Linking Cyanometallate [Fe2Co2] Squares into One-Dimensional Chains via Benzoquinones

The construction of functional cyanometallate clusters connected by secondary bridges is a highly sought-after area of research in chemistry and materials science. Our investigation has led to the discovery of three novel compounds, {[(Tp*)Fe(CN)₃Co(bpy)]₂(μ-CA)·4MeOH}_n (1), {[(Tp*^Me)Fe(CN)₃Co(dpa)]₂(μ-CA)}_n (2), and {[(Tp*^Me)Fe(CN)₃Co(bpy)]₂(μ-dhbq)}_n (3) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, Tp*^Me = hydrotris(3,4,5-trimethylpyrazolyl)borate, H₂CA = 2,5-dichloro-3,6-dihydroxy-2,5-cyclohexadiene-1,4-dione, dhbq = 2,5-dihydroxy-1,4-benzoquinone, bpy = 2,2′-bipyridyl, and dpa = 2,2′-dipyridylamine). These compounds were synthesized via a self-assembly reaction of the [(Tp^R)Fe^III(CN)₃]⁻ building block, Co(II) salts, and chelating ligands of bpy or dpa, followed by addition of benzoquinone dianions. X-ray crystallographic analyses revealed that 1–3 exhibited similar structures, where cyanide-bridged [Fe₂Co₂] squares are connected by benzoquinones to form a one-dimensional chain. Magnetic studies demonstrated a ferromagnetic interaction between the cyanide-bridged Fe and Co ions but an antiferromagnetic interaction between the benzoquinone-bridged Co–Co pairs. Notably, compounds 2 and 3 displayed metamagnetic behaviors with antiferromagnetic orderings below 4 K.