Electronic Structure of Linear Thiophenolate-Bridged Heterotrinuclear Complexes [LFeMFeL]n+ (M = Cr, Co, Fe; n = 1−3): Localized vs Delocalized Models

The reaction of mononuclear [LFeIII] where L represents the trianionic ligand 1,4,7-tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane with CrSO4·5H2O, CoCl2·6H2O, or Fe(BF4)2·6H2O and subsequent oxidation with ferrocenium hexafluorophosphate or NO(BF4) or reduction with [(tmcn)Mo(CO)3] (tmcn = 1,4,7-trimethyl-1,4,7-triazacyclononane) produced an isostructural series of [LFeMFeL]n+ complexes, the following salts of which were isolated as crystalline solids:  (i) [LFeCrFeL](PF6)n with n = 1 (1a), n = 2 (1b), and n = 3 (1c); (ii) [LFeCoFeL]Xn with X = BPh4 and n = 2 (2b) and X = PF6 and n = 3 (2c); (iii) [LFeFeFeL](BPh4)n with n = 2 (3b) and n = 3 (3c). All compounds contain linear trinuclear cations (face-sharing octahedral) with an N3Fe(μ-SR)3M(μ-SR)3FeN3 core structure. The electron structure of all complexes has been studied by Fe and M K-edge X-ray absorption near edge structure (XANES), UV−vis, and EPR spectroscopy, variable-temperature, variable-field susceptibility measurements, and Mossbau...