Do secondary and tertiary ammonium cations act as structure-directing agents in the formation of layered uranyl selenites?

Two new layered uranyl selenites, [C(4)H(12)N(2)](0.5)[UO(2)(HSeO(3))(SeO(3))] (1) and [C(6)H(14)N(2)](0.5)[UO(2)(HSeO(3))(SeO(3))].0.5H(2)O.0.5CH(3)CO(2)H (2), have been isolated from mild hydrothermal reactions. The preparation of 1 was achieved by reacting UO(2)(C(2)H(3)O(2))(2).2H(2)O with H(2)SeO(4) in the presence of piperazine at 130 degrees C for 2 d. Crystals of 2 were synthesized by reacting UO(2)(C(2)H(3)O(2))(2).2H(2)O, H(2)SeO(4), and 1,4-diazabicyclo[2.2.2]octane at 150 degrees C for 2 d. The structure of 1 consists of UO(2)(2+) cations that are bound by bridging HSeO(3)(-) anions and chelating/bridging SeO(3)(2)(-) anions to yield UO(7) pentagonal bipyramids. The joining of the uranyl moieties by the hydrogen selenite and selenite anions creates two-dimensional 2(infinity) [UO(2)(HSeO(3))(SeO(3))](-) layers that extend in the bc-plane. The stereochemically active lone pair of electrons on the HSeO(3)(-) and SeO(3)(2)(-) anions align along the a-axis making each layer polar. The 2(infinity)[UO(2)(HSeO(3))(SeO(3))](-) layers and piperazinium cations stack in a AA'BAA'B sequence where two layers stack on one another without intervening piperazinium cations. While each 2(infinity)[UO(2)(HSeO(3))(SeO(3))](-) layer is polar, in the AA' stacking, the polarity of the second sheet is reversed with respect to the first, yielding an overall structure that is centrosymmetric. The structure of 2 is constructed from uranyl cations that are bound by three bridging SeO(3)(2)(-) and two bridging HSeO(3)(-) anions to create UO(7) pentagonal bipyramids. The linking of the uranyl cations by the HSeO(3)(-) and SeO(3)(2-) anions creates 2(infinity)[UO(2)(HSeO(3))(SeO(3))](-) layers that extend in the ac-plane. In 1 and 2, the organic ammonium cations form hydrogen bonds with the anionic uranyl selenite layers. Crystallographic data: 1, monoclinic, space group P2(1)/c, a = 10.9378(5) A, b = 8.6903(4) A, c = 9.9913(5) A, beta = 90.3040(8) degrees, Z = 4; 2, orthorhombic, space group Pnma, a = 13.0858(8) A, b = 17.555(1) A, c = 10.5984(7) A, Z = 8.     

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)

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.     

Near- and mid-infrared spectroscopy of the uranyl selenite mineral haynesite (UO2)3(SeO3)2(OH)2.5H2O

Near- and mid-infrared spectra of uranyl selenite mineral haynesite (UO(2))(3)(SeO(3))(2)(OH)(2).5H(2)O, were studied and assigned. Observed bands were assigned to the stretching vibrations of uranyl and selenite units, stretching, bending and libration modes of water molecules and hydroxyl ions, and delta U-OH bending vibrations. U-O bond lengths in uranyl and hydrogen bond lengths O-H...O were inferred from the spectra.     

Hydrothermal synthesis and structure of a new one-dimensional, mixed-metal U(VI) iodate, Cs(2)[(UO(2))(CrO(4))(IO(3))(2)

The reaction of the molecular transition metal iodate, Cs[CrO(3)(IO(3))], with UO(3) under mild hydrothermal conditions provides access to a new low-dimensional, mixed-metal U(VI) compound, Cs(2)[(UO(2))(CrO(4))(IO(3))(2)] (1). The structure of 1 is quite unusual and consists of one-dimensional (1)(infinity)[(UO(2))(CrO(4))(IO(3))(2)](2-) ribbons separated by Cs(+) cations. These ribbons are formed from [UO(7)] pentagonal bipyramids that contain a uranyl core, [CrO(4)] tetrahedra, and both monodentate and bridging iodate anions. Crystallographic data: 1, 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 (T = 193 K).     

