Eight new silver(I) trifluoroacetate complexes based on a series of designed ligands, each featuring an alicyclic ring with enediyne functionality, have been synthesized and characterized by single-crystal X-ray diffraction. Each ethynide terminal is inserted into an Agn(n= 4–5) basket, leading to the generation of coordination chain or layer structures, but the well shielded ethenyl group does not take part in silver-olefin bonding. Variation in ring size of the alicycles is shown to influence the construction of the organosilver(I) coordination networks, which are consolidated by weak intermolecular interactions in the crystal structures. The effect of adding ancillaryN-donor ligands to the reaction system on the coordination and supramolecular network assembly is also investigated.
Oxidation of diiodoethylenedithiotetrathiafulvalene (EDT-TTF-I2), C8H4I2S6, with the strong oxidizer tetrafluorotetracyanoquinodimethane (TCNQF4), C12F4N4, affords, depending on the crystallization solvent, two polymorphs of the 2:1 charge-transfer salt (EDT-TTF-I2)2(TCNQF4), represented as D2A. In both salts, the TCNQF4 is reduced to the radical anion state, and is associated through short C-I...NC halogen bonds to two EDT-TTF-I2 molecules. The two polymorphs differ in the solid-state association of these trimeric D-A-D motifs. In polymorph (I) the trimeric motif is located on an inversion centre, and hence both EDT-TTF-I2 molecules have +0.5 charge. Together with segregation of the TTF and TCNQ derivatives into stacks, this leads to a charge-transfer salt with high conductivity. In polymorph (II) two crystallographically independent EDT-TTF-I2 molecules bear different charges, close to 0 and +1, as deduced from an established correlation between intramolecular bond lengths and charge. Overlap interactions between the halogen-bonded D(0)-A-∙D+∙ motifs give rise, in a perpendicular direction, to diamagnetic A2(2-) and D(0)-D2(2+)-D(0) entities, where the radical species are paired into the bonding combination of respectively the acceptor LUMOs and donor HOMOs. The strikingly different solid-state organization of the halogen-bonded D-A-D motifs provides an illustrative example of two modes of face-to-face interaction between π-type radicals, into either delocalized, uniform chains with partial charge transfer and conducting behaviour, or localized association of radicals into face-to-face A2(2-) and D2(2+) dyads.
Racemic 2,4,6,8-tetracarbomethoxybicyclo[3.3.0]octa-2,6-diene-3,7-diol, C16H18O10 (1), was known previously to yield two solvent-free polymorphs and also a clathrate inclusion crystal form. Crystallization of (1) yields two inclusion compounds containing tetrahydrofuran (THF): (1)4·THF is obtained from a mixture of THF and methanol, whereas (1)2·THF is obtained from pure THF. The X-ray crystal structures reveal that the two compounds are extremely similar and that their host arrangements are essentially identical. They differ, however, in the proportion, orientation and host-guest interaction of the included THF molecules. The disordered guest molecules in (1)4·THF are oriented along the guest channel direction, whereas in (1)2·THF they lie across the channel. This unusual solvent-guest control of inclusion structures has implications relating to the formation of polymorphic structures and other competing crystal forms.
The creation of ternary multi-component crystals through the introduction of 18-crown-6 to direct the hydrogen-bonding motifs of the other molecular components was investigated for 3,5-dinitrobenzoic acid (3,5-dnba) with 4-aminobenzoic acid (4-aba). The creation of a binary complex between 18-crown-6 and 4-aba (C12H24O6·2C7H7NO2)2and a ternary salt between 3,5-dnba, 18-crown-6 and 4-aba (C12H24O6·C7H8NO2+·C7H3N2O6−·C7H4N2O6) were confirmed by single-crystal structure determination. In both structures, the amino molecules bind to the crown ether through N—H...O hydrogen bonds, leaving available only a single O atom site on the crown with restricted geometry to potentially accept a hydrogen bond from 3,5-dnba. While 3,5-dnba and 4-aba form a binary co-crystal containing neutral molecules, the shape-selective nature of 18-crown-6 preferentially binds protonated amino molecules, thereby leading to the formation of the ternary salt, despite the predicted low concentration of the protonated species in the crystallizing solution. Thus, through the choice of crown ether it may be possible to control both location and nature of the available bonding sites for the designed creation of ternary crystals.
This paper presents a study on orientation domains in the vacancy-ordered titanium monoxide TiOx. Transmission electron microscopy analysis revealed the co-existence of 12 possible TiOx monoclinic domain variants, which are induced by the cubic-to-monoclinic phase transition attributed to the Ti and O vacancy ordering. These 12 monoclinic domain variants which are predicted by group theory might be randomly arranged. Furthermore, several hours of electron beam irradiation can lead to the vacancy ordering-disordering transition (i.e. monoclinic-to-cubic phase transformation) in TiOx. Our results shed light on the structural characteristics in TiOx nanostructures and thus contribute to the fabrication and design of the related nanostructures.
