Silver(I) ions bridged by pyridazine: doubling the ligand functionality for the design of unusual 3D coordination frameworks

Nitrogen donor tetradentate ligands 4,4'-bipyridazine (bpdz) and pyridazino[4,5-d]pyridazine (pp) were prepared by inverse electron demand Diels-Alder cycloaddition reactions of 1,2,4,5-tetrazine. Examination of their behaviour towards silver(I) ions revealed a special potential of the ligands for the design of 3D coordination frameworks involving characteristic polynuclear and polymeric silver(I)-pyridazine motifs and multiple coordination of the ligands. Ag4(pp)5(ClO4)4 and Ag4(pp)5(SiF6)(BF4)(2).4H2O adopt a unique 3D trinodal 4,4,5-connected topology based upon five-fold coordination of the metal ions and tetradentate bridging function of the organic modules. Complexes Ag3(L)3(SO3CF3)3.nH2O and Ag4(L)3(X)4.nH2O (L = bpdz, pp; X = BF4-, 0.5SiF(6)(2-)) illustrate formation of highly-connected frameworks incorporating trinuclear clusters as an origin of the net connectivity. In the carboxylate complexes Ag2(L)(R(F)COO)2 (R(F) = CF3, C2F5, C3F7) the pyridazine and acido ligands act as complementary linkers for generation of 3D frameworks involving helicate motifs. Fused bicyclic pyridazine pp is a unique system combining very efficient sigmaN-donor ability and pronounced pi-acidity. The coordination frameworks commonly exhibit strong anion-pi interactions, including unprecedented examples of double anion-pi,pi binding that occur between pyridazino[4,5-d]pyridazine as a double pi,pi-receptor for geometry complementary SiF(6)(2-) anions.