Amine-templated cobalt(II) coordination polymer exhibiting novel magnetic properties: effect of dehydration

Abstract

An amine-templated 2D coordination polymer of Co^II with the formula {[EDAH₂][Co₂F₂(SO₄)₂(H₂O)₂]}_n (1) (EDA=ethylenediamine), has been synthesised and structurally characterised. It consists of a 1D chain bridged by F⁻ ions, which are interconnected by SO₄²⁻ tetrahedra forming a 2D [Co₂F₂(SO₄)₂(H₂O)₂]_n²⁻ corrugated sheet. The diprotonated cation [EDAH2] is intercalated between the sheets. Temperature-dependent magnetic measurements reveal the presence of spin-canted antiferromagnetism and hard-magnet-like behaviour with large a magnetic hysteresis with a coercive field (H_c) of 16.2 kOe and a remnant magnetisation (M_R) of 1.64 μB. The coordinated water molecules in 1 can be removed by heating at 250°C under vacuum to obtain the dehydrated phase {[EDAH₂][Co₂F₂(SO₄)₂]}_n (1'), which- upon exposure to water vapour for 24 h- gave the monoaqua compound, {[EDAH₂][Co₂F₂(SO₄)₂(H₂O)]}_n (1"). This dehydration/rehydration process is accompanied by a structural transformation and a magnetic phase transition between the spin-canted antiferromagnetic state of the hydrated phase to the antiferromagnetic state of the dehydrated phase.