Kristallstruktur,Schwingungsspektren und Normalkoordinatenanalyse von K2[IrCl5(NH3)]

Crystal Structure, Vibrational Spectra, and Normal Coordinate Analysis of K₂[IrCl₅(NH₃)] The X-ray structure determination of K₂[IrCl₅(NH₃)] (orthorhombic, space group Pnma, a = 13.426(4), b = 10.015(2), c = 6.8717(7) Å, Z = 4) revealed the C_s point symmetry of the complex anion [IrCl₅(NH₃)]^2? (Ir? Cl = 2.337–2.365, Ir? N = 2.067(10); N? H = 0.73–0.79 Å). Using the molecular parameters the IR and Raman spectra are assigned by normal coordinate analysis. The valence force constants are f_d(NH) = 5.88, f_d(IrN) = 2.66, f_d(IrCl) = 1.68 mdyn/Å.     

Synthesis and spectral and structural characterization of a bridging chloropicolinatocopper(II) complex,Cu(C5H4NCOO)Cl

Summary The title complex of copper(II) chloride with picolinic acid was prepared and characterized by spectroscopic and X-ray crystallographic methods. The complex, Cu(C₅H₄NCOO)Cl, crystallizes tetragonal, space group P4₂/n (No. 86),a=976.4(1),c=1499.6(4) pm,N=8;R _w=0.048 for 543 observed MoK diffractometer data. In the structure of the complex two -chloro bridges form only slightly bent Cu₂Cl₂ rings [Cu-Cl=224.2(4) and 275.6(4) pm] with Cu...Cu separation of 359.4(2) pm and Cl...Cl separation of 348.7(5) pm. These edge-sharing copper coordination polyhedra are further linked via the N and O donor atoms of the picolinato anions at Cu-N distances of 199.6(12) pm and Cu-O bond lengths of 195.7(8) and 200.6(10) pm, to form a two-dimensional layer structure in which these layers are arranged along theab plane. Each picolinate anion functions as a tetra-dentate ligand: N(1) and O(2) are coordinated to the same Cu(II) center whereas O(1) is bonded to a neighbouring Cu(II) center. O(2) is further bonded to the latter Cu(II) center at a long Cu-O distance of 256.5(8) pm. The electronic, infrared and Raman spectra of the solid complex are reported and discussed.

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Synthese und spektroskopische und strukturelle Charakterisierung eines verbrückten Chloropicolinatokupfer(II) Komplexes, Cu(C₅H₄NCOO)Cl

Zusammenfassung Der Titelkomplex aus Kupfer(II)chlorid und Picolinsäure wurde dargestellt und mit spektroskopischen und Röntgen-Einkristall-Methoden charakterisiert. Cu(C₅H₄NCOO)Cl kristallisiert tetragonal, Raumgruppe P4₂/n (No. 86),a=976.4(1),c=1499.6(4) pm,N=8;R _w=0.048 für 543 beobachtete Mok-Diffraktometerdaten. In der Kristallstruktur bilden zwei -chloro-Brücken nur wenig gewinkelte Cu₂Cl₂-Ringe aus [Cu-Cl=224.2(4) und 275.6(4) pm], mit Cu...Cu Abständen von 359.4(2) pm und Cl...Cl Abständen von 348.7(5) pm. Die kantenverknüpften Koordinationspolyeder der Kupferatome sind in Richtung derab-Ebene über die N- und O-Donoratome der Picolinat-Anionen [mit Cu-N Abständen von 199.6(12) pm und Cu-O Abständen von 195.7(8) und 200.6(10) pm] zu einer zweidimensionalen Schichtstruktur verknüpft. Jedes Picolinat-Anion fungiert als vierzähniger Ligand: N(1) und O(2) sind zum selben Cu(II)-Zentrum gebunden; O(1) ist zum benachbarten Cu(II)-Zentrum koordiniert, zu dem O(2) einen langen Cu-O-Abstand von 256.5(8) pm ausbildet. Die elektronischen, Infrarot- und Raman-Spektren des Festkörper-Komplexes werden berichtet und diskutiert.

     

A multiconfigurational SCF computational method for the resolution of the vibrational Schrödinger equation in polyatomic molecules

Summary A new variational method for solving the molecular vibration problem is proposed. The so-called VMCSCF method (vibrational multiconfigurational self-consistent field) is based on the super-CI algorithm, previously developed in the framework of electronicab initio calculations. This approach makes direct use of the generalised Brillouin theorem to ensure self-consistency. The method is dedicated to the study of strongly interacting states (vibrational resonances), which are one of the main sources of perturbation in vibrational spectra. The interest of the method to tackle resonance interactions is illustrated by means of test calculations performed on the water and formaldehyde molecules.     

