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We describe a single crystal X-ray diffraction study and computational analysis of three guanidinium (Gua) based low-dimensional iodoplumbates with one edge-sharing and two corner-sharing octahedral connectivities, respectively. (Gua)3PbI5, which is reported for the first time, has a 1D corner-sharing octahedral chain structure. GuaPbI3 adopts a 1D edge-sharing octahedral chain structure in preference to structures that are either 3D and corner-sharing (i.e., perovskite) or 1D and face-sharing. (Gua)2PbI4 exhibits 2D corner-sharing octahedral connectivity in agreement with previous work. Density functional theory calculations are used to gain insight into the relative stabilities of the three polymorphs of GuaPbI3 and to assess how the connectivity and dimensionality of the octahedral framework influence the electronic structure of each of the hybrid perovskites studied. [ABSTRACT FROM AUTHOR]

We investigate the variable temperature (100–450 K) and high-pressure (p = ambient − 0.74 GPa) crystal chemistry of the black perovskite formamidinium lead iodide, [(NH2)2CH]PbI3, using single crystal X-ray diffraction. In both cases we find a phase transition to a tetragonal phase. Our experimental results are combined with first principles calculations, providing information about the electronic properties of [(NH2)2CH]PbI3 as well as the most probable orientation of the [(NH2)2CH]+ cations. [ABSTRACT FROM AUTHOR]

Three highly crystalline Cu(ii)-polyoxometalate (POM) complexes, [Cu1.5(H2O)7.5PW12O40]·4.75H2O and cis- and trans-[Cu2(H2O)10SiW12O40]·6H2O, were successfully synthesized and characterized by single crystal and powder X-ray diffraction as well as thermogravimetric analysis. All complexes feature octahedrally coordinated, Jahn–Teller-distorted CuII centres, which are coordinated by one terminal oxygen atom of the POM anion and five water molecules. The crystal structure of [Cu1.5(H2O)7.5PW12O40]·4.75H2O, reveals four-fold disorder at one of the two Cu-sites, whereas [Cu2(H2O)10SiW12O40]·6H2O crystallizes in two fully-ordered polymorphic forms: a monoclinic structure containing an angled cis configuration of the Cu-POM-Cu molecule and a triclinic structure containing a linear trans configuration. Density functional theory (DFT) calculations show that the cis polymorph of [Cu2(H2O)10SiW12O40]·6H2O is more stable than the trans form by about 30 kJ mol−1. [ABSTRACT FROM AUTHOR]

Eleven novel coordination compounds, composed of chrysazin (1,8-dihydroxyanthraquinone) and different first-row transition metals (Fe, Co, Ni, Cu), were synthesised and the structures determined by single-crystal X-ray diffraction. The synthetic trends were investigated using high-throughput synthesis under systematic variation of concentration and reagent stoichiometry: for complexes containing Co, Ni or Cu crystallisation was improved by low ligand : metal ratios, while the effect of concentration depended on the metal used. The compounds crystallise as discrete clusters, apart from two, which contain long Cu–O bonds which may allow the two compounds to be considered one-dimensional coordination polymers. One of these compounds shows a distance between aryl rings of less than 3.26 Å, which is shorter than that in graphite, suggesting applications as an organic–inorganic semiconductor. The compound was found to be insulating by single-crystal and powder AC-impedance measurements, and this result is discussed with reference to the electronic structure calculated using density-functional theory. [ABSTRACT FROM AUTHOR]

X-ray diffraction has been used to investigate the kinetics of amorphization through ball-milling at 20 Hz, for five zeolitic imidazolate frameworks (ZIFs) – ZIF-8, ZIF-4, ZIF-zni, BIF-1-Li and CdIF-1. We find that the rates of amorphization for the zinc-containing ZIFs increase with increasing solvent accessible volume (SAV) in the sequence ZIF-8 ＞ ZIF-4 ＞ ZIF-zni. The Li–B analogue of the dense ZIF-zni amorphizes more slowly than the corresponding zinc phase, with the behaviour showing a correlation with their relative bulk moduli and SAVs. The cadmium analogue of ZIF-8 (CdIF-1) amorphizes more rapidly than the zinc counterpart, which we ascribe primarily to its relatively weak M–N bonds as well as the higher SAV. The results for the ZIFs are compared to three classical zeolites – Na-X, Na-Y and ZSM-5 – with these taking up to four times longer to amorphize. The presence of adsorbed solvent in the pores is found to render both ZIF and zeolite frameworks more resistant to amorphization. X-ray total scattering measurements show that amorphous ZIF-zni is structurally indistinguishable from amorphous ZIF-4 with both structures retaining the same short-range order that is present in their crystalline precursors. By contrast, both X-ray total scattering measurements and 113Cd NMR measurements point to changes in the local environment of amorphous CdIF-1 compared with its crystalline CdIF-1 precursor. [ABSTRACT FROM AUTHOR]

