Die Struktur des Pentaphenyldisiloxans

Structure of Pentaphenyldisiloxane Pentaphenyldisiloxane was obtained by reaction of triphenylsilanol with diphenylchlorosilane and triethylamine. The compound crystallizes as colourless triclinic platelets (P1 ; a = 1069.6; b = 1389.6; c = 925.5 pm; α = 106.17; β = 9239; γ = 95.93°; Z = 2). The X-ray structure analysis shows a bent configuration of the molecule with Si? ;O? Si = 163.3°. The structure of the molecules is discussed in relation to the structures of 1,1,3,3-tetraphenyldisiloxane, 1,3-dimethyl-1,1,3,3-tetraphenyldisiloxane and pentaphenylmethyldisiloxane.     

Embedding graphs in Cayley graphs

IfY is a finite graph then it is known that every sufficiently large groupG has a Cayley graph containing an induced subgraph isomorphic toY. This raises the question as to what is sufficiently large. Babai and Sós have used a probabilistic argument to show that |G| > 9.5 |Y|³ suffices. Using a form of greedy algorithm we strengthen this to (2 + \sqrt 3 )|Y|^3 $$ " align="middle" border="0"> . Some related results on finite and infinite groups are included.     

Phase diagram and phase transitions of Krypton on graphite in the extended monolayer regime

We report high resolution x-ray diffraction studies of the structures and phase transitions of monolayer krypton, adsorbed on both powder and single crystal graphite substrates. A comprehensive series of powder diffraction profiles is used to construct the two dimensional phase diagram. The melting of the commensurate solid is shown to be strongly first order throughout the region where tricritical behavior was previously thought to occur; fluid solid coexistence extends up to the termination of the commensurate phase at 130 K. A disordered weakly incommensurate phase is shown to be a reentrant fluid, a system which may be described as a disordered network of domain walls and which evolves continuously into a more conventional 2D fluid. This evolution is marked by the disappearance of satellite peaks which are caused by the modulation of the overlayer by the substrate. The freezing of the reentrant fluid into the commensurate phase is shown to be consistent with a chiral Potts transition, its freezing into the incommensurate solid consistent with a dislocation binding transition.Single crystal experiments reveal the orientation of the weakly incommensurate phase. The reentrant fluid is found to have no visible orientational fluctuations, manifesting isotropic diffraction peaks. This is attributed to the strong epitaxy of domain walls. The incommensurate solid is shown to undergo an aligned-rotated transition which is well described by zerotemperature calculations.     

Synthesis of the (dialkylamino)borate, [Ph(2)B(CH(2)NMe(2))(2)](-), affords access to N-chelated rhodium(I) zwitterions

This paper reports the synthesis of the first bis(amino)borate ligand, [Ph(2)B(CH(2)NMe(2))(2)](-), an anionic equivalent of tertiary diamines. Anionic [Ph(2)B(CH(2)NMe(2))(2)] is an excellent bidentate ligand auxiliary and is used to prepare a series of N-chelated, zwitterionic rhodium(I) complexes.     

Syntheses and oxygenation of iron(II) “strapped” porphyrin complexes

A general route to ‘strapped’ porphyrins which are bridged between diagonally opposite meso-positions is described. Studies on the oxygenation and carbonylation of their iron(II) complexes have shown that they are inferior to ‘capped’ porphyrins as models for the oxygen-carrying haemoproteins. The results reported herein suggest that strapping structures which do not enforce well-defined and rigid cavities for oxygen binding afford little protection against irreversible oxidation of (dioxygen) (porphyrin) iron(II) complexes.     

Einen Gasentwicklungsapparat

Ohne Zusammenfassung