A study of the pyramidality index in tris(2,4,6-triisopropylphenyl)phosphonium perchlorate

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Boeré, René T.
Zhang, Yuankui
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International Union of Crystallography
The title compound, C45H70P+ ClO4 or [Tripp3PH+][ClO4 ], was produced from the perchlorate salt of the corresponding radical cation Tripp3P + through very slow H-atom abstraction reactions in a solution of 1,2-dimethoxyethane (Tripp is 2,4,6- triisopropylphenyl). The H atom on the P atom was located in a difference map and was freely refined with an isotropic displacement consistent with full occupancy [P—H = 1.37 (3) A ° ]. It is the most sterically congested triarylphosphonium salt yet to be reported and has a ‘propeller’ arrangement of the three Tripp groups around the P atom, with the protonation site located along the molecular threefold axis. There are short contacts between the flanking isopropyl methine H atoms and the P atom [P H = 1.99 (2)– 2.17 (2) A ° ]. The sum of the angles around the P atom [ (C—P—C) = 349.9 (6) ] is a convenient index of pyramidality for tricoordinate centres. This value is significantly larger than in analogous Mes3PH+ salts (Mes is mesityl or 2,4,6- trimethylphenyl), for which the average of the three reported structures in the literature is (C—P—C) = 345.3 (6) . For comparison, in the ubiquitous Ph3PH+ salts, this parameter has a typical average value of only 333.3 (9) . The value of (C— P—C) in the title compound is midway between that of the neutral phosphane Tripp3P [334.4 (6) ] and the phosphoniumyl radical cation Tripp3P + [359.8 (2) ]. This geometrical feature provides additional support for the assignment as a phosphonium salt.
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Crystal structure , Triarylphosphonium ions , Pyramidality index , Phosphoniumyl radical cations
Boere, R. T., & Zhang, Y. (2013). A study of the pyramidality index in tris(2,4,6-triisopropylphenyl)phosphonium perchlorate. Acta Crystallographical Section C, Crystal Structure Communications, C69, 1051-1054. doi:10.1107/S0108270113020647