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 Ag ₄(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^-, 0.5SiF₆^2-) illustrate formation of highly-connected frameworks incorporating trinuclear clusters as an origin of the net connectivity. In the carboxylate complexes Ag₂(L)(R_FCOO)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 σ_N-donor ability and pronounced π-acidity. The coordination frameworks commonly exhibit strong anion-π interactions, including unprecedented examples of double anion-π,π binding that occur between pyridazino[4,5-d]pyridazine as a double π,π-receptor for geometry complementary SiF₆^2- anions.