Spectroscopic Characterization of Platinum(IV) Terpyridyl Complexes

Pt(tpy)X3+ [X = Cl (1), Br (2); tpy = 2,2′:6′,2″-terpyridine] salts were prepared by the oxidative addition of Pt(tpy)X+ with X2 as originally reported by Morgan and Burstall in 1934. The complexes have been fully characterized by 1H NMR spectroscopy, elemental analysis, mass spectrometry, and X-ray crystallography. The electronic structures of 1 and 2 were investigated using absorption and emission spectroscopy, and the accumulated data are consistent with stabilization of the singlet ligand-centered and potentially singlet ligand field/singlet ligand-to-metal charge-transfer states for 1 and 2 compared to those for Pt(tpy)Cl+ (3) and Pt(tpy)Br+ (4). The changes in the lowest-energy-absorbing state result in drastic differences in the emission behavior among 1–4. Specifically, 1 emits from a lowest-energy state that appears to have triplet ligand field/triplet ligand-to-metal charge-transfer character, whereas 2 exhibits no appreciable emission between 400 and 800 nm.