Two heterometallic complexes, [Pt₂MCl(bipy)(PPh₃)₄(μ₃-S)₂][PF₆] (M = Zn, 2, Cd, 3) were synthesized from [Pt₂(PPh₃)₄(μ-S)₂] and characterized by single-crystal X-ray diffraction and electrospray ionization mass spectrometry. Two unusual square-based pyramidal (sbp) Zn(II) and Cd(II) structures are evident. VT 31P-{1H} NMR studies showed that 2 and 3 are fluxional at rt whereby rapid ligand exchange takes place by a non-dissociative mechanism. At intermediate temperatures, this motion slows down to a flipping movement of the {Pt₂S₂} ligand. At 183 K, all four phosphines are inequivalent in a distorted sbp model similar to that observed in the solid state. Nonlocal density functional theory calculations reveal that the formation of a trigonal bipyramidal intermediate in the fluxional process is favored over that of the tetrahedral species for both 2 and 3. The M–Cl (M = Zn, Cd) bonds are notably strong.