A surface and catalytic study of heterogenised Os-3(CO)(12) species in MCM-41 structures

Immobilised Os species prepared via chemical vapour deposition (CVD) of Os-3(CO)(12) onto MCM-41 are active and selective catalysts for the dihydroxylation of trans-stilbene in acetone and water, using N-methylmorpholine N-oxide as the oxidant. A detailed temperature programmed decomposition study of the solids enables to identify the active sites as Os-x(CO)(y) surface species. The initial loading of the MCM-41 with the trinuclear precursor, as well as the temperature of the post-synthesis oxidising treatment, are found to have a significant impact on the structure/geometry of the resulting surface species, and thus their catalytic properties. We show how it is also affected by the confined environment of the MCM-41 mesopores and especially the curvature of the 30 Angstrom diameter channels. Finally, a careful study of the catalytic properties of the materials together with a study of the reactivity of the reaction products under similar conditions enable to suggest a mechanism involving the reaction of the oxidant with the osmium carbonyl surface species to form the catalytically active Os-oxo sites, and the formation of an osmoate-type species (through adsorption of the alkene onto the Os-oxo site) which subsequently reacts with the solvent to produce the diol. (C) 2003 Elsevier B.V. All rights reserved.

Syntheses and spectroscopy of diamine complexes of Zn(II) and Cd(II) ethylxanthates and the molecular structures of [M(S2COEt)(2)TMEDA]: formation of US nanoparticles from [Cd(S2COEt)(2)] and [Cd(S2COEt)(2)TMEDA]

The zinc and cadmium ethylxanthate complexes of N,N,N',N'-tetramethylethylenediamine (TMEDA), [M(S2COEt)(2)TMEDA], were synthesized and characterized with infrared, H-1 and C-13 NMR spectroscopy, mass spectrometry and X-ray crystallography. Whereas the cadmium complex has a six-coordinate {CdS4N2} centre with bidentate xanthate ligands, the zinc complex contains four coordinate {ZnS2N2} zinc with two monodentate xanthate groups. The cadmium species [Cd(S2COEt)(2)(diamine)] (where diamine = N,N-dimethylethylenediamine or N,N'-diisopropylethylenediamine) were also synthesized. The surfactant-assisted formation of nanoparticles from [Cd(S2COEt)(2)] and [Cd(S2COEt)(2)TMEDA] was studied with TEM, XRD and XRF techniques. From [Cd(S2COEt)(2)], spherical nanoparticle aggregates 140-200 nm in diameter were obtained but from [Cd(S2COEt)(2)TMEDA], single nanoparticles were produced with estimated diameters in the range of 4-7 nm and almost no aggregation. (C) 2004 Elsevier Ltd. All rights reserved.

Syntheses and crystal structures of two new coordination polymers of Cd(II) using organic spacer and inorganic-bridging ligands

Two new cadmium (II) complexes [Cd(hmt)(dca)(2)] (n) (1) and [Cd-3(hmt)(2)(SeCN)(6)(H2O)(2)] (n) (2) (hmt=hexamethylenetetramine, dca=dicyanamide) have been synthesized and characterized by X-ray single-crystal analysis. The complex 1 is a 2D rectangular grid of octahedral cadmium (II) with CdN6 chromophore where cadmium centers are doubly bridged by dicyanamide and hmt along a-axis, which are interlinked by dicyanamide running along c-axis. Whereas, complex 2 is a 1D chain of octahedral cadmium (II) with a three-leg ladder topology running along a-axis. The Cd(II) centers are doubly bridged through SeCN (infinite rail) along a-axis and singly bridged by hmt (two-step rung) along c-axis, having cadmium centers with CdSe2N3O and CdSe2N4 chromophores. The adjacent chains through H-bonding between coordinated water and hmt, and (SeSe)-Se-... interaction are extended to 2D supramolecular architecture.

