Understanding the Structural Properties of a Homologous Series of Bis-diphenylphosphine Oxides

Abstract

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.

The solid-state, solution and gas–phase interactions of diphosphane monooxide spacers with heavier group 8,9 transition metals and gallium in novel organometallic assemblies: An experimental and computational study

“…The OseOs bond lengths in 1 and 2 fall in the range from 2.847(2) to 2.9255(2) Å and the Os(1)eP(1) bond lengths are equal to 2.352(5) and 2.361(6) Å, respectively. As a result, the observed values of the bond lengths are comparable to those in other previously reported [Os 3 (CO) 11 (2) Å in 2, are similar to those found in free phosphane oxides [27,28]. In addition, 1 and 2 comprise coordination sites at the O(12) atom of the DPMO that are accessible for further electrophilic attack of a Lewis acid.…”

Contemporary Advances in the Use of Powder X-Ray Diffraction for Structure Determination

“…The structure determination of Ph 2 P(O)(CH 2 ) 7 P(O)Ph 2 ,57 which is described in detail in Section 3.3, was also part of a wider crystal‐engineering study58 of materials in the family Ph 2 P(O)(CH 2 ) n P(O)Ph 2 . The structure solution of the unsolvated crystal form of Ph 2 P(O)(CH 2 ) 5 P(O)Ph 2 has also been tackled recently from powder diffraction data 59…”

Room-temperature electrophosphorescence from an all-organic material

“…This has been observed in phosphine oxides, which can form extended structures through strong P-O and H-C interactions. [24] Burrows et al [22] observed a similar phenomenon and attributed these shifts to aggregation rather than the formation of excimers, as no change was observed in either the UV-visible absorption or the excitation scan for corresponding emissions.…”