Vertex-Fused Metallaborane Clusters: Synthesis, Characterization and Electronic Structure of [(eta(5)-C5Me5Mo)(3)MoB9H18]

The reaction of the [(eta(5)-C5Me5)MoCl4] complex with [LiBH4 - TH F] in toluene at - 70 degrees C, followed by pyrolysis at 110 degrees C, afforded dark brown [(eta(5)-C5Me5Mo)(3)MoB9H18], 2, in parallel with the known [(eta(5)-C5Me5Mo)(2)B5H9], 1. Compound 2 has been characterized in solution by H-1, B-11, and C-13 NMR spectroscopy and elemental analysis, and the structural types were unequivocally established by crystallographic studies. The title compound represents a novel class of vertex-fused clusters in which a Mo atom has been fused in a perpendicular fashion between two molybdaborane clusters. Electronic structure calculations employing density functional theory yield geometries in agreement with the structure determinations, and on grounds of density functional theory calculations, we have analyzed the bonding patterns in the structure,

Synthesis and Characterization of a Class of Donor-Acceptor Conjugated Molecules: Experiments and Theoretical Calculations

A class of conjugated molecules containing donor (thiophene) and acceptor (malononitrile) is synthesized by Knoevenagel condensation reaction between 2-(2,6-dimethy1-4H-pyran-4-ylidene) malononitrile and thiophene carbaldehyde containing two and three thiophene units. The resulting molecules are characterized by H-1 and C-13 NMR. We have performed UV-vis absorption, fluorescence, and cyclic voltammetry measurements on these materials. The spectroscopic and electrochemical measurements proved beyond doubt that these materials possess lowexcitation gap and are suitable for being an active material in various electronic devices. We have also performed electronic structure calculations using density functional theory (DFT) and INDO/SCI methods to characterize the ground and excited states of this class of molecules. These donor-acceptor molecules show a strong charge transfercharacter that increases with the increase in the number of thiophene rings coupled to the malononitrile acceptor moiety. We have also calculated the pi-coherence length, Stoke's shift, and effect of solvents on excited states for this class of molecules, Our theoretical values agree well with experimental results.

Adsorption of anionic dyes on chitosan grafted poly(alkyl methacrylate)s

Chitosan grafted poly(alkyl methacrylate)s (namely chitosan grafted poly(methyl methacrylate) (ChgPMMA), chitosan grafted poly(ethyl methacrylate)(ChgPEMA), chitosan grafted poly(butyl methacrylate) (ChgPBMA) and chitosan grafted poly(hexyl methacrylate) (ChgPHMA)) were synthesized and characterized by using FT-IR and C-13 NMR techniques. The adsorption batch experiments on these grafted copolymers were conducted by using an anionic sulfonated dye. Orange-G. A pseudo-second-order kinetic model was used to determine the kinetics of adsorption. The effect of grafting, effect of process variables and the effect of different sulfonated anionic dyes (Orange-C, Congo Red, Remazol Brill Blue R and Methyl Blue) on the adsorption kinetics was determined. The Langmuir and Freundlich models were used to fit the adsorption isotherms and from the values of correlation coefficients (R-2), it was observed that the experimental data fits very well to the Langmuir model. The values of the maximum adsorption capacity of the adsorbents follow the order: ChgPMMA > ChgPEMA > ChgPBMA > ChgPHMA > chitosan. (C) 2010 Elsevier B.V. All rights reserved.

Synthesis and characterization of polyaniline salts with phenoxy acetic acids by emulsion polymerization

Polyaniline salts have been synthesized by chemical oxidative polymerization of aniline in the presence of phenoxy acetic acid and its two derivatives using emulsion method at room temperature and characterized by different techniques such as infrared, H-1 and C-13 NMR, UV-visible spectroscopy, SEM, wide angle X-ray diffractograms and conductivity measurements. These polyaniline salts have the desirable property of high solubility for processibility in solvents such as DNIF, DMSO and a mixture of CHCl3 and acetone and they exhibit fairly good conductivity of similar to 3.0 x 10(-3) S cm(-1). The variations in solubility, conductivity and morphology with the protonating strength of the dopants are examined.