Synthesis and structure of Ag(6)[(UO(2))(3)O(MoO(4))(5)]: a novel sheet of triuranyl clusters and MoO(4) tetrahedra

The new uranyl molybdate Ag(6)[(UO(2))(3)O(MoO(4))(5)] (1) with an unprecedented uranyl molybdate sheet has been synthesized at 650 degrees C. The structure (monoclinic, C2/c, a = 16.4508(14) A, b = 11.3236(14) A, c = 12.4718(13) A, beta = 100.014(4)(o), V = 2337.4(4) A(3), Z = 4) contains [(UO(2))(3)O(MoO(4))(5)] sheets composed of triuranyl [(UO(2))(3)O] clusters that are connected by MoO(4) tetrahedra. The topology of the uranyl molybdate sheet in 1 represents a major departure from sheets observed in other uranyl compounds. Of the approximately 120 known inorganic uranyl compounds containing sheets of polyhedra, 1 is the only structure that contains trimers of uranyl pentagonal bipyramids that are connected only by the sharing of vertexes with other polyhedra. The sheets are parallel to (001) and are linked by Ag cations.     

Expanding the remarkable structural diversity of uranyl tellurites: hydrothermal preparation and structures of K[UO(2)Te(2)O(5)(OH)], Tl(3)[(UO(2))(2)[Te(2)O(5)(OH)](Te(2)O(6))].2H(2)O,beta-Tl(2)[UO(2)(TeO(3))(2)], and Sr(3)[UO(2)(TeO(3))(2)](TeO(3))(2)

The reactions of UO(2)(C(2)H(3)O(2))(2).2H(2)O with K(2)TeO(3).H(2)O, Na(2)TeO(3) and TlCl, or Na(2)TeO(3) and Sr(OH)(2).8H(2)O under mild hydrothermal conditions yield K[UO(2)Te(2)O(5)(OH)] (1), Tl(3)[(UO(2))(2)[Te(2)O(5)(OH)](Te(2)O(6))].2H(2)O (2) and beta-Tl(2)[UO(2)(TeO(3))(2)] (3), or Sr(3)[UO(2)(TeO(3))(2)](TeO(3))(2) (4), respectively. The structure of 1 consists of tetragonal bipyramidal U(VI) centers that are bound by terminal oxo groups and tellurite anions. These UO(6) units span between one-dimensional chains of corner-sharing, square pyramidal TeO(4) polyhedra to create two-dimensional layers. Alternating corner-shared oxygen atoms in the tellurium oxide chains are protonated to create short/long bonding patterns. The one-dimensional chains of corner-sharing TeO(4) units found in 1 are also present in 2. However, in 2 there are two distinct chains present, one where alternating corner-shared oxygen atoms are protonated, and one where the chains are unprotonated. The uranyl moieties in 2 are bound by five oxygen atoms from the tellurite chains to create seven-coordinate pentagonal bipyramidal U(VI). The structures of 3 and 4 both contain one-dimensional [UO(2)(TeO(3))(2)](2-) chains constructed from tetragonal bipyramidal U(VI) centers that are bridged by tellurite anions. The chains differ between 3 and 4 in that all of the pyramidal tellurite anions in 3 have the same orientation, whereas the tellurite anions in 4 have opposite orientations on each side of the chain. In 4, there are also additional isolated TeO(3)(2-) anions present. Crystallographic data: 1, orthorhombic, space group Cmcm, a = 7.9993(5) A, b = 8.7416(6) A, c = 11.4413(8) A, Z = 4; 2, orthorhombic, space group Pbam, a = 10.0623(8) A, b = 23.024(2) A, c = 7.9389(6) A, Z = 4; 3, monoclinic, space group P2(1)/n, a = 5.4766(4) A, b = 8.2348(6) A, c = 20.849(3) A, beta = 92.329(1) degrees, Z = 4; 4, monoclinic, space group C2/c, a = 20.546(1) A, b = 5.6571(3) A, c = 13.0979(8) A, beta = 94.416(1) degrees, Z = 4.     

