Uranyl and/or rare-earth mellitates in extended organic-inorganic networks: a unique case of heterometallic cation-cation interaction with U(VI)═O-Ln(III) bonding (Ln = Ce, Nd)

A series of uranyl and lanthanide (trivalent Ce, Nd) mellitates (mel) has been hydrothermally synthesized in aqueous solvent. Mixtures of these 4f and 5f elements also revealed the formation of a rare case of lanthanide-uranyl coordination polymers. Their structures, determined by XRD single-crystal analysis, exhibit three distinct architectures. The pure lanthanide mellitate Ln(2)(H(2)O)(6)(mel) possesses a 3D framework built up from the connection of isolated LnO(6)(H(2)O)(3) polyhedra (tricapped trigonal prism) through the mellitate ligand. The structure of the uranyl mellitate (UO(2))(3)(H(2)O)(6)(mel)·11.5H(2)O is lamellar and consists of 8-fold coordinated uranium atoms linked to each other through the organic ligand giving rise to the formation of a 2D 3(6) net. The third structural type, (UO(2))(2)Ln(OH)(H(2)O)(3)(mel)·2.5H(2)O, involves direct oxygen bondings between the lanthanide and uranyl centers, with the isolation of a heterometallic dinuclear motif. The 9-fold coordinated Ln cation, LnO(5)(OH)(H(2)O)(3), is linked to the 7-fold coordinated uranyl (UO(2))O(4)(OH) (pentagonal bipyramid) via one μ(2)-hydroxo group and one μ(2)-oxo group. The latter is shared between the uranyl bonding (U═O = 1.777(4)/1.779(6) ?) and a long Ln-O bonding (Ce-O = 2.822(4) ?; Nd-O = 2.792(6) ?). This unusual linkage is a unique illustration of the so-called cation-cation interaction associating 4f and 5f metals. The dinuclear motif is then further connected through the mellitate ligand, and this generates organic-inorganic layers that are linked to each other via discrete uranyl (UO(2))O(4) units (square bipyramid), which ensure the three-dimensional cohesion of the structure. The mixed U-Ln carboxylate is thermally decomposed from 260 to 280 °C and then transformed into the basic uranium oxide (U(3)O(8)) together with U-Ln oxide with the fluorite structural type ("(Ln,U)O(2)"). At 1400 °C, only fluorite type "(Ln,U)O(2)" is formed with the measured stoichiometry of U(0.63)Ce(0.37)O(2) and U(0.60)Nd(0.40)O(2-δ).     

Lanthanide diruthenium(II,III) compounds showing layered and PtS-type open framework structures

Two types of lanthanide diruthenium phosphonate compounds, based on the mixed-valent metal-metal bonded paddlewheel core of Ru(2)(hedp)(2)(3-) [hedp = 1-hydroxyethylidenediphosphonate, CH(3)C(OH)(PO(3))(2)], have been prepared with the formulas Ln(H(2)O)4[Ru(2)(hedp)(2)(H(2)O)2].5.5H(2)O (1.Ln, Ln = La, Ce) and Ln(H(2)O)4[Ru(2)(hedp)(2)(H(2)O)(2)].8H(2)O (2.Ln, Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er). In both types, each Ru(2)(hedp)2(H2O)23- unit is linked by four Ln(3+)ions through four phosphonate oxygen (OP) atoms and vice versa. The geometries of the {LnO(P4)} group, however, are different in the two cases. In 1.Ln, the geometry of {LnO(P4)} is closer to a distorted plane, and thus a square-grid layer structure is found. In 2.Ln, the geometry of {LnO(P4)} is better described as a distorted tetrahedron; hence, a unique PtS-type open-framework structure is observed. The channels generated in structures 2.Ln are filled with water aggregates with extensive hydrogen-bond interactions. The magnetic and electrochemical properties are also investigated.     

