Crystal Structures and ab Initio Calculations of New Dicationic Telluranes (λ4-Tellane), [10−Te−4(C2X2)]2+ (X = S, Se): Positively Charged Hypervalent Bonding Systems

Abstract

The reactions of 2,6-bis[(phenylthio- or phenylseleno)methyl]phenyl phenyl telluride or the corresponding Te-oxide, with NOBF4 or trifluoromethanesulfonic anhydride afforded the new telluranes, [10−Te−4(C2X2)]2+·2Y- (λ4-tellane) (X = S or Se, Y = BF4 or CF3SO3). These compounds were characterized by elemental and spectroscopic (FABMS, 1H, 13C, and 125Te NMR) analyses. X-ray structure determinations revealed that the hypervalent tellurium atoms are at the center of a distorted trigonal bipyramid, with two apical sulfonio or selenonio ligands connected via transannular bonds. The Te−S distances are in the range 2.652−2.706 Å, the Te−Se distances in the range 2.759−2.807 Å, and the X−Te−X bond angles in the range 160.41−163.92 °. Ab initio calculations indicate that the positive charges in the dications are exclusively on the three chalcogen atoms that form three-center, four-electron bonds.