Three Redox States of Metallonitrosyls in Aqueous Solutions

BARI, SARA ELIZABETH; OLABE, JOSÉ A.; SLEP, LEONARDO D.

Advances in Inorganic Chemistry

Elsevier

Año: 2015; p. 87 - 144

This contribution deals with the structure and reactivity of bound nitrosyl in transitionmetalcenters (group8: Fe, Ru, Os). The focus is set onpseudooctahedralnitrosyl-complexes with coordination number 5 and 6, containing ancillary coligands of both heme- and nonhemetype. The discussion is organized in terms of Enemark and Feltham´s classification,selecting complexes within the {MNO}n framework (n¼6, 7, and 8). The examples havebeen chosen for a best description of the electronic structures in terms of modern structural,spectroscopical, and computational methodologies. The selected {MNO}6,7,8 speciesreflect the occurrence of three redox states of bound nitrosyl, frequently (though notalways) described as NO+, NO, and NO for n¼6, 7, and 8, respectively. The analysis is centeredon the members of a series of complexes for which the three redox states have beenobserved on the same platform, viz., [Fe(CN)5(NO)]2,3,4 and [Ru(Me3[9]aneN3)(bpy)(NO)]3,2,1+, in aqueous solutions. The influence of the donor?acceptor character of the coligandsis specifically addressed withemphasis on the ligand trans- to nitrosyl, showing thatthe latter group may exert a delabilizing influence (as NO+), as well as a labilizing one(NONO) on the trans-ligand.Onthe other hand, typical electrophilic reactivity patterns(toward different nucleophiles) are analyzed for M?NO+, and nucleophilic reactivity (withO2) is described for the reduced species, M?NO and M?(NO). In the latter case, protonationis described by characterizing the bound HNO species. Important differences arehighlighted in the chemistry of boundNO andHNO, revealing the strong and mild reductantabilities of these species, respectively. The chemistry is analyzed in terms of the biologicalrelevance to the behavior of nitrite- and NO-reductases and other NO-relatedenzymes.