Magnetic Properties of LnIII–CuII 15‐Metallacrown‐5 Dimers with Terephthalate (LnIII = Pr, Nd, Sm, Eu)

Abstract

Metathesis of the isomorphous 15‐metallacrown‐5 complexes {[LnCu5(GlyHA)5(SO4)(H2O)6.5]}2(SO4)·6H2O (LnIII = Pr, Nd, Sm, Eu; GlyHA2– = glycinehydroxamate) with excess p‐bdc2– (p‐bdc2– = terephthalate) gave pairs of isomorphous complexes {[LnCu5(GlyHA)5(CO3)(H2O)4]2(p‐bdc)}·15H2O [Ln = Pr (1) and Nd (2)] and {[LnCu5(GlyHA)5(SO4)(H2O)x]2(p‐bdc)}·yH2O [Sm (3) x = 5, y = 12; Eu (4), x = 4, y = 14] as outcomes of partial sulfate replacement. Complexes 1–4 are discrete dimers with two 15‐metallacrown‐5 blocks {LnCu5}3+, a bridging p‐bdc2– and a bidentate capping anion on each Ln3+. The anion caps in 1 and 2 are carbonates from atmospheric CO2 capture, while in 3 and 4 the anion caps are sulfates. Between 3 K and 300 K, intrametallacycle antiferromagnetic exchange interactions amongst the Cu2+ dominate the magnetic properties of 1–4, while for the Ln3+, spin‐orbit coupling and crystal field effects are significant, the former being greater for Sm3+ and Eu3+. The experimental χMT vs. T data were fitted with an additive model reflecting the dominance of the Cu···Cu superexchange, while Ln3+···Cu2+ exchange interactions were taken into account through a molecular field approach. The best‐fit values (–2JCu–Cu) for the intercopper superexchange interactions range from 88 to 120 cm–1; the g‐factors, spin‐orbit coupling (λ) and axial crystal field splitting (Δ) parameter values are typical for LnIII.