Interplay of Anisotropic Exchange Interactions and Single-Ion Anisotropy in Single-Chain Magnets Built from Ru/Os Cyanidometallates(III) and Mn(III) Complex

Abstract

Two novel 1D heterobimetallic compounds {[MnIII(SB2+)MIII(CN)6]·4H2O}n (SB2+ = N,N′-ethylenebis(5-trimethylammoniomethylsalicylideneiminate) based on orbitally degenerate cyanidometallates [OsIII(CN)6]3− (1) and [RuIII(CN)6]3− (2) and MnIII Schiff base complex were synthesized and characterized structurally and magnetically. Their crystal structures consist of electrically neutral, well-isolated chains composed of alternating [MIII(CN)6]3− anions and square planar [MnIII(SB2+)]3+ cations bridged by cyanide groups. These -ion magnetic anisotropy of MnIII centers. These results indicate that the presence of compounds exhibit single-chain magnet (SCM) behavior with the energy barriers of Δτ1/kB = 73 K, Δτ2/kB = 41.5 K (1) and Δτ1/kB = 51 K, Δτ2 = 27 K (2). Blocking temperatures of TB = 2.8, 2.1 K and magnetic hysteresis with coercive fields (at 1.8 K) of 8000, 1600 Oe were found for 1 and 2, respectively. Theoretical analysis of the magnetic data reveals that their single-chain magnet behavior is a product of a complicated interplay of extremely anisotropic triaxial exchange interactions in MIII(4d/5d)–CN–MnIII fragments: −JxSMxSMnx−JySMySMny−JzSMzSMnz, with opposite sign of exchange parameters Jx = −22, Jy = +28, Jz = −26 cm−1 and Jx = −18, Jy = +20, Jz = −18 cm−1 in 1 and 2, respectively) and single orbitally degenerate [OsIII(CN)6]3− and [RuIII(CN)6]3− spin units with unquenched orbital angular momentum in the chain compounds 1 and 2 leads to a peculiar regime of slow magnetic relaxation, which is beyond the scope of the conventional Glaubers’s 1D Ising model and anisotropic Heisenberg model.