Periana et al. [Science 1998, 280, 560] previously reported two catalysts for low-temperature methane activation to methanol: PtCl2(NH3)2 and PtCl2(bpym). It was shown that the ammine catalyst is much more active, but it decomposes rapidly in sulfuric acid to form a PtCl2 precipitate, while the bpym system is long-lived. To have a basis for developing new catalysts that would not decompose, we undertook a study of the structure, bonding, and stability of the PtCl2(NH3)2 and PtCl2(bpym) catalysts, using quantum mechanics (QM) [density functional theory (DFT) at the B3LYP/LACVP**(+) level] including solvation in sulfuric acid via the Poisson−Boltzmann continuum approximation. Critical results include the following: (1) The influence of a trans ligand Y on the Pt−X bond follows the order Cl- > NH3 (bpym) > OSO3H- > □ (empty site). Thus the Pt−N bond length is longer (up to 0.04 A) and the Pt−N bond is weaker (up to 18 kcal/mol) when trans to a Cl- as compared to trans to OSO3H-. (2) The bpym ligand acts as...