Crystal engineering with aroyl hydrazones of diacetyl monooxime – Molecular and supramolecular structures of two Ni(II) and two Zn(II) complexes

Four new Schiff bases of aroyl hydrazides with diacetyl monooxime have been prepared, and Ni(II) and Zn(II) complexes of these ligands have been synthesized. Two Ni(II) and two Zn(II) complexes have been characterized by X-ray crystallography. The aroyl hydrazone ligands were designed in such a way that there is a systematic variation in the H-bond forming abilities of their aroyl moiety, e.g. both H-bond acceptor and donor (salicyloyl), only H-bond donor (anthraniloyl), only H-bond acceptor (isonicotinoyl). It is shown in this work that such a variation in the H-bond donor acceptor properties of the ligands leads to considerable diversity in their supramolecular architecture.     

Significant improvement in the pore properties of SBA-15 brought about by carboxylic acids and hydrothermal treatment

A comparative study of the pore properties of SBA-15 samples prepared under nonhydrothermal and hydrothermal conditions, in the absence and presence of carboxylic acids such as succinic, tartaric and citric acids has been carried out. In the absence of carboxylic acid, flake-like and spheroid particles were generally obtained irrespective of the preparative procedures. On the other hand, stirring of the pre-mix induces a rod-like morphology in presence of carboxylic acids. The samples prepared under non-hydrothermal conditions exhibit a higher degree of silicate condensation compared to those synthesized under hydrothermal conditions. SBA-15 samples prepared under hydrothermal conditions show higher values of the d (100) spacing independent of the presence of carboxylic acids. Presence of carboxylic acids as well as hydrothermal treatment improves the pore properties of SBA-15.     

Cold microwave chemistry: synthesis using pre-cooled reagents

A novel experimental procedure for chemical reactions has been devised that involves mixing and then freezing the reagents (organic solvent-free) to a sub-zero temperature such as −30 °C. This frozen mixture is exposed to microwave irradiation for a brief period of time. The use of pre-cooled reagents may give a single product not obtained by traditional microwave irradiation at room temperature. Interestingly, such a product may provide information about mechanisms by identifying the first step of a multiple step reaction.     

One-shot multigrid method for aerodynamic shape optimization

This paper presents a numerical method for aerodynamic shape optimization problems. It is based on simultaneous pseudotime-stepping in which the optimality is reached simultaneously with the state and costate feasibility. An optimization-based multigrid strategy results in efficient convergence of the method. The total effort of optimization is less than two forward simulation runs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simultaneous pseudo-time stepping for aerodynamic shape optimization

In this paper we discuss about numerical methods for aerodynamic shape optimization problems. These problems require efficient CFD techniques to solve the state (as well as costate) equations and fast algorithms for solving the optimization problems. Both of these are independent active areas of research since long time. Wide range of applications in science and engineering involve solution of optimization problems where the governing PDEs appear as constraints. Therefore, merging the two for the purpose of practical applicability is relatively new. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Versatility of 2,6-diacetylpyridine (dap) hydrazones in stabilizing uncommon coordination geometries of Mn(II): synthesis, spectroscopic, magnetic and structural characterization

Five seven- or eight-coordinate manganese complexes of hydrazone ligands have been prepared. Three seven-coordinate neutral Mn(II) complexes: [Mn(dapA2)]n (1), [Mn(dapB2)(H2O)2] (2), [Mn(dapS2)(H2O)2] (3) have been synthesized from the bis-Schiff bases of 2,6-diacetylpyridine: dap(AH)2, dap(BH)2 and dap(SH)2 (AH = anthraniloyl hydrazide, BH = benzoyl hydrazide, SH = salicyloyl hydrazide), respectively. Two eight-coordinate Mn(II) complexes: [Mn(dapS)2] (4) and [Mn(dapB)2].3H2O (5) have been synthesized from the mono-Schiff bases dapBH and dapSH, respectively. The complexes have been characterized by elemental analyses and by IR, UV-Vis., FAB mass, EI mass and EPR spectroscopy. The molecular structures of 1, 3.DMF and 4.DMF have been determined by single-crystal X-ray diffraction. The mono-Schiff bases are monoanionic and the bis-Schiff bases are dianionic. The octa-coordinated mono-Schiff base complex 4 adopts a dodecahedral geometry, while the hepta-coordinated bis-Schiff base complex 1 forms a one-dimensional linear polymeric chain. A weak antiferromagnetic exchange interaction (J=-0.15 cm(-1)) between the Mn(II) ions in is attributed to weak Mn...Mn interaction through the PhNH(2) moiety of the ligand, as indicated by extended-Hückel molecular orbital calculations. A good simulation of the EPR spectrum of a frozen solution (DMSO at 4 K) of compound 1 was obtained with g=2.0, D=0.1 cm(-1), E=0.01 cm(-1). The EPR spectrum of a powdered sample of compound 1 shows a large broadening of the signal, due in part, to the important zero-field splitting of the hepta-coordinated Mn(II) ion.     

