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Orientational Disorder (orientational + disorder)
Selected AbstractsOrientational disorder and phase transitions in crystals of dioxofluoromolybdate, (NH4)2MoO2F4ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010Anatoly A. Udovenko Dioxotetrafluoromolybdate, (NH4)2MoO2F4, was synthesized in a single-crystal form and its structures [(I) at 297,K and (II) at 223,K] were determined by X-ray diffraction. Two independent states of a cis -MoO2F4 octahedron are characteristic of static and dynamic disorder in structure (I). The dynamically disordered Mo atom is displaced from the symmetry axis producing four possible orientations of an anion that allow O and F atoms to be identified in separate orientations owing to the inherent differences between the Mo,O and Mo,F bonding. After the phase transition at lower temperature, (I) transforms into the statically disordered structure (II) with three possible orientations of the cis -MoO2F4 octahedron. In this case, it also seemed possible to distinguish between O and F atoms on a local scale. H atoms of two independent NH4 groups in (II) which form bifurcated N,H...F(O) hydrogen bonds were localized. [source] Orientational disorder and phase transitions in crystals of (NH4)2NbOF5ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2008Anatoly A. Udovenko Ammonium oxopentafluoroniobate, (NH4)2NbOF5, was synthesized in a single-crystal form and the structures of its different phases were determined by X-ray diffraction at three temperatures: phase (I) at 297,K, phase (II) at 233,K and phase (III) at 198,K. The distorted [NbOF5]2, octahedra are of similar geometry in all three structures, with the central atom shifted towards the O atom. The structure of (I) is disordered, with three spatial orientations of the [NbOF5]2, octahedron related by a jump rotation around the pseudo-threefold local axis such that the disorder observed is of a dynamic nature. As the temperature decreases, the compound undergoes two phase transitions. The first is accompanied by full anionic ordering and partial ordering of the ammonium groups (phase II). The structure of (III) is completely ordered. The F and O atoms in the structures investigated were identified via the Nb,X (X = O and F) distances. The crystals of all three phases are twinned. [source] Orientational disorder in ,-cobalt(III) sepulchrate trinitrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Andreas Schönleber The crystal structure of ,-(1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane)cobalt(III) trinitrate, [Co(C12H30N8)](NO3)3, consists of a sepulchrate moiety that serves as a macrobicyclic nitrogen cage for the Co3+ cation, which is six-coordinated by N atoms, and three nitrate anions. The Co,sepulchrate group lies on a threefold axis (site symmetry 32), as do two symmetry-related and ordered nitrate groups (site symmetry 3), with which it is connected via N,H...O hydrogen bonds [Co,N = 5.1452,(12),Å]. The third nitrate group is disordered as a result of symmetry requirements around the origin (site symmetry 32), and is further away from the Co,sepulchrate cage [Co,N = 6.3160,(8),Å]. The structure is described by applying orientational disorder over six equivalent orientations for the disordered nitrate group, which is considered as an ideal planar molecule of regular trigonal geometry with its molecular plane rotated out of the ab plane and the molecular centre of gravity slightly shifted away from the origin. This new model for disorder clearly improves a previous crystal structure determination. [source] Orientational disorder in 4-chloronitrobenzeneACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2008Lynne H. Thomas The crystal structure of 4-chloronitrobenzene, C6H4ClNO2, a material that exhibits disorder in the solid state, is re-examined using multiple-temperature single-crystal X-ray diffraction. Our results show a marked improvement on previous crystal structure determinations and our comprehensive multiple temperature measurements help to rationalize the structural anomalies. 