Effect of the nature of mendiaxon  –X þ interactions (X þ ¼ Na þ , Cu þ ,H þ ) and the hydrogen bonding on the m(C@O) behavior: theoretical and spectroscopic study q Ivelina Georgieva a , Tzvetan Mihaylov a ,G€ unther Bauer b , Natasha Trendafilova a, * a Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria b Institute of Chemical Technologies and Analytics, Technical University of Vienna, Vienna A-1060, Austria Received 5 November 2003; accepted 14 January 2004 Abstract Theoretical and spectroscopic (IR and Raman) study of different 7-hydroxy-4-methylcoumarin (mendiaxon) systems (mend  , mendNa, mendCu, mendH and mendH  2H 2 O) were performed at B3LYP/6-31G(d) and B3LYP/6-31++G(d,p) levels of theory. The geometric and electronic structures as well as the vibrational behavior of the systems studied were discussed: (1) as to the changes that occurred in the anion coumarin ring upon the mend  –X þ (X þ ¼ Na þ , Cu þ ,H þ ) interactions and (2) as to the changes that occurred in mendH due to hydrogen bondings in mendH  2H 2 O. The largest bond length changes in the anion coumarin ring were obtained for mendH and the smallest ones for mendNa. The bond length changes were mainly produced from the electrostatic effect of the positive charge of X. The induced polarization of the C@O bond upon the mend  –X þ interactions was found to be opposite to the basic one and it led to shorter C@O bond lengths (higher m(C@O) frequencies) in the order: mendNa, mendCu and mendH. Conversely, upon the hydrogen bonding the induced polarization of the C@O bond was found in the same direction as the basic one and it produced elongation to the C@O bond length (lower m(C@O) frequency). On the basis of the correlations found, the m(C@O) positions in mendNa, mendCu, mendH and mendH  2H 2 O were explained. Ó 2004 Elsevier B.V. All rights reserved. Keywords: 7-Hydroxy-4-methylcoumarin (mendiaxon); DFT study; Hydrogen bondings; Vibrational spectra; Transition metal complexes 1. Introduction Coumarin derivatives were extensively investigated due to their remarkable properties. 7-Hydroxycouma- rins exhibit strong fluorescence in the VIS region, which makes them suitable for use as colorants, dye laser media and as non-linear optical chromophores [1,2]. The electronic structure of hydroxycoumarins, including their UV light absorption ability, has become a subject of many investigations [3–10]. At the same time, cou- marin derivatives have shown distinct biological activ- ity. They have been described as enzyme inhibitors or as agents with anticoagulant [11–14], spasmolytic [15–18] and anticancer activity [19–22]. Coumarin derivatives are known to have good complexing ability as well. It was found that in some cases the metal complexes ob- tained revealed higher biological activity than their li- gands. The cytotoxic profile of some complexes of coumarin derivatives (mendiaxon, warfarin, acenocou- marol and coumachlor) with lanthanides against P3HR1, K-562 and THP-1 cell lines has recently been proved [23,24]. Novel mendiaxon sodium salt complexes with transition metals were investigated as to their ap- plication as anticoagulants and spasmolytical agents [25]. It was suggested that mendiaxon acts as a bidentate ligand, which coordinates to the metal ions by both deprotonated hydroxyl and carbonyl oxygens and forms chelate complexes of the general formula ML 2  nH 2 O (M ¼ Cu(II), Zn(II), Ni(II), Co(II), L ¼ mend  ) [25]. However, the M(II) complexes and the mendiaxon q Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.chemphys.2004.01.012. * Corresponding author. Tel.: +359-2-9792592; fax: +359-2-8- 705024. E-mail address: ntrend@svr.igic.bas.bg (N. Trendafilova). 0301-0104/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2004.01.012 Chemical Physics 300 (2004) 119–131 www.elsevier.com/locate/chemphys