Unique Double and Triple Decker Arrangements of Rare-Earth 9,10-Diborataanthracene Complexes Featuring Single-Molecule Magnet Characteristics

Abstract

Herein, we present the first report on the synthesis of rare-earth complexes featuring a 9,10-diborataanthracene ligand. This 14-π-electron ligand is highly reductive and was previously used in small-molecule activation. Salt elimination reactions between dipotassium 9,10-diethyl-9,10-diborataanthracene [K₂(DEDBA)] and [Ln^III(η⁸-Cot^TIPS)(BH₄)(thf)_x] (Cot^TIPS=1,4-(ⁱPr₃Si)₂C₈H₆) in a 1 : 1 ratio yielded heteroleptic sandwich complexes [K(η⁸-Cot^TIPS)Ln^III(η⁶-DEDBA)] (Ln=Y, Dy, Er). These compounds form Lewis-base-free one-dimensional coordination polymers when crystallised from toluene. In contrast, reaction of [K₂(DEDBA)] and [Ln^III(η⁸-Cot^TIPS)(BH₄)(thf)_x] in a 1 : 2 ratio led to the formation of heteroleptic triple-decker complexes [(η⁸-Cot^TIPS)Ln^III(μ-η⁶:η⁶-DEDBA)Ln^III(η⁸-Cot^TIPS)] (Ln=Y, Dy, Er). Notably, these are not only the first lanthanide triple-decker compounds featuring a six-membered ring as a deck but also the first trivalent lanthanide triple-decker featuring a heterocycle in the coordination sphere. Magnetic investigations reveal that [K(η⁸-Cot^TIPS)Ln^III(η⁶-DEDBA)] (Ln=Dy, Er) and [(η⁸-Cot^TIPS)Er^III(μ-η⁶:η⁶-DEDBA)Er^III(η⁸-Cot^TIPS)] exhibit Single-Molecule Magnet (SMM) behaviour. In the case of [(η⁸-Cot^TIPS)Ln^III(μ-η⁶:η⁶-DEDBA)Ln^III(η⁸-Cot^TIPS)] (Ln=Dy, Er), the introduction of a second near lanthanide ion results in strong antiferromagnetic interactions, allowing the enhancement of the magnetic characteristic of the system, compared to the quasi isolated counterpart. This research renews the overlooked coordination chemistry of the DBA ligand and expands it to encompass rare-earth elements.

Keywords: boron chemistry; coordination chemistry; heterocycle; lanthanides; triple-decker complexes.