Evidence for stereoelectronic effects in the N—C—N group of 8,10,12-triaza-1-azoniatetracyclo[8.3.1.18,12.02,7]pentadecane 4-nitrophenolate 4-nitrophenol monosolvate from the protonation of aminal (2R,7R)-1,8,10,12-tetraazatetracyclo[8.3.1.18,12.02,7]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 anR44(24) ring motif. These units are linkedviaC—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.