The structures of the single crystals of compounds K2UO2(tca)4(tcaH)2 (I), K4NpO2(tca)6(tcaH)(H2O)3 (II), Rb4UO2(tca)6(tcaH)(H2O)3 (III), and Cs3UO2(tca)5(tcaH)2·H2O (IV), where tca is the trichloroacetate ion, were established by X-ray diffraction analysis. The crystals of II-IV have a framework structure, whereas in the layered crystals of I, neighboring layers are connected to each other via halogen bonds. In this regard, the crystals of I possess perfect cleavage along the (001) plane: the crystals are easily cut into stacks of very thin layers. Halogen bonds in the structures of all title compounds were characterized using the method of molecular Voronoi-Dirichlet polyhedra. The donor-acceptor halogen bond synthon, where the same halogen atom is both the donor towards one halogen atom and the acceptor from the second halogen atom, is recognized for its usefulness in the crystal design. The description of the ligand coordination modes and crystal chemical formulae of complexes is adapted for cases when ligands have chemically non-equivalent and unobvious donor atoms (for example, oxygen and halogen atoms in halogen-substituted carboxylate anions).
Synthesis and X-ray diffraction studies of {N(C2H5)4}[AnO2(C2H4BrCOO)3] [An = U (I), Np (II), or Pu (III)] and C2H4BrCOOH (IV), where C2H4BrCOO- is an anion of the 3-bromopropionic acid, are reported. The isostructural coordination compounds I-III contain mononuclear anionic complexes [AnO2(C2H4BrCOO)3]- belonging to the crystal chemical group AB013 (A = AnO22+; B01 = C2H4BrCOO-). In the crystal structure of IV, the C2H4BrCOOH molecules are hydrogen bonded into centrosymmetric dimers R22(8). Using the method of molecular Voronoi-Dirichlet (VD) polyhedra, the features of intermolecular interactions in crystals of I-IV are discussed in support of the results of IR and UV spectroscopy experiments. Actinide contraction in I-III manifests itself in a regular reduction of the average length of the axial and equatorial bonds in hexagonal bipyramids AnO8, in an increase in νas(AnO22+) wavenumbers, and in a simultaneous decrease in the volume and sphericity degree of VD polyhedra of An atoms in the U-Np-Pu series. The title compounds represent an interesting architecture, where 3-bromopropionate ions penetrate through the square 44 net of tetraethylammonium ions and thus bind adjacent nets via the "locking effect".
Using the parameters of Voronoi-Dirichlet (VD) polyhedra the authors have verified the maximum space-filling principle in substructures constructed of actinide atoms (from thorium to einsteinium) in all crystal structures from the Inorganic Crystal Structure Database (ICSD) and Cambridge Structural Database (CSD). It is shown that most of the actinide atoms in such substructures are surrounded by 14 or 12 neighboring atoms. It was discovered that U substructures with greater than or equal to 20 crystallographically independent U atoms in the unit cell feature 15-faceted VD polyhedra as the most common type. Analogous unimodal distributions of VD polyhedra with maxima at 15 faces are observed for F and H substructures and the model system `ideal gas', which has no order in the arrangement of atoms. This similarity allows one to assume that substructures of crystal structures with greater than or equal to 20 crystallographically independent atoms in the unit cell do not possess short-range (local) order in the mutual arrangement of atoms, but feature long-range order (translational symmetry). Thus, crystalline compounds with such substructures can formally be regarded as `antiliquid', that is the antipode of a liquid, whose structure possesses short-range order but lacks translational symmetry.
Single crystals of Na[(UO2)(i-C3H7COO)3]·0.7H2O (I), Cs[(UO2)(i-C3H7COO)3] (II) and (NH4)[(UO2)(i-C4H9COO)3] (III) were obtained via isothermal evaporation and their structures were solved using X-ray diffraction techniques. Even though the ligands are branched, bulky and spatial, many carbon and hydrogen atoms are still disordered in these crystal structures at low temperature. A new type of Na coordination is observed for the first time for this family of compounds, proposing high sensitivity of compound I to humidity. Depolymerization of the metal-oxygen frameworks for the new compounds is compared with the known ones. Coordination sequences of sodium/cesium and uranyl complexes with aliphatic monocarboxylate ions are calculated to show different crystal-chemical function of crystallographically independent atoms. As there are analogous compounds to the title ones with straight-chain ligands, such groups of similar compounds with single varying parameters are very advantageous for establishing correlations between composition and crystal structure.
