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

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)(-)center dot 4-NP, (3). This is the first crystal structure of a PT complex of TATD, whose structure is stabilized by N+-Hai center dot center dot center dot O and O-center dot center dot center dot H-O hydrogen bonds. The characterization was performed using FTIR and H-1 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-d(6) 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.