Abstract: In the present computational study we discuss the behavior of the MgH(+)(X(1)I (+)) pound molecular ion interacting with Rb((2)S) and argue that it constitutes an amenable system for ultracold chemistry studies in a Coulomb crystal environment. In particular, we find from our calculations that there is a number of different ways in which this system can chemically evolve and we present results from a diabatic representation of the potential energy surfaces (PESs) of the electronic states which are relevant for the realistic description of an experimental setup in which a cloud of ultracold laser-cooled Rb atoms is superimposed onto a Coulomb crystal arrangement of MgH(+) molecular ions. Our findings suggest the most likely pathways for either the formation of a new Coulomb crystal of Rb ions or the combination of cold Mg(+), MgH(+) and Rb(+) mixtures within the trap under consideration.