X-ray characterization

Holland, by contrast, reported the existence of three well-defined phases in this system, corresponding to ZnO ZnClj HjO ratios of 5 1 8, 1 1 1 and 1 1 2 respectively (Holland, 1930). More recently it was pointed out that these claims lack any unequivocal support such as X-ray characterization of the phases, so that their validity must remain in doubt (Sorrell, 1977). 

Figure 13b. x-Ray characterization of POM. Key top, Laue diagram bottom left, morphology and bottom right, Lambot method compared to a simitar sample of Sifor which the penetration depth is smaller. 

In the reaction of 1 with alkynes possessing electron-withdrawing substituents, the corresponding silacyclopropene derivatives 66 and 67 are formed, as described in Scheme 23.29 An unexpected pathway was observed in the reaction with the electron-poor hexafluorobutyne(2) the X-ray characterized heterocycle 68 was most likely obtained by nucleophilic attack of 1 at the triple bond. A subsequent shift of a fluorine atom from carbon to silicon creates an allene-type molecule which was stabilized by a [2 + 2] cycloaddition process involving a double bond from the pentamethylcyclopentadienyl unit, as described in Scheme 24.33... 

Irradiation of [Pt(hfac)2] with an excess of ethene at 350 nm produced an X-ray-characterized five-coordinated intermediate containing both hfac ligands still bidentate (i.e. limiting A mechanism) (208). Quenching of photoexcited [Pt(terpy)Cl]+, and 4 -substituted terpy and NCS- analogues variously, by a range of Lewis bases, such as MeCN, DMSO, py, acetone, has been documented (209). 

Wyime, S. A., et al. (1999). Crystallization of hepatitis B virus core protein shells determination of cryoprotec-tant conditions and preliminary X-ray characterization. Acta Crystallogr. D 55, 557-560. 

Carroll JB, Waddon AJ, Nakade H, Rotello VM. Plug and play polymers. Thermal and X-ray characterizations of noncovalently grafted polyhedral oligomeric silsesquioxane (POSS)-polystyrene nanocomposites. Macromolecules 2003 36 6289-6291. 

The monomeric [NbCl3(py)3] has been used for the preparation of [Nb(NCS)3(py)3].593 Ks[Nb(CN)g], obtained by electrosynthesis,536 is the only X-ray-characterized monomeric homoleptic Nb111 compound. A dodecahedral D2d geometry with two sets of Nb—C distances was found in the solid.635 IR data suggest a change to a D4d geometry in solution. 13CNMR data are compatible with either a D or a fluxional Did polyhedron. 

An X-ray characterization of the various compounds formed in the NaCl-CdCl2 system has been reported.963... 

Lifsliin, E X-Ray Characterization of Materials, John Wiley Sons, Inc, New York, NY, 1999. 

A recent X-ray characterization of the cyclopentyl cation 33 generated with methyl carboranes has shown a perfect planar structure around the carbocation center [bond angles CH3-C+-CH2= 124.9 and 125.2°, CH2-C+-CH2= 109.9° bond distances CH3-C+ = 1.46 A, CH2-C+ = 1.45 A).123... 

If a carbocation or a dication at the same time is also a Hiickeloid An + 2)jt aromatic system, resonance can result in substantial stabilization. The simplest 2jt aromatic system is the Breslow s cyclopropenium ion 206.434 439 Recently, electronic and infrared spectra of the parent ion cyclo-C3H3+ (206, R = H) in neon matrices440 and the X-ray characterization of the tris(trimethylsilyl) derivative were reported.441 The destabilizing effect of the silyl groups was found to be significantly smaller than in vinyl cations. The ion was computed to be more stable than the parent cyclopropenium ion by 31.4 kcal mol1 [MP3(fc)/6-31 lG //6-31G +ZPVE level]. The alkynylcy-clopropenylium ions 207 have been reported recently.442... 

The X-ray characterization of the Sbly, salt of cation 250 by Laube et al.516 corroborates the above findings. The short C+-C1 distance (1.668 A versus 1.734 A for C ,2-CI) indicates significant chlorine back-donation resulting in partial double bond character in agreement with experimental findings and theoretical calculations. 

---