Temperature-induced solvent assisted single-crystal-to-single-crystal transformation of Mg(II)-Ln(III) heterometallic coordination polymers

Abstract Two new heterometallic coordination polymers (CPs) [Ln2 (pydc)6Mg3(H2O)6]·11H2O (Ln ​= ​Eu (1), Tb (2); H2pydc ​= ​pyridine-2,6-dicarbolylic acid) were synthesized by solvothermal method at 120 ​°C in 48 ​h. Interestingly, after being left in the mother liquor for 3 days at room temperature, the crystal structures of the coordination polymers transform into anionic complexes 2 [Mg(H2O)6]·2 [Ln (pydc)3]·2Him·im•8H2O (Ln ​= ​Eu (3), Tb (4); im ​= ​imidazole; Him ​= ​protonated imidazole) by single-crystal-to-single-crystal transformation. The four complexes were characterized by elemental analysis, IR, TG, XRD as well as single-crystal X-ray diffraction. Coordination polymers 1 and 2 exhibit three-dimensional network structure and their topology symbol is {44.62}3{49.66}2, whereas complexes 3 and 4 are zero dimensional molecules. The luminescence properties of the complexes were determined at solid state. They show characteristic emission spectra of Eu(III) and Tb(III) ions, respectively. The quantum yield Фtotal is 48.42 ​± ​10%, 95.65 ​± ​10%, 44.22 ​± ​10%, and 76.97 ​± ​10% for coordination polymers 1 (Mg–Eu), 2 (Mg–Tb), 3 (Mg–Eu), and 4 (Mg–Tb), respectively. The corresponding fluorescence decay lifetime of 1–4 is τobs1 ​= ​1884.72 ​± ​1.51, 1777.75 ​± ​1.45, 1625.17 ​± ​1.40, and 1487.75 ​± ​1.36 ​μs? The effect of Mg(II) on the fluorescence properties of the lanthanide coordination polymers was investigated.