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

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 Cu-2(4,4'-bpdz)(CH3CO2)(4)center dot 4H(2)O 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 Cu-2(4,4'-bpdz)(3)(CF3CO2)(4) and the unprecedented 3D binodal net ({8(6)}{6(3);8(3)}) in [Cu-3(4,4'-bpdz)(6)(H2O)(4)](BF4)(6)center dot 6H(2)O were based upon a combination of linear and angular organic bridges. Complex [Cu-3(OH)(2)(4,4'-bpdz)(3)(H2O)(2){CF3CO2}(2)](CF3CO2)(2)center dot 2H(2)O 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-pi interactions (O-pi 3.02-3.20; Cl-pi 3.35 angstrom), which may be involved as a factor for controlling the supramolecular structure.