The reaction of VOSO 4 with K 2 cbdc (cbdc 2is cyclobutane-1,1-dicarboxylate anion) and Ln(NO 3 ) 3 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, Lu) yielded 17 novel heterometallic Ln III -V IV compounds comprising stable bischelate units {V IV O(cbdc) 2 (H 2 O)}. Three structural types of compounds are formed depending on the nature of the rare-earth metal: 1D polymers {[Ln(VO)(cbdc) 2 (H 2 O) 7 ]·0.5[VO(cbdc) 2 ]} n (structural type I) [Ln = La (1), Ce (2)], 3D polymers {[KLn(VO) 2 (cbdc) 4 (H 2 O) 9 ]·3.5H 2 O} n (structural type II) [Ln = La 5075 [Ln = Y (13), Er (14), Tm (15), Yb (16), Lu (17)] containing dinuclear units {LnV}. Magnetic properties were investigated for all isolated compounds. The Gd III -V IV compound has ferromagnetic and antiferromagnetic exchange interactions between isotropic V IV and Gd III ions. Calculations using the DFT method at the UB3LYP/6-31G(d,p)/SDD level of theory were performed in order to explain the different nature of exchange interactions in two Gd III -V IV pairs. The Yb III -V IV complex displays single-molecule magnet properties; the effective energy barrier was estimated at ΔE eff /k B = 26 K. The magnetic properties of Ln III -V IV compounds with heavy lanthanide ions (Ln III = Er, Tm, Yb) were rationalized in terms of crystal-field calculations for Ln III ions. and clear magnetic hysteresis of purely molecular origin, which are characteristic of single-molecule magnets (SMM). [3] Complexes of 3d-4f metals are considered as good candidates for SMMs due to high anisotropy of some lanthanide ions (Tb III , Dy Meanwhile 3d-4f compounds containing a vanadyl ion V IV O 2+ as the 3d center with a single 3d electron (S = 1 / 2 ) are quite rare, although they may provide insight into the mechanism of spin-spin exchange interactions. Despite quite a large number of V IV -4f complexes were described in recent literature, [11] only a few of them were magnetically characterized. [11a,11b,11d,11e,11g,11j,11l] For example, some V IV -Ln III complexes with ferromagnetically coupled V IV and Ln III ions have been reported. [11d,11e] Ishida et al. [11j] performed AC magnetic susceptibility measurements for five isostructural V IV -Ln III complexes, but these compounds did not exhibit SMM behavior. Besides, 3d-4f complexes are of interest as precursors of complex oxides. [12] One synthetic approach to prepare 3d-4f compounds is based on the use of stable 3d-metal complexes with free functional groups capable of acting as metal-containing ligands, Eur. J. Inorg. Chem. 2018, 5075-5090 www.eurjic.org