Structures and properties of porous coordination polymers based on lanthanide carboxylate building units

A series of 3-D lanthanide porous coordination polymers, [Ln(6)(BDC)(9)(DMF)(6)(H(2)O)(3)·3DMF](n) [Ln = La, 1; Ce, 2; Nd, 3], [Ln(2)(BDC)(3)(DMF)(2)(H(2)O)(2)](n) [Ln = Y, 4; Dy, 5; Eu, 6], [Ln(2)(ADB)(3)(DMSO)(4)·6DMSO·8H(2)O](n) [Ln = Ce, 7; Sm, 8; Eu, 9; Gd, 10], {[Ce(3)(ADB)(3)(HADB)(3)]·30DMSO·29H(2)O}(n) (11), and [Ce(2)(ADB)(3)(H(2)O)(3)](n) (12) (H(2)BDC = benzene-1,4-dicarboxylic acid and H(2)ADB = 4,4'-azodibenzoic acid), have been synthesized and characterized. In 1-3, the adjacent Ln(III) ions are intraconnected to form 1-D metal-carboxylate oxygen chain-shaped building units, [Ln(4)(CO(2))(12)](n), that constructed a 3-D framework with 4 × 7 ? rhombic channels. In 4-6, the dimeric Ln(III) ions are interlinked to yield scaffolds with 3-D interconnecting tunnels. Compounds 7-10 are all 3-D interpenetrating structures with the CaB6-type topology structure. Compound 11 is constructed by ADB spacers and trinulcear Ce nodes with a NaCl-type topology structure and a 1.9-nm open channel system. In 12, the adjacent Ce(III) ions are intraconnected to form 1-D metal-carboxylate oxygen chain-shaped building units, [Ln(4)(CO(2))(12)](n), and give rise to a 3-D framework. Moreover, 6 exhibits characteristic red luminescence properties of Eu(III) complexes. The magnetic susceptibilities, over a temperature range of 1.8-300 K, of 3, 6, and 7 have also been investigated; the results show paramagnetic properties.     

Chemical equilibria in the uranyl(vi)-peroxide-carbonate system; identification of precursors for the formation of poly-peroxometallates

The focus of this study is on the identification of precursors in solution that might act as building blocks when solid uranyl(vi) poly-peroxometallate clusters containing peroxide and hydroxide bridges are formed. The precursors could be identified by using carbonate as an auxiliary ligand that prevented the formation of large clusters, such as the ones found in solids of fullerene type. Using data from potentiometric and NMR ((17)O and (13)C) experiments we identified the following complexes and determined their equilibrium constants: (UO(2))(2)(O(2))(CO(3))(4)(6-), UO(2)(O(2))CO(3)(2-), UO(2)(O(2))(CO(3))(2)(4-), (UO(2))(2)(O(2))(CO(3))(2)(2-), (UO(2))(2)(O(2))(2)(CO(3))(2-) and [UO(2)(O(2))(CO(3))](5)(10-). The NMR spectra of the pentamer show that all uranyl and carbonate sites are equivalent, which is only consistent with a ring structure built from uranyl units linked by peroxide bridges with the carbonate coordinated "outside" the ring; this proposed structure is very similar to [UO(2)(O(2))(oxalate)](5)(10-) identified by Burns et al. (J. Am. Chem. Soc., 2009, 131, 16648; Inorg. Chem., 2012, 51, 2403) in K(10)[UO(2)(O(2))(oxalate)](5)·(H(2)O)(13); similar ring structures where oxalate or carbonate has been replaced by hydroxide are important structure elements in solid poly-peroxometallate complexes. The equivalent uranyl sites in (UO(2))(2)(O(2))(2)(CO(3))(2-) suggest that the uranyl-units are linked by the carbonate ion and not by peroxide.     

