Structural investigations of phosphorus-nitrogen compounds. 6. Relationships between molecular parameters in per-X-substituted bridged spermine derivatives and basicity constants SigmaalphaR 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, Sigmaalpha(R), obtained in nitrobenzene solution, and ten molecular parameters of the N3P3 ring (the internal bond angles alpha, beta, gamma, delta and theta;, and the P-N bond lengths a, b, c, d and e) as well as the difference between the bond lengths a and b, Delta(P-N). It is found that the systematic change in molecular parameters of compounds (2a)-(2g) is in line with changes in alphaR 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].