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Various 2-thienyllithium derivatives were investigated in the solid state by X-ray diffraction and in solution by 2D NMR experiments. The determined structures of [(Et2O)Li(C4H3S)]4 (1), [(THF)2Li(C4H3S)]2 (2), [(DME)Li(C4H3S)]2 (3), [(TMEDA)Li(C4H3S)]2 (4), and [(PMDETA)Li(C4H3S)] (5) (DME = 1,2-dimethoxyethane, TMEDA = N,N,N',N'-tetramethylethylene-1,2-diamine, and PMDETA = N,N,N',N?,N?-pentamethyldiethylenetriamine) were solved in nondonating toluene and provide firm ground for diffusion-ordered NMR spectroscopy as well as heteronuclear Overhauser enhancement NMR spectroscopy. The distance relation of nuclear Overhauser effects with a factor of r-6 is employed to gain further insight into the aggregation degree of 1-5 in solution. Comparison of the slope provided by the linear region of the buildup curves and of the Σr-6 calculated distances from the crystal structures offers a handle to judge the structure retention versus conversion in solution. The structures of 3-5 are maintained in toluene solution. The data of 2, however, indicate a partial dissociation or a rapid exchange between the vertices of a tetrameric core and free THF molecules. Auxiliary exchange spectroscopy investigations showed that the signals of the nitrogen donor base containing compounds 4 and 5 exchange with the signals of nonlithiatedthiophene. This is explained by exchange of the deuterium by a hydrogen atom via lithiation of toluene molecules. [ABSTRACT FROM AUTHOR]

The four-coordinate iron(II) phosphoraniminato complex PhB(MesIm)3Fe-N-PPh3 undergoes an S = 0 to S = 2 spin transition with TC = 81 K, as determined by variable-temperature magnetic measurements and Mössbauer spectroscopy. Variable-temperature single-crystal X-ray diffraction revealed that the S = 0 to S = 2 transition is associated with an increase in the Fe-C and Fe-N bond distances and a decrease in the N-P bond distance. These structural changes have been interpreted in terms of electronic structure theory. [ABSTRACT FROM AUTHOR]

A series of designed palladium biscarbene complexes including saturated and unsaturated N-heterocyclic carbene (NHC) moieties have been prepared by the carbene transfer methods. All of these complexes have been characterized by 1H and 13C NMR spectroscopy as well as X-ray diffraction analysis. The reactivity of Pd-C(saturated NHC) is distinct from that of Pd-C(unsaturated NHC). The Pd-C(saturated NHC) bonds are fairly stable toward reagents such as CF3COOH, AgBF4 and I2, whereas Pd-C(unsaturated NHC) bonds are readily cleaved under the similar conditions. Notably, the catalytically activity of these palladium complexes on Suzuki-Miyaura coupling follows the order: (sat-NHC)2PdCl2 > (sat-NHC)(unsat-NHC)PdCl2 > (unsat-NHC)2PdCl2. [ABSTRACT FROM AUTHOR]

Quaterthiophenes 4T, Oct-4T, and Tol-4T based on a central 2,2'-bithiophene core α,ψ-terminated with 4,4-unsubstituted and 4,4-disubstituted n-octyl or p-tolyl indeno[1,2-b]thiophene have been synthesized by Stille or Miyaura-Suzuki couplings. Compound 4T was also synthesized by an alternative route involving a soluble precursor bearing solubilizing trimethylsilyl groups which have been eliminated in the last step. The electronic properties of the compounds have been analyzed by cyclic voltammetry, UV-vis absorption and fluorescence emission spectroscopy. Thermal evaporation of 4T and Oct-4T leads to crystalline thin films and UV-vis absorption and X-ray diffraction data for these films suggest that the molecules adopt a quasi-vertical orientation onto the substrate. Strong π-π intermolecular interactions have been observed for 4T but not for molecules Oct-4T due to the presence of n-octyl chains. Sublimed thin films of Tol-4T show an amorphous character. The characterization of field-effect transistors fabricated from these three materials gave a hole-mobility of 2.2 x 10-2 cm2 V-1 s-1 with an on/off ratio of 2.2 x 104 for 4T while no field-effect was observed for Oct-4T and Tol-4T. [ABSTRACT FROM AUTHOR]

A new series of isostructural ternary rare-earth zinc antimonides RE6Zn1+xSb14+y (RE = Pr, Sm, Gd-Ho) has been obtained by direct reaction of the elements at 1050-1100 °c. Single-crystal X-ray diffraction studies revealed that these compounds adopt an orthorhombic structure type (space group Immm (no. 71), Z= 2, a = 4.28-4.11 A, b = 15.15-14.73 A, c = 19.13-18.56 A in the progression from RE = Pr to Ho) that may be regarded as stuffed variants of a (U0.5Ho0.5)3Sb7-type host structure. Columns of face-sharing RE6 trigonal prisms, centered by Sb atoms, occupy channels defined by an extensive polyanionic Sb network. This network is constructed from three-atom-wide and four-atom-wide Sb strips, the latter being linked together by single Sb atoms in RE6Zn1+xS14 (RE = Sm, Gd-Ho; y 0), but also by additional Sb-Sb pairs in a disordered fashion in Pr6Zn1+xSb14+y (y = ∼0.6). Interstitial Zn atoms then partially fill tetrahedral sites (occupancy of 0.5-0.7) and, to a lesser extent, square pyramidal sites (occupancy of 0.04-0.12), accounting for the observed nonstoichiometry with variable x. Except for the Gd member, these compounds undergo antiferromagnetic ordering below TN < 9 K, with the magnetic susceptibilities of the Tb, Dy, and Ho members following the Curie-Weiss law above TN. For the Ho member, the thermal conductivities are low and the Seebeck coefficients are small and positive, implying p-type character consistent with the occurrence of partial Zn occupancies. At low temperatures (down to 5 K), electrical resistivity measurements for the Tb, Dy, and Ho members indicated metallic behavior, which persists at high temperatures (up to 560 K) for the Ho member. Band structure calculations on an idealized "Gd6Zn2Sb14" model revealed the existence of a pseudogap near the Fermi level. [ABSTRACT FROM AUTHOR]

