We previously reported the spin-crossover (SC) properties of [Fe(tacn)](OTf) () (tacn = 1,4,7-triazacyclononane) [ , 2115]. Upon heating under dynamic vacuum, 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 via loss of an H atom. The resulting complex was hypothesized to have the formulation [Fe(tacn)(tacn-H)](OTf) () where tacn-H is -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 ( = 1.98, 2.10, 2.19). We have indirectly detected H formation during the heating of by reacting the headspace with HgO. Formation of water (HNMR in anhydrous d-DMSO) and elemental mercury were observed. To further support this claim, we independently synthesized [Fe(tacn)](OTf) () and treated it with one equiv base yielding . The structures of was characterized by X-ray crystallography. Compound also exhibits a low spin iron(III) rhombic signal ( = 1.97, 2.11, 2.23) in DMF at 77 K. Variable temperature magnetic susceptibility measurements indicate that undergoes gradual spin increase from 2 to 400 K. DFT studies indicate that the deprotonated nitrogen in forms a bond to iron(III) exhibiting double bond character (Fe-N, 1.807 Å).
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| http://dx.doi.org/10.1002/ejic.201701190 | DOI Listing |
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