title: AAAA-DDDD quadruple hydrogen-bond arrays featuring NH···N and CH···N hydrogen bonds.
abstract: The X-ray crystal structure of a previously reported extremely strong quadruple NH···N AAAA-DDDD hydrogen-bond array [5·4] (K(a) = 1.5 × 10(6) M(-1) in CH3CN; K(a) > 3 × 10(12) M(-1) in CH2Cl2) features four short linear hydrogen bonds. Changing the two benzimidazole groups of the DDDD unit to triazole groups replaces two of the NH···N hydrogen bonds with CH···N interactions (complex [5·6]), but only reduces the association constant in CH3CN by 2 orders of magnitude (K(a) = 2.6 × 10(4) M(-1) in CH3CN; K(a) > 1 × 10(7) M(-1) in CH2Cl2). Related complexes without the triazole groups range in K(a) from 18 to 270 M(-1) in CH3CN, suggesting that the CH···N interactions can be considered part of a strong AAAA-DDDD quadruple hydrogen-bonding array. The NH···N/CH···N AAAA-DDDD motif can be repeatedly switched "on" and "off" in CDCl3 through successive additions of acid and base.
authors.affiliation: School of Chemistry, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh EH9 3JJ, UK. david.leigh@manchester.ac.uk
authors.forename: David A
authors.initials: DA
authors.lastname: Leigh
authors.forename: Craig C
authors.initials: CC
authors.lastname: Robertson
authors.forename: Alexandra M Z
authors.initials: AM
authors.lastname: Slawin
authors.forename: Patrick I T
authors.initials: PI
authors.lastname: Thomson
mesh_terms: D001562:Benzimidazoles / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D014230:Triazoles / Q000737:chemistry*
chemical_list: D001562:Benzimidazoles; D014230:Triazoles