Control of Lanthanide Coordination Environment: Synthesis, Structure, and Oxygen-Sensitive Luminescence Properties of an Eight-Coordinate Tb(III) Complex

Coordination environment of the Tb³⁺ ion in oxygen-sensitive luminescent complexes can be successfully controlled through the size of alkyl substituents on ligands {(^RMeArOH)₄cyclen} (R = tBu or Me; cyclen = 1,4,7,10-tetraazacyclododecane); a newly prepared eight-coordinate complex 1^tBu shows higher oxygen sensitivity (K_SV = 17 600) and lower luminescence quantum yield (φ = 0.67 under N₂) than those of the previously reported seven-coordinate analogues 1^Me and [{(^MeMeArO)₃tacn}Tb^III(THF)] (K_SV = 12 600 and 8300, φ = 0.91 and 0.91 under N₂, respectively; tacn = 1,4,7-triazacyclononane; THF = tetrahydrofuran). The oxygen-sensitive mechanism is discussed on the basis of the photophysical properties of the corresponding Gd(III) complexes.