The chalcogel CoMo3S13 is obtained from the reaction of (NH4)(2)[Mo3S13] with cobalt acetate in solution. The chalcogel has a BET surface area of 570 m(2) g(-1), and pair distribution function analysis (PDF) and infrared spectroscopy indicate that the [Mo3S13](2-) cluster is a building block in the porous network. The CoMo3S13 chalcogel exhibits high selectivity for separating ethane and carbon dioxide from hydrogen and methane.