We report the synthesis of ion-exchangeable molybdenum sulfide chalcogel through an oxidative coupling process, using (NH4)(2)MoS4 and iodine. After supercritical drying, the MoSx amorphous aerogel shows a large surface area up to 370 m(2)/g with a broad range of pore sizes. X-ray photoelectron spectroscopic and pair distribution function analyses reveal that Mo6+ species undergo reduction during network assembly to produce Mo4+-containing species where the chalcogel network consists of [Mo3S13] building blocks comprising triangular Mo metal clusters and S-2(2-) units. The optical band gap of the brown-black chalcogel is similar to 1.36 eV. The ammonium sites present in the molybdenum sulfide chalcogel network are ion-exchangeable with K+ and Cs+ ions. The molybdenum sulfide aerogel exhibits high adsorption selectivities for CO2 and C2H6 over H-2 and CH4. The aerogel also possesses high affinity for iodine and mercury.