Uranyl sensitization of samarium(III) luminescence in a two-dimensional coordination polymer

Heterometallic carboxyphosphonates UO(2)(2+)/Ln(3+) have been prepared from the hydrothermal reaction of uranyl nitrate, lanthanide nitrate (Ln = Sm, Tb, Er, Yb), and phosphonoacetic acid (H(3)PPA). Compound 1, (UO(2))(2)(PPA)(HPPA)(2)Sm(H(2)O)·2H(2)O (1) adopts a two-dimensional structure in which the UO(2)(2+) metal ions bind exclusively to the phosphonate moiety, whereas the Ln(3+) ions are coordinated by both phosphonate and carboxylate functionalities. Luminescence studies of 1 show very bright visible and near-IR samarium(III)-centered emission upon direct excitation of the uranyl moiety. The Sm(3+) emissive state exhibits a double-exponential decay with lifetimes of 67.2 ± 6.5 and 9.0 ± 1.3 μs as measured at 594 nm, after excitation at both 365 and 420 nm. No emission is observed in the region typical of the uranyl cation, indicating that all energy is either transferred to the Sm(3+) center or lost to nonradiative processes. Herein we report the synthesis, crystal structure, and luminescent behavior of 1, as well as those of the isostructural terbium, erbium, and ytterbium analogues.     

Homochiral frameworks formed by reactions of lanthanide ions with a chiral antimony tartrate secondary building unit

A chiral cluster compound, dipotassium bis(μ-tartrato)diantimony(III), K(2)Sb(2)L(2) (H(4)L = L-tartaric acid), was used as a secondary building unit to react with lanthanide ions. Three series of homochiral coordination compounds were obtained: 0D [La(H(2)L)(H(2)O)(4)](2)[Sb(2)L(2)]·7H(2)O (0D-La), 1D Ln(Sb(2)L(2))(H(2)O)(5)(NO(3))·H(2)O (1D-Ln) (Ln = La-Lu or Y, expect Pm), 2D(I) [(Ln(H(2)O)(5))(2)(Sb(2)L(2))(3)]·5H(2)O (2D(I)-Ln) (Ln = La, Ce, Pr), and 2D(II) [(La(H(2)O)(5))(2)(Sb(2)L(2))(3)]·6H(2)O (2D(II)-La). Single-crystal X-ray diffraction studies indicated that 0D-La crystallizes in space group P1, and the structure contains isolated Sb(2)L(2)(2-) units located between chains of composition La(H(2)L)(H(2)O)(4). The series of 1D-Ln compounds is isostructural and crystallizes in space group P2(1)2(1)2(1). In the structure, Sb(2)L(2)(2-) units are coordinated to two Ln ions by two out of the four free tartrate oxygen atoms to form a linear chain. To the best of our knowledge, this is the first example of a homochiral structure that can be formed for the whole lanthanide series. In the 2D(I)-Ln structure series, which crystallizes in space group P2(1), the Sb(2)L(2)(2-) units have two distinct coordination modes: one is the same as that found in the 1D structure, while in the other all four free tartrate oxygen atoms are coordinated to four Ln ions in a very distorted tetrahedral arrangement. The connectivity between Sb(2)L(2)(2-) secondary units and LnO(9) polyhedra gives rise to infinite layers. 2D(II) [(La(H(2)O)(5))(2)(Sb(2)L(2))(3)]·6H(2)O, which crystallizes in space group C2, has a similar network to the 2D(I)-Ln compounds. The trends in lattice parameters, bond lengths, and ionic radii in the 1D-Ln series were analyzed to show the effect of the lanthanide contraction.     

Three-dimensional lanthanide(III)-copper(II) compounds based on an unsymmetrical 2-pyridylphosphonate ligand: an experimental and theoretical study

