Secondary metal coordination using a tetranuclear complex as ligand leading to hexanuclear complexes with enhanced thermal barriers for electron transfer

Abstract

Postsynthesis of the paramagnetic square-shaped complex {[(Tp*Me)Fe(μ-CN)2(CN)][Co(dmbpy)2]}2 (BPh4)2·6MeCN·H2O [1, Tp*Me = tris(3,4,5-trimethylpyrazole)-borate; dmbpy = 4,4′-dimethyl-2,2′-bipyr-idine)] by grafting transition metal(II) thiocyanates via its terminal cyano groups afforded three hexanuclear [Fe2Co2M2] clusters (M = Zn, 2; Co, 3; Cd, 4). The peripheral metal-complex units serving as excellent electron acceptors were found to help stabilize the low-temperature state of FeII,LS-CoIII,LS within the complex core. As a result, the desolvated complexes 2-4 underwent reversible and sharp thermally induced electron-transfer behavior with the transition temperatures (T1/2) up to 312, 296, and 365 K, respectively, demonstrating an effective means of manipulating thermal barriers of the celebrated cyano-bridged square core.