Modulation of Metal–Metal Separations in a Series of Ag(I) and Intensely Blue Photoluminescent Cu(I) NHC-Bridged Triangular Clusters

A series of picolyl-substituted NHC-bridged triangular complexes of Ag(I) and Cu(I) were synthesized upon reaction of the corresponding ligand precursors, [Him(CH2py)2]BF4 (1a), [Him(CH2py-3,4-(OMe)2)2]BF4 (1b), [Him(CH2py-3,5-Me2-4-OMe)2]BF4 (1c), [Him(CH2py-6-COOMe)2]BF4 (1d), and [HSim(CH2py)2]BF4 (1e), with Ag2O and Cu2O, respectively. Complexes [Cu3(im(CH2py)2)3](BF4)3 (2a), [Cu3(im(CH2py-3,4-(OMe)2)2)3](BF4)3 (2b), [Cu3(im(CH2py-3,5-Me2-4-OMe)2)3](BF4)3, (2c), [Ag3(im(CH2py-3,4-(OMe)2)2)3](BF4)3, (3b), [Ag3(im(CH2py-3,5-Me2-4-OMe)2)3](BF4)3 (3c), [Ag3(im(CH2py-6-COOMe)2)3](BF4)3 (3d), and [Ag3(Sim(CH2py)2)3](BF4)3 (3e) were easily prepared by this method. Complex 2e, [Cu3(Sim(CH2py)2)3](BF4)3, was synthesized by a carbene-transfer reaction of 3e, [Ag3(Sim(CH2py)2)3](BF4)3, with CuCl in acetonitrile. The ligand precursor 1d did not react with Cu2O. All complexes were fully characterized by NMR, UV–vis, and luminescence spectroscopies and high-resolution mass spectrometry. Complexes 2a–2c, 2e, and 3b–3e were additionally characterized by single-crystal X-ray diffraction. Each metal complex contains a nearly equilateral triangular M3 core wrapped by three bridging NHC ligands. In 2a–2c and 2e, the Cu–Cu separations are short and range from 2.4907 to 2.5150 Å. In the corresponding Ag(I) system, the metal–metal separations range from 2.7226 to 2.8624 Å. The Cu(I)-containing species are intensely blue photoluminescent at room temperature both in solution and in the solid state. Upon UV excitation in CH3CN, complexes 2a–2c and 2e emit at 459, 427, 429, and 441 nm, whereas in the solid state, these bands move to 433, 429, 432, and 440 nm, respectively. As demonstrated by 1H NMR spectroscopy, complexes 3b–3e are dynamic in solution and undergo a ligand dissociation process. Complexes 3b–3e are weakly photoemissive in the solid state.