Metal-organic frameworks built from alkali metal ions (Li+-Cs+) and 1,2,3,4-cyclobutanetetracarboxylic acid

International audienceSix complexes formed by alkali metal ions with 1,2,3,4-cyclobutanetetracarboxylic acid (H4cbtc) have been synthesized and crystallographically characterized. In the complexes obtained at room temperature, the original cis,trans,cis form of the ligand (c-H4cbtc) is retained, while in the complexes synthesized under hydrothermal conditions, isomerization occurs to give the trans,trans,trans form (t-H4cbtc). [Li2(t-H2cbtc)(H2O)2] (1) crystallizes as a two-dimensional (2D) assembly, with only four oxygen atoms of the ligand being involved in the bis-chelating coordination of two Li+ cations. A 2D polymer is also obtained with the aliphatic analogue 1,2,3,4-butanetetracarboxylic acid (H4btc) in the complex [Li4(btc)(H2O)4][middle dot]H2O (2), with a much larger ligand denticity of 10. All the other complexes in this series crystallize as three-dimensional (3D) frameworks, with the cation coordination number and ligand denticity increasing when going from the lighter to the heavier cations. In [Na(t-H3cbtc)] (3), the cation octahedral coordination polyhedra are isolated and the 4[middle dot]65 framework contains only four-fold nodes. In the case of K+, the complexes formed with both isomers of the ligand could be isolated. The structure of [K2(c-H2cbtc)(H2O)4] (4) displays [K(H2O)2]+[infinity] planar subunits which are assembled into a 3D network by the hexacoordinated c-H2cbtc2- ligands, while the 412[middle dot]63 network built in [K(t-H3cbtc)] (5) contains only six-fold nodes, K+ being chelated by two ligands, with four more donors resulting in a distorted square antiprismatic coordination polyhedron. Although [Rb(c-H3cbtc)] (6) contains the other ligand isomer, it displays a coordination mode and an overall architecture similar to those in 5, but for the quite different cation coordination polyhedron, which is a distorted dodecahedron with triangular faces. Finally, [Cs(t-H3cbtc)] (7) displays the highest coordination number and ligand denticity in the series, both equal to 10. The cation coordination polyhedron is derived from the cuboctahedron through removal of two vertices in a square face. The 424[middle dot]64 network formed contains chains of tightly packed Cs+ cations with face-sharing coordination polyhedra, thus confirming the prevalence of face-sharing subunits previously noticed in the case of the heavier alkali cations. With packing indexes larger than 0.80 in the whole series, none of these 3D frameworks exhibits appreciable porosity

Chiral one- to three-dimensional uranyl-organic assemblies from (1R,3S)-(+)-camphoric acid

International audienceFour complexes were obtained from reaction of uranyl nitrate with (1R,3S)-(+)-camphoric acid under solvo-/hydrothermal conditions with either acetonitrile or N-methyl-2-pyrrolidone (NMP) as the organic component. All complexes crystallize in chiral space groups and are enantiopure species. Complexes [(UO2)4(L)3(OH)2(H2O)4][middle dot]3H2O (1) and [(UO2)8K8(L)12(H2O)12][middle dot]H2O (2) were obtained in water-acetonitrile in the presence of LiOH or KOH in excess beyond or equal to that simply required to neutralize the acid, respectively. Whereas 1 is a 1D coordination polymer including hydroxide ions resulting from hydrolysis of the uranyl aqua-ion, 2 contains octanuclear uranyl camphorate cages analogous, but for their crystallographic symmetry, to those previously published; these cages are assembled into a 3D framework by bridging potassium ions. The two complexes obtained in water-NMP, [UO2(L)(NMP)] (3) and [(UO2)2Cu(L)3(NMP)2] (4), are devoid both of water molecules and any solvent-derived anions, and they crystallize as 2D assemblies. The sheets in 4, with a thickness of ~14 A, display a central layer of copper(ii) ions surrounded by two layers of uranyl ions. These and previous results suggest that solvo-/hydrothermal conditions using NMP provide a new means of avoiding the formation of uranyl-containing oligomeric or 1D polymeric hydrolysis products which are frequent and often unpredictable outcomes in the synthesis of uranyl-organic assemblies under aqueous conditions, especially in the presence of cosolvents which in themselves are susceptible to hydrolysis. The emission spectrum of compound 3 under excitation at 350 nm displays the usual vibronic fine structure in the ~460-600 nm range, while uranyl luminescence is quenched by Cu(ii) cations in complex 4

Synthesis, structure and photophysical properties of pyrene–based [5]helicenes : an experimental and theoretical study

Pyrene-cored [5]helicenes were prepared by a facile, efficient Wittig reaction and an intramolecular photocyclization reaction utilising 2,7-di-tert-butylpyrene-4-carbaldehyde and naphthalene/pyrene-based phosphorus ylides. Optical properties based on UV−vis absorption and fluorescence spectra were investigated. X-ray crystallography revealed that the pyrene-based [5]helicenes exhibited strong face-to-face π−π interactions and edge-to-face π−π interactions. HOMO and LUMO energies and molecular orbitals were also studied by density functional theory (DFT) calculations. This study has revealed that the torsion angle of the helical structure plays a role in determining the π−π interactions and the frontier molecular orbital energy levels. Thus, pyrene-based helicenes need to be considered when one designs new highly efficient organic light-emitting diodes and organic semiconductor materials

