Structural investigations of phosphorus–nitrogen compounds. 6. Relationships between molecular parameters in per-X-substituted bridged spermine derivatives and basicity constants ΣαR of substituents
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 NHBut, respectively. A comparison has been made between the sum of the substituent basicity constants, ΣαR, obtained in nitrobenzene solution, and ten molecular parameters of the N3P3 ring (the internal bond angles α, , , and , 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 αR 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 [Beşli et al. (2002). Acta Cryst. B58, 1067–1073].