The pendant amino groups in isoreticular metal-organic framework-3 (IRMOF-3) were subjected to postsynthetic modification with 10 linear alkyl anhydrides (O(CO(CH2)nCH3)2 (where n = 1 to 18) and the extent of conversion, thermal and structural stability, and Brunauer-Emmett-Teller (BET) surface areas of the resulting materials were probed. ¹H NMR of digested samples showed that longer alkyl chain anhydrides resulted in lower conversions of IRMOF-3 to the corresponding amide framework (designated as IRMOF-3-AM2 to IRMOF-3-AM19). Percent conversions ranged from essentially quantitative (~99%, -AM2) to ~7% (-AM19) with IRMOF-3 samples. Modified samples were thermally stable up to approximately 430 °C and remained crystalline based on powder X-ray diffraction (PXRD) measurements. Under specific reaction conditions, significant conversions were obtained with complete retention of crystallinity, as verified by single-crystal X-ray diffraction experiments. Single crystals of modified IRMOF-3 samples all showed that the F-centered cubic framework was preserved. All single crystals used for X-ray diffraction were analyzed by electrospray ionization mass spectrometry (ESI-MS) to confirm that these frameworks contained the modified 1,4-benzenedicarboxylate ligand. Single crystals of each modified IRMOF-3 were further characterized by measuring the dinitrogen gas sorption of each framework to determine the effects of modification on the porosity of the MOF. BET surface areas (m²/g) confirmed that all modified IRMOF-3 samples maintained microporosity regardless of the extent of modification. The surface area of modified MOFs was found to correlate to the size and number of substituents added to the framework. [ABSTRACT FROM AUTHOR]

The extraordinary stability of the photoinduced red form of a cationic spiropyran ( k≈ 10 −6s −1in water and ∼10 −6to less than 10 −8s −1in the solid state) was employed to obtain in situ X-ray diffraction evidence of its molecular structure. By UV excitation under selected experimental conditions, on average, approximately one third of the cations in a single crystal of spiropyran iodide salt was converted and retained as the red form during the experiment. According to the structure of the mixed crystal, the ring opening, which is due to increased distance between the spiro oxygen and carbon atoms, is associated with slight molecular flattening caused by concurrent out-of-plane shift (11.2(5)°) of the pyranopyridinium half and in-plane shift (4.8(7)°) of the indoline half. The overall geometry change of the cation fits the steric requirements imposed by the ion packing in the crystal and can be viewed as molecular flattening caused by breaking of the spiroconjugation. The structure of the cation confirms that (at least in the case of cationic spiropyrans) the product is confined in the crystal mainly as a zwitterionic resonance structure in cis configuration similar to the (early) transition state. Although the positive charge of the closed form facilitates the ring-opening reaction by moving the reactant closer to the transition state, neither the weakening of the spiropyran C−O bond nor the space provided by the iodide alone can account for the stability of the product. Instead, the density functional theory calculations indicate that the stabilization of the red form of the cationic relative to the neutral spiropyran is thermodynamically controlled, probably through compensation of the charge within the zwitterion by the methylpyridinium group. [ABSTRACT FROM AUTHOR]

The balance of weak CH···N bonds involving the H 3C− and −CN groups has been related to the structural rearrangement between centrosymmetric and polar acetonitrile structures. The linear highly polar molecules arrange antiparallel in phase α below a freezing temperature of 225 K/0.1 MPa and above a freezing pressure of 0.38(5) GPa/296 K and in a polar mode in phase β below 206 K/0.1 MPa and at pressures higher than 0.63(5) GPa/296 K. The α ↔ β phase transition has been considered as a supramolecular reaction between 2-dimensional and 3-dimensional hydrogen-bonding networks, the latter favoring the polar association. Acetonitrile has been in situ pressure-frozen, and its structure has been determined at room temperature by single-crystal X-ray diffraction at 0.57(5), 0.63(5), and 1.50(5)GPa. The crystallization pressure at 296 K has been determined as 0.38(5) GPa both by ruby fluorescence in a diamond anvil-cell and by the compressibility measurement in a cylinder-and-piston device. Acetonitrile mixed with methanol trimerized at 1.60 GPa and 473 K yielding 4-amino-2,6-dimethylpyrimidine: it was in situ crystallized, and the structure of a single crystal, recovered at ambient conditions, was determined. [ABSTRACT FROM AUTHOR]

There is currently substantial interest and activity in the development and application of a new technique, called “charge flipping” (CF), that has emerged in the past few years for carrying out structure solution from X-ray diffraction data. We report here a new variant of this technique, termed “residue-based charge flipping” (RBCF), in which the residues of calculated and experimental structure factor amplitudes, together with the corresponding electron density residues, are introduced within the CF algorithm. An important feature of this approach is that it does not require a positive threshold electron density value (δ) to be specified to control the charge-flipping step within the algorithm (in contrast, it is well established that the success of standard CF calculations can depend critically on choosing a suitable value of δ for a given structural problem). Methodological details of the RBCF algorithm are described, and the results of the application of this technique for structure solution of three test structures are reported. The RBCF technique is shown to lead to the correct structure solution in all cases, with success rates of at least 90% (for independent calculations from different sets of initial random phases). Significantly, the convergence behavior of RBCF calculations is found to contrast markedly with that generally observed for standard CF calculations. In particular, convergence (assessed from the evolution of R-factor versus iteration number) typically progresses rapidly and immediately from the earliest iterations of RBCF calculations, rather than displaying an extended plateau region. This feature, and the fact that the RBCF technique does not use the δ parameter that is required in standard CF calculations, suggest that the RBCF algorithm may be a promising approach in future applications. [ABSTRACT FROM AUTHOR]

