Search

Bimodal magnetic resonance imaging (MRI)/optical probes for bioimaging were obtained by grafting two types of lanthanide metal ions, Gd3+and Eu3+/Tb3+, on the surface of SiO2nanoparticles. The resulting systems were endowed with relaxometry and photoluminescent properties, respectively. Grafting a pyridine‐based aromatic backbone on to the silica surface enhances the emission quantum yield of the Eu3+‐containing nanoparticles fivefold compared to similar systems that bear no aromatic antennae. The emission properties of the mixed Ln3+/Gd3+‐based nanoparticles are not influenced by the presence of Gd3+. The relaxometric properties of these samples are slightly better than the properties of commercial [Gd(DTPA)]2(DTPA = diethylenetriaminepentaacetate). When taken up by RAW 264.7 cells (mouse macrophage cell line), such bimodal probes exhibit both T1‐weighted MRI increased contrast and fluorescence tracking.

Two germanium–hedp4– solids with heteroaromatic amines 8-hydroxyquinoline (hqn) and 1,10-phenanthroline (phen), (HL)6[Ge6(OH)6(hedp)6]·2(L)·nH2O (L = hqn or phen), in I and II respectively, have been prepared and characterised by single-crystal XRD, thermogravimetry, FTIR and UV/Vis spectroscopy. The complex hydrogen-bond networks, particularly in compound I, have been studied by advanced high-resolution solid-state NMR spectroscopy that combines homonuclear recoupling techniques (two-dimensional 1H-1H DQF and 1H-1H RFDR MAS NMR) and combined rotation and multiple-pulse spectroscopy (two-dimensional 1H-1H FS-LG, 1H-31P FS-LG). The fine details of the crystal structure of I have been elucidated, mainly those involving the π–π stacking of 8-hydroxyquinoline and the relative orientation of adjacent such molecules. Compound II exhibits an emission from the lowest triplet-state energy (π–π* 0-phonon transition) of the aromatic rings at 320 nm (31250 cm–1) from 14 K to room temperature. In contrast, the triplet emission of I at 530 nm (18868 cm–1) is only detected at low temperature, because of thermally activated non-radiative mechanisms. The emission spectra of I and II display a lower-energy component with a larger life time, which results from the formation of an excimer state that originated from the π–π phenanthroline and hydroxyquinoline interactions, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A novel phosphovanadate layered structure intercalated by 4,4′-bipyridinium cations, (C10H10N2)[(VO2)4(PO4)2], was synthesised under hydrothermal conditions and its crystal structure determined using single-crystal X-ray diffraction. The anionic [(VO2)4(PO4)2]n2n− perforated layers are strongly hydrogen bonded to the interlayer 4,4′-bipyridinium cations and are assembled by an unprecedented secondary tetrametallic VV building unit constructed from a distorted cubane-like {V4O4} cluster. The compound was further characterised by IR, Raman, 1H, 1H-13C, 31P and 51V MAS NMR spectroscopy, and by thermal and elemental analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

No Abstract

Using crystal engineering concepts, the first three-dimensional (3D) mixed-metal-centre inorganic-organic hybrid frameworks incorporating N-(phosphonomethyl)iminodiacetate (pmida4−) were synthesised under mild hydrothermal conditions (100 °C) and characterised structurally. The crystal structures, obtained by the displacement of the coordinated water molecules in [Co2V2O2(pmida)2(H2O)10]·2(H2O) (1) [P21/c monoclinic space group, Z = 2, a = 9.996(2) Å, b = 14.854(3) Å, c = 10.781(2) Å, β = 110.90(3)° and V = 1495.5(5) Å3] by the rod-like bridging 4,4′-bipyridine (4,4′-bpy) ligand — [CdVO(pmida)(4,4′-bpy)(H2O)2]·(4,4′-bpy)0.5·H2O (2) and [CoVO(pmida)(4,4′-bpy)(H2O)2]·(4,4′-bpy)0.5 (3) — are isostructural and were also determined in the P21/c monoclinic space group (Z = 4) by single-crystal X-ray diffraction studies at low temperature (180 K): for 2, a = 9.1267(18) Å, b = 17.610(4) Å, c = 15.361(3) Å, β = 93.06(3)° and V = 2465.3(9) Å3; for 3, a = 8.7734(18) Å, b = 17.264(4) Å, c = 15.507(3) Å, β = 93.94(3)° and V = 2343.2(8) Å3. All the crystal structures contain centrosymmetric dimeric [V2O2(pmida)2]4− units connected to neighbouring M2+ cations (Cd2+ for 2, and Co2+ for 1 and 3) through the phosphonate group. In 2 and 3, extended two-dimensional [MVO(pmida)(H2O)2]n layers are formed, with the 4,4′-bpy molecules acting as pillars between adjacent layers, leading to porous 3D supramolecular structures, [MVO(pmida)(4,4′-bpy)(H2O)2]∞, with a topology resembling that of the NbO net. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The dioxomolybdenum(VI) complex [MoO2Cl2(L-L)], containing the bidentate 1,4-diazabutadiene ligand RN=C(Ph)−C(Ph)=NR [R = (CH2)3Si(OEt)3], was immobilised in the ordered mesoporous silica MCM-41 by carrying out a grafting reaction in dichloromethane. The grafted material (3.3 wt.-% Mo) was tested as a catalyst for the epoxidation of cyclooctene with tert-butyl hydroperoxide (TBHP) at 55 °C. Selectivity to the epoxide was very high and the observed kinetic profile was similar to that of the complex [MoO2Cl2(L-L)] in the homogeneous phase. On recycling several times, some activity was lost from the first to second runs, but thereafter stabilised. Tethered complexes of this type were also prepared by a stepwise approach. The mesoporous silicas MCM-41 and MCM-48 were first treated with a toluene solution of the ligand L-L under reflux. Before isolating the grafted materials, the silylating agent Me3SiCl was added to remove the residual Si−OH groups on the surface of the mesoporous materials. Oxomolybdenum species were subsequently introduced into the ligand-silicas by pore volume impregnation of a solution of the complex [MoO2Cl2(THF)2] in CH2Cl2 at room temperature. The modified materials have been characterised by powder X-ray diffraction, N2 adsorption, and solid-state MAS NMR (¹³C, ²⁹Si). Despite having lower metal loadings (1 wt.-% Mo), the materials exhibited similar catalytic activities for the epoxidation of cyclooctene to that of the modified MCM-41 with 3.3 wt.-% of Mo. However, selectivities to the epoxide were lower. The MCM supported catalysts have also been tested for the epoxidation of cyclododecene and α-pinene with TBHP. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

We report the synthesis and structural characterization of a thermally stable and highly crystalline novel metal-organic framework with cadmium(II) ions. The crystal structure is formed by a threefold interpenetration of identical three-dimensional modular frameworks, assembled by the repetition of a binuclear secondary building unit. This unit contains 1,2-bis(4-pyridyl)ethane and introduces biphenyl-4,4'-dicarboxylate as an effective rigid large spacer between metal centres. Water molecules are hydrogen bonded to carboxylate groups and act as bridges between each independent framework. To the best of our knowledge, CUmof-1 is the first structure in which the paddlewheel motif is associated with a distribution of cavities in a concertina manner. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)