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Showing papers on "Tetrahedral molecular geometry published in 1979"


Journal ArticleDOI
TL;DR: In this article, the authors used the pocket state formalism to calculate the tunnel splitting for tetrahedral molecules in tetralayer fields, and provided reliable results for splittings from 200 μeV down to about 1μeV.
Abstract: With improved neutron scattering and nuclear magnetic resonance techniques it has been possible to observe the splitting of the torsional ground state—commonly referred to as tunnel splitting—of a number of high symmetry molecules in various crystal fields. The tunnel splitting depends nearly exponentially on the strength of the potential experienced by a molecule as it rotates in the crystal. Tunneling spectroscopy may thus be developed into a sensitive probe for measuring rotational potentials once the relation between the potentials and the tunnel splitting is known. We have used the pocket state formalism to calculate the splitting for tetrahedral molecules in tetrahedral fields. With increasing potentials the wave function becomes smaller in the overlap region making an accurate prediction of the tunnel splittings more difficult. Our calculation provides reliable results for splittings from 200 μeV down to about 1 μeV. Detailed predictions are made for the isotope effect in solid methane and for the ...

78 citations


Journal ArticleDOI
TL;DR: In this paper, collision induced isotropic and anisotropic spectra of light scattered from fluids of tetrahedral molecules are examined and the interaction function used includes the dipole-induced dipole effect (DID) and the collision induced rotational Raman effect (CIRR) to lowest order.
Abstract: The collision induced isotropic and anisotropic spectra of light scattered from fluids of tetrahedral molecules are examined. The interaction function used includes the dipole-induced dipole effect (DID) and the collision induced rotational Raman effect (CIRR) to lowest order. The spectra are expressed as the Fourier transforms of four point correlation functions which contain the number density and the orientational density of the particles. The polarization ratio I VV CIRR(ω)/I VH CIRR(ω) for the CIRR contributions considered is shown to be 37/9 for all densities. The various terms contributing to the integrated intensity for the pair and triplet collisions are expressed in terms of the irreducible expansion coefficients of the orientation dependent pair distribution function. As an example, these terms are evaluated numerically for carbon tetrachloride for two different densities corresponding to a liquid and a vapour state.

56 citations


Journal ArticleDOI
TL;DR: In this paper, the crystal and molecular structure of (..mu..-H)/sub 2/Os/sub 3/(CO)/sub 10/(..mu.-CH/sub 2/) has been determined by using single-crystal neutron diffraction.
Abstract: The crystal and molecular structure of (..mu..-H)/sub 2/Os/sub 3/(CO)/sub 10/(..mu..-CH/sub 2/) has been determined by using single-crystal neutron diffraction. The complex crystallizes in the orthorhombic space group Pn2/sub 1/a with lattice parameters at 110 K of a = 18.502(9), b = 10.096(5), and c = 8.763(4)A. The molecule consists of a triangular array of Os atoms with one nonbridged edge (Os-Os = 2,855(3)A), one edge bridged by a single hydride (Os-Os = 3.053(3)A), and a third edge doubly bridged by a hydride atom and a methylene ligand (Os-Os = 2,824(3)A). The complex contains no terminal hydride ligands. The methylene carbon atom has a distorted tetrahedral geometry with an Os-C-Os angle of 82.1(1)/sup 0/ and a H-C-H angle of 106.0(8)/sup 0/.

40 citations


Journal ArticleDOI
TL;DR: In this article, the concept of rotational form factor analysis of molecular crystalline structures is generalized by allowing correlations between the orientation of a molecule and its centre-of-mass position.
Abstract: The concept of a 'rotational form factor' analysis of molecular crystalline structures is generalized by allowing correlations between the orientation of a molecule and its centre-of-mass position. This coupling results in correction terms to the well known rotational form factor. The method is illustrated with the example of (i) tetrahedral molecules and (ii) dumbells at a site of cubic symmetry (m3m) and the ro1e of the site symmetry as well as the magnitude of the mean-squared amplitude (u2) of the centre-of-mass motion are investigated.

34 citations


Journal ArticleDOI
TL;DR: The lattice vibrations of carbon tetrachloride have been studied by Raman and infrared spectroscopic techniques over the temperature range 18 K to the melting point at 250 K.

33 citations


Journal ArticleDOI
TL;DR: The structure of tricyclohexyltin chloride has been determined by X-ray analysis as mentioned in this paper, which is consistent with the tetrahedral geometry when distortions are taken into account in the treatment of the point charge model.

