HYDROGEN BONDING IN BETAINE:PHENOL COCRYSTALS. G.Buczak, A.Katrusiak, M.Szafran, Z.Dega-Szafran, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland

Formation of hydrogen bonds in cocrystals built of betaine (BET) or its pyridine derivative (PBET) with pentachloro- or dichloronitrophenols has been studied. In these cocrystals short hydrogen bonds are formed between carboxyl groups of betaine and the hydroxyl groups of the phenols, linking these molecules into aggregates at 1:1 or 1:2 stoichiometries. The position of the H-atoms in these hydrogen bonds depends primarily on the proton-donor and accetor properties of these molecules, however this study is also aimed at investigating the geometrical factors which may influence the hydrogen bond structure. The following cocrystals have been studied and their structures determined by X-ray diffraction:

(i) BET:dichloronitrophenol 1:1 cocrystal; space group P-1, R=0.0332;

(ii) PBET:dichloronitrophenol 1:1 cocrystal; space group P2(1)/c, R=0.0381;

(iii) PBET:dichloronitrophenol 1:2 cocrystal; space group P2(1)/c, R=0.0335;

(iv) PBET:pentachlorophenol 1:2 cocrystal; space group P-1, R=0.0487;

The O...O distances in the hydrogen bonds in these substances range from 2.419(3)A in (i), to 2.623(4)A in (ii). The structural data obtained for these copmpounds indicate that the geometrical and angular criteria described previously for chemically equivalent donor and acceptor groups [A.Katrusiak,J.Mol.Struct.269 (1992) 329; Phys.Rev. B48 (1993) 2992] can be also applied to the hydrogen bonds between the donor and acceptor groups which are chemically different.