4-Chloronitrobenzene exhibits twofold orientational disorder of the NO2/Cl substituents, with the molecule lying across an inversion centre. There is also evidence of large thermal motion, which exists at all temperatures and reflects the presence of significant disorder in this material. The nitro group shows possible libration, with one O atom exhibiting larger thermal motion than the other across the whole temperature range. This is explained by a difference in hydrogen-bonding environment. [source] Orientational disorder of [Mg(H2O)6] octahedra in the novel magnesium selenite hydrate Mg(SeO3)·7.5H2OACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2007Michel Fleck The crystal structure of magnesium selenite 7.5-hydrate, Mg(SeO3)·7.5H2O (space group P63/mmc), is characterized by two crystallographically distinct [Mg(H2O)6]2+ octahedra, one of which is disordered over two different orientations. The selenite groups and water molecules (with partially disordered H atoms) bridge the octahedra via hydrogen bonds. All the atoms are located on special positions, except for one water molecule. [source] The crystal structure of perdeuterated methanol hemiammoniate (CD3OD·0.5ND3) determined from neutron powder diffraction data at 4.2 and 180,KJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010A. D. Fortes The crystal structure of perdeuterated methanol hemiammoniate, CD3OD·0.5ND3, has been solved from neutron powder diffraction data collected at 4.2 and 180,K. The structure is orthorhombic, space group Pn21a (Z = 4), with unit-cell dimensions a = 12.70615,(16), b = 8.84589,(9), c = 4.73876,(4),Å, V = 532.623,(8),Å3 [,calc = 1149.57,(2),kg,m,3] at 4.2,K, and a = 12.90413,(16), b = 8.96975,(8), c = 4.79198,(4),Å, V = 554.656,(7),Å3 [,calc = 1103.90,(1),kg,m,3] at 180,K. The crystal structure was determined by ab initio methods from the powder data; atomic coordinates and isotropic displacement parameters were subsequently refined by the Rietveld method to Rp, 2% at both temperatures. The crystal structure comprises a three-dimensionally hydrogen-bonded network in which the ND3 molecules are tetrahedrally coordinated by the hydroxy moieties of the methanol molecule. This connectivity leads to the formation of zigzag chains of ammonia,hydroxy groups extending along the c axis, formed via N,D···O hydrogen bonds; these chains are cross-linked along the a axis through the hydroxy moiety of the second methanol molecule via N,D···O and O,D···O hydrogen bonds. This `bridging' hydroxy group in turn donates an O,D···N hydrogen bond to ammonia in adjacent chains stacked along the b axis. The methyl deuterons in methanol hemiammoniate, unlike those in methanol monoammoniate, do not participate in hydrogen bonding and reveal evidence of orientational disorder at 180,K. The relative volume change on warming from 4.2 to 180,K, ,V/V, is + 4.14%, which is comparable to, but more nearly isotropic (as determined from the relative change in axial lengths, e.g.,a/a) than, that observed in deuterated methanol monohydrate, and very similar to what is observed in methanol monoammoniate. [source] Observation of orientational disorder in the hexagonal stuffed tridymite Sr0.864Eu0.136Al2O4 by the maximum-entropy methodJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2004H. Yamada The crystal structure of a strontium europium aluminate, Sr0.864Eu0.136Al2O4, with a novel hexagonal form was investigated by a combination of Rietveld analysis and the maximum-entropy method (MEM) with synchrotron X-ray powder diffraction data. The electron density image calculated by the MEM/Rietveld method revealed that the apical oxygen ion in the AlO4 tetrahedron has a broad distribution corresponding to an extraordinarily large atomic displacement parameter. This structure could be expressed by a split-atom model, with which the Rietveld refinement gave Rwp = 2.99% and RB = 4.16%. Subsequently, MEM-based pattern fitting (MPF) decreased the R factors to Rwp = 2.81% and RB = 2.34% and the electron density image clearly showed that the apical oxygen ions of the AlO4 tetrahedra are split over three sites around a threefold axis involving an elongated distribution of the residual O ions along the c axis. These results suggest that AlO4 tetrahedra in Sr0.864Eu0.136Al2O4 are orientationally disordered. [source] Crystal structure and polarized vibrational spectra of 2-bromo-4-nitropyridine N -oxide single crystalJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2002J. Hanuza 2-Bromo-4-nitropyridine N -oxide is orthorhombic, space group Pbca, with eight molecules per unit cell of dimensions a = 5.979(1), b = 9.899(1), c = 23.249(5) Å. The Br ion is nearly coplanar with the pyridine ring, while the two oxygen atoms of the nitro group are displaced above and below the ring by (,0.214 Å) and (+0.053 Å). The hydrogen bond of the type C,H···O links the molecules into pairs around centers