Two novel isotypic polyborate cluster compounds Na5[MB24O34(OH)12] · nH2O (M = Cr3+, Al3+) have been synthesized in a boric acid flux closed system at 220 00 by using gel as precursors. The structure of the Cr compound was determined by low-temperature single-crystal X-ray diffraction, and the Al compound was confirmed to be isostructural by powder X-ray diffraction and similar FT-IR spectra and thermal behavior. Na5[CrB24O34(OH)12] · nH2O crystallizes in the monoclinic space group P21/c with the cell parameters a = 17.4549(3) Å, b = 11.1976(2) Å, c = 21.2403(3) Å, β = 94.644(2)°, V = 4137.85(12) ų, and Z = 4. The predominant feature of the structure are the spherelike polyborate clusters [MB24O34(OH)12]5-. The M3+ cation is located at the center of the cluster, around which four hexaborate units ([B6O10(OH)3]5-) are tetrahedrally assembled in almost a perfect Td symmetry. To the best of our knowledge, [MB24O34(OH)12]5- is the first example of a polyborate cluster that contains 24 boron atoms. Upon heating, the compounds show two steps of weight loss, including the loss of the disengaged water and dehydration of the hydroxy groups. The first step is reversible, retaining the structure framework. The second weight loss is continuous and irreversible. [ABSTRACT FROM AUTHOR]

A new potassium gallosilicate zeolite with a natrolite topology (approximate formula K8.2Ga8.2- Si11.8O40·11.5H2O) was synthesized under hydrothermal conditions and characterized as a function of temperature using monochromatic synchrotron X-ray powder diffraction and Rietveld analyses. Unlike the previously known tetragonal K8Ga8Si12O40·6H2O phase, the assynthesized material contains twice the amount of water molecules in an ordered arrangement throughout the channels in an orthorhombic (/212121) symmetry. The ordered configuration of water molecules is stabilized below 300 K, whereas heating above 300 K results in a selective dehydration and subsequent disordering of water molecules in a tetragonal (/42d) symmetry. Above 400 K, the material transforms to a fully dehydrated tetragonal phase with a concomitant volume reduction of ca. 15%. The fully dehydrated material transforms back to its original state when rehydrated over a period of up to 2 weeks. The distribution of potassium cations within the channels remains largely unperturbed during the water rearrangements and their order-disorder transition within the channels. [ABSTRACT FROM AUTHOR]

Unique PbS nanowires with x-shaped cross sections, with diameters in the range of 300-800 nm with an average of 598 nm (σ = ±21.7% ), and lengths of up to several tens of micrometers, have been made by a solventless method. Such nanowires show high adsorptivities of the PbS nanooctahedra, which can be washed off by ultrasound. The suitable precursor is obtained from a Pb(NO3)2/octanoate/ethylenediamine/dodecanethiol molar ratio of 1:2:1: 1.6, and the PbS nanowires are produced by the thermolysis of such precursors at 280 °C for 1 hour. The X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterizations of the products and the keys of the morphological control have been reported. For the formation of such products, two cooperative effects are found to be crucial, the roles of ethylenediamine and a second salt, lead octanonate. [ABSTRACT FROM AUTHOR]

By judicious selection of crystallization conditions, it has been possible to obtain the salts of a common building block, [(RNC)4RhI]+, in single-crystal form suitable for X-ray diffraction. Salts that contain a single type of cation include deep green [(C6H11NC)12RhI3](SbF6)3, deep green [(C6H11NC)12RhI3](AsF6)3, and straw yellow [(C6H11NC)8RhII2- Cl2](BF4)2 (in addition to the previously isolated trimeric deep green [(i-PrNC)12RhI3]Cl3-4.5H2O, monomeric, [(C6H11-NC)4 RhI](BPh4), and [(i-PrNC)4RhI](BPh4) (both yellow), and red, dimeric [(C6H11NC)8RhI2]Cl2·0.5C6H6·2H2O). Ordered crystals of [(C6H11NC)12RhI3](SbF6)3 contain linear Rh3 units, while those of [(C6H11NC)12RhI3](AsF6)3 show disorder which is consistent with the presence of linear or bent Rh3 units. The formation of green [(C6H11NC)12RhV/III3Cl2]-[(C6H11NC)12RhI3]Cl6, and brown [(C6H11NC)12RhV/III3Cl2][(C6H11NC)8RhI2][(C6H11NC)4RhI]Cl6·16H2O·3C6H6 along with unidentified red-brown cubes from an air-exposed solution of [(C6H11NC)4RhI]Cl is reported. As their formulas indicate, green [(C6H11NC)12RhV/III3Cl2][(C6H11NC)12RhI3]Cl6, and brown [(C6H11NC)12RhV/III3Cl2][(C6H11NC)8RhI2][(C6H11NC)8RhI]Cl6·16H2O·3C6H6 contain two or three chemically distinct cations, respectively, but again are built from a common precursor, [(C6H11NC)4RhI]+. [ABSTRACT FROM AUTHOR]

The effect of partial substitution, up to x = 0.4, of La by trivalent Eu on the phase stability, thermal expansion, and transport properties of La2Mo2O9 are investigated using temperature-controlled X-ray powder diffraction, differential thermal analysis, and complex impedance spectroscopy. Allow europium content (x ≤ 0.1), the α-β phase transition is observed at a temperature dependent on the sample shaping (powder, pellet, etc.). At high europium content (x ≥ 0.25), the samples remain cubic (β phase), regardless of the shaping. In the intermediate range of europium content (x = 0.15, 0.2), the phase stability is highly sensitive to the thermal history and the sample shaping, with a double-reversed β-α-β transition suppressed by the shaping/sintering process. The influence of the amount of europium on the transport mechanisms and parameters is studied in both low- (Arrhenius) and high-temperature (Vogel-Tammann-Fulcher = VTF) regimes. If the effect of substitution is rather mild and monotonous within each transport regime and crystallographic phase, an abrupt change in the Arrhenius parameters between the α- and β-type phases is observed. [ABSTRACT FROM AUTHOR]