Excision of uranium oxide chains and ribbons in the novel one-dimensional uranyl iodates K(2)[(UO(2))3(IO(3))(4)O(2)] and Ba[(UO(2)2(IO(3))(2)O(2)](H(2)O)

The alkali metal and alkaline-earth metal uranyl iodates K(2)[(UO(2))(3)(IO(3))(4)O(2)] and Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) have been prepared from the hydrothermal reactions of KCl or BaCl(2) with UO(3) and I(2)O(5) at 425 and 180 degrees C, respectively. While K(2)[(UO(2))(3)(IO(3))(4)O(2)] can be synthesized under both mild and supercritical conditions, the yield increases from <5% to 73% as the temperature is raised from 180 to 425 degrees C. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), however, has only been isolated from reactions performed in the mild temperature regime. Thermal measurements (DSC) indicate that K(2)[(UO(2))(3)(IO(3))(4)O(2)] is more stable than Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) and that both compounds decompose through thermal disproportionation at 579 and 575 degrees C, respectively. The difference in the thermal behavior of these compounds provides a basis for the divergence of their preparation temperatures. The structure of K(2)[(UO(2))(3)(IO(3))(4)O(2)] is composed of [(UO(2))(3)(IO(3))(4)O(2)](2)(-) chains built from the edge-sharing UO(7) pentagonal bipyramids and UO(6) octahedra. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) consists of one-dimensional [(UO(2))(2)(IO(3))(2)O(2)](2)(-) ribbons formed from the edge sharing of distorted UO(7) pentagonal bipyramids. In both compounds the iodate groups occur in both bridging and monodentate binding modes and further serve to terminate the edges of the uranium oxide chains. The K(+) or Ba(2+) cations separate the chains or ribbons in these compounds forming bonds with terminal oxygen atoms from the iodate ligands. Crystallographic data: K(2)[(UO(2))(3)(IO(3))(4)O(2)], triclinic, space group P_1, a = 7.0372(5) A, b = 7.7727(5) A, c = 8.9851(6) A, alpha = 93.386(1) degrees, beta = 105.668(1) degrees, gamma = 91.339(1) degrees, Z = 1; Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), monoclinic, space group P2(1)/c, a = 8.062(4) A, b = 6.940(3) A, c = 21.67(1), beta= 98.05(1) degrees, Z = 4.     

Syntheses, structural studies, and magnetic properties of divalent Cu and Co selenites with organic constituents

Six new divalent metal selenites have been synthesized by hydro-/solvothermal methods which leads to the incorporation of the organic template as a cation or a ligand. The structure of [H(2)pip][Cu(SeO(3))(2)] (1) (pip=piperazine) features 1D anionic chains of [Cu(SeO(3))(2)](2-) which are cross-linked by the template cations through hydrogen bonds into a 2D layer. In [Cu(C(3)H(4)N(2))(SeO(3))] (2) the organic template is coordinated to the copper(II) ion of the inorganic Cu(SeO(3)) layer. The isostructural compounds [H(2)en][M(HSeO(3))(2)Cl(2)] (en=ethylenediamine; M=Cu (3), Co (4)) contain layers of [MCl(2)(HSeO(3))(2)](2-) units (M=Cu, Co), which are cross-linked by the template cations via hydrogen bonds into a 3D network. The structure of [H(2)en][Cu(2)(SeO(3))(2)(HSeO(3))](2)H(2)O (5), consists of a pillared layered architecture in which the Cu(SeO(3)) layers are further interconnected by bridging hydrogen selenite groups (the pillar). The compound [H(2)pip][Cu(2)(Se(2)O(5))(3)] (6), which crystallizes as a 3D open framework represents the first organically templated metal diselenite. These new compounds are thermally stable up to at least 170 degrees C. All of the compounds exhibit fairly strong antiferromagnetic interactions. More interestingly, compounds 3 and 4 behave as a weak ferromagnets below the critical temperatures of T(c)=12 and 8 K, respectively, and both of them exhibit spin-flop phase transitions around 800+/-100 Oe.     