of symmetry. These dimers, arranged into layers related by glide planes, are held together solely by contacts of the van der Waals type. The polarized Fourier transform IR and Raman spectra, measured in the regions 30,3500 and 80,3500 cm,1, respectively, are correlated with x-ray structural data. Comparison of the spectrum of the dissolved sample with the spectra obtained from the polycrystalline sample and single crystals shows the attractive character of the intermolecular C,H···O contacts for these molecules. The temperature-dependent IR spectra suggest the presence of orientational disorder at higher temperatures. Copyright © 2002 John Wiley & Sons, Ltd. [source] Excitonic spectra of orientationally disordered molecular aggregatesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2004D. B. Balagurov Abstract We study the Frenkel exciton dynamics in a one-dimensional molecular aggregate with disorder in both the on-site energies and transition dipole moments. Using a tensorial generalization of the coherent-potential approximation, we calculate the linear absorption spectra, the exciton density of states, and the coherence length responsible for the linear optics. In particular, we consider the purely orientational disorder in the transition dipoles, and show that our theory agrees well with the numerical simulations. In addition to features shared by other disordered aggregate models, we show that the strength of orientational disorder affects the anisotropy degree of the optical response with the main components of the optical susceptibility tensor being characterized by nonequal coherence lengths. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Diffuse scattering from large-angle, thermally induced, orientational disorder in molecular crystalsACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2007John Reid Large-angle rotational motion (libration) characteristic of molecular solids has not been properly included in many scattering calculations because of the need to develop scattering theory through small-angle approximations. A simple but effective approach to calculating the influence of large-angle librations on the thermal disorder scattering given by molecular solids is to treat the molecules as independent librators, each in a harmonic potential well, using the mathematics appropriate for large-angle rotations. The resulting probability distribution for angular misorientations is Gaussian and this distribution can be used to smear the molecular form factor, enabling the librational influence on the scattering to be calculated. It is shown how to apply this direct approach quite generally and by way of examples the technique is used with the molecular solids sulfur hexafluoride (SF6), adamantane (C10H16) and buckminsterfullerene (C60). For these materials, the molecular Fourier transform (i.e. the molecular form factor) have been calculated in selected planes in reciprocal space, followed by the separate effects of librational and translational smearing. It is found that the librational smearing produces a large effect on the form factor, particularly at larger scattering vectors, that is not sensitive to approximations in the argument. Additionally, the Debye,Waller effect of vibrational motion is included in the calculations, showing quantitatively the decreasing influence of vibrations on the scattering with increasing scattering vector. Both effects illustrate with pedagogic clarity how different processes modify the basic molecular scattering. [source] Superspace description of the modulated structure of the metal-salt-hybrid Bi7,,,,Ni2Br5,,,2, (, = 1/9)ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2009B. Wahl The compound Bi7,,,,Ni2Br5,,,2, = (Bi3Ni)2[Bi1,,,,Br4]Br1,,2, (, = 1/9) is a sub-bromide of the intermetallic phase Bi3Ni. Its crystal structure contains metallic rods, [Bi3Ni], which are embedded in a salt-like matrix of bromido-bismuthate(III) and bromide anions. The non-stoichiometry originates from the variation of the number n of trans edge-sharing octahedra in the [BinBr4n,+,2](n,+,2), oligomers (3 ,n, 5), as well as from vacancies on the sites of the isolated Br atoms. The simplified structure is described in the orthorhombic space group Cmcm with a = 4.0660,(4), b = 23.305,(3), c = 17.130,(2),Å. It shows a statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vector q = a*/9 + b*/2, the additional weak reflections of the diffraction pattern can be indexed. In the [3,+,1]-dimensional superspace