Synthesis and properties of crown ether isocyanide silver(I) derivatives: X-ray structure of a self-assembled 22-membered diargentacycle

The crown ether isocyanide CNR (R = benzo-15-crown-5) reacts with silver(I) salts in the appropriate molar ratio to give [Ag(CNR)n]X (n = 1, 2; X = CF3SO3, BF4). X-ray diffraction studies of [Ag(CF3SO3)(CNR)] show the molecules associated in a dinuclear manner with an antiparallel orientation. The silver centers are tetracoordinated to the isocyanide and to three oxygens, one from the triflate anion and two from the second crown ether in the dimer. The molecular structure displays five cycles: the two 15-crown ether rings, two five-membered argentacycles and a 22-membered diargentacycle. The crown ether in these complexes is able to detect alkaline cations from M(CF3SO3) (M = Li, Na, K) by NMR in d6-acetone solutions, and to distinguish Li+–Na+ from K+.