Extending interstitial tetrelides into carbides: synthesis and crystal and electronic structures- of RE2Co2AlC (RE = La, Pr, Nd).

New quaternary compounds RE2Co2AlC (RE = La, Pr, Nd) of the filled W2CoB2 structure type were synthesized by the reaction of samples with the nominal composition RE40Co40Al20 (RE = La, Pr, Nd) and carbon. Single crystal X-ray diffraction data show that the RE2Co2AlC compounds crystallize in a body-centered orthorhombic space group Immm (oI12) with Z = 2 and a = 4.1841(11) Å, b = 6.1161(15) Å, c = 9.091(2) Å (La2Co2AlC); a = 4.1290(9) Å, b = 6.1152(18) Å, c = 8.844(3) Å (Pr2Co2AlC); a = 4.1168(15) Å, b = 6.1131(17) Å, c = 8.792(5) Å (Nd2Co2AlC) and are isotypic to the recently reported Nd2Co2SiC. The structures can be described as interstitial carbides of the W2CoB2 structure type with carbon atoms fully occupying the octahedral voids, which leads to the anisotropic expansion of the unit cell, more pronounced along the b-axis. Electronic structure calculations predict the RE2Co2AlC (RE = La, Pr, Nd) compounds to be metallic. The relative stability of the La2Co2AlX structures where X = C, O, Si, or a vacancy was investigated based on the bonding analysis, which emphasizes the important role that carbon plays in stabilizing the structural motif.

Synthesis and crystal structure of a new Cu3Au-type ternary phase in the Au-In-Pd system: distribution of atoms over crystallographic positions.

A new Cu3Au-type ternary phase (τ phase) is found in the AuPd-rich part of the Au-In-Pd system. It has a broad homogeneity range based on extensive (Pd,Au) and (In,Au) replacement, with the composition varying between Au17.7In25.3Pd57.0 and Au50.8In16.2Pd33.0. The occupancies of the crystallographic positions were studied by single-crystal X-ray diffraction for three samples of different composition. The sites with m-3m symmetry are occupied by atoms with a smaller scattering power than the atoms located on 4/mmm sites. Two extreme structure models were refined. Within the first, the occupation type changes from (Au,In,Pd)3(Pd,In) to (Au,Pd)3(In,Pd,Au) with an increase in the Au gross content. For the second model, the occupation type (Au,In,Pd)3(Pd,Au) remains essentially unchanged for all Au concentrations. Although the diffraction data do not allow the choice of one of these models, the latter model, where Au substitutes In on 4/mmm sites, seems to be preferable, since it agrees with the fact that the homogeneity range of the τ phase is inclined to the Au corner and provides the same occupation type for all the studied samples of different compositions.

Lanthanum ruthenium indide, La(21)Ru(9+x)In(5-x) (x = 1.2).

La(21)Ru(9+x)In(5-x) (Pearson symbol tI140) is isotypic to the filled Y(3)Rh(2)-type structure, from which it can be derived through an ordered substitution at two sites. One of the square-prismatic sites (site symmetry ..m) is occupied by a mixture of Ru and In atoms and one of the square-antiprismatic sites (4/m..) is fully occupied by In atoms.

Ring contraction of 1,2,4,5,7,8-hexaoxa-3-silonanes by selective reduction of COOSi fragments. Synthesis of new silicon-containing rings, 1,3,5,6-tetraoxa-2-silepanes.

The reducing agents Ph(3)P, (C(8)H(17))(3)P, or NH(2)C(S)NH(2) promote the ring contraction of nine-membered triperoxides, viz., 1,2,4,5,7,8-hexaoxa-3-silonanes, giving rise to seven-membered rings belonging to the previously unknown class of monoperoxides, viz., 1,3,5,6-tetraoxa-2-silepanes, in yields from 67% to 91%. Therefore, the selective reduction of the SiOOC fragments to SiOC in molecules containing simultaneously the COOC fragment was performed for the first time.

Synthesis of cyclic peroxides containing the Si-gem-bisperoxide fragment. 1,2,4,5,7,8-Hexaoxa-3-silonanes as a new class of peroxides.

A method was developed for the synthesis of the previously unknown class of organic peroxides, 1,2,4,5,7,8-hexaoxa-3-silonanes, based on the reaction of dialkyldichlorosilanes with 1,1'-dihydroperoxyperoxides. 1,2,4,5,7,8-Hexaoxa-3-silonanes are rather stable under ambient conditions and were characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. Their yields are in a range of 59-96%. The attempts were made to prepare 1,2,4,5-tetraoxa-3-silinanes by the reaction of dialkyldichlorosilanes with gem-bishydroperoxides. 1,2,4,5-Tetraoxa-3-silinanes were detected by NMR spectroscopy; these compounds rapidly decompose upon isolation.