Structural investigations of phosphorus-nitrogen compounds. 6. Relationships between molecular parameters in per-X-substituted bridged spermine derivatives and basicity constants ??R of substituents

Coles, S.J., Davies, D.B., Hursthouse, M.B., Kilic, A., Mayer, T.A., Shaw, R.A. and Ciftci, G.Y. (2004) Structural investigations of phosphorus-nitrogen compounds. 6. Relationships between molecular parameters in per-X-substituted bridged spermine derivatives and basicity constants ??R of substituents. Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 60 (6), 739-747. (doi:10.1107/S0108768104025947).

Abstract

A systematic study is reported of the products of the nucleophilic substitution reactions of the spermine-bridged cyclotriphosphazene, [N₃P₃X₄(NHCH₂CH₂CH₂N)CH₂CH₂]₂ [where X = Cl (2a)], to give a number of new structures [(2b)-(2g)] in which X = OPh, [spiro-O(CH₂)₃O]_0.5, Ph, NHPh, NC₄H₈ and NHBu^t, respectively. A comparison has been made between the sum of the substituent basicity constants, Σα_R, obtained in nitrobenzene solution, and ten molecular parameters of the N₃P₃ ring (the internal bond angles α, β, γ, δ and θ, and the P-N bond lengths a, b, c, d and e) as well as the difference between the bond lengths a and b, Δ(P-N). It is found that the systematic change in molecular parameters of compounds (2a)-(2g) is in line with changes in α_R values, indicating the similarity in relative electron-releasing capacity of substituents X in the solid state and in solution. It is also found that the effect on molecular parameters of (2a)-(2g) with two X substituents in PX₂ groups is greater than that for one X substituent in P(OR)X groups in an analogous series of compounds observed previously [Besli et al. (2002). Acta Cryst. B58, 1067-1073].

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Contributors

Author: S.J. Coles

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