M. Asahara et al., Bis(2,6-dimethoxyphenyl)tellurium dihalides (Cl, Br or I) and dithiocyanate: crystal structure and temperature-dependent NMR spectra, J CHEM S DA, (20), 2000, pp. 3493-3499
Citations number
50
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
Tris(2,6-dimethoxyphenyl)telluronium chloride hydrate, [R3Te]Cl . nH(2)O 1a
[R = 2,6-(MeO)(2)C6H3, n = 2-2.5] was prepared by the reaction of RLi and
TeCl4. It decomposed in hot 0.1 M hydrochloric acid to give R2TeCl2 3a, exc
lusively, from which R2TeX2 (X = Br 3b, I 3c or SCN 3d) were derived by hal
ogen exchange. The X-ray crystallographic analyses of 3a-3d showed that the
se compounds have a twofold axis (except for 3d) with essentially pseudo-tr
igonal bypyramidal co-ordination with two R groups and a lone pair of elect
rons occupying the equatorial sites and two halogen atoms the apical sites.
The thiocyanate groups in 3d bind to tellurium atom via sulfur. No intermo
lecular Te ... X secondary bond was observed for 3a-d. The Te-C bond distan
ces of 3a-c [2.09 +/- 0.01 Angstrom] are somewhat shorter than those report
ed for phenyl derivatives, and those of 3d [2.042(3) and 2.073(2) Angstrom]
are the shortest ever reported. The C-Te-C bond angle is much larger [107.
6(2)-104.37(9)degrees] than those reported. The X-Te-X bond angles are very
close to 180 degrees. The Te ... O distances of 3a-d [2.880-3.323 Angstrom
] are significantly shorter than the sum of the O and Te van der Waals radi
i [3.60 Angstrom]. The H-1 NMR spectra of 3a-3c were halogen-, solvent-, an
d temperature-dependent showing that the rotation of R-Te bonds was restric
ted due to the barrier between R groups and halogen atoms. The activation e
nergies Delta G double dagger decreased in the order 3a (90 kJ mol(-1) in D
MSO-d(6)) > 3b (80 kJ mol(-1) in DMSO-d(6)) > 3d (greater than or equal to
65 kJ mol(-1) in CDCl3) > 3c (60 kJ mol(-1) in CDCl3) greater than or equal
to 3d (59 kJ mol(-1) in CD3CN).