Polyoxamacrobicyclic diamines. Structure of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane and of its bisborohydride, C18H36N2O6·2BH3

Abstract

The crystal structures of C₁₈H₃₆N₂O₆·2BH₃(I) and C₁₈H₃₆N₂O₆(II) have been determined from diffractometer data by direct methods and refined by least-squares to R 0.054 [(I), 877 independent observed reflections] and 0.054 [(II), 1 774 independent observed reflections] respectively. (I) Exists in the exo-exo-conformation, while (II), which forms remarkably stable complexes with various metal cations, possesses the endo-endo conformation (i.e., the lone pairs of the nitrogen atoms are both inside the molecular cavity). The values of the nonbonding N ⋯ N distance in both (I) and (II) are very close [6.76 (I), and 6.87 Å(II)]. The conformations of (I) and (II) can be related to those of bicyclic [8.8.8]hexacosanes corresponding to paths on the diamond lattice. Crystals of both compounds are monoclinic: (I), space group C2/c with a= 18.849(6), b= 9.610(4). c= 13.291(5)Å, β= 102.25(6)°. Z= 4; (II), space group P2₁/c, a= 16.832(7), b= 7.450(3), c= 16.921 (8)Å, β= 95.77(5)°, Z= 4.