Showing papers on "Tetrahedral molecular geometry published in 1981"
TL;DR: In this article, a cumulant expansion in powers of the angular velocity and rotation operators was used to derive reorientational and angular velocity autocorrelation functions for tetrahedral molecules.
Abstract: Molecular dynamics simulations have been carried out on fluids of tetrahedral molecules for several sets of temperatures and pressures. The results were analysed to give reorientational and angular velocity autocorrelation functions. It was found that these could be related by a cumulant expansion in powers of the angular velocity and rotation operators. This type of analysis is likely to prove simple and useful for relating orientational correlation functions to the angular velocity correlation function in dense fluids where reorientation is hindered.
62 citations
TL;DR: In this paper, the copper(II) complex of the deprotonated form of di-2-pyridylamine has been prepared by treating the ligand with freshly prepared copper (II) hydroxide, and the crystal structure determined.
Abstract: The copper(II) complex of the deprotonated form of di-2-pyridylamine has been prepared by treating the ligand with freshly prepared copper(II) hydroxide, and the crystal structure determined. Crystal data: Monoclinic, space group C2/c, a= 14.691(6), b= 12.256(9), c= 11.945(2)A, β= 124.24(3)°, and Z= 4. The final R value was 0.039 for 1 052 independent, observed reflections. The copper atom environment is pseudo-tetrahedral with a dihedral angle of 58.8° between the two CuN2 ligand planes. It is demonstrated that the observed molecular structure and the ligand field spectra in the literature are in good agreement. The extent of distortion from pure tetrahedral geometry in a series of related copper bis(bidentate ligand) complexes, as estimated from ligand-field spectra, correlates very well with the observed crystallographic dihedral angle values. This structural result is now available for calibration of the electronic and e.s.r. spectral data for small-molecule pseudo-tetrahedral copper(II) complexes and the presumed four-co-ordinated Type I ‘blue’ copper protein sites.
24 citations
TL;DR: An X-ray crystal structure determination showed the gold(I) complex with four methyldiphenylphosphine ligands to have symmetry with all Au-P bond lengths equal and nearly tetrahedral angles as mentioned in this paper.
Abstract: An X-ray crystal structure determination shows the gold(I) complex with four methyldiphenylphosphine ligands to have symmetry with all Au–P bond lengths equal and nearly tetrahedral angles; further, 31P n.m.r. spectroscopy at –80 °C indicates that the nearly tetrahedral species persists in solution.
23 citations
TL;DR: In this article, X-ray crystal-structure determinations of the title anion series have been reported and their anion structures are discussed; the P(CN)2Br2-anion shows the ψ-trigonal-bipyramidal co-ordination expected on the basis of Valence Shell Electron Pair Repulsion Theory.
Abstract: Salts of the title anion series have been prepared with the sodium–[18]crown-6 cation (n= 1 and 2)([18]crown-6 = 1,4,7,10,13,16-hexaoxacyclo-octadecane) or tetra-alkylammonium cations (n= 4) by addition of Br– to P(CN)3 or PBr3, or by Br2 or BrCN oxidation of P(CN)2–. Contrary to this, CN– addition to P(CN)3, in a reductive elimination, gives P(CN)2–. X-Ray crystal-structure determinations of the above mentioned three salts are reported and their anion structures are discussed. The P(CN)2Br2– anion shows the ψ-trigonal-bipyramidal co-ordination expected on the basis of Valence Shell Electron Pair Repulsion Theory (V.S.E.P.R.), P(CN)3Br– has ψ-octahedral co-ordination in a dimeric, bromide double-bridge structure, and PBr4– a structure intermediate between the two. Here the trigonal-bipyramidal co-ordination is distorted towards a tetrahedral geometry. This is in contradiction to V.S.E.P.R. and presumably the result of ligand–ligand repulsion. The structures are of interest as transition-state models of phosphorus(III) nucleophilic substitution.
23 citations
TL;DR: In this paper, the 13 C and 19 F NMR spectra of the nickel, zinc and cobalt complexes of 1,1-difluoro-4-mercapto-4-(2′-thienyl)but-3-en-2-one, 1, 1-1-trifluoromethyl group, 4-(2.5)-naphthyl) but-een-1.
19 citations
TL;DR: In this paper, the crystal and molecular structures of the copper-pyridine complexes [CuL2Br] and [{Cu(LH)Br2}2] have been determined by single-crystal X-ray diffraction techniques, from diffractometer data.
