Trends in trigonal prismatic Ln-[1]ferrocenophane complexes and discovery of a Ho3+ single-molecule magnet. Issue 15 (1st April 2020)

• Record Type: Journal Article
• Authors: Latendresse, Trevor P.; Vieru, Veacheslav; Upadhyay, Apoorva; Bhuvanesh, Nattamai S.; Chibotaru, Liviu F.; Nippe, Michael
• Is Part Of: Chemical science. Volume 11:Issue 15(2020)
• Page Start: 3936
• Page End: 3951
• Publication Date: 2020-04-01
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0sc01197e
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Lanthanide ferrocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to iron ions. Abstract : Lanthanide metallocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to transition metal ions. Herein, we present a systematic study of the structural and magnetic properties of the ferrocenophanes, [LnFc3 (THF)2 Li2 ] −, of the late trivalent lanthanide ions (Ln = Gd (1 ), Ho (2 ), Er (3 ), Tm (4 ), Yb (5 ), Lu (6 )). One major structural trend within this class of complexes is the increasing diferrocenyl (Fc 2− ) average twist angle with decreasing ionic radius ( r ion ) of the central Ln ion, resulting in the largest average Fc 2− twist angles for the Lu 3+ compound 6 . Such high sensitivity of the twist angle to changes in r ion is unique to the here presented ferrocenophane complexes and likely due to the large trigonal plane separation enforced by the ligand (>3.2 Å). This geometry also allows the non-Kramers ion Ho 3+ to exhibit slow magnetic relaxation in the absence of applied dc fields, rendering compound 2 a rare example of a Ho-based single-molecule magnet (SMM) with barriers to magnetization reversal ( U ) of 110–131 cm −1 . In contrast, compounds featuring Ln ions with prolate electron density (3–5 ) don't show slow magnetization dynamics under the same conditions. The observed trends in magnetic properties of 2–5 are supported by state-of-the-art ab initio calculations. Finally, the magneto-structural relationship of the trigonal prismatic Ho-[1]ferrocenophane motif was further investigated by axial ligand (THF in 2 ) exchange to yield [HoFc3 (THF*)2 Li2 ] − (2-THF* ) and [HoFc3 (py)2 Li2 ] − (2-py ) motifs. We find that larger average Fc 2− twist angles (in 2-THF* and 2-py as compared to in 2 ) result in faster magnetic relaxation times at a given temperature.