The Impact of Anion‐Modulated Structural Variations on the Magnetic Coupling in Trinuclear Heterometallic CuII–CoII Complexes Derived from a Salen‐Type Schiff Base Ligand

Abstract

AbstractThree new trinuclear heterometallic [(CuIIL)2CoIIX2] complexes [H2L = N,N′‐bis(salicylidene)‐1,3‐propanediamine and X = thiocyanate (1), benzoate (2), or azide (3)] have been synthesized by reacting the metalloligand [CuL] with Co(ClO4)2·6H2O and the NH4+ or Na+ salt of the corresponding anion in methanol. Structural characterization reveals that the central CoII ion is connected to two terminal metalloligands through μ1,1‐diphenoxido bridges in all three complexes. However, two monodentate thiocyanato ions, which are mutually cis coordinated to the Co atom in 1, generate a “bent” structure, whereas the trans‐coordinated syn–syn bridging benzoato (1κO:2κO′) and the end‐on bridging azido (μ1,1) coligands in 2 and 3, respectively, produce linear structures. The changes in the number and nature of the bridges with a shortening of the distances between the metal centers leads to a concomitant decrease of the average CuII–O–CoII bridging angle from 99.3(2) to 97.1(4) and 91.5(1)° for 1, 2 and 3, respectively. Variable‐temperature magnetic susceptibility measurements show the presence of a dominant antiferromagnetic coupling between the Cu–Co pairs in all three complexes. However, a steady decrease of the magnitude of the exchange coupling constant (JCu‐Co) is observed from –33.4 (for 1) to –11.4 (for 2) and –2.15 cm–1 (for 3). This trend suggests that larger Cu–O–Co angles are associated with stronger antiferromagnetic coupling.