Richard E. Sykora

Bio: Richard E. Sykora is an academic researcher from Auburn University. The author has contributed to research in topics: Iodate & Hydrothermal circulation. The author has an hindex of 19, co-authored 45 publications receiving 970 citations. Previous affiliations of Richard E. Sykora include University of Alberta & Oak Ridge National Laboratory.

Structural modulation of molybdenyl iodate architectures by alkali metal cations in AMoO3(IO3) (A = K, Rb, Cs): a facile route to new polar materials with large SHG responses.

Abstract: Three new molybdenyl iodates, KMoO3(IO3) (1), RbMoO3(IO3) (2), and CsMoO3(IO3) (3), have been prepared through the hydrothermal reactions of MoO3 with AIO4 (A = K, Rb, or Cs) at 180 °C. These compounds are isolated as nearly colorless, air-stable crystals. Single-crystal X-ray diffraction experiments reveal that 1 possesses a corrugated layered structure constructed from molybdenum oxide chains that are bridged by iodate anions. The puckering of the layers is caused by the alignment of bent molybdenyl (MoO22+) groups along one side of the molybdenum oxide chains. The K+ cations separate these layers from one another and serve to balance charge. In contrast, compounds 2 and 3, which are isostructural, form three-dimensional structures with small cavities filled with Rb+ or Cs+ cations. The differences between the structures of 1 and those of 2 and 3 are due to rotation of the molybdenyl units as translation occurs down the molybdenum oxide chains in order to accommodate the increased size of the Rb+ and Cs...

Cation-cation interactions in neptunyl(V) compounds: hydrothermal preparation and structural characterization of NpO2(IO3) and alpha- and beta-AgNpO2(SeO3).

Abstract: The hydrothermal reaction of NpO(2) with IO(3)(-) in the presence of nitrate results in the formation of NpO(2)(IO(3)) (1). Under similar conditions, NpO(2) reacts with AgNO(3) and SeO(2) to yield alpha-AgNpO(2)(SeO(3)) (2) and beta-AgNpO(2)(SeO(3)) (3). The structure of 1 consists of distorted pentagonal bipyramidal Np(V) centers that are bridged by iodate anions. In addition, the oxo atoms of the neptunyl(V) cations coordinate adjacent Np(V) centers creating layers that are linked into a three-dimensional network structure by the iodate anions. The structure is polar owing to the alignment of the stereochemically active lone pair of electrons on the iodate anions along the c-axis. alpha-AgNpO(2)(SeO(3)) (2) forms a layered structure consisting of hexagonal bipyramidal NpO(8) polyhedra that are bound by chelating and bridging selenite anions. The primary and secondary structures of 3 are similar to those of 1, and neptunyl-neptunyl interactions are partially responsible for the creation of a three-dimensional network structure. However, the selenite anions in 3 are rotated with respect to the iodate anions found in 1, and the structure is centrosymmetric. The network found in 3 consists of interconnecting, approximately square channels that house the Ag(+) cations. A bond-valance sum parameter of 2.036 A for Np(V) bound exclusively to oxygen has been developed with b = 0.37 A. Crystallographic data: 1, orthorhombic, space group Pna2(1), a = 13.816(2) A, b = 5.8949(8) A, c = 5.5852(8) A, Z = 4; 2, monoclinic, space group P2(1)/n, a = 4.3007(3) A, b = 9.5003(7) A, c = 11.5877(9) A, beta = 95.855(1) degrees, Z = 4; 3, triclinic, space group Ponemacr;, a = 7.1066(6) A, b = 8.3503(7) A, c = 8.3554(7) A, alpha = 89.349(1) degrees, beta = 77.034(1) degrees, gamma = 76.561(1) degrees, Z = 2.

Mixed-metal uranium(VI) iodates: hydrothermal syntheses, structures, and reactivity of Rb[UO(2)(CrO(4))(IO(3))(H(2)O)], A(2)[UO(2)(CrO(4))(IO(3))(2)] (A = K, Rb, Cs), and K(2)[UO(2)(MoO(4))(IO(3))(2)].

