SYNTHESIS AND X-RAY STRUCTURE OF N[(CH2)2O(2,6-C6H3N)O(CH2)2]3N - D3 MACROBICYCLIC LIGAND CAPPED BY 2 SP2 NITROGEN-ATOMS

In 1970 (in a preliminary form), Weiss et al.1 reported the molecular structure of the noncomplexed diazabicyclopolyether 1 (C-2.2.2) as well as of the corresponding rubidium cryptate 2 [Rb+c2.2.2]. The free ligand 1 was shown to possess the endo-endo (in-in)2 N configurations, in which the N-N distance was 6.872 (9) Å, a value slightly larger than that of 2 (6.008 Å).1 In free cryptands, it has been generally assumed that the N lone pairs are either in the in-in. in-out. or out-out configurations.3 In published structural representations of cryptands, these molecules are generally depicted in the in-in configuration for convenience in seeming correlation with the corresponding cryptates. However, a brief synopsis of cryptand literature suggests that few researchers are aware of the Weiss et al.1 paper, since ~30-40% of the structural representations of C-2.2.2 are inadvertently and/or erroneously drawn in the out-out configuration. The correctness of the generally accepted concept of describing cryptand bridging nitrogen atoms as being only in the in or out configuration is now in question, since we herein report the X-ray crystal structure of 3, in which the bridgehead nitrogen atoms possess.© 1979, American Chemical Society. All rights reserved.