The synthesis and solid-state characterization of a complete series of new heterometallic aqueous nanoscale Ga/In tridecameric clusters is presented. These hydroxo-aquo species significantly expand the library of discrete, aqueous group 13 clusters. This report details the synthetic and structural characterization of these compounds, which are of interest as precursors (inks) for thin-film oxides with materials applications. Single-crystal X-ray diffraction (XRD) data show that the hexagonal unit cell lengths of these clusters fall within the range a, b = 20.134-20.694 Å and c = 18.266-18.490 Å. The unit cell volumes become larger (V = 6494-6774 A(3)) with increasing indium occupancy. The compositions of several Ga/In clusters determined by electron probe microanalysis and elemental analysis are in agreement with single-crystal XRD results. The transformation of the Ga/In clusters to metal oxides at high temperature was studied using variable-temperature powder XRD. With heating, the Ga/In clusters with lower indium occupancies convert to the β-Ga2O3 structure. For clusters with higher indium occupancies, phase separation occurs, and an In2O3 bixbyite-type structure forms. The stoichiometric control at the molecular level demonstrated herein is important in designing functional thin films of metal oxides due to the tunable nature of these heterometallic solution precursors. In addition, information about the solid-state structure of these compounds leads to a fundamental understanding of the materials properties of these clusters for future thin-film and precursor development.