Fully relativistic structures at Dirac-Coulomb-Kohn-Sham (DFT) level of theory for thallium(I)hydride and thallium(I)formiate are reported. The influence of spin-orbit coupling (SOC) on Tl-H and Tl-O distances were quantified. SOC shortens the Tl-H distance in TlH by 0.008 Å and the Tl-O distance in Tl[O2CH] by 0.006 Å.