Electronic structures of the electron transfer series [M(bpy) _3] ~n, [M(tpy) _2] ~n, and [Fe(~tbpy) _3] ~n (M = Fe, Ru; N = 3+, 2+, 1+, 0, 1-): A m?ssbauer spectroscopic and DFT study (Conference Paper)

摘要

The five-membered electron-transfer series [M(bpy) _3] ~n and [M(tpy) _2] ~n (M = Fe, Ru; bpy = 2,2'-bipyridine, tpy = 2,2':6',2″-terpyridine) and [Fe(~tbpy) _3] ~n (tbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; n = 3+, 2+, 1+, 0, 1-) have been investigated and the electronic structure of the so called "low-valent" complexes (n = 1+, 0, 1-) have been established by a combination of electro- and magnetochemistry, electron paramagnetic resonance (EPR) and M?ssbauer spectroscopy, X-ray crystallography, and DFT calculations. These complexes are accessed by reduction of the d ~6 S = 0 dicationic starting materials [M(bpy) _3] ~(2+) and [M(tpy) _2] ~(2+) (M = Fe, Ru) and [Fe(~tbpy) _3] ~(2+). The monocations [M(bpy ~·)(bpy ~0) _2] ~(1+) (S = 1/2) and [M(tpy ~·) (tpy ~0)] ~(1+) (S = 1/2) (M = Fe ~(II), Ru ~(II)) also contain a low-spin (t _(2g)) ~6 divalent metal center, plus a single radical monoanion (bpy ~·) ~(1-) or (tpy ~·) ~(1-), and two or one neutral (bpy ~0) or (tpy ~0) ligands, respectively. The unpaired electron resides in a ligand π~* orbital. The neutral complexes [Fe ~(II)(bpy ~·) _2(bpy ~0)] ~0 and [Ru ~(II)(tpy ~·) _2] ~0 were found, by DFT calculations, to possess an S = 1 ground state that is attained by weak intramolecular ferromagnetic coupling between two ligand radical anions and a singlet excited state (S = 0). In contrast, the neutral species [Ru ~(II)(bpy ~·) _2(bpy ~0)] ~0 possesses an S = 0 ground state. The metal centers of these neutral complexes retain a low-spin (t _(2g)) ~6 configuration. Remarkably, the corresponding neutral complex [Fe ~(II)(tpy ~·) _2] ~0 contains high-spin Fe ~(II) (S _(Fe) = 2). Strong intramolecular antiferromagnetic metal-radical coupling yields an experimentally observed S = 1 ground state. The monoanions [M ~(II)(bpy ~·) _3] ~(1-) (M = Fe, Ru) are composed of a low-spin metal ion [Fe, Ru; (t _(2g)) ~6; S _M = 0] and three (bpy ~·) ~(1-) radical anions.