Homodinuclear Iron Thiolate Nitrosyl Compounds [(ON)Fe(S,S-C₆H₄)₂Fe(NO)₂]^- and [(ON)Fe(SO₂,S-C₆H₄)(S,S-C₆H₄)Fe(NO)₂]^- with {Fe(NO)}⁷−{Fe(NO)₂}⁹ Electronic Coupling: New Members of a Class of Dinitrosyl Iron Complexes

Reaction of Fe(CO)2(NO)2 and [(ON)Fe(S,S-C6H3R)2]- (R = H (1), CH3 (1-Me))/[(ON)Fe(SO2,S-C6H4)(S,S-C6H4)]- (4) in THF afforded the diiron thiolate/sulfinate nitrosyl complexes [(ON)Fe(S,S-C6H3R)2Fe(NO)2]- (R = H (2), CH3 (2-Me)) and [(ON)Fe(S,SO2-C6H4)(S,S-C6H4)Fe(NO)2]- (3), respectively. The average N−O bond lengths ([Fe(NO)2] unit) of 1.167(3) and 1.162(4) Å in complexes 2 and 3 are consistent with the average N−O bond length of 1.165 Å observed in the other structurally characterized dinitrosyl iron complexes with an {Fe(NO)2}9 core. The lower ν(15NO) value (1682 cm-1 (KBr)) of the [(15NO)FeS4] fragment of [(15NO)Fe(S,S-C6H3CH3)2Fe(NO)2]- (2-Me-15N), compared to that of [(15NO)Fe(S,S-C6H3CH3)2]- (1-Me-15N) (1727 cm-1 (KBr)), implicates the electron transfer from {Fe(NO)2}10 Fe(CO)2(NO)2 to complex 1-Me/1 may occur in the process of formation of complex 2-Me/2. Then, the electronic structures of the [(NO)FeS4] and [S2Fe(NO)2] cores of complexes 2, 2-Me, and 3 were best assigned according to the Feltham−Enemark notation as the {Fe(NO)}7−{Fe(NO)2}9 coupling (antiferromagnetic interaction with a J value of −182 cm-1 for complex 2) to account for the absence of paramagnetism (SQUID) and the EPR signal. On the basis of Fe−N(O) and N−O bond distances, the dinitrosyliron {L2Fe(NO)2} derivatives having an Fe−N(O) distance of ∼1.670 Å and a N−O distance of ∼1.165 Å are best assigned as {Fe(NO)2}9 electronic structures, whereas the Fe−N(O) distance of ∼1.650 Å and N−O distance of ∼1.190 Å probably imply an {Fe(NO)2}10 electronic structure.