O2 Cr Research Articles

3D Uranyl Organic Frameworks Supported by Rigid Octadentate Carboxylate Ligand: Synthesis, Structure Diversity, and Luminescence Properties.

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH4 ][(UO2 )3 (HTTDS)(H2 O)] (1), [(UO2 )4 (HTTDS)2 ](HIM)6 (2, IM=imidazole), [(UO2 )4 (TTDS)(H2 O)2 (Phen)2 ] (3, Phen=1,10-phenanthroline), [Zn(H2 O)4 ]0.5 [(UO2 )3 (HTTDS)(H2 O)4 ] (4), and {(UO2 )2 [Zn(H2 O)3 ]2 (TTDS)} (5), {Zn(UO2 )2 (H2 O)(Dib)0.5 (HDib)(HTTDS)} (6, Dib=1,4-di(1H-imidazol-1-yl)benzene) and [Na]{(UO2 )4 [Cu3 (u3 -OH)(H2 O)7 ](TTDS)2 } (7) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5-dicarboxyphenyl)silicon(H8 TTDS). These UOFs have different 3D self-assembled structures as a function of co-ligands, structure-directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO7 pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N-donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO2 ]2+ units as co-ligands. The second metal centers were introduced in the syntheses of 4-7, and in all cases, they are part of the final structures, either as a counterion (4) or as a component of framework (5-7). Interesting, in 7, a rare polyoxometalate [Cu3 (μ3 -OH)O7 (O2 CR)4 ] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO2 )2 (O2 CR)4 ] unit. Those uranyl carboxylates were sufficiently determined by single crystal X-ray diffraction, and their topological structures and luminescence properties were analyzed in detail.

Computational Comparative Mechanistic Study of C-E (E=C,N,O,S) Coupling Reactions through CO2 Activation Mediated by Uranium(III) Complexes.

A DFT mechanistic study is undertaken on the functionalization of CO2 to form C-C, C-N, C-S, and C-O bonds promoted by trivalent uranium complexes (Tp*)2 UR [Tp*=hydrotris(3,5-dimethylpyrazolyl)-borate ligand, R= -C≡CPh (Cpda-CC), -C≡CSiMe3 (Cpda-CSi), -NHPh (Cpda-N), -SPh (Cpda-S), and -OPh (Cpda-O)]. These model systems are similar in view of their two-step reaction mechanisms, that is, the insertion of CO2 into the U-E (E=C, N, O, S) bond to form a [U-κ1 -O2 C] intermediate, followed by the reorientation of the carboxylate group to coordinate with the U atom in the κ2 manner (Cpdb-X, X=CC, CSi, N, S, O). However, the free energy barriers to the rate-determining steps are substantially different, increasing in the order Cpda-S<Cpda-CC<Cpda-Csi<Cpda-N<Cpda-O, which suggests that the bond property of the U-E bonds and the nucleophilicity of the R groups govern the reactivity of the trivalent U complexes. The insertion product may then be silylated in the presence of trimethylsilyl iodide. Two potential mechanisms have been investigated with the -O2 CR group attacking the Si atom from the side cis (frontside) or trans (backside) to the I atom. The backside pathway was found to be more feasible in view of the free energy barriers and thermicity.

Synthesis, Structure and Catalytic Activity of NHC-Ag(I) Carboxylate Complexes.

A general synthetic route was used to prepare 15 new N-heterocyclic carbene (NHC)-Ag(I) complexes bearing anionic carboxylate ligands [Ag(NHC)(O2 CR)], including a homologous series of complexes of sterically flexible ITent ligands, which permit a systematic spectroscopic and theoretical study of the structural and electronic features of these compounds. The complexes displayed a significant ligand-accelerated effect in the intramolecular cyclisation of propargylic amides to oxazolidines. The substrate scope is highly complementary to that previously achieved by NHC-Au and pyridyl-Ag(I) complexes.

Coordination Polymers of Palladium Bridged by Carboxylate and Dimethylaminoalkylselenolate Ligands.

Coordination polymers of palladium stabilized by dimethylaminoalkylselenolate and carboxylate ligands are reported. The reaction of [PdCl(SeCH2 CH2 NMe2 )]3 with AgOTf followed by treatment with sodium acetate afforded [Pd(0) Pd(II) 4 (SeCH2 CH2 NMe2 )3 (OAc)3 ](OTf)2 (1) in which one of the Pd atoms is in the zero oxidation state. In the absence of NaOAc, a tetranuclear complex, [Pd(II) 4 (SeCH2 CH2 NMe2 )4 (OTf)](OTf)3 (2), is isolated from the same reaction. Subsequent treatment with NaO2 CR afforded [Pd4 (SeCH2 CH2 NMe2 )4 (O2 CR)4 ] (R=tBu (3) and Ph (4)). The reaction of [PdCl(SeCH2 CH2 CH2 NMe2 )]2 with AgOTf and NaOAc yielded an ionic binuclear complex, [Pd(II) 2 (SeCH2 CH2 CH2 NMe2 )2 (OAc)](OTf) (5). These complexes have been characterized by NMR spectroscopy, crystal structures, and in some cases by X-ray photoelectron spectroscopy, cyclic voltammetry and mass spectrometry. Complexes 1 and 5 are associated through secondary interactions and coordinate bonds, respectively, to generate polymeric structures in the solid state.

