Synthesis and characterization of Pt(CN-p-(C2H5)C6H4)2(CN)2, a crystalline vapoluminescent compound that detects vapor-phase aromatic hydrocarbons

The vapochromic and vapoluminescent compound Pt(CN-p-(C2H5)C6H4)(2)(CN)(2) (abbreviated PtC2) is conveniently synthesized by the thermal rearrangement of [Pt(CN-p-(C2H5)C6H4)(4)][Pt(CN)(4)]. Recrystallization of PtC2 gives a crystalline orange morph (O-PtC2) and an amorphous purple morph (P-PtC2) that both contain the cis isomer and differ only in their solid-state packing arrangements. Both compounds were fully characterized by elemental analysis, X-ray powder diffraction, NMR, IR, and TGA. O-PtC2 is vapochromic and vapoluminescent: it reversibly sorbs aromatic hydrocarbons and ethanol from air or nitrogen with resulting color changes and shifts in the emission spectrum. The lambda(max) values (nm) for emission from O-PtC2.(guest) are as follows: no guest, 611; toluene, 565; benzene, 586; chlorobenzene, 592; p-xylene, 585; mesitylene, 565; ethanol, 587. In the case of toluene and mesitylene, intermediate emitting phases are observed. Recrystallization of O-PtC2 from dichloromethane/toluene gave single crystals of PtC2.0.5(toluene). The single-crystal X-ray structure of PtC2.0.5(toluene) contains infinite stacks of cis geometry and planar molecules with chains of platinum atoms parallel to the c axis of the monoclinic, unit cell. The average Pt-Pt separation in PtC2.0.5(toluene) is c/4 = 3.288(2) Angstrom. There are solvent channels parallel with the c axis that contain the toluene molecule guests. Thin films of O-PtC2 rapidly sorb toluene from the gas phase to form PtC2.0.25(toluene) and PtC2.0.5 (toluene). Long-term exposure gives PtC2. 1.0(toluene). Removal of the toluene source causes rapid desorption to PtC2.0.5(toluene) and then to PtC2.0.25(toluene). The remaining 0.25(toluene) lattice guests require heating for rapid removal. X-ray powder diffraction identified the PtC2, PtC2.0.25(toluene), and PtC2.0.5(toluene) phases and showed that the sorption of toluene is accompanied by small changes in the unit cell dimensions that include lengthening the Pt-Pt distances in the structure. The sorption process improves the packing in the structure by utilizing some of the free volume for the toluene lattice guests.