Properties of light-induced degradation and the electronic properties of nanocrystalline silicon solar cells grown under functionally graded hydrogen dilutions

The electronic properties of hydrogenated nanocrystalline silicon (nc-Si:H) were studied using drive-level capacitance profiling (DLCP) to obtain defect density profiles as well as transient photocapacitance (TPC) and transient photocurrent (TPI) spectroscopies to study the spectra of defect related optical transitions. These measurements were performed on a series of n–i–p solar cell devices with intrinsic layer thickness of roughly 1 μm. The nc-Si:H intrinsic layers were deposited using RF or MVHF glow discharge with various hydrogen dilution profiles predominantly on specular stainless steel substrates (SS/n⁺/i nc-Si:H/p⁺/ITO), but also on textured back reflectors (SS/Ag/ZnO/n⁺/i nc-Si:H/p⁺/ITO) in some cases. Crystallite fractions were estimated using Raman spectroscopy. The electronic properties determined by our measurements could be correlated with variations in structural device parameters and with the degree of hydrogen dilution profiling during growth. We also found, depending on the growth conditions, that the devices exhibited markedly different behaviors after prolonged light exposure (100 h using light at 610 nm and 500 mW/cm² intensity). We discuss one specific microscopic mechanism that may be responsible for the light-induced changes that we have observed.     

Solid State Annular Tautomerism in a Molecule Containing Two Imidazole Moieties

Abstract  The X-ray crystal structure of the 1:2 condensate (1) of hydrazine hydrate and 4-methyl-imidazole-5-carboxaldehyde has been determined. The molecule is centrosymmetric crystallising in the space group Fddd with cell dimensions: a = 10.557(14), b = 17.062(22), c = 24.759(27) ?. Fourier map shows that the NH hydrogen atom of each imidazole moiety has equal possibility of occupying any of its two ring N atoms. This poses the possibility of finding three tautomers in 1 in the solid state. Consideration of the H-bonding pattern observed in 1 and related B3LYP/6-311+G(2d,p) calculations show that only two tautomers are present in the solid state. The situation is compared with that in the structure of 4(5)-nitro-5(4)-methoxy-imidazole reported previously by Kubicki. Graphical Abstract   The inherent disorder of the ring N–H hydrogen atoms in the shown centrosymmetric molecule (blue, C; deep blue, N; grey, H) which contains two imidazole moieties, poses the possibility of the coexistence of three tautomers in the solid state. The observed and theoretical [from B3LYP/6-311+G(2d,p) calculations] H-bonding pattern indicate that only two tautomers are present in the solid state.      

Synthesis and X-ray Crystal Structures of Two Luminescent Imidazopyridinium Derivatives from the Corresponding N-(aryl)-Pyridine-2-aldimines

Syntheses and X-ray structural characterizations of two new luminescent imidazopyridinium derivatives, 2-(phenyl)-N(3)-(4(methyl)phenyl)-imidazo[1,5a] pyridinium perchlorate (1) and 2-(pyridyl)-N(3)-(4-(chloro)phenyl)-imidazo[1,5a] pyridinium perchlorate (2) are reported. The compounds are prepared in one step from N-(4-(methyl)phenyl) pyridine-2-aldimine and N-(4-(chloro)phenyl) pyridine-2-aldimine respectively in a transformation mediated by Mn(OAc)₂-KMnO₄ mixture. It is found that the molecular structures of the two compounds are similar. In the solid state, 1 forms a three-dimensional network through a series of hydrogen bonds between the cations and anions in the lattice while 2 forms a similar but less extensively linked network. The substitution of hydrogen at the 2-position of the imidazopyridinium ring by phenyl or 2-(pyridyl) affects the nature of their first excited states as detected by changes in their emission and absorption spectra.