Structural precursors of poly(diphenylsilane) II. Crystal and molecular structure of HO(SiPh2)4OH and HO(SiPh2)7OH

Article abstract of DOI:10.1016/0022-328X(87)87104-8

An X-ray diffraction study was carried out on HO(SiPh2)4OH (I) and HO(SiPh2)7OH (II), which were prepared from phenylcyclopolysilanes.H bonds, found in both cases, strongly affect the conformation of polysilane chain.The intramolecular H bond in crystal I (O...O 2.81 Angstroem) closes the six-membered pseudocycle OSi4O to give "chair" conformation, with one of the OH groups participating in the intermolecular H bond (O...O 2.75 Angstroem).Two of these bonds link the molecules into the centrosymmetric dimer.In crystal II there are intermolecular H bonds linking the molecules into head-to-tail type chains (O...O distance of 2.78 Angstroem, Si-Si-Si-Si torsion angles of 149-160 deg), and in addition there is an O-H...? intramolecular H bond formed by one of the two terminal OH groups with the ?-system of the Ph ring (the distances from the O and H atoms to the Ph plane are 3.2 and 2.52 Angstroem respectively).The Si-chain conformation of molecule II is intermediate between trans-planar and gauche, the chain is twisted and the degree of twisting increases steadily in both directions from the middle towards each chain end.The Si-Si bond lengths in I and II are 2.361-2.412 Angstroem, the terminal bonds in the molecule II (av. 2.368 Angstroem) are somewhat shorter than the others (av. 2.400 Angstroem).In I the Si-Si bond angles are 108.6 and 113.3 deg, in II the bond angle at the central Si atom is 118.9 deg, significantly exceeding other angles (109.6-117.7 deg).