New vanadium selenites: centrosymmetric Ca2(VO2)2(SeO3)3(H2O)2, Sr2(VO2)2(SeO3)3, and Ba(V2O5)(SeO3), and noncentrosymmetric and polar A4(VO2)2(SeO3)4(Se2O5) (A = Sr2+ or Pb2+)

Five new vanadium selenites, Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2), Sr(2)(VO(2))(2)(SeO(3))(3), Ba(V(2)O(5))(SeO(3)), Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), have been synthesized and characterized. Their crystal structures were determined by single crystal X-ray diffraction. The compounds exhibit one- or two-dimensional structures consisting of corner- and edge-shared VO(4), VO(5), VO(6), and SeO(3) polyhedra. Of the reported materials, A(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) (A = Sr(2+) or Pb(2+)) are noncentrosymmetric (NCS) and polar. Powder second-harmonic generation (SHG) measurements revealed SHG efficiencies of approximately 130 and 150 × α-SiO(2) for Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), respectively. Piezoelectric charge constants of 43 and 53 pm/V, and pyroelectric coefficients of -27 and -42 μC/m(2)·K at 70 °C were obtained for Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), respectively. Frequency dependent polarization measurements confirmed that the materials are not ferroelectric, that is, the observed polarization cannot be reversed. In addition, the lone-pair on the Se(4+) cation may be considered as stereo-active consistent with calculations. For all of the reported materials, infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements were performed. Crystal data: Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2), orthorhombic, space group Pnma (No. 62), a = 7.827(4) ?, b = 16.764(5) ?, c = 9.679(5) ?, V = 1270.1(9) ?(3), and Z = 4; Sr(2)(VO(2))(2)(SeO(3))(3), monoclinic, space group P2(1)/c (No. 12), a = 14.739(13) ?, b = 9.788(8) ?, c = 8.440(7) ?, β = 96.881(11)°, V = 1208.8(18) ?(3), and Z = 4; Ba(V(2)O(5))(SeO(3)), orthorhombic, space group Pnma (No. 62), a = 13.9287(7) ?, b = 5.3787(3) ?, c = 8.9853(5) ?, V = 673.16(6) ?(3), and Z = 4; Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), orthorhombic, space group Fdd2 (No. 43), a = 25.161(3) ?, b = 12.1579(15) ?, c = 12.8592(16) ?, V = 3933.7(8) ?(3), and Z = 8; Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), orthorhombic, space group Fdd2 (No. 43), a = 25.029(2) ?, b = 12.2147(10) ?, c = 13.0154(10) ?, V = 3979.1(6) ?(3), and Z = 8.     

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

The reaction of NpO(2) with SeO(2) in the presence of CsCl at 180 degrees C results in the formation of Np(NpO(2))(2)(SeO(3))(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), O[double bond]Np[double bond]O(+), unit that is further ligated in the equatorial plane by three chelating SeO(3)(2-) anions to create a hexagonal bipyramidal NpO(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(7), unit. The third neptunium center, Np(3), which contains Np(IV), is found in a distorted NpO(8) dodecahedron. Np(3) is bound by five bridging selenite anions and by three neptunyl units via cation-cation interactions. The NpO(7) pentagonal bipyramids and NpO(8) hexagonal bipyramids share both corners and edges. Both of these polyhedra share corners via cation-cation interactions with the NpO(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 follow Curie-Weiss behavior over the entire temperature range measured (5 < or = T < or = 320 K). The effective moment, mu(eff) = 2.28 mu(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) A and Z = 8 (T = 193 K).     

