A porous Co(II)-MOF (1) was synthesized by the combination of a bent imidazole-bridged ligand and p-phthalic acid (PTA) with Co(OAc)(2) under solvothermal conditions. This Co(II)-MOF (1) is able to undergo a reversible MeOH substitution reaction on the Co(II) center via a single-crystal-to-single-crystal process. The desolvated Co(II)-MOF (2) with the open Co(II) sites is very stable (up to 350 degrees C). Furthermore, 2 is a highly active heterogeneous catalyst for various organic substrates oxidation in the presence of tertbutyl hydropercodde (TBHP) under milder conditions. The importance of open Co(II) sites in 2 for the organic substrates oxidation is directly evidenced by the single-crystal X-ray diffraction.