Di-, tri-, and tetranuclear silver(I) complexes of phenanthroline-functionalized NHC ligands

A few polynuclear silver(I)–NHC complexes have been synthesized via the reactions of phenanthroline-functionalized imidazolium salts with Ag2O at room temperature. The structures of di-, tri-, and tetranuclear silver complexes were fully characterized. The two N-phenanthrolinylimidazolylidene ligands in [Ag4(L1)4](PF6)4 (1), [Ag2(L2)2](PF6)2 (2), and [Ag2(L3)2](PF6)2 (3) are head-to-head arranged. Complex 1 contains a short ligand-unsupported Ag–Ag bond being 3.152(1) Å representing the first example of strictly linear Ag4 cluster stabilized by NHCs. Trinuclear [Ag3(L4)2](PF6)3 (4) of phenanthroline-bridged biscarbene ligands contains a linearly arranged Ag3 core. [Ag3(L5)2](PF6)3 (5) and [Ag3(L4)2](PF6)3 (7) are also trinulear Ag(I) complexes. Binuclear [Ag2(L6)2](PF6)2 (6) exhibits a twisted macrocyclic structure with the Ag–Ag separation at 3.162(1) Å. In 1–4, the silver ions are held together by two ligands in close proximity with the Ag–Ag distances between 2.810(1) and 2.922(1) Å. The fluorescent properties of these silver complexes have also been briefly studied.