Showing papers on "Tetrahedral molecular geometry published in 1998"
TL;DR: In this article, the origin of chemical anisotropy in the dissolution of single-crystal silicon in alkaline solutions is discussed in terms of the atomic configuration of silicon in the pentacoordinated transition state for (100) and (111) surfaces.
Abstract: The origin of chemical anisotropy in the dissolution of single-crystal silicon in alkaline solutions is discussed in terms of the atomic configuration of silicon in the pentacoordinated transition state for (100) and (111) surfaces. It is proposed that tetravalent silicon, which is bonded in a tetrahedral geometry, is attacked in the etch process by the hydroxide ion, forming a pentacoordinated transition state. Owing to the number of bond angles that are fixed by the atomic arrangement at the surface, the energetically favoured trigonal bipyramidal geometry for a pentacoordinated complex is only slightly distorted for the former plane but significantly distorted for the latter, resulting in a higher activation energy for the dissolution of (111) surfaces. The difference in the activation energies for the dissolution of Si(100) and (111) surfaces, arising from steric hindrance in the transition state, can be estimated from the activation energy for a pseudo-rotation of a similar system.
41 citations
TL;DR: In this paper, transition metal complexes of CoII, NiII and CuII with 4-(4-azidosulfophenylazo)-5-phenyl-3,4-dihydro-2H-pyrazol-3-one HL1, HL2 and HL3 were prepared and characterized by elemental analyses, molar conductances and magnetic susceptibilities.
Abstract: Transition metal complexes of CoII, NiII and CuII with 4-(4-azidosulfophenylazo)-5-phenyl-3,4-dihydro-2H-pyrazol-3-oneHL1, 4-(4-azidosulfophenylazo)-5-methyl-2-phenyl-3,4-dihydro-2H-pyrazol-3-one HL2 and 4-(3-azidosulfo-6-methoxyphenylazo)-5-methyl-2-phenyl-3,4-dihydro-2H-pyrazol-3-one HL3 were prepared and characterized by elemental analyses, molar conductances and magnetic susceptibilities and by i.r., electronic and e.s.r. spectral measurements as well as thermal (d.t.a and t.g.a.) analysis. The i.r. spectra indicate that HL acts as a bidentate ligand coordinating via the azo and enolic-oxygen linkages. The electronic spectral data and magnetic moments suggest a tetragonally distorted octahedral geometry for the complexes having the formula ML2·2H2O, (M = CoII, NiII and CuII), square pyramidal geometry for CuL23H2O and tetrahedral geometry for CoL23. The X-band e.s.r. spectra of the copper(II) complexes reveal anaxial symmetry for both CuL222H2O and CuL23H2O while CuL21O is isotropic in the solid state at room temperature. The d.t.a. curves show two exothermic peaks for all three complexes CoL23,NiL232H2O and CuL23H2O and one endothermic peak for the latter two aqua complexes.
31 citations
TL;DR: In this article, the authors reported the preparation of four and five-coordinate aluminum and gallium bis(amidophosphine) derivatives using toluene at 25 °C and showed that the solution NMR spectra are consistent with Cs symmetry.
Abstract: Investigations on the preparation of four- and five-coordinate aluminum and gallium bis(amidophosphine) derivatives are reported. The reaction of the macrocyclic ligand precursor anti-Li2(THF)2[P2N2] ([P2N2] = [PhP(CH2SiMe2NSiMe2CH2)2PPh]) with AlCl3 or GaCl3 in toluene at 25 °C leads to the formation of the four-coordinate species anti-MCl[P2N2] (M = Al (1), Ga (2)). An X-ray diffraction study of anti-GaCl[P2N2] shows it to be monomeric with a distorted tetrahedral geometry at Ga; only one of the phosphine donors of the [P2N2] ligand binds to the gallium, resulting in the retention of the anti-configuration. The solution NMR spectra are consistent with Cs symmetry. The addition of AlCl3 or GaCl3 to the macrocyclic ligand precursor syn-Li2(dioxane)[P2N2] in toluene at 25 °C yields the five-coordinate complexes syn-MCl[P2N2] (M = Al (3), Ga (4)). The X-ray crystal structure of syn-GaCl[P2N2] reveals a trigonal bipyramidal geometry about the metal atom, necessitating the coordination of both phosphorus atom...
29 citations
TL;DR: In this article, the absolute total cross section (TCS) of the electron collision with molecules has been measured in a linear transmission experiment for impact energies from 0.5 to 250 eV.