Based on an unsymmetrical 2-pyridylphosphonate ligand, two types of Ln(III)-Cu(II) compounds with three-dimensional structures were obtained under hydrothermal conditions, namely, Ln(2)Cu(3)(C(5)H(4)NPO(3))(6).4H(2)O (1.Ln; Ln=La, Ce, Pr, Nd) and Ln(2)Cu(3)(C(5)H(4)NPO(3))(6) (2.Ln; Ln=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho). Compounds 1.Ln are isostructural and crystallize in chiral cubic space group I2(1)3. In these structures, each Ln ion is nine-coordinate and has a tricapped triprismatic geometry, while each Cu center is six-coordinate with an octahedral environment. The {LnO(9)} polyhedra and {CuN(2)O(4)} octahedra are connected by edge sharing to form an inorganic open framework structure with a 3-connected 10-gon (10,3) topology in which the Ln and Cu atoms are alternately linked by the phosphonate oxygen atoms. Compounds 2.Ln are isostructural and crystallize in trigonal space group R3. In these structures, the {LnO(6)} octahedra are triply bridged by the {CPO(3)} tetrahedra by corner sharing to form an infinite chain along the c axis. Each chain is connected to its six equivalents through corner sharing of {CPO(3)} tetrahedra and {CuN(2)O(2)} planes to form a three-dimensional framework structure in which the Ln and Cu atoms are linked purely by O-P-O units. The formation of these two types of structures is rationalized by quantum chemical calculations, which showed that both the lanthanide contraction and the electron configuration of Cu(II) play important roles. When Cu(II) was replaced by Zn(II), only the first type of compounds resulted. The magnetic properties of complexes 1.Ln and 2.Ln were investigated. The nature of Ln(III)-Cu(II) (Ln=Ce, Pr, Nd) interactions is illustrated by comparison with their Ln(III)-Zn(II) analogues.     

Uranyl heteropolyoxometalate: synthesis, structure, and spectroscopic properties

A novel uranium heteropolyoxometalate, [H(3)O](4)[Ni(H(2)O)(3)](4){Ni[(UO(2))(PO(3)C(6)H(4)CO(2))](3)(PO(4)H)}(4)·2.72H(2)O, has been prepared under mild hydrothermal conditions using the diethyl(2-ethoxycarbonylphenyl)phosphonate ligand and in situ ligand synthesis of the HPO(4)(2-) anion. The cluster is derived from a common UO(7), pentagonal bipyramid and is constructed by employing nickel(II) metal ions as linkers. The 3d-5f heteropolyoxometalate core incorporates 12 classical pentagonal uranyl groups and four Ni(2+) octahedral units.     

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.     

Large cluster formation through multiple substitution with lanthanide cations (La, Ce, Nd, Sm, Eu, and Gd) of the polyoxoanion

Several new large polyoxotungstates have been synthesized by reaction of lanthanide cations with the well-known "As(4)W(40)" anion, [(B-alpha-AsO(3)W(9)O(30))(4)(WO(2))(4)](28-) (1). The heteropolyanions [(H(2)O)(11)Ln(III)(Ln(III)(2)OH)(B-alpha-AsO(3)W(9)O(30))(4)(WO(2))(4)](20)(-) (Ln = Ce, Nd, Sm, Gd) (2-4) (Ln(3)As(4)W(40)) and [M(m)()(H(2)O)(10)(Ln(III)(2)OH)(2)(B-alpha-AsO(3)W(9)O(30))(4)(WO(2))(4)]((18-m)(-)) (Ln = La, Ce, Gd and M = Ba, K, none) (5-7) (Ln(4)As(4)W(40)) have been isolated as alkali metal and ammonium salts, respectively, and characterized by single-crystal X-ray analysis, elemental analysis, and IR and (183)W-NMR spectroscopy. The X-ray analyses revealed interanionic W-O-Ln bonds between adjacent Ln(x)()As(4)W(40) units forming a "dimer" for x = 3 and chains for x = 4. Upon dissolving in water these bonds hydrolyze and the monomeric species form. The straightforward syntheses which require the use of concentrated NaCl solutions (1-4 M) and the addition of stoichiometric amounts of Ba(2+) or K(+) reemphasize the importance of the presence of appropriate countercations for the assembly of large polyoxometalate structures.     

