A large negative magnetoresistance effect in semiconducting crystals composed of an octahedrally ligated phthalocyanine complex with high-spin manganese(iii)

Abstract

A design for an octahedrally ligated phthalocyanine complex with high-spin manganese(III) (S = 2) and Mn^III(Pc)Cl₂ (Pc = phthalocyanine) is presented. The presence of high-spin state Mn^III in the fabricated Ph₄P[Mn^III(Pc)Cl₂]₂ (Ph₄P = tetraphenylphosphonium) semiconducting molecular crystal is indicated by the Mn–Cl distance, which suggests an electronic configuration of (d_yz, d_zx)²(d_xy)¹(d_z²)¹. This was confirmed by the Curie constant (C = 5.69 emu K mol⁻¹), which was found to be significantly larger than that of the isostructural Ph₄P[Mn^III(Pc)(CN)₂]₂, where Mn^III adopts a low-spin state (S = 1). The magnetoresistance (MR) effects of Ph₄P[Mn^III(Pc)Cl₂]₂ at 26.5 K under 9 T static magnetic fields perpendicular and parallel to the c-axis were determined to be −30% and −20%, respectively, which are significantly larger values than those of Ph₄P[Mn^III(Pc)(CN)₂]₂. Furthermore, the negative MR effect is comparable to that of Ph₄P[Fe^III(Pc)(CN)₂]₂ (S = 1/2), which exhibits the largest negative MR effect reported for [M^III(Mc)L₂]-based systems (Mc = macrocyclic ligand, L = axial ligand). This suggests that the spin state of the metal ion is the key to tuning the MR effect.