A series of new heterotetranuclear lanthanide complexes (Ln₂Ln′₂) is synthesized to study Ln-to-Ln′ energy transfer. Using stable dinuclear precursors, Tb₂Yb₂ and Nd₂Tb₂ are prepared and show visible/NIR emission. Reduced Tb³⁺ lifetimes suggest energy transfer to Yb³⁺ or Nd³⁺, offering a modular route to mixed-lanthanide systems.

A set of structurally related heterotetranuclear lanthanide(III) (Ln) complexes containing Ln¹ ₂Ln² ₂ cores has been synthesized as potential downshifting materials for solar applications. The Ln¹ ₂Ln² ₂ complexes can be regarded as intermediate model systems between classical doped systems and dinuclear molecular systems. The choice of Ln¹ and Ln² is based on commonly used codoped solid-state systems to evaluate the effect of energy transfer in the tetranuclear unit. The complexes are obtained by a new systematic approach involving the reactions of stable, solvent-free dinuclear homometallic precursors (Ln¹ ₂ + Ln² ₂ →Ln¹ ₂ + Ln² ₂). The new complexes Tb₂Yb₂q₆(hfac)₄(μ₃-OH)₂ (Tb ₂ Yb ₂ ) and Nd₂Tb₂q₆(hfac)₄(μ₃-OH)₂ (Nd ₂ Tb ₂ ) (q⁻ = 8-hydroxyquinolate; hfac⁻ = hexafluoroacetylacetonate), show emission both in the visible and near-IR regions. In both Nd ₂ Tb ₂ and Tb ₂ Yb ₂ , a reduction in the excited-state lifetime of the donor, Tb³⁺ is observed relative to the acceptor-free complex, Tb₂Y₂q₆(hfac)₄(μ₃-OH)₂ (Tb ₂ Y ₂ ), thus, signifying an energy transfer to the acceptors, Nd³⁺ or Yb³⁺, respectively. Overall, this work provides a versatile approach to controlling the aggregation and composition of mixed-lanthanide complexes while introducing new building blocks for exploring Ln-to-Ln′ energy transfer in discrete heteropolynuclear systems.