Understanding the driving forces controlling crystallization is essential for the efficient synthesis and design of new materials, particularly metal-organic frameworks (MOFs), where mild solvothermal synthesis often allows access to various phases from the same reagents. Using high-energy in situ synchrotron X-ray powder diffraction, we monitor the crystallization of lithium tartrate MOFs, observing the successive crystallization and dissolution of three competing phases in one reaction. By determining rate constants and activation energies, we fully quantify the reaction energy landscape, gaining important predictive power for the choice of reaction conditions. Different reaction rates are explained by the structural relationships between the products and the reactants; larger changes in conformation result in higher activation energies. The methods we demonstrate can easily be applied to other materials, opening the door to a greater understanding of crystallization in general. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of MnB4 were studied by high-temperature powder X-ray diffraction and measurements of the conductivity and Seebeck coefficient on spark-plasma-sintered samples. A transition from the room-temperature monoclinic structure (space group P21/ c) to a high-temperature orthorhombic structure (space group Pnnm) was observed at about 650 K. The material remained semiconducting after the transition, but its behavior changed from p-type to n-type. 55Mn NMR measurements revealed an isotropic chemical shift of −1315 ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr1− xMn xB4 (two phases in space groups Pnnm and P21/ c) were synthesized for the first time. In addition, nanoindentation studies yielded values of (496±26) and (25.3±1.7) GPa for the Young's modulus and hardness, respectively, compared to values of 530 and 37 GPa obtained by DFT calculations. [ABSTRACT FROM AUTHOR]

Upon heating, lithium L-malate undergoes topotactic dehydration to form a phase containing the unsaturated fumarate ligand, in which the original 3-D framework remains intact. Insight into this unusual transformation has been obtained by single crystal X-ray diffraction, MAS-NMR, in situ powder X-ray diffraction and DFT calculations. [ABSTRACT FROM AUTHOR]

Pressure-induced phase transformations (PIPTs) occur in a wide range of materials. In general, the bonding characteristics, before and after the PIPT, remain invariant in most materials, and the bond rearrangement is usually irreversible due to the strain induced under pressure. A reversible PIPT associated with a substantial bond rearrangement has been found in a metal-organic framework material, namely [tmenH2][Er(HCOO)4]2 (tmenH22+= N, N, N′, N′-tetramethylethylenediammonium). The transition is first-order and is accompanied by a unit cell volume change of about 10 %. High-pressure single-crystal X-ray diffraction studies reveal the complex bond rearrangement through the transition. The reversible nature of the transition is confirmed by means of independent nanoindentation measurements on single crystals. [ABSTRACT FROM AUTHOR]

The effect of cation valency on the complex structures of divalent and trivalent transition metal gallates has been examined using a combination of neutron and synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and XANES spectroscopy. In the divalent frameworks, M(C7H4O5)·2H2O (M = Mn, Co and Ni), it was found that charge balance was achieved viathe presence of protons on the meta-hydroxyl groups. It was also established that these compounds undergo a discontinuous phase transition at lower temperatures, which is driven by the position of the extra-framework water molecules in these materials. By contrast, in the trivalent Fe gallate, Fe(C7H3O5)·2H2O, it was found that the stronger bonding between the meta-hydroxy oxygen and the cations leads to a weakening of the bond between this oxygen and its proton. This is turn is thought to lead to stronger hydrogen bonding with the extra-framework water. The lattice water is disordered in the Fe(iii) case, which prevents the phase transition found in the M(ii) gallates. Refinement against the neutron diffraction patterns also revealed that the relatively mild microwave synthesis of gallate frameworks in D2O led to an extensive deuteration of the ortho-hydrogen sites on the aromatic ring, which may suggest a more versatile method of deuterating aromatic organics. The antiferromagnetic structure of Co gallate has also been determined. [ABSTRACT FROM AUTHOR]

Abstract: Four new magnesium containing metal–organic hybrid compounds have been synthesized in an effort to prepare low-density materials for hydrogen storage. The compounds were prepared hydrothermally and characterized using single crystal X-ray diffraction. Three of these compounds are analogs of known transition metal structures with squarate (I, Pn-3n, a =16.276(5)Å), diglycolate (II, P212121, a =6.860(1)Å, b =9.993(1)Å, c =10.884(1)Å, R 1 =0.0341), and glutarate (III, R-3, a =10.744(2)Å, c =28.677(5)Å, R 1 =0.0554) ligands; the fourth is a novel structure using cyclobutanetetracarboxylate (IV, Pccn, a =9.382(1)Å, b =14.410(2)Å, c =8.725(1)Å, R 1 =0.0465) which contains potassium as well as magnesium cations. [Copyright &y& Elsevier]

