Dual magnetic behavior of an Fe(<scp>iii</scp>)-dioxolene complex with tri-substituted catechol

Magnetically bistable compounds attract considerable attention due to their possible applications in molecular electronics and spintronics devices. Of special interest are spin-crossover (SCO) systems that can interconvert between the low-spin and high-spin states leading to switching of the magnetic properties. Synthesis and comprehensive characterization of a family of ionic ferric-dioxolene complexes [(TPA)Fe(HO-DBCat)]ClO₄ (1), [(TPA)Fe(NO₂-DBCat)]ClO₄ (2) and [(TPA)Fe(MeOCH₂-DBCat)]ClO₄ (3) (TPA = tris(2-pyridylmethyl)amine; HO-DBCat = dianion of 4,6-di-<i>tert</i>-butyl-1,2,3-trihydroxybenzene, NO₂-DBCat = dianion of 4,6-di-<i>tert</i>-butyl-3-nitro-1,2-dihydroxybenzene and MeOCH₂-DBCat = dianion of 4,6-di-<i>tert</i>-butyl-3-methoxymethyl-1,2-dihydroxybenzene) are reported. Variable temperature structural, magnetic and spectral analyses revealed that compounds 1-3 undergo a thermally induced SCO in the solid state between the high-spin (<i>S</i> = 5/2) and low-spin (<i>S</i> = 1/2) states. Alternating current magnetic susceptibility measurements indicated that the nitro-substituted complex 2 shows a field supported slow magnetic relaxation in the low-spin state at 5000 Oe. Such duality of magnetic properties makes complex 2 the first ferric compound which demonstrates a complete <i>S</i> = 5/2 → <i>S</i> = 1/2 SCO with a single molecule magnet behavior (SMM, <i>S</i> = 1/2). Electronic structures and magnetic properties of 1, 2 and 3 were investigated with the aid of DFT and SA-CASSCF/NEVPT2 calculations.