COMPLEXATION OF GLYCYLGLYCINE BY THE METHYLMERCURY CATION - A VIBRATIONAL SPECTROSCOPY AND X-RAY-DIFFRACTION STUDY

Two different crystalline complexes have been obtained from aqueous mixtures of glycylglycine (GlyGly) and methylmercury(II), and they were studied by vibrational spectroscopy and X-ray diffraction. In the first compound, a hydrogen atom of the protonated amino group of GlyGly is substituted by the CH3Hg+ cation, giving (CH3Hg)GlyGly: orthorhombic, Pna21, a = 7.920(6) .ANG., b = 13.473(5) .ANG., c = 8.059(3) .ANG., and Z = 4. Further complexation on the carboxylate group yielded the complex [(CH3Hg)2GlyGly]ClO4:monoclinic, P21/c, a = 6.407(4) .ANG., b = 24.439(6) .ANG., c = 8.461(2) .ANG., .beta. = 93.82(4).degree., and Z = 4. The sites of complexation and the conformations of these solid complexes are well reflected in their vibrational spectra. Raman spectra indicate that complexation in aqueous solutions is limited to substitution on the -NH3+ group of GlyGly.