Slow magnetic relaxation in a {EuCu5} metallacrown.

A 3d-4f heterometallic metallacrown with formula of [EuCu5(quinha)5(sal)2(py)5]CF3SO3·py·3H2O (1) (H2quinha = quinaldichydroxamic acid; Hsal = salicylaldehyde) has been synthesized. This complex shows field-induced slow magnetic relaxation via a Raman-like process, where studies of the isostructural {LuCu5} (2) and {YCu5} (3) complexes show that the slow dynamics mainly arise from the {Cu5} S = 1/2 ground state rather than the EuIII ion. However, the EuIII ion enhances the relaxation rates of the {Cu5} unit which likely arises from second-order effects in the formally diamagnetic 7F0 ground state of EuIII.