The structure-factor phase method of convergent-beam electron diffraction (CBED) has been widely applied as an effective tool in determining the polarity of binary compound materials, for example, the typical sphalerite material, GaAs. However, its validity on other polar materials is still unknown. In this paper we extensively investigated its potential applicability onto 11 AB-type semiconductors by dynamical simulations of CBED. Two key factors during the simulation, the difference between A and B atomic numbers and the sample thickness, are discussed in detail. It was found that this method is efficient to determine the polarity for a sphalerite structure under certain conditions, and, reversely, limited to determine the polarity for a wurtzite structure even though it is very similar to the sphalerite structure.
The structure of low-temperature grown GaAs with equidistant δ-layers of Sb and P was studied by analysis of the X-ray curves, which was supported by optical absorption measurements and transmission electron microscopy. The simultaneous fitting of the X-ray reflectivity curve and diffraction ones for GaAs (004) and GaAs (115) crystallographic planes provided reliable information about the period of δ-layer superlattice, thickness of the Sb and P δ-layers, and amount of excess As. Variation of these parameters was documented when excess As precipitated into As nanoinclusions upon annealing. The Sb and P δ-layers impact differently on the As precipitation processes in low-temperature grown GaAs. The combination of Sb and P δ-layers appears to be an effective tool for spatial patterning of the nanoinclusion array and prevention of the defect formation under annealing.
Monocationic acetamidate-bridged dinuclear units are two-dimensionally connected by axially coordinating group 6 oxometallate ions in the structures [{M2(acam)4}2(M'O4)] (M = Rh, Ru; M' = Cr, Mo, W; Hacam = acetamide). In these sheet structures, dinuclear units are connected to each other by NH...O hydrogen bonds. The sheets are also connected with NH...O hydrogen bonds. Amidate-bridged dirhodium units that have bulkier alkyl groups reacted with CrO4(2-) or MoO4(2-) give three-dimensional diamondoid structures [{Rh2(pram)4}2(CrO4)] · 1.08H2O, [{Rh2(pram)4}2(MoO4)] · 2.44H2O and [{Rh2(buam)4}2(MoO4)] (Hpram = propionamide; Hbuam = butyramide). In these structures the NH group of the amidate ligands hydrogen bonds with O atoms in metallate ions.
Kermesite, Sb2S2O, is a desymmetrized order-disorder (OD) structure of layers. Two data sets were recorded using twinned crystals from Pezinok, Slovakia (named as Pz21, Pz24). The primitive unit cell is triclinic, P1, Z = 4, cell parameters are a = 8.1416 (3), b = 10.6968 (3), c = 5.7835 (2) Å, α = 102.758 (3), β = 110.657 (3), γ = 101.020 (3)°, R(obs) = 0.0243 (Pz21), and a = 8.1372 (2), b = 10.6969 (2), c = 5.7840 (1) Å, α = 102.787 (2), β = 110.606 (2), γ = 100.983 (2)°, R(obs) = 0.0321 (Pz24). The structure can also be described in the non-standard pseudo-monoclinic octuple (Z = 32), F-centered (Kupčík) cell with extra points in 1/4,1/4,0; 1/4,3/4,1/2; 3/4,1/4,1/2; 3/4,3/4,0, with parameters a = 21.6466 (9), b = 8.1416 (3), c = 20.3824 (9) Å, α = 90.079 (4), β = 101.985 (5), γ = 89.948 (4)° (Pz21), and a = 21.6558 (5), b = 8.1372 (2), c = 20.3859 (8) Å, α = 90.028 (3), β = 101.994 (3), γ = 89.986 (2)° (Pz24). The structure is built of layers parallel to the bc plane, stacked along the a vector of the octuple cell, composed of ribbons parallel to the b vector: (i) ribbon of two strips of SbO5 flattened quadrangular pyramids, sharing apical edges; (ii) ribbon of edge-sharing corrugated lozenges SbO3S. Basal S atoms of pyramids share corners of lozenges. Sb atoms are displaced out of coordination polyhedra into the inter-layer space. The OD layer comprises adjacent halves of the structure building layers. The layer group is A(1)2/m1, the protocell is defined by b, c, (a/4)sin β. The MDO1 (4A) polytype is generated by repetition of the t(1,1/4,0) [or alternatively t(1,-1/4,0)] translation. The co-existence of two kinds of domains give rise to the twinning. The twin operation is 2[010], twin index 2. The total continuation of [. a2 .] generates the MDO2 (2M) polytype, space group A12/a1. Simulated and real diffraction patterns are presented. The important values (edges, angles) and displacements of atoms due to the desymmetrization were evaluated. The comparison with structures of stibnite, bismuthinite and aikinite is added.
