Pyramidal carbon crystal structure

Laube and Hollenstein [21, 61] studied the single crystal structures of cyclohexanone derivatives complexed with a Lewis acid and found pyramidalization of the carbonyl carbon (4, Fig. 4), in agreement with the observed selectivity [61]. 

It was formerly considered that nitrenes attack only the carbons atom of thiophene (84CHEC-(4)74i). Since 1984, several S,N-ylides formed by the attack of a nitrene on the ring sulfur atom of thiophene have been prepared (89AHC(45)l5l). Thus, ethoxycarbonyl nitrene with polyhalogenothiophenes forms the S,N-ylide (46) in 44% yield (84CC190). The X-ray crystal structure reveals that the sulfur in such ylides is pyramidal. 

A stable zwitterionic carbene-plumbylene adduct has been reported (equation 64)80. According to its X-ray crystal structure, the central carbon atom is almost planar while the lead atom is pyramidal. As expected, the P — C+ bond length (2.54 A) is longer than a covalent P—C (about 2.38 A) and a P=C bond, which is expected to be about 2.05 A80. 

An X-ray crystal structure determination of di- i3-bromo-di-/i3-cyclopropyl-tetralithio-tetrabis (diethyl ether) [2LiBr -2c-C3H5Li -4(C2H5)20] published by Schmidbaur and coworkers shows nicely the pyramidal configuration of the anionic carbon atom, in agreement with the calculations. The cyclopropyl anion in the gas phase has been studied by Sguires and coworkers . ... 

According to X-ray crystal structure determinations of 6 and 8, the best description of the coordination geometry of the tin center in these compounds is a -trigonal bipyramidal one, with the carbon ligands and the lone pair at the equatorial sites and both intramolecular coordinating nitrogen atoms at the apical positions (74,75). Compound 10 has a square-pyramidal structure, with the lone pair at the apex of the pyramid. Most... 

The crystal structure of Ni Ses quenched from 420 °C has been determined. " The selenium atoms form a zig-zag pattern, with the nickel atoms in deformed tetrahedral, octahedral, or pyramidal positions in the selenium lattice. AgaSe is formed during heating a suspension of Ag powder and selenium in alkaline solution. The temperature of reaction was found to decrease with increasing alkali concentration because of activation of selenium by hydroxide ion. The ternary selenides CsaPd3Se4, Rb,Pd3Se4, and KaPd3Se4 have been prepared by fusion of alkali-metal carbonates with palladium and selenium at 850 °C. 

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