Metal Isotope Effects on the Vibrational Spectra of [Bis(glycylglycinato)calcium Chloride]_n

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The infrared and Raman spectra of [bis(glycylglycinato)calcium chloride]_n and its isotopic complexes containing metal and hydrogen isotopes have been measured. A large isotope shift of more than 4 cm^-1 on ⁴⁰Ca and ⁴⁴Ca substitution has been observed in the infrared-active bands at 345, 267 and 242 cm^-1. These bands have been assigned to Ca-O antisymmetric stretching vibrations. The Raman-active bands at 305, 158 and 111 cm^-1 have been assigned to Ca-O symmetric stretching vibrations with no displacement of the calcium atom. The result of a normal coordinate analysis is consistent with both the empirical assignments and the experimental isotope shifts. These results indicate that Ca-ligand bond forces are almost similar to those of copper- and zinc-amino acid complexes.