Two novel violurate and squarate salts of cinchonine – Structures and physical properties B.B. Koleva a,b, * , R. Bakalska c , R.W. Seidel b , T. Kolev b , H. Mayer-Figge b , W.S. Sheldrick b , M. Spiteller a a Institut für Umweltforschung, Universität Dortmund, Otto-Hahn-Strasse 6, 44221 Dortmund, Germany b Lehrstuhl für Analytische Chemie, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany c University of Plovdiv ‘‘P. Hilendarski”, Department of Organic Chemistry, Plovdiv 4000, Bulgaria article info Article history: Received 9 September 2009 Received in revised form 13 November 2009 Accepted 13 November 2009 Available online 20 November 2009 Keywords: Cinchoninium violurate monohydrate Cinchoninium squarate tetrahydrate Crystal structures Physical properties Quantum chemical calculations abstract The correlation between the structural and the physical properties in solid state of two novel salts of cin- chonine, cinchoninium violurate monohydrate (1) and cinchoninium squarate tetrahydrate (2), has been studied in dependence on protonation mode, using the methods of single crystal X-ray diffraction, IR-LD spectroscopy of oriented samples as a suspension in nematic liquid crystals, UV–vis spectroscopy and 1 H and 13 C NMR spectroscopy. HPLC tandem mass spectrometry (HPLC ESI MS/MS) and thermal methods were also employed. Quantum chemical calculations have been performed with a view to obtaining the physical properties of the cinchoninium mono- and di-cation. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Cinchona alkaloids find a large number of applications as chi- ral auxiliaries in organic chemistry. They have been employed as chiral catalysts in asymmetric syntheses [1,2]. As chiral selectors for the preparation of new chiral stationary phases, this class of alkaloids has also been studied using computational or spectro- scopic methods [3]. These investigations were undertaken with the aim of providing contributions to help understand the mechanism of the chiral discrimination processes. However, cal- culations were carried out considering such molecules as mono- mers. Actually, auto-association phenomena are possible which, in principle, could affect the thermodynamics and kinetics of selector–selectand interactions in chiral discrimination processes [4]. A detailed nuclear magnetic resonance study in solution has been performed leading to confirmation of the presence of dimers in chloroform solution [5]. However, the self-association of these compounds in the solid state can be expected to be different and for this reason it is important to characterize their structures by single crystal X-ray diffraction. Moreover the presence of more than one basic N-atoms in the cinchonan moiety leads to obser- vation of mono- or di-protonated salts of both these compounds. Therefore we investigated the self-association of cinchonine depending on the number of protonated N-atoms in the molecule (Scheme 1) and its affect on the spectroscopic properties in the solid state and in solution. The model salts cinchoninium violu- rate (1) and cinchoninium squarate (2), were synthesized and structurally characterized by single crystal X-ray diffraction (Scheme 1). The possibilities of linear-polarized IR-spectroscopy of oriented colloids were used for the assignment of the IR-bands of the studied compounds. The self-organization of the cincho- nine ions in solution was also investigated by 1 H and 13 C NMR spectroscopy. Quantum chemical calculations were performed with a view to obtaining the electronic structure and vibrational properties of the mono- and di-protonated cinchonine cations. The protonation of the cinchonine molecule, in dependence on the properties of the acid and the molar ratio of acid and base is discussed as well. For a complete elucidation of the self-assem- bly phenomenon in the solid state a comparison of the new struc- tures with those previously reported (Table 1) for cinchonine and its different protonated salts was carried out. For first time in this paper we demonstrate the potency of the alkaloids as suitable counter ions for tuning the physical properties of organic salts in solid state. The presented results allow future investigations in this respect with a view to modelling of the optical as well as non-linear-optical properties of these salts. Moreover the chiral centre gives an opportunity for obtaining of the non-centrosym- metric crystals. 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.11.043 * Corresponding author. Address: Institut für Umweltforschung, Universität Dortmund, Otto-Hahn-Strasse 6, 44221 Dortmund, Germany. Tel.: +49 0231 755 7069. E-mail address: B.Koleva@infu.tu-dortmund.de (B.B. Koleva). Journal of Molecular Structure 965 (2010) 89–97 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc