IR study of complex between salicylalbenzoylhydrazone (SBH) and iron III: Normal mode assignment assisted by quantum mechanical calculation.

A theoretical investigation of SBH and a bicomplex ion, [(Fe III (SBH)(2))] (+) is used as a basis to control and clarify previous vibrational assignme nts for complexes formed between iron and ligands related to SBH. Main conc lusions are the following : 1. Complexation shifts the nu C=O vibration by about 100 cm(-1) towards low wavenumbers. 2. nu C=N and delta HC=N modes are enhanced by complexation. 3. In the complex, the enhanced nu C=N mode hides the amide II vibration. 4. The nu phi-O- stretching mode is expected to be near 1400 cm(-1) in the complex. 5. Point 1 provides a criterion for carbonyl involvement in complexation. P oints 2 and 4 are possible probes for hydrazide nitrogen and phenate involv ement. 6. Despite ab initio calculations, the vibration at 1360 cm(-1) is, as prev iously, assigned to the amide III mode.