Crystal Structures and Luminescence Properties of Platinum(II) Complexes Containing 3,3‘-Biisoquinoline

Three new platinum complexes containing 3,3‘-biisoquinoline (i-biq), [Pt(CN)2(i-biq)] (1), [PtCl2(i-biq)] (2), and [Pt(i-biq)2](PF6)2 (3), have been synthesized as orange-red, yellow, and colorless crystals, respectively. Their crystal structures and luminescence properties are reported. Crystal data: for 1·0.5H2O, PtO0.5N4C20H13, orthorhombic, Pbcm, a = 13.989(2) Å, b = 18.304(1) Å, c = 6.682(3) Å, V = 1710.9(6) Å3, Z = 4, and final R = 0.039 (Rw = 0.033) for 970 independent reflections; for 2·DMF·H2O, PtCl2O2N3C21H21, triclinic, P1̄, a = 11.047(1) Å, b = 12.397(3) Å, c = 8.000(2) Å, α = 106.56(1)°, β = 100.15(1)°, γ = 76.15(1)°, V = 1012.8(3) Å3, Z = 2, and final R = 0.058 (Rw = 0.077) for 4219 independent reflections; for 3·2DMF, PtP2F12O2N6C42H38, triclinic, P1̄, a = 10.795(2) Å, b = 13.511(2) Å, c = 8.281(1) Å, α = 105.22(1)°, β = 112.17(1)°, γ = 85.02(1)°, V = 1079.2(3) Å3, Z = 1, and final R = 0.038 (Rw = 0.042) for 3606 independent reflections. Square-planar complexes of 1 are stacked in the crystal to form a columnar structure with the Pt−Pt distance of 3.34 Å. The crystal emits strongly, even at room temperature, and the emission spectrum is similar to that for the [Pt(CN)2(bpy)] crystal (bpy = 2,2‘-bipyridine), which is due to a 3dπ*[dσ*(Pt) → π*(i-biq)] transition. The single crystal emission spectrum at 77 K is, however, observed as a superposition of broad 3dπ* and sharp 3ππ*(i-biq) emissions. The crystal structure of 2 has a completely different stacking structure from that of 1. The stacking occurs on the i-biq ligands, and the Pt atoms are separated more than 6 Å. The complex exhibits only a structured emission component assigned to the 3ππ*(i-biq) transition in the crystal at 77 K, in agreement with the crystal structure with no Pt−Pt interaction. In the crystal of 3, the [Pt(i-biq)2]2+ complexes are stacked but offset, being in close contact between parts of adjacent i-biq ligands. There is no Pt−Pt interaction also in this case. Two i-biq ligands in the complex are distorted to adopt the bowed conformation due to the steric crowding of the α-hydrogens on opposite ligands. Nevertheless, 3 provides almost the same 3ππ* emission spectrum as 1 and 2 in dilute glassy solution at 77 K. The 3ππ* emission spectra observed in the crystals of these Pt(II) complexes are red-shifted compared with those in dilute glassy solution. The fact is attributable to the π−π intermolecular interactions between the ligands in the crystals. The factors controlling the crystal structures for these complexes are also discussed.