Structural transformation and magnetic properties of Co(II) coordination polymers with pyrazole-3,5-dicarboxylate and pyrazine

A two-dimensional (2D) Co(II) coordination polymer with rectangular channel, namely {[Co2(Hpzdc)2(pyz)(CH3OH)(H2O)2]& BULL;3H2O}n (1) was synthesized under the solvothermal condition (Hpzdc = pyrazole-3,5-dicarboxylate and pyz = pyrazine). Both Co(II) centers exhibit octahedral geometry. The coordinated methanol and all water molecules in 1 can be removed by heating to give rise to the amorphous phase of desolvated 1 (1a). After 1a was immersed in the mixture of water and methanol, a new isostructural {[Co2(Hpzdc)2(pyz)(H2O)3]& BULL;3H2O}n (2) was obtained. The replacement of water for methanol in 1 leads to an alteration in the intermolecular packing, which gives rise to the color variations. The single-crystal to amorphous to single-crystal transformations accompanied by the color changes were confirmed by single crystal X-ray structure analysis, XRPD, TGA, elemental analysis, and spectroscopic techniques. The magnetic properties of 1 and 2 exhibit the antiferromagnetic interaction and spin-orbit coupling of octahedral high-spin Co(II) ion.

Automated summary

A 2D Co(II) coordination polymer with rectangular channel was synthesized and transformed into an amorphous phase upon removal of coordinated methanol and water molecules. The amorphous phase was then converted back to a single crystal with color changes. The magnetic properties of these materials were also studied.