Dehydrogenation of ammonia borane in fluoro alcohols

Dehydrogenation of ammonia borane was carried out in fluor alcohol solvent in order to obtain compounds that are more likely candidates suitable for regeneration. Even though ammonia borane undergoes self-dissociation in 2,2,2-trifluoroethanol to liberate H-2, decent hydrogen release rates were obtained by using Co-Co2B, Ni-Ni3B, and Co-Ni-B nanocomposites as catalysts. These catalysts are magnetic in nature and hence can be separated from the reaction mixture using a magnet for re-use. The final by-product NH4+ B(OCH2CF3)(4)(-) obtained after the catalytic dehydrogenation of ammonia borane was thoroughly characterized using H-1, B-11, and C-13 NMR and IR spectroscopies. The FTIR data showed that the B-O bond in NH4+ B(OCH2CF3)(4)(-) is slightly weaker compared to boric acid. Preliminary investigations on the regenerative routes for ammonia borane from the by-product NH4+ B(OCH2CF3)(4)(-) showed indications of the formation of BNHx species. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Synthesis, Reactivity, Structural Aspects, and Solution Dynamics of Cyclopalladated Compounds of N,N `,N `'-Tris(2-anisyl)guanidine

N,N',N `'-Tris(2-anisyl)guanidine, (ArNH)(2)C=NAr (Ar = 2-(MeO)C6H4), was cyclopallaclated with Pd(OC(O)R)(2) (R = Me, CF3) in toluene at 70 degrees C to afford palladacycles Pd{kappa(2)(C,N)-C6H3-(OMe)-3(NHC(NHAr)(=NAr))-2}(mu-OC(O)R)](2)(R = Me (1a) and CF3 (1b)) in 87% and 95% yield, respectively. Palladacycle 1a was subjected to a metathetical reaction with LiBr in aqueous ethanol at 78 degrees C to afford palladacycle Pd{kappa(2)(C,N)-C6H3(OMe)-3(NHC(NHAr)(=NAr))-2}(mu-Br)](2) (2) in 90% yield. Palladacycle 2 was subjected to a bridge-splitting reaction with Lewis bases in CH2Cl2 to afford the monomeric palladacycles Pd{kappa(2)(C,N)-C6H3(OMe)-3(NHC(NHAr)(=NAr))-2}Br(L)] (L = 2,6-Me2C5H3N (3a), 2,4-Me2C5H3N (3b), 3,5-Me2C5H3N (3c), XyNC (Xy = 2,6-Me2C6H3; 4a), (BuNC)-Bu-t (4b), and PPh3 (5)) in 87-95% yield. Palladacycle 2 upon reaction with 2 equiv of XyNC in CH2Cl2 afforded an unanticipated palladacycle, Pd{kappa(2)(C,N)-C(=NXy)(C6H3(OMe)-4)-2(N=C-(NH Ar)(2))-3} Br(CNXy)] (6) in 93% yield, and the driving force for the formation of 6 was ascribed to a ring contraction followed by amine-imine tautomerization. Palladacycles 1 a,b revealed a dimeric transoid in-in conformation with ``open book'' framework in the solid state. In solution, 1 a exhibited a fluxional behavior ascribed to the six-membered ``(C,N)Pd'' ring inversion and partly dissociates to the pincer type and kappa(2)-O,O'-OAc monomeric palladacycles by an anchimerically assisted acetate cleavage process as studied by variable-temperature H-1 NMR data. Palladacycles 3a,b revealed a unique trans configuration around the palladium with lutidine being placed trans to the Pd-C bond, whereas cis stereochemistry was observed between the Pd-C bond and the Lewis base in 4a (as determined by X-ray diffraction data) and 5 (as determined by P-31 and C-13 NMR data). The aforementioned stereochemical difference was explained by invoking relative hardness/softness of the donor atoms around the palladium center. In solution, palladacycles 3a-c exist as a mixture of two interconverting boat conformers via a planar intermediate without any bond breaking due to the six-membered ``(C,N)Pd'' ring inversion, whereas palladacycles 4a,b and 5 exist as a single isomer, as deduced from detailed H-1 NMR studies.

