The controlled and reversible formation of transiently soluble alkanethiolate- and tiopronin-monolayer-protected cluster (MPC) aggregates is demonstrated by using Cu2+-carboxylate chemistry to form cluster-Cu2+-cluster linkages. The aggregation process and its reversibility were monitored using UV-vis and FTIR spectroscopy. The amount of Cu2+ required to induce aggregation of dissolved tiopronin-MPCs is a strong function of pH, increasing at lower pH. Cu2+-carboxylate chemistry can also be utilized to prepare surface-attached films of tiopronin-MPCs in a manner analogous to alkanethiolate-MPCs, monitoring the dim formation using FTIR external reflectance spectroscopy. Experiments exploring the diffusional and capacitive properties of tiopronin-MPCs are also reported.