4 years ago

Supramolecular Maleate Adducts of Copper(II) 12-Metallacrown-4: Magnetism, EPR and Alcohol Sorption Properties

Mikhail A. Kiskin, Vadim V. Minin, Elena A. Ugolkova, Anna V. Pavlishchuk, Matthias Zeller, Anthony W. Addison, Vladimir M. Novotortsev, Samuel E. Lofland, Sergey V. Kolotilov, Nikolay N. Efimov
With maleate, [Cu5(ahpha)4]2+ gives two complexes, [Cu5(ahpha)4(DMF)2](MalH)2·2DMF (1) and [Cu5(ahpha)4(MalH)2] (2) (ahpha2- is 3-amino-3-hydroximinopropane hydroxamate; MalH2 is maleic acid). Both 1 and 2 contain non-oligomerised [Cu5(ahpha)4]2+ metallacrown blocks; in 1, two MalH- are bound to [Cu5(ahpha)4]2+ only via H-bonds, while in 2, they coordinate to Cu2+. X-Band EPR of 1 was observed at 20 K, 100 K and 295 K. The EPR at 20 K was of an S = 1/2 ground state, while at room temperature anisotropic |ΔMs| = 1 and |ΔMs| = 2 resonances around 3200 G (g ≈ 2.19) and 1600 G (g ≈ 4.25) were observed for the Cu5 system, due to partial occupation of an S =3/2 state. The room temperature EPR of 1 was simulated as the weighted sum of the spectra of its various S = 1/2, 3/2 and 5/2 states. Its magnetic behaviour was fitted with a χMT vs. T model using a spin Hamiltonian accounting for central-peripheral (J1), peripheral-peripheral (J2) Cu2+-Cu2+ and intercrown (zJ') spin interactions, yielding J1= -156(4) cm-1, J2= -63(1) cm-1 and zJ'= -4.5(3) cm-1. For sorption of methanol and ethanol vapours at 293 K by a desolvated polycrystalline sample of 1, the shape of the absorption and desorption isotherms indicated a "gates opening" phenomenon.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201700976

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