A series of three-dimensional architectures constructed from lanthanide-substituted polyoxometalosilicates and lanthanide cations or lanthanide-organic complexes as linkers

Six 3D architectures based on lanthanide-substituted polyoxometalosilicates, KLn[(H(2)O)(6)Ln](2)[(H(2)O)(4)LnSiW(11)O(39)](2)·nH(2)O (Ln = La 1, n = 42; Ce 2, n = 40), H[(H(2)O)(6)Nd](2)[(H(2)O)(7)Nd][(H(2)O)(4)NdSiW(11)O(39)][(H(2)O)(3)NdSiW(11)O(39)]·13H(2)O (3), H(2)K(2)[(Hpic)(H(2)O)(5)Ln](2)[(H(2)O)(4)LnSiW(11)O(39)](2)·nH(2)O (Ln = La 4, n = 18.5; Ce 5, n = 35; Nd 6, n = 36; Hpic = 4-picolinic acid), have been synthesized and characterized by elemental analysis, IR and UV-vis spectroscopy, TG analysis, powder X-ray diffraction and single crystal X-ray diffraction. Compounds 1 and 2 are isostructural, built up of lanthanide-substituted polyoxoanions [{(H(2)O)(4)Ln(SiW(11)O(39))}(2)](10-) linked by Ln(3+) cations to form a 3D open framework with 1D channels. The polyoxoanion [{(H(2)O)(4)Ln(SiW(11)O(39))}(2)](10-) consists of two α(1)-type mono-Ln-substituted Keggin anions. When Nd(3+) ion was used instead of La(3+) or Ce(3+) ions, compound 3 with a different structure was obtained, containing two kinds of polyoxoanions [{(H(2)O)(4)Nd(SiW(11)O(39))}(2)](10-) and [{(H(2)O)(3)Nd(SiW(11)O(39))}(2)](10-) which are connected together by Nd(3+) ions to yield a 3D framework. When 4-picolinic acid was added to the reaction system of 1-3, isostructural compounds 4-6 were obtained, constructed from the polyoxoanions [{(H(2)O)(4)Ln(SiW(11)O(39))}(2)](10-) linked by picolinate-chelated lanthanide centers to form a 3D channel framework. From a topological viewpoint, the 3D nets of 1, 2, 4, 5 and 6 exhibit a (3,6)-connected rutile topology, whereas the 3D structure of 3 possesses a rare (3,3,6,10)-connected topology. The magnetic properties of 2, 3, 5 and 6 have been studied by measuring their magnetic susceptibilities in the temperature range 2-300 K.     

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.     

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.     

Mixed-valent uranium(IV,VI) diphosphonate: synthesis, structure, and spectroscopy

A mixed-valent uranium(IV,VI) diphosphonate, (H(3)O)(2)(UO(2))(3)U(H(2)O)(2)[CH(2)(PO(3))(2)](3)·6H(2)O (UC1P2S), has been synthesized under hydrothermal conditions. S-2-butanol was used to reduce uranium VI to IV. The tetravalent uranium centers adopt eight-coordinate geometries, while hexavalent uranyl units are all tetragonal bipyramids. The UV-vis-NIR spectrum of UC1P2S shows absorption features for both U(VI) and U(IV).     

Evidence for the formation of UO2(NO3)4(2-) in an ionic liquid by EXAFS

The complexation between uranium(vi) and nitrate ions in a hydrophobic ionic liquid (IL), namely [BMI][NO(3)] (BMI = 1-butyl-3-methylimidazolium(+)), is investigated by EXAFS spectroscopy. It was performed by dissolution of uranyl nitrate UO(2)(NO(3))(2)·6H(2)O or UO(2)(Tf(2)N)(2) (Tf(2)N = bis(trifluoromethylsulfonyl)imide (CF(3)SO(2))(2)N(-)). The formation of the complex UO(2)(NO(3))(4)(2-) is evidenced.     