Extraction and coordination studies of the unexplored bifunctional ligand carbamoyl methyl sulfoxide (CMSO) with uranium(VI) and cerium(III) nitrates. Synthesis and structures of [UO2(NO3)(2)((PhSOCH2CONBu2)-Bu-i)] and [Ce(NO3)(3)(PhSOCH2CONBu2)(2)]

The bifunctional carbamoyl methyl sulfoxide ligands, PhCH2SOCH2CONHPh (L-1), PhCH2SOCH2CONHCH2Ph (L-2), (PhSOCH2CONPr2)-Pr-i (L-3), PhSOCH2CONBu2 (L-4), (PhSOCH2CONBu2)-Bu-i (L-5) and PhSOCH2CON(C8H17)(2) (L-6) have been synthesized and characterized by spectroscopic methods. The selected coordination chemistry of L-1, L-3, L-4 and L-5 with [UO2(NO3)(2)] and [Ce(NO3)(3)] has been evaluated. The structures of the compounds [UO2(NO3)(2)((PhSOCH2CONBu2)-Bu-i)] (10) and [Ce(NO3)(3)(PhSOCH2CONBu2)(2)] (12) have been determined by single crystal X-ray diffraction methods. Preliminary extraction studies of ligand L-6 with U(VI), Pu(IV) and Am(III) in tracer level showed an appreciable extraction for U(VI) and Pu(IV) in up to 10 M HNO3 but not for Am(III). Thermal studies on compounds 8 and 10 in air revealed that the ligands can be destroyed completely on incineration. The electron spray mass spectra of compounds 8 and 10 in acetone show that extensive ligand distribution reactions occur in solution to give a mixture of products with ligand to metal ratios of 1 : 1 and 2 : 1. However, 10 retains its solid state structure in CH2Cl2.

Coordination and separation studies of the uranyl ion with iso-butyramide based ligands: Synthesis and structures of [UO2(NO3)(2)((C3H7CON)-C-i{(C4H9)-C-i}(2))(2)] and [UO2(C6H5COCHCOC6H5)(2)((C3H7CON)-C-i{(C3H7)-C-i}(2))]

The coordination chemistry of iso-butyramide based ligands such as: (C3H7CON)-C-i((C3H7)-C-i)(2), (C3H7CON)-C-i(C4H9)(2) and (C3H7CON)-C-i((C4H9)-C-i)(2) with [UO2(NO3)(2) center dot 6H(2)O], [UO2(OO)(2) center dot 2H(2)O] {where OO = C4H3SCOCHCCCF3 (TTA), C6H5COCHCOCF3 (BTA) and C6H5COCHCOC6H5 (DBM)), [Th(NO3)(4) center dot 6H(2)O] and [La(NO3)(3) center dot 6H(2)O] has been evaluated. Structures for the compounds [UO2(NO3)(2)CC3H7CON{(C4H9)-C-i}(2))(2)] and [UO2(C6H5COCHCOC6H5)(2)((C3H7CON)-C-i{(C3H7)-C-i)(2))] have been determined by single crystal X-ray diffraction methods. Preliminary separation studies from nitric acid medium using the amide (C3H7CON)-C-i((C4H9)-C-i)(2) with U(VI), Th(IV) and La(Ill) ions showed the selective precipitation of uranyl ion from the mixture. Thermal study of the compound [UO2(NO3)(2)((C3H7CON)-C-i((C4H9)-C-i)(2))(2)] in air revealed that the ligands can be destroyed completely on incineration. (C) 2008 Elsevier Ltd. All rights reserved.

Formation of fibrillar structures through self-assembly of designed peptide turns

Three tripeptides Boc-Phe-Aib-Val-OMe (1), Boc-Leu-Aib-p-NA-NO2 (2) and Boc-Pro-Aib-m-NA-NO2 (3) (Aib: alpha-aminoisobutyric acid; p- and m-NA: para- and meta-nitroaniline) have been designed by incorporating aromatic rings to study the self-assembly and fibril formation. Single crystal X-ray diffraction studies show that all the peptides adopt turn-like structures that are self-assembled through intermolecular hydrogen bonds and van der Waals interactions to create layers of beta-sheets. Solvent dependent NMR titration and CD studies show that the turn structures of the peptides also exist in the solution phase. The field emission scanning electron microscopic (FE-SEM) images of the peptides in the solid state reveal fibrillar structures of flat morphology that are formed through beta-sheet mediated self-assembly of the preorganized turn building blocks.

