A polymorphic platinum(II) complex: Yellow, red, and green polymorphs and X-ray crystallography of [Pt(fdpb)Cl] [Hfdpb = 1,3-Bis(5-trifluoromethyl-2- pyridyl)benzene]

We investigated polymorphism in [Pt(fdpb)Cl] [Hfdpb = 1,3-bis(5- trifluoromethyl-2-pyridyl)benzene]. The following polymorphs of the complex were crystallized: yellow [Form Y; orthorhombic, Pca2₁, a = 23.4336(14) Å, b = 4.6377(2) Å, c = 15.7845(9) Å, Z = 4], red [Form R; monoclinic, C2/c, a = 21.3619(12) Å, b = 13.5629(7) Å, c = 13.6974(6) Å, β = 122.301(2)°, Z = 8], and dark green [Form G; monoclinic,P2₁/a, a = 6.7953(4) Å, b = 18.2519(12) Å, c = 13.5199(8) Å, β = 96.039(2)°, Z = 4]. The yellow color of Form Y was due to the influence of stacking on the π,π* absorption of the Pt molecule; the red color of Form R originated from a MMLCT absorption due to Pt-Pt interactions in a closely stacked dimer; and the dark green of Form G was attributed to the absorption of a linear array of Pt^II complexes. The polymorphs emitted luminescence at around 550 (Form Y), 670 (Form R), and 750 nm (Form G). Mechanical grinding of the crystals changed the polymorphs from the crystalline to the amorphous phase; the emission spectra of ground samples of Forms Y and R, observed at 750 nm, were identical. When the amorphous solid was heated to around 500 K, the emission spectrum was blueshifted to 670 nm due to a phase transition from amorphous to crystalline. Heating also caused a crystal-crystal transformation; phase transitions from Form G to Form R and Form R to Form Y proceeded at 430-470 and 540-560 K, respectively. Polymorphs of a platinum(II) complex were prepared, and their crystal structures were clarified by X-ray crystallography. Mechanical grinding changed the polymorphs from the crystalline to the amorphous phase. Heating caused the transition between the amorphous and the crystal phase and the crystal-crystal transformations of the green form to the red from and of the red form to the yellow form.