A model for vitamin B6--amino-acid-related metal complexes. Neutron diffraction study of aqua(N-salicylideneglycinato)copper(II) hemihydrate at 130 K.

A neutron diffraction study of aqua(N-salicylideneglycinato)copper(II) hemihydrate, [Cu(C9H7NO3)-(H2O)].0.5H2O, Mr = 267.7, a model for vitamin B6-amino-acid-related metal complexes, has been carried out at 130 K. Least-squares refinement based on 3800 reflections [(sin theta/lambda)max = 0.786 A-1] converged at R(F2) = 4.5%. The crystal is monoclinic, space group C2/c, Z = 8 with cell parameters at 130 K: a = 17.030 (3), b = 6.665 (1), c = 17.469 (5) A, beta = 111.13 (1) degree, V = 1849.50 A3. The bond distances between non-H atoms have been determined with estimated standard deviations in the range 0.0008-0.0012 A; the corresponding values for distances involving H atoms are 0.0017-0.0020 A. The presence of a Cu11 ion does not significantly change the bond distances around the alpha-C atom from those observed in glycine or glycylglycine. There are, however, indications of differences in distance and direction relative to the pi system for the two alpha-C-H bonds. These bond vectors are inclined at angles of 30 and 71 degrees to the plane of the conjugated pi system. A planar conjugated pi-system is stabilized by chelation to the Cu ion.