Crystal structures of poly(di-n-butyl silane) and poly(di-n-pentyl silane)

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Abstract
The crystal structures of poly(di-n-butyl silane) and poly(di-n-pentyl silane) have been determined by comparing the experimental X-ray diffraction pattern with the theoretical pattern. The side-chain conformation is mostly determined by the intramolecular steric hindrance as well as the van der Waals interaction between the side chains. The Si backbone conformation of both crystals is a 7/3 helix, which is mainly determined by the intramolecular van der Waals interaction between the nearest-neighbour side chains. On the other hand. The Si backbone conformation of both crystals after a pressure treatment of 1500 MPa is all trans, which is caused by the van der Waals interaction between the side chains attached to the second-nearest-neighbour Si atoms; In all cases, one of the two C-Si-C-C groups in Si(C4H9)2 or Si(C5H11)2 is an essentially trans conformation. Whereas the other C-C-Si-C group has a cis-like conformation, which is different from that generally accepted.