1,3,5-Triphenyladamantane and 1,3,5,7-tetraphenyladamantane.

In 1,3,5-triphenyladamantane, C(28)H(28), (I), and 1,3,5,7-tetraphenyladamantane, C(34)H(32), (II), the molecules possess symmetries 3 and 4, and are situated across threefold and fourfold improper axes, respectively. The molecules aggregate by means of extensive C-H...pi interactions. In (I), the pyramidal shape of the molecules dictates the formation of dimers through a ;sixfold phenyl embrace' pattern. The dimers are linked to six close neighbors and constitute a primitive cubic net [H...pi = 2.95 (2) and 3.02 (2) A]. Compound (II) is isomorphous with tetraphenyl derivatives EPh(4) of group 14 (E = C-Pb) and ionic salts [EPh(4)][BPh(4)] (E = P, As and Sb). The multiple C-H...pi interactions arrange the molecules into chains, with a concerted action of CH (phenyl) and CH(2) (adamantane) groups as donors [H...pi = 3.15 (2) and 3.44 (2) A, respectively]. The additional interactions with the methylene groups (four per molecule) are presumably important for explaining the high melting point and insolubility of (II) compared with the EPh(4) analogs.