Structural studies on layered alkylpyridinium iodopalladate networks

The reaction of alkylpyridinium (CnH2n + 1NC5H5, hereafter Cn-Py) iodide salts in aqueous acetonitrile with a preformed palladium iodide precursor afforded two different types of organic-inorganic phases depending on the molar ratio. A 2:1 ratio yielded the phase [Cn-Py]2[PdI4] (3, n = 14, 16), which crystallized in the triclinic crystal system. The X-ray crystal structure of 3, (n = 14), refined in the space group P1 (a = 8.918(3) A, b = 9.894(3) A, c = 29.062(12) A, alpha = 93.51(3) degrees, beta = 94.17(3) degrees, gamma = 115.60(3) degrees, and Z = 2), consists of interdigitated bilayers with a basal spacing of 29.0 A. The aliphatic chains of the cations, which run almost parallel to the stacking direction, are fully stretched between polar planes built on isolated [PdI4]2- anions and cation headgroups. Changing the organic cation to palladium ratio to 1:1 led to a new phase [Cn-Py]2[Pd2I6] (4, n = 14, 16), which crystallizes in the triclinic P1 space group (a = 9.399(4) A, b = 14.264(6) A, c = 29.415(13) A, alpha = 92.11(4) degrees, beta = 90.07(4) degrees, gamma = 104.53(3) degrees, Z = 3 for 4(n = 14); a = 9.417(2) A, b = 14.215(3) A, c = 31.552(6) A, alpha = 87.96(3) degrees, beta = 87.63(3) degrees, gamma = 75.67(3) degrees, Z = 3 for 4(n = 16)). The layered structure is basically of a continuously interdigitated single-layer type, with a bilayer sublattice superimposed. Isolated [Pd2I6]2- anions contribute to the inorganic planes. A high degree of interdigitation and tilting of the aliphatic chains lead to basal spacings of 29.4 and 31.5 A for 4(n = 14) and 4(n = 16), respectively. The [Cn-Py]2[PdI4] and [Cn-Py]2[Pd2I6] phases were characterized by thermal analysis. Mesomorphic behavior was observed only for 3(n = 16), which was confirmed by variable-temperature powder XRD and optical microscopy.     

Formulas for evaluation of expectation values of monoelectric operators with modified gaussian functions

Formulas are presented for the evaluation of the expectation values of various monoelectronic operators. The integrals are based on ?Hermite-Gausian”? or ?Modified Gaussian Functions”? and are expressed in suitable form for a computer programming. It is pointed out that the final expresions are simpler than the analogou omes obtained from the usual Gausian functions and can be written as linear combinations of a few baic integrals.     

Recurrence relations for the evaluation of electron repulsion integrals over spherical Gaussian functions

Recurrence relations are derived for the evaluation of two-electron repulsion integrals (ERIs) over Hermite and spherical Gaussian functions. Through such relations, a generic ERI or ERI derivative may be reduced to “basic” integrals, i.e., true and auxiliary integrals involving only zero angular momentum functions. Extensive use is made of differential operators, in particular, of the spherical tensor gradient ??(?). Spherical Gaussians, being nonseparable in the x, y, and z coordinates, were not included in previous formulations. The advantages of using spherical Gaussians instead of Cartesian or Hermite Gaussians are briefly discussed. © 1993 John Wiley & Sons, Inc.     

Ab initio calculation of some low-lying electronic excited states of methane

The energies of some low-lying electronic excited states of methane are calculated by using wave functions built up in terms of plane waves modulated by multicenter Gaussian factors. The wave functions of the various states are evaluated by a two steps iterative process. In the first step, each excited orbital is determined while keeping all other rigid; in the second, rearrangement effects are introduced. Final results are in good agreement with experimental data and allow to enhance an assignement hypothesis for the first electronic transitions.     

A numerical integration scheme for the evaluation of correlation energy functionals

A numerical integration scheme is presented for three-dimensional integrals occurring in electronic structure calculations, concentrating attention on the evaluation of the correlation energy through a density-functional expression. The scheme is based on the choice of density-based weight functions that naturally partition the space into “atomic” volumes (in which the integration is performed in terms of spherical coordinates) and “diatomic” volumes (in which the integration is performed in terms of confocal elliptical coordinates). Such a choice is justified on the basis of the analytical behavior of the integrand. The attainable accuracy and the required computational effort within the proposed scheme are discussed in detail in a test application on the C₆₀ molecule in the symmetrical configuration. Finally, a comparison with previously proposed schemes is presented. © 1993 John Wiley & Sons, Inc.     

X-ray diffraction study of the smectic mesophase of some azobenzene-containing polyacrylates

Abstract

An X-ray study is performed on powder specimens and on stretched oriented fibres of two liquid crystalline polyacrylates containing the azobenzene mesogenic unit with either a 4′-n-pentyloxy (sample 1–4) or 4′-n-hexyloxy (sample 1–5) substituent. The X-ray diffraction patterns of both samples showed the presence of a bilayer smectic C mesophase with the mesogneic groups tilted by an angle β ～ 45° (1–4) or β ～ 38° (1–5) with respect to the layer normal. The electron density profile p(z) along the direction normal to the smectic layers was calculated by Fourier inversion and possible structural models of the smectic mesophase are discussed. A partial interdigitation of the terminal alkyloxy substituents appears to occur.     

