other hand, the valence bond method would have to be carried well past the convenient approximation of perfect pairing. McWeeny and Ohno (23) were quite optimistic about the frozen inner atomic shell approximation in their treatment of H2O. As far as the strained small-ring compounds it appears the bending of a bond is a function of where one decides to draw the line between localized and delocalized character. Finally, no more appropriate ending could be contrived than a classic quote by Professor R. S. Mulliken (37), "I believe the chemical bond is not so simple as some people seem to think."

Two Novel Diamagnetic-metal Coordination Polymers of Nitronyl Nitroxide Radical Incorporating Isophthalate Bridges

Abstract: Two novel coordination polymers of formula [Zn(NIT4py)2(ip)]n (1) and [Cd(NIT4py)2(ip)(H2O)]n (2) (NIT4py=2-(4′-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and ip=isophthalate dianion), have been synthesized and determined by X-ray diffraction. The crystal structures of the complexes are both neutral 1-D chains. The Zn(II) ion adopts a distorted tetrahedral geometry and the Cd(II) ion adopts a distorted pentagonal bipyramidal geometry. Each isophthalate dianion binds two metal ions in bis-monodentate mode for complex (1) and in bis-bidentate mode for complex (2) leading to the 1-D chains. In complex (2) the 1-D chains develop into two-dimensional network via the hydrogen bond interactions. The magnetic studies show a weak antiferromagnetic coupling between two radicals through the diamagnetic Zn(II) in complex (1).

Studies of Some Cadmium(II) and Mercury(II) Complexes With Dicyclohexylphosphino-N-Phenylthioformamide, LH: Crystal and Molecular-Structures of [Cdl2(LH)]2, ([HgCl2(LH)]2.CH2Cl2) And HgCl2(LH)2

Abstract: The crystal and molecular structures of the title compounds, [CdI2(LH)]2, (1), [HgCl2(LH)]2.CH2Cl2(2), and HgCl2(LH)2(3)[where LH = dicyclohexylphosphino-N-phenyl-thioformamide,* (c-C6H11)2PC(S)N(H)Ph] have been determined by single-crystal X-ray diffraction techniques. Crystals of (1) are monoclinic, space group P21/n, a 13.051(2), b 10.183(1), c 18.106(1)Ǻ and β 101.55(8)° with Z 2; R and Rw were 0.047 and 0.044 respectively for 2320 unique, observed reflections. The unit cell contains two equivalent centrosymmetric, halogen-bridged cadmium dimers. Crystals of (2) are triclinic, space group Pī, with a 10.668(4), b 14.978(3), c 16.838(4)Ǻ, and α 111.80(2), β 101.03(2), γ 92.06(2)° with Z 2; R and Rw were 0.069 and 0.067 respectively for 3379 unique observed reflections. The structure shows two independent centrosymmetric halogen-bridged dimers within the unit cell. Crystals of (3) are monoclinic, space group C2/c, a 24.719(6), b 12.247(3), c 26.818(6) Ǻ, and β 94.62(2)° with Z 8; R and Rw were 0.075 and 0.071 respectively for 2698 unique, observed reflections. The structure shows the complex to be monomeric. In all three compounds the metal atom is in an approximately tetrahedral environment with the potentially multidentate ligand, LH, coordinating only through the phosphorus atom. The mercury compounds show a much larger deviation from ideal tetrahedral geometry than does the cadmium compound.

Model Anisotropic Intermolecular Potentials for Saturated Hydrocarbons

Abstract: The use of explicit orientation-dependent functions, to represent the effects of non-spherical features in the molecular charge distribution, in model intermolecular pair potentials is developed in order to produce more accurate transferable anisotropic sitesite potentials for organic molecules. An isotropic atom-atom intermolecular potential-energy surface for methane is analysed using the orientation-dependent expansion functions appropriate to a pair of tetrahedral molecules, to determine the ability of a wide variety of one-centred anisotropic model potentials to reproduce the surface. The analysis is used to develop a simple anisotropic carbon potential scheme for CH3 and CH2 groups, which can predict the crystal structures of pentane, hexane and octane as accurately as the widely used isotropic atom-atom potential, and has the advantage of being more computationally efficient and more flexible for future development. The derivation of the appropriate orientationdependent functions for tetrahedral molecules, using angular momentum theory, in a form which is very convenient for crystal structure analysis is given. These functions are also used to examine the use of van der Waals radii to predict molecular packing.