The chemical bonding in the isostructural intermetallic compounds TiSb2 and VSb2, crystallizing in the CuAl2 type, was investigated by means of quantum chemical calculations, particularly the electron localization function (ELF), as well as by Raman spectroscopy, Hall effect and conductivity measurements on oriented single crystals, and high-pressure X-ray powder diffraction. The homogeneity ranges of the compounds were determined by powder X-ray diffraction, WDXS, and DSC measurements. TiSb2 exhibits no significant homogeneity range, while VSb2 shows a small homogeneity range of approximately 0.3 at. %. According to the ELF calculations, the Sb atoms form dumbbells via a two-center two-electron bond, while the T atoms (T = Ti, V) build up chains along the crystallographic c-axis. Both building units are connected by covalent T-Sb-T three-center bonds, thus forming a three-dimensional network. The strength of the bonds involving Sb was determined by fitting a force constant model to the vibrational mode frequencies observed by polarized Raman measurements on oriented single crystals. The resulting bond order of the Sb2 dumbbells is 1, while the strength of the three-center bonds resembles a bond order of 1.5. The weak pressure dependence of the da ratio confirms the slightly different bonding picture in TiSb2 compared to that in CuAI2. Electrical transport measurements show the presence of free charge carriers, as well as a metal-like temperature dependence of the electrical resistivity. [ABSTRACT FROM AUTHOR]

β-NaYF4:Ln3+ (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (FL) spectra as well as kinetic decays were used to characterize the samples. It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Eu3+, Tb3+, Yb3+/Er3+, or Yb33+/Tm3+). Under the excitation of 397 nm ultraviolet light, NaYF4:xEu3+ (x = 1.5, 5%) shows the emission lines of Eu3+ corresponding to 5D0-3 → 7FJ (J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity, resulting in yellow and red down-conversion (DC) light emissions, respectively. When doped with 5% Tb3+ ions, the strong DC fluorescence corresponding to 5D4 → 7FJ (J = 6, 5, 4, 3) transitions with 5D4 → 7F5 (green emission at 544 nm) being the most prominent group that has been observed. In addition, under 980 nm laser excitation, the Yb3+/Er3+- and Yb3+/Tm3+-codoped β-NaYF4 samples exhibit bright green and whitish blue up-conversion (UC) luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed. [ABSTRACT FROM AUTHOR]

A nonmetal pentaborate C2H10N2B5O8(OH) (I) was synthesized by a solvothermal method at 150 °C and characterized by elemental analysis, IR, thermogravimetric analysis, and X-ray diffraction. The structure of Iwas determined by a single-crystal technique. It crystallizes in the monoclinic system with space group Cc, a6.7085 (13) Å, b11.437(2) Å, c12.530(3) Å, and 95.41(3)°. Powder second-harmonic generation (SHG) efficiency measurements with Nd:YAG laser (1064 nm) radiation show that C2H10N2B5O8(OH) has a SHG efficiency approximately 1.2 times of that of potassium dihydrogen phosphate (KDP). [ABSTRACT FROM AUTHOR]

The reaction of 2,6-[2-{RNC(H)}C6H4]2C6H3I [R = Ph (4), Cy (5), 2,6-Me2C6H3 (6), 2,4,6-Me3C6H2 (7), (S)-α-methylbenzyl (8)] with Pd2(dba)3 afforded the NCN diimine pincer palladium complexes [2,6-[2-{RNC(H)}C6H4]2C6H3-Pdl] (9-13) by oxidative addition of the C-I bonds of the ligand precursors. Single-crystal X-ray diffraction analyses of complexes 9-13 reveal formal C2-symmetric environments. Variable-temperature NMR studies of complexes 11 and 12 show hindered rotation about the N-Ar bonds and also suggest that atropisomers of complexes 9-13 do not interconvert on the NMR time scale. Consistent with this proposal, isolation of the two possible isomers of 13 (13a and 13b) was possible, and their structures and NMR properties have been examined in detail. [ABSTRACT FROM AUTHOR]

A novel orthoborate, NaMgBO3, has been successfully synthesized by a standard solid-state reaction, and the crystal structure has been determined from powder X-ray diffraction data. It crystallizes in the monoclinic space group C2/c with lattice parameters a = 5.01313(6) Å, b = 8.8007(1) Å, c = 5.52831 (7) Å, and β = 99.6962(6)°. Isolated [BO3]3 anionic groups, which are the fundamental building units, are distributed perfectly parallel to each other. It is a typical structure of big birefringent crystals. The overall structure is similar to that of NaSrBO3, which crystallizes in P21/c. The correlation between these two structures is discussed. The Mg atoms in NaMgBO3 are used instead of the position of Na in NaSrBO3, while the Na atoms occupy the position of Sr. Then the directions of the BO3 triangles are changed to balance the bond valence, which leads to a higher symmetry. They are the first pair of alkali-alkaline earth orthoborates with close space groups by exchange of the cation positions. [ABSTRACT FROM AUTHOR]

Highly uniform and well-dispersed CeO2 and CeO2:Eu3+ (Sm3+, Tb3+) nanocrystals were prepared by a nonhydrolytic solution route and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), UV/vis absorption, and photoluminescence (PL) spectra, respectively. The result of XRD indicates that the CeO2 nanocrystals are well crystallized with a cubic structure, The TEM images illustrate that the average size of CeO2 nanocrystals is about 3.5 nm in diameter. The absorption spectrum of CeO2:Eu3+ nanocrystals exhibits red-shifting with respect to that of the undoped CeO2 nanocrystals. Under the excitation of 440 nm (or 426 nm) light, the colloidal solution of the undoped CeO2 nanocrystals shows a very weak emission band with a maximum at 501 nm, which is remarkably enhanced by doping additional lanthanide ions (Eu3+, Tb3+, Sm3+) in the CeO2 nanocrystals. The emission band is not due to the characteristic emission of the lanthanide ions but might arise from the oxygen vacancy which is introduced in the fluorite lattice of the CeO2 nanocrystals to compensate the effective negative charge associated with the trivalent ions. [ABSTRACT FROM AUTHOR]

