The First Series of Heterometallic LnIII -VIV Complexes Based on Substituted Malonic Acid Anions: Synthesis, Structure and Magnetic Properties

The reaction of VOSO₄ with K₂cbdc (cbdc^2– is cyclobutane‐1,1‐dicarboxylate anion) and Ln(NO₃)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 bis‐chelate units {V^IVO(cbdc)₂(H₂O)}. Three structural types of compounds are formed depending on the nature of the rare‐earth metal: 1D polymers {[Ln(VO)(cbdc)₂(H₂O)₇]·0.5[VO(cbdc)₂]}_n (structural type I) [Ln = La (1), Ce (2)], 3D polymers {[KLn(VO)₂(cbdc)₄(H₂O)₉]·3.5H₂O}_n (structural type II) [Ln = La (3), Ce (4), Pr (5), Nd (6), Sm (7), Eu (8), Gd (9), Tb (10), Dy (11), Ho (12)] comprising trinuclear units {LnV₂}, and octanuclear complexes {[KLn(VO)₂(cbdc)₄(H₂O)₁₁]·2H₂O}₂ (structural type III) [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.