Crystal structure and magnetic properties of the charge-transfer complex (BDTA)2(H3O)2[Fe(II)(CN)6]

• A salt including a cyclic thiazole cation, (BDTA)2(H3O)2[Fe(CN)6], (1) was prepared.
• In 1, weak charge-transfer interactions worked between BDTA+ and Fe(CN)64–.
• Complex 1 was diamagnetic but a paramagnetic change occurred above 360 K.
• The origin of the magnetic change was related to decomposition of 1.

The crystal structure and magnetic properties of (BDTA)2(H3O)2[Fe(II)(CN)6] (1), a charge-transfer complex, were investigated. The charge transfer interaction works between BDTA+ and Fe(CN)64–in 1 from UV, IR spectra, and single crystal X-ray analyses, although the degree of charge transfer is quite small. Complex 1 forms dark green crystals and is composed of closed-shell ions BDTA+, H3O+, and Fe(CN)64–, as deduced from X-ray analysis and magnetic measurements. Although complex 1 is diamagnetic, a paramagnetic material is irreversibly formed upon heating beyond 360 K. The paramagnetic material thus formed remains in the paramagnetic state even upon cooling to 2 K. DSC, TGA, and powder X-ray diffraction measurements revealed that the heating of 1 results in the evaporation of two water molecules per formula unit, leading to large structural changes and decomposition of 1. The diamagnetic-to-paramagnetic change in 1 may result from the formation of high-spin iron species due to changes in the coordination environment.

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