Search

We report the unusual linkage photoisomerization for [Co(NH3)5NO2]2I3Cl. The reaction [Co(NH3)5NO2]2+ → [Co(NH3)5ONO]2+ occurs upon irradiation by visible light for complex cations in certain crystallographic positions only. This feature, suggesting "crystallographic control" of reactivity within the same crystal structure, has been analysed via detailed analysis of crystal structures and IR spectra of the reagent and product. [ABSTRACT FROM AUTHOR]

The crystal structure of lithium xanthinate hydrate was studied by single crystal X‐ray diffraction and Raman spectroscopy on cooling to 100 K and under compression to 5.3 GPa. A phase transition at ∼4 GPa is observed. No phase transitions occur on cooling. Anisotropy of lattice strain and changes in intermolecular interactions are compared. [ABSTRACT FROM AUTHOR]

A new photoactive cobalt coordination compound, [Co(NH3)5NO2]BrNO3 (I), was obtained. Its crystal structure was shown to be isostructural with previously known [Co(NH3)5NO2]ClNO3 (II) for which linkage isomerization accompanied with mechanical response of the crystal has been already reported. Single crystals of I are transformed into nitrito isomer [Co(NH3)5ONO]BrNO3 (III) on irradiation with blue light (λ = 465 nm) without being destroyed. The crystal structure of III was also solved using single‐crystal X‐ray diffraction and compared with previously known [Co(NH3)5ONO]ClNO3 (IV). A detailed comparison of the structures of I, II, III and IV, including unit‐cell parameters, the distribution of free space (in particular, reaction cavities around the nitro ligand), the lengths of hydrogen bonds, coordination and Voronoi–Dirichlet polyhedra has been performed. Single‐crystal X‐ray diffraction data were complemented with IR spectra. The effect of the replacement of Cl− by Br− on the crystal structure and on the nitro–nitrito photoisomerization is discussed. [ABSTRACT FROM AUTHOR]

The crystal structure of potassium guaninate hydrate, K+·C5H4N5O−·H2O, was studied in the pressure range of 1 atm to 7.3 GPa by single‐crystal diffraction using synchrotron radiation and a laboratory X‐ray diffraction source. Structural strain was compared to that of the same salt hydrate on cooling, and in 2Na+·C5H3N5O2−·7H2O under hydrostatic compression and on cooling. A polymorphic transition into a new, incommensurately modulated, phase was observed at ∼4–5 GPa. The transition was reversible with a hysteresis: the satellite reflections disappeared on decompression to ∼1.4 GPa. [ABSTRACT FROM AUTHOR]

Two novel bismuth succinate hydrates, namely, poly[[diaqua(μ3‐butane‐1,4‐dicarboxylato)hemi(μ‐butane‐1,4‐dicarboxylato)bismuth] monohydrate], {[Bi(C4H4O4)1.5(H2O)2]·H2O}n (1), and poly[[μ‐aqua‐aqua(μ3‐butane‐1,4‐dicarboxylato)(μ‐butane‐1,4‐dicarboxylato)‐μ‐oxido‐dibismuth] monohydrate], {[Bi2(C4H4O4)2O(H2O)2]·H2O}n (2), have been synthesized. Their crystal structures were determined by single‐crystal X‐ray diffraction and the compounds were characterized by IR and Raman spectroscopy, powder X‐ray diffraction and thermal analysis. The crystal structure analysis revealed that the compounds are coordination polymers, with 1 having a two‐dimensional layered structure and 2 displaying a three‐dimensional (3D) framework. Fully deprotonated succinate anions (C4H4O42−) in two different conformations (trans and gauche) are included in their composition. The Bi3+ cations are surrounded by O atoms from the carboxylate groups of succinate anions and aqua ligands. BiO9 coordination polyhedra in 1 are connected in pairs by edges. These pairs are bound together by bridging succinate ligands to form layers. Bismuth coordination polyhedra of two different types (BiO9 and BiO7) in 2 are connected by edges to form infinite ribbons. Ribbons of polyhedra with bridging succinate ligands form a 3D polymeric structure. [ABSTRACT FROM AUTHOR]

This note reports a study of the coating of a crystal with 'ice' at temperatures below 45 K during single‐crystal in‐house diffraction experiments when using an open‐flow helium cryostat. The 'ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single‐crystal X‐ray diffraction using laboratory diffractometers – periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument. [ABSTRACT FROM AUTHOR]

A series of polyhalogenated diaminobenzonitriles and 18-crown-6 ether were used to reveal the dependence of the stoichiometry and supramolecular structure of co-crystals on various factors. 2,6-Diamino-3,5-difluoro-, 2,6-diamino-4-chloro-3,5-difluoro-, and 2,6-diamino-4-chloro-3-fluorobenzonitriles, as well as 2,4-diamino-3,5-difluorobenzonitrile give 1 : 1 co-crystals regardless of the diamine : crown ratio in the crystallization solution (from 2.5 : 1 to 1 : 2.5) and the nature of the solvent. According to X-ray diffraction data, the supramolecular structures of these co-crystals can be considered as 1D assemblies with the only structure-forming N–H⋯Ocr hydrogen bond. 2,4-Diamino-3,5,6-triflurobenzonitrile forms no 1 : 1 co-crystal, but yields co-crystals of 4 : 3 (under most of the studied conditions) and 2 : 1 (in CCl4 solution) stoichiometry. The N–H⋯NC hydrogen bond and p⋯π electron interactions, along with the N–H⋯Ocr H-bond, participate in the formation of the 3D supramolecular structures of these co-crystals. The effect of the number of F atoms on the co-crystallization behaviour of difluoro- and trifluoro-2,4-diaminobenzonitriles was rationalized using quantum-chemical computations of the interaction energies of N–H⋯NC bonded pairs of these diamines in the experimental crystals and DFT simulated models. The DSC curves of each co-crystal contain a single peak corresponding to a crystal-to-liquid phase transition (melting), which does not change in melting–crystallization cycles, indicating that the stoichiometry and crystal structure are reproducible. [ABSTRACT FROM AUTHOR]