Effect of protonation on the structure of 1,3,6,8-tetraazatricyclo[4.4.1.13,8] dodecane (TATD) adamanzane: Crystal structure and DFT analysis of 3,6,8-triaza-1-azoniatricyclo[4.4.1.13,8]dodecane 4-nitrophenolate 4-nitrophenol

Abstract

The reaction between 1,3,6,8-tetraazatricyclo[4.4.1.1^3,8]dodecane (TATD) and 4-nitrophenol (4-NP) under solvent-free conditions results in the formation of a proton transfer (PT) complex, (TATD)⁺(4-NP)⁻·4-NP, (3). This is the first crystal structure of a PT complex of TATD, whose structure is stabilized by N⁺–H⋯O and O⁻⋯H–O hydrogen bonds. The characterization was performed using FTIR and ¹H NMR spectroscopy, and X-ray crystallography. From X-ray diffraction data collected at 173(2) K, it is concluded that it crystallizes in the monoclinic system (C2/c space group) containing one 4-nitrophenolate anion and one neutral 4-nitrophenol molecule. The stoichiometry of the proton transfer species in DMSO-d₆ solution is in agreement with the structural data. A combined theoretical and experimental correlation of the structural parameters of free and protonated TATD are in good agreement. The discrepancies in the C–C bond distances between the experimental and calculated results can be attributed to hyper-conjugative interactions and electron delocalization.