X-ray diffraction was applied to the elucidation of crystal structures of single crystals of Cs2Ba[AnO2(C2H5COO)3]4, where An = U(I), Np(II), Pu(III), and KR2(H2O)8[UO2(C2H5COO)3]5, where R = Sr(IV), Ba (polymorphs V-a and V-b). FTIR spectra were analyzed for the uranium-containing crystals I, IV, and V-b. Isostructural cubic crystals I-III are constructed of typical mononuclear anionic complex units [AnO2(C2H5COO)3]- and charge-balancing Cs and Ba cations. Features of actinide contraction in the six U-Np-Pu isostructural series known to date are analyzed. In crystal structures of IV and V two typical complexes [UO2(C2H5COO)3]- bind with a hydrated Sr or Ba cation to form the rare trinuclear neutral complex unit {R(H2O)4[UO2(C2H5COO)3]2}, where R = Sr, Ba. Two such trinuclear units and one typical mononuclear unit further bind with a K cation to form the unprecedented octanuclear neutral complex unit K[UO2(C2H5COO)3]{R(H2O)4[UO2(C2H5COO)3]2}2. As the derived polynuclear complexes of uranyl ion with carboxylate ligands in the crystal structures of IV and V are not the first but are rare examples, the equilibrium between mono and polynuclear complex units in aqueous solutions is discussed. The two polymorphic modifications V-a and V-b were studied at 100 K and at room temperature, respectively. Peculiarities of noncovalent interactions in crystal structures of the two polymorphs are revealed using Voronoi-Dirichlet tessellation. The nonlinear optical activity of noncentrosymmetric crystals I was estimated by its ability for second harmonic generation.
Synthesis and X-ray crystallography of single crystals of [Mg(H2O)6][AnO2(C2H5COO)3]2, where An = U (I), Np (II), or Pu (III), are reported. Compounds I-III are isostructural and crystallize in the trigonal crystal system. The structures of I-III are built of hydrated magnesium cations [Mg(H2O)6](2+) and mononuclear [AnO2(C2H5COO)3](-) complexes, which belong to the AB(01)3 crystallochemical group of uranyl complexes (A = AnO2(2+), B(01) = C2H5COO(-)). Peculiarities of intermolecular interactions in the structures of [Mg(H2O)6][UO2(L)3]2 complexes depending on the carboxylate ion L (acetate, propionate, or n-butyrate) are investigated using the method of molecular Voronoi-Dirichlet polyhedra. Actinide contraction in the series of U(VI)-Np(VI)-Pu(VI) in compounds I-III is reflected in a decrease in the mean AnâO bond lengths and in the volume and sphericity degree of Voronoi-Dirichlet polyhedra of An atoms.
Investigation of chemical bonding and electronic structure of coordination polymers that do not form high-quality single crystals requires special techniques. Here, we report the molecular and electronic structure of the first cesium butyratouranylate, Cs[UO(2)(n-C(3)H(7)COO)(3)][UO(2)(n-C(3)H(7)COO)(OH)(H2O)], as obtained from DFT-assisted powder X-ray diffraction data because of the low quality of crystalline sample. The topological analysis of the charge distribution within the quantum theory of atoms-in-molecules (QTAIM) space partitioning and the distribution of electron localization function (ELF) is reported. The constancy of atomic domain of the uranium(VI) atom at different coordination numbers (7 and 8) and the presence of three ELF maxima in equatorial plane of an uranyl cation attributed to the 6s and 6p electrons were demonstrated for the first time. Details of methodologies applied for additional verification of the correctness of powder XRD refinement (Voronoi atomic descriptors and the Morse restraints) are discussed.
