Application of the method for visualization of noncovalent interactions in conformational polymorphs of four organic acids.

A method for the visualization of noncovalent interactions using examples of the conformational polymorphs of four organic compounds: 2-(phenylamino)nicotinic, 2-(3-chloro-2-methylphenylamino)nicotinic, N-(3-chloro-2-methylphenyl)anthranilic and 2-(methylphenylamino)nicotinic acids is examined. The changes in noncovalent contacts are plotted against the angle between the planes of aromatic rings allowing a visual representation of conformational adjustment of molecules as well as packing features of crystal structures. According to the k-Φ criterion, the studied structures represent conformational polymorphs. Different types of hydrogen bonding are discussed within the framework of the method of visualization and molecular Voronoi-Dirichlet polyhedra. Good correlations are found between calculated and experimental data for several cases, such as the agreement between π stacking and polymorphic transition temperatures as well as between the area of a contact and the energy of conjugation. Also, an attempt has been made to assess the relative contributions of conformational and packing polymorphism in the formation of polymorphs.

New Complexes of Actinides with Monobromoacetate Ions: Synthesis and Structures.

Synthesis, FTIR spectral study, and X-ray diffraction analysis of single crystals of (CH3)4N[UO2(mba)3] (I), (CH3)4N[NpO2(mba)2(NO3)] (II), (CH3)4N[PuO2(mba)2(NO3)] (III), and (CH3)4N[NpO2(mba)(NO3)2] (IV), where mba is a monobromoacetate ion (CH2BrCOO-), were conducted. The main structural units of crystals I-IV are mononuclear anionic complexes of the [AnO2(mba)3]-, [AnO2(mba)2(NO3)]-, or [AnO2(mba)(NO3)2]- composition. All these complex units are characterized with the same crystal-chemical formula AB 01 3 (A = AnO2 2+ and B 01 = CH2BrCOO- or NO3 -). Using the method of molecular Voronoi-Dirichlet polyhedra, the contributions of various types of noncovalent interactions into the formation of supramolecular structures of the obtained complexes were characterized. The analysis of coordination modes of all monobromoacetate-containing compounds from the Cambridge Structural Database was accomplished. Actinide contraction in the studied compounds is discussed.

Halogen bonding in uranyl and neptunyl trichloroacetates with alkali metals and improved crystal chemical formulae for coordination compounds.

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).

Peculiarities of the Supramolecular Assembly of Tetraethylammonium and 3-Bromopropionate Ions in Uranyl, Neptunyl, and Plutonyl Coordination Compounds.

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".

Aspects of the topology of actinide atom substructures in crystal structures and the concept of antiliquid.

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.

A method for visualization of the variation of noncovalent interactions in crystal structures of conformational polymorphs.

A method for clear visualization of the variation of noncovalent interactions in crystal structures of conformational polymorphs is developed and introduced. The first stage of the method establishes the characteristics of all, without exception, noncovalent interactions in all crystal structures under discussion. This is possible using a strict and objective method of construction of Voronoi-Dirichlet polyhedra within the framework of the stereoatomic model of crystal structures. The second stage of the method then involves plotting of diagrams, showing the relation between parameters characterizing interatomic interactions and chosen geometric parameters of molecules. Application of the title method to highly polymorphic systems of ROY and flufenamic acid allows several imperceptible features of real crystal structures to be revealed and determines the value of different types of interactions in their conformational polymorphs. The method is universal as it can be readily adapted to any system of crystal structures in which noncovalent interactions change as a function of any parameters. Employment of the title method along with quantum chemical calculations offers opportunities for the correlation of potential energy of crystalline materials with noncovalent interactions in their structures, which is a giant step forward towards a more complete understanding of the relationship between the structure and properties of compounds.

Crystal structures of uranyl complexes with isobutyrate and isovalerate anions.

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.

Syntheses, Structures, and Comparisons of Heterometallic Uranyl Iodobenzoates with Monovalent Cations.

The syntheses and crystal structures of six new heterometallic compounds containing the UO22+ cation, o-, m-, and p-iodobenzoic acid ligands, and Tl+, Rb+, and Cs+ cations which adopt the role of both charge balancing cation and secondary metal center are described, as are the luminescent properties for Tl+ containing compounds 1, 4, and 6. The structures of compounds 1-3 are isomorphous and contain uranyl monomers bound by o-iodobenzoic acid ligands with Tl+, Rb+, and Cs+ cations acting as secondary metal centers. Compounds 4 and 5 are also isomorphous and feature m-iodobenzoic acid ligands bound to the uranyl cation along with Tl+ and Rb+ cations. Compound 6 is unique in this series as it is assembled from a dimeric uranyl unit and features p-iodobenzoic acid ligands and Tl+ cations which function as charge balancing secondary metal centers. Single crystal X-ray diffraction analysis of these materials suggests that the secondary metal cations are incorporated based on the size of their ionic radius (Tl+ < Rb+ < Cs+), which is directly related to the size of the "pocket" observed in 1-6. Further, Voronoi-Dirichlet tessellation and Hirshfeld surface analysis were used to probe the coordination environment of the secondary metal centers as part of ongoing efforts to develop metrics for determining the coordination number of secondary metal cations in similar systems.

Syntheses, Crystal Structures, and Nonlinear Optical Activity of Cs2Ba[AnO2(C2H5COO)3]4 (An = U, Np, Pu) and Unprecedented Octanuclear Complex Units in KR2(H2O)8[UO2(C2H5COO)3]5 (R = Sr, Ba).

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 [Mg(H2O)6][AnO2(C2H5COO)3]2 (An = U, Np, or Pu).

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 An═O bond lengths and in the volume and sphericity degree of Voronoi-Dirichlet polyhedra of An atoms.

Electronic structure of cesium butyratouranylate(VI) as derived from DFT-assisted powder X-ray diffraction data.

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.

The first uranyl complexes with valerate ions.

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).