ESR Spectra of Fe-NO Complexes with Some Organic Ligands

E SR has been used in the study of iron(I)-nitrosyl complexes w ith organic ligands in solution. Four types of complexes have been identified on basis of the ESR param eters, namely Fe (NO) L 5, Fe (NO) L 2, Fe (NO)2L 2, and Fe (NO)2L. In the iron-nitrosyl complexes with the organic ligands used, the groups more often involved in the coordination are: —C —N H 2; —C —N H ; — C = 0 ; and —C = S (eventually in the tautom eric forms). Urea and derivatives, either in w ater or in ethanol solutions, seem to give rise only to Fe (NO)2L 2 type complexes. Similar results were obtained w ith phenylamino-derivatives and hetero­ cycles. Equilibria between different types of complexes — F e(N O )L 2 and Fe(NO )2L — were established w ith hydrazides and substitu ted hydrazides.