Triple