Structural Study of Compounds Modelling Elementary Polymer Units, 5.† Molecular and Crystal Structures of C, C′-Disubstituted O-Carboranes
Macromolecular Chemistry and Physics
With the aim to determine the main structural characteristics of amorphous (branched and different‐unit) polymers of the polyphenylene type, prepared by polycyclocondensation of carborane‐containing mono‐ and diacetylaromatic compounds, an X‐ray structural study of four model compounds was carried out, viz. of 1,2‐bis[4‐(4‐acetylphenoxy)phenyl]‐1,2‐dicarba‐closo‐dodecaborane(12) (1) (triclinic crystals, a = 8,205 Å, b = 13,505 Å, c = 14,019 Å, α = 90,44°, β = 97,08°, γ = 97,24°, space group P1, Z = 2, R = 0,045 for 2663 reflections), 1,2‐bis(4‐phenoxyphenyl)‐1,2‐dicarba‐closo‐dodecaborane(12) (2) (monoclinic crystals, a = 14,813 Å, b = 17,133 Å, c = 11,211 Å, β = 112,43°, space group P21/c, Z = 4, R = 0,066 for 3 286 reflections), 1,2‐bis(4′‐acetylbiphenyl‐4‐yl)‐1,2‐dicarba‐closo‐dodecaborane(12) (3) (orthorhombic crystals, at −120°C a = 13,405 Å, b = 9,276 Å, c = 22,86 Å, space group Pnam, Z = 4 molecules on the m plane, R = 0,039 for 1 147 reflections), and 1,2‐bis(4‐acetylbenzyl)‐1,2‐dicarba‐closo‐dodecaborane(12) (4) (orthorhombic crystals, at −120°C a = 22,03 Å, b = 26,23 Å, c = 8,026 Å, space group Fdd2, Z = 8 molecules lie on the two‐fold axis, R = 0,051 for 577 reflections). The strained structure of the C,C′‐o‐diphenyl‐substituted carboranyl fragment is established, the high conformational flexibility of 4‐phenoxyphenyl linkages is confirmed and a tendency toward separate autoassociation of acetyl‐containing polar groups and carborane nuclei is shown, with the autoassociation of polar groups completely suppressing that of carborane nuclei in case of conformational rigidity and shortness of the arylene linkages. These and other structural characteristics of the investigated model compounds and their crystals, in case they turn out to be characteristic also for the corresponding polymers and their precursors, should largely determine the structure and physico‐chemical properties of their corresponding polymers.