Heteroleptic, polynuclear dysprosium(iii)-carbamato complexes through in situ carbon dioxide capture

Abstract

Amine groups are among the most effective systems for carbon dioxide capture. Reminiscent of the activation of nature's most abundant enzyme RuBisCO, the treatment of amines with CO₂ in the presence of oxophilic metal ions, e.g. Mg²⁺, results in the formation of carbamates. Here we report the synthesis, structure and magnetic properties of three new dysprosium-carbamato complexes. The reaction of gaseous CO₂ with N,N-diisopropylamine and DyCl₃(DME)₂ (DME = Dimethoxyethane) in toluene leads to the formation of the tetrametallic complex [Dy₄(O₂CNⁱPr₂)₁₀(O-C₂H₄–OMe)₂]. The addition of 2-hydroxy-3-methoxybenzaldehyde-N-methylimine yields the hexametallic compound [Dy₆(O₂CNⁱPr₂)₈(O-C₂H₄–OMe)₂(CO₃)₂(C₉O₂NH₁₀)₄] in which the metal sites form a chair-like configuration; The same hexanuclear motif is obtained using N,N-dibenzylamine. We show that by employing CO₂ as a feedstock, we are able to capture up to 2.5 molecules of CO₂ per Dy ion. Magnetic measurements show a decreasing χ_MT at low temperatures. Combining the experimental magnetic data with ab initio calculations reveils tilting of the easy axes and implies the presence of antiferromagnetic interactions between the Dy(III) metal ions.