Two Zn16Ln (Ln = Dy, Sm) Metallacrowns: Synthesis, Magnetism and Their Efficient Catalysis for Knoevenagel Condensation

Two Zn(16)Ln complexes, {H[DyZn16(picha)(16)(Py)(8)](OTf)(4)center dot(Py)(2)center dot 4MeOH center dot 12H(2)O} (1), {Na[SmZn16 (picha)(16)(Py)(8)](OTf)(4)center dot 4MeOH center dot 16H(2)O} (2) (H-2 picha = picoline hydroxamic acid, Py = pyridine, HOTf = trifluoromethanesulfonic acid) were easily achieved and fully characterized by X-ray analyses of single crystal (XRD), elemental analysis, infrared spectra (IR) and thermal gravimetric analysis (TGA). The complexes 1-2 show two concave 12-MCZn-4 units that sandwich an eight-coordinate Ln(3+) central metal, and the sandwich structure is enclosed in a cavity of a 24-MCZn-8 unit. In the supramolecular structure of complexes 1-2, the one-dimensional chain is formed by the weak interactions of C-H center dot center dot center dot O bonds. Additionally, magnetic measurements reveal field-dependent slow magnetic relaxation in 1. Furthermore, these complexes acted as efficient catalysts for the Knoevenagel condensation with yield up to 97.2%, and the catalyst can be readily recovered and reused in subsequent reactions without considerable loss of reactivity.