Selective arrangement of three types of calcium–terbium tetranuclear cores by a thiacalixarene ligand using thermodynamic and kinetic strategies

Abstract

In this study, we report thermodynamic and kinetic strategies for arranging three types of Ca–Tb heterotetranuclear cores in a square configuration sandwiched by thiacalix[4]arene-p-tetrasulfonate (TCAS) ligands in aqueous solutions. In the thermodynamic strategy, the components were mixed under optimum pH conditions to afford a complex with a desired ratio of Ca:Tb:TCAS. In the kinetic strategy, the Ca₁Tb₃TCAS₂ complex was formed via mixing kinetically stable Tb₃TCAS₂ with Ca²⁺. Interestingly, the resulting complexes (Ca_xTb_4−xTCAS₂, x = 1–3) exhibited Tb-centered luminescence upon excitation of the TCAS center with a high quvdantum yield (ϕ = 0.11–0.14) and a long luminescence lifetime (approximately 1.2 ms). The thermodynamic strategy can be applied to Sr²⁺ instead of Ca²⁺, but it is not suitable for first transition metal ions. However, the kinetic strategy is versatile and can be applied to first transition metal ions to afford M₁Tb₃TCAS₂ (M = Sr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺).