Assembly of MnIII ions into di-, tetra-, deca-nuclear coordination complexes, zero- to three-dimensional molecular frameworks: molecular spin flop to and short-range bulk magnetic spin flop ordering

Abstract

Octahedral Mn^III ions possess significant magnetic anisotropy due to second-order orbital contribution combined with Jahn–Teller distortion. This study reports the influence of O₂N/O₃N-donor ligands (H₂L¹, H₂L², H₂L³, and H₃L⁴) towards the coordination compound structures and their reaction with Mn(OAc)₂·4H₂O, leading to the isolation of complexes with different nuclearities, such as four Mn^III ions containing [Mn^III₄(μ₃-O)₂(L¹)₂(OAc)₄(HOMe)₄] (1), dimeric [Mn^III₂(L²)₂(μ-OMe)₂(HOMe)₂] (2), 2D multinuclear coordination polymer [Mn^III(L³)(OMe)]_n (3), and a decanuclear crown-like complex [Mn₁₀(L⁴)₁₀(L⁴O)₂(DMF)₄(MeOH)₄(H₂O)₂] (4), respectively. Complexes 1 and 2 exist in tetrameric and dimeric forms in the crystal lattice with tetra and binuclear Mn^IIIO cores, respectively, while 3 forms a 2D polymeric network. Complex 4 reveals a macrocyclic crown-like topology. The temperature-dependent magnetic susceptibilities have been investigated for these complexes in the temperature range of 1.8–300 K under an applied dc magnetic field of 1000 Oe. The Mn^III ions of all complexes are antiferromagnetically coupled. Tetranuclear complex 1 shows spin flop type behavior, which purely arises from its molecular origin above a critical dc field of 32 000 Oe at low temperature due to some extent of spin frustration in the Mn^III₄O₆ core with two sets of orthogonal Jahn-Teller axes. The 2D Mn^III-polymer 3 displays conventional spin flop due to bulk magnetic ordering below 11 K. The macrocyclic crown-like complex 4 exhibits strong antiferromagnetic coupling between the Mn^III-ions. In addition, ab initio calculations were performed to prove the spin flop behavior in 1. The spin–flop type behavior in 1 and 3 was confirmed by field-dependent heat capacity measurements. The sigmoidal shape of the M vs. H plot of 1 was also further supported by ab initio calculations.