Four-step iron(ii) spin state cascade driven by antagonistic solid state interactions

Abstract

A four-stepped cascade of Fe(II) high spin (HS) to low spin (LS) states is demonstrated in a family of 2-D Hofmann materials, [Fe₃^II(saltrz)₆(M^II(CN)₄)₃]·8(H₂O) (M^II = Pd (1^Pd), Pt (1^Pt); saltrz = (E)-2-(((4H-1,2,4-triazol-4-yl)imino)methyl)phenol). Alongside the fully HS and LS Fe(II) states, fractional spin state stabilization occurs at HS/LS values of 5/6, 2/3, and 1/6. This unconventional spin state periodicity is driven by the presence of multiple spin crossover (SCO) active Fe(II) sites which are in subtly distinct environments driven by a network of antagonistic host–host and host–guest interactions. Alternating long- and short-range magnetostructural ordering is achieved over the five distinct spin state ratios HS^1.0LS^0.0, HS^0.833LS^0.167, HS^0.667LS^0.333, HS^0.167LS^0.833, and HS^0.0LS^1.0 owing to the flexibility of this 2-D interdigitated lattice topology interconnected by intermolecular interactions. A distinct wave-like spin state patterning is structurally evidenced for each intermediate phase.