Homometallic Silver(I) Complexes of a Heterotopic NHC-Bridged Bis-Bipyridine Ligand

By varying the metal to ligand ratio, stepwise formation
of a series
of homonuclear silver­(I) complexes of a carbene-bridged bis-bipyridine
ligand (L) was achieved. In the mononuclear 1:2 complex [AgL2]Br (1) only the carbene carbon is involved in the metal
coordination, while both of the 2,2′-bipyridine (bpy) arms
are free. When the amount of silver­(I) ion was increased, isomorphous
2:2 dinuclear complexes with different counteranions, [Ag2L2]­X2 (X = Br– (2a), PF6– (2b), BPh4– (2c)), were synthesized from the
ligand LX, in which the carbene carbon and one of the bpy units participate
in the coordination with silver­(I) ions. Further addition of AgI salt afforded the one-dimensional coordination polymer {[Ag3L2]­(PF6)3·4CH3CN}n (3), wherein the hanging
bipyridine units also coordinate with AgI and thus all
the coordination sites of the ligand are employed. The results reveal
the preference of AgI ion for the carbene carbon donor
rather than the bpy units. The synthesis, structures, and interconversion
of the complexes and the counteranion effects on the structures are
reported, and the luminescent properties of the ligand LX and the
silver complexes have also been studied.