New lanthanide(III) sandwich and half-sandwich complexes with bulky cyclooctatetraenyl ligands - Synthesis, structures, and magnetic properties

3 years ago

New lanthanide(III) sandwich and half-sandwich complexes with bulky cyclooctatetraenyl ligands - Synthesis, structures, and magnetic properties

Axel Buchholz, Felix Engelhardt, Sabine Busse, Niklas Geue, Liane Hilfert, Volker Lorenz, Phil Liebing, Frank T. Edelmann, Winfried Plass, Cristian G. Hrib, Michael Böhme

Five new lanthanide(III) sandwich and half-sandwich complexes with bulky cyclooctatetraenyl ligands have been prepared and fully characterized, including single-crystal X-ray structure determination. Treatment of anhydrous lanthanide(III) chlorides, LnCl3 (Ln = Pr, Tb, Yb), with 2 equiv. of Li2COT'' (COT'' = 1,4-bis(trimethylsilyl)-cyclooctatetraene dianion) followed by crystallization in the presence of coordinating solvent afforded the anionic sandwich complexes [Li(THF)4][Pr(COT″)2] (1), [Li(DME)3][Tb(COT″)2] (2), and [Li(TMEDA)2][Yb(COT″)2] (3). Attempted oxidation of 2 with silver iodide did not afford the neutral terbium(IV) sandwich complex Tb(COT″)2. Instead, the tri(µ-iodido)-bridged dinuclear half-sandwich complex Li(DME)2Tb2(µ-I)3(COT'')2 was isolated in 72% yield. In this complex, a Li(DME)2 fragment is attached to one of the µ-iodido ligands. A closely related binuclear lutetium complex, [Li(DME)3][Lu2(µ-Cl)3(COTbig)2]∙DME (5), was obtained using the "superbulky" COTbig ligand (COTbig = 1,4-bis(triphenylsilyl)cyclooctatetraenyl dianion). In addition to the spectroscopic and structural characterization, the magnetic properties of the paramagnetic terbium(III) derivative 2 have been investigated and further complemented by ab initio computational methods. These results are used to discuss the structural requirement for potential terbium(III) single-ion magnets.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201700878