Exploring the self-assembly of dumbbell-shaped polyoxometalate hybrids,from molecular building units to nanostructured soft materials

The formation of hierarchical nanostructures using preformed dumbbell-like species made of covalent organic–inorganic polyoxometalate (POM)-based hybrids is herein described. In this system, the presence of charged subunits (POM, metal linkers, and counter ions) in the complex molecular architecture can drive their aggregation, which results from a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions. We show that the nature of the POM and the charge of the metal linker are key parameters for the hierarchical nanoorganization. The experimental findings were corroborated with a computational investigation combining DFT and molecular dynamics simulation methods, which outlines the importance of solvation of the counter ion and POM/counter ion association in the aggregation process. The dumbbell-like species can also form gels, in the presence of a poorer solvent, displaying similar nanoorganization of the aggregates. We show that starting from the designed molecular building units whose internal charges can be controlled by redox trigger we can achieve their implementation into soft nanostructured materials through the control of their supramolecular organization.

The formation of hierarchical nanostructures using supramolecular dumbbell-like species made of organic–inorganic polyoxometalate-based hybrids is investigated by combination of SAXS and computational methods.     

Mechanism of imidazole catalysis in the curing of epoxy resins

The mechanism of imidazole catalysis in the curing of epoxy resins was studied using the PGE/1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole model systems and another model system based on trichloromethylethylene oxide. It was demonstrated that imidazolium systems, generated in the curing reaction, show an inherent instability leading to cleavage of an N? C bond or the 2-C? H bond (2-unsubstituted imidazoles). Fourier-transform infrared spectroscopy was used to follow specific changes in the IR spectrum of the curing mixture during polymerization. The identification of carbonyl absorptions occurring during the polymerization led to the conclusion that ketone formation is a general occurrence in the cure of epoxides with nitrogen compounds. We have also shown that imidazoles are regenerated during the curing process by at least two routes. One pathway for the regeneration of the catalyst involves N-dealkylation of the imidazole via a substitution process. Another route, β-elimination, afforded carbonyl compounds, which account for the previously unexplained appearence of infrared bands in the 1650–1770 cm^?1 region during the curing process. These investigations demonstrated the true catalytic function of the imidazole. Possible mechanisms for the regeneration of the catalyst are also suggested.     

Dearomatising rearrangements of lithiated thiophenecarboxamides

Thiophene-3-carboxamides bearing allyl or benzyl substituents at nitrogen undergo dearomatising cyclisation on treatment with LDA. Rearrangements transform the dearomatised products into pyrrolinones, azepinones or partially saturated azepinothiophenes.     

1,2,3-triazolate-bridged tetradecametallic transition metal clusters [M14(L)6O6(OMe)18X6] (M=FeIII, CrIII and VIII/IV) and related compounds: ground-state spins ranging from S=0 to S=25 and spin-enhanced magnetocaloric effect

We report the synthesis, by solvothermal methods, of the tetradecametallic cluster complexes [M14(L)6O6(OMe)18Cl6] (M=FeIII, CrIII) and [V14(L)6O6(OMe)18Cl6-xOx] (L=anion of 1,2,3-triazole or derivative). Crystal structure data are reported for the {M14} complexes [Fe14(C2H2N3)6O6(OMe)18Cl6], [Cr14(bta)6O6(OMe)18Cl6] (btaH=benzotriazole), [V14O6(Me2bta)6(OMe)18Cl6-xOx] [Me2btaH=5,6-Me2-benzotriazole; eight metal sites are VIII, the remainder are disordered between {VIII-Cl}2+ and {VIV=O}2+] and for the distorted [FeIII14O9(OH)(OMe)8(bta)7(MeOH)5(H2O)Cl8] structure that results from non-solvothermal synthetic methods, highlighting the importance of temperature regime in cluster synthesis. Magnetic studies reveal the {Fe14} complexes to have ground state electronic spins of S相似文献   

