The complex [(CH3)(4)N](3)[Pt(SnCl3)(5)] was selected as a molecular precursor to prepare PtSn/gamma (c)-Al2O3 reforming catalysts. The spectroscopic fingerprints of the starting complex were obtained by Pt-195 and Sn-119 NMR and diffuse reflectance UV-visible spectroscopy. A series of supported catalysts were synthesized by wet impregnation of alumina with a solution of the precursor in acetone. Well-dispersed species are obtained for Pt loadings below 1 wt.%; at higher loadings, a second species is formed that has spectroscopic features reminiscent of the initial complex and precipitates as a separate phase. Apparently, the Pt-Sn bonds are hydrolyzed in the low-loading species and preserved in the high-loading species. The thermal transformations of PtSn/gamma (c)-Al2O3 catalysts are also studied and compared with those of the bulk precursor. In particular, it is shown that the nature of the atmosphere of thermal treatment (neutral or oxidizing) can orient the final catalyst towards preservation of an intimate Pt-Sn interaction, or towards demixtion.