Self-Assembly of Tunable Heterometallic Ln-Ru Coordination Polymers with Near-Infrared Luminescence and Magnetocaloric Effect.

A series of heterometallic lanthanide (Ln)-Ru coordination polymers, denoted Gd-1, Yb-2, and Nd-3, were prepared by solvothermal reaction of a carboxylate derivative of [Ru(bpy) ] (Rubpy, bpy=2,2'-bipyridine), oxalic acid, and Ln(OAc) by using the metalloligand strategy. Single-crystal X-ray diffraction indicated that the resulting isostructural heterometallic complexes have 1D butterfly-shaped Ln-Ru-based coordination chains but show slight differences in the coordination environments of the Ln centers. The introduced Ru(bpy) metalloligands could act as good light-harvesting antennas to effectively sensitize near-infrared (NIR) luminescence by energy transfer from the triplet metal-to ligand charge transfer state of Rubpy units to Ln (Yb or Nd) under the excitation in the visible-light region. Additionally, dopant-concentration-dependent behavior of the Ru-based emission and sensitized NIR emission was demonstrated in Gd-1. Finally, the magnetocaloric effect of Gd-1 was studied. The preparation of such heterometallic coordination polymers offers a versatile platform to investigate dimensionally controlled properties.