The structural and spectroscopic characterisation of three actinyl complexes with coordinated and uncoordinated perrhenate: [UO2(ReO4)2(TPPO)3], [[(UO2)(TPPO)3]2(mu2-O2)][ReO4]2 and [NpO2(TPPO)4][ReO4

The first structural characterization of an actinide complex with coordinated perrhenate is reported, [UO2(ReO4)2(TPPO)3] (1). In this [UO2]2+ complex two [ReO4]- anions and three TPPO (triphenylphosphine oxide) P=O donor ligands are coordinated in the equatorial plane in a cisoid arrangement. This bonding arrangement, and apparent strain observed in the equatorially bonded ligands, is attributed to the solid state packing in adjacent molecules in which hydrophobic TPPO ligands form an effective "shell" around a hydrophilic core of two UO2(ReO4)2 moieties. Solid state vibrational spectroscopy (infrared and Raman), 31P CP MAS NMR and elemental analysis are also consistent with the formula of 1. Solution state vibrational spectroscopy and 31P NMR measurements in EtOH indicate the lability of the TPPO and [ReO4]- groups. The photolytic generation of peroxide in EtOH solutions of 1 leads to the formation of trace quantities of [[(UO2)(TPPO)3]2(mu2-O2)][ReO4]2, 2, in which the coordinated [ReO4]- groups of 1 have been displaced by bridging O2(2-), derived from atmospheric O2. Finally, attempts to synthesise a [NpO2]+ analogue of have resulted only in the formation of [NpO2(TPPO)4][ReO4], 3, in which [ReO4]- acts solely as a counter anion. From these results it can be concluded that [ReO4]- will bond to [UO2]2+, but will be readily displaced by a more strongly coordinating ligand (e.g. peroxide) and will not coordinate to an actinyl cation with a lower charge, [NpO2]+, under the same reaction conditions.     

Surface Coordination Chemistry: Corrosion Inhibition by Tetranuclear Cluster Formation of Iron with Salicylaldoxime

A tetranuclear iron cluster is the principal component of the purple coatings produced by treating a mild steel surface with a salicylaldoxime corrosion inhibitor. This was shown by comparison of the spectroscopic data with those of the cluster [{Fe(salH)(HsalH)}₄], which was obtained from FeCl₃ and salicylaldoxime (H₂salH) and has a distorted tetrahedral arrangement of Fe^III atoms coordinated by terminal (1−) and bridging (2−) salicylaldoximate ligands (the central core of the cluster is depicted).     

Oxoneptunium(v) as part of the framework of a polyoxometalate

(NH4)14Na4[(Np3W4O15)(H2O)3(BiW9O33)3].62H2O (1) and (NH4)14.5Na3.5[(Np3W4O15)(H2O)3(SbW9O33)3].40.5H2O (2) each contain three neptunyl(v) moieties encapsulated within heteropolyoxotungstate frameworks in which axial {NpO2}+ oxygens form one face of a WO6 octahedron.     

Two (Z)‐N‐aryl‐3‐benzylideneisoindolin‐1‐ones

Two isoindolin‐1‐one derivatives, (Z)‐3‐benzyl­idene‐N‐phenyl­isoindolin‐1‐one, C₂₁H₁₅NO, (II), and (Z)‐3‐benzyl­idene‐N‐(4‐methoxy­phenyl)­isoindolin‐1‐one, C₂₂H₁₇NO₂, (III), were synthesized by the palladium‐catalysed heteroannulation. The mol­ecules of both compounds have a Z configuration. The interplanar angles between the five‐ and six‐membered rings of the isoindolinone moiety in (II) and (III) are 1.66 (11) and 2.26 (7)°, respectively. The phenyl rings at the N‐position in (II) and (III) are twisted out of the C₄N ring plane by 62.77 (11) and 67.10 (7)°, respectively. The substitutions at the N and C‐3 positions of the isoindolinone system have little influence on the molecular dimensions of the resulting compounds.