Synthesis, Structure, and Characterization of New Li(+) - d(0) -Lone-Pair - Oxides: Noncentrosymmetric Polar Li(6)(Mo(2)O(5))(3)(SeO(3))(6) and Centrosymmetric Li(2)(MO(3))(TeO(3)) (M = Mo(6+) or W(6+))

New quaternary lithium - d(0) cation - lone-pair oxides, Li(6)(Mo(2)O(5))(3)(SeO(3))(6) (Pmn2(1)) and Li(2)(MO(3))(TeO(3)) (P2(1)/n) (M = Mo(6+) or W(6+)), have been synthesized and characterized. The former is noncentrosymmetric and polar, whereas the latter is centrosymmetric. Their crystal structures exhibit zigzag anionic layers composed of distorted MO(6) and asymmetric AO(3) (A = Se(4+) or Te(4+)) polyhedra. The anionic layers stack along a 2-fold screw axis and are separated by Li(+) cations. Powder SHG measurements on Li(6)(Mo(2)O(5))(3)(SeO(3))(6) using 1064 nm radiation reveal a SHG efficiency of approximately 170 × α-SiO(2). Particle size vs SHG efficiency measurements indicate Li(6)(Mo(2)O(5))(3)(SeO(3))(6) is type 1 nonphase-matchable. Converse piezoelectric measurements result in a d(33) value of ～28 pm/V and pyroelectric measurements reveal a pyroelectric coefficient of -0.43 μC/m(2)K at 50 °C for Li(6)(Mo(2)O(5))(3)(SeO(3))(6). Frequency-dependent polarization measurements confirm that Li(6)(Mo(2)O(5))(3)(SeO(3))(6) is nonferroelectric, i.e., the macroscopic polarization is not reversible, or 'switchable'. Infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements and electron localization function calculations were also done for all materials.     

U(VI) uranyl cation-cation interactions in framework germanates

The isomorphous compounds NH(4)[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (1), K[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (2), Li(3)O[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (3), and Ba[(UO(6))(2)(UO(2))(9)(GeO(4))(2)] (4) were synthesized by hydrothermal reaction at 220 °C. The structures were determined using single crystal X-ray diffraction and refined to R(1) = 0.0349 (1), 0.0232 (2), 0.0236 (3), 0.0267 (4). Each are trigonal, P(3)1c. 1: a = 10.2525(5), c = 17.3972(13), V = 1583.69(16) ?(3), Z = 2; 2: a = 10.226(4), c = 17.150(9), V = 1553.1(12) ?(3), Z = 2; 3: a = 10.2668(5), c = 17.0558(11), V = 1556.94(15) ?(3), Z = 2; 4: a = 10.2012(5), c = 17.1570(12), V = 1546.23(15) ?(3), Z = 2. There are three symmetrically independent U sites in each structure, two of which correspond to typical (UO(2))(2+) uranyl ions and the other of which is octahedrally coordinated by six O atoms. One of the uranyl ions donates a cation-cation interaction, and accepts a different cation-cation interaction. The linkages between the U-centered polyhedra result in a relatively dense three-dimensional framework. Ge and low-valence sites are located within cavities in the framework of U-polyhedra. Chemical, thermal, and spectroscopic characterizations are provided.     

Synthesis, thermal, spectroscopic and magnetic studies of the Mn(SeO3).2H2O and Fe2(SeO3)3.3H2O selenites

