Investigation of slow magnetic relaxation in a series of 1D polymeric cyclobutane-1,1-dicarboxylates based on LnIIIV IV2 units (LnIII = Tb, Dy, Ho, Er, Tm, Yb): rare examples of VIV-4f single-molecule magnets

Abstract

The reactions of VOSO₄·3H₂O with Na₂(cbdc) (cbdc²⁻ – dianion of cyclobutane-1,1-dicarboxylic acid) and lanthanide(III) nitrates taken in a molar ratio of 1 : 2 : 1 were found to yield a series of isostructural heterometallic compounds [NaLn(VO)₂(cbdc)₄(H₂O)₁₀]_n (1_Ln, Ln = Tb, Dy, Ho, Er, Tm, Yb). These compounds are constructed from trinuclear anionic units [Ln(VO)₂(cbdc)₄(H₂O)₈]⁻ ({LnV₂}⁻) linked by Na⁺ ions into 1D polymeric chains. The crystal structures of 1_Dy and 1_Er were determined by single-crystal X-ray diffraction (XRD), and their isostructurality with 1_Tb, 1_Ho, 1_Tm, and 1_Yb was proved by powder X-ray diffraction (PXRD). According to alternating current (ac) magnetic susceptibility measurements, 1_Dy, 1_Er, and 1_Yb exhibited field-induced slow relaxation of magnetization. Compound 1_Er is the first representative of Er^III–V^IV single-molecule magnets. Measuring the temperature dependences of the phase memory time (T_m) for 1_Dy and 1_Yb using pulsed EPR spectroscopy allowed us to observe the phenomenon of phase relaxation enhancement (PRE) at temperatures below 30 K. In future, this phenomenon may contribute to the evaluation of relaxation times of the lanthanide ions.