The charge-flipping algorithm (CFA) is a member of the diverse family of dual-space iterative phasing algorithms. These algorithms use alternating modifications in direct and reciprocal space to find a solution to the phase problem. The current state-of-the-art CFA is reviewed and it is put in the context of related dual-space algorithms with relevance for crystallography. The CFA has found applications in many crystallographic problems. The principal applications in various fields are described with sections devoted to routine structure solution, the solution of complex structures from powder diffraction data, the solution of incommensurately modulated crystals and quasicrystals, macromolecular crystallography and single-particle imaging.
As a result of the high-temperature and high-pressure treatment of graphite we obtained a powder containing diamond and lonsdaleite. The structure and properties of the powder were studied by transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). It was found that the synthesized material contains not only diamond nanoparticles, but also some relatively large (up to several nanometers) fragments of lonsdaleite. 4H and 6H polytypes were found in some of the diamond particles. Incoherent twin boundaries were observed in the diamond particle containing fragments of lonsdaleite.
During the systematic investigation of the tin-rich side of the Tb-Sn binary system temperatures of non-variant transformations were established. The crystal structure of βTb3Sn7 was determined for the first time from single-crystal diffraction data. Parameters of the unit cell have been determined previously by Manfrinetti & Palenzona [(1993), J. Alloys Compd. 201, 43-47], but the structure was not solved until now. The compound belongs to a new structure type with space group Pmmm. The unit cell contains two split positions: Sn7 (Wyckoff 1a), Sn7A (Wyckoff 2q) and Sn8 (Wyckoff 1d), Sn8A (Wyckoff 2s). Structures of both α- and β-modifications of Tb3Sn7 can be described as close packing of the coordination polyhedra of Tb atoms. In turn these polyhedra can be constructed of fragments of simple AuCu3 and CsCl types.
Tris(N,N-dimethyldithiocarbamato-S,S')antimony(III) has been isolated as a dimer in acetonitrile. Single-crystal X-ray analysis shows that the molecule possesses both Sb···S and C-H···S interactions, which results in a supramolecular association in the absence of hydrogen-bonding functionality on the R group. The co-existence in the title compound of such interactions is a unique character of known dimeric antimony(III) alkyl and/or aryl dithiocarbamate complexes. The literature reveals that the species where the alkyl and/or aryl dithiocarbamates carry the following groups: R = methyl (chloroform solvated), ethyl, n-propyl, pyrrolidine, morpholine, piperidine, azepane, benzyl, methylphenyl, are not capable of forming significant hydrogen-bonding interactions. However, either Sb···S or C-H···S intermolecular interactions dominate between two centrosymmetrically related molecules leading to a supramolecular aggregation. In the species where the R group carries hydrogen-bonding functionality, i.e. 2-hydroxylethyl, the C-H···S interactions are subverted by O-H···O hydrogen bonding. In addition, the title compound does not have steric hindrance or any hydrogen-bonding group but is stabilized with the co-existence of Sb···S and C-H···S interactions. Analysis of the secondary interactions of a series of analogues previously reported reveals that steric bulk is unnecessary for the mitigation of Sb···S interactions and for the establishment of C-H···S secondary bonding.
The sequence of hexagonal ordered distributions of trivalent cations that are possible in the octahedral layer of layered double hydroxides is clarified, including the link between the composition and the supercell a parameter. A plausible explanation is provided for the observed variation in the lower solid-solution limit.
The high-temperature clinoenstatite (HT-CEn) is one of the most important MgSiO3 pyroxene polymorphs, but the details of its structure and stability have been uncertain. The single crystal of the C2/c HT-CEn end-member is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 1173-2173 K. The single-crystal X-ray diffraction analysis shows unusual bonding distances and static disorder of the atoms frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 175° for HT-CEn. The chain angle for HP-CEn is substantially smaller (135°), but the angle for L-CEn is in the opposite direction at -160° (= 200°). The degree of kinking increases by being curved by more than 180° for the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists at the point of the continuity. It is suggested that the reason why a structure can be quenched under ambient conditions is as follows: the present HT-CEn single crystal has been formed by the isosymmetric phase transition from the high-pressure C2/c clinoenstatite (HP-CEn). The presence of HT-CEn from HP-CEn in natural rocks is an indicator of quenching history, which leads to the possibility that it exists in shocked meteorites and impact materials.
