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⁻, 0.5SiF₆²⁻) 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 SiF₆²⁻ anions.