The reactions of chromium(III) nitrate with M2(cpdc) (cpdc2− – dianion of cyclopropane-1,1-dicarboxylic acid, M = K, Na) and rare-earth metal nitrates taken in a molar ratio of 1 : 3 : 1 yielded heterometallic coordination polymers {[Ln2Cr2(cpdc)6(H2O)9]·8.5H2O}n (1Ln, Ln = Eu, Gd, Tb), crystallizing in tetragonal space group P43212 (P41212). A single crystal X-ray diffraction (XRD) study showed that the crystal structures of these compounds are formed by tris-chelate fragments {Cr(cpdc)3} linked into {Ln–Cr} layers and further into a 3D framework structure due to the bridging coordination of carboxylate groups to Ln atoms. When passing to Ln = Dy, Ho, Y, Er, Yb, the crystals of compounds 2Ln form, where the structure of {Ln–Cr} layers is retained, but the disorder of the interlayer Ln atoms, a decrease in the size of a crystal cell, and a change in the space group to I4 are observed. The use of K2(cpdc) in the syntheses of 1Ln and 2Ln is found to lead to the isolation of a side product, namely, mononuclear complex [Cr(cpdc)(Hcpdc)(H2O)2]·2H2O (3), with the reactions with Na2(cpdc) enabling obtaining only the crystals of heterometallic LnIII–CrIII compounds. Alternating current magnetic susceptibility measurements for the series 1Ln and 2Ln revealed the presence of slow relaxation of magnetization only for 1Eu and 2Y, which is due to the magnetic anisotropy of chromium ions in the presence of magnetic field and their magnetic isolation in a crystal lattice. For 1Eu, 1Gd, 1Tb, 2Dy, and 2Ho, thermal decomposition in an Ar atmosphere was studied. The end product of solid-state thermolysis of 2Dy in air at 1000 °C is shown to be submicron DyCrO3 particles (300–400 nm).