Vibrational spectra of complexes of cyclic imines with zinc(II) and cadmium(II)

Conclusions

• 1. The IR and Raman spectra of 13 complexes of ethylenimine, trimethylenlmine, pyrrolidine, and piperidine with salts of Zn(II) and Cd(II) were investigated in the region of 4000-60 cm⁻¹. An assignment of the vibrations of the coordinated ligands (symmetry C_s) was proposed.

• 2. With increasing size of the coordinated ring, the frequency of the valence vibration^vNH drops, which is explained by a decrease in the s-character of the orbital participating in the formation of the N-H bond.

• 3. In complexes with composition 3∶1, the third ligand molecule evidently exists on account of a hydrogen bond with the other two coordinated molecules.

• 4. On the basis of data on the longwave spectra, hypotheses were advanced on the structure of the investigated complexes, and the values of the metal-ligand force constants were found.

• 5. The frequencies of the metal-nitrogen valence vibrations in complexes of piperidine are substantially higher than those in complexes of the remaining imines.