Static and dynamic disorder in organotin compounds: A bis(amido)stannylene coordinated by N,N′-diisopropyl-1,8-diamidonaphthalene

The root-mean-square amplitude of vibration of the tin atom in the bis(amido)stannylene Sn[1,8-(NⁱPr)₂C₁₀H₆] has been determined from temperature-dependent ¹¹⁹Sn Mössbauer effect measurements over the range 98 < T < 225 K and compared with the U_i,j value extracted from a single crystal X-ray diffraction study. The large difference in these values (at 238 K) is associated with the flexibility in the bonding between the Sn center and chelating diamido ligand in this complex.     

Partial Hessian vibrational analysis: the localization of the molecular vibrational energy and entropy

The partial Hessian vibrational analysis (PHVA), in which only a subblock of the Hesssian matrix is diagonalized to yield vibrational frequencies for partially optimized systems, is extended to the calculation of vibrational enthalpy and entropy changes for chemical reactions. The utility of this method is demonstrated for various deprotonation reactions by reproducing full HVA values to within 0.1–0.4 kcal/mol, depending on the number atoms included in the PHVA. When combined with the hybrid effective fragment potential method [Gordon MS, et al. (2001) J Phys Chem A 105:293–307], the PHVA method can provide (harmonic) free-energy changes for localized chemical reactions in very large systems. Received: 21 September 2001 / Accepted: 30 October 2001 / Published online: 22 March 2002     

“Expanded” local mode approach for XY2 (C2v) molecules

For XY₂ (C_2v symmetry) molecules, the local mode method is modified on the basis of a careful analysis of the transformation coefficients l_Nαλ and the properties of the intramolecular potential function, and an expanded local mode approach is derived. It is shown that relationships between known spectroscopic parameters, found in the spectroscopic literature, can be improved. New relationships between the centrifugal distortion coefficients are obtained. It is shown that knowledge of the centrifugal distortion coefficients of the ground vibrational state allows the possibility of predicting values of both the band centres and the spectroscopic parameters of deformational bands, even under conditions of a total absence of initial information on these deformational bands. The prediction possibility of the derived expanded local mode approach is analyzed.     

Vibrational spectrum of 3-methyl and 4-methylpyridine

The assignments of the vibrational spectra of the 3-methyl and 4-methylpyridine molecules have been carried out following the SQMFF methodology (scaled quantum mechanical force field). The theoretical frequencies have been obtained by calculating the RHF/3-21G force field, using the scale factors for pyridine and 2-methylpyridine and are correlated in a satisfactory manner with the frequencies recorded in the IR and Raman of these methyl derivatives.     

Compared performances of the molecular orbital and density functional theories for fragments of biomolecules

As a preliminary to quantum-mechanical studies of nucleic acids, the possibilities of the molecular orbital (MO) method at the MP2 level and of the density functional theory (DFT) have been examined for typical fragments of nucleosides: methanol, tetrahydrofuran, 3-hydroxytetrahydrofuran and uracil. The results obtained from both methods using polarized split-valence basis sets are found to be consistent with each other, except for small but significant differences that are possibly related to the neglect of DFT self-interaction corrections.     

Präparation,Kristallstruktur, Schwingungsspektren und thermische Analyse von Kupfer‐tetrahydrogen‐decaoxo‐diperiodat‐hexahydrat CuH4I2O10·6H2O

On Copper‐tetrahydrogen‐decaoxo‐diperiodate‐hexahydrate CuH₄I₂O₁₀·6H₂O: Crystal Structure, Vibrational Spectroscopy and Thermal Analysis By crystallization from a strongly acidic aqueous solution copper‐tetrahydrogen‐decaoxodiperiodate‐hexahydrate CuH₄I₂O₁₀· 6H₂O has been obtained. In the structure of this compound (S.G. P 2₁/c, Nr.14), Z = 2, a = 1060.2(2) pm, b = 551.1(1) pm, c = 1164.7(2) pm, β = 111, 49(3)°) centrosymmetric [H₄I₂O₁₀]^2— anions in the form of two edge sharing octahedra form layers via hydrogen bonds originating from the acidic, trans‐configurated OH groups of the anions. Raman spectra are given and analyzed with respect to the internal vibrations of the periodate anion. The dehydration of the compound takes place via CuH₄I₂O₁₀·3H₂O and Cu(H₂IO₅)₂ which decomposes at 170 °C to Cu(IO₃)₂.     

A compact model system for electron–phonon calculations in discotic materials

Electron–phonon coupling underlies the unwanted rapid relaxation of electrically excited states in potential organic solar-cell materials. A compact model for the vibrational dynamics of 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) is derived from the combined use of inelastic neutron scattering (INS) spectroscopy and first-principles calculations. Because this model reproduces the essential features of the vibrational dynamics and electronic structure on the aromatic core of HAT6 it can be used as a basis for future calculations of the relaxation mechanisms of the electronically excited states.