Superconductivity in the new Platinum Germanides APt$_4$Ge$_{12}$ (A=Sr,Ba,La,Pr)

New germanium-platinum compounds with the filled-skutterudite crystal structure were synthesized. Magnetic susceptibility, specific heat, and electrical resistivity measurements find superconductivity in LaPt$_4$Ge$_{12}$ and PrPt$_4$Ge$_{12}$ below ca.\ 8\,K. The parameters of the normal and superconducting states were established. Strong electron-phonon coupling and a crystal electric field singlet groundstate is found for the Pr compound. Electronic structure calculations show a large density of states at the Fermi level, predominantly due to Ge $4p$ orbitals. Similar behavior, albeit with lower $T_c$, was observed for SrPt$_4$Ge$_{12}$ and BaPt$_4$Ge$_{12}$.