Calcagno P, Kariuki BM, Kitchin SJ, Robinson JM, Philp D, Harris KD
School of Chemistry, University of Birmingham, Edgbaston, UK.
Chemistry. 2000 Jul 3;6(13):2338-49. doi: 10.1002/1521-3765(20000703)6:13<2338::aid-chem2338>3.0.co;2-n.
A homologous series of bis-diphenylphosphine oxides (C6H5)2PO(CH2)(n)PO(C6H5)2 (with n = 2-8; denoted 2-8] have been investigated to explore the effects of a range of competing and cooperative intermolecular and intramolecular interactions on the structural properties in the solid state. The important factors influencing the structural properties include intramolecular aspects such as the conformation of the aliphatic chain and the intramolecular interaction between the two P=O dipoles in the molecule, and intermolecular aspects such as long-range electrostatic interactions (dominated by the arrangement of the P=O dipoles), C-H...O interactions, C-H...pi interactions and pi...pi interactions. Compounds 3 and 5 could be crystallized only as solvate co-crystals (3 water and 5 x (toluene)2], whereas the crystal structures of all the other compounds contain only the bis-diphenylphosphine oxide molecule. The crystal structures have been determined from single-crystal X-ray diffraction data, with the exception of 7 (which has been determined here from powder X-ray diffraction data) and 4 (which was known previously). The compounds with even n represent a systematic structural series, exhibiting characteristic, essentially linear P=O...P=O...P=O dipolar arrays, together with C-H...O and C-H...pi interactions. For the compounds with odd n, on the other hand, uniform structural behaviour is not observed across the series, although certain aspects of these crystal structures contribute in a general sense to our understanding of the structural properties of bis-diphenylphosphine oxides. Importantly, for the compounds with odd n, there is "frustration" with regard to the molecular conformation, as the preferred all-anti conformation of the aliphatic chain gives rise to an unfavourable parallel alignment of the two P=O dipoles within the molecule. Clearly the importance of avoiding a parallel alignment of the P=O dipoles becomes greater as n decreases. Local structural aspects (investigated by high-resolution solid-state 31P NMR spectroscopy) and thermal properties of the bis-diphenylphosphine oxide materials are also reported.
研究了一系列双二苯基氧化膦同系物（C6H5）2PO（CH2）（n）PO（C6H5）2（n = 2 - 8；记为2 - 8），以探究一系列竞争性和协同性分子间及分子内相互作用对固态结构性质的影响。影响结构性质的重要因素包括分子内方面，如脂肪链的构象以及分子中两个P=O偶极之间的分子内相互作用，还有分子间方面，如长程静电相互作用（由P=O偶极的排列主导）、C-H...O相互作用、C-H...π相互作用和π...π相互作用。化合物3和5只能以溶剂化物共晶体形式结晶（3为水合物，5为（甲苯）2合物），而所有其他化合物的晶体结构仅包含双二苯基氧化膦分子。除7（此处由粉末X射线衍射数据确定）和4（先前已知）外，晶体结构均由单晶X射线衍射数据确定。偶数n的化合物代表一个系统的结构系列，呈现出特征性的、基本为线性的P=O...P=O...P=O偶极阵列，以及C-H...O和C-H...π相互作用。另一方面，对于奇数n的化合物，尽管这些晶体结构的某些方面在总体上有助于我们理解双二苯基氧化膦的结构性质，但整个系列并未观察到一致的结构行为。重要的是，对于奇数n的化合物，在分子构象方面存在“挫折”，因为脂肪链优选的全反式构象会导致分子内两个P=O偶极产生不利的平行排列。显然，随着n减小，避免P=O偶极平行排列的重要性变得更大。还报道了双二苯基氧化膦材料的局部结构方面（通过高分辨率固态31P核磁共振光谱研究）和热性质。