Abstract: Absolute total cross section (TCS) of the electron collision with molecules has been measured in a linear transmission experiment for impact energies from 0.5 to 250 eV. The TCS function is dominated by a steep rise towards low energies below 3 eV. At energies above the minimum at 3 eV the TCS shows another enhancement spanned up to about 70 eV on which some resonant-like features are visible: the maximum centred near 6.5 eV and two weak peaks at 16 and 25 eV, respectively. A comparison with the recent measurements taken in the same laboratory for and and for other targets of the same symmetry is made to search for similarities and/or differences between electron scattering TCSs for tetrahedral molecules. The data demonstrate that the general shape of the low-energy TCS for tetrahedral molecules depends on external rather than on central atoms.
28 citations
TL;DR: In this article, the synthesis, spectral characterisation and X-ray structure determination of the first zinc(II) ferrocenedicarboxylate [Zn(1,1′-Ferdc)(1-methylimidazole)2]2, 1, (1, 1′-H2ferdc = 1,1''-ferrocenedricarboxylic acid) is described.
21 citations
TL;DR: Two mercury(II) complexes of 4,5-ethylenedithio-3,3-dithiole-2-thione (C5H4S5) and [Hg2(C5 H4 S5)2Br4] were synthesized and the structure of complex 1 was characterized in this paper.
20 citations
TL;DR: In this article, single-crystal X-ray structure determinations were performed for complexes 1 and 2, which were characterized by 1H and 31P NMR spectroscopy and showed that the coordination geometry around the metal atom is markedly distorted tetrahedral with the two dppfSe moieties acting as chelating ligands.
19 citations
TL;DR: In this article, the synthesis, spectral characterisation of the zinc(II) pyrrolecarboxylates, [Zn(2-Hpyrrc)2(H2O)] (1) and Zn(1-methylimidazole)2] (2) (2H2pyrr = 2-pyrrole-carboxylic acid) is reported as well as the X-ray structure determination of the latter compound.
17 citations
TL;DR: In this paper, high level ab initio and density functional theory approaches have been used to study the structure and bonding of the stationary points of the As4H+ potential energy surface, and the geometries and the harmonic vibrational frequencies of the different species investigated were obtained through the use of allelectron MP2(full) and B3LYP methods using 6-311G(d) basis expansions.
Abstract: High level ab initio and density functional theory approaches have been used to study the structure and bonding of the stationary points of the As4H+ potential energy surface. The geometries and the harmonic vibrational frequencies of the different species investigated were obtained through the use of all-electron MP2(full) and B3LYP methods using 6-311G(d) basis expansions. Final energies were obtained in G2(MP2) and B3LYP/6-311+G(3df,2p) calculations. The global minimum is the result of the side protonation of As4 tetrahedral molecule. The corner-protonated species is significantly less (∼23 kcal/mol) stable, while the face-protonated form is a second-order saddle point. The open structure 5 resulting from the fission of two As–As bonds lies 18 kcal/mol above the global minimum. In the global minimum the proton is covalently attached to two As atoms through the formation of a three-center delocalized bonding orbital. The relative stability of this “nonclassical” structure is enhanced with respect to tha...
15 citations
TL;DR: A new boron dibromide featuring intramolecular Lewis base coordination, ArBBr2 (4; Ar = 2-[dimethylamino)methyl]phenyl) has been prepared via the salt-elimination reaction of [2-(Me2NCH2)C6H4]Li with BBr3.
Abstract: A new boron dibromide featuring intramolecular Lewis base coordination, ArBBr2 (4; Ar = 2-[(dimethylamino)methyl]phenyl) has been prepared via the salt-elimination reaction of [2-(Me2NCH2)C6H4]Li with BBr3. Single-crystal X-ray diffraction experiments reveal that 4 rystallizes in two polymorphs, both of which ave orthorhombic. The principal difference between the two polymorphs is the presence or absence of weak Br ... Br intermolecular contacts. The metrical parameters for the individual molecules of 4 are very similar for both polymorphs; the amine "arm" is coordinated strongly, and the boron atom adopts a somewhat distorted tetrahedral geometry. Compound 4 is surprisingly unreactive toward a variety of hydride transfer reagents. (C) 1998 John Wiley & Sons, Inc.
14 citations
TL;DR: In this article, the crystal structures of Ph3Sn (o-Tol) and PhSn (tol)3 were determined and compared to 16 known structures, subject to the distanced (M-C), an interplay between through-space ππ repulsion and π−σ attraction leads to either elongated or compressed tetrahedral geometry.
