Acta Crystallographica Section B-structural Science最新文献

As part of an effort to design more efficient dyes for dye-sensitized solar cells (DSCs), structure-property relationships are established in the world's best-performing chemical series of dyes: 2,2'-bipyridyl-4,4'-carboxylatoruthenium(II) complexes. Statistical analysis, based on crystallographic data from the Cambridge Structural Database, is used to determine common structural features and the effects of structural change to its salient molecular constituents. Also included is the report of two new crystal structures for tris(2,2'-bipyridyl)dichlororuthenium(II)hexahydrate and tris(2,2'-bipyridyl)iron(II)dithiocyanate; these add to this statistical enquiry. Results show that the metal (M) core exhibits a distorted octahedral environment with M-N π-backbonding effects affording the propensity of the metal ion towards oxidation. The same characteristics are observed in iron-based analogues. The role of carboxylic groups in this series of dyes is assessed by comparing complexes which contain or are devoid of COOH groups. Space-group variation and large molecular conformational differences occur when COOH groups are present, while such structural features are very similar in their absence. The nature of the anion is also shown to influence the structure of COOH-containing complexes. These structural findings are corroborated by solution-based UV-vis absorption spectroscopy and DSC device performance tests. The presence of COOH groups in this series of compounds is shown to be mandatory for dye-uptake in TiO(2) in the DSC fabrication process. Throughout this study, results are compared with those of the world's most famous DSC dye, N3 (N719 in its fully protonated form): cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II). Overall, the molecular origins of charge-transfer in these complexes are ascertained. The findings have important implications to the materials discovery of more efficient dyes for DSC technology.

The crystal structure of the inclusion complex of β-cyclodextrin with lipoic acid was determined from laboratory powder diffraction data. Thermogravimetric data was used to estimate the number of water molecules in the crystal structure. Lipoic acid is included in β-cyclodextrin through its primary face with the five-membered ring reaching the center plane of the cyclodextrin cavity and its fatty acid chain adopting a bent conformation. Lipoic acid and β-cyclodextrin form a channel-like packing which is stabilized by guest-host hydrogen bonding and close contacts, host-host intermolecular interactions and hydrogen bonding involving the water molecules.

The incommensurately modulated crystal structures of Ca(0.28)Ba(0.72)Nb(2)O(6) (CBN28) and Ce(0.02)Ca(0.25)Ba(0.72)Nb(2)O(6) (Ce:CBN28) were refined in the supercentred setting X4bm(AA0,-AA0) of the 3 + 2-dimensional superspace group P4bm(aa½,-aa½). Both compounds are isostructural with a tetragonal tungsten bronze-type structure. The modulation of CBN28 consists of a wavy distribution of Ba and Ca atoms as well as vacancies on the incompletely occupied Me2 site with 15-fold oxygen coordination. The occupational modulation is coupled with a modulation of the atomic displacement parameters and a very weak modulation of the positional parameters of Me2. The surrounding O atoms show strong displacive modulations with amplitudes up to ca 0.2 Å owing to the cooperative tilting of the rigid NbO(6) octahedra. The Me1 site with 12-fold coordination and Nb atoms are hardly affected by the modulations. Only first-order satellites were observed and the modulations are described by first-order harmonics. In Ce:CBN28 cerium appears to be located on both the Me2 and Me1 sites. Wavevectors and structural modulations are only weakly modified upon substitutional incorporation of 0.02 cerium per formula unit of calcium.

A detailed description of the procedures utilized in the non-routine X-ray single-crystal structural determination and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallography how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and atomic positional disorder.

It is evident from the literature that the 122 iron arsenides, XFe(2)As(2) with X = Ca, Sr, Ba or Eu, undergo one or more phase transitions from a higher-temperature paramagnetic tetragonal structure in grey group I4/mmm1' to an antiferromagnetic structure with magnetic space group C(A)mca. Symmetry analysis is used to enumerate the possibilities for the transition (or transitions) between the higher- and lower-symmetry structures, and the results are used as a basis for comment on published experimental results.