Abstract: The ligand 2-(3,3-dimethyl-2-thiabutyl)pyridine (L) and its protonated cation, 2-(3,3-dimethyl-2-thiabutyl)-pyridinium ion (LH+), have been used to prepare the copper(I) complexes [CuLnBr](n= 1 or 2) and [Cu(LH)X2](X = Cl or Br). Electronic and i.r. spectroscopic data for these complexes are presented, and the chemical relationships between them discussed. The crystal and molecular structures of [CuL2Br] and [{Cu(LH)Br2}2] have been determined by single-crystal X-ray diffraction techniques, from diffractometer data. Crystals of [CuL2Br] are monoclinic, space group P21/n, with a= 16.927(3), b= 8.867(1), c= 15.371(2)A, β= 100.61(1)°, and Z= 4. Crystals of [{Cu(LH)Br2}2] are also monoclinic, space group P21/n, with a= 15.700(3), b= 9.038(3), c= 9.926(2)A, β= 98.66(1)°, and Z= 2. After full-matrix least-squares refinement final R values are 0.066 (for 2 032 observed reflections) and 0.047 (for 1 538 observed reflections) respectively. The complex [CuL2Br] is monomeric, the distorted tetrahedral geometry round the copper atom being completed by a bromide ion [Cu–Br 2.424(2)A], the pyridyl nitrogen and thioether sulphur of a bidentate ligand L [Cu–N 2.109(9), Cu–S 2.357(3)A], and the thioether sulphur of a unidentate ligand L [Cu–S 2.310(3)A]. The complex [{Cu(LH)Br2}2] exists as a centrosymmetric dimer with the distorted tetrahedral copper(I) centres dibromo-bridged [Cu–Br 2.597(1)A]. The two remaining co-ordination positions round each copper are occupied by a terminal bromide ion [Cu–Br 2.363(1)A] and the thioether sulphur [Cu–S 2.276(2)A] of an LH+ cation.
13 citations
TL;DR: The X-ray structure of the disulfide trichlorocuprate of bis[4-N-methylpiperidi-nium] disulfides was determined by diffraction methods as mentioned in this paper.
9 citations
TL;DR: The crystal and molecular structure of (η5-C5H5)Mn(CO)2(η2-C7H8) has been determined at 170 K using single crystal X-ray diffraction as discussed by the authors.
7 citations
TL;DR: In this paper, two compounds [bzpipzn][CuCl4]·0.5H2O (yellow) and [cpl4]-n-benzylpiperazinium dication have been prepared and investigated by means of electronic and vibrational spectra, magnetic moments, and crystal-structure measurements.
Abstract: Two compounds [bzpipzn][CuCl4]·0.5H2O (yellow) and [bzpipzn][CuCl4](green)([bzpipzn]2+=N-benzylpiperazinium dication) have been prepared and investigated by means of electronic and vibrational spectra, magnetic moments, d.s.c., and crystal-structure measurements. The crystal structures were determined by three-dimensional X-ray diffraction. The two compounds crystallize in the space groups P21/a(yellow) and P21(green) with unit-cell dimensions a= 17.015(1), b= 16.977(2), c= 11.377(2)A, β= 97.156(4)°, Z= 8 and a= 12.075 7(3), b= 28.479 8(10), c= 9.925 8(9)A, β= 109.54(1)°, Z= 8, for the yellow and green compounds respectively. The structures have been refined to R 0.036 and 0.067, respectively. The yellow complex consists of two crystallographically independent [CuCl4]2– anions with moderately flattened tetrahedral geometry, two [bzpipzn]2+ cations, and a water molecule of crystallization. The green complex consists of four independent discrete [CuCl4]2– anions, unequally flattened, and four independent [bzpipzn]2+ cations, which bridge the anions through hydrogen bonds involving their N-bonded H atoms. The role of hydrogen bonding in the flattening of the tetrahedral [CuCl4]2– ions is discussed. The spectroscopic and magnetic properties of the complexes are explained in the light of their known crystal structures. The transformation of the yellow form to the green form by heating (quasi-irreversible thermochromism) is also discussed.
5 citations
TL;DR: Using the grand canonical ensemble, series approximations have been obtained to both the thermodynamic properties and order parameters for a bcc lattice gas of hard core tetrahedral molecules as discussed by the authors.
Abstract: Using the grand canonical ensemble, series approximations have been obtained to both the thermodynamic properties and order parameters for a bcc lattice gas of hard‐core tetrahedral molecules. A molecule in the model can occupy a lattice site in either of the two orientations in which the molecular bonds point toward neighboring lattice sites. An analysis of the Pade aproximants to the series indicates an order–disorder transition, which was previously proved to exist, occurs at a number density ρ = 0.44ρ0, a pressure P = 0.83ρ0kT, and an activity z = 1.2, where ρ0 is the number density at closest packing.
4 citations
01 Jan 1981
TL;DR: In this article, a rotational transition among the rotational manifold of the triply degenerate vibration of a tetrahedral molecule has been observed in infrared-microwave double resonance.
Abstract: A tetrahedral molecule has a vibrationally induced dipole moment in its triply degenerate vibrational state [1,2]. This dipole moment allows a pure rotational transition among the rotational manifold of the triply degenerate vibration. Such transitions have been observed in CH4[3], SiH4[4] and GeH4[5] by infrared-microwave double resonance. Because the lasers used in these previous works could not be tuned over a wide frequency range, however, the experiments had to rely upon accidental coincidences of the molecular absorption lines and laser frequencies.