Structure, vibrations, and hydrogen bond parameters of dibenzotetraaza[14]annulene

Searching for correlations between geometric and spectroscopic parameters of intramolecular hydrogen bonds in porphyrin-like macrocycles

Chemical bond lengths and angles are characteristic structural parameters of a molecule. Similarly, the frequencies of the vibrational modes and the NMR chemical shifts are unique "chemical fingerprints" specific to a compound. These are the basic parameters describing newly obtained compounds and enabling their identification. Intramolecular hydrogen bonding significantly influences the physicochemical properties of macrocyclic compounds with a porphyrin-like structure. This work presents the verification for correlations between geometric and spectroscopic parameters related to hydrogen bonds in this type of macrocyclic compounds. In particular, such relationships were investigated for a large group of porphyrin, porphycene, and dibenzotetraaza[14]annulene derivatives and a group of other macrocycles with similar structure. A very strong linear correlation was found only between the vibrational frequencies of the NH groups involved in a hydrogen bond and the length of this bond, which applied to all macrocyclic compounds of this type. Several other relationships were found between spectroscopic (IR, Raman, NMR) and geometric (X-ray) parameters, highlighting differences and similarities between different families of macrocycles. Apart from providing a better understanding of the nature of hydrogen bonds and their characteristics in porphyrin-like macrocyclic compounds, these relationships will facilitate the identification of new macrocycles and the extrapolation of their spectroscopic properties.

Noncovalent functionalization of graphene with a Ni(II) tetraaza[14]annulene complex

The few-layer graphene, produced by exfoliation of graphite in 4-methylanisole, was noncovalently functionalized with the Ni(ii) complex of 5,7,12,14-tetramethyldibenzo-1,4,8,11-tetraazacyclotetradeca-3,5,7,10,12,14-hexaene (Ni(ii)-tetramethyldibenzotetraaza[14]annulene, or NiTMTAA), which is a simple model of more complex porphyrins and phthalocyanines. The resulting hybrid materials with different content of NiTMTAA were characterized by means of thermogravimetric analysis, scanning and transmission electron microscopy (SEM and TEM, respectively), atomic force microscopy (AFM), energy dispersive X-ray, Fourier-transform infrared (FTIR), Raman and UV-visible spectroscopy, as well as fluorescence and conductivity measurements. Additional information on the mechanisms of NiTMTAA interaction with graphene was obtained from density functional theory (DFT) and molecular mechanics (MM) calculations. Both experimental and theoretical results suggest that NiTMTAA forms a full double-sided adsorption layer on the graphene surface. The presence of NiTMTAA molecules in the hybrid materials obtained manifests itself in the appearance of characteristic bands in all types of electromagnetic spectra recorded; in FTIR, they are relatively weak as compared to graphene absorption bands, but dominate in Raman spectra. The morphology of the nanohybrids observed by SEM, TEM and AFM, as well as their electrical conductivity, depends on the NiTMTAA content. According to the results of DFT calculations of NiTMTAA adsorption on different graphene models, flat orientation of the complex with respect to graphene is energetically preferable, with a little difference depending on whether benzo or methyl groups contact the sheet.