group Pmnm(,½0)000, an ordered structure model is achieved. The modulated crystal structure bears a strong resemblance to the somewhat higher oxidized sub-bromide Bi7,,,,Ni2Br5 (, = 1/9). [source] Monothioindigo, determined by microcrystal structure analysisACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Jürgen Brüning Indigo and thioindigo pigments are used for a wide range of applications. The crystal structure of the mixed compound monothioindigo [systematic name: (E)-2-(3-oxo-2,3-dihydro-1-benzothiophen-2-ylidene)-2,3-dihydro-1H -indol-3-one], C16H9NO2S, has been determined by microcrystal structure analysis from a crystal with a size of just 1 × 2 × 10,µm. The crystal structure of monothioindigo resembles those of indigo and thioindigo. The molecules show orientational disorder, with site-occupation factors of 0.962,(2) and 0.038,(2) for the major and minor disorder components, respectively. The indigo fragment donates an intermolecular hydrogen bond, leading to a criss-cross arrangement of molecules similar to that in indigo, whereas the thioindigo fragment exhibits only van der Waals interactions and molecular stacking, similar to that in thioindigo. [source] Orientational disorder in ,-cobalt(III) sepulchrate trinitrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Andreas Schönleber The crystal structure of ,-(1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane)cobalt(III) trinitrate, [Co(C12H30N8)](NO3)3, consists of a sepulchrate moiety that serves as a macrobicyclic nitrogen cage for the Co3+ cation, which is six-coordinated by N atoms, and three nitrate anions. The Co,sepulchrate group lies on a threefold axis (site symmetry 32), as do two symmetry-related and ordered nitrate groups (site symmetry 3), with which it is connected via N,H...O hydrogen bonds [Co,N = 5.1452,(12),Å]. The third nitrate group is disordered as a result of symmetry requirements around the origin (site symmetry 32), and is further away from the Co,sepulchrate cage [Co,N = 6.3160,(8),Å]. The structure is described by applying orientational disorder over six equivalent orientations for the disordered nitrate group, which is considered as an ideal planar molecule of regular trigonal geometry with its molecular plane rotated out of the ab plane and the molecular centre of gravity slightly shifted away from the origin. This new model for disorder clearly improves a previous crystal structure determination. [source] Sterically shielded pyramidal amino groups in two 4,4,-(arylmethylene)bis(6-allyl-3-chloro-2-methylaniline) derivativesACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2009Maria C. Blanco 4,4,-(Phenylmethylene)bis(6-allyl-3-chloro-2-methylaniline), C27H28Cl2N2, (I), and 4,4,-(2-thienylmethylene)bis(6-allyl-3-chloro-2-methylaniline), C25H26Cl2N2S, (II), adopt similar molecular conformations, although the thienyl group in (II) exhibits orientational disorder over two sets of sites with occupancies of 0.614,(3) and 0.386,(3). The amino groups in both compounds are pyramidal. A single N,H...N hydrogen bond links the molecules of (I) into cyclic centrosymmetric dimers. Molecules of (II) are linked by an ordered C,H...,(arene) hydrogen bond to form cyclic centrosymmetric dimers, and these dimers are linked into statistically interrupted chains by a second C,H...,(arene) hydrogen bond involving a donor in the minor component of the disordered thienyl unit. [source] Bis[S -6-(2,2:6,,2,,-terpyridin-4,-yloxy)hexyl thioacetate]manganese(II) bis(hexafluorophosphate)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Kasper Moth-Poulsen The structure of a manganese(II) complex of terpyridine functionalized with acetylsulfanyl-terminated hexyloxy chains, [Mn(C23H25N3O2S)2](PF6)2, is described. This type of complex is of interest in the study of single-molecule transport properties in open-shell systems. The manganese coordination environment is distorted octahedral but, importantly, with no larger deviations from the idealized geometry than those observed for other metal,terpyridine complexes. The Mn,N bond lengths range from 2.192,(2) to 2.272,(3),Å. The title compound crystallizes with the cation and anions all on general positions, with the hexafluorophosphate anions exhibiting orientational disorder. When compared with other bis-terpyridine complexes, this structure demonstrates that manganese(II) is no more prone to undergo low-symmetry distortions than systems with ligand field stabilization energy contributions. [source] Orientational disorder in 4-chloronitrobenzeneACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2008Lynne H. Thomas The crystal structure of 4-chloronitrobenzene, C6H4ClNO2, a material that exhibits disorder in the solid state, is re-examined using multiple-temperature single-crystal X-ray diffraction. Our results show a marked improvement on previous crystal structure determinations and our comprehensive multiple temperature measurements help to rationalize the structural anomalies. 