Explorations of new quaternary phases in the Ln(III)-V(V)(d0)-Se(IV)-O (Ln = Nd, Eu, Gd, Tb) systems

Systematic explorations of new phases in the Ln(III)-V(V)-Se(IV)-O systems by hydrothermal syntheses led to four new quaternary compounds, namely, Nd(2)(V(V)(2)O(4))(SeO(3))(4)·H(2)O (1), Ln(V(V)O(2))(SeO(3))(2) (Ln = Eu 2, Gd 3, Tb 4). The structure of Nd(2)(V(V)(2)O(4))(SeO(3))(4)·H(2)O features a 3D framework composed of the 2D layers of [N d(SeO(3))](+) bridged by the infinite [VO(2)(SeO(3))](-) chains with the lattice water molecules located at the 6-membered ring tunnels formed. The structure of Ln(V(V)O(2))(SeO(3))(2) (Ln = Eu, Gd, Tb) also features a 3D framework composed of 2D layers of [Ln(SeO(3))](+) bridged by the infinite [(VO(2))(SeO(3))](-) double chains. The 1D vanadium oxide selenite chain of 1 differs significantly from those in compounds 2-4 in terms of the coordination modes of the selenite groups and the connectivities between neighbouring VO(6) octahedra. Luminescent and magnetic properties of these compounds were also measured.     

Solid-State and solution studies of [Ln(n)(SiW11O39)] polyoxoanions: an example of building block condensation dependent on the nature of the rare earth

The reactivity of the [alpha-SiW(11)O(39)](8-) monovacant polyoxometalate with lanthanide has been investigated for four different trivalent rare-earth cations (Ln = Nd(III), Eu(III), Gd(III), Yb(III)). The crystal structures of KCs(4)[Yb(alpha-SiW(11)O(39))(H(2)O)(2)] x 24H(2)O (1), K(0.5)Nd(0.5)[Nd(2)(alpha-SiW(11)O(39))(H(2)O)(11)] x 17H(2)O (2a), and Na(0.5)Cs(4.5)[Eu(alpha-SiW(11)O(39))(H(2)O)(2)] x 23H(2)O (3a) are reported. The solid-state structure of compound 1 consists of linear wires built up of [alpha-SiW(11)O(39)](8-) anions connected by Yb(3+) cations, while the linkage of the building blocks by Eu(3+) centers in 3a leads to the formation of zigzag chains. In 2a, dimeric [Nd(2)(alpha-SiW(11)O(39))(2)(H(2)O)(8)](10-) entities are linked by four Nd(3+) cations. The resulting chains are connected by lanthanide ions, leading to a bidimensional arrangement. Thus, the dimensionality, the organization of the polyoxometalate building units, and the Ln/[alpha-SiW(11)O(39)](8-) ratio in the solid state can be tuned by choosing the appropriate lanthanide. The luminescent properties of compound 3a have been studied, showing that, in solution, the polymer decomposes to give the monomeric complex [Eu(alpha-SiW(11)O(39))(H(2)O)(4)](5-). The lability of the four exogenous ligands connected to the rare earth must allow the functionalization of this lanthanide polyanion.     

Diverse lanthanide coordination polymers tuned by the flexibility of ligands and the lanthanide contraction effect: syntheses, structures and luminescence

Two new flexible exo-bidentate ligands were designed and synthesized, incorporating different backbone chain lengths bearing two salicylamide arms, namely 2,2'-(2,2'-oxybis(ethane-2,1-diyl)bis(oxy))bis(N-benzylbenzamide) (L(I)) and 2,2'-(2,2'-(ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl))bis(oxy)bis(N-benzylbenzamide) (L(II)). These two structurally related ligands are used as building blocks for constructing diverse lanthanide polymers with luminescent properties. Among two series of lanthanide nitrate complexes which have been characterized by elemental analysis, TGA analysis, X-ray powder diffraction, and IR spectroscopy, ten new coordination polymers have been determined using X-ray diffraction analysis. All the coordination polymers exhibit the same metal-to-ligand molar ratio of 2?:?3. L(I), as a bridging ligand, reacts with lanthanide nitrates forming two different types of 2D coordination complexes: herringbone framework {[Ln(2)(NO(3))(6)(L(I))(3)·mC(4)H(8)O(2)](∞) (Ln = La (1), and Pr (2), m = 1, 2)} as type I,; and honeycomb framework {[Ln(2)(NO(3))(6)(L(I))(3)·nCH(3)OH](∞) (Ln = Nd (3), Eu (4), Tb (5), and Er (6), n = 0 or 3)} as type II, which change according to the decrease in radius of the lanthanide. For L(II), two distinct structure types of 1D ladder-like coordination complexes were formed with decreasing lanthanide radii: [Ln(2)(NO(3))(6)(L(II))(3)·2C(4)H(8)O(2)](∞) (Ln = La (7), Pr (8), Nd (9)) as type III, [Ln(2)(NO(3))(6)(L(I))(3)·mC(4)H(8)O(2)·nCH(3)OH](∞) (Ln = Eu (10), Tb (11), and Er (12), m, n = 2 or 0) as type IV. The progressive structural variation from the 2D supramolecular framework to 1D ladder-like frameworks is attributed to the varying chain length of the backbone group in the flexible ligands. The photophysical properties of trivalent Sm, Eu, Tb, and Dy complexes at room temperature were also investigated in detail.     