The addition of small amounts of iodine to thermodynamically instable TeCl2 yields amorphous, glassy tellurium(II) halides TeCl2-xIx (0.1 < x < 0.5), which were prepared by rapid quenching of melts with the respective compositions. At ambient temperature, these glassy solids are sufficiently stable to be handled and investigated by analytical methods. High-energy X-ray diffraction and reverse Monte Carlo simulations of two compositions TeCl2-xIx, x = 0.1 and 0.5, show that these glasses are made up of structural fragments that are present in both tellurium tetrahalides and in low-valent tellurium subhalides. In both glasses, the Te-Te bonding shows narrow coordination distribution with a mean total coordination number for the Te atoms of 4.1 ± 1.3 and a mean Te-Te coordination number of 0.7 ± 0.7. Accordingly, the mean Cl-Te coordination number is 1.7 ± 0.8 and the mean I-Te coordination number is 1 .6 ± 0.7. The medium-range order increases with increasing iodine content. [ABSTRACT FROM AUTHOR]

Atom transfer radical polymerization (ATRP) generally requires a catalyst/initiator molar ratio of 0.1 to 1 and catalyst/monomer molar ratio of 0.001 to 0.01 (i.e., catalyst concentration: 1000–10 000 ppm versus monomer). Herein, we report a new copper-based complex CuBr/N,N,W,N'-tetrakis(2-pyridylmethyl)- ethylenediamine (TPEN) as a versatile and highly active catalyst for acrylic, methacrylic, and styrenic monomers. The catalyst mediated ATRP at a catalyst/initiator molar ratio of 0.005 and produced polymers with well-controlled molecular weights and low polydispersities. ATRP occurred even at a catalyst/initiator molar ratio as low as 0.001 with copper concentration in the produced polymers as low as 6—8 ppm (catalyst/ monomer molar ratio = 10-5). The catalyst structures were studied by X-ray diffraction and NMR spectroscopy. The activator CuIBr/TPEN existed in solution as binuclear and mononuclear complexes in equilibrium but as a binuclear complex in its single crystals. The deactivator CuIIBr2/TPEN complex was mononuclear. High stability and appropriate KATRP (ATRP equilibrium constant) were found crucial for the catalyst working under high dilution or in coordinating solvents/monomers. This provides guidance for further design of highly active ATAP catalysts. [ABSTRACT FROM AUTHOR]

The knowledge of the structure of a molecular crystal is frequently a prerequisite for the understanding of its solid state properties. Even though single-crystal diffractometry is the method of choice when it comes to crystal structure determination, methods using powder diffraction data become more and more competitive. There has been much recent interest in the development of a new generation of “direct-space” approaches that are particularly suited for molecular crystals. The crystallographic structure of a steroid derivative molecule (17,17-di-n-propyl-17a-aza-D-homo-5-androstan-3-ol) was obtained in two independent ways:  from a single crystal by laboratory X-rays and from a polycrystalline powder by high-resolution synchrotron powder diffraction. The molecule crystallizes in the orthorhombic space group P212121(a 6.5346, b 17.6006 and c 19.6978 Å). Hydrogen bonds form infinite chains of molecules parallel to the caxis. [ABSTRACT FROM AUTHOR]

There has been considerable debate in the literature about the true room-temperature structure of ZrP2O7 and related materials. In this article we describe how a combination of information from solid-state 31P NMR and powder diffraction data can be used to determine the structure of this 136 unique-atom material. The structure has been solved using a combination of simulated annealing and Rietveld refinement performed simultaneously on X-ray and neutron diffraction data. Despite the close to cubic metric symmetry of the material, we show how its true orthorhombic structure (space group Pbca) can be refined to a high degree of precision. [ABSTRACT FROM AUTHOR]

The focus of this study consists of examining how corrosion potential measurements can contribute in providing information on the effectiveness of storage and stabilization treatments of copper alloys in aqueous solutions. We report on the electrochemical behavior of artificial copper alloy coupons (covered or not with corrosion layers), simulating the behavior of real artifacts, immersed in sodium sesquicarbonate solutions. Particular attention is given to the transformation of the corrosion layer as a function of time. In addition, synchrotron radiation X-ray diffraction measurements are performed before and after the treatment in order to understand the reactions that take place during the immersion processes. [ABSTRACT FROM AUTHOR]

Molecular orientation analysis in a single monolayer deposited on a glass substrate has been a difficult matter, since the glass substrate absorbs infrared rays so strongly that the measurements of infrared spectra are difficult to perform, and the single monolayer is not suitable for X-ray diffraction analysis because no periodical structure is available. When a thin glass is used as the substrate, in particular, the infrared analysis becomes more difficult, since optical fringes appear strongly on the absorption spectra due to the multiple reflections in the glass. In the present study, infrared multiple-angle incidence resolution spectrometry (MAIRS) has been employed to remove the fringes from the spectra of single- and five-monolayer Langmuir-Blodgett (LB) films of cadmium stearate deposited on a thin glass plate. The MAIRS in-plane spectra gave quantitatively reliable infrared transmission spectra for both films with little fringes, which made it possible for the first time to analyze the molecular orientation in the single-monolayer LB film on glass. As a result, it has been revealed that the molecule in the single-monolayer LB film on thin glass exhibits a significantly larger molecular tilt angle than those prepared on other substrates such as gold and germanium. [ABSTRACT FROM AUTHOR]

The structure of Holliday junctions has now been well characterized at the atomic level through single-crystal X-ray diffraction in symmetric (inverted-repeat) DNA sequences. At issue, however, is whether the formation of these four-stranded complexes in solution is truly sequence dependent in the manner proposed or is an artifact of the crystallization process arid, therefore, has no relevance to the behavior of this central intermediate in homologous recombination and recombination-dependent cellular processes. Here, we apply analytical ultracentrifugation to demonstrate that the sequence d(CCGGTAC-CGG), which crystallizes in the stacked-X form of the junction, assembles into four-stranded junctions in solution in a manner that is dependent on the DNA and cation concentrations, with an equilibrium established between the junction and duplex forms at 100–200 μM DNA duplex. In contrast, the sequence d(CCGCTAGCGG), which has been crystallized as B-DNA, is seen to adopt only the double-helical form at all DNA and salt concentrations that were tested. Thus, the ACC trinucleotide core is now shown to be important for the formation of Holliday junctions in both crystals and in solution and can be estimated to contribute approximately -4 kcal/mol to stabilizing this recombination intermediate in inverted-repeat sequences. [ABSTRACT FROM AUTHOR]

