Molybdenum tetracarbonyl complexes of (aryloxy) lambda(3)-cyclotriphosphazanes; X-ray crystal structure of [Mo(CO)(4){EtNP(OC6H4Br-4)}(3)]

Treatment of the lambda(3)-cyclotriphosphazanes, cis-{EtNP(OR)}(3) [R = C6H4Br-4 (L-1) or C6H4Br-2 (L-2)] with [Mo(CO)(4)(NBD)] (NBD = norbornadiene) yields the mononuclear complexes [Mo(CO)(4)L-1] (1) and [Mo(CO)(4)L-2] (2). which have been characterised by IR, NMR (P-31 and H-1) and FAB mass spectral data. The structure of 1 has been confirmed by single crystal X-ray analysis. The structural and conformational changes brought about by complexation are discussed in terms of a bonding model based on "negative hyperconjugation". (C) 1998 Elsevier Science Ltd. All rights reserved.

Synthesis based on cyclohexadienes Part 36: an efficient methodology for the construction of spiro[4.5]decanes: a formal synthesis of acorone

An efficient strategy for the contruction of spiro[4.5] decanes is described and involves a bridgehead substitution of a methoxyl group by a methyl group followed by an oxidative cleavage of the tricyclo[5.2.2.0(1,5)] undecane 25 to produce the spiro[4.5] decanes 31 & 32 which are intermediates in the synthesis of acorone. A novel one-pot conversion of alpha-methoxy carboxylic acid to alpha-methyl carboxylic acid is described.

(2E)-1-(5-Chlorothiophen-2-yl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-1-one

In the title molecule, C(16)H(15)ClO(4)S, the chlorothiophene and trimethoxyphenyl rings make a dihedral angle of 31.12 (5)degrees. The C = C double bond exhibits an E conformation. In the crystal, C-H center dot center dot center dot O interactions generate bifurcated bonds, linking the molecules into chains along the b axis.

Hexa-arm star shaped hydrazone derivatives from hexakis(4-formylphenoxy)-cyclotriphosphazene core

A series of novel hexasubstituted cyclophosphazene hydrazones [N(3)P(3)(-OC(6)H(4)-p-CH=N-NH-C(O)-C(6)H(4)-p-X)(6)] (X = H, Br, Cl, F, OH, OCH(3), CH(3), NO(2), NH(2)) were prepared by a sixfold condensation reaction of [N(3)P(3)(-OC(6)H(4)-p-CHO)(6)] with para-substituted benzoic hydrazides [NH(2)-NH-C(O)-C(6)H(4)-p-X] with excellent yields (91-98%). The structures of the compounds were confirmed by elemental analysis, FT-IR, (1)H, (13)C, (31)P, 2D-HSQC NMR and mass spectrometry (MALDI-TOF). All the synthesized cyclophosphazene hydrazones exhibit high thermal stability. The crystal structure of a homogeneously substituted hexakis(4-formylphenoxy)-cyclotriphosphazene was determined by X-ray diffraction analysis. The compound crystallizes in the monoclinic system, space group P2(1)/n with a = 16.558(3) angstrom, b = 10.250(2) angstrom, c = 23.429(5) angstrom, alpha = gamma = 90.00 degrees, beta = 90.461(4)degrees, V = 3976.5(14) angstrom(3) and Z = 4. The R value is 0.0823 for 4290 observed reflections. The conformations of the 4-formylphenoxy-groups are different at the three phosphorus atoms. (C) 2011 Elsevier B.V. All rights reserved.

Maximum rate of 3- and 4-real-symbol ML decodable unitary weight STBCs

It has been shown recently that the maximum rate of a 2-real-symbol (single-complex-symbol) maximum likelihood (ML) decodable, square space-time block codes (STBCs) with unitary weight matrices is 2a/2a complex symbols per channel use (cspcu) for 2a number of transmit antennas [1]. These STBCs are obtained from Unitary Weight Designs (UWDs). In this paper, we show that the maximum rates for 3- and 4-real-symbol (2-complex-symbol) ML decodable square STBCs from UWDs, for 2a transmit antennas, are 3(a-1)/2a and 4(a-1)/2a cspcu, respectively. STBCs achieving this maximum rate are constructed. A set of sufficient conditions on the signal set, required for these codes to achieve full-diversity are derived along with expressions for their coding gain.

