Three discrete and elongated Wells–Dawson type clusters [Ln24(DMC)36(μ4-CO3)18(μ3-H2O)2]·nH2O (Ln=Tb (1), n=4.5; Ln=Ho (2), n=6; Ln=Er (3), n=9; DMC=N, N-dimethylcarbamic acid anions) were synthesized by solvothermal. The ligands DMC and CO32− derived from the oxide reaction of DMF in situ. The metal skeleton of the cluster can be ascribed as an elongated Wells–Dawson type polyoxometalate (POM) polyhedron comprised of eighteen Ln4(μ4-CO3) square units and two Ln3(μ3-H2O) triangles. The magnetic properties of three clusters were explored, and all of them did not exhibit frequency-dependence. The compound 1 shows the typical luminescence of Tb3+. Interestingly, water molecules can significantly decrease the luminescent intensity, and other organic solvents including nitrobenzene have almost no effect on emission.