Dinuclear and tetranuclear copper 2,6-bis(2-hydroxyphenyl)pyridine (H2L) complexes Cu2(L)2(py)2 (1) and Cu4(L)4(DMF) (2) were synthesized. The complexes 1 and 2 were characterized by elemental analyses, mass spectrometry, and single-crystal X-ray diffraction analyses. 1 crystallizes in the monoclinic space group P21/n with a = 13.330(2) Å, b = 9.361(1) Å, c = 14.676(1) Å, β = 100.94(1)°, V = 1798.1(3) ų, and Z= 2.2 crystallizes in the monoclinic space group P21/n with a = 13.360(1) Å, b = 14.884(1) Å, c = 15.462(2) Å, β = 97.50(4)°, V = 3048.4(1) ų, and Z = 2. Tetranuclear zinc complex Zn4(L)4(py)4 (3) was prepared and characterized by X-ray diffraction. 3 crystallizes in the triclinic space group P1 with a = 13.770(1) Å, b = 15.465(1) Å, c = 16.409(2) Å, α = 88.877(9)°, β = 88.035(4)°, γ = 82.956(3)°, V = 3465.6(5) ų, and Z = 2. The di- and tetranuclear complexes 1–3 contain phenoxo bridges. 1 is a dinuclear complex with two Cu(II) centers, two py ligands, and two L ligands, and each L ligand donates its pyridyl ring and one of the phenolate groups to one metal and shares the other phenolate group between both metals, affording a Cu2(μ-O)2 core. 2, in contrast, is a tetranuclear complex with four Cu(II) centers and four L ligands. Two of the L ligands have the same coordination mode as 1, and the other two L ligands donate their pyridyl rings to one metal and share both phenolate groups between four metals, resulting in three four-membered Cu2(μ-O)2 rings, which joined each other and showed great distortion from planarity. 3 is a tetranuclear complex with four Zn(II) centers, four pyridine ligands, and four L ligands, and the L ligands have the same coordination modes as those of 2. Single-crystal X-ray analysis showed that hydrogen-bonding and π-π stacking interactions exist in complexes 1 and 2 resulting in two- and three-dimensional molecular arrangements, and the parallel arrangement of the ligand in the crystal of complex 3 resulted in a close inter- and intramolecular π-π interactions. Investigation of the crystals, as well as an amorphous thin film and powder of 3, by photoluminescence (PL) allowed the effect of the molecular packing on the emission properties to be elucidated. Furthermore, the electroluminescent (EL) properties of 3 were examined by fabricating a multilayer device with structure of [ITO/NPB/(ZnL)n-/Alq3/LiF/Al] (NPB = N,N′-bis(α-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine, Alq3 = tris(8-hydroxyquinolinato)aluminum). [ABSTRACT FROM AUTHOR]

Cyanide-catalyzed aldimine coupling was employed to synthesize compounds with 1,2-ene-diamine and α-imine-amine structural motifs: 1,2,N,N′-tetraphenyletheylene-1,2-diamine (13) and (±)-2.3-di-(2-hydroxyphenyl)-1,2-dihydroqainoxaline (17), respectively. Single-crystal X-ray diffraction provided solid-state structures and density functional theory calculations were used to probe isomeric preferences within this and the related hydroxy-ketone]ene-diol system. The ene-diamine and imine-amine core structures were calculated (B3LYP/6-311++G(d,p)) to be essentially identical in energy (ΔG 0.2 kcal/mol in favor of the imine-amine, within the error of the calculation). However, additional effects-such as π conjugation-in 13 render an ene-diamine structure that is slightly more stable than the imine-amine tautomer (14) (ΔG = 0.2–0.7 kcal/mol, within the error of the calculation). In contrast, the intramolecular hydrogen bonding present in 17 significantly favors the imine-amine isomer over the ene-diamine tautomer (18) (ΔG = 7.2–8.9 kcal/mol). For both 13 and 17, the optimized calculated structures (B3LYP/6-31+G(d′)) are identical to those observed by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

The article discusses a crystallographic study of manganese(III) acetylacetonate. An approach is described that was used successfully in an advanced undergraduate inorganic chemistry laboratory course. The crystal structure of one of the most frequently synthesized complexes in inorganic chemistry laboratory courses, manganese(III) acetylacetonate, was determined at room temperature and also at low temperature to investigate the Jahn-Telier effect. The students synthesized and crystallized the manganese(III) acetylacetonate, complex using various protocols. They selected and mounted single crystals suitable for X-ray analysis, acquiring the skill for the recognition of crystal properties necessary for diffraction experiments.

Two nanocrystalline NaY samples were synthesized with Si/Al ratios of 1.8 and crystal sizes of 23 and 50 nm, respectively. The synthesized NaY zeolites were characterized by powder X-ray diffraction, scanning electron microscopy, nitrogen adsorption isotherms, silicon solid-state magic angle spinning NMR and FTIR spectroscopy. A commercial NaY sample was analogously characterized for comparison with the synthesized nanocrystalline NaY. FTIR spectroscopy of adsorbed pyridine was used to elucidate the adsorption sites on the different NaY samples. More Bronsted acid sites and more silanol sites were detected on the nanocrystalline NaY zeolites, relative to the commercial NaY. The nanocrystalline NaY exhibited increased adsorption capacities for representative pollutant molecules, such as toluene (∼10%) and nitrogen dioxide (∼30%), relative to commercial NaY. Functionalization of nanocrystalline NaY was examined as a method for tailoring the properties of nanocrystalline zeolites for specific environmental applications through the control of zeolite properties, such as hydrophobicity. [ABSTRACT FROM AUTHOR]

A family of novel chiral ‘calixsalen’ Schiff base macrocycles R,R-H3L4, R,R-H3L5, containing three chiral diamino moieties were synthesized by an efficient self-assembly and characterized by 1H and 13C NMR, mass spectrometry, and X-ray diffraction. The systematic synthesis, structure, and coordination properties of the [2 + 2] and [3 + 3] Robson-type Schiff base macrocyclic mono-, di-, tri-, and tetranuclear metal complexes were explored. [ABSTRACT FROM AUTHOR]

