Hydrothermal synthesis, crystal structure and properties of two new coordination polymers structured by two mixed ligands and strict quadrangular {Ln3}8 Units (Ln = Er and Ho)

► Compounds 1 and 2 have been hydrothermally assembled by HIN and H2bdc. ► They exhibit the first strict quadrangular {Ln3}8 structural building unit. ► Both of them feature a continuous array of face-to-face π interactions along a axis.