TL;DR: The Ag atom in the title complex [Ag(C2F3O2)(C18H15P)2], is bonded to two triphenylphosphine ligands and a chelating trifluoroacetate anion in a distorted tetrahedral geometry as mentioned in this paper.
Abstract: The Ag atom in the title complex [Ag(C2F3O2)(C18H15P)2], is bonded to two triphenylphosphine ligands and a chelating trifluoroacetate anion in a distorted tetrahedral geometry.
TL;DR: A series of cobalt(II) complexes of general formula [CoX 2 L 2 ] (X = Cl, Br, I, NO 3, ClO 4, NCS; L 2 = Ph 2 PCH 2 Si(CH 3 ) 2 CH 2 PPh 2 ) have been synthesised and characterised by electronic and infrared spectroscopy and by magnetic moment studies.
TL;DR: The synthesis and characterization by elemental analysis, IR and 1H NMR of (Z)-1- [2] -1-cyclopentanol, CH2(CH2)3C(OH)CHCHSnPh3 (1) and (Z]-1-[2]-1-cyclopentanol compounds were described in this paper.
TL;DR: In this paper, the stretching and bending vibrational spectrum and the intensities of infrared transitions in a tetrahedral molecule are studied in two boson-realization models, where the interactions between stretching and vibrational vibrations are described by a quadratic cross term and by Fermi resonance terms, called harmonically coupled and Ferman resonance bosonrealization model, respectively.
TL;DR: In this paper, the diamine precursors N, N-diphenylethylenediamine or N,N-dibenzylethlyenediamines were treated with the commercial reagent dibutyl-magnesium in the presence of a donor solvent (THF or HMPA) and their crystal structures were determined.
TL;DR: In this paper, the new ligand 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine (L1) has been synthesized.
Abstract: The new ligand 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine, 2,6-(Ph2PCH2CH2SCH2)2C5H3N (L1), has been synthesized. Reaction of [Cu(MeCN)4][CF3SO3] or AgNO3 with 1 molar equivalent of L1 gave [CuL1][CF3SO3] 1 or [AgL1][NO3] 2, in good yield. Reaction of equimolar quantities of L1 and AuI, followed by precipitation with AgO3SCF3, gave [AuL1][CF3SO3] 3. In the crystal structure of 2·H2O, L1 co-ordinates to Ag via a P2S2 donor set in a distorted tetrahedral geometry. Reaction of M(O3SCF3)2 (M = Zn or Cd) with 1 molar equivalent of L1 gave [ML1(O3SCF3)2] (M = Zn 4 or Cd 5). Crystal structure analysis of 5 showed that the molecule has symmetry 2, with all five donor atoms of L1 and a pair of monodentate CF3SO3– ligands arranged in an unusual distorted pentagonal bipyramidal co-ordination geometry about the cadmium centre.
TL;DR: In this paper, a single crystal structure of [Zn2dpt]2(μ-OH)](ClO4)3 (dpt = bis(3-aminopropyl) amine) showed that two units of Zn(dpt) are bridged by oxygen atom of the hydroxo group.
TL;DR: In this paper, both the stretch and bend vibrational spectrum and the intensity of infrared transitions in a tetrahedral molecule are studied in a U(2) algebraic model, where the spurious states in the model Hamiltonian and the wavefunctions are exactly removed.
TL;DR: In this paper, trinuclear and tetranuclear aluminum compounds were obtained from the reaction of bis(diethylamino dimethylaluminum) and the tripodal ligands containing N, S, O and N, O donor atoms.
Abstract: Trinuclear and tetranuclear aluminum compounds were obtained from the reaction of bis(diethylamino dimethylaluminum) and the tripodal ligands containing N, S, O and N, O donor atoms. The single-crystal X-ray diffraction study of the novel tetranuclear compound indicates that the central aluminum atom is in octahedral geometry while the peripheral aluminum atoms assume tetrahedral geometry.
TL;DR: In this paper, highly excited stretching vibrational energy levels and the intensities of infrared transitions in tetrahedral molecules are studied in a U(2) algebraic model and applications to silane and silicon tetrafluoride are presented, with smaller standard deviations than those of other models.
Abstract: The highly excited stretching vibrational energy levels and the intensities of infrared transitions in tetrahedral molecules are studied in a U(2) algebraic model Its applications to silane and silicon tetrafluoride are presented, with smaller standard deviations than those of other models
TL;DR: In this paper, the L-furanose ring adopts a C4-endo-envelope pucker, with C4 displaced 0.544 (3) A from the mean plane of the remaining four atoms.