The crystal structures of malachite Cu(2)(OH)(2)CO(3) and rosasite (Cu,Zn)(2)(OH)(2)CO(3), though not isotypic, are closely related. A previously proposed approach explaining this relation via a common hypothetical parent structure is elaborated upon on the basis of group-subgroup considerations, leading to the conclusion that the aristotype of malachite and rosasite should crystallize in the space group Pbam (No. 55). An ICSD database search for actual representatives of this aristotype leads to the interesting observation that the structure type of ludwigite (Mg,Fe)(2)FeO(2)BO(3), which is adopted by several natural and synthetic oxide orthoborates M(3)O(2)BO(3), is closely related to the proposed malachite-rosasite aristotype and thus to the malachite-rosasite family of hydroxide carbonates M(2)(OH)(2)CO(3) in general. Relations within both structure families and their analogies are summarized in a joint simplified Bärnighausen tree.

Ab-initio crystal structure analysis of organic materials from electron diffraction data is presented. The data were collected using the automated electron diffraction tomography (ADT) technique. The structure solution and refinement route is first validated on the basis of the known crystal structure of tri-p-benzamide. The same procedure is then applied to solve the previously unknown crystal structure of tetra-p-benzamide. In the crystal structure of tetra-p-benzamide, an unusual hydrogen-bonding scheme is realised; the hydrogen-bonding scheme is, however, in perfect agreement with solid-state NMR data.

The β''-alumina structure is examined in detail and an analysis is presented of the three-dimensional integrity of the lattice. The layer structure that is responsible for the very high sodium conduction rate is the specific focus. Rigid layers that are derived from the cubic spinel structure are interleaved by more open honeycomb pathways where rapid ion diffusion takes place. The three-dimensional rigidity of the spinel block in this structure makes it possible to accurately quantify the conduction layer thickness based only on the hexagonal unit-cell dimensions, as suggested originally by Harbach [(1983), J. Mater. Sci. 18, 2437-2452]. His calculation is tested rigorously against the many single-crystal structure determinations that have been made on the β''-alumina family compounds and excellent correlation is found.

Pyridinium chlorochromate, [C(5)H(5)NH](+)[ClCrO(3)](-) (hereafter referred to as PyClCrO(3)), was studied by X-ray diffraction, differential scanning calorimetry (DSC) and dielectric methods. Studies reveal three reversible phase transitions at 346, 316 and 170 K with the following phase sequence: R ̅3m (I) → R3m (II) → Cm (III) → Cc (IV), c' = 2c. PyClCrO(3) is the first pyridinium salt in which all four phases have been successfully characterized by a single-crystal X-ray diffraction method. Structural results together with dielectric and calorimetric studies allow the classification of the two intermediate phases (II) and (III) as ferroelectric with the Curie point at 346 K, and the lowest phase (IV) as most probably ferroelectric. The ferroelectric hysteresis loop was observed only in phase (III). The high ionic conductivity hindered its observation in phase (II).

An isomer grid of nine fluoro-N-(pyridyl)benzamides (Fxx) (x = para-/meta-/ortho-) has been examined to correlate structural relationships between the experimental crystal structure and ab initio calculations, based on the effect of fluorine (Fx) and pyridine N-atom (x) substitution patterns on molecular conformation. Eight isomers form N-H⋅⋅⋅N hydrogen bonds, and only one (Fom) aggregates via intermolecular N-H⋅⋅⋅O=C interactions exclusively. The Fpm and Fom isomers both crystallize as two polymorphs with Fpm_O (N-H⋅⋅⋅O=C chains, P-syn) and Fpm_N (N-H⋅⋅⋅N chains, P-anti) both in P2(1)/n (Z' = 1) differing by their meta-N atom locations (P-syn, P-anti; N(pyridine) referenced to N-H), whereas the disordered Fom_O is mostly P-syn (Z' = 6) compared with Fom_F (P-anti) (Z' = 1). In the Fxo triad twisted dimers form cyclic R(2)(2)(8) rings via N-H⋅⋅⋅N interactions. Computational modelling and conformational preferences of the isomer grid demonstrate that the solid-state conformations generally conform with the most stable calculated conformations except for the Fxm triad, while calculations of the Fox triad predict the intramolecular N-H⋅⋅⋅F interaction established by spectroscopic and crystallographic data. Comparisons of Fxx with related isomer grids reveal a high degree of similarity in solid-state aggregation and physicochemical properties, while correlation of the melting point behaviour indicates the significance of the substituent position on melting point behaviour rather than the nature of the substituent.