Structure-composition relations for the partly disordered Hume-Rothery phase Ir7+7deltaZn97-11delta (0.31< or =delta< or =0.58)

The crystal structure, its variation within the homogeneity range and some physical properties of the new zinc-rich, partly disordered phase Ir7+7deltaZn97-11delta (0.31< or =delta< or =0.58) are reported. The structures of three phases with distinct composition were determined by means of single crystal X-ray diffraction. Ir7+7deltaZn97-11delta exhibits a significant homogeneity range, adopts a complex gamma-brass related cubic structure (cF403-406), is stable up to 1201(2) K, and transforms sluggishly below 1048(4) K into a phase with 394 atoms in the monoclinic primitive unit cell. It is a diamagnetic, moderate metallic conductor. Six distinguishable clusters consisting of 22-29 atoms comprise the structure. The clusters are situated about the 16 high symmetry points of the cubic F lattice. The structure can be subdivided into two partial structures, one with constant composition IrZn5 and 192 atoms per unit cell and a second being significantly richer in zinc with variable composition and 211-214 atoms per unit cell. The meandering triply periodic minimal surface of two interpenetrating diamond-like nets separates the compositionally variable from its complementary invariant part. The phase width is coupled with substitutional and positional disorder. A comprehensive analysis of composition-dependent site occupancy factors reveals a linear correlation between the various types of disorder which can be conclusively interpreted in terms of an incoherent intergrowth of distinctive partial structures in variable proportions on a length scale comparable to the size of the approximately 2 nm large unit cell. On the basis of the structural findings we derive the structure chemically meaningful formula Ir7+7delta)Zn97-11delta which quantitatively accounts for the interrelation between substitutional and positional disorder and provides a measure for the homogeneity range in structural terms.     

Structures induced by irradiation of femto-second laser pulse in polymeric materials

We investigated the structures induced by irradiation of near-infrared femto-second laser pulse in various polymer materials; olefin gel, acrylic adhesive, poly(ether sulphone) (PES), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and block copolymers of methyl-methacrylate and ethyl acrylate-butyl acrylate. Line irradiation that was performed by scanning laser spots in polymer bulk formed volcano-like upheaval structures on the surfaces of PES, PMMA, and PC, which have relatively high glass-transition temperatures (T_g's); on the other hand, cave or channel structures on the surfaces of olefin gel and acrylic adhesive have low T_g's. For the block copolymers containing both low and high T_g's, aggregation of the submicron scale deposit was induced in the polymer bulk. The submicron scale deposit may be reproduced structures after photodecomposition or photocrosslinking of polymer-chain components induced by multiphoton excitation with femto-second laser irradiation. This deposit aggregation with a stripelike structure had different optical properties from the un-irradiated region. These structures induced by irradiation of femto-second laser pulse might be applicable for optical devices such as diffraction grating and optical guide. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 537–544, 2002; DOI 10.1002/polb.10111     

Surface studies of tetraalkylammonium bromides and iodides using atomic force microscopy

The surface structures of two series of tetra-n-alkylammonium halides, N(C_xH_2×+1)4I and N(C_xH_2x+1)4 Br have been investigated with atomic force microscopy (AFM) and compared to hexatriacontane (C₃₆H₇₄). The surfaces could be imaged with atomic resolution. The observed primitive, square surface-patterns of tetra-n-butyl chloride and bromide are in good accord with x-ray single-crystal structure. For n > 4, x-ray powder diffraction showed that increasing the alkyl chain-length leads mainly to an appropriate increase of the unit cell along the c-axis, which suggests similar layer structures for all long-chain salts beyond the butyl homologue. Within the centers of the molecular layers of these crystals reside the halide anions and the quaternary nitrogens. The surfaces accessible for AFM consist of methyl end-groups. As the number of carbon atoms increases beyond four, the surface symmetry changes to the face-centered square patterns characteristic of many paraffins. The chains of the tetraalkyl ammonium salts pack, however, less dense than paraffins. © 1994 John Wiley & Sons, Inc.     

