Slow Magnetic Relaxation of a 12-Metallacrown-4 Complex with a Manganese(III)-Copper(II) Heterometallic Ring Motif

Abstract

The heterobimetallic metallacrown (MC), (TMA)${}_2${Mn(OAc)${}_2$[12-MC${}_{Mn(III)Cu(II)N(shi)}$-4](CH${}_3$OH)}$\cdot$2.90CH${}_3$OH, 1, where TMA${}^{+}$ is tetramethylammonium, ${}^{-}$OAc is acetate, and shi${}^{3-}$ is salicylhydroximate, consists of a Mn${}^{II}$ ion captured in the central cavity and alternating unambiguous and ordered manganese(III) and copper(II) sites about the MC ring, a first for the archetypal MC structure design. DC-magnetometry characterization and subsequent simulation with the Spin Hamiltonian $$H=-J_1({\mathbf{s}}_1+{\mathbf{s}}_3)\cdot {\mathbf{s}}_5-J_2({\mathbf{s}}_2+{\mathbf{s}}_4)\cdot {\mathbf{s}}_5-J_3\sum _{i=1}^4{\mathbf{s}}_i\cdot {\mathbf{s}}_{i+1}+d(s_{z,1}^2+s_{z,3}^2)+{\mu }_B\sum _{j=1}^5{g}_j{\mathbf{s}}_j\cdot \mathbf{B}$$ indicates an S = 5/2 ground state and a sizable axial zero-field splitting on Mn${}^{III}$. AC-susceptibility measurements reveal that 1 displays slow magnetization relaxation akin to single-molecule magnet (SMM) behavior.