Crystal and molecular structure of dodecamethylcyclohexasilane

Abstract

Crystals of dodecamethylcyclohexasilane are monoclinic, space group A 2/a, with four molecules per unit cell having lattice parameters a= 14.026, b= 10.158, c= 18.168 ~ and fl= 109-0 °. The data were collected on a four-circle automatic diffractometer with Cu Ke radiation. The structure was solved by the symbolic-addition procedure and was refined by full-matrix least-squares methods. The least-squares refinement of the positional and anisotropic thermal parameters of the silicon and carbon atoms, using 1440 observed reflections, yielded a final R of 0.053. The molecules of [5i(CH3)216 have site symmetry T and have the flattened chair conformation of cyclohexane. The Si-C bond lengths have been corrected for riding motion, and a slight difference between equatorial and axial carbon to silicon bond distances is noted: 1.935 + 0.006 and 1.913 + 0.004/~,, respectively.

Synthesis, 1H, 13C, and 29Si nuclear magnetic resonance spectra and crystal structure of trans-1,4-diphenyldecamethylcyclohexasilane

“…The compound exists as discrete molecules as shown in Fig. 2 (6), and Ph6Me6Si6, 2.359(2) A (7). These distances agree well with the Si-Si covalent bond length of 2.34 A (8).…”

“…Hereo, the structure differs from Me12Si6 where a difference of 0.033 A is reported between axial and equatorial Si-C bond distances (6). However, the difference between averaged Si-C (Me), 1.888 (8) A and Si-C(Ph) 1.897 (3) A is of the same magnitude as has been observed in Ph6Me6Si6 (7).…”

“…1". These and other torsion angles (Table 4) are closer to the ideal angles of 109.5", 60°, and 180" for a six-membered chair conformation than the respective angles in other hexasilane structures studied so far (6,7,9). This indicates that the structure of trans-1 ,4-Ph2Me10Si6 has the least distorted cyclohexasilane ring relative to those of Me12Si6 (6), all transPh6Me6Si6 (7), and Phl2si6.7C6H6 (9).2…”

The crystal and molecular structure of 1,4-diphenyl-2,2′,3,3′,5,5′,6,6′-octamethylcyclo-1,4-diphospha-2,3,5,6-tetrasilahexane, a phosphorus–silicon heterocycle

“…Many of the structural features observed in (PhPSi,Me,), are related to those found in the ho~nocyclic inolecules (SiMe,), (1) and (PhP), (3), and, for purposes of comparison, the valence, dihedral and torsion angles of the three inolecules are listed in Table 5,5 along with those expected for an idealized cyclohexa~le chair. All three inolecules have chair conformatioris and, as in (PhP),, the phenyl groups 011 phosphorus in (PhPSi,Me,), occupy equatorial positions.…”

Intramolecular excimer and exciplex emission of 1,4-dipyrenyl substituted cyclohexasilane

“…The redox potentials can be used to obtain the free energy of charge separation DG CS via [22] DG CS ¼ eðE A zero-zero excitation energy of E 00 ¼ 3:21 eV and a donor-acceptor distance of R DA ¼ 6:6 A A, taken from the crystal structure of 2 [6], were used. Effective radical cat-and anion radii r dþ (5.3 A A) and r aÀ (4.0 A A) were obtained by r ¼ ð3V m =4pÞ 1=3 , with the molecular volumes V m adapted from the crystal structures of dodecamethylcyclohexasilane [23] and pyrene [24]. Application of these data reveals that in acetonitrile (dielectric constant e s ¼ 35:9) charge separation is allowed since DG CS ¼ À0:16 eV.…”