Hydrogen bond studies. 85. A very short, asymmetrical, intramolecular hydrogen bond: A neutron diffraction study of pyridinehyphen;2,3hyphen;dicarboxylic acid (C7H5NO4)

摘要

A neutron diffraction study of pyridinehyphen;2,3hyphen;dicarboxylic acid (quinolinic acid) has been carried out. The intensities for 3780 reflexions were measured at the Brookhaven High Flux Beam Reactor. The structure was refined to anR(F2) of 0.054 using starting parameters from a previous xhyphen;ray study. The short intramolecular hydrogen bond O middot;middot;middot; O: 2.398(3) Aring; has no symmetry restriction operating on the hydrogen atom position and is asymmetric. The two O middot;middot;middot; H distances are 1.163(5) and 1.238(5) Aring;, respectively, and the Osngbnd;Hsngbnd;O angle is 174.4(4)deg;. The asymmetry of the bond can be explained by the intramolecular environment. The strain in the molecule caused by the short hydrogen bond results in long carbonhyphen;carbon bonds to the carboxyl groups 1.516(2) and 1.541(2) Aring;. The Csngbnd;O bond lengths 1.219(3), 1.263(2), 1.222(3), and 1.270(2) Aring; vary depending on the hydrogenhyphen;bond involvement of the oxygen atoms. The mean Csngbnd;H distance is 1.087 Aring; and the Nsngbnd;H distance is 1.036(4) Aring;. The nitrogen atom is involved in an intermolecular Nsngbnd;H middot;middot;middot; O hydrogen bond N middot;middot;middot; O: 2.725(2), H middot;middot;middot; O: 1.845(4) Aring; and angle Nsngbnd;H middot;middot;middot; O: 140.5(2)deg;. There are a number of short intermolecular O middot;middot;middot; Hsngbnd;C contacts. The refined neutron scattering length for the nitrogen atom isbmacr;Nequals;0.925(4)times;10minus;12cm.