Abstract: We report the synthesis, crystal structures, magnetic properties, and thermal behavior of a family of isostructural transition metal gallate dihydrates containing infinite chains of trans-corner-sharing octahedra. The gallates crystallize in the enantiomorphic space groups and , chirality being imparted by helical motifs in the structure. Ni(C7O5H4)⋅2H2O: , ; Mn(C7O5H4)⋅2H2O: , ; Co(C7O5H4)⋅2H2O: , . The Co(II) and Ni(II) gallates exhibit antiferromagnetic behavior, with and 19 K, respectively, while Mn(II) gallate is paramagnetic down to 5 K. High-temperature X-ray powder diffraction indicates that crystallinity is lost near 200 °C in all of the compounds. Decarboxylation of the gallate moieties is believed to facilitate this thermal decomposition. [Copyright &y& Elsevier]

Several new forms of transition metal diglycolates (C4H4O5) and iminodiacetates (C4H5O4N) have been synthesized hydrothermally, and their structures solved using single crystal XRD. Isostructural diglycolates of the formula M(H2O)(dga) · H2O (M=Co, Mn) contain 1D cavities occupied by water (Co: [1] P212121, a=6.8220(11) Å, b=9.9700(17) Å, c=10.9102(18) Å, R1=0.0206, Mn: [1] P212121, a=6.8796(18) Å, b=9.856(3) Å, c=11.067 Å, R1=0.0287). In the case the cobalt phase [1], a color change and significant structural changes accompany dehydration at 200 °C, yielding a new phase with reversible water absorption/desorption. A dense, anhydrous phase forms at higher temperatures, Co(dga) [2] (P212121, a=5.8462(12) Å, b=8.1152(17) Å, c=11.223(2) Å, R1=0.0311). Two layered iminodiacetates are also described: Ni(H2O)2(ida) [3] (Pca21, a=13.921(7) Å, b=5.131(3) Å, c=9.595(5) Å, R1=0.0315) and Co(H2O)(ida) [4] (P21/c, a=7.925(3) Å, b=10.628(4) Å, c=7.358(3) Å, β=109.598(7)°, R1=0.0250). These materials further illustrate both the role of higher reaction temperatures in reducing the framework water content and the importance of ligand flexibility in determining the metal–oxygen–metal dimensionality in hybrid systems. [Copyright &y& Elsevier]

The structure of Tb2Ti2O7, Tb2Sn2O7, and Tb2TiSnO7 were studied at high pressures (P<1 Mbar) using synchrotron radiation and angular dispersive x-ray diffraction. The cubic lattice was shown to distort into a monoclinic phase before exhibiting total structural disorder (amorphization) in all three samples. Our experiments demonstrate that partial replacement of Sn with Ti significantly enhances the bulk modulus and increases the structural stability (crystalline state) to much higher pressures. Furthermore, pressure induces anion before cation disorder during the order-disorder transition. These results are compared to radiation damage studies that show order-disorder transitions. [ABSTRACT FROM AUTHOR]

Epitaxial thin films of BiMnO[sub 3] were deposited on single-crystal substrates of (100)-oriented SrTiO[sub 3] by pulsed-laser deposition. Structural analysis by x-ray diffraction, electron diffraction, and transmission electron microscopy (TEM) indicated that the films were monoclinic and twinned with two dominant orientation relationships. The first is (111) BiMnO[sub 3] ∥ (100) SrTiO[sub 3] and ∼[101] BiMnO[sub 3] ∥ <010> SrTiO[sub 3]; the second is (101) BiMnO[sub 3] ∥ (100) SrTiO[sub 3] and ∼[121] BiMnO[sub 3] ∥ <010> SrTiO[sub 3]. High-resolution TEM images revealed that there is no reaction or appreciable interdiffusion at the substrate/film interface, despite the high temperature of the substrate during deposition (∼1000 K). Magnetic characterization was carried out (both magnetization versus temperature and hysteresis loops) and the results agree with previous reports of a ferromagnetic transition with T[sub C]∼105 K. The actual value of T[sub C] in the films is a few degrees lower than the bulk material, the discrepancy being attributed to strain, nonstoichiometry, or size effects. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: A hydrothermal reaction of a mixture of iron oxalate, arsenic acid, 1,2-diaminopropane and water at 150 °C gave rise to a new three-dimensional iron oxalatoarsenate, [NH3(CH2)CH(NH3)CH3]3[Fe6(AsO4)2(HAsO4)6(C2O4)3], I. Crystal data: hexagonal, space group=P-3c1, , , . The structure consists of layers of vertex-sharing FeO6 octahedral and AsO4 tetrahedral units that form 12-membered apertures. The layers are connected together by the oxalate units, forming a uniform one-dimensional channel that is occupied by protonated amine molecules. Variable temperature powder XRD studies indicates that I loses crystallinity at ∼300 °C forming an amorphous phase that gives way to crystalline FeAsO4 at ∼650 °C. Magnetic studies reveal that I is antiferromagnetic with . [Copyright &y& Elsevier]

