Synthesis, Structural Characterization, and Luminescence of New Silver Aggregates Containing Short Ag−Ag Contacts Stabilized by Functionalized Bis(<i>N</i>-heterocyclic carbene) Ligands

Abstract

The imidazolium salts bis(N-(pyridylmethyl)imidazoliumyl)methane hexafluorophosphate (H2L1·(PF6)2), 2,2‘-bis(N-(pyridylmethyl)imidazoliumyl)ethyl ether (H2L2·(PF6)2), 2,6-bis(N-(pyridylmethyl)imidazoliumyl)pyridine (H2L3·(PF6)2), and 3,6-bis(N-(pyridylmethyl)imidazoliumyl)pyridazine (H2L4·(PF6)2) have been prepared and characterized. They reacted with Ag2O in acetonitrile to produce the silver complexes [Ag4(L1)2(CH3CN)2](PF6)4·2CH3CN (1), [Ag4(L2)2](PF6)4·2CH3CN (2), [Ag4(L3)2](PF6)4·Et2O·CH3CN (4), and [Ag6(L4)4](PF6)6 (5), respectively. The reaction of 2 with 4 equiv of Au(Et2S)Cl afforded the dimetallic gold complex [Au2(L2)](PF6)2·2CH3CN (3). Complexes 1−4 were characterized by 1H NMR, 13C NMR, luminescence spectroscopy, elemental analyses, and X-ray crystallography. Complex 1 is a tetrasilver complex consisting of a zigzag silver chain with silver−silver separations of 2.911(1) and 3.288(1) Å. Complexes 2 and 4 have orthogonal tetrasilver cores in which four silver atoms are held together by two L2 or L3 ligands with relatively short Ag−Ag contacts ranging from 2.790(1) to 3.293(2) Å. The digold complex consists of a macrometallocycle formed by two gold atoms and one L2 ligand, and the intramolecular Au−Au bond distance is 3.267(1) Å. Complex 5 is a hexamer with six silver atoms bridged by four L4 ligands forming three silver−silver bonds of distances 3.249(2), 3.014(2), and 3.089(2) Å. ESI-MS spectra show that these multinuclear silver cores are retained in acetonitrile solution. All of these silver complexes are intensely luminescent in their solid state.