Showing papers on "Tetrahedral molecular geometry published in 1987"
TL;DR: The structure of poplar plastocyanin in the reduced (CuI) state has been determined and refined, using counter data recorded from crystals at pH 3.8 and 7.8, and the trigonal geometry of the Cu atom strongly favours CuI, so that this form of the protein should be redox-inactive.
304 citations
26 citations
TL;DR: In this paper, the stability of registry lattices at monolayer condensation, and triangular tripod-down lattices relative to a denser monolayers packing are treated, and the Novaco-McTague perturbation theory is extended to molecular adsorbates with orientational degrees of freedom.
Abstract: Monolayer solids of CH4, CD4, and CF4 adsorbed on the basal plane surface of graphite are modeled with atom–atom interaction models and quasiharmonic lattice dynamics. Single molecule adsorption, the stability of registry lattices at monolayer condensation, and the stability of triangular tripod‐down lattices relative to a denser monolayer packing are treated. The Novaco–McTague perturbation theory of the modulation of an incommensurate monolayer by the substrate is extended to molecular adsorbates with orientational degrees of freedom. Experimental data for monolayers of tetrahedral molecules on graphite are summarized; the model calculations give a fair account of the data, with some discrepancies in the energies of monolayer condensation.
20 citations
TL;DR: In this article, a molecular orbital model has been elaborated to determine the orbit-lattice coupling coefficients to strains of symmetry E of the orbital triplet states of d5 ions in tetrahedral symmetry.
Abstract: A molecular orbital model has been elaborated to determine the orbit–lattice coupling coefficients to strains of symmetry E of the orbital triplet states of d5 ions in tetrahedral symmetry. The wave functions and energies of the monoelectronic molecular orbitals have been determined for a tetrahedral molecule MnX4 in a crystal and for a slightly distorted molecule of symmetry D2d corresponding to a strain Eθ. It is shown that in D2d symmetry, the splitting of the monoelectronic molecular orbitals e and t2 is due to the variations of the group overlap integrals and the variation of the crystal electrostatic field with respect to their values in cubic symmetry. The orbit–lattice coupling coefficients which are independent of the spin–orbit interactions, are obtained by diagonalizing the Tanabe–Sugano matrices for the orbital triplet states and then using the molecular orbitals in D2d symmetry as zero‐order wave functions in a first‐order perturbation scheme. The proposed model for the orbit–lattice coupling...
16 citations
TL;DR: In this paper, the N-H stretching and H-N-H bending regions of the infrared spectrum of the title compound (ATPB) have been examined with care, and the stretching bands show rotation-like structure that they attribute to rotational motion of NH+4 in a very low barrier.
Abstract: The N–H stretching and H–N–H bending regions of the infrared spectrum of the title compound (ATPB) have been examined with care. The stretching bands show rotation‐like structure that we attribute to rotational motion of NH+4 in a very low barrier. The barrier has the symmetry of a tetrahedral molecule in a tetrahedral site and is characterized by the dimensionless parameter β=1. The J=0 and J=1 levels are below the barrier and the J=2 levels are above it. Slow interconversion of nuclear spin species is seen in keeping with the low barrier model. The spectra of the ATPB with some NH3D+, with a high concentration of K+ and with deuterated phenyl groups have been examined, and show spectra in keeping with the model.
15 citations
TL;DR: In this article, the reaction of [Os6H(CO)16(NCMe)2] with [Pt(C8H12)2 ] with cyclo-octa-1,5-diene was studied.
Abstract: The reaction of [Os6(CO)16(NCMe)2] with [Pt(C8H12)2](C8H12= cyclo-octa-1,5-diene) results in the formation of [Os6Pt2H2(CO)16(µ-C8H10)(C8H12)](1). The geometry of (1) may be derived from that of [Os6(CO)18] by bridging one edge of the central Os tetrahedron with one Pt atom of the dimer unit Pt2(µ-C8H10)(C8H12). One C8H12 group has been dehydrogenated to C8H10 and the two resulting hydride ligands are terminally bound to different metals of the Os6 core. The C8H10 ligand is bound in an η3-ally1 fashion to one Pt atom and by an η2-olefinic bond and σ-alkyl bond to the second Pt atom. Upon heating in toluene, complex (1) rearranges to the known complex [Os6Pt2(CO)16(C8H12)2](3). Complex (3) is without hydride ligands and possesses a geometry of two edge-fused Os tetrahedra, one of which is Pt-bicapped. The complex [Os6H(CO)16(µ-C8H11)](2) was isolated from the reaction of [Os6H(CO)16(NCMe)2] with C8H12. Complex (2) has the bicapped tetrahedral geometry of [Os6(CO)18] with the µ-C8H11 group bridging two Os atoms of the central tetrahedron. The hydride ligand caps a triangulated Os face. This complex reacts with CO to afford the parent cluster [Os6(CO)18].
