Heteronuclear Iron(III)–Schiff Base Complexes with the Hexacyanidocobaltate(III) Anion: On the Quest To Understand the Governing Factors of Spin Crossover

Two heteronuclear compounds (1 and 2) containing three ferric centers linked in facial-like mode with the magnetically silent hexacyanidocobaltate(III) anion were prepared and studied. The structural investigation revealed that both compounds are tetranuclear complexes with molecular formulas of [{Fe(L1)NC}3Co(CN)3]·2CH3OH·2.5CH3CN (1) and [{Fe(L2)NC}3Co(CN)3]·2H2O·1CH3OH (2). The magnetic properties of both complexes are controlled by the molecular design of the corresponding pentadentate Schiff base anions L12– and L22–. While compound 2 with a symmetric ligand prepared from salicylaldehyde shows high-spin state properties, compound 1 containing the asymmetric ligand with naphthalene units either is low-spin in its solvated form or shows a gradual but hysteretic spin crossover event when desolvated. The magnetic behavior was analyzed with respect to the Ising-like model and spin Hamiltonian, respectively, and the results were confronted with ab initio calculations. Additionally, the influence of structu...