Modular [Fe^III ₈M^II ₆]ⁿ⁺ (M^II = Pd, Co, Ni, Cu) coordination cages

Sanz, Sergio, O'Connor, Helen M., Comar, Priyanka, Baldansuren, Amgalanbaatar, Pitak, Mateusz B., Coles, Simon J., Weihe, Høgni, Chilton, Nicholas F., McInnes, Eric J.L., Lusby, Paul J., Piligkos, Stergios and Brechin, Euan K. (2018) Modular [Fe^III ₈M^II ₆]ⁿ⁺ (M^II = Pd, Co, Ni, Cu) coordination cages. Inorganic Chemistry, 57 (7), 3500-3506. (doi:10.1021/acs.inorgchem.7b02674).

Abstract

The reaction of the simple metalloligand [Fe^IIIL₃] [HL = 1-(4-pyridyl)butane-1,3-dione] with a variety of different M^II salts results in the formation of a family of heterometallic cages of formulae [Fe^III ₈Pd^II ₆L₂₄]Cl₁₂ (1), [Fe^III ₈Cu^II ₆L₂₄(H₂O)₄Br₄]Br₈ (2), [Fe^III ₈Cu^II ₆L₂₄(H₂O)₁₀](NO₃)₁₂ (3), [Fe^III ₈Ni^II ₆L₂₄(SCN)₁₁Cl] (4), and [Fe^III ₈Co^II ₆L₂₄(SCN)₁₀(H₂O)₂]Cl₂ (5). The metallic skeleton of each cage describes a cube in which the Fe^III ions occupy the eight vertices and the M^II ions lie at the center of the six faces. Direct-current magnetic susceptibility and magnetization measurements on 3-5 reveal the presence of weak antiferromagnetic exchange between the metal ions in all three cases. Computational techniques known in theoretical nuclear physics as statistical spectroscopy, which exploit the moments of the Hamiltonian to calculate relevant thermodynamic properties, determine J_Fe-Cu = 0.10 cm^-1 for 3 and J_Fe-Ni = 0.025 cm^-1 for 4. Q-band electron paramagnetic resonance spectra of 1 reveal a significantly wider spectral width in comparison to [FeL₃], indicating that the magnitude of the Fe^III zero-field splitting is larger in the heterometallic cage than in the monomer.

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Contributors

Author: Mateusz B. Pitak

Author: Simon J. Coles

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