PNAS 2002-04-16

Self-assembly directed by NH...O hydrogen bonding: new layered molecular arrays derived from 4-tert- butylbenzoic acid and aliphatic diamines.

Robert S Armstrong, Ian M Atkinson, Elizabeth Carter, Myrna S Mahinay, Brian W Skelton, Peter Turner, Gang Wei, Allan H White, Leonard F Lindoy

Index: Proc. Natl. Acad. Sci. U. S. A. 99(8) , 4987-92, (2002)

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Abstract

(1H) and (13)C NMR titrations in both CDCl(3) and CD(3)OD demonstrate that 4-tert-butylbenzoic acid interacts with both propane-1,2-diamine and propane-1,3-diamine to yield 1:2 host-guest complexes in these solvents. Based on this observation, the isolation of new three-dimensional molecular arrays through cocrystallization of the above diamines and 4-tert-butylbenzoic acid (in a 1:2 molar ratio) has been achieved. X-ray studies of these self-assembled structures show that they incorporate [propane-1,2-diamine x (4-tert-butylbenzoic acid)(2)] or [propane-1,3-diamine x (4-tert-butylbenzoic acid)(2)] hydrogen-bonded motifs. Three structural derivatives of the latter type (two monohydrate forms and one anhydrous form) have been characterized. The structures are compared with a previously described three-dimensional array based on the "parent" [ethane-1,2-diamine x (benzoic acid)(2)] motif. Similarities occur between each of the structures. In each, a two-dimensional "ionic" layer consisting of an extensive network of hydrogen bonds is sandwiched between two "less polar" aromatic ring-containing layers. In the respective ionic layers, the carboxylic acid protons have been transferred onto the amines to yield diammonium cations, with all ammonium protons being involved in hydrogen bonding. In part, the adoption of these unusual layered structures seems to reflect a tendency toward maximization of both the number and strengths of the hydrogen bond interactions in the respective ionic layers.