Electronic structure of linear thiophenolate-bridged heterotrinuclear complexes [LFeMFeL](n+) (M = Cr, Co, Fe; n = 1-3): Localized vs delocalized models

Thorsten Glaser, Thomas Beissel, Eckhard Bill, Thomas Weyhermüller, Volker Schünemann, Wolfram Meyer-Klaucke, Alfred X. Trautwein, Karl Wieghardt*

*Corresponding author for this work
72 Citations (Scopus)

Abstract

The reaction of mononuclear [LFe(III)] 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]X(n) 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 Mossbauer spectroscopy (in zero and applied field). The following electronic structures have been established: (1a) Fe(II)(ls)Cr(III)Fe(II)(ls) (ls = low- spin) with a spin ground state of S(t) = 3/2; (1c) Fe(III)(ls)Cr(III)Fe(III)(ls) with an S(t) = 1/2 ground state; (2c) Fe(III)(ls)Co(III)(ls)Fe(III)(ls) with an S(t) = 1 ground state; (3c) Fe(III)(ls)Fe(III)(ls)Fe(III)(ls) with an S(t) = 1/2 ground state. For 1b (S(t) = 2) it is found that the two iron ions are spectroscopically equivalent (Fe(2.5)) and, therefore, the excess electron is delocalized (class III): [LFe(2.5)Cr(III)Fe(2.5)L]2+. For 2b clearly two different iron sites prevail at low temperatures (4.2 K); at higher temperatures (>200 K) they become equivalent on the Mossbauer time scale. Thus, 2b is class II with temperature-dependent electron hopping between the Fe(II) and Fe(III) ions. 3b is again fully delocalized (class III) with an S(t) = 1 ground state; the excess electron is delocalized over all three iron sites. The electronic structure of all complexes is discussed in terms of double exchange and superexchange mechanisms.

Original languageEnglish
JournalJournal of the American Chemical Society
Volume121
Issue number10
Pages (from-to)2193-2208
Number of pages16
ISSN0002-7863
DOIs
Publication statusPublished - 17.03.1999

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