Bromenium-Catalysed Tandem Ring Opening/Cyclisation of Vinylcyclopropanes and Vinylcyclobutanes: A Metal-Free 3+2+1]/4+2+1] Cascade for the Synthesis of Chiral Amidines and Computational Investigation

We present a detailed study of a 3+2+1] cascade cyclisation of vinylcyclopropanes (VCP) catalysed by a bromenium species (Brd+?Xd-) generated in situ, which results in the synthesis of chiral bicyclic amidines in a tandem one-pot operation. The formation of amidines involves the ring-opening of VCPs with Br?X, followed by a Ritter-type reaction with chloramine-T and a tandem cyclisation. The reaction has been further extended to vinylcyclobutane systems and involves a 4+2+1] cascade cyclisation with the same reagents. The versatility of the methodology has been demonstrated by careful choice of VCPs and VCBs to yield bicyclo4.3.0]-, -4.3.1]- and -4.4.0]amidines in enantiomerically pure form. On the basis of the experimental observations and DFT calculations, a reasonable mechanism has been put forth to account for the formation of the products and the observed stereoselectivity. We propose the existence of a p-stabilised homoallylic carbocation at the cyclopropane carbon as the reason for high stereoselectivity. DFT studies at B3LYP/6-311+G** and M06-2X/6-31+G* levels of theory in gas-phase calculations suggest the ring-opening of VCP is initiated at the p-complex stage (between the double bond and Br?X). This can be clearly perceived from the solution-phase (acetonitrile) calculations using the polarisable continuum model (PCM) solvation model, from which the extent of the ring opening of VCP was found to be noticeably high. Studies also show that the formation of zero-bridge bicyclic amidines is favoured over other bridged bicyclic amidines. The energetics of competing reaction pathways is compared to explain the product selectivity.

Synthesis, structural analysis and solvatochromic behaviour of 4,6-bis (4-butoxyphenyl)-2-methoxynicotinonitrile mesogen

In this communication, we report the synthesis and characterisation of a new luminescent liquid crystalline material, 4,6-bis (4-butoxyphenyl)-2-methoxynicotinonitrile (3). We have confirmed its structure by Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy, elemental analysis and X-ray single crystal diffraction studies. The newly synthesised compound crystallises in a monoclinic system with the space group C2/c and its cell parameters are found to be a?=?25.181(4) angstrom, b?=?15.651(4)angstrom, c?=?12.703(19) angstrom, V?=?4880.4 (16) angstrom, Z?=?8. The results indicate that the presence of weak CH center dot center dot center dot O and CH center dot center dot center dot N hydrogen bonding as short-range intermolecular interactions are responsible for the formation of its crystal assembly. The measured torsion angle shows the existence of a distorted structure for the molecule wherein 4-butoxyphenylene ring substituent at the fourth position of the central pyridine ring forms a torsion angle chiC(4), C(3), C(10), C(19)] of 40.55 degrees. Its liquid crystalline behaviour was investigated with the aid of polarised optical microscopy and differential scanning calorimetry. The study reveals that the compound displays a broad nematic phase in the range of 78112 degrees C. Further, solution phase optical studies indicate that it is a blue light emitter in different non-polar and polar organic solvents at a concentration of 10-5M.

Dual Stress and Thermally Driven Mechanical Properties of the Same Organic Crystal: 2,6-Dichlorobenzylidene-4-fluoro-3-nitroaniline

An elastic organic crystal, 2,6-dichlorobenzylidine-4-fluoro-3-nitroaniline (DFNA), which also shows thermosalient behavior, is studied. The presence of these two distinct properties in the same crystal is unusual and unprecedented because they follow respectively from isotropy and anisotropy in the crystal packing. Therefore, while both properties lead from the crystal structure, the mechanisms for bending and thermosalience are quite independent of one another. Crystals of the low-temperature (a) form of the title compound are bent easily without any signs of fracture with the application of deforming stress, and this bending is within the elastic limit. The crystal structure of the a-form was determined (P2(1)/c, Z = 4, a = 3.927(7) angstrom, b = 21.98(4) angstrom, c = 15.32(3) angstrom). There is an irreversible phase transition at 138 degrees C of this form to the high-temperature beta-form followed by melting at 140 degrees C. Variable-temperature X-ray powder diffraction was used to investigate the structural changes across the phase transition and, along with an FTIR study, establishes the structure of the beta-form. A possible rationale for strain build-up is given. Thermosalient behavior arises from anisotropic changes in the three unit cell parameters across the phase transition, notably an increase in the b axis parameter from 21.98 to 22.30 angstrom. A rationale is provided for the existence of both elasticity and thermosalience in the same crystal. FTIR studies across the phase transition reveal important mechanistic insights: (i) increased pi...pi repulsions along 100] lead to expansion along the a axis; (ii) change in alignment of C-Cl and NO2 groups result from density changes; and (iii) competition between short-range repulsive (pi...pi) interactions and long-range attractive dipolar interactions (C-Cl and NO2) could lie at the origin of the existence of two distinctive properties.