Three-dimensional hydrogen-bonded structures in the guanidinium salts of the monocyclic dicarboxylic acids rac -trans -cyclohexane-1,2-dicarboxylic acid (2:1, anhydrous), isophthalic acid (1:1, monohydrate) and terephthalic acid (2:1, trihydrate)
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The structures of bis(guanidinium) rac-trans-cyclohexane-1,2-dicarboxylate, 2CH6N3+烸H10O42-, (I), guanidinium 3-carboxybenzoate monohydrate, CH6N3+烸H5O4-爲O, (II), and bis(guanidinium) benzene-1,4-dicarboxylate trihydrate, 2CH6N3+烸H4O42-糈2O, (III), all reveal three-dimensional hydrogen-bonded framework structures. In anhydrous (I), both guanidinium cations form classic cyclic R22(8) N-H...O,O'carboxylate and asymmetric cyclic R21(6) hydrogen-bonding interactions, while one cation forms an unusual enlarged cyclic interaction with O-atom acceptors of separate ortho-related carboxylate groups [graph set R22(11)]. Cations and anions also associate across inversion centres, giving cyclic R42(8) motifs. In the 1:1 guanidinium salt, (II), the cation forms two separate cyclic R21(6) interactions, one with a carboxyl O-atom acceptor and the other with the solvent water molecule. The structure is unusual in that both carboxyl groups form short interanion O...H...O contacts, one across a crystallographic inversion centre [O...O = 2.483 (2) ŝ and the other about a twofold axis of rotation [O...O = 2.462 (2) ŝ, representing shared sites on these elements for the single acid H atom. The water molecule links the cation-anion ribbon structures into a three-dimensional framework. In (III), the repeating molecular unit comprises a benzene-1,4-dicarboxylate dianion which lies across a crystallographic inversion centre, two guanidinium cations and two solvent water molecules (each set related by twofold rotational symmetry), and a single water molecule which lies on a twofold axis. Each guanidinium cation forms three types of cyclic interaction with the dianions: one R21(6), the others R32(8) and R33(10) (both of these involving the water molecules), giving a three-dimensional structure through bridges down the b-cell direction. The water molecule at the general site also forms an unusual cyclic R22(4) homodimeric association across an inversion centre [O...O = 2.875 (2) ŝ. The work described here provides further examples of the common cyclic guanidinium-carboxylate hydrogen-bonding associations, as well as featuring other less common cyclic motifs.
Acta Crystallographica. Section C: Crystal Structure Communications
Copyright 2010 International Union of Crystallography. Published by Blackwell Publishing Ltd. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal's website for access to the definitive, published version.
Physical Chemistry not elsewhere classified