A. V. Yatsenko

Double stabilization of nanocrystalline silicon: a bonus from solvent

Double stabilization of the silicon nanocrystals was observed for the first time by 29Si and 13C MAS NMR spectroscopy. The role of solvent, 1,2-dimethoxyethane (glyme), in formation and stabilization of silicon nanocrystals as well as mechanism of modification of the surface of silicon nanocrystals by nitrogen-heterocyclic carbene (NHC) was studied in this research. It was shown that silicon nanocrystals were stabilized by the products of cleavage of the C–O bonds in ethers and similar compounds. The fact of stabilization of silicon nanoparticles with NHC ligands in glyme was experimentally detected. It was demonstrated that MAS NMR spectroscopy is rather informative for study of the surface of silicon nanoparticles but it needs very pure samples.Graphical Abstract

Stabilization of silicon nanoparticles by carbenes

Sodium reduction of a mixture of tetrabromosilane with imidazole ionic liquids in organic solvents gives dispersions of silicon nanoparticles stabilized by carbene ligands. It was shown that the size of silicon nanoclusters depends on the size of substituents at nitrogen atoms of 1,3-dialkylimidazol-2-ylidenes.

Visible spectra of crystalline anthraquinone colorants: the impact of crystal packing

Abstract The crystal structures of purpurin monohydrate and 1,4-dihydroxy-5,8-di-p-toluidinoanthraquinone were determined from single-crystal and powder X-ray diffraction data, respectively, and the visible reflection spectra of 18 crystalline colorants, (anthraquinones and related compounds) were obtained. Twelve of the compounds showed moderate (440–1090 cm−1) bathochromic shifts of their absorption maxima, compared to the solutions; other compounds exhibited greater bathochromic (up to 2900 cm−1) or hypsochromic (up to −1130 cm−1) shifts. For some of the compounds, the differences in colour between crystals and solutions are ascribable to the changes in molecular conformations or to the impact of hydrogen bonds.

Crystal and molecular structures of complexes of diethyldibromotin with triphenylphosphine oxide and hexamethylphosphoric triamide

The crystal and molecular structures of the Et/sub 2/SnBr/sub 2/ x 2TPPO complex and two crystal modifications of the Et/sub 2/SnBr/sub 2/ x 2HMPT complex were determined by x-ray diffraction analysis. The complexes are mononuclear, and the coordination polyhedron of the tin atom is a slightly distorted octahedron. The regularities of cis weakening of the Sn-Br and Sn-O bonds under the influence of donor ethyl groups were ascertained.

An INDO/S study of the second ππ* transition in the spectra of 1,4-diaminoanthraquinones responsible for their green hue

Abstract The INDO/S approach is used to study the structure/spectra relationship for some N,N′-disubstituted 1,4-diaminoanthraquinones. The calculated intensity and position of the short-wavelength absorption band depend on the molecular conformation, in agreement with the experimental data. The reflection spectra of crystalline 1,4-bisanilinoanthraquinone and 1,4-bis(mesitylamino)anthraquinone are reported and the crystal structure of the latter compound has been determined.

Syntheses and solid-state structures of some dialkyltin derivatives of α-methoxy- and α-acetoxy-phenylacetic acids

Several di-n-butyltin and diethyltin biscarboxylates and distannoxanes of α-methoxy- and α-acetoxy-phenylacetic acids were synthesized and (two of) their structures were studied by means of X-ray diffraction analysis as well as by means of IR and Mossbauer spectroscopies. It was shown for {[(n-Bu) 2 - SnOC(O)CH(OMe)Ph] 2 O} 2 that there is an interaction between the OMe group and one of the endocyclic tin atoms, resulting in a distorted pentagonal-bipyramidal geometry with the pentagonal plane defined by five O atoms and an uncommon seven coordination number for this tin atom. Spectral data indicate that biscarboxylates have trans-octahedral structures.

Modification of MCM-41 and SBA-15 mesoporous silicas by imidazolium ionic liquids

MCM-41 and SBA-15 mesoporous molecular sieves are modified with imidazolium ionic liquid (IL) via both physical adsorption and covalent grafting. The considerable effect of IL grafting on the porous structure and the particle morphology of mesoporous supports is shown. The pore size of these supports is found to be a key parameter determining the possibility of loading IL into such support materials.

Powder diffraction study of the hydrogen bonds in nitroxoline and its hydrochloride.

The crystal structures of 8-hydroxy-5-nitroquinoline, C9H6N2O3, (I), and 8-hydroxy-5-nitroquinolinium chloride, C9H7N2O3+*Cl-, (II), have been determined from X-ray powder data. In (I), the molecules are linked via moderately strong hydrogen bonds to form dimers. Such a packing motif is likely to be responsible for the low solubility of (I) in water. In (II), the inversion-related cations form stacks, and anions fill the interstack channels.

Structures and tautomeric interconversions of anthraquinone imine derivatives

Substituted 1-hydroxy-9,10-anthraquinone-9-imines have been found to exhibit tautomeric interconversions between the 9,10- and 1,10-quinonoid forms in the solid state as well as in solution. Single-crystal X-ray crystallography was used to study the structures of 4-(N-acetyl-p-tolylamino)-9-amino-1,10-anthracenedione and 4-hydroxy-1-phenylamino-10-mesitylimino-9(10H)-anthracenone at ambient and low temperatures. The former compound gave crystals belonging to the monoclinic space group P2l/c and, at 295 K,a=9.684(2),b=16.371(3),c=12.097(2) å,Β=110.41(1)‡, V=1797 å3,Z=4, R(F)=0.042, and GOF=0.863. The latter compound gave crystals belonging to the monoclinic space group C2/c and, at 295 K,a=38.158(8),b=6.322(2),c=19.325(4) å,Β=101.78(2)‡,V=4564 å3,Z=8, R(F)=0.052, and GOF=0.981, while at 150 K,a=37.852(6),b=6.245(1),c=19.235(4) å,Β=102.81(1)‡,V=4434 å3,R(F)=0.047, and GOF=1.006. Comparison of the geometric parameters of the two compounds illustrates the considerable zwitterionic nature of the first, a distinctive feature of which is a very short bond N(9)-C(9) whose length is essentially equal to that of a double bond. Molecular modeling studies using AMI semiempirical calculations were shown to be capable of satisfactorily reproducing the energetics of the tautomeric equilibrium once the medium effect was taken into account.

X-ray structural study of Ph2PbCl2(DMSO)2, Ph2PbCl2(HMPT)2 and Ph3PbCl(HMPT)

Abstract An X-ray structural investigation of Ph2PbCl2(DMSO)2 (I), Ph2PbCl2(HMPT)2 (II) and Ph3PbCl(HMPT) (III) was carried out (DMSO = dimethylsulphoxide, HMPT = hexamethyltriamide phosphoric acid). Complexes I and II have octahedrally coordinated PbIV, but in III the coordination is trigonal-bipyramidal. Comparison with the analogous tin compounds indicates the relative shortening of PbC bonds and lengthening of PbCl, PbN and PbO bonds. This phenomenon can be explained in terms of rehybridization of orbitals of the central atom.