Thermotropic mesomorphism in penta- and hepta-coordinated metal complexes

New Ni(II) and UO₂(II) metallomesogens obtained from mesomorphic N,N'-salicyliden(3,3'-diamine-N-methyldipropylamine) ligands containing a pentadentate N₃O₂ chelating cavity and bearing two or four lateral substituents, are isolated and fully characterized. Some of the synthesized nickel and dioxouranium complexes show a SmC mesophase. To the best of our knowledge, these species are the first pentacoordinated Ni(II) and heptacoordinated UO₂(II) metallomesogens to be reported.     

An X-ray diffraction study of the different nematic mesophases of liquid-crystalline poly(urethane-ester)s

An x-ray investigation on powder specimens and stretched oriented fibers of poly(urethaneester)s TDI-CmCn, derived from various mesogenic alkylene di[4-(ω-hydroxyalkyloxy-4-oxybenzoyl)oxybenzoate]s (CmCn; m = 2, 4, or 6, and n = 4, 6, 8, or 10) and 2, 4-toluenediisocyanate (TDI), is reported. Evidence is provided for the formation of two different nematic mesophases in the polymers, namely a cybotactic nematic and a conventional nematic mesophase. Whereas samples TDI-C2C6, TDI-C6C4, and TDI-C6C10 formed one cybotactic nematic mesophase, samples TDI-C4C6, TDI-C6C6, and TDI-C6C8 exhibited both cybotactic nematic and conventional nematic mesophases in a sequence with increasing temperature, which were connected by a first-order transition. The analysis of the various features of the small-angle x-ray diffraction patterns indicates that two structural arrangements, namely smectic C-like and conventional nematic structures, coexist inside the cybotactic nematic mesophase of these poly(urethane-ester)s. © 1995 John Wiley & Sons, Inc.     

Phase transitions and structural studies of new compounds belonging to homologous series

Summary Since few years, we have been studying the synthesis and the physical properties of homologous series with the following general structure: CH₃-(CH₂) _m -CO-C₆H₄-N=N-C₆H₄-O-CO-(CH₂) _n -CH₃, withn ranging from zero to sixteen. In this work we report the results of the diffractometric study of the liquid crystalline series 4-butanoyl-4′-n-alkanoyloxy azobenzenes (m=2) and 4-pentanoyl-4′-n-alkanoyloxy azobenzenes (m=3): in particular all the ordered smectic phases of them=3 series have been identified and some structural parameters are discussed. Considering the smecticA phase, we have determined the layer thickness as a function ofn for both them=2 andm=3 series: the results have been compared with those of the homologous series withm=0 andm=1. In particular an appreciable decrease of the thickness increment due to a CH₂ group and a corresponding increase of the thickness of aromatic sublayer were observed: these results are interpreted by means of a proposed model.

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Riassunto Da alcuni anni si stanno studiando la sintesi e le proprietà fisiche di alcune serie omologhe aventi la seguente struttura generale: CH₃-(CH₂) _m -CO-C₆H₄-N=N-C₆H₄-O-CO-(CH₂) _n -CH₃, conn variabile da zero a sedici. In questo lavoro vengono descritti i risultati di uno studio diffrattometrico della serie liquido cristallina dei 4-butanoil-4′-n-alkanoilossi azobenzeni (m=2) e dei 4-pentanoil-4′-n-alkanoilossi azobenzeni (m=3): in particolare le fasi smettiche ordinate della seriem=3 sono state identificate e ne vengono discussi i parametri strutturali. Per quanto riguarda la fase smetticaA, abbiamo misurato lo spessore degli strati in funzione din sia nella seriem=2 chem=3: i risultati ottenuti sono stati confrontati con quelli delle serie omologhe conm=0 em=1. In particolare sono state osservate un'apprezzabile diminuzione dell'incremento dello spessore dovuto al gruppo CH₂ ed un corrispondente aumento dello spessore del substrato aromatico: il modello che viene proposto permette di interpretare tali fenomeni.

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Резюме В течение нескольких лет мы исследовали синтез и физические свойства гомологических рядов со следующей структурой: CH₃-(CH₂) _m -CO-C₆H₄-N=N-C₆H₄-O-CO-(CH₂) _n -CH₃, гдеn находится в области от 0 до 16. В этой работе мы приводим результаты дифрактометрических исследований жидких кристаллических соединений сm=2 сm=3, в частности, индентифицируются все упорядоченные смектические фазы дляm=3 и обсуждаются некоторые структурные параметры. Рассчитывая смектическуюА фазу, мы определяем зависимость толщины слоя от для рядов сm=2 и сm=3. Полученные результаты сравниваются с результатами для гомологических рядов сm=0 и сm=1. В частности, наблюдается заметное уменьшение приращения толщины, обусловленное группой CH₂, и соответствующее увеличение толщины ароматического подслоя. Полученные результаты интерпретиружтся с помощью предложенной модели.

     

X-ray diffraction study of the smectic mesophase of some azobenzene-containing polyacrylates

An X-ray study is performed on powder specimens and on stretched oriented fibres of two liquid crystalline polyacrylates containing the azobenzene mesogenic unit with either a 4'-n-pentyloxy (sample 1-4) or 4'-n-hexyloxy (sample 1-5) substituent. The X-ray diffraction patterns of both samples showed the presence of a bilayer smectic C mesophase with the mesogneic groups tilted by an angle β ∼ 45° (1-4) or β ∼ 38° (1-5) with respect to the layer normal. The electron density profile p(z) along the direction normal to the smectic layers was calculated by Fourier inversion and possible structural models of the smectic mesophase are discussed. A partial interdigitation of the terminal alkyloxy substituents appears to occur.