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-(C 2 H 5 )C 6 H 4 ) 2 (CN)2 (abbreviated PtC 2 ) is conveniently synthesized by the thermal rearrangement of [Pt(CN-p-(C 2 H 5 )C 6 H 4 ) 4 ][Pt(CN) 4 ]. Recrystallization of PtC 2 gives a crystalline orange morph (O-PtC 2 ) and an amorphous purple morph (P-PtC 2 ) 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-PtC 2 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 λ max values (nm) for emission from O-PtC 2 -(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-PtC 2 from dichloromethane/toluene gave single crystals of PtC 2 -0.5(toluene). The single-crystal X-ray structure of PtC 2 -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 PtC 2 -0.5(toluene) is c/4 = 3.288(2) A. There are solvent channels parallel with the c axis that contain the toluene molecule guests. Thin films of O-PtC 2 rapidly sorb toluene from the gas phase to form PtC 2 -0.25(toluene) and PtC 2 -0.5(toluene). Long-term exposure gives PtC 2 -1.0(toluene). Removal of the toluene source causes rapid desorption to PtC 2 -0.5(toluene) and then to PtC 2 -0.25(toluene). The remaining 0.25(toluene) lattice guests require heating for rapid removal. X-ray powder diffraction identified the PtC 2 , PtC 2 -0.25(toluene), and PtC 2 -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.