Two families of Ln(III)-V(IV) compounds (Ln(III) = Eu, Tb, Dy, Ho) of different structural types mediated by Rb+ and Cs+ cations: Slow magnetic relaxation of Eu(III)- and Ho(III)-containing members

Abstract

The reactions of oxidovanadium(IV) sulfate with Rb2(cbdc) or Cs2(cbdc) (cbdc2− – dianion of cyclobutane-1,1-dicarboxylic acid) and lanthanide(III) nitrates in water solutions gave two series of heterometallic compounds, namely {[RbLn(VO)2(cbdc)4(H2O)10]·2.5H2O}n (1Ln, Ln = Eu, Tb, Dy, Ho) and {[CsLn(VO)2(cbdc)4(H2O)11]·5H2O}2 (2Ln, Ln = Eu, Tb, Dy, Ho), respectively. The crystal structures of these compounds were determined by X-ray diffraction and were found to be built of similar trinuclear anionic units [Ln(VO)2(cbdc)4(H2O)8]− ({LnV2}−). Due to the structure-forming role of alkali metal ions, the heterometallic {LnV2} cores of these units differ in geometric characteristics (the V⋯Ln and V⋯V distances) and spatial arrangement in a crystal. In 1Ln, the {LnV2}− units are bound by rubidium ions into a 3D framework structure, whereas in 2Ln, cesium ions provide the formation of a discrete molecular structure. According to alternating current (ac) magnetic susceptibility measurements, only Eu(III)- and Ho(III)-containing compounds (1Eu, 1Ho, 2Eu, and 2Ho) exhibited field-induced slow relaxation of magnetization.