A theoretical investigation of SBH and a bicomplex ion, [(Fe III (SBH)2)]+is used as a basis to control and clarify previous vibrational assignments for complexes formed between iron and ligands related to SBH. Main conclusions are the following:1.Complexation shifts the vC=0 vibration by about 100 cm−1towards low wavenumbers.2.vC=N and δHC=N modes are enhanced by complexation.3.In the complex, the enhanced vC=N mode hides the amide II vibration.4.The v-O-stretching mode is expected to be near 1400 cm−1in the complex.5.Point 1 provides a criterion for carbonyl involvement in complexation. Points 2 and 4 are possible probes for hydrazide nitrogen and phenate involvement.6.Despiteab initiocalculations, the vibration at 1360 cm−1is, as previously, assigned to the amide III mode.