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

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, [Fe(3) (II)(saltrz)(6)(M(II)(CN)(4))(3)]·8(H(2)O) (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(1.0)LS(0.0), HS(0.833)LS(0.167), HS(0.667)LS(0.333), HS(0.167)LS(0.833), and HS(0.0)LS(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.