Co-ordinative versatility of 3,5-bis(2-pyridyl)pyrazole in silver and copper compounds

Abstract

Two silver(I) and one copper(II) complex with 3,5-bis(2-pyridyl)pyrazole (Hbpypz) have been synthesized and their molecular structures determined by X-ray crystallography. In the dinuclear complex [Ag₂(Hbpypz)₄][CIO₄]₂·2Me₂CO there are two crystallographically independent monomeric units linked by intramolecular hydrogen bonds. In each unit Hbpypz only uses two of its four nitrogen atoms, acting as a typical bidentate chelate ligand. In the polymeric complex {[Ag(Hbpypz)]CIO₄}∞ each silver(I) ion is co-ordinated to three nitrogen atoms of two different Hbpypz molecules and each ligand in turn bridges two spearate Ag atoms forming an infinite-chain structure of macrocations with non-interacting CIO₄^– anions. The tetranuclear complex [Cu₄(bpypz)₄(CIO₄)₄]·2H₂O consists of two weakly associated dimeric units coupled via intramolecular stacking between the pyridine and pyrazole rings with an average spacing of 3.50 Å, which gives rise to charge-transfer absorption bands in the near-UV region. The temperature dependence of the ESR spectrum and magnetic susceptibility indicates the presence of an antiferromagnetic interaction in the system. While Hbpypz is strictly planar in the copper(II) complex, a non-coplanar conformation is observed in both silver(I) complexes, indicative of the unique co-ordinative versatility of the pyrazole derivative.