41842-30-2

NMR chemical shifts of 1H, 13C, and 73Ge, molecular modeling, and single-crystal X-ray diffraction results are reported for a series of substituted tris- and tetrakis(phenyl)germanes of the type (XC6H4)3GeY and (XC6H 4)4Ge, where X = o-, m-, and p-OCH3, o-, m-, and p-OC2H5, m- and p-CF3, H, p-C(CH 3)3, p-Cl; and Y = Cl and H. Chemical shifts and X-ray data are also reported for o-CH3 and o-OCH3 tetrakis(phenoxy)- ((XC6H4O)4Ge) and thiophenoxygermanes ((XC6H4S)4Ge). For tetrakis derivatives, 73Ge resonances are observed for all but the o-methoxyphenoxy compound, for which the inability to detect a resonance is attributed to rapid quadrupolar relaxation caused by intramolecular interactions of the methoxy oxygen with the central atom. The observation of a relatively broad, slightly upfield 73Ge resonance in the analogous phenyl and thiophenoxy derivatives suggests, as do the results of molecular modeling, that in these compounds there is some hypercoordination. The solid-state structures show bond angles at the aromatic carbon bearing the alkoxy group that suggest an interaction of the alkoxy oxygen with germanium. Oxygen-germanium bond distances are about 17% shorter than the sum of the van der Waals radii.

Further to earlier work on the liquid crystal properties of fluoro-1,1':4',1"-terphenyls we have now extended this series to include terminally fluoro- and cyano-substituted 2'-fluoro-1,1':4',1"-terphenyls, chiral 2'-fluoro-1,1':4',1"-terphenyls, and esters derived from 2'-fluoro-1,1':4',1"-terphenyls and incorporating the alkylcyclobutyl group.The preparations and transition temperatures for these series of compounds are presented and their transition temperatures and mesophase types are discussed.An interesting result from this work was the appearence of an S*C phase for one chiral homologue and of SC phases for the esters incorporating the alkylcyclobutyl group.The SC formation is attributed to the presence of the fluoro-substituent.Keywords: terphenyls, fluoroterphenyls, smectic C phases, cyclobutyl esters.