Dimensionally Controlled Assembly of an External Stimuli-Responsive [Co2Fe2] Complex into Supramolecular Hydrogen-Bonded Networks

A stimuli-responsive tetranuclear complex was assembled into new aggregates with controllable dimensionality through directional hydrogen bonds (HBs). A cyanide-bridged tetranuclear complex cation, [Co2Fe2(CN)(6)(tp*)(2)(bpy*)(4)](2+) (abbreviated to 1(2+)) (tp*= hydrotris(3,5-dimethylpyrazol-1-yl) borate and bpy*= 4,4'-dimethyl- 2,2'-bipyridine) has two terminal cyanide nitrogens and acts as a hydrogen-bond acceptor (HBA) with a linear bridging mode. Co-crystallization of 1(2+) with p-hydroquinone (H(2)Q), a hydrogen-bond donor (HBD) with two donor sites, led to a one-dimensional aggregate, 1(BPh4)(2) center dot (H(2)Q) center dot 2H(2)O (2), while a two-dimensional sheet with a honeycomb structure, 1(3)(PF6)(6) center dot (H(3)PG)(2) center dot 4CH(3)CN center dot 8H(2)O (3), was obtained by co-crystallization with phloroglucinol (H(3)PG) acting as a three-way structure-directing HBD. Magnetic measurements revealed that 2 and 3 exhibited thermal and light-induced electron-transfer-coupled spin transitions (ETCSTs).