In this contribution we demonstrate that metal-organic frameworks (MOFs) with suitable underlying topological structure are amenable for the preparation of MOF-based substitutional solid-solutions (SSS) that follow Vegard's law. Preparation of multivariate (MTV) libraries of Porous Interpenetrated Zirconia Organic Frameworks (PIZOF) using homeomorphic links of different length (18.6 and 19.3 Å) result in the formation of SSS that exhibit linearity between composition and structure. We prepared seven MTV MOF libraries (40 unique compositions) and observed relations in composition input/output ratio, composition/lattice parameter (Vegard's law), and between composition obtained from NMR and from PXRD. We further show that SSS formation has dependence on linker solubility, stability, and steric hindrance caused by the presence of functional groups. We demonstrate that solid-solution strategies can be utilized as part of the synthetic toolkit for the preperation of reticular crystals with desired composition, structure, and properties. In this contribution we demonstrate that metal-organic frameworks (MOFs) with suitable underlying topological structure are amenable for the preparation of MOF-based substitutional solid-solutions (SSS) that follow Vegard's law.