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 (H 2 L 1 ·(PF 6 ) 2 ), 2,2‘-bis( N -(pyridylmethyl)imidazoliumyl)ethyl ether (H 2 L 2 ·(PF 6 ) 2 ), 2,6-bis( N- (pyridylmethyl)imidazoliumyl)pyridine (H 2 L 3 ·(PF 6 ) 2 ), and 3,6-bis( N- (pyridylmethyl)imidazoliumyl)pyridazine (H 2 L 4 ·(PF 6 ) 2 ) have been prepared and characterized. They reacted with Ag 2 O in acetonitrile to produce the silver complexes [Ag 4 (L 1 ) 2 (CH 3 CN) 2 ](PF 6 ) 4 ·2CH 3 CN ( 1 ), [Ag 4 (L 2 ) 2 ](PF 6 ) 4 ·2CH 3 CN ( 2 ), [Ag 4 (L 3 ) 2 ](PF 6 ) 4 ·Et 2 O·CH 3 CN ( 4 ), and [Ag 6 (L 4 ) 4 ](PF 6 ) 6 ( 5 ), respectively. The reaction of 2 with 4 equiv of Au(Et 2 S)Cl afforded the dimetallic gold complex [Au 2 (L 2 )](PF 6 ) 2 ·2CH 3 CN ( 3 ). Complexes 1 − 4 were characterized by 1 H NMR, 13 C 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 L 2 or L 3 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 L 2 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 L 4 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.