Structural study of compounds modelling elementary polymer units, 1. Molecular and crystal structures of 1,3,5-tris(4-biphenylyl)-benzene and 1,3,5-tris[4-(C-o-carboranylmethyl)phenyl]benzene

For elucidating the structural features of elementary units of polyphenylene type polymers, prepared by polycondensation of di- and mono-acetylaromatic compounds, and X-ray study of two model compounds was performed, viz. 1,3,5-tris(4-biphenylyl)benzene (1) and 1,3,5-tris[4-(C-o- carboranylmethyl)phenyl]benzene (2) (diffractometer: R = 0,063 (1) and 0,061 (2) )· 1 0,5 C₆H₆ crystals were found to be rhombohedral, a = 20,168 (3), c = 13,678 (3) ǎ, space group R3c, Z = 6;2· CHCl₃ crystals are triclinic, a = 15,7528 (2), b = 12,7004 (6), c = 15,460 (2) Å, α = 109,97(1) β = 111,92(1) γ = 100,69 (2) °, space group P1, Z = 2. In the crystal the molecule 1 has a 32 symmetry with a propeller-like orientation of the biphenyl fragments with respect to the central ring (the rotation of the disubstituted benzene rings relative to the central one is 47,2° and relative to the therminal ones, it is 35,9°). In 2 the disubstituted benzene rings are rotated with respect to the central one by different values (dihedral angeles are 31,7 - 30,7, and 52,5°). In all benzene rings of both molecules a decrease of the endocyclic bond angles at the ipso-atoms is observed which in 2 depends on the dihedral angeles between the planes of bonded benzene rings. All there carboranylmethylphenyl fragements in 2 have the same conformation: the CH-group of the carborane skeleton “hangs” over the benzene ring plane. The crystal packing of 1 and 2 is characterized by sufficiently large cavities which are occupied by solvent molecules. In crystals of 2 the carborane parts of the molecules are associated into separate structural motives.