Szilárd-Chalmers reactions are a potential alternative route to the production of medically important 99Mo. In this work, four substituted molybdenum(IV) oxophthalocyanines were synthesised, irradiated and analysed regarding syntheses and purification, thermal stability, radiochemical yield of 99Mo in the target material and substitution effects on the retention. Molybdenum(IV) oxophthalocyanines were synthesized from substituted (-F, -NO2, -CH3) 1,2-dicyanobenzenes with ammonium heptamolybdate tetrahydrate in a melt at 170 C. Purification by sublimation at 450 C and 0.06 mbar was successful for the unsubstituted material and gave a dark blue powder. The compounds were characterized by IR, UV/VIS and powder diffraction. The Mo=O vibration in IR spectra of the unsubstituted Molybdenum(IV) oxophthalocyanine (965 cm-1) and the calculated vibration at 994 cm-1 show good agreement and indicates the desired oxidation state of +IV for molybdenum - the absence of the MoN vibration at 1078 cm-1 confirms this. Irradiation experiments were carried out in dry irradiation tubes at the edge of the core (neutron flux: 2·1012 cm-2s-1) of the TRIGA mark II research reactor at the TU Wien. The highest radiochemical yields were obtained with the unsubstituted Molybdenum(IV) oxophthalocyanine, whereas the highest yields of carrier-free 99Mo after separation were obtained with the NO2 and CH3 substituted phthalocyanines (>90 %). Using a Linear Free Energy Relationships (LFER; Hammett-equation) substitution effects during irradiation were investigated. No substituent effect were observed in the radiochemical yields, whereas an influence on the retention seems likely. It seems that the recombination reaction resulting in retention of the activated nucleus involves a positive charge, but further experiments are required. From the results obtained in this work the methyl-substituted molybdenum(IV) oxophthalocyanine is the most promising candidate regarding synthesis, purification, irradiation and retention for further investigations.