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A diamagnetic iron complex and its twisted sister – structural evidence on partial spin state change in a crystalline iron complex

2021; Royal Society of Chemistry; Volume: 50; Issue: 43 Linguagem: Inglês

10.1039/d1dt01607e

1477-9234

Esko Salojärvi, Anssi Peuronen, Jani O. Moilanen, H. Huhtinen, J. Lindén, Akseli Mansikkamäki, Mika Lastusaari, Ari Lehtonen,

Metal complexes synthesis and properties

We report here the syntheses of a diamagnetic Fe complex [Fe(HL)2] (1), prepared by reacting a redox non-innocent ligand precursor N,N'-bis(3,5-di-tert-butyl-2-hydroxy-phenyl)-1,2-phenylenediamine (H4L) with FeCl3, and its phenoxazine derivative [Fe(L')2] (2), which was obtained via intra-ligand cyclisation of the parent complex. Magnetic measurements, accompanied by spectroscopic, structural and computational analyses show that 1 can be viewed as a rather unusual Fe(III) complex with a diamagnetic ground state in the studied temperature range due to a strong antiferromagnetic coupling between the low-spin Fe(III) ion and a radical ligand. For a paramagnetic high-spin Fe(II) complex 2 it was found that, when crystalline, it undergoes a thermally induced process where 25% of the molecules in the material change to a diamagnetic low-spin ground state below 100 K. Single crystal X-ray studies conducted at 95 K afforded detailed structural evidence for this partial change of spin state of 2 showing the existence of crystallographically distinct molecules in a 3 : 1 ratio which exist in high- and low-spin states, respectively. Also, the magnetic behaviour of 2 was found to be related with the crystallinity of the material as demonstrated by near-IR radiation to unpaired electrons conversion ability of amorphous sample of 2.