A Cu-azolate metal-organic framework (MOF) uptakes stoichiometric loadings of Groups 1 and 2 metal halides, demonstrating efficient reversible release and reincorporation of immobilized anions within the framework. Ion-pairing interactions lead to anion-dependent Li+ and Mg2+ transport in Cu-4(ttpm)(2)center dot 0.6CuCl(2), whose high surface area affords a high density of uniformly distributed mobile metal cations and halide binding sites. The ability to systematically tune the ionic conductivity yields a solid electrolyte with a Mg2+ ion conductivity rivaling the best materials reported to date. This MOF is one of the first in a promising class of frameworks that introduces the opportunity to control the identity, geometry, and distribution of the cation hopping sites, offering a versatile template for application-directed design of solid electrolytes.