A combined experimental and theoretical study of one oxaphosphinane derivative was made on the basis of a topological analysis of its electron density distributions. The electron density was determined from a high-resolution X-ray diffraction data set measured with synchrotron radiation at 100 K, whereas theoretical calculations were performed using density functional theory (DFT) methods at the B3LYP\6-311++G(3df,3pd) level of approximation. The charge-density distribution and analysis of topological properties revealed that the P-O bond is of the transit closed-shell type. The crystal structure possesses one intra- and several intermolecular hydrogen bonds. They were characterized quantitatively by topological properties using Bader's Atoms in Molecules theory. All hydrogen bonds were classified as weak. Further analysis of the experimental electron density by the source function allowed the intramolecular hydrogen bond to be characterized as an isolated hydrogen bond, in contrast to the resonance-assisted hydrogen bond in related molecules, such as chromone derivatives.
The new compound [Fe(H2cit)(H2O)]n (NICS-2) is the first neutral ferrous citrate carboxylate that has been synthesized up to now. The iron citrate coordination polymer was hydrothermally synthesized and the structure was solved using single-crystal X-ray diffraction. It crystallizes in an orthorhombic space group P2(1)2(1)2(1) (No. 19), with a = 5.9470 (4), b = 10.402(1) (5), c = 13.5773 (7) Å, V = 839.91 (8) Å(3), Z = 4. Its structure consists of one-dimensional chains of corner-sharing Fe(II)O6 octahedra that are additionally cross-linked with citrate ligands. Chains are additionally stabilized into a pseudo-three-dimensional structure by hydrogen bonds. The measurement of magnetic properties revealed that the magnetic moment is almost constant above 100 K (μeff = 5.1 µB), but decreases rapidly below this temperature most probably due to the appearance of weak antiferromagnetic interactions between Fe atoms. Additionally, analysis of Mossbauer spectra confirmed the presence of divalent Fe atoms in the structure. Thermogravimetrical and X-ray high-temperature diffraction analyses showed the thermal stability of the material up to 548 K.
The X-ray single-crystal diffraction intensities of the intermetallic compound TiGePt were analysed. These showed beyond doubt that the crystal structure is non-centrosymmetric. The analysis revolves around the resonant-scattering contribution to differences in intensity between Friedel opposites hkl and \bar h\bar k\bar l. The following techniques were used: R(merge) factors on the average (A) and difference (D) of Friedel opposites; statistical estimates of the resonant-scattering contribution to Friedel opposites; plots of 2A(obs) against 2A(model) and of D(obs) against D(model); the antisymmetric D-Patterson function. Moreover it was possible to show that a non-standard atomic model was unnecessary to describe TiGePt. Two data sets are compared. That measured with Ag Kα radiation at 295 K to a resolution of 1.25 Å(-1) is less conclusive than the one measured with Mo Kα radiation at 100 K to the lower resolution of 0.93 Å(-1). This result is probably due to the fact that the resonant scattering of Pt is larger for Mo Kα than for AgKα radiation.
The Distortion Theorem implies that the irregularity of bond distances in a distorted coordination polyhedron causes an increase of mean bond distance. Examination of 40 polyhedra containing the lone-pair cation Te(IV) shows that this does not imply an increase in polyhedral volume. Volumes of these polyhedra are 10.3-23.7 Å(3), compared with the 12.83 Å(3) expected for a hypothetical regular octahedron. There is little correlation between volume and measures of polyhedral distortion such as quadratic elongation, bond-angle variance or vector bond valence. However, the oxygens of our polyhedra lie very close to a sphere of best fit, centred at ~ 1 Å from the Te(IV) atom. The Te(IV)-centre distance is an index of lone-pair stereoactivity and is linearly related to the radius Rsph of the sphere; this is explained by a more localized lone pair repelling the anions more strongly, leading to a longer non-bonded distance between the lone pair and anions. Polyhedral volume still varies considerably for a given Rsph, because the oxygen ligands may be distributed over the whole sphere surface, or confined to a small portion of it. The uniformity of this distribution can be estimated from the distance between the sphere centre and the centroid of the O6 polyhedron. Te(IV)-centre and centroid-centre distances alone then account for 95% of the variation observed in volume for polyhedra which are topologically octahedral. Six of the polyhedra studied that are outliers are closer in shape to pentagonal pyramids than octahedra. These have short distances from the central Te(IV) cation to other Te(IV) and/or to large, polarizable cations, suggesting additional weak bonding interactions between these species and the central lone pair. The flexibility of lone-pair polyhedra is further enhanced by the ability of a single polyhedron to accommodate different cations with different degrees of lone-pair activity, which facilitates more diverse solid solution behaviour than would otherwise be the case.
