Studies of a linear single-molecule magnet

Abstract

Reaction of the dinuclear complex [Mn₂O₂(bpy)₄](ClO₄)₃ with H₃cht (cis,cis-1,3,5-cyclohexanetriol) in MeCN produces the complex [Mn₃(Hcht)₂(bpy)₄](ClO₄)₃·Et₂O·2MeCN (1·Et₂O·2MeCN). Dc magnetic susceptibility measurements reveal the existence of weak ferromagnetic exchange between the three Mn ions, leading to a spin ground state of S = 7, with D = −0.23 cm⁻¹. W-Band (94 GHz) EPR measurements on restrained powdered crystalline samples confirm the S = 7 ground state and determine the ground state zero-field splitting (ZFS) parameters of D = −0.14 cm⁻¹ and B₄⁰= +1.5 × 10⁻⁵ cm⁻¹. The apparent 4th order behaviour is due to a breakdown of the strong exchange limit approximation (J ≈ d, the single-ion ZFS). Single crystal dc relaxation decay and hysteresis loop measurements reveal the molecule to have an appreciable energy barrier to magnetization relaxation, displaying low temperature sweep rate and temperature-dependent hysteresis loops. Density functional studies confirm the ferromagnetic exchange coupling between the Mn ions.