Challenges in the Search for Magnetic Coupling in 3d/4f Materials: Syntheses, Structures, and Magnetic Properties of the Lanthanide Copper Heterobimetallic Compounds, RE₂Cu(TeO₃)₂(SO₄)₂

Twelve new lanthanide copper heterobimetallic compounds, RE 2 Cu(TeO 3 ) 2 (SO 4 ) 2 (RE = Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), with two different structural topologies, have been prepared by hydrothermal treatment. Both structure types crystallize in the triclinic space group, P 1̅, but the unit cell parameters and structures are quite different. The earlier RE 2 Cu(TeO 3 ) 2 (SO 4 ) 2 (RE = Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm) share a common structural motif consisting of edge-sharing LnO 8 chains and [Cu(TeO 3 ) 2 (SO 4 ) 2 ] 6– units. The later lanthanide version (Yb and Lu) is composed of edge-sharing LnO 7 dimers bridged by similar [Cu(TeO 3 ) 2 (SO 4 ) 2 ] 6– units. The change in the structure type can be attributed to the decreasing ionic radii of the lanthanides. The compounds containing RE 3+ ions with diamagnetic ground states (Y 3+ and Eu 3+ ) exhibit antiferromagnetic ordering at 12.5 K and 15 K, respectively, owing to the magnetic exchange between Cu 2+ moments. No magnetic phase transition was observed in all the other phases. The lack of magnetic ordering is attributed to the competing magnetic interactions caused by the presence of paramagnetic RE 3+ ions. The magnetism data suggests that substantial 3d–4f coupling only occurs in the Yb analogue.