A single crystal of an iron compound containing a Fe-OH2 bond, on exposure to methanol vapor at an ambient condition, transforms to another single crystal with the formation of a Fe-O(H)Me covalent bond at the cost of breaking the Fe-OH2 bond. The methanol complex, upon exposure to atmospheric water vapor at room temperature, goes back to an original water-coordinated complex. The full reversibility of this gas-solid system was established by X-ray crystallography and IR spectroscopy.