Solvothermal Syntheses,Crystal Structures,and Luminescent Properties of Two Coordination Polymers with Different Interpenetrated Diamond Topology

Two coordination polymers, namely, {[Zn(bpea) (bmp)] · H₂O}_n ( 1 ) and {[Ni(bpea)(bimb)] · DMF}_n ( 2 ) [H₂bpea = biphenylethene‐4,4′‐dicarboxylate, bmp = 1,4‐bis(2‐methylimidazol‐3‐ium‐1‐yl)biphenyl and bimb = 1,4‐bis(1‐imidazol‐yl)‐2,5‐dimethyl benzene], were synthesized under solvothermal conditions with mixed organic ligands. Single crystal X‐ray diffraction reveals that complex 1 features a three‐dimensional (3D) structure with a sixfold interpenetrating dia net. Complex 2 shows a 3D fivefold interpenetrating dia topology. Furthermore, the solid state luminescent properties of complexes 1 and 2 were investigated at room temperature.     

Syntheses,Crystal Structures,and Luminescent Properties of ZnII/CdII Coordination Polymers with Different Interpenetrating Networks

Zn^II and Cd^II coordination polymers with dicarboxylate and imidazole‐containing ligands, namely, [Cd (2,3‐PDC)(L)]_n ( 1 ) and {[Zn(3,4‐PDC) (L)_0.5] · H₂O}_n ( 2 ), [2,3‐H₂PDC = 2,3‐pyridine dicarboxylate, 3,4‐H₂PDC = 3,4‐pyridine dicarboxylate, and L = 1,4‐bis(2‐methylimidazol‐3‐ium‐1‐yl)biphenyl], were prepared and characterized by elemental analysis, IR spectroscopy, and X‐ray diffraction. Complex 1 shows a three‐dimensional (3D) structure with threefold interpenetrating diamond topology. Complex 2 features a 3D framework with twofold interpenetrating dmc topology. Moreover, the luminescent properties of complexes 1 and 2 were also investigated.     

Pseudopolymorphic Clathrate Structures Formed by an Alicyclic Dialcohol Inclusion Host

Dialcohol host 2,7-dimethyltricyclo[4.3.1.0^3,8]undecane-syn-2,syn-7-diol 1 can form either ellipsoidal clathrate or helical tubulate inclusion compounds where only dispersion forces operate between the hosts and guests. The former (tetragonal space group I4₁/acd), built from two interpenetrating sublattices containing both diol enantiomers, encloses the guests in rugby ball-shaped cavities. The latter (trigonal space group P3₁21 or P3₂21), containing only one diol enantiomer, traps the guests within parallel tubes. Which inclusion type is produced is determined by the guest size and shape and, hence, control is possible over these structures. At room temperature, cyclohexane gives the tetragonal structure, but fluorocyclohexane yields the trigonal structure. Chloroform produces both pseudopolymorphs: the tetragonal form at higher and the trigonal form at lower temperatures. Powder and single-crystal structural X-ray data are reported for these clathrate compounds.     

Complex Phase Behaviour and Structural Transformations of Metal-Organic Frameworks with Mixed Rigid and Flexible Bridging Ligands

Two new heteroleptic metal-organic framework materials show strong adsorption of H₂ and ethanol. [Co₂(L1)(bdc)₂], where L1=N¹,N⁴-bis(4-pyridinylmethyl)-2,5-dimethylbenzene-1,4-diamine and bdc is benzene-1,4-dicarboxylate, has a twofold interpenetrating pillared layer structure with pcu topology. It has a stepped, hysteretic EtOH adsorption that can be related to complicated phase and structural transformation behaviour that occurs on de-solvation and re-solvation, including major conformational changes to the geometry of the flexible L1 ligand. [Co₂(L1)(bpdc)₂], where bpdc=biphenyl-4,4′-dicarboxylate, has a unique six-connected self-catenating framework structure. Solvation changes occur without significant structural change and a partially-hydrolysed material binds its own decomposition products as guests.     

