Structural, spectroscopic and theoretical studies on 3,4,7,8-tetramethyl-1,10-phenantroline complex with picric acid

• Published in: Chemical physics 2013-01, Vol.410, p.55-65
• Main Authors: Bator, G., Sobczyk, L., Sawka-Dobrowolska, W., Wuttke, J., Pawlukojć, A., Grech, E., Nowicka-Scheibe, J.
• Format: Article
• Language: English
• Subjects: 2,4,6-trinitrophenol; 3,4,7,8-tetramethyl-1,10-phenantroline; Crystal structure; DFT; Infrared spectroscopy; Molecular complex; Neutron backscattering; X-ray diffraction
• ISSN: 0301-0104
• DOI: 10.1016/j.chemphys.2012.10.012

[Display omitted] ► We synthesized a novel complex of Me4phen⋅PA. ► The complex was studied using infrared spectroscopy and inelastic neutron scattering. ► The crystal structures at 100K of pure Me4phen and Me4phen⋅PA was described. ► The molecular structure in the crystalline state was theoretically calculated. The almost planar molecular complex, formed by 3,4,7,8-tetramethyl-phenantroline (Me4phen) and picric acid (2,4,6-trinitrophenol, PA), has been investigated by using X-ray diffraction, vibrational spectroscopy, tunnel splitting and theoretical analysis. In the crystal of Me4phen·PA two short bifurcated hydrogen bonds N+–H···O− [2.6238(14)Å] and N+–H···N [2.6898(15)Å] are created. Infra-red spectra show the hydrogen bonds are short. The neutron backscattering spectrum of Me4phen⋅PA at 3K shows two tunneling peaks at ca. 1 and 3μeV. The number of the peaks is consistent with X-ray diffraction studies, which disclosed the inequivalence of methyl groups in the crystal structure. The comparison of the tunnel splitting for neat Me4phen and for its complex with picric acid indicates that in the latter case the methyl groups are more strongly engaged in the intermolecular interactions, particularly with nitro group oxygen atoms of picric acid, leading to an increase of the CH3 rotational barrier height.