The reaction of zirconium salts with meso-tetra(4-carboxyphenyl)porphyrin (TCPP) in the presence of different modulators results in the formation of a diverse set of metal-organic frameworks (MOFs), each displaying distinct crystalline topologies. However, the synthesis of phase-pure crystalline frameworks remains challenging due to the concurrent formation of different polymorphs. The acidity and concentration of the modulator greatly influence the outcome of the MOF synthesis. By systematically varying these two parameters, selective framework formation can be achieved. In the present study, we aimed to elucidate the effect of modulator on the synthesis of zirconium-based TCPP MOFs. With the help of powder X-ray diffraction and scanning electron microscopy, modulator candidates and the optimal synthetic conditions yielding phase-pure PCN-222, PCN-223, and MOF-525 were identified. H-1 nuclear magnetic resonance analysis, thermogravimetric analysis, and N-2 gas sorption measurements were performed on select MOFs to gain insight into the relationship between their defectivity and modulator properties.