The columnar mesophases of two series of hexacatenar palladium(ll) mesogens have been studied in detail by a combination of X-ray diffraction on aligned and unaligned samples and dilatometry. The results of these studies, combined with the results of two single crystal structure determinations, have allowed a model of the molecular arrangement in the columnar phases to be proposed. This model differs in detail from that generally accepted for the arrangement of polycatenar mesogens in columnar phases, and a new model is proposed which accounts for both new and existing data. [ABSTRACT FROM AUTHOR]

Ab initio calculations and X-ray diffraction experiments were carried out to study the structure of solutions of calcium chloride in water and methanol. Ab initio calculations were performed at MP2 level and density functional calculations at B3LYP level on calcium-water and calcium-methanol clusters yielding the formation of stable calcium-water clusters with up to eight water molecules and calcium-methanol clusters with up to seven methanol molecules. The experiments were performed in a wide concentration range both in water and in methanol (1-6 M and 1-2 M, respectively). The coordination number of the cation in low-concentration (1 M) aqueous and methanol solutions could only be determined with great uncertainty due to the low weights of cation-solvent contributions to the X-ray scattering intensity for both series of solutions. It was found that in 1 M solutions the Ca2+ ion is surrounded by eight (five to ten) water and six (four to seven) methanol molecules, respectively. The coordination numbers decrease with an increase in concentration. The accuracy of the coordination numbers determined increases with increasing concentration. The solvation shell of Cl- ion is composed of six solvent molecules in each solution. We have found evidence of both contact and solvent-separated Ca-Cl ion pair formation at higher concentrations. On the basis of the stoichiometry of the solution and structural parameters obtained, different models are suggested to explain the liquid structure of the solutions. [ABSTRACT FROM AUTHOR]

The hexahalorhenate(IV) salts of formula [Fe(C5H5)2]2[ReX8], with X = Cl (1), Br (2), and I (3), and [Fe(C5Me5)2]2- [ReX6], with X = Cl (4), Br (5), and I (6) ([Fe(C5Me5)2]+ = decamethylferroconium cation), have been synthesized and the structures of 1, 2, and 4 determined by single-crystal X-ray diffraction. 1, 2, and 4 crystallize in the orthorhombic system, space groups Pbca (1 and 2) and Ibam (4), with a = 14.099(2) Å, b = 16.125(2) Å, and c = 22.133(15) Å, for 1, a = 14.317(3) Å, b = 16.848(3) Å, and c = 22.099(2) Å for 2, and a = 15.8583(5) Å, b = 15.9368(5) Å, and c = 16.9816(6) Å for 4. The three structures are made up of discrete [ReX6]2- anions and ferrocenium cations held together by electrostatic forces. There are anion—anion contacts in 1 and 2 but only through one direction. The [ReX6]2- octahedra are arranged along the y axis forming chains of Re and X atoms, —Re—X...X—Re—X...X—Re—, where the intermolecular X...X distances are shorter than the van der Waals distances. A somewhat greater separation between the anions occurs in 4. The magnetic properties of 1–6 were investigated in the temperature range 2.0–300 K. 1, 2, 4, and 5 exhibit an antiferromagnetic coupling between the anions, whereas a ferromagnetic coupling between anions and cations is the dominant interaction in 3.6 behaves as a magnetically isolated compound, its susceptibility being the simple addition of the independent contributions of the uncoupled paramagnetic cations and anions. [ABSTRACT FROM AUTHOR]

Information about the orientation and dynamics of a chloroform molecule encaged in cryptophane-A and cryptophane-E is obtained by means of Raman microspectrometry. The microscopy technique allows us to study the two observed crystalline structures of the CDCl3-cryptophane-A complexes separately. The spectra, recorded under different polarization conditions, are compared with those of CHCl3-D30-cryptophane-A and analyzed in light of the crystalline structures determined by X-ray diffraction. The spectral analysis is improved by ab initio calculations performed for the isolated guest and host molecules. The orientation of the encaged chloroform with the C-H bond pointing toward the center of the cyclotriveratrylene structures is confirmed. The νCD (or νCH) stretching wavenumber of chloroform is red shifted upon complexation as compared to the wavenumber of the gaseous isolated state. This red shift, larger for the CDCl3-cryptophane-E complex than for the CDCl3-cryptophane-A complex, is the signature of stronger binding host-guest interactions with cryptophane-E. In addition, the analysis of the band shape of the νCD stretching vibration of chloroform suggests different rotational dynamics for the guest molecule encaged in cryptophane-A or in cryptophane-E. This work illustrates the capability of the Raman microspectrometry technique to investigate molecular recognition phenomena in solids. [ABSTRACT FROM AUTHOR]

Hexagonal mesoporous silica materials (PHTS) are synthesized with a high TEOS/EO20PO70EO20 ratio containing microporous nanocapsules or plugs inside the mesoporous channels. This PHTS material exhibits a tunable amount of open and plugged pores, has a high micropore volume (up to 0.24 mL/g), and is more stable than conventional micellar templated structures known so far. This study focuses on a thourough investigation of the influence of the amount of TEOS, the stirring temperature, the aging temperature, and the stirring time on the material characteristics using N2 sorption, X-ray diffraction, and scanning electron microscopy. PHTS materials with different amounts of TEOS were synthesized at stirring temperatures between 60 and 100 °C. At 60 °C, materials synthesized with a molar ratio TEOS/P123 of 125 proved to have a more rigid silicate framework than materials synthesized with lower amounts of TEOS resulting in PHTSs with a smaller diameter. The amount of TEOS and the stirring temperatures proved to play an important role in the material formed. Unlike SBA-15, the micropore volume of PHTS tended to increase with increasing temperature where the maximum value was found for the highest amount of TEOS used (TEOS/P123 = 125). The influence of the aging temperature on the structural characteristics of PHTS is the same as that of the stirring temperature but less pronounced. An aging temperature of 80 °C improved the structural characteristics greatly and also enlarged the particle size, whereas 4 h was shown as the minimum stirring time required. [ABSTRACT FROM AUTHOR]

