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.