Mn(SeO(3)).2H(2)O (1) and Fe(2)(SeO(3))(3).3H(2)O (2) have been synthesized by slow evaporation from an aqueous solution in the case of (1) and using mild hydrothermal conditions for (2). The crystal structures of both phases have been refined by the Rietveld method. The compounds crystallize in different spatial groups, the P2(1)/n monoclinic one with parameters a=6.649(1)A, b=6.542(1)A, c=10.890(1)A and beta=103.85(1) degrees being Z=4 for (1) and the R3c trigonal space group with parameters a=9.361(1)A, c=20.276(1)A and Z=6 for (2). The crystal structure of compound (1) consists of a three-dimensional framework formed by MnO(6) octahedra and (SeO(3))(2-) oxoanions with trigonal pyramidal geometry, which gives rise to Mn(2)O(10) dimers of edge-sharing octahedra. The crystal structure of phase (2) can be described as a three-dimensional framework formed by MnO(6) octahedra and (SeO(3))(2-) oxoanions with trigonal pyramidal geometry. In this phase the octahedral entities are linked along the three crystallographic axes through the selenite anions. Diffuse reflectance spectrum and luminescent measurements for (1) indicate the existence of Mn(2+) cations in a slightly distorted octahedral environment. Diffuse reflectance spectrum and M?ssbauer spectroscopy, in the paramagnetic region, for (2) show the existence of Fe(3+) cations in slightly distorted octahedral symmetry. ESR spectra of both compounds are isotropic with a g-value of 1.99(1) and 2.00(1), respectively. Magnetic measurements of both phases indicate an antiferromagnetic behavior. For phase (2), both, the ESR and magnetic measurements suggest a spin change from Fe(3+) (S=5/2) to Fe(2+) (S=2) at low temperatures.     

(CH3)2NH(CH2)2NH(CH3)2][(UO2)2F2(HPO4)2]: a new organically templated layered uranium phosphate fluoride--synthesis, structure, characterization, and ion-exchange reactions

A new organically templated layered uranium phosphate fluoride, [(CH(3))(2)NH(CH(2))(2)NH(CH(3))(2)][(UO(2))(2)F(2)(HPO(4))(2)] has been synthesized by hydrothermal reaction of UO(3), H(3)PO(4), HF, and (CH(3))(2)NCH(2)CH(2)N(CH(3))(2) at 140 degrees C. [(CH(3))(2)NH(CH(2))(2)NH(CH(3))(2)][(UO(2))(2)F(2)(HPO(4))(2)] has a layered crystal structure consisting of seven-coordinated UO(5)F(2) pentagonal bipyramids and four-coordinated HPO(4) tetrahedra. Each anionic layer containing three-, four-, and six-membered rings is separated by [(CH(3))(2)NH(CH(2))(2)NH(CH(3))(2)](2+) cations. The [(CH(3))(2)NH(CH(2))(2)NH(CH(3))(2)](2+) cations may be readily exchanged with the M(2+) ions (M = Ba, Sr and Ca) in water to give high crystalline AE(UO(2))(2)(PO(4))(2).6H(2)O (AE = Ca, Sr, Ba).     

Syntheses, crystal structures and properties of new lead(II) or bismuth(III) selenites and tellurite

Four new lead(II) or bismuth(III) selenites and a tellurite, namely, Pb(3)(TeO(3))Cl(4), Pb(3)(SeO(3))(2)Br(2), Pb(2)Cd(3)(SeO(3))(4)I(2)(H(2)O), Pb(2)Ge(SeO(3))(4) and BiFe(SeO(3))(3), have been prepared and structurally characterized by single crystal X-ray diffraction (XRD) analyses. These compounds exhibit five different types of structures. The structure of Pb(3)(TeO(3))Cl(4) features a three-dimensional (3D) lead(II) chloride network with tellurite anions filling in the 1D tunnels of Pb(4) 4-member rings (MRs) along the c-axis. Pb(3)(SeO(3))(2)Br(2) contains a 3D network composed of lead(II) selenite layers interconnected by bromide anions. Pb(2)Cd(3)(SeO(3))(4)I(2)(H(2)O) is a 3D structure based on 2D cadmium(II) selenite layers which are further connected by 1D lead(II) iodide ladder chains with lattice water molecules located at the 1D tunnels of the structure. Pb(2)Ge(SeO(3))(4) features a 3D framework constructed by the alternate arrangement of lead(II) selenite layers and germanium(iv) selenite layers in the [100] direction. The structure of BiFe(SeO(3))(3) is built on the 3D anionic framework of ion(III) selenite with the bismuth(III) ions located at its Fe(6)Se(6) 12-MR tunnels. Pb(3)(TeO(3))Cl(4) (Pna2(1)) is polar and BiFe(SeO(3))(3) (P2(1)2(1)2(1)) is noncentrosymmetric. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicate that BiFe(SeO(3))(3) exhibits a weak SHG efficiency of about 0.2 × KH(2)PO(4) (KDP). Magnetic property measurements for BiFe(SeO(3))(3) show a dominant antiferromagnetic interaction with weak spin-canting at low temperatures. IR, UV-vis and thermogravimetric, as well as electronic structure calculations were also performed.     

