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.