Complexes and salts of the nitrogen-rich triazole–tetrazole hybrid ligand with alkali and alkaline earth metal cations: experimental and theoretical findings
Reaction of the nitrogen-rich triazole–tetrazole hybrid ligand 5-(4H-1,2,4-triazol-yl)-2H-tetrazole (trz–tetH) with Li+, Na+, K+ and Ba2+ in water leads to the coordination polymers [Li(trz–tet)H2O]n, [Na(trz–tet)(H2O)2]n, [K(trz–tetH)(trz–tet)(H2O)2]n and [Ba2(trz–tet)4(H2O)9]n, exhibiting different topologies and coordination modes. Salt-like structures with anionic triazole–tetrazole building blocks [Mg(H2O)6](trz–tet)2 and [Ca(H2O)8](trz–tet)2 were also obtained. All structures were simplified by topological analysis, which showed that the structures of [Mg(H2O)6](trz–tet)2 and [Ca(H2O)8](trz–tet)2 can be considered as underlying networks, constructed from the hydrogen bonded [Mg(H2O)6]2+ or [Ca(H2O)8]2+ cations and trz–tet ligands, with the rare binodal 5,10-connected topology alb-5,10,P21/c-1 and a unique binodal 5,12-connected topology, respectively. According to TGA/DTA analysis, all compounds show endothermic mass losses below 200 °C due to dehydration processes. The dehydrated residues are stable up to 300 °C. It was also established that the anionic form of the coordinated ligand trz–tet decomposes with an abrupt mass loss accompanied by a sharp and intense exothermic effect, while the non-coordinated trz–tet, as in the structures of the Mg- and Ca-based compounds, decomposes with a more gradual mass loss and significantly broad exothermic effect. Static DFT, ab initio molecular dynamics simulations as well as charge and energy decomposition (ETS-NOCV) based studies are performed in order to shed light on the stability of the newly obtained crystals.