12 citations
TL;DR: In this article, the ambiguity among parameters of the effective Hamiltonian for tetrahedral XY4 molecules was studied using the contact transformation technique in the presence of three interacting states 0200, 0101, 0002.
Abstract: Ambiguities among parameters of the effective Hamiltonian for the three interacting states 0200, 0101, 0002 of tetrahedral XY4 molecules are studied. Using the contact transformation technique in t...
9 citations
TL;DR: In this paper, the magnetic susceptibilities of NiLX complexes were investigated in terms of the diamagnetic spin-paired ground state and low lying triplet state, and a distorted tetrahedral geometry was indicated for all the complexes except the chloro-complex.
Abstract: Nickel(II) complexes ofN-phenyl 1-2-[1-(2-pyridyl) ethylidene] hydrazinecarbothioamide (HL) of general composition [NiLX] (where X=Cl, Br, OAc or NO3 and L=deprotonated ligand) have been synthesized and characterized by elemental analysis, conductivity measurements, i. r. spectra, electronic spectra and magnetic measurements. The electronic spectra were recorded in Nujol and dimethylformamide (DMF) whereas magnetic susceptibilities were recorded in the range 80–300 K. A distorted tetrahedral geometry is indicated for all the complexes except the chloro-complex. The paramagnetic behaviour of square-planar [NiLCl] is explained in terms of an equilibrium between the diamagnetic spin-paired ground state and low lying triplet state.
8 citations
TL;DR: In this article, a preliminary X-ray crystallographic determination of dithiophosphoric acid derivatives of organogermanium has been made by means of 1 H, 13 C NMR and vibrational spectroscopy and mass spectrometry.
5 citations
TL;DR: In this article, the first two diffraction peaks of CCl4/SnCl4 liquid mixtures were measured using a hard core model in which the effective diameter of the chlorine atoms was evaluated from the Barker-Henderson criterion.
Abstract: Neutron diffraction measurements have been made for CCl4/SnCl4 liquid mixtures. The tetrahedral molecules have different sizes but the scattering from the central atom is identical. The results indicate a systematic effect of the anisotropy on the magnitude of the first two diffraction peaks and are in good agreement with the theoretical predictions obtained by solving the RISM integral equation using a hard core model in which the effective diameter of the chlorine atoms was evaluated from the Barker-Henderson criterion. We also discuss the main features of the interlocking arrangement of these molecules as shown in the various pair correlation functions and the possibility of using a two-fluid model for describing the intermolecular structure factor of these mixtures.
5 citations
TL;DR: Anomalous temperature effects of the ESR spectra were found in copper doped zinc (II)−bis-(histidine) powders as mentioned in this paper, where the phase transitions can be induced by rearrangements of the water molecules coordinated to the copper ions into their regular positions in the zinc lattice.
Abstract: Anomalous temperature effects of the ESR spectra were found in copper doped zinc (II)‐bis‐(histidine) powders. In the L‐histidine complex, reversible transitions between solid‐like and liquid‐like spectra were observed at 8 °C by increasing, and at 0 °C by decreasing temperature. In the mixed L‐histidine–D‐histidine complex, the magnetic parameters of solid‐like spectra change strongly around −20 °C. The anomalies were explained by Jahn–Teller effect stabilized square planar geometry around the doping copper centers in the lattice of zinc complex with tetrahedral geometry. The phase transitions can be induced by rearrangements of the water molecules coordinated to the copper ions into their regular positions in the zinc lattice. This molecular displacement can facilitate either uniaxial rotation or torsional oscillation of the histidine molecules in the respective lattices.
TL;DR: In this paper, the authors proposed a Co( II ) tetrahedral complex composed of two chlorides and two tri n-butyl phosphate (TBP) ligands, which was obtained by removing excess TBP at low pressure and 180 °C.
TL;DR: In this article, a double-decker host skeleton for the inclusion compound [CoHg(SCN)4(H2O)2]n has been obtained, and its crystal and molecular structure has been determined by the X-ray diffraction technique using its single crystal.