4-Chloronitrobenzene exhibits twofold orientational disorder of the NO2/Cl substituents, with the molecule lying across an inversion centre. There is also evidence of large thermal motion, which exists at all temperatures and reflects the presence of significant disorder in this material. The nitro group shows possible libration, with one O atom exhibiting larger thermal motion than the other across the whole temperature range. This is explained by a difference in hydrogen-bonding environment. [source] Five symmetrically substituted 2-aryl-3-benzyl-1,3-thiazolidin-4-ones: supramolecular structures in zero, one and two dimensionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2007Wilson Cunico There are no direction-specific interactions between the molecules of 3-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1,3-thiazolidin-4-one, C18H19NO3S, (I); the molecules of 3-(4-nitrobenzyl)-2-(4-nitrophenyl)-1,3-thiazolidin-4-one, C16H13N3O5S, (II), are linked by four independent C,H,O hydrogen bonds into complex chains of fused rings. In 3-(4-methoxybenzyl)-2-(4-methoxyphenyl)-1,3-thiazolidin-4-one, (III), isomeric with (I), the molecules are linked into sheets by a combination of C,H,O and C,H,,(arene) hydrogen bonds, while in 3-(2-nitrobenzyl)-2-(2-nitrophenyl)-1,3-thiazolidin-4-one, (IV), isomeric with (II), the sheets are built from three independent C,H,O hydrogen bonds and one C,H,,(arene) hydrogen bond, and reinforced by an aromatic ,,, stacking interaction. In 3-(2-fluorobenzyl)-2-(2-fluorophenyl)-1,3-thiazolidin-4-one, C16H13F2NOS, (V), where the 2-aryl ring exhibits orientational disorder, the molecules are linked into sheets by a combination of C,H,O and C,H,,(arene) hydrogen bonds, and the sheets are linked in pairs, forming bilayers, by an aromatic ,,, stacking interaction. [source] trans -Chlorobis(ethylenediamine- N,N,)nitrocobalt(III) perchlorateACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2000Shigeru Ohba In the title compound, trans -[CoCl(NO2)(C2H8N2)2]ClO4, there are two independent CoIII complexes with a distorted octahedral coordination, and they show an orientational disorder such that the positions of the nitro and chloro ligands are exchanged. As a result, the averaged structure has inversion centres at the Co atoms. The perchlorate-O atoms are disordered over two sites. [source] Unprecedented Association of [Mo6Bri7YiBra6]3, Cluster Units and [MoIIIBr6]3, Complexes: Synthesis, Crystal Structures, and Properties of the Double Salts Rb3[Mo6Bri7YiBra6](Rb3[MoBr6])3 (Y=Se, Te)CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2006Kaplan Kirakci Abstract The double salts Rb3[Mo6Bri7YiBra6](Rb3[MoBr6])3 (Y=Se, Te) result from the partial disproportionation of the Mo6Br12 octahedral-cluster-based bromide, in the presence of corresponding chalcogenides and RbBr salt (crystal data: Rb12[MoBr6]3[Mo6Bri7TeiBra6] (1), Pmm (No. 221), a=12.1558(2) Å, Z=1, R1=0.028; wR2=0.050; Rb12[MoBr6]3[Mo6Bri7SeiBra6] (2), Pmm, a=12.144(3) Å, Z=1, R1=0.028; wR2=0.050). The structures of 1 and 2 are built up from [MoIIIBr6]3, complexes and [Mo6Bri7YiBra6]3, cluster units characterised by a random distribution of seven bromine and one chalcogen ligands on all the eight inner positions that face cap the Mo6 clusters. Such a distribution implies a static orientational disorder of the [Mo6Bri7YiBra6]3, units around the origin of the unit cell. Close-packed anionic layers based on [MoIIIBr6]3, complexes and [Mo6Bri7YiBra6]3, cluster units are stacked in the sequence ABC. This arrangement leads to very short BraBra intercluster unit distances of 3.252 Å, much lower than the sum of the van der Waals radii (3.70 Å). The trivalent oxidation state of molybdenum in the Mo complexes and 24 valence electrons per Mo6 cluster have been confirmed by magnetic susceptibility measurements. Salts 1 and 2 constitute the first examples of structurally characterised bromides containing discrete [MoIIIBr6]3, complexes obtained by means of solid-state synthesis. [source] | ||||||||||