Distinctive MS/MS Fragmentation Pathways of Glycopeptide‐Generated Oxonium Ions Provide Evidence of the Glycan Structure

Post‐translational glycosylation of proteins play key roles in cellular processes and the site‐specific characterisation of glycan structures is critical to understanding these events. Given the challenges regarding identification of glycan isomers, glycoproteomic studies generally rely on the assumption of conserved biosynthetic pathways. However, in a recent study, we found characteristically different HexNAc oxonium ion fragmentation patterns that depend on glycan structure. Such patterns could be used to distinguish between glycopeptide structural isomers. To acquire a mechanistic insight, deuterium‐labelled glycopeptides were prepared and analysed. We found that the HexNAc‐derived m/z 126 and 144 oxonium ions, differing in mass by H₂O, had completely different structures and that high‐mannose N‐glycopeptides generated abundant Hex‐derived oxonium ions. We describe the oxonium ion decomposition mechanisms and the relative abundance of oxonium ions as a function of collision energy for a number of well‐defined glycan structures, which provide important information for future glycoproteomic studies.     

Thermal history and enthalpy relaxation of an interpenetrating network polymer with exceptionally broad relaxation time distribution

Differential scanning calorimetry (DSC) of an interpenetrating network polymer of composition 25% polyurethane–75% poly(methyl methacrylate) shows a slowly increasing heat capacity, instead of the usual glass transition endotherm, whose onset temperature is not clearly discernible. On aging of the polymer at several temperatures between 193 and 333 K, an endothermic peak is observed whose onset is in the vicinity of the respective temperature of aging. The area under these peaks increases with increasing aging time at a fixed temperature. The effects are attributed to a very broad distribution of relaxation times, which may be represented by either a sum of discrete structural relaxation times of local network arrangement or by a nonexponential relaxation function which is equivalent to a distribution of relaxation times. In either view the vitrified state of the polymer can be envisaged as containing local structures whose own T_gs extend over a wide range of temperature. Aging decreases the enthalpy and produces an endothermic region which resembles an increase in C_p on heating because of relaxation of that local structure. The interpretation is supported by simulation of DSC scans in which the distribution of relaxation times is assumed to be exceptionally broad and in which aging introduced at several temperatures over a wide range produces endothermic effects (or regions of DSC scans) qualitatively similar to those observed for the interpenetrating network polymer. © 1994 John Wiley & Sons, Inc.     

Negatively curved graphite and triply periodic minimal surfaces

The Weierstrass representation has been used to construct negatively curved graphite in which atoms rest no a perfect triply periodic minimal surface. By applying the Bonnet transformation on a patch of the D surface decorated with graphite we have been able to construct the Gyroid and P minimal surfaces. Curvatures, densities and lattice parameters have been calculated. It has been found that the maximum Gaussian curvature for our negatively curved structures is less in magnitude than the Gaussian curvature ofC ₆₀. In addition, a new periodic graphitic set with the same topology as the I-WP minimal surface has been obtained by introducing pentagonal and octagonal rings.     

以D-樟脑酸与1，4-二（咪唑-1-基）丁烷为配体构筑的两个配位聚合物的结构与磁性

水热合成了2个以D-樟脑酸（D-H₂cam）与1,4-二（咪唑-1-基）丁烷（1,4-bimb）为配体的配位聚合物：[Co（D-cam）（1,4-bimb）]_n·4nH₂O（1）和[Ni（D-cam）（1,4-bimb）]_n（2）。通过X-射线单晶衍射,元素分析,红外光谱,XRD分析,热重,和磁性分析对其结构进行了表征。测定了这两个聚合物的磁性。结构分析表明,1为P2空间群,其链状结构由氢键作用连接形成二维结构;2为Pna2₁空间群,呈四重穿插的dia网络结构。     

