Direct observation of oxygen molecules adsorbed on a Microporous Coordination Polymer. Charge density mapping of synchrotron radiation powder data were carried out by the MEM/Rietveld method. The equi-contour level is 1.0 eÅ-3. One dimentional array of adsorbed O2 molecules( colour in red) were found for the first time in 2002. (Science, 298 (2002), 2358-2361)