R. Boese et al., C-3-SYMMETRICAL HEXAKIS(TRIMETHYLSILYL)[7]PHENYLENE [TRIS(BIPHENYLENOCYCLOBUTADIENO)CYCLOHEXATRIENE], A POLYCYCLIC BENZENOID HYDROCARBON WITH SLIGHTLY CURVED TOPOLOGY, Angewandte Chemie, International Edition in English, 34(13-14), 1995, pp. 1478-1481