Abstract: The title inclusion compound, which has a new-type “double decker” host skeleton, has been obtained, and its crystal and molecular structure has been determined by the X-ray diffraction technique using its single crystal. 2-Pyrrolidone molecules are not directly coordinated to any metal atoms, but are hydrogen-bonded with coordinated water-oxygen atoms in the two-dimensional polymer planes of [CoHg(SCN)4(H2O)2]n. In the complex polymer, each pair of adjacent Hg(4S(SCN) four-coordinated in a tetrahedral geometry) and Co(4N(SCN), 2O(water, trans) six-coordinated in an octahedral geometry) atoms are bridged with a thiocyanate (SCN) ion. Such two types of networks are spread approximately parallel to the (010) plane at 1/4 and 3/4 heights, and the included Lewis base molecule layers are also doubled. Compared with the previously reported single-layer host skeleton of [CoHg(SCN)4(H2O)2]·2L (L=Lewis base), the present one is short in its inter-complex layer distance, in spite of the analogous size of the includ...
TL;DR: In this paper, the e.s. spectra of crystalline powders of Cs2[Zn(N3)4] containing up to 0.2 mol % of either Cu2+ or Co2+ have been studied at Q-(34 GHz) and X-band (9.2 GHz) frequencies at temperatures down to 2 K.
Abstract: The e.s.r. spectra of crystalline powders of Cs2[Zn(N3)4] containing up to 0.2 mol % of either Cu2+ or Co2+ have been studied at Q-(34 GHz) and X-band (9.2 GHz) frequencies at temperatures down to 2 K. Comparison with electronic reflectance spectra at 77 K indicates that in a dehydrated form, the Cu2+ ion occupies the zinc site but with compressed tetrahedral geometry. As crystallized however, the crystals contain water and it is suggested that in this case the Cu2+ co-ordination is trigonal bipyramidal, having one water molecule in the equatorial plane. For Co2+, optical spectra indicate a distorted tetrahedral geometry and in the e.s.r. spectra the major component is consistent with, but not diagnostic of, this. At least two other minor e.s.r. subspectra are also observed.
01 Jan 1987
TL;DR: The blue color of an aqueous solution of cobalt(II) chloride is known to be due to that of the 6-coordinate octahedral hexaaqua cation, [Co(H2O)6]2+ as mentioned in this paper.
Abstract: The pink color of an aqueous solution of cobalt(II) chloride is known to be due to that of the 6-coordinate octahedral hexaaqua cation, [Co(H2O)6]2+. However, anhydrous CoCl2 is blue and its solutions in various organic solvents, such as alcohols or acetone, are also blue. In general, the blue color is ascribed to the formation of tetrahedral 4- coordinate complexes. These are often formed when the Co-L (L: ligand) bond is rather weak and ionic, and the ligand is bulky (hence, interhgand repulsion favors a tetrahedral geometry). For example, the spectral and conductometric studies of a number of investigators (e.g. Katzin, Libuś, Osugi, and their collaborators [14,17,31]) have indicated that the blue neutral species of the composition [Co(Solv)2Cl2] predominates in ethanol and higher alcohols (Solv = a solvent molecule; cf. Chap. B.II).
01 Jan 1987
TL;DR: In this paper, the influence of spherical impurities (Kr atoms) on the orientational states and excitations of the tetrahedral molecules in solid methane was studied. But the experiments were performed at the TOF spectrometer IN5 of the ILL with an energy resolution (FWHM) between 17 and 160 μeV.
Abstract: Rotational spectra have been determined with inelastic neutron scattering for polycrystalline (CH4)1−xKrx mixtures (x ≤ 0.35) at temperatures T = 1.6,…,77 K /1,2/. The measurements were performed at the TOF spectrometer IN5 of the ILL with an energy resolution (FWHM) between 17 and 160 μeV. The aim of the experiment was to study the influence of spherical impurities (Kr atoms) on the orientational states and excitations of the tetrahedral molecules in solid methane. Solid methane can be described in the most simple approximation as a system of electrostatic octopoles with fixed center-of-mass structure (fcc).
TL;DR: In this paper, a preliminary X-ray crystallographic determination of dithiophosphoric acid derivatives of organogermanium has been made by means of 1 H, 13 C NMR and vibrational spectroscopy and mass spectrometry.
Abstract: Organogermanium derivatives of dithiophosphoric acid of general formula R 4 − n Ge[SP(S)(OR′) 2 ] n , where n = 1–3, R, = Me, Ph and R′ = Me, Et, have been prepared and characterized by means of 1 H, 13 C NMR and vibrational spectroscopy and mass spectrometry. The spectroscopic results indicate that the dithiophosphate groups are monodenate and that an approximate tetrahedral geometry about the germanium atom is maintained. This is in part confirmed by a preliminary X-ray crystallographic determination of PhGe[SP(S)(OMe) 2 ] 3 , whose crystals are orthorhombic, space group Pn 2 2 1 a , a 13.674(4), b 14.566(3), c 13.154(3) A, V 26201(1) A 3 and Z = 4 from 1225 observed reflections [1 > 2σ I ].