Geometric conditions for the formation of short intramolecular hydrogen bonds in dicarboxylic acids and their acid salts. Crystal structures of two cyclopropane derivatives containing such bonds: ammonium hydrogen caronate and potassium hydrogen caronate hydrate

Abstract

Abstract (I) Ammonium hydrogen 3,3-dimethyl-cis-1,2-cyclopropanedicarboxylate (NH4H caronate), C7H13NO4, Mr = 175.2, orthorhombic Pbca, a = 6.530(1) Å, b = 18.366(5) Å, c = 14.956(2) Å, V = 1793.7(6) Å3, Z = 8, Dx = 1.290 g/cm3, μ = 0.10 mm−1, F(000) = 752, wR = 0.041, R = 0.062 for 723 observed reflections [I > 2σ(I)]. (II) Potassium hydrogen 3,3-dimethyl-cis-1,2-cyclopropanedicarboxylate (KH caronate) monohydrate, C7H9KO4 · H2O, Mr = 214.3, triclinic P[unk], a = 6.156(2) Å, b = 9.276(3) Å, c = 9.619(3) Å, α = 97.47(1)°, β = 107.94(2)°, γ = 107.29(1)°, V = 483.9(3) Å3, Z = 2, Dx = 1.469 g/cm3, μ = 0.53 mm−1, F(000) = 220, wR = 0.037, R = 0.044 for 1904 observed reflections [I > 2σ(I)]. Both compounds show short intramolecular hydrogen bonds with O…O distances of 2.477(5) Å in (I) and 2.425(3) Å in (II). The present structures complement a series of comparable chelate systems. The different geometries in these chelates influence the hydrogen bond lengths (O…O) and produce distortions of the anions to different extents. These considerations, which make the tendency to form intramolecular hydrogen bonds (instead of intermolecular ones) plausible, are in accordance with predictions of the formation of intramolecular hydrogen bonds in aqueous solution by interpretation of the ratio between first and second dissociation constants of the respective dibasic acids.