4,4′-Bipyridazine: a new twist for the synthesis of coordination polymers

Abstract

A new polydentate ligand 4,4′-bipyridazine (4,4′-bpdz) was prepared by employing inverse electron demand cycloaddition of 1,2,4,5-tetrazine. A unique combination of structural simplicity, ampolydentate character and efficient donor properties towards Cu(I), Cu(II) and Zn(II) provide wide new possibilities for the synthesis of coordination polymers incorporating the 4,4′-bpdz module either as a bi-, tri- or tetradentate connector between the metal ions. 1D coordination polymers Cu₂(4,4′-bpdz)(CH₃CO₂)₄·4H₂O and Zn(4,4′-bpdz)(NO₃)₂, and interpenetrated (4,4)-nets in [Cu(4,4′-bpdz)₂(H₂O)₂]S₂O₆ were closely related to 4,4′-bipyridine compounds. 1D “ladder-like” polymer Cu₂(4,4′-bpdz)₃(CF₃CO₂)₄ and the unprecedented 3D binodal net ({8⁶}{6³;8³}) in [Cu₃(4,4′-bpdz)₆(H₂O)₄](BF₄)₆·6H₂O were based upon a combination of linear and angular organic bridges. Complex [Cu₃(OH)₂(4,4′-bpdz)₃(H₂O)₂{CF₃CO₂}₂](CF₃CO₂)₂·2H₂O has a “NbO-like” 3D topology incorporating discrete dihydroxotricopper(II) clusters linked by tri- and tetradentate ligands. The tetradentate function of the 4,4′-bpdz ligand was especially relevant for copper(I) complexes, which adopt layered Cu₂X₂(4,4′-bpdz) (X = Cl, Br) or 3D chiral framework (X = I) structures based upon infinite (CuX)_n chains. The electron deficient character of the ligand was manifested by short anion–π interactions (O–π 3.02–3.20; Cl–π 3.35 Å), which may be involved as a factor for controlling the supramolecular structure.