Structure of 3-methyl-1,2,3,4,5,6-hexahydro-1,6-methano-3-benzazocinium hydrogen oxalate.

C13H18N+.C2HO4-, Mr = 277.3, orthorhombic, P2(1)2(1)2(1), a = 5.752 (1), b = 15.502 (2), c = 15.910 (2) A, V = 1418.6 (6) A3, Z = 4, Dx = 1.298 g cm-3, Mo K alpha (lambda = 0.71069 A), mu = 1.01 cm-1, F(000) = 592, T = 295 K. Final R = 0.035, wR = 0.042 for 1003 reflections with I greater than 3 sigma(I). The compound is an ammonium hydrogen oxalate. Both O atoms of the ionized carboxyl group act as acceptors in the formation of two hydrogen bonds: (a) an N--H...O bond linking the cation and anion with N...O and H...O distances of 2.722 (4) and 1.78 (5) A and (b) a strong O--H...O bond linking a chain of oxalate ions along a with O...O and H...O distances of 2.578 (4) and 1.59 (6) A. The relative stereochemistry of the heterocyclic and aromatic rings in the cation is similar to that in morphine.