Polymorph Control of Luminescence Properties in Molecular Crystals of a Platinum and Organoarsenic Complex and Formation of Stable One-Dimensional Nanochannel

The
mononuclear diiodoplatinum­(II) complex (trans-PtI2(cis-DHDAMe)2), where cis-DHDAMe = cis-1,4-dihydro-1,4-dimethyl-2,3,5,6-tetrakis­(methoxycarbonyl)-1,4-diarsinine,
forms three different crystalline polymorphs that can be either concomitantly
or separately obtained on varying the recrystallization conditions.
Cubic red crystals (α-phase) and red-orange needles (β-phase)
exhibit solid-state red emissions at room temperature. Cubic red crystals
of the γ-phase show no solid-state emission at room temperature.
All crystalline structures were confirmed by X-ray crystallography.
Room-temperature strongly luminescent crystals (α-phase) (λem = 657 nm, Φ = 0.52) have a triclinic P1̅ (No. 2) structure and no voids in the crystal structure.
Red-orange needle-shaped crystals of the β-phase exhibit moderate
red luminescence (λem = 695 nm, Φ = 0.09) at
room temperature and have a trigonal, R3̅ (No.
148), structure. In the needlelike crystals of the β-phase,
stable hexagonal arrays of nanoporous channels, 5.0 Å in diameter,
are formed. Room-temperature nonluminescent crystals (γ-phase)
have an orthorhombic, Pbca (No. 61), structure with
a void volume that is 4.9% of the total crystal volume. After heating
the α-phase crystals at 150 °C for 2 min, a powder XRD
pattern different from the original crystal is obtained, and its solid-state
emission at room temperature decreased. After heating the β-phase
crystals at 150 °C for 2 min, the emission wavelength and the
quantum yield of the solid-state emission at room temperature and
the powder XRD pattern are the same as those of the α-phase
after heating at 150 °C. A crystal-to-crystal transition triggered
by the thermal stimulus produces a different stable polymorph of the
mononuclear diiodoplatinum­(II) complex. The one-dimensional nanoporous
crystals encapsulated iodine without distorting the crystal packing.