Abstract: In the title compound, [Sn(C 6 H 5 ) 3 (C 8 H] 3 O 4 )], the L-furanose ring adopts a C4-endo-envelope pucker, with C4 displaced 0.544 (3) A from the mean plane of the remaining four atoms. The isopropylidene ring adopts a C6-envelope conformation, with C6 displaced -0.439 (3) A from the mean plane of the remaining four atoms. The Ph 3 Sn group has an irregular propeller conformation and the Sn atom has slightly distorted tetrahedral geometry, with Sn-C distances in the range 2.131 (2)-2.150 (2) A and C-Sn-C angles in the range 106.55 (8)-114.27 (8)°.
TL;DR: In this paper, it was shown that the temperature dependencies for the four components of the spin were markedly different and the individual components were anisotropic, particularly for the 5f 0 and 5f 1 orbitals, even though the total spin is isotropic.
TL;DR: In this article, the phenylsulfonyl group is nearly perpendicular to the indole ring system, while the other phenyl ring (of the benzoyloxymethyl substituent) is inclined at an angle of 85.9°.
Abstract: In the title compound, C22H16BrNO4S, the phenylsulfonyl group is nearly perpendicular [94.7 (1)°] to the indole ring system, while the other phenyl ring (of the benzoyloxymethyl substituent) is inclined at an angle of 85.9 (2)° to it. The two phenyl rings are inclined at an angle of 112.9 (3) ° with respect to one another. The geometry around the S atom is distorted from the ideal tetrahedral geometry. This is evident from the deviations of the values of the bond angles around sulfur from 108.8°.
TL;DR: In this article, the mass dependence of the local vibrational frequency of a cubic zinc-blende semiconductor was studied in the rigid-cage model and the molecular model, where the four nearest neighbors of the magnetic ion are allowed to move and the LVM then behaves as the Φ5 mode of a MX4 tetrahedral molecule.
TL;DR: The longest Si-N bond is the longest among those found in Me 3 SiN imidazole fragments in the literature as discussed by the authors, and the protonated N atom forms a hydrogen bond to the Br- ion, and one further contact less than 3 A from the Br ion to an aromatic H atom can be found.
Abstract: The title compound [1-(trimethylsilyl)imidazolium bromide, C 6 H 13 N 2 Si + .Br - ] exhibits a 'tetracoordinated' Si centre with bond angles deviating from ideal tetrahedral geometry. The Si-N bond is the longest among those found in Me 3 SiN imidazole fragments in the literature. The protonated N atom forms a hydrogen bond to the Br - ion, and one further contact less than 3 A from the Br - ion to an aromatic H atom can be found.
TL;DR: In this paper, an anharmonically coupled local mode model is used to study highly excited stretching vibrational spectra and intensities of infrared transition in a tetrahedral molecule.
Abstract: An anharmonically coupled local mode model is used to study highly excited stretching vibrational spectra and intensities of infrared transition in a tetrahedral molecule. This model is successfully applied to silane and silicon tetrafluoride.
TL;DR: The crystal and molecular structure of triclinic trimethylstannane has been determined at room temperature as discussed by the authors using a full-matrix least-squares procedure on F to final R = 0.049 using 3736 reflections with I > 3.0σ(I).
Abstract: The crystal and molecular structure of {8-[2-(6-methoxy-2-naphthyl)-1-ethynyl]-1-naphthyl}-trimethylstannane, [Me3Sn(C 10 H 6 C=CC 10 H 6 OMe)], C 26 H 24 OSn, has been determined at room temperature. The colorless crystals are triclinic, space group P1 with unit cell dimensions a = 9.489(1) A, b = 16.931(4) A, c = 7.174(2) A, α - 97.61(2)°, β = 106.58(1) C , y = 94.76(2)°, Z = 2 and D x = 1.441 Mg m -3 . The structure was refined by a full-matrix least-squares procedure on F to final R = 0.049 using 3736 reflections with I > 3.0σ(I). The tin center exists in a distorted tetrahedral geometry defined by four carbon atoms with Sn-C in the range 2.137(6)A to 2.168(5) A. Steric hindrance in the molecule, indicated by a close Sn... C≡C contact of 3.192(5) A, is responsible for the major distortions from the ideal geometry.
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TL;DR: In this paper, highly excited stretching vibrational energy levels and the intensities of infrared transitions in tetrahedral molecules are studied in a U(2) algebraic model with smaller standard deviations than those of other models.
Abstract: The highly excited stretching vibrational energy levels and the intensities of infrared transitions in tetrahedral molecules are studied in a U(2) algebraic model. Its applications to silane and silicon tetrafluoride are presented with smaller standard deviations than those of other models.