Synthesis and structural determination of four novel metal-organic frameworks in a Zn-3-amino-1,2,4-triazole system

Four new coordination polymer compounds have been prepared using 3-amino-1,2,4-triazole (AmTRZ) as an organic linker, namely, ZnCl(AmTRZ) (1), Zn(HCO ₂)(AmTRZ) (2), Zn ₅(OH) ₂(AmTRZ) ₆(NO ₃) ₂·6H ₂O (3), and Zn ₅(OH)(AmTRZH)-(AmTRZ) ₆(HCO ₂) ₃·5H ₂O (4). They were synthesized under mild hydro- or solvothermal conditions using water or dimethylformamide as solvent. Their crystal structures were characterized by single-crystal X-ray diffraction techniques, and thermal properties of all compounds were examined by thermogravimetric analysis. Isostructural compounds 1 and 2 (Pbca, a = 9.389(1) Å, b = 10.115(1) Å, c= 11.571(2) Å, V = 1098.9(3) Å ³, Z = 8 for 1 and a = 9.198(1) Å, b = 10.341(1) Å, c = 12.577(2) Å, V= 1196.2(3) Å, Z = 8 for 2) display a two-dimensional layer structure where Zn centers are linked by AmTRZ molecules to form gridlike layers containing eight-membered rings. Structure 3 (Pa3̄, a = 15.0448(6) Å, V = 3405.3(2) Å ³, Z = 4) is a dense three-dimensional framework, featuring seven-membered channels where water and nitrate anions are located. Structure 4 (I4/m, a = 19.2576(9) Å, c = 20.286(2) Å, V= 7523.2(9) Å ³, Z = 8) is built from porous Zn-AmTRZ layers containing 12- and 8-membered rings, which are connected to each other by dinuclear Zn tetrahedra building units. Water and formate anions occupy the void inside the framework.