We report the formation of M−M dimers (M = Pt or Pd) of cationic [M(dpb)(CH 3 CN)] + [dpbH = 1,3-di(2pyridyl)benzene] and neutral [M(dpb)Cl] complexes resulting from the rapid freezing of solutions. Dimers based on M−M dz 2 overlap were found to preferentially form rather than the thermodynamically favored head-to-tail π-stacking structures typically observed in the crystalline state. Kinetic dimers in glassy frozen solutions generated broad metal-metal-to-ligand chargetransfer emissions within the range of 600−800 nm at 77 K. These emissions were red-shifted relative to monomer emissions. As expected, the degree of aggregation of these complexes was affected by the concentration in each solution. Photoexcitation evidently accelerated Pt−Pt dimerization even at ambient temperature. Electrostatic attraction between [Pt(dpb)Cl] + and [Pt(dpb)Cl] − ions resulting from disproportionation due to photoinduced electron transfer is thought to have driven excimer formation. [Pt(dpb)(CH 3 CN)]OTf (OTf − = trifluoromethanesulfonate ion) and its Pd(II) analogue were determined to have isostructural crystals, but a Pd−Pd stacked polymorph was not observed and the photophysics of the two complexes are evidently different.