"On-off" Au(I)...Cu(I) interactions in a Au(NHC)2 luminescent vapochromic sensor.

Reaction of the Au(I) N-heterocyclic carbene (NHC) compound [Au(im(CH(2)py)(2))(2)]PF(6) with 2 equiv of [Cu(MeCN)(4)]PF(6) affords the tricationic compound [Au(im(CH(2)py)(2))(2)(Cu(MeCN)(2))(2)](PF(6))(3) (1), which exhibits blue luminescence (lambda(max) = 462 nm). Reaction of 1 with either liquid MeOH or MeOH vapor affords [Au(im(CH(2)py)(2))(2)(Cu(MeOH))(2)](PF(6))(3) (2), which produces green luminescence (lambda(max) = 520 nm) under UV excitation. The molecular structures of 1 x 2MeCN and 2 x 2MeOH.2Et(2)O were determined by single-crystal X-ray diffraction. Compound 1 contains a linearly coordinated [Au(NHC)(2)](+) core in which each picolyl side arm bridges a [Cu(MeCN)(2)](+) center. The Au...Cu separations are long at 4.596 A. Compound 2 exhibits two short Au...Cu interactions of 2.7195(7) A, with the Au(NHC)(2) core acting as an additional ligand toward each copper center to complete its tetrahedral coordination mode. Exposure of 2 to atmosphere produces a partial loss of MeOH accompanied by a luminescence color change to yellow (lambda(max) = 543 nm). The uptake and loss of MeOH vapor is rapid and reversible. Exposure of 2 to vacuum affords complete loss of MeOH, and the luminescence changes to yellow-orange (lambda(max) = 573 nm). Treatment of 2 with MeCN vapor regenerates 1. The interconversion of 1 and 2 was confirmed by powder X-ray diffraction. Compound 1 also reacts with acetone and H(2)O vapors, leading to species that produce yellow-orange (lambda(max) = 591 nm) and green (lambda(max) = 519 nm) emission, respectively. Compounds 1 and 2 are examples of molecular vapochromic materials that exhibit large changes in the emission though ligand substitution reactions between the solid complex and solvent vapors. The dramatic color change likely results from the "on-off" Au...Cu interactions induced by the ligand exchange reaction.