Organometallic chemistry of diphosphazanes. Part IX: Syntheses and spectroscopic studies of molybdenum and tungsten tetracarbonyl complexes of unsymmetrical diphosphazanes

The unsymmetrical diphosphazanes X2PN(Pr(i))PYY'(1a-1h) {X = Ph, YY' = O2 C6H4 (1a) or YY' = O2C12H8 (1b); X = Ph, Y = Ph, Y' = OC6H4Me-4 (1c), OC6H4Br-4 (1d), OC6H3Me2-3,5 (1e), OC5H4N-2 (1f), N2C3HMe2-3,5 (1g) or Cl (1h)} react with [M(CO)4(NHC5H10)2] (M = Mo, W) to yield the cis-chelate complexes [M(CO)4{X2PN(Pr(i)) PYY'}] {M = Mo (2a-2h); M = W (3-f,3-g)}. These complexes have been characterized by H-1, P-31 and C-13 NMR and IR spectroscopic studies.

Potassamide induced in situ benzylation of 5,6-dihydroisoquinolines: Structure of novel products

Potassamide induced in situ benzylation of 1-alkyl-4-cyano-3-methoxy-5,6-dihydroisoquinolines (1a-b) with benzyl iodide gave the 5-benzyl-, 5,9-dibenzyl- and 4,4-dibenzyl-5,6-dihydroisoquinolines (9a-b, 8a-b and 10a-b), isoquinoline derivatives (4a-b) and diastereomeric mixture of 4-benzyl-1,2,3,4-tetrahydroisoquinolin-3(2H)-ones (11a-b & 11'a-b). Structures were assigned on the basis of spectral data [Mass, H-1 & C-13 NMR, 2D NOESY]. A few reactions carried out to transform the diastereomeric mixture of compounds 11a and 11's to the spirobenzylisoquinoline system 7a isomeric with naturally occurring ochotensane system ga are discussed.

A novel (main chain) (side chain) polymeric peroxide: Synthesis and initiating characteristics of poly(alpha-(tert-butylperoxymethyl)styrene peroxide)

A novel (main chain)-(side chain) vinyl polyperoxide, poly(alpha-(tert-butylperoxymethyl)styrene peroxide) (MCSCPP), an alternating copolymer of alpha-(tert-butylperoxymethyl)styrene (TPMS) and oxygen, has been synthesized by the oxidative polymerization of TPMS. The MCSCPP was characterized by H-1 NMR, C-13 NMR, IR, DSC, EI-MS, and GC-MS studies. The overall activation energy (E(a)) for the degradation of MCSCPP was found to be 27 kcal/mol. Formaldehyde and alpha-(tert-butylperoxy)acetophenone (TPAP) were identified as the primary degradation products of MCSCPP; TPAP was found to undergo further degradation. The side chain peroxy groups were found to be thermally more stable than those in the main chain. Polymerization of styrene in the presence of MCSCPP as initiator, at 80 degrees C, follows classical kinetics. The presence of peroxy segments in the polystyrene chain was confirmed by both H-1 NMR and thermal decomposition studies. Interestingly, unlike other vinyl polyperoxides, the MCSCPP initiator shows an increase in molecular weight with conversion.

Synthesis and characterization of poly(vinyl acetate peroxide)

Poly(vinyl acetate peroxide) (PVACP) was prepared from vinyl acetate by free-radical-initiated oxidative polymerization. The polyperoxide was isolated and characterized by different spectroscopic methods. The extreme instability of PVACP was demonstrated by FTIR spectroscopy. The H-1- and C-13-NMR studies show the irregularities in the polyperoxide chain due to the cleavage reactions of the propagating peroxide radical. Thermal degradation studies using differential scanning calorimetry revealed that PVACP degrades at a lower temperature and the heat of degradation is in the same range as reported for other vinyl polyperoxides. (C) 1996 John Wiley & Sons, Inc.

Synthesis and mesogenic behavior of metal-containing liquid crystalline networks

A new hydroxy functionalized liquid crystalline (LC) polyazomethine has been synthesized by the solution polycondensation of a dialdehyde with a diamine. The polymer was characterized by IR, H-1-, and C-13-NMR spectroscopy. Studies on the liquid crystalline properties reveal the nematic mesomorphic behavior. This polymer functions as a polymeric chelate and forms a three-dimensional network structure through the metal complexation. Influence of various metals and their concentration on the liquid crystalline behavior of the network has been studied. Networks up to 30 mol % of the metal show LC phase transitions; above this the transitions are suppressed and the network behaves like an LC thermoset. (C) 1996 John Wiley & Sons, Inc.

