Three novel 4f-4d heterometallic coordination polymers (CPs), [Ln(H2O)3CdL2(NO3)]·6H2O (L ​= ​ethyl 5-methyl-1-(pyridin-4-ylmethyl)-1H-1,2,3-triazole-3,4-dicarboxylate; Ln ​= ​Eu, Gd, Tb 1, 2 and 3, respectively) have been successfully synthesized by hydrothermal treatment and slow cooling-down crystallization. These CPs have been structurally characterized by single-crystal X-ray diffraction. 1–3 are isostructural and consist of a three-dimensional network showing channels. The networks are reinforced via hydrogen bonds and π-π stacking interactions. The crystal topology analysis shows an infinite 2D layer topology with net symbol {4,4} (sql). The magnetic behavior of these compounds is explained by the expected contribution of almost isolated Ln (III) ions. An energy gap of 375 ​cm−1 between the 7F0 ground state and the first excited state of compound 1 has been deduced from magnetic data showing an excellent agreement with the spectroscopic data.