Molecular and electronic structures of new iron complexes containing N,S-coordinated o-iminothionebenzosemiquinonate(1-) π radical ligands: An experimental and density functional theoretical study

Two new o-aminothiophenol type ligands have been synthesized, namely 1,3-propanediamine-N,N′-bis(benzenethiol), H 4 ( 1 L), and 1,2-bis(2-mercapto-3,5-di- tert -butylaniline)ethane, H 4 ( 2 L). The reactions of these ligands with FeBr 2 in dry acetonitrile in the presence and absence of air (and other oxidants such as iodine) afforded seven new complexes which were characterized by single-crystal X-ray crystallography and Mossbauer spectroscopy (as well as EPR- and UV–Vis spectroscopies). Their magnetochemistry has been studied and their electronic structures have been established and verified by broken symmetry (BS) density functional theoretical (DFT) calculations using the B3LYP functional. The ligands are redox-active and the o-iminothiophenolate(2-)-o-iminothiobenzosemiquinonate(1-) oxidation levels are chemically readily accessible. The complexes characterized comprise the dimers [Fe III ( 1 L )] 2 ( S T  = 0) ( 1 ); [Fe III ( 2 L )] 2 ( S T  = 0) ( 2 ), and the mononuclear, five coordinate species: [Fe III ( 1 L )I] ( S T  =  1 / 2 ) ( 3 ); [Fe III ( 2 L )I] ( S T  =  1 / 2 ) ( 4 ); [Fe II ( 1 L ){P(CH 3 ) 3 }] ( S T  = 0) ( 5 ); [Fe II ( 2 L ){P(C 6 H 5 ) 3 }] ( S T  = 0) ( 6 ), and [Fe III ( 2 L gma )( t py)] ( S T  = 1) ( 7 ). ( tBu py) represents 4- tert -butylpyridine and ( 2 L gma ) 3− is the π radical trianion of the one-electron reduced ( 2 L gma ) 2− which in turn is the oxidized form of ( 2 L) 4− (−4H + , −2e).