Advances in f-element cyanide chemistry

International audienceThis Dalton perspective gives an overview of the development of cyanide chemistry of 4f- and 5f-elements, a field which was poorly explored in contrast to the attention paid to the cyanide complexes of the d transition metals. The use of the cyanide ligand led to the discovery of mono- and polycyanide complexes which exhibit unprecedented and unexpected coordination geometries. A new type of linear metallocenes including [U(Cp*)2(CN)5]3- (Cp* = C5Me5) and the first bent actinocenes [An(Cot)2(CN)]- (An = Th, U; Cot = C8H8) were isolated. Thorocene was found to be much more reactive than uranocene since a series of sterically crowded cyanide complexes have been obtained only from [Th(Cot)2]. A series of cyanido-bridged dinuclear compounds and mononuclear mono-, bis- and tris(cyanide) complexes were prepared by addition of cyanide salts to [MN*3] (M = Ce, U) and [UN*3]+ (N* = N(SiMe3)2]. The CeIII, UIII and UIV ions were clearly differentiated in these reactions by cyanide linkage isomerism, as shown for example by the structures of the cyanide complex [UIIIN*3(CN)2]2- and of the isocyanide derivatives [CeIIIN*3(NC)2]2- and [UIVN*3(NC)]-. While the U-CN/NC coordination preference towards the UIII/UIV pair is related to the subtle balance between steric, covalent and ionic factors, DFT computations and in particular the calculated total bonding energies between the metal and the cyanide ligand allowed the observed coordination mode to be predicted. The ability of the cyanide ligand to stabilize the high oxidation states was assessed with the synthesis of UV and UVI complexes in the inorganic and organometallic series

Catalytic hydrosilylation of oxalic acid: chemoselective formation of functionalizedC2-products

International audienceOxalic acid is an attractive entry to functionalized C2-products because it can be formed by C–C coupling of two CO2 molecules under electrocatalytic reduction. Herein, we describe the first attempts to reduce oxalic acid by catalytic hydrosilylation. Using B(C6F5)3 as a Lewis acidic catalyst, oxalic acid can be converted to reduced C2-molecules, with high chemoselectivity, under mild reaction conditions

Synthesis and Structure of 1,2-Dimethylene[2.10]metacyclophane and Its Conversion into Chiral [10]Benzenometacyclophanes: Synthesis and Structure of 1,2-Dimethylene[2.10]metacyclophane and Its Conversion into Chiral [10]Benzenometacyclophanes

Bromination of 5,21-di-tert-butyl-8,24-dimethoxy-1,2-dimethyl[2.10]metacyclophan-1-ene (MCP-1-ene; 1) with benzyltrimethylammonium tribromide exclusively afforded 1,2-bis(bromomethyl)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-1-ene (2). Debromination of 2 with Zn and AcOH in CH₂Cl solution at room temperature for 24 h produced dimethylene[2.10]MCP 7 in 92 % yield, which is a stable solid compound. Compound 7 was treated with dimethyl acetylenedicarboxylate (DMAD) to provide 1,2-(3′,6′-dihydrobenzo)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-4′,5′-dimethylcarboxylate (8) in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiral areno-bridged dimethoxy[2.10]MCP-4′,5′-dimethylcarboxylate 9, possessing C₁ symmetry, by aromatization with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). A new type of N-phenyl-maleimide substituted 1,2-(3′,6′-dihydrobenzo)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-4′,5′-N-phenylmaleimide 10 was also synthesized from 7 through treatment with N-phenylmaleimide in toluene at 110 °C followed by aromatization with DDQ. Single-crystal X-ray analysis of 9 revealed the formation of a syn-isomer

Europium(II) Compounds: Simple Synthesis of a Molecular Complex in Water and Coordination Polymers with 2,2'-Bipyrimidine Mediated Ferromagnetic Interactions

International audienceReaction between EuCl2 and 2,2'-bipyrimidine (bpm) in de-oxygenated water afforded a cationic molecular complex [EuCl(bpm)2(H2O)4][Cl]∙H2O (1). When performed in an organic solvent such as THF or methanol, the same reaction yielded a 3-dimensional coordination polymer of formula [EuCl2(bpm)(MeOH)0.5] (2) in which both bpm and the chloride ions act as linkers between the Eu(II) ions. Upon replacing Cl- by I-, two coordination polymers of formula {[Eu(bpm)2(H2O)3][I]2*0.5bpm}∞ (3) and {[Eu(I)(bpm)(MeOH)]- [I]}∞ (4) were obtained from reaction in water and methanol, respectively. All these compounds were characterized by X-ray crystallography. Investigations of the magnetic properties revealed a weak antiferromagnetic coupling in 2, while 3 and 4 showed a weak ferromagnetic coupling at low temperature

Nitrite complexes of the rare earth elements

International audienceThe coordination chemistry of the nitrite anion has been investigated with rare earth elements, and the resulting complexes were structurally characterized. Among them, the first homoleptic examples of nitrite complexes of samarium, ytterbium and yttrium are described. The coordination behavior of the nitrite ion is directly controlled by the ionic radius of the metal cation. While the nitrito ligand is stable in the coordination sphere of cerium(III), it is readily reduced by SmI2

Charge Localisation in Heavy Alkali Metal Ion Complexes of 4,4′-Biphenyldicarboxylate

International audienceCrystal structure determinations on the isomorphous RbI and CsI complexes of 4,4′-biphenyldicarboxylate have shown the carboxylate entities to be coordinated in an unusual fashion where both oxygen atoms are in a tetrahedral environment indicative of negative charge localisation on each. The metal ions also show a highly irregular form of six-coordination, while the biphenyl units are planar, seemingly as a result of attractive interactions between the ortho hydrogen atoms