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 {[EDAH(2)][Co(2)F(2)(SO(4))(2)(H(2)O)(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 SO(4)(2-) tetrahedra forming a 2D [Co(2)F(2)(SO(4))(2)(H(2)O)(2)](n)(2-) 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 mu(B). The coordinated water molecules in 1 can be removed by heating at 250 C under vacuum to obtain the dehydrated phase {[EDAH(2)][Co(2)F(2)(SO(4))(2)]}(n) (1'), which - upon exposure to water vapour for 24 h - gave the monoaqua compound, {[EDAH(2)][Co(2)F(2)(SO(4))(2)(H(2)O)]}(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.