Metal Vacancy Ordering in an Antiperovskite Resulting in Two Modifications of Fe2SeO

Small, red Fe₂SeO single crystals in two modifications were obtained from a CsCl flux. The metastable α‐phase is pseudo‐tetragonal (Cmce, a=16.4492(8) Å, b=11.1392(4) Å, c=11.1392(4) Å), whereas the β‐phase is trigonal (P3₁, a=9.8349(4) Å, c=6.9591(4) Å)) and thermodynamically stable within a narrow temperature range. Both crystal structures were solved from twinned specimens. The enantiomers of the β‐phase appear as racemic mixtures. Selenium and oxygen form two individual interpenetrating primitive cubic lattices, giving a bcc packing. A quasi‐octahedrally coordinated iron atom is found close to the center of each surface of the selenium sublattice. The difference between the α‐ and β‐phases is the distribution of iron at 2/3 of the surfaces. α‐ and β‐Fe₂SeO are comparable with metal‐vacancy‐ordered antiperovskites. Each Fe/O lattice can also be described in terms of vertex‐sharing OFe₄ tetrahedra, with a crystal structure similar to that of an antisilicate. Iron is divalent and has a high‐spin d⁶ (S=2) configuration. The β‐phase exhibits magnetoelectric coupling.     

Molecular orbital studies of Al2F6 and Al2Cl6 using a minimal basis set

Ab initio minimal basis LCAO-SCF molecular orbital (MO ) calculations have been carried out on various structures of the AIF₃ and AlCl₃ dimers. A bridged D_2h structure is found to be the most stable of the structures investigated for Al₂F₆. A similar structure was obtained for Al₂Cl₆ in agreement with the experimental evidence.     

Design of scaffold-like metal-organic coordination polymers based on dinuclear zinc(<Emphasis Type="SmallCaps">II</Emphasis>) carboxylate complexes

Two new scaffold-like metal-organic coordination polymers, [Zn₂ndc₂bpe]·DMF and [Zn₂ndc₂dedpbp] ·4DMF (ndc is 2,6-naphthalenedicarboxylate, bpe is trans-bis(4-pyridyl)ethylene, and dedpbp is 4,4′-diethynyl-4″,4′″-dipyridylbiphenyl), were synthesized by heating stoichiometric amounts of zinc(II) nitrate, H₂ndc, and bpe or dedpbp in DMF. The structures of the polymers were established by X-ray diffraction. Coordination of linear dicarboxylate ligands to zinc cations gives rise to planar square-grid networks, and additional coordination of the bifunctional nitrogen-containing ligands results in the formation of scaffold-like triply interpenetrating structures with a primitive cubic topology. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 219–223, February, 2007.     

First Isolation and Structure Elucidation of GDNT-β-Glu – Tetraether Lipid Fragment from Archaeal Sulfolobus Strains

Due to their special chemical structure, tetraether lipids (TEL) represent essential elements of archaeal membranes, providing these organisms with extraordinary properties. Here we describe the characterization of a newly isolated structural element of the main lipids. The TEL fragment GDNT-β-Glu was isolated from Sulfolobus metallicus and characterized in terms of its chemical structure by NMR- and MS-investigations. The obtained data are dissimilar to analogically derived established structures – in essence, the binding relationships in the polar head group are re-determined and verified. With this work, we provide an important contribution to the structure elucidation of intact TEL also contained in other Sulfolobus strains such as Solfulobus acidocaldarius and Sulfolobus solfataricus.     

A nickel 1-D zigzag chain coordination polymer of 2-pyrazinecarboxylic acid

[Ni(pyza)₂H₂O] _n has been synthesized by hydrothermal reaction of 2-pyrazinecarboxylic acid (Hpyza) and Ni(CH₃COO)₂ ·?4H₂O in the presence of 1,10-phenanthroline and structurally characterized by elemental analysis, IR, UV and single crystal X-ray diffraction. The title complex displays an infinite zigzag chain structure in which each nickel(II) center is coordinated by three nitrogen and three oxygen atoms to generate a NiN₃O₃ octahedral geometry. The existence of hydrogen bond leads to formation of the interpenetrating stacked structure.     

