Here we report a highly porous, water stable Co based ZIF [CoNIm (RHO)] and its solution mediated phase transformation to a less porous and water unstable ZIF [CoNIm (SOD)]. CoNIm (RHO) has high Langmuir surface area [2087 m2 g−1] as well as high water adsorption [200 cm3 (STP) g−1] capacity. © 2012 The Royal Society of Chemistry.