Dimensionally Controlled Assembly of an External Stimuli-Responsive [Co2 Fe2 ] 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, [Co2 Fe2 (CN)6 (tp*)2 (bpy*)4 ]2+ (abbreviated to 12+ ) (tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate and bpy*=4,4'-di-methyl-2,2'-bipyridine) has two terminal cyanide nitrogens and acts as a hydrogen-bond acceptor (HBA) with a linear bridging mode. Co-crystallization of 12+ with p-hydroquinone (H2 Q), a hydrogen-bond donor (HBD) with two donor sites, led to a one-dimensional aggregate, 1(BPh4 )2 ⋅(H2 Q)⋅2 H2 O (2), while a two-dimensional sheet with a honeycomb structure, 13 (PF6 )6 ⋅(H3 PG)2 ⋅4 CH3 CN⋅8 H2 O (3), was obtained by co-crystallization with phloroglucinol (H3 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).