Improving spin crossover characteristics in heteroleptic [FeIII(qsal-5-I)(qsal-5-OMe)]A complexes

Abstract

A family of heteroleptic spin crossover (SCO) [Fe^III(qsal-5-I)(qsal-5-OMe)]A·sol (qsal-5-X = 5-X-2-[(8-quinolylimino)methyl]phenolate; A = NO₃⁻1 sol = 2MeOH, NCS⁻2 sol = 0.75MeOH·1.3H₂O, BF₄⁻3 sol = MeOH, OTf⁻4, sol = MeOH) complexes have been synthesized. Most of the complexes exhibit gradual SCO, with the exception of NCS, which is principally high spin. In contrast, the OTf complex shows an abrupt hysteretic SCO (35 K) after solvent loss. The magnetic properties of this complex are significantly improved in comparison to the related homoleptics, [Fe(qsal-I)₂]OTf 5 (hysteresis, 8 K) and [Fe(qsal-5-OMe)₂]OTf·CH₂Cl₂6 (gradual SCO). Structural studies reveal that slight changes in the crystal packing cause stronger interactions improving the cooperativity. These findings are supported by DFT calculations using the r²SCAN functional in which the calculated structures show that SCO from the LS to the HS state causes pronounced scissoring of the 1D π–π chains and substantial changes in their relative orientation following loss of MeOH.