Anisometric cyclometalated palladium(II) and platinum(II) complexes. Structural and photophysical studies

Article abstract of DOI:10.1021/ic9703540

The potentially tridentate ligand 4′-[4-(dodecyloxy)phenyl]-6′-phenyI-2,2′-bipyridine (HL¹) easily undergoes metalation at the ortho-C atom, yielding the rodlike complexes [Pd(L¹)Cl] (1) and [Pt(L¹)Cl] (2). The solid state features and the photophysical properties of the complexes have been studied. Crystal data for 2: PtC₃₄H₃₉ClN₂O, triclinic, P1?, a = 9.043(2) A?, b = 10.874(2) A?, c = 15.710(4) A?, α = 96.95(2)°, β= 92.51(2)°, γ = 102.32(2)°, V = 1494.3(6) A?³, Z = 2, and final R = 0.0387 (R_w = 0.0335) for 4333 independent reflections. The electronic spectra of complexes 1 and 2 show intense absorption bands in the UV region due to metal-perturbed ligand-centered (LC) transitions. In addition, complex 2 shows a moderately intense metal-to-ligand charge-transfer (MLCT) band in the visible region. Both complexes 1 and 2 show luminescence, although under different conditions. Strong emission has been observed for a 77 K glassy solution (highest energy feature 495 nm; τ = 74 μs) or room-temperature crystal (λ_max = 490 nm) of 1. In both cases, the emission was assigned to a triplet LC excited state. Complex 2 exhibits emission from a ³MLCT level both in solution at room temperature (λ_max, = 590 nm; τ = 700 ns; φ = 0.037) and in glass at 77 K (λ_max = 545 nm; τ = 18 μs). The room-temperature emission of crystalline 2 (highest energy feature 590 nm) is also similar in energy to that observed in fluid solution and exhibits the typical MLCT vibrational progression, thus ruling out a contribution from either metal-metal or strong π-π interactions.