Structure, Luminescence, and Vapochromism of Bridged Cationic Copper(I) Dimers and Polymers

Abstract

The dimeric complex of Cu(I) [Cu2(PPh3)4(MeCN)2(Bpy)](BF4)2 (1a, Bpy = 4,4′-dipyridyl) self-assembles in CH2Cl2 or acetone and shows intense photoluminescence (excitation λmax = 356 nm, emission λmax = 486 nm, ϕ = 0.47). The MeCN ligands are readily removed from 1a, producing [Cu2(PPh3)4(Bpy)](BF4)2 (1b) and altering the photophysical behavior (excitation λmax = 336 nm, emission λmax = 568 nm, ϕ = 0.07). The desolvated compound 1b reversibly absorbs many vapor phase nucleophiles, as revealed by thermogravimetry. Intense luminescence emission is restored for 1b/Nu, Nu = MeCN (1a), acetone, tetrahydrothiophene (THT), and Et2S. Films of 1b are produced when CH2Cl2 solutions of 1a are cast onto glass. The films also react with Nu vapor, again producing intense emission. The pyrazine-bridged dimer [Cu2(PPh3)4(MeCN)2(Pyz)](BF4)2 (2a) is produced in CH2Cl2, while [Cu2(PPh3)4(MeCN)(acetone)(Pyz)](BF4)2∙½[Cu2(PPh3)4(MeCN)2(Pyz)](BF4)2 (2b) is formed in acetone. The crystal structure of the polymer {[Cu(PPh3)2(Bpy)](BF4)∙acetone} n (3) is reported, as is the mixed polymer/dimer structure {[Cu(PPh3)2(Pyz)](BF4)} n ∙½n[Cu2(PPh3)4(BF4)2(Pyz)] (4b) in which the dimer units show Cu–FBF3 coordination. The Pyz dimer and the Pyz and Bpy polymers show much weaker luminescence behavior than that of Bpy dimers 1a and the related 1b/Nu adducts. Nucleophile adduct structures [Cu2(PPh3)4(THT)2(Bpy)](BF4)2∙½ethyl ether (5) and [Cu2(PPh3)4(Py)2(Bpy)](BF4)2∙CH2Cl2 (6) confirmed the coordination of one Nu per Cu to 1b.