Evidence for stereoelectronic effects in the N—C—N group of 8,10,12-triaza-1-azoniatetracyclo[8.3.1.1^8,12.0^2,7]pentadecane 4-nitrophenolate 4-nitrophenol monosolvate from the protonation of aminal (2R,7R)-1,8,10,12-tetraazatetracyclo[8.3.1.1^8,12.0^2,7]pentadecane: X-ray and natural bond orbital analysis

Abstract

The title molecular salt, C11H21N4(+)·C6H4NO3(-)·C6H5NO3, (II), crystallizes with two independent three-component aggregates in the asymmetric unit. In the cations, the cyclohexane rings fused to the cage azaadamantane systems both adopt a chair conformation. In the crystal structure, the aggregates are connected by C-H···O hydrogen bonds, forming a supramolecular unit enclosing an R4(4)(24) ring motif. These units are linked via C-H···O and C-H···N hydrogen bonds, forming a three-dimensional network. Even hydrogen-bond formation to one of the N atoms is enough to induce structural stereoelectronic effects in the normal donor→acceptor direction. The C-N bond distances provide structural evidence for a strong anomeric effect. The structure also displays O-H···O and N-H···O hydrogen bonding. Geometric optimization and natural bond orbital (NBO) analysis of (II) were undertaken by utilizing DFT/B3LYP with the 6-31+G(d,p) basis set. NBO second-order perturbation theory calculations indicate donor-acceptor interactions between nitrogen lone pairs and the antibonding orbital of the C-C and C-N bonds for the protonated polyamine, in agreement with the occurrence of bond-length and bond-angle changes within the aminal cage structure.