Overlapping double turn conformations adopted by tetrapeptides containing non-coded alpha-Amino Isobutyric Acid (AIB) and formation of tape-like structures through supramolecular helix mediated self-assembly

Single crystal X-ray diffraction studies and solvent dependent H-1 NMR titrations reveal that a set of four tetrapeptides with general formula Boc-Xx(1)-Aib(2)-Yy(3)-Zz(4)-OMe, where Xx, Yy and Zz are coded L- amino acids, adopt equivalent conformations that can be described as overlapping double turn conformations stabilized by two 4 -> 1 intramolecular hydrogen bonds between Yy(3)-NH and Boc C=O and Zz(4)-NH and Xx(1)C=O. In the crystalline state, the double turn structures are packed in head-to-tail fashion through intermolecular hydrogen bonds to create supramolecular helical structures. Field emission scanning electron microscopic (FE-SEM) images of the tetrapeptides in the solid state reveal that they can form flat tape-like structures. The results establish that synthetic Aib containing supramolecular helices can form highly ordered self-aggregated amyloid plaque like human amylin.

Design of supramolecular beta-sheet forming beta-turns containing aromatic rings and non-coded alpha-aminoisobutyric acid and the formation of flat fibrillar structures through self-assembly

Single crystal X-ray diffraction studies show that the three designed tripeptides Boc-Leu-Aib-m-NA-NO2 (I), Boc-Phe-Aib-m-NA-NO2 (II) and Boc-Pro-Aib-m-ABA-OMe (III) (Aib, -aminoisobutyric acid; m-NA, m-nitroaniline; m-ABA, m-aminobenzoic acid; Boc, t-butyloxycarbonyl) containing aromatic rings in the backbones adopt -turn structures that are self-assembled through intermolecular hydrogen bonds and van der Waals interactions to create layers of -sheets. Solvent-dependent NMR titration and CD studies show that the -turn structures of the peptides also exist in the solution phase. The field emission scanning electron microscopic and transmission electron microscopic images of the peptides in the solid state reveal fibrillar structures of flat morphology that are formed through -sheet mediated self-assembly of the preorganised -turn building blocks.

The syntheses, structures and redox properties of phosphine-gold(I) and triruthenium-carbonyl cluster derivatives of tolans

The syntheses of several ethynyl-gold(I) phosphine substituted tolans (1,2-diaryl acetylenes) of general form [Au(C=CC6H4C=CC6H4X)(PPh3)] are described [X = Me (2a), OMe (2b), CO2Me (2c), NO2 (2d), CN (2e)]. These complexes react readily with [Ru-3(CO) 10(mu-dppm)] to give the heterometallic clusters [Ru3(mu-AuPPh3)(mu-eta(1), eta(2)-C2C6H4C, CC6H4X)(CO)(7)(mu-dppm)] (3a-e). The crystallographically determined molecular structures of 2b, 2d, 2e and 3a-e are reported here, that of 2a having been described on a previous occasion. Structural, spectroscopic and electrochemical studies were conducted and have revealed little electronic interaction between the remote substituent and the organometallic end-caps. (C) 2007 Elsevier B. V. All rights reserved.

Syntheses of two new 1D and 3D networks of Cu(II) and Co(II) using malonate and urotropine as bridging ligands: Crystal structures and magnetic studies

Two new metal-organic based polymeric complexes, [Cu-4(O2CCH2CO2)(4)(L)].7H(2)O (1) and [CO2(O2CCH2CO2)(2)(L)].2H(2)O (2) [L = hexamethylenetetramine (urotropine)], have been synthesized and characterized by X-ray crystal structure determination and magnetic studies. Complex 1 is a 1D coordination polymer comprising a carboxylato, bridged Cu-4 moiety linked by a tetradentate bridging urotropine. Complex 2 is a 3D coordination polymer made of pseudo-two-dimensional layers of Co(II) ions linked by malonate anions in syn-anticonformation which are bridged by bidentate urotropine in trans fashion, Complex 1 crystallizes in the orthothombic system, space group Pmmn, with a = 14,80(2) Angstrom, b = 14.54(2) Angstrom, c = 7.325(10) Angstrom, beta = 90degrees, and Z = 4. Complex 2 crystallizes in the orthorhombic system, space group Imm2, a = 7.584(11) Angstrom, b = 15.80(2) Angstrom, c = 6.939(13) Angstrom, beta = 90.10degrees(1), and Z = 4. Variable temperature (300-2 K) magnetic behavior reveals the existence of ferro- and antiferromagnetic interactions in 1 and only antiferromagnetic interactions in 2. The best fitted parameters for complex 1 are J = 13.5 cm(-1), J = -18.1 cm(-1), and g = 2.14 considering only intra-Cu-4 interactions through carboxylate and urotropine pathways. In case of complex 2, the fit of the magnetic data considering intralayer interaction through carboxylate pathway as well as interlayer interaction via urotropine pathway gave no satisfactory result at this moment using any model known due to considerable orbital contribution of Co(II) ions to the magnetic moment and its complicated structure. Assuming isolated Co(II) ions (without any coupling, J = 0) the shape of the chi(M)T curve fits well with experimental data except at very low temperatures.