Occurence of an octanuclear motif of uranyl isophthalate with cation-cation interactions through edge-sharing connection mode

An uranyl isophthalate has been hydrothermally synthesized at 200 °C for 24 h, from a mixture of uranyl nitrate, isophthalic acid, and hydrazine in water. It was characterized by single-crystal analysis [triclinic, P ?1, a = 7.3934(3) ?, b = 13.3296(5) ?, c = 15.4432(5) ?, α = 111.865(2)°, β = 90.637(2)°, γ = 104.867(2)°, V = 1355.49(9) ?(3)] and different spectroscopic techniques (Raman, IR-ATR, UV-visible). The 3D structure of the phase (UO(2))(8)O(2)(OH)(4)(H(2)O)(4)(1,3-bdc)(4)·4H(2)O (1,3-bdc = 1,3-benzenedicarboxylate) reveals octanuclear units based on the association of 7-fold coordinated uranyl cations (pentagonal bipyramid) involving a rare case of cation-cation interaction together with edge-sharing polyhedral connection mode. UV-visible absorption spectroscopy confirmed that uranium was only involved in the structure as uranyl forms (excluding the presence of tetravalent or pentavalent uranium). Additionally, μ-Raman and IR-ATR experiments allowed assigning four uranyl contributions to the four types of uranyl entities in the structure, in agreement with the XRD analysis.     

Uranyl peroxide pyrophosphate cage clusters with oxalate and nitrate bridges

Two complex cage clusters built from uranyl hexagonal bipyramids and multiple types of bridges between uranyl ions, U(30)Py(10)Ox(5) and U(38)Py(10)Nt(4), were crystallized from aqueous solution under ambient conditions. These are built from 30 uranyl hexagonal bipyramids, 10 pyrophosphate groups, and five oxalate bridges in one case, and 38 uranyl hexagonal bipyramids, 10 pyrophosphate groups, and four nitrate groups in the other. The crystal compositions are (H(3)O)(10)Li(18)K(22)[(UO(2))(30)(O(2))(30)(P(2)O(7))(10)(C(2)O(4))(5)](H(2)O)(22) and Li(24)K(36)[(UO(2))(38)(O(2))(40)(OH)(8)(P(2)O(7))(10)(NO(3))(4)](NO(3))(4)(H(2)O)(n) for U(30)Py(10)Ox(5) and U(38)Py(10)Nt(4), respectively. Cluster U(30)Py(10)Ox(5) crystallizes over a narrow range of solution pH that encourages incorporation of both oxalate and pyrophosphate, with incorporation of oxalate only being favored under more acidic conditions, and pyrophosphate only under more alkaline conditions. Cluster U(38)Py(10)Nt(4) contains two identical lobes consisting of uranyl polyhedra and pyrophosphate groups, with these lobes linked into the larger cluster through four nitrate groups. The synthesis conditions appear to have prevented closure of these lobes, and a relatively high nitrate concentration in solution favored formation of the larger cluster.