28 citations



Journal ArticleDOI
Reuben Rudman1
TL;DR: In this article, equal-sphere closest-packing principles control the crystal structures of both orientationally disordered and ordered phases of tetrahedral, pseudo-spherical molecules.

17 citations


Journal ArticleDOI
TL;DR: In this paper, an ab initio spin-restricted SCF and perturbative configuration interaction study of the silyl radical is presented, which predicts a nearly tetrahedral geometry for the radical with an inversion barrier of 5.85 kcal/mol.

15 citations


Journal ArticleDOI
TL;DR: Clustering of tetrahedral levels is shown to occur in combination bands of spherical top molecules due to Coriolis and vibrational anharmonic interactions in this article, and cluster correlation diagrams are shown for cases where the vibrational splitting is both large and small compared to the Coriolais splitting, and cluster approximations are given for both cases.

15 citations


Journal ArticleDOI
TL;DR: In this paper, high-spin iron(II) and iron(III) complexes with urea, thiourea and related ligands have been characterized by electronic, infrared, magnetic and Mossbauer measurements.

Journal ArticleDOI
TL;DR: In this article, a general expression for the integrated intensity of rotational transitions in the vibronic ground state of tetrahedral molecules, taking into account the nuclear spin statistics, is derived.
Abstract: A general expression is derived for the integrated intensity of rotational transitions in the vibronic ground state of tetrahedral molecules, taking into account the nuclear spin statistics. It is ...

Journal ArticleDOI
TL;DR: X-ray crystal structure analysis of [PtCl2{(t-Bu)2P(CH2)3P(tBu)-2}]·0.5C6H5Cl has been carried out as discussed by the authors.
Abstract: X-Ray crystal structure analysis of [PtCl2{(t-Bu)2P(CH2)3P(t-Bu)2}]·0.5C6H5Cl has been carried out. Crystals belong to monoclinic system: a=11.532(2), b=14.984(5), c=16.455(4) A, β=106.96(2)°, space group P21/c with Z=4. The structure, solved by the heavy-atom method, has been refined anisotropically by least-squares procedure to R=0.056 for 5019 non-zero reflections. The coordination around the platinum atom is approximately square-planar, however, it showed a slight deviation toward the tetrahedral geometry; Pt–P=2.281(3) and 2.282(3), Pt–Cl=2.359(3) and 2.362(3) A, P–Pt–P=99.05(9) and Cl–Pt–Cl=83.18(11)°.

Journal ArticleDOI
TL;DR: In this paper, an attempt has been made to characterize the stereochemical requirements of an aluminium atom coordinated by five hydroxyl groups within the framework of CNDO/2 molecular orbital formalism.
Abstract: An attempt has been made to characterize the stereochemical requirements of an aluminium atom coordinated by five hydroxyl groups (AlO5H52-) within the framework of CNDO/2 molecular orbital formalism. Total energy surfaces calculated for this system as the valence angles are varied within the constraints of C2v symmetry clearly show the 'reaction coordinate' for the so-called Berry pseudo- rotation mechanism. With all Al-O and O-H bond lengths fixed at 1.84 and 1.00 Ǻ respectively, the activation energy for trigonal-bipyramidal/square-pyramidal interconversion is 7.1 kJ mol-1. In addition, the minimum energy O(axial)-Al-O(basal) angle for the square-pyramidal group is estimated to be c. 103.5°. When one bond is lengthened relative to the other four the trigonal-bipyramidal configuration is further stabilized, but approaches tetrahedral geometry. When one bond is shortened square-pyramidal geometry is stabilized and the minimum energy O(ax)-Al-O(bs) angle increases. With two bonds lengthened (or shortened) the favoured trigonal-bipyramidal configuration is the one with long bonds directed towards the axial positions and at no stage is there a stabilization of square-pyramidal geometry. These results agree with trends in calculated Mulliken bond overlap populations and with observed ratios of axial-to-basal bond lengths in suggesting that for trigonal- bipyramidal stereochemistry the axial bonds are weaker, whereas for square-pyramidal geometry the axial bond is stronger. Moreover, consideration of the total energy for various isomers of Al(OH)4F2- indicates that more electronegative substituents prefer to enter the apical and basal positions in a trigonal bipyramid and a square pyramld respectively. For a cluster Al2(OH)82-, consisting of two aluminium trigonal-bipyramidal groups sharing a common edge of variable length, an energy minimum (62.2 kJ mol-1 lower than the undistorted case) is found at a shared edge length of 2.246 A, 13 % shorter than for the undistorted polyhedron. The corresponding observed distance for a similar dimer in the mineral andalusite, Al2SiO5, is 2.247(7) Ǻ. Plots of minimum energy shared edge length against mean bond length for various clusters M2(OH)8n-, where M = Al or Mg, clearly demonstrate an essentially linear relationship between the two parameters consistent wlth trends observed for natural systems in which M = Co, Cu, Mn and Zn.

