Assembly of tetra-nuclear YbIII-containing selenotungstate clusters: synthesis, structures, and magnetic properties

Two tetra-nuclear YbIII-incorporated selenotungstate clusters, Keggin (C2H8N)6Na14[Yb4Se6W44O160(H2O)12]·40H2O (1) and Wells–Dawson (C2H8N)4Na14[Yb4Se6W45O159(OH)6(H2O)11]·38H2O (2), have been isolated through a pH-controlled assembly, which exhibit the first YbIII-containing polyoxotungstates with selenium heteroatoms. Their assemblies rely on the structure-directing effects of SeO32− anion templates to give rise to available Se-containing Keggin-/Wells–Dawson-type motifs. Both compounds were characterized by single-crystal X-ray diffraction, IR spectroscopy, power X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) as well as electrospray ionization mass spectrometry (ESI-MS). Furthermore, systematic magnetic studies revealed that 1 exhibits field-induced single-molecule magnetic behavior with a pre-exponential factor of τ0 = 6.60(7) × 10−8 s and a relaxation energy barrier of ΔE/kB = 39.44(2) K, while 2 only displays antiferromagnetic interactions between the ytterbium centers.