Spectroscopic properties of luminescent platinum(II) complexes containing 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine (tBu3tpy). Crystal structures of [Pt(tBu3tpy)Cl]ClO4 and [Pt(tBu3tpy){CH2C(O)Me}]ClO4

Abstract

The 77 K emission spectrum of [Pt(tBu3tpy)Cl]ClO4, 1(ClO4) (tBu3tpy = 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine), in a 10-3 mol dm-3 MeOH/EtOH glassy solution exhibits a 625 nm band attributed to tBu3tpy π-π interactions, whereas a dilute solution (10-6 mol dm-3) shows a vibronic intraligand emission at λmax 467 nm. By comparing the UV-vis spectra of 1 with the 1IL-dominated spectrum of [Au(tBu3tpy)Cl]2+ (4) in CH3CN, the moderately intense absorption band at λmax 373-386 nm for the former is ascribed to a 1MLCT [(5d)Pt → π*(tBu3tpy)] transition. The absorption spectrum of 1 contains a weak shoulder at 465 nm (∈ = 57 dm3 mol-1 cm-1) which obeys Beer's law in the concentration range 5 × 10-4 to 1 × 10-2 mol dm-3, and a 3MLCT assignment is proposed. Ketonyl platinum(II) complexes [Pt(tBu3tpy){CH2C(O)R}]ClO4 (R = Me, 2 and R = Ph, 3) have been prepared from 1(ClO4) in the presence of aqueous NaOH and the corresponding methyl ketone. The molecular structures of 1(ClO4) and 2(ClO4)·C2H5OH reveal π-stacking orientations for the tBu3tpy ligands with interplanar separations of ca. 3.8 and 3.6 Å, respectively. Complexes 2 and 3 are luminescent in solution at room temperature, and 3MLCT excited states are assigned, while 1 is nonemissive. The superior photophysical properties of 2 and 3 are ascribed to the stronger σ-donating ability of the ketonyl ligands. Like 1, complexes 2 and 3 also display low-energy emission at ca. 620 nm in 10-3 mol dm-3 MeOH/EtOH glass at 77 K. Complex 1(ClO4) is emissive in crystalline form at 77 K only (λmax 560 nm). Solid-state emissions of 2(ClO4) and 3(ClO4) at room temperature (λmax 607 and 615 nm, respectively) are derived from weak stacking interactions between tBu3tpy groups, while their emission maxima are red-shifted at 77 K. © 1999 American Chemical Society.