Kinetic Formation of Pt–Pt Dimers of Cationic and Neutral Platinum(II) Complexes under Rapid Freeze Conditions in Solution

• Published in: Inorganic chemistry 2023-06, Vol.62 (24), p.9491-9500
• Main Authors: Hattori, Shingo, Kawajiri, Shusei, Sekine, Akiko, Sumi, Keisuke, Narumiya, Hitomi, Sato, Kyouhei, Shinozaki, Kazuteru
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.3c00820

We report the formation of M–M dimers (M = Pt or Pd) of cationic [M­(dpb)­(CH3CN)]+ [dpbH = 1,3-di­(2-pyridyl)­benzene] and neutral [M­(dpb)­Cl] complexes resulting from the rapid freezing of solutions. Dimers based on M–M dz2 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 charge-transfer 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)­(CH3CN)]­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.