Experimental and computational studies of the molybdenum-flanking arene interaction in quadruply bonded dimolybdenum complexes with terphenyl ligands.

To clarify the nature of the Mo-Carene interaction in terphenyl complexes with quadruple Mo-Mo bonds, ether adducts of composition [Mo2 (Ar')(I)(O2 CR)2 (OEt2)] have been prepared and characterized (Ar'=Ar(Xyl) 2 , R=Me; Ar'=ArMes2, R=Me; Ar'=Ar(Xyl2), R=CF3) (Mes=mesityl; Xyl=2,6-Me2 C6 H3, from now on xylyl) and their reactivity toward different neutral Lewis bases investigated. PMe3 , P(OMe)3 and PiPr3 were chosen as P-donors and the reactivity studies complemented with the use of the C-donors CNXyl and CN2 C2 Me4 (1,3,4,5-tetramethylimidazol-2-ylidene). New compounds of general formula [Mo2 (Ar')(I)(O2 CR)2 (L)] were obtained, except for the imidazol-2-ylidene ligand that yielded a salt-like compound of composition [Mo2 (Ar(Xyl2))(O2 CMe)2 (CN2 C2 Me4)2]I. The Mo-Carene interaction in these complexes has been analyzed with the aid of X-ray data and computational studies. This interaction compensates the coordinative and electronic unsaturation of one of the Mo atoms in the above complexes, but it seems to be weak in terms of sharing of electron density between the Mo and Carene atoms and appears to have no appreciable effect in the length of the Mo-Mo, Mo-X, and Mo-L bonds present in these molecules.

Nuclearity Control in Molecular Iron Phosphates through Choice of Iron Precursors and Ancillary Ligands

The potential of a mono-organophosphate ester in assembling low to medium nuclearity iron complexes with novel topological architectures has been investigated. Reaction of 2,6-diisopropylphenyl dihydrogen phosphate (dipp-H(2)) with ferrous acetate under an inert atmosphere resulted in the formation of mononuclear, [Fe(II)(dipp-H)(2)(py)(4)] (1) (py = pyridine), dinuclear [Fe(III) (2)O(dipp-H)(4)(3,5-dmpz)(3)(thf)](3,5-dmpz)(thf)(3) (2) (3,5-dmpz = 3,5-dimethylpyrazole, thf = tetrahydrofuran), and trinuclear [Fe(III) (2)Fe(II)O(dipp-H)(6)(thf)(3)](collidine) (3) complexes by changing the ancillary amine used in the reaction. Use of a preformed mu(3)-oxo bridged trinuclear complex, [Fe(III) (3)O(O(2)CR)(6)(H(2)O)(3)]X (X = Cl and NO(3)), as the precursor yielded two tetranuclear iron phosphates, [Fe(III) (4)O(dipp)(3)(py)(4)(PhCOO)(4)](toluene)(3) (4) and [Fe(III) (4)O(dipp)(3)(OAc)(4)(py)(4)](py)(2) (5), having a core structure similar to those found in tetranuclear iron phosphonates. When FeCl(3)6H(2)O was used as the iron precursor, an unprecedented pentanuclear iron phosphate complex, [Fe(III) (5)O(dipp)(6)(py)(4)Cl(2)][pyH] (6) with a novel structure was isolated. Another pentanuclear complex having a similar core structure, [Fe(5)O(dipp)(6)(HO(2)CPh)(3)(CH(3)CN)(3)Cl] (7) was isolated on treatment of dipp-H(2) with the triangular complex, [Fe(III) (3)O(O(2)CPh)(6)(H(2)O)(3)]Cl in the absence of any added amine co-ligand. Compounds 1-7 have been characterized by analytical techniques, spectroscopic studies, single crystal X-ray diffraction studies, and magnetic measurements. The Mössbauer studies carried out at room temperature support the formulation of all the compounds.

Single-Molecule Magnets: Different Rates of Resonant Magnetization Tunneling in Mn12 Complexes.

Two new molecular magnets, the dodecanuclear manganese complexes of the type [Mn12 O12 (O2 CR)16 (H2 O)4 ] (known for R = CH3 , new for R = o-ClC6 H4 , o-BrC6 H4 ) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization hysteresis loops of these high-spin clusters are attributed to changes in the rates of magnetization tunneling from one complex to another.