We investigated the halogenation reactivity of copper cluster anions produced via a magnetron-sputter source after introduction into a fast-flow tube reaction apparatus simultaneously with chlorine gas. Interesting cluster products corresponding to [CunCln+1](-) (n = 1-6) were observed with notable stability, and the mass distribution of these clusters exhibits an exponential decay with increasing values of n. Reaction kinetics analysis is provided on the gas-phase reactivity of copper cluster anions with chlorine. First-principle calculations suggest a series of cubic-like structures for these species similar to the structure of alkali halide clusters due to their similar electronic configurations. These structures act as a starting point in the formation of ionic crystals.