Syntheses, characterization and X-ray crystal structures of Ni(II) complexes of tridentate monocondensed and tetradentate dicondensed Schiff bases

Two octahedral complexes [Ni(HL1)(2)](ClO4)(2) (1) and [Ni(HL2)(2)](ClO4)(2) (2) and a square planar complex [Ni(HL3)]ClO4 (3) have been prepared, where [HL1 = 3-(2-amino-ethylimino)-butan-2-one oxime, HL2 = 3-(2-amino-propylimino)butan-2-one oxime] and H2L3 = 3-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-1-methyl-ethylimino]-buta n-2-one oxime. All the complexes have been characterized by elemental analyses, spectral studies and room temperature magnetic moment measurements. The molecular structures of all three compounds were elucidated on the basis of X-ray crystallography: complexes 1 and 2 are seen to be the met isomers. (C) 2008 Elsevier Ltd. All rights reserved.

Two new mu-(1,3-azido)-bridged polymers: alternating single and double bridges in a 1D nickel(II) complex and uniform bridge in a 2D copper(II) complex: Syntheses, single-crystal structures and magnetic studies

Two polymeric azido bridged complexes [Ni2L2(N-3)(3)](n)(ClO4). (1) and [Cu(bpdS)(2)(N-3)],(ClO4),(H2O)(2.5n) (2) [L = Schiff base, obtained from the condensation of pyridine-2-aldehyde with N,N,2,2-tetramethyl-1,3-propanediamine; bpds = 4,4'-bipyridyl disulfide] have been synthesized and their crystal structures have been determined. Complex 1, C26H42ClN15Ni2O4, crystallizes in a triclinic system, space group P1 with a 8.089(13), b = 9.392(14), c = 12.267(18) angstrom, a = 107.28(l), b 95.95(1), gamma = 96.92(1)degrees and Z = 2; complex 2, C20H21ClCuN7O6.5S4, crystallizes in an orthorhombic system, space group Pnna with a = 10.839(14), b = 13.208(17), c = 19.75(2) angstrom and Z = 4. The crystal structure of I consists of 1D polymers of nickel(L) units, alternatively connected by single and double bridging mu-(1,3-N-3) ligand with isolated perchlorate anions. Variable temperature magnetic susceptibility data of the complex have been measured and the fitting,of magnetic data was carried out applying the Borris-Almenar formula for such types of alternating one-dimensional S = 1 systems, based on the Hamiltonian H = -J Sigma(S2iS2i-1 + aS(2i)S(2i+1)). The best-fit parameters obtained are J = -106.7 +/- 2 cm(-1); a = 0.82 +/- 0.02; g = 2.21 +/- 0.02. Complex 2 is a 2D network of 4,4 topology with the nodes occupied by the Cu-II ions, and the edges formed by single azide and double bpds connectors. The perchlorate anions are located between pairs of bpds. The magnetic data have been fitted considering the complex as a pseudo-one-dimensional system, with all copper((II)) atoms linked by [mu(1,3-azido) bridging ligands at axial positions (long Cu...N-3 distances) since the coupling through long bpds is almost nil. The best-fit parameters obtained with this model are J = -1.21 +/- 0.2 cm(-1), g 2.14 +/- 0.02. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).

Syntheses, crystal structures and magnetic properties of carboxylato-bridged polymeric networks of Mn-II

