Versatile binding behaviour of 4,6-dimethyl-1,2,3-triazolo[4,5-d]-pyrimidin-5,7-dionato in the presence of bipyrimidine. Supramolecular H-bond architectures

Abstract

Complexes with the ligand 4,6-dimethyl-1,2,3-triazolo-[4,5-d]-pyrimidin-5,7-dionato (dmax⁻) and the auxiliary chelating-bridging ligand bipyrimidine (bpym) have been synthesized and structurally characterized for the divalent cations of Zn, Cd and Cu. For Zn and Cd, dinuclear complexes with the formulae [Zn₂(dmax)₄(H₂O)₂(bpym)]·2H₂O and [Cd₂(dmax)₄(H₂O)₄(bpym)]·6H₂O have been isolated whereas for Cu, the one-dimensional polymer {[Cu₂(dmax)₄(bpym)]·5H₂O}_n has been obtained. Bpym acts as a chelating-bridging ligand in the three compounds, joining couples of metal ions. Two crystallographically and chemically different dmax⁻ ligands are present in each of these complexes, one monodentately linked via the triazole N atom furthest from the pyrimidine ring (N2) and the other either monodentately linked via the triazole N atom closer to a carbonyl group (N1, Zn and Cd compounds) or in bridging N1-N2 mode (Cu compound), in the latter case generating an one-dimensional polymer with alternating bpym and (dmax)₂ bridges. The magnetic interaction across the bpym bridge gives rise to a strong antiferromagnetic interaction (2J = −201 cm⁻¹), whereas that across the (dmax)₂ bridge is negligible and cannot be reliably determined (obscured by the strong one). The hydrogen bonds between water molecules and the triazolopyrimidine derivative build the 3-D structure of the compounds.