Nanoscale Hemispheres in Novel Mixed-Valent Uranyl Chromate(V,VI), (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6)

The structure of a novel mixed-valent chromium uranyl compound, (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6) (1), obtained by the combination of a hydrothermal method and evaporation from aqueous solutions with isopropylammonium, contains uranyl chromate hemispheres with lateral dimensions of 18.9 × 18.5 ?(2) and a height of about 8 ?. The hemispheres are centered by a UO(8) hexagonal bipyramid surrounded by six dimers of Cr(5+)O(5) square pyramids, UO(7) pentagonal bipyramids, and Cr(6+)O(4) tetrahedra. The hemispheres are linked into two-dimensional layers so that two adjacent hemispheres are oriented in opposite directions relative to the plane of the layer. From a topological point of view, the hemispheres have the formula U(21)Cr(23) and can be considered as derivatives of nanospherical cluster U(26)Cr(36) composed of three-, four-, and five-membered rings.     

Aqueous reactions of U(VI) at high chloride concentrations: syntheses and structures of new uranyl chloride polymers

The reactions of UO(3) with acidic aqueous chloride solutions resulted in the formation of two new polymeric U(VI) compounds. Single crystals of Cs(2)[(UO(2))(3)Cl(2)(IO(3))(OH)O(2)].2H(2)O (1) were formed under hydrothermal conditions with HIO(3) and CsCl, and Li(H(2)O)(2)[(UO(2))(2)Cl(3)(O)(H(2)O)] (2) was obtained from acidic LiCl solutions under ambient temperature and pressure. Both compounds contain pentagonal bipyramidal coordination of the uranyl dication, UO(2)(2+). The structure of 1 consists of infinite [(UO(2))(3)Cl(2)(IO(3))(mu(3)-OH)(mu(3)-O)(2)](2-) ribbons that run down the b axis that are formed from edge-sharing pentagonal bipyramidal [UO(6)Cl] and [UO(5)Cl(2)] units. The Cs(+) cations separate the chains from one another and form long ionic contacts with terminal oxygen atoms from iodate ligands, uranyl oxygen atoms, water molecules, and chloride anions. In 2, edge-sharing [UO(3)Cl(4)] and [UO(5)Cl(2)] units build up tetranuclear [(UO(2))(4)(mu-Cl)(6)(mu(3)-O)(2)(H(2)O)(2)](2-) anions that are bridged by chloride to form one-dimensional chains. These chains are connected in a complex network of hydrogen bonds and interactions of uranyl oxygen atoms with Li(+) cations. Crystal data: 1, orthorhombic, space group Pnma, a = 8.2762(4) A, b = 12.4809(6) A, c = 17.1297(8) A, Z = 4; 2, triclinic, space group P1, a = 8.110(1) A, b = 8.621(1) A, c = 8.740(1) A, Z = 2.     