Three new carboxylato-bridged polymeric networks of Mn-II having molecular formula [Mn(ox)(dpyo)](n) (1), {[Mn-2(mal)(2)(bpee)(H2O)(2)]center dot 0.5(bpee)center dot 0.5(CH3OH)}n, (2) and {[Mn-3(btc)(2)(2,2'-bipy)(2)(H2O)(6)]center dot 4H(2)O}(n) (3) [dpyo, 4,4'-bipyridine N,N'dioxide; bpee, trans-1,2 bis(4-pyridyl) ethylene; 2,2'-bipy, 2,2'-bipyridine; ox = oxalate dianion; mal = malonate dianion; btc = 1,3,5-benzenetricarboxylate trianion] have been synthesized and characterized by single-crystal X-ray diffraction studies and low temperature magnetic measurements. Structure determination of complex I reveals a covalent bonded 2D network containing bischelating oxalate and bridging dpyo; complex 2 is a covalent,bonded 3D polymeric architecture, formed by bridging malonate and bpee ligands, resulting in an open framework with channels filled by uncoordinated disordered bpee and methanol molecules. Whereas complex 3, comprising btc anions bound to three metal centers, is a 1D chain which further extends its dimensionality to 3D via pi-pi and H-bonding interactions. Low temperature magnetic measurements reveal the existence of weak antiferromagnetic interaction in all these complexes. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).

Tuning of redox potential and visible absorption band of ruthenium(II) complexes of (benzimidazolyl) derivatives: synthesis, characterization, spectroscopic and redox properties, X-ray structures and DFT calculations

Six ruthenium(II) complexes have been prepared using the tridentate ligands 2,6-bis(benzimidazolyl) pyridine and bis(2-benzimidazolyl methyl) amine and having 2,2'-bipyridine, 2,2':6',2 ''-terpyridine, PPh3, MeCN and chloride as coligands. The crystal structures of three of the complexes trans-[Ru(bbpH(2))(PPh3)(2)(CH3CN)I(ClO4)(2) center dot 2H(2)O (2), [Ru(bbpH(2))(bpy)Cl]ClO4 (3) and [Ru(bbpH(2))(terpy)](ClO4)(2) (4) are also reported. The complexes show visible region absorption at 402-517 nm, indicating that it is possible to tune the visible region absorption by varying the ancillary ligand. Luminescence behavior of the complexes has been studied both at RT and at liquid nitrogen temperature (LNT). Luminescence of the complexes is found to be insensitive to the presence of dioxygen. Two of the complexes [Ru(bbpH(2))(bpy)Cl]ClO4 (3) and [Ru(bbpH(2))(terpy]ClO4)(2) (4) show RT emission in the NIR region, having lifetime, quantum yield and radiative constant values suitable for their application as NIR emitter in the solid state devices. The DFT calculations on these two complexes indicate that the metal t(2g) electrons are appreciably delocalized over the ligand backbone. (C) 2006 Elsevier B.V. All rights reserved.

Influence of counter anions on the structures and magnetic properties of trinuclear Cu(II) complexes containing a mu(3)-OH core and Schiff base ligands

Four trinuclear Cu(II) complexes, [(CuL1)(3)(mu(3)-OH)](NO3)(2) (1), [(CuL2)(3)(mu(3)-OH)](I)(2)center dot H2O (2), [(CuL3)(3)(mu(3)-OH)](I)(2) (3) and [(CuL1)(3)(mu(3)-OH)][(CuI3)-I-1] (4), where HL1 (8-amino-4-methyl-5-azaoct-3-en-2-one), HL2 [7-amino-4-methyl-5-azaoct-3-en-2-one] and HL3 [7-amino-4-methyl-5-azahept-3-en-2- one] are the three tridentate Schiff bases, have been synthesized and structurally characterized by X-ray crystallography. All four complexes contain a partial cubane core, [(CuL)(3)(mu(3)-OH)](2+) in which the three [CuL] subunits are interconnected through two types of oxygen bridges afforded by the oxygen atoms of the ligands and the central OH- group. The copper(II) ions are in a distorted square-pyramidal environment. The equatorial plane consists of the bridging oxygen of the central OH- group together with three atoms (N, N, O) from the Schiff base. The oxygen atom of the Schiff base also coordinates to the axial position of Cu(II) of another subunit to form the cyclic trimer. Magnetic susceptibilities have been determined for these complexes over the temperature range of 2-300 K. The isotropic Hamiltonian, H = -J(12)S(1)S(2) - J(13)S(1)S(3) - J(23)S(2)S(3) has been used to interpret the magnetic data. The best fit parameters obtained are: J = - 54.98 cm(-1) g = 2.24 for 1; J = - 56.66 cm(-1), g = 2.19 for 2; J = -44.39 cm(-1), g = 2.16 for 3; J = - 89.92 cm(-1), g = 2.25 for 4. The EPR data at low temperature indicate that the phenomenon of spin frustration occurs for complexes 1-3. (c) 2007 Elsevier B.V. All rights reserved.