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Thermally Induced Oxidation of [Fe II (tacn) 2 ](OTf) 2 (tacn = 1,4,7‐triazacyclononane)
Author(s) -
Li Jia,
Banerjee Atanu,
Preston Debra R.,
Shay Brian J.,
Adhikary Amitiva,
Sevilla Michael D.,
Loloee Reza,
Staples Richard J.,
Chavez Ferman A.
Publication year - 2017
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201701190
Subject(s) - chemistry , deprotonation , electron paramagnetic resonance , crystallography , ligand (biochemistry) , spin crossover , magnetic susceptibility , inorganic chemistry , medicinal chemistry , nuclear magnetic resonance , organic chemistry , ion , biochemistry , physics , receptor
We previously reported the spin‐crossover (SC) properties of [Fe II (tacn) 2 ](OTf) 2 ( 1 ) (tacn = 1,4,7‐triazacyclononane). Upon heating under dynamic vacuum, 1 undergoes oxidation to generate a low‐spin iron(III) complex. The oxidation of the iron center was found to be facilitated by initial oxidation of the ligand through loss of a H atom. The resulting complex was hypothesized to have the formulation [Fe III (tacn)(tacn‐H)](OTf) 2 ( 2 ) where tacn‐H is N ‐deprotonated tacn. The formulation was confirmed by ESI‐MS. The powder EPR spectrum of the oxidized product at 77 K reveals the formation of a low‐spin iron(III) species with rhombic spectrum ( g = 1.98, 2.10, 2.19). We have indirectly detected H 2 formation during the heating of 1 by reacting the headspace with HgO. Formation of water ( 1 H NMR in anhydrous [D 6 ]DMSO) and elemental mercury were observed. To further support this claim, we independently synthesized [Fe III (tacn) 2 ](OTf) 3 ( 3 ) and treated it with one equivalent of base yielding 2 . The structures of 3 were characterized by X‐ray crystallography. Compound 2 also exhibits a low‐spin iron(III) rhombic signal ( g = 1.97, 2.11, 2.23) in DMF at 77 K. Variable temperature magnetic susceptibility measurements indicate that 3 undergoes gradual spin increase from 2 to 400 K. DFT studies indicate that the deprotonated nitrogen in 2 forms a bond to iron(III) exhibiting double‐bond character (Fe–N, 1.807 Å).