Effect of Alkyl Chain Arrangement on Conformation and Dynamics in a Surfactant Intercalated Layered Double Hydroxide: Spectroscopic Measurements and MD Simulations

The anionic surfactant dodecyl sulfate (DDS) has been intercalated in an Mg-Al layered double hydroxide (LDH). Monolayer and bilayer arrangements of the alkyl chains of the intercalated surfactant can be engineered by tuning the Al/Mg ratio of the LDH. In both arrangements the anionic headgroup of the surfactant is tethered to the LDH sheets, and consequently translational mobility of the chains is absent. The degrees of freedom of the confined alkyl chains are restricted to changes in conformation. The effects of the arrangement of the intercalated surfactant chains on conformational order and dynamics have been,investigated by spectroscopic measurements and molecular dynamics simulations. Infrared, Raman, and C-13 NMR spectroscopies were used to investigate conformation of the alkyl chains in the monolayer and bilayer arrangements and variable contact time cross-polarization magic angle spinning (VCT CPMAS) NMR measurements to probe molecular motion. The alkyl chains in the monolayer arrangement of the intercalated DDS chains showed considerably greater conformational disorder and faster dynamics as compared to chains in the bilayer arrangement, in spite of the fact that the volume available per chain in the monolayer is smaller than that in the bilayer. Atomistic MD simulations of the two arrangements of the intercalated surfactant were carried out using an isothermal-isobaric ensemble. The simulations are able to reproduce the essential results of the experiment-greater conformational disorder and faster dynamics for the alkyl chains in the monolayer arrangement of the intercalated surfactant. The MD simulations show that these results are a consequence of the fact that the nature of conformational disorder in the two arrangements is different. In the monolayer arrangement the alkyl chains can sustain isolated gauche defects, whereas in the bilayer arrangement gauche conformers occur only as part of a kink a gauche(+) trans gauche(-) sequence.

Photolysis of arene chromium tricarbonyl complexes in presence of amine-boranes: Observation of sigma-borane complexes in solution

Activation of the B-H sigma-bond of amine-boranes on the chromium(0) center of arene chromium tricarbonyl complexes (eta(6)-arene) Cr(CO)(3) (arene = fluorobenzene, 1a; benzene, 1b and mesitylene, 1c) has been studied. Photolysis of 1b in presence of ammonia-borane (H3N center dot BH3, AB) and tert-butylamine-borane ((BuH2N)-Bu-t center dot BH3, TBAB) resulted in H-2 evolution and precipitation of a BNHx polymer. On the other hand, photolysis in the presence of trimethylamine-borane (Me3N center dot BH3, TMAB) resulted in the formation of a sigma-borane complex (2) along with Cr(CO)(5)(eta(1)-HBH2 center dot NMe3) (3). The sigma-borane complexes (eta(6)-arene) Cr-( CO)(2)(eta(1)-HBH2 center dot NMe3) (arene = fluorobenzene, 2a; benzene, 2b and mesitylene, 2c) were characterized in solution by H-1, B-11, and C-13 NMR spectroscopy. Electron withdrawing substituents on the arene ring provide the more stable sigma-borane moiety in this series of complexes. (C) 2011 Elsevier B.V. All rights reserved.

Nematogens with more flexible chains than aromatic rings in the core

Mesogens containing four rings in the main core can accommodate one terminal and two nearby lateral chains on each outside aromatic ring. These compounds containing six chains present an enantiotropic nematic range which is influenced by the rigidity of the links. The conformational behaviour of the first methyleneoxy group within the chains was investigated by one and two dimensional C-13 NMR. The sign of the jump in chemical shifts when entering the nematic phase indicates the folding of each lateral branch. Dipolar oscillations during cross-polarization contact provide the values of the bond order parameter. The two First lateral fragments do not behave in the same way, demonstrating the influence of the fragment along which the chain is back: folded.

Synthesis, properties, and comparative analyses on the chain flexibility of an ultrastable vinyl polyperoxide

The most stable vinyl polyperoxide, namely, poly(indene peroxide) (PINDP), an alternating copolymer of indene and oxygen, was synthesized by the oxidative polymerization of indene. It was characterized by H-1-NMR and C-13-NMR, Fourier transform infrared, differential scanning calorimetry, direct pyrolysis mass spectrometry, and gas chromatography mass spectrometry studies. The overall activation energy for the degradation and the glass-transition temperature of PINDP were 47 kcal/mol and 327 K respectively, which were very high compared to those of other vinyl polyperoxides. (C) 2002 Wiley Periodicals, Inc.