New wheel-shaped Ln6 clusters for conversion of CO2 and magnetic properties

Abstract

A series of novel hexanuclear lanthanide clusters, namely, [Ln6(HL)6(NO3)6]·3CH3CN (Ln = Gd(1), Tb(2), Dy(3) and Er(4)) was assembled using a multidentate ligand H3L (trolamine). The clusters 1–4 show a wheel-shaped Ln6 topology with the approximate diameter and thickness of 1.5 and 0.7 nm, respectively. All of them show high thermal stability. In the aspect of the catalytic capacities for the cycloaddition reactions of CO2 and epoxide, the reaction conditions, the substrate scope, and possible catalytic mechanism were investigated. The highest yield for clusters 1–4 is up to 99% at 333 K for 12 h. In particular, cluster 1 can be reused at least three times with no obvious loss of catalytic performance and keep the integrity of the crystal structure. Magnetic investigations reveal that cluster 1 exhibits a relatively large magnetocaloric effect with −ΔSm = 41.43 J/(kg⋅K) (T = 3.0 K, 7.0 T); while cluster 3 displays slow magnetic relaxation behavior under zero dc field with Ueff = 0.51 K and τ0 = 2.54 × 10−5 s.