The structure of a 1,7,7-triaryl norbornane (compound 3) has been determined by X-ray diffraction and was found essentially equal to that predicted by molecular mechanics calculations. Restricted rotation of the aryl groups also has been observed by dynamic NMR spectroscopy in this compound and in a number of analogously substituted norbornanes. The aryl-norbornane bond rotation barriers were measured by line shape analysis of the [sup 13]C NMR spectra obtained at temperatures lower than -100 °C and were found to cover the range 6.0 to 7.9 kcal mol[sup -1]. An exception was the rotation involving the o-anisyl group in compound 5, which occurs near ambient temperature since the corresponding barrier is much higher (14.4 kcal mol[sup -1]). In one case (compound 4) configurational enantiomers could be separated by chiral HPLC and the corresponding CD spectra recorded. [ABSTRACT FROM AUTHOR]

Single-crystal X-ray diffraction of MC(SiMe 3) 2(SiMe 2hpp) (M = Li, K; hppH = 1,3,4,6,7,8,-hexahydro-2 H-pyrimido[1,2- a]pyrimidine) showed nonsolvated organometallic compounds in which the iminonitrogen of the guanidine forms strong intramolecular bonds to generate six-membered metallacycles. [ABSTRACT FROM AUTHOR]

The strained ansa-complex [(Me 2Si) 2Cp 2Ni] was synthesized by dilithiaton of 1,2-bis(cyclopentadienyl)-1,1,2,2-tetramethyldisilane with BuLi and subsequent reaction with [NiCl 2(dme)]. The molecular structure was confirmed by X-ray diffraction analysis. Reaction of the ansa-complex with nickeltetra( tert-butylisonitrile) leads to rearrangement of the ligand framework to form a dinuclear compound. [ABSTRACT FROM AUTHOR]

An icelike 2T6(2) water tape was formed in the organic host, 1,10-bis(2-pyrazinylcarbonyl)-1,4,7,10-tetraazadecane (BPTA), and characterized by X-ray diffraction. Each BPTAmolecule crystallizes with six water molecules with a molecular formula of BPTA·6H2O. The 2T6(2) water tape is constructed of fused six-membered water rings with chair conformations. The 2T6(2) water tape and BPTAmolecules assemble into a network of water tapes sandwiched between BPTAtapes. The network is stabilized by − stacking between BPTAmolecules and three types of hydrogen-bonding interactions:  between BPTAmolecules, between the water molecules, and between the water and BPTAmolecules. [ABSTRACT FROM AUTHOR]

The first organically templated 3D borogermanate with a novel zeolite-type topology, (C4N3H15)[(BO2)2(GeO2)4] FJ-17, has been solvothermally synthesized and characterized by IR spectroscopy, powder X-ray diffraction (PXRD), TGA, and single-crystal X-ray diffraction. The compound crystallized in the monoclinic space group P2(1)/c with a = 6.967(1) Å, b = 10.500(1) Å, c = 20.501-(1) Å, β = 90.500(3)°, V = 1499.68(8) Å3, and Z = 4. The framework topology of this compound is the previously unknown topology with the vertex symbols 3·4·3·9·3·82 (vertex 1), 3·8. ·3·4·62·92 (vertex 2), 3·82·4·62·62·8 (vertex 3), 4·8·4·8·83·12 (vertex 4), 4·8·4·8·82·12 (vertex 5), and 3·8·4·62·6·82 (vertex 6). The structure is constructed from Ge8O24 and B2O7 clusters. The Ge8O24 cluster contains eight GeO4 tetrahedra that share vertices; the B2O7 unit is composed of two BO4 tetrahedra sharing a vertex. The cyclic Ge8O24 clusters connect to each other through vertices to form a 2D layer with 8,12-nets, The adjacent layers are further linked by the dimeric B2O7 cluster units, resulting in a 3D framework with 12- and 8-ring channels along the a and b axes, respectively. In addition, there is a unique B2GeO9 3-ring in the structure. [ABSTRACT FROM AUTHOR]

The article offers information on a research conducted in order to determine the X-ray structure of native scorpion toxin BmBKTx1 using racemic protein crystallization. In BmBKTx1, racemic crystallization was used for the facile production of diffraction quality crystals. Racemic crystallography is stated to be a viable approach for obtaining structures of recalcitrant proteins.

The article discusses a study on volumetric analysis of a solid acid monitored by the diffraction of X-ray. Objective of the study is to introduce students to an important class of solid state reactions while reinforcing the concepts of volumetric analysis. Each student pair mixes the correct volume of 0.1 M NaOH solution with fixed amount of ZrP in order to obtain the desired molar ratio. The pH of each mixture is measure with a pH electrode. It shows that the weakest part of the study is the pH data, which is due to the fact that student are not properly trained in the use of pH meters. The study also shows that interest of student in instrumentation is increased when forensic scientist use powder X-ray diffraction is explained.

The article presents information about polymorphs of molecular substance. These substances usually involve differences in molecular conformation, molecular orientation, or crystal packing, factors, including crystal packing effects. At present, only a limited number of polymorphs are known in which such metallophilic interactions differ within them. Diffraction quality crystals of the red polymorph were removed from the reaction mixture and characterized by single-crystal X-ray crystallography. The article further discusses a portion of the structure of the yellow polyrnorph.

Reaction between the cluster salts [(η5-Cp')3M3S4][pts] (M=Mo, W; Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) and [Co2(CO)8] yielded the electroneutral clusters [(η5-Cp')3M3S4Co- (CO)]. The molecular structure of [η5-Cp')3W3S4Co(CO)] was determined by single-crystal X-ray diffraction methods. The unprecedented 60 electron W3S4C0 cluster completes a homologous series of heterobimetallic clusters, [(η5-Cp')3M3S4Co(CO)] (M = Cr, Mo, W), containing a cubane like core motif. [ABSTRACT FROM AUTHOR]

Describes a lipid cubic phase with large water channels. Determination of the temperature dependence of the bilayer thickness in the cubic monoolein/octylglucoside/water system; Discovery of a unique diamond-type lipid cubic phase through x-ray diffraction studies; Possibility of the allowance of an entrapment efficiency of biomolecules by the larger water channels; Crystallization of membrane proteins in nonlamellar media.