The charge distributions in α-Na2UO4, Na3NpO4, α-Na2NpO4, Na4NpO5, Na5NpO6, Na2PuO3, Na4PuO5, and Na5PuO6 are investigated in this work using X-ray absorption near-edge structure (XANES) spectroscopy at the U-L3, Np-L3, and Pu-L3 edges. In addition, a Rietveld refinement of monoclinic Na2PuO3, in space group C2/c, is reported for the first time, and the existence of the isostructural Na2NpO3 phase is revealed. In contrast to measurements in solution, the number of published XANES data for neptunium and plutonium solid phases with a valence state higher than IV is very limited. The present results cover a wide range of oxidation states, namely, IV to VII, and can serve as reference for future investigations. The sodium actinide series show a variety of local coordination geometries, and correlations between the shape of the XANES spectra and the local structural environments are discussed herein. [ABSTRACT FROM AUTHOR]

The mechanical properties of calcium fumarate trihydrate, a 1D coordination polymer considered for use as a calcium source for food and beverage enrichment, have been determined via nanoindentation and high-pressure X-ray diffraction with single crystals. The nanoindentation studies reveal that the elastic modulus (16.7-33.4 GPa, depending on crystallographic orientation), hardness (1.05-1.36 GPa), yield stress (0.70-0.90 GPa), and creep behavior (0.8-5.8 nm/s) can be rationalized in view of the anisotropic crystal structure; factors include the directionality of the inorganic Ca-O-Ca chain and hydrogen bonding, as well as the orientation of the fumarate ligands. High-pressure single-crystal X-ray diffraction studies show a bulk modulus of ~20 GPa, which is indicative of elastic recovery intermediate between small molecule drug crystals and inorganic pharmaceutical ingredients. The combined use of nanoindentation and high-pressure X-ray diffraction techniques provides a complementary experimental approach for probing the critical mechanical properties related to tableting of these dietary supplements. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) are prone to exhibit phase transitions under stimuli such as changes in pressure, temperature, or gas sorption because of their flexible and responsive structures. Here we report that a dense MOF, ((CH3)2NH2)2 [Li2Zr(C2O4)4], exhibits an abrupt increase in proton conductivity from <10-9 to 3.9 x 10-5 S/cm at 17 °C (activation energy, 0.64 eV) upon exposure to humidity. The conductivities were determined using single crystals, and the structures were analyzed by X-ray diffraction and X-ray pair distribution function analysis. The initial anhydrous structure transforms to another dense structure via topotactic hydration (H2O/Zr = 0.5), wherein one-fourth of the Li ions are irreversibly rearranged and coordinated by water molecules. This structure further transforms into a third crystalline structure by water uptake (H2O/Zr = 4.0). The abrupt increase in conductivity is reversible and is associated with the latter reversible structure transformation. The H2O molecules coordinated to Li ions, which are formed in the first step of the transformation, are considered to be the proton source, and the absorbed water molecules, which are formed in the second step, are considered to be proton carriers. [ABSTRACT FROM AUTHOR]

The hexavalent and heptavalent sodium neptunate compounds Na4NpO5 and Na5NpO6 have been investigated using X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, and specific heat measurements. Na4NpO5 has tetragonal symmetry in the space group I4/m, while Na5NpO6 adopts a monoclinic unit cell in the space group C2/m. Both structures have been refined for the first time using the Rietveld method. The valence states of neptunium in these two compounds, i.e., Np(VI) and Np(VII), respectively, have been confirmed by the isomer shift values of their Mössbauer spectra. The local structural properties obtained from the X-ray refinements have also been related to the quadrupole coupling constants and asymmetry parameters determined from the Mössbauer studies. The absence of magnetic ordering has been confirmed for Na4NpO5. However, specific heat measurements at low temperatures have suggested the existence of a Schottky-type anomaly at around 7 K in this Np(VI) phase. [ABSTRACT FROM AUTHOR]

