Crystal structures of 3/4-pyridyl-based thiosemicarbazones and related Cu and Ni coordination compounds

In this investigation, the crystal structures of the thio-ligands 3-formylpyridine 4-phenylthiosemicarbazone (C13H12N4S, 1) and 4-benzoylpyridine 4-ethylthiosemicarbazone (C15H16N4S, 2), and of two new coordination compounds, chlorido(3-formylpyridine 4-phenylthiosemicarbazone-κS)bis(triphenylphosphane-κP)copper(I) acetonitrile monosolvate, [CuCl(C13H12N4S)(C18H15P)2]·CH3CN, 3, and bis(3-formylpyridine 4-ethylthiosemicarbazonato-κ2 N 1,S)nickel(II), [Ni(C9H11N4S)2], 4, are reported. In complex 3, the thio-ligand coordinates in a neutral form to the Cu atom through its S-donor atom, and in complex 4, the anionic thio-ligand chelates to the Ni atom through N- and S-donor atoms. The geometry of complex 3 is distorted tetrahedral [bond angles 99.70 (5)–123.23 (5)°], with the P—Cu—P bond angle being the largest, while that of complex 4 is square planar, with trans-S—Ni—S and N—Ni—N bond angles of 180°.

What’s in an Atom? a Comparison of Carbon and Silicon-Centered Amidinium···carboxylate Frameworks

<div><div><div><p>Despite their apparent similarity, framework materials based on tetraphenylmethane and tetraphenylsilane building blocks often have quite different structures and topologies. Herein, we describe a new silicon tetraamidinium compound and use it to prepare crystalline hydrogen bonded frameworks with carboxylate anions in water. The silicon-containing frameworks are compared with those prepared from the analogous carbon tetraamidinium: when biphenyldicarboxylate or tetrakis(4-carboxyphenyl)methane anions were used similar channel-containing networks are observed for both the silicon and carbon tetraamidinium. When terephthalate or bicarbonate anions were used, different products form. Insights into possible reasons for the different products are provided by a survey of the Cambridge Structural Database and quantum chemical calculations, both of which indicate that, contrary to expectations, tetraphenylsilane derivatives have less geometrical flexibility than tetraphenylmethane derivatives, i.e. they are less able to distort away from ideal tetrahedral bond angles.</p></div></div></div>

What’s in an Atom? a Comparison of Carbon and Silicon-Centered Amidinium···carboxylate Frameworks

<div><div><div><p>Despite their apparent similarity, framework materials based on tetraphenylmethane and tetraphenylsilane building blocks often have quite different structures and topologies. Herein, we describe a new silicon tetraamidinium compound and use it to prepare crystalline hydrogen bonded frameworks with carboxylate anions in water. The silicon-containing frameworks are compared with those prepared from the analogous carbon tetraamidinium: when biphenyldicarboxylate or tetrakis(4-carboxyphenyl)methane anions were used similar channel-containing networks are observed for both the silicon and carbon tetraamidinium. When terephthalate or bicarbonate anions were used, different products form. Insights into possible reasons for the different products are provided by a survey of the Cambridge Structural Database and quantum chemical calculations, both of which indicate that, contrary to expectations, tetraphenylsilane derivatives have less geometrical flexibility than tetraphenylmethane derivatives, i.e. they are less able to distort away from ideal tetrahedral bond angles.</p></div></div></div>

Dependence of Tetrahedral Bond Lengths on the Surface Passivation and Stacking-Fault Density of CdSe Nanocrystals

We have investigated the surface effect of colloidally prepared CdSe nanocrystals (NCs) with the size range of 23-40 Å on their structural properties by changing the organic capping ligands. The TOPO/HDA-passivated NCs reveal a size-dependent behavior involving an elongated axial bondR(1)of an atomic tetrahedron and a shrunken equatorial bondsR(2). After treatment of the NCs with pyridine, the bond lengthR(1)decreases significantly whereasR(2)remains unchanged relative to the TOPO/HDA-passivated NCs, suggesting that a tensile stress along the [001] direction is contributed from the surface modification. In addition, we find that the expansion ratio of the pyridine-treated NCs along the c axis depends strongly on the density of stacking faults, which provides an evidence for the relaxation of atomic positions near the interface of stacking faults.

N-(3,5-Dimethylphenyl)-P,P-diphenylphosphinic amide

In the title compound, C20H20NOP, the P atom, with a distorted tetrahedral geometry, is attached to an O atom, two phenyl groups, and a 3,5-dimethylaniline group. The N—P—C [102.29 (12) and 108.97 (12)°] and C—P—C [107.14 (12)°] bond angles are all smaller than the ideal 109.5° tetrahedral bond angle, whereas the O—P—C [113.07 (12) and 110.62 (12)°] and O—P—N [114.24 (13)°] angles are all larger than 109.5°. A weak intramolecular C—H...O hydrogen bond helps to establish the molecular conformation. In the crystal, the molecules are linked by N—H...O hydrogen bonds, generating [001] chains.

MICROSTRUCTURAL EVOLUTION OF SiC DURING MELTING PROCESS

Microstructural evolution of SiC during melting process is simulated with Tersoff potential by using molecular dynamics. Microstructural characteristics are analyzed by radial distribution function, angle distribution function and Voronoi polyhedron index. The results show that the melting point of SiC with Tersoff potential is 3249 K. Tersoff potential can exactly describe the changes of bond length, bond angle and Voronoi clusters during the process of melting. Before melting, the length of the C – C bond, Si – Si bond and Si – C bond is 3.2, 3.2 and 1.9 Å, respectively. The bond angle distributes near the tetrahedral bond angle 109°, and the Voronoi clusters are all (4 0 0 0) tetrahedron structures. After melting, the C – C bond and Si – Si bond are reduced, while the Si – C bond is almost unchanged. The range of bond angle distribution is wider than before, and most of the (4 0 0 0) structures turn into three-fold coordinated structures, (2 3 0 0), (0 6 0 0) and (2 2 2 0) structures. The simulation results clearly present the microstructural evolution properties of SiC during the melting process.