Inorganic Chemistry, Vol.58, No.11, 7385-7392, 2019
Stability Tuning of Vapor-Adsorbed State of Vapochromic Pt(II) Complex by Introduction of Chiral Moiety
New luminescent Pt(II) complexes with chiral ester chains, [PtCl2(R,R-bpybe)] (R-1; bpybe = 2,2'-bipyridine-4,4'-dicarboxylic acid dibutyl ester) and its racemic mixture (rac-1) with the chiral isomer, S-1, were synthesized, and their vapochromic behavior was investigated. Single-crystal X-ray structural analysis revealed that the rac-1 crystal was composed of only one crystallographically independent column formed by alternating stacking of R-1 and S-1 by the effective intermolecular PtPt interaction. In contrast, three types of columnar structures with different PtPt interactions were found for the R-1 crystal, probably because of the different packing of the chiral ester chains between the columns. Consequently, the estimated molecular volume of R-1 was slightly larger than that in the racemic crystal rac-1, although they have the same chemical formula. The X-ray structure of the toluene-adsorbed rac-1 (rac-1toluene) also indicated that the intermolecular PtPt interaction, which was effective for unsolvated rac-1, was completely canceled out by adsorption of toluene vapor. Both the rac-1 and R-1 crystals exhibited similar vapochromism driven by toluene vapor adsorption/desorption that switched the emission origin between the strongly emissive 3MMLCT (metalmetal-to-ligand charge transfer) to the weakly emissive 3 pi pi* phosphorescence. Although both crystals had the same chemical formula, the toluene vapor desorption temperature of R-1toluene (84 degrees C) was obviously lower than that of rac-1toluene (107 degrees C), suggesting that the binding interaction with toluene molecules was weaker in R-1toluene than in rac-1toluene.