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Computationally‐Assisted Approach to the Vibrational Spectra of Molecular Crystals: Study of Hydrogen‐Bonding and Pseudo‐Polymorphism
Author(s) -
Nolasco Mariela M.,
Amado Ana M.,
RibeiroClaro Paulo J. A.
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200600308
Subject(s) - intermolecular force , chemistry , hydrogen bond , raman spectroscopy , infrared spectroscopy , ab initio , ab initio quantum chemistry methods , crystal structure , molecular vibration , crystallography , computational chemistry , molecule , polymorphism (computer science) , organic chemistry , biochemistry , physics , genotype , optics , gene
A new computationally‐assisted methodology ( PiMM ), which accounts for the effects of intermolecular interactions in the crystal, is applied to the complete assignment of the Raman and infrared vibrational spectra of room temperature forms of crystalline caffeine, theobromine, and theophylline. The vibrational shifts due to crystal packing interactions are evaluated from ab initio calculations for a set of suitable molecular pairs, using the B3LYP/6‐31G* approach.The proposed methodology provides an answer to the current demand for a reliable assignment of the vibrational spectra of these methyl‐xanthines, and clarifies several misleading assignments. The most relevant intermolecular interactions in each system and their effect on the vibrational spectra are considered and discussed. Based on these results, significant insights are obtained for the structure of caffeine in the anhydrous form (stable at room temperature), for which no X‐ray structure has been reported. A possible structure based on C (8) H⋅⋅⋅N (9) and C (1,3) H⋅⋅⋅O intermolecular interactions is suggested.