Metal-controlled assembly of uranyl diphosphonates toward the design of functional uranyl nanotubules

Two uranyl nanotubules with elliptical cross sections were synthesized in high yield from complex and large oxoanions using hydrothermal reactions of uranyl salts with 1,4-benzenebisphosphonic acid or 4,4'-biphenylenbisphosphonic acid and Cs(+) or Rb(+) cations in the presence of hydrofluoric acid. Disordered Cs(+)/Rb(+) cations and solvent molecules are present within and/or between the nanotubules. Ion-exchange experiments with A(2){(UO(2))(2)F(PO(3)HC(6)H(4)C(6)H(4)PO(3)H)(PO(3)HC(6)H(4)C(6)H(4)PO(3))}·2H(2)O (A = Cs(+), Rb(+)), revealed that A(+) cations can be exchanged for Ag(+) ions. The uranyl phenyldiphosphonate nanotubules, Cs(3.62)H(0.38)[(UO(2))(4){C(6)H(4)(PO(2)OH)(2)}(3){C(6)H(4)(PO(3))(2)}F(2)]·nH(2)O, show high stability and exceptional ion-exchange properties toward monovalent cations, as demonstrated by ion-exchange studies with selected cations, Na(+), K(+), Tl(+), and Ag(+). Studies on ion-exchanged single crystal using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS) provide evidence for chemical zonation in Cs(3.62)H(0.38)[(UO(2))(4){C(6)H(4)(PO(2)OH)(2)}(3){C(6)H(4)(PO(3))(2)}F(2)]·nH(2)O, as might be expected for exchange through a diffusion mechanism.     

A novel open framework uranyl molybdate: synthesis and structure of (NH4)4[(UO2)5(MoO4)7](H2O)5

Single crystals of (NH(4))(4)[(UO(2))(5)(MoO(4))(7)](H(2)O)(5) have been synthesized hydrothermally using (NH(4))(6)Mo(7)O(24), (UO(2))(CH(3)COO)(2).2H(2)O, and H(2)O at 180 degrees C. The phase has been characterized by single-crystal X-ray diffraction using a merohedrally twinned single crystal: it is hexagonal, P6(1), a = 11.4067(5) A, c = 70.659(5) A, V = 7961.9(7) A(3), and Z = 6. The structure is based upon an open framework with composition [(UO(2))(5)(MoO(4))(7)](4-) that is composed of UO(7) pentagonal bipyramids that share vertexes with MoO(4) tetrahedra. The framework has large channels (effective pore size: 4.8 x 4.8 A(2)) parallel to the c axis and a system of smaller channels (effective pore size: 2.5 x 3.6 A(2)) parallel to [100], [110], [010], [110], [110], and [110]. The channels are occupied by NH(4)(+) cations and H(2)O molecules. The topological structure of the uranyl molybdate framework can be described either in terms of fundamental chains of UO(7) pentagonal bipyramids and MoO(4) tetrahedra or in terms of tubular building units parallel to the c axis.     

K(VO)(SeO(3))(2)H: A New One-Dimensional Compound with Strong Hydrogen Bonding

The hydrothermal synthesis, X-ray single crystal structure, magnetic properties, and solid state NMR and infrared spectroscopic data of a new compound, K(VO)(SeO(3))(2)H, are described. K(VO)(SeO(3))(2)H crystallizes in the monoclinic space group P2(1)/m (No. 11), with a = 7.8659(7) ?, b = 10.4298(7) ?, c = 4.0872(7) ?, beta = 96.45(1) degrees, and Z = 4. The structure is described as parallel linear strands made of repeating [(VO)(SeO(3))(2)](2-) units. The chains are held together through hydrogen bondings between selenite oxygens, weak V=O.V=O bonds, and ionic bonds to the interchain K(+) ions. The hydrogen bonding in this compound shows many characteristics of the strong hydrogen bonding with a short O-O distance of 2.459(6) ?, a large down field shift of the proton NMR signal of 19 +/- 1 ppm, and a low O-H absorption frequency. However, the exact position of the hydrogen atom and, thus, the nature of the hydrogen bonding in this compound is unclear. Possible models for the hydrogen atom positions are discussed based on experimental and literature data. The magnetic susceptibility data show an antiferromagnetic coupling below 19 K. The curve can be explained with a 1-D Heisenberg model for S = (1)/(2) with J/k = 13.8 K and g = 1.97.