PH dependent synthesis of structurally diverse praseodymium(III) coordination polymers based on isomeric ligands

Abstract

Reactions of two isomeric ligands, 5-(n-pyridyl)tetrazole-2-acetato potassium salt (Kn-pytza, n=2,4) and PrCl3·6H2O under solvothermal conditions, afforded three new complexes, [Pr(2-pytza)(SO4)(H2O)3]·H2O(1), [Pr(4-pytza)3(H2O)2]·2H2O (2) and [Pr4(4-pytza)5(OH)4(H2O)7Cl]Cl2·4H2O (3), whose structures are controlled by not only the different positions of the nitrogen atom of the pyridine ring but also the pH value of the solvent system. These compounds have been characterized by elemental analysis, IR and single crystal X-ray diffraction. The X-ray analysis reveals that compound 1 is a two dimensional layer structure made up of a Pr2O6 binuclear unit and the tridentate bridging SO42− ligand; compound 2 is an unusual one dimensional ladder like chain structure consisting of a Pr2O10 binuclear unit and 4-pytza which acts as a tetradentate ligand via the pyridine-N and the carboxylate group in a μ1,1,3-COO bridging mode while compound 3 is an unprecedented two dimensional network composed of a tetranuclear cubane-shaped Pr4(OH)48+ cluster (SBU) and tridentate 4-pytza via the pyridine-N and the carboxylate group in a μ1,3-COO bridging mode. Various hydrogen bonds exist to assemble the 1D chains or 2D layers into 3D supramolecular network structures. Furthermore, the luminescence properties investigated at room temperature in the solid state show only intraligand emission for 1 and both intraligand and characteristic peaks of Pr3+ for either compound 2 or 3.