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

A design for an octahedrally ligated phthalocyanine complex with high-spin manganese(iii) (S = 2) and Mn(III)(Pc)Cl(2) (Pc = phthalocyanine) is presented. The presence of high-spin state Mn(III) in the fabricated Ph(4)P[Mn(III)(Pc)Cl(2)](2) (Ph(4)P = 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(z(2)))(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 Ph(4)P[Mn(III)(Pc)(CN)(2)](2), where Mn(III) adopts a low-spin state (S = 1). The magnetoresistance (MR) effects of Ph(4)P[Mn(III)(Pc)Cl(2)](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 Ph(4)P[Mn(III)(Pc)(CN)(2)](2). Furthermore, the negative MR effect is comparable to that of Ph(4)P[Fe(III)(Pc)(CN)(2)](2) (S = 1/2), which exhibits the largest negative MR effect reported for [M(III)(Mc)L(2)]-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.