Abstract: The reactions of the molecular transition metal iodates A[CrO(3)(IO(3))] (A = K, Rb, Cs) with UO(3) under mild hydrothermal conditions provide access to four new, one-dimensional, uranyl chromatoiodates, Rb[UO(2)(CrO(4))(IO(3))(H(2)O)] (1) and A(2)[UO(2)(CrO(4))(IO(3))(2)] (A = K (2), Rb (3), Cs (4)). Under basic conditions, MoO(3), UO(3), and KIO(4) can be reacted to form K(2)[UO(2)(MoO(4))(IO(3))(2)] (5), which is isostructural with 2 and 3. The structure of 1 consists of one-dimensional[UO(2)(CrO(4))(IO(3))(H(2)O)](-) ribbons that contain uranyl moieties bound by bridging chromate and iodate anions as well as a terminal water molecule to create [UO(7)] pentagonal bipyramidal environments around the U(VI) centers. These ribbons are separated from one another by Rb(+) cations. When the iodate content is increased in the hydrothermal reactions, the terminal water molecule is replaced by a monodentate iodate anion to yield 2-4. These ribbons can be further modified by replacing tetrahedral chromate anions with MoO(4)(2)(-) anions to yield isostructural, one-dimensional [UO(2)(MoO(4))(IO(3))(2)](2)(-) ribbons. Crystallographic data: 1, triclinic, space group P(-)1, a = 7.3133(5) A, b = 8.0561(6) A, c = 8.4870(6) A, alpha = 88.740(1) degrees, beta = 87.075(1) degrees, gamma = 71.672(1) degrees, Z = 2; 2, monoclinic, space group P2(1)/c, a = 11.1337(5) A, b = 7.2884(4) A, c = 15.5661(7) A, beta = 107.977(1) degrees, Z = 4; 3, monoclinic, space group P2(1)/c, a = 11.3463(6) A, b = 7.3263(4) A, c = 15.9332(8) A, beta = 108.173(1) degrees, Z = 4; 4, monoclinic, space group P2(1)/n, a = 7.3929(5) A, b = 8.1346(6) A, c = 22.126(2) A, beta = 90.647(1) degrees, Z = 4; 5, monoclinic, space group P2(1)/c, a = 11.3717(6) A, b = 7.2903(4) A, c = 15.7122(8) A, beta = 108.167(1) degrees, Z = 4.

Self-assembly of a polar open-framework uranyl vanadyl hexaoxoiodate(VII) constructed entirely from distorted octahedral building units in the first uranium hexaoxoiodate: K2[(UO2)2(VO)2(IO6)2O].H2O

Abstract: The reaction of UO3 with V2O5 and KIO4 under mild hydrothermal conditions produces K2[(UO2)2(VO)2(IO6)2O]·H2O (1) in the form of orange acicular crystals. The structure of 1 consists of UO6, VO6, and IO6 distorted octahedra that are assembled into a polar, open-framework structure. The distorted VO6 and IO6 octahedra edge-share to form chains that run down the c-axis. Each VO6 octahedron also shares a vertex with an adjacent vanadium atom to link the chains together into a ribbon. The IO6 units also partake in corner-sharing with the UO6 units to create interconnected elliptical tubes. The major channels in 1 are filled with K+ cations and water molecules. The polarity of this compound is caused by alignment of distorted vanadyl hexaoxoiodate ribbons and UO6 trapezoidal bipyramids resulting in a large second-harmonic generation response of 300 times that of α-quartz. Crystallographic data: 1, orthorhombic, space group Pba2, a = 9.984(2) A, b = 16.763(3) A, c = 4.977(1) A, Z = 4 (T = 193 K).

Hydrothermal synthesis, structure, and magnetic properties of the mixed-valent Np(IV)/Np(V) Selenite Np(NpO2)2(SeO3)3.

Abstract: The reaction of NpO{sub 2} with SeO{sub 2} in the presence of CsCl at 180 {sup o}C results in the formation of Np(NpO{sub 2}){sub 2}(SeO{sub 3}){sub 3} (1). The structure of 1 consists of three crystallographically unique Np centers with three different coordination environments in two different oxidation states. Np(1) is found in a neptunyl(V), ONpO{sup +}, unit that is further ligated in the equatorial plane by three chelating SeO{sub 3}{sup 2-} anions to create a hexagonal bipyramidal NpO{sub 8} unit. A second neptunyl(V) cation also occurs for Np(2); it is bound by four bridging selenite anions and by the oxo atom from the Np(1) neptunyl cation to form a pentagonal bipyramidal, NpO{sub 7}, unit. The third neptunium center, Np(3), which contains Np(IV), is found in a distorted NpO{sub 8} dodecahedron. Np(3) is bound by five bridging selenite anions and by three neptunyl units via cation-cation interactions. The NpO{sub 7} pentagonal bipyramids and NpO{sub 8} hexagonal bipyramids share both corners and edges. Both of these polyhedra share corners via cation-cation interactions with the NpO{sub 8} dodecahedra creating a three-dimensional structure with small channels that house the stereochemically active lone pair of electrons on the selenite anions. Magnetic susceptibility data followmore » Curie-Weiss behavior over the entire temperature range measured (5 {<=} T {<=} 320 K). The effective moment, {mu}{sub eff} = 2.28 {mu}{sub B}, which represents an average over the three crystallographically inequivalent Np atoms, is within the expected range of values. There is no evidence of long-range ordering of the Np moments at temperatures down to 5 K, consistent with the negligible Weiss constant determined from fitting the susceptibility data. Crystallographic data: 1, orthorhombic, space group Pbca, a = 10.6216(5), b = 11.9695(6), and c = 17.8084(8) {angstrom} and Z = 8 (T = 193 K).« less