Synthesis,crystal structure and luminescence of a two-dimensional interpenetrating supermolecular complex {[Cd(phen)2(sube)] · 2H2O} n

A coordination polymer {[Cd(phen)₂(sube)]·2H₂O} _n (1) (phen?=?1,10-phenanthroline; H₂sube?=?suberic acid) has been synthesized by reaction of phen and suberic acid with cadmium(II). Elemental analysis, thermal analyses, IR spectra and X-ray crystal structure analysis were carried out to determine the composition and crystal structure of 1. The Cd(II) is six-coordinate in a distorted octahedral configuration. A 2-D interpenetrating framework supramolecular structure was formed by π–π stacking interaction between phen of neighboring chains. Moreover, 1 displayed luminescent properties in the blue range at room temperature.     

Absolute‐structure reports

All the 139 noncentrosymmetric crystal structures published in Acta Crystallographica Section C between January 2011 and November 2012 inclusive have been used as the basis of a detailed study of the reporting of absolute structure. These structure determinations cover a wide range of space groups, chemical composition and resonant‐scattering contribution. Defining A and D as the average and difference of the intensities of Friedel opposites, their level of fit has been examined using 2AD and selected‐D plots. It was found, regardless of the expected resonant‐scattering contribution to Friedel opposites, that the Friedel‐difference intensities are often dominated by random uncertainty and systematic error. An analysis of data collection strategy is provided. It is found that crystal‐structure determinations resulting in a Flack parameter close to 0.5 may not necessarily be from crystals twinned by inversion. Friedif_stat is shown to be a robust estimator of the resonant‐scattering contribution to Friedel opposites, very little affected by the particular space group of a structure nor by the occupation of special positions. There is considerable confusion in the text of papers presenting achiral noncentrosymmetric crystal structures. Recommendations are provided for the optimal way of treating noncentrosymmetric crystal structures for which the experimenter has no interest in determining the absolute structure.<!?tpb=25.7pt>     

Curved graphite and its mathematical transformations

Mathematical transformations for graphite with positive, negative and zero Gaussian curvatures are presented. When the Gaussian curvatureK is zero, we analyse a bending transformation from a planar sheet into a cone. The Bonnet, the Goursat and a mixed transformation are studied for graphitic structures with the same topologies as triply periodic minimal surfaces (K < 0). We have found that using the Kenmotsu equations for surfaces of constant mean curvature it is possible to invert spherical and cylindrical graphite. A bending transformation for surfaces of revolution is also studied; during this transformation the helical arrangement of cylinders changes. All these transformations can give an insight into kinematic processes of curved graphite and into new shapes.     

Charge Transfer and Chemical Hardness along a Substitution Path in Metastable Au‐Sb Alloys

In the present study the synthesis of metastable alloys of the noble metal Au and the semimetal Sb is realized by using high pressure techniques. The influence of Au on bulk Sb is shown experimentally by stepwise substitution. In addition to the effect of the most electronegative noble metal on Pauling's scale in the binary Au‐Sb phases, some ternary compounds with In, Sn, As, and Te in addition to Au and Sb are discussed. The experiments are planned to obtain a better knowledge on the reasons for building up a simple cubic Sb partial lattice, and their crystallographic results are used to construct model structures for new electronic structure calculations from first principles on the metastable π‐phases. Using the LCAO‐CO ansatz and density‐functional methods, we study total energies, band structures, densities of states and charge transfer properties according to Bader's method by integrating zero flux surfaces. Finally, from electronic band structure analysis, the quantities “chemical potential” μ, and “chemical hardness”, η, are derived according to the original ideas of Pearson and Parr and are applied to solid state problems using special points of the Brillouin zones within a band structure approximation for the first time. The results are shown to support the experimental findings about the substitution path within the system Au‐Sb.