Cesium/chemistry , Uranium/chemistry , Cations/chemistry , Computer Simulation , Electrons , Models, Chemical , Molecular Structure , Quantum Theory , X-Ray Diffraction
FT-IR spectroscopy and single-crystal X-ray structure analysis were used to characterize the discrete neutral compound diaquadioxidobis(n-valerato-κ(2)O,O')uranium(VI), [UO2(C4H9COO)2(H2O)2], (I), and the ionic compound potassium dioxidotris(n-valerato-κ(2)O,O')uranium(VI), K[UO2(C4H9COO)3], (II). The U(VI) cation in neutral (I) is at a site of 2/m symmetry. Potassium salt (II) has two U centres and two K(+) cations residing on twofold axes, while a third independent formula unit is on a general position. The ligands in both compounds were found to suffer severe disorder. The FT-IR spectroscopic results agree with the X-ray data. The composition and structure of the ionic potassium uranyl valerate are similar to those of previously reported potassium uranyl complexes with acetate, propionate and butyrate ligands. Progressive lengthening of the alkyl groups in these otherwise similar compounds was found to have an impact on their structures, including on the number of independent U and K(+) sites, on the coordination modes of some of the K(+) centres and on the minimum distances between U atoms. The evolution of the KUO6 frameworks in the four homologous compounds is analysed in detail, revealing a new example of three-dimensional topological isomerism in coordination compounds of U(VI).
The non-bonded interactions in five sets of polymorph substances with photochromic properties have been investigated within the Voronoi-Dirichlet approach. Twenty compounds with the general formula C(w)H(x)N(y)O(z) were analyzed. Among ten possible types of non-bonded interactions at least five types are observed in the crystal structures of compounds under discussion. For all the structures the majority of interactions involve H atoms, namely London forces (H...H and H...C) and hydrogen bonds (H...O and H...N). A conformational polymorph was stated to be characterized by a unique set of inter- and intramolecular non-bonded interactions. It was quantitatively demonstrated that molecules in the same conformation can pack in a different way, and, vice versa, the change in conformation of a molecule does not prevent a substance from realising the same set of intermolecular contacts. In accordance with the data obtained for 2,4-dinitrobenzylpyridine derivatives, only conformational polymorphs with an intramolecular N...N interaction between a nitro group and a pyridine are photochromic.
Compounds (299) containing 494 symmetrically independent pyridine-2,6-dicarboxylate moieties have been investigated. Among them the structures of Na(3)[Nd(Pydc)(3)].14H(2)O and Na(3)[Er(Pydc)(3)].11.5H(2)O, where H(2)Pydc is pyridine-2,6-dicarboxylic acid, were determined by single-crystal X-ray diffraction, while the others were taken from the Cambridge Structural Database. The characteristics of any complex by means of the ;method of crystallochemical analysis' are described, and the coordination types of all the Pydc ions and crystallochemical formulae of all the compounds were determined. Although the ion can act as a mono-, bi-, tri-, tetra- and pentadentate ligand, 96% of Pydc ions are coordinated to the central A atom in the tridentate-chelating mode. The dependence of the denticity and geometry of pyridine-2,6-dicarboxylate, as well as of the composition of Pydc-containing complexes, was studied as a function of the nature of the A atom, the molar ratio Pydc:A and the presence of neutral or acidic ligands in the reaction mixture.
Metals/chemistry , Organometallic Compounds/chemistry , Picolinic Acids/chemistry , Crystallography, X-Ray , Databases, Factual , Ligands , Models, Chemical , Molecular Structure , Organometallic Compounds/chemical synthesis , Picolinic Acids/chemical synthesis
We present the first example of a compound containing Ba2+, C2O42-, water and some additional halide or pseudo-halide anions, viz. hexa-mu2-aqua-mu6-oxalato-dibarium(II) diisothiocyanate, [[Ba2(C2O4)(H2O)6](NCS)2]n. The structure consists of positively charged planar covalent layers of Ba2+ cations, oxalate anions and water molecules. The first coordination sphere of the Ba2+ cation contains six water molecules and four O atoms from two planar oxalate anions. The oxalate anion lies on an inversion centre and is coordinated to six Ba2+ cations, each donor O atom being bonded to two cations. Pairs of water molecules are coordinated by two Ba2+ cations. The layers are interspersed with non-coordinated NCS- anions.