Old materials with new tricks: multifunctional open-framework materials.

Abstract: The literature on open-framework materials has shown numerous examples of porous solids with additional structural, chemical, or physical properties. These materials show promise for applications ranging from sensing, catalysis and separation to multifunctional materials. This critical review provides an up-to-date survey to this new generation of multifunctional open-framework solids. For this, a detailed revision of the different examples so far reported will be presented, classified into five different sections: magnetic, chiral, conducting, optical, and labile open-frameworks for sensing applications. (413 references.)

Aurophilic interactions as a subject of current research: an up-date

Abstract: Recently accumulated experimental evidence for aurophilic interactions in and between molecular gold(I) compounds and the results of pertinent theoretical calculations are reviewed for the period from 2007 to mid-2011. The influence of the intra- and intermolecular bonding contacts between the closed-shell metal centres, Au–Au, on the molecular and crystal structures, and the consequences of these effects for the chemical and physical properties of gold compounds are summarized for the various classes of mono- and polynuclear systems. The literature survey builds on the contents of previous reviews and relates new experimental and theoretical findings to earlier observations (353 references).

U6+ minerals and inorganic compounds: insights into an expanded structural hierarchy of crystal structures

Abstract: The crystal structures of uranyl minerals and inorganic uranyl compounds are important for understanding the genesis of U deposits, the interaction of U mine and mill tailings with the environment, transport of actinides in soils and the vadose zone, the performance of geological repositories for nuclear waste, and for the development of advanced materials with novel applications. Over the past decade, the number of inorganic uranyl compounds (including minerals) with known structures has more than doubled, and reconsideration of the structural hierarchy of uranyl compounds is warranted. Here, 368 inorganic crystal structures that contain essential U6+ are considered (of which 89 are minerals). They are arranged on the basis of the topological details of their structural units, which are formed by the polymerization of polyhedra containing higher-valence cations. Overarching structural categories correspond to those based upon isolated polyhedra (8), finite clusters (43), chains (57), sheets (204), and frameworks (56) of polyhedra. Within these categories, structures are organized and compared upon the basis of either their graphical representations, or in the case of sheets involving sharing of edges of polyhedra, upon the topological arrangement of anions within the sheets.

Asymmetric Cation Coordination in Oxide Materials: Influence of Lone-Pair Cations on the Intra-octahedral Distortion in d0 Transition Metals

Abstract: The oxides that contain both a d0 transition metal (Ti4+, Nb5+, W6+, etc.) and a lone-pair cation (Sn2+, Se4+, Te4+, etc.) are examined to investigate the influence of the lone-pair cation on the i...

BiO(IO3): a new polar iodate that exhibits an aurivillius-type (Bi2O2)2+ layer and a large SHG response.

Abstract: A new noncentrosymmetric (NCS) and polar material containing two lone-pair cations, Bi3+ and I5+, and exhibiting an Aurivillius-type (Bi2O2)2+ layer has been synthesized and structurally characterized. The material, BiO(IO3), exhibits strong second-harmonic generation (SHG), ∼12.5 × KDP (or ∼500 × α-SiO2), using 1064 nm radiation, and is found in the NCS polar orthorhombic space group Pca21 (No. 29). The structure consists of (Bi2O2)2+ cationic layers that are connected to (IO3)− anions. The macroscopic polarity, observed along the c-axis direction, may be attributed to the alignment of the IO3 polyhedra. In addition to the crystal structure and SHG measurements, polarization and piezoelectric measurements were performed, as well as electronic structure analysis.