Journal ArticleDOI
TL;DR: In this article, the X-ray properties of copper(II) perchlorate have been analyzed and shown to have an unusual pseudo-tetrahedral geometry about CuII.
Abstract: Condensation of acetone with bis-(1,4-diaminobutane)copper(II) perchlorate yields a purple product, [(5SR,10RS)-2,4,4,11,11,13-hexamethyl-1,5,10,14-tetra-azacyclo-octadeca-1,13-diene]copper(II) perchlorate, which has an unusual pseudo-tetrahedral geometry about CuII, as indicated by X-ray analysis.

Journal ArticleDOI
TL;DR: The complete series of tetrakis(halomercuri)methanes C(HgX)₄ (X = F, Cl, Br and I) was prepared by metathesis of aqueous hydrofluoric acid and solutions of halides (Cl-, Br-, and I-), respectively as discussed by the authors.
Abstract: The complete series of tetrakis(halomercuri)methanes C(HgX)₄ (X = F, Cl, Br and I) was prepared by metathesis of tetrakis(acetoxymercuri)methane and aqueous hydrofluoric acid and solutions of halides (Cl-, Br-, and I-), respectively. All compounds are insoluble in most common solvents, but partly soluble in dimethylsulfoxide. Complete vibrational spectra indicate more or less ideally tetrahedral molecules C(HgX)₄ in all cases. The originally triply degenerate valence vibrations of the CHg₄ entities and the force constants for the C-Hg bonds show distinct correlations with the electronegativities of the halides X. On the other hand the totally symmetrical valence vibrations of CHg₄ were found to be highly sensitive to variations in X, mainly due to coupling with the valence vibrations of the Hg-X-groups of the same symmetry species. Some analogies in the vibrational behaviour of the CHg₄ fragments and of the isosteric NHg₄ core in tetramercurioammonium complexes were observed and discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors have shown that cobalt(II) halides react with 3,6-disubstituted-2,7-dihydro-1,4,5-thiadiazepine derivatives(L) to form highly hygroscopic complexes of the general formulae, [(CuCl 2 ) 2 L] 2 nH 2 O; [(CuBr 2 ) 3 L 2 ]nH 2O] and [CoX 2L] 2 N 2 O] respectively.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of the Ni2O2 group were investigated and it was demonstrated that this is important in explaining the ferromagnetic intradimer interaction and provides a possible pathway for the antiferromagnetic interdimer exchange interaction.
Abstract: The crystal and molecular structure of the complex bis-[μ-2-(p-nitrophenyliminomethyl)phenolato- N,O]-bis(ethanol)bis(nitrato-O,O')dinickel(11) and its magnetic properties are reported. Crystal data: space group PI, Z 1, a 8.882(2), b 9.332(3), c 12.533(4) A, α 94.40(2),B 109.99(2), γ 111.61(2)o, U 883 A3, R 2.8%, Rw 3.3% for 2154 reflections. The compound is prepared from the reaction of bis(N-p-nitrophenylsalicylaldimine)nickel(II) with nickel nitrate in hot triethoxymethane, and on cooling the solution deposited pale green transparent crystals. The structure contains neutral dimeric units with bridging through the phenolic oxygen atoms and has distorted octahedral geometry about each crystallographically identical nickel atom. The six donor atoms are made up of two oxygen atoms from the bidentate nitrate, oxygen from ethanol, nitrogen from the imine group and two bridging phenolic oxygen atoms. The Ni2O2 group is strictly planar possessing a crystallographic centre of symmetry. The angles subtended at the bridging oxygen atoms indicate a tetrahedral geometry and it is demonstrated that this is important in explaining the ferromagnetic intradimer interaction. The presence of hydrogen bonding between the ethanol hydrogen and the nitrate group of an adjacent molecule appears to be an important stabilizing factor in determining the structure and provides a possible pathway for the antiferromagnetic interdimer exchange interaction.