The crystal structure of trisodium uranate, which forms following the interaction between sodium and hyperstoichiometric urania, has been solved for the first time using powder X-ray and neutron diffraction, X-ray absorption near-edge structure spectroscopy, and solid-state 23Na multiquantum magic angle spinning nuclear magnetic resonance. The compound, isostructural with Na3BiO4, has monoclinic symmetry, in space group P2/c. Moreover, it has been shown that this structure can accommodate some cationic disorder, with up to 16(2)% sodium on the uranium site, corresponding to the composition α-Na3(U1-x,Nax)O4 (0 < × < 0.18). The α phase adopts a mixed valence state with the presence of U(V) and U(VI). The two polymorphs of this compound described in the literature, m- and β-Na3(U1-x,Nax)O4, have also been investigated, and their relationship to the α phase has been established. The completely disordered low-temperature cubic phase corresponds to a metastable phase. The semiordered high-temperature β phase is cubic, in space group Fd3m. [ABSTRACT FROM AUTHOR]

A 3D hybrid zinc formate framework, [NH4] [Zn(HCOO)3], possessing an acs topology, shows a high degree of mechanical anisotropy and negative linear compressibility (NLC) along its c axis. High-pressure single-crystal X-ray diffraction studies and density func- tional theory calculations indicate that contraction of the Zn∔O bonds and tilting of the formate ligands with increasing pressure induce changes in structure that result in shrinkage of the a and b axes and the NLC effect along c. [ABSTRACT FROM AUTHOR]

Abstract: A new form of cobalt succinate has been discovered using high-throughput methods and its structure was solved by single crystal X-ray diffraction. Co7(C4H4O4)4(OH)6(H2O)3⋅7H2O crystallizes in the monoclinic space group with cell parameters: , , , , , . This complex structure, containing 55 crystallographically distinct non-hydrogen atoms, is compared to the previously reported nickel phase, characterized using ab initio structure solution from synchrotron powder diffraction data. [Copyright &y& Elsevier]

A new one-dimensional copper (II) phosphate, [C3N2H5][Cu(H2PO4)2Cl]·H2O, I, with pseudo-10-membered channels along the b-axis formed by the hydrogen bonded chains, containing imidazolium ions has been synthesized and characterized by single-crystal X-ray diffraction. The compound being the first example of an organically templated copper (II) phosphate, crystallizes in the monoclinic space group P21/n (No. 14) with a=8.9998(14) Å, b=7.0189(11) Å, c=18.986(3) Å; β=102.964(3)°; V=1168.8(3) Å3; Z=4. The copper chlorophosphate chains in I are topologically similar to those observed in fornacite and vauquelinite. [Copyright &y& Elsevier]

Ni5.4(OH,F)4[O3P&z.sbnd;(CH2)3PO3]2(H2O)1.4·1.2H3O or VSB-6 was prepared under hydrothermal conditions (4–6 days, 180 °C, autogenous pressure). It was structurally characterized, ab initio, from laboratory X-ray powder diffraction data: orthorhombic, space group Pmmn (n∘59), a=17.937(1), b=6.4299(4), c=4.4936(3) A˚, V=518.27(4) A˚3, Dc=2.694 g·cm−3. The structure is built up from inorganic layers, Ni5.4(OH,F)4O12P4(H2O)1.4, constructed from chains of edge-sharing octahedra onto which are grafted phosphonate groups and statistically occupied nickel octahedra. The alkyl chain of the organic moiety connects the inorganic layers to form a pillared solid. VSB-6 is stable under air up to 400 °C. On cooling to 6 K, VSB-6 orders magnetically with a canted antiferromagnetic structure. [Copyright &y& Elsevier]

In the frame of a potential contact of MOX fuels with the Na coolant in fast breeder reactors, the chemistry and charge distributions in α-Na2UO4, Na3NpO4, α-Na2NpO4, Na4NpO5, Na5NpO6, Na2PuO3, Na4PuO5, and Na5PuO6 are investigated by XANES spectroscopy at the U-L3, Np-L3, and Pu-L3 edges. [ABSTRACT FROM AUTHOR]

The article offers information on the chemical reaction between technetium (Tc) metal and bromine, which has led to the formation of binary technetium bromides, namely TcBr3 and TcBr4. TcBr3 and TcBr4 have been synthesized by reaction between Tc metal and bromine and characterised by single crystal X-ray diffraction (XRD). The TcBr3 exhibits the Til3 structure type, whereas the TcBr4 is isomorphous with TcCl4.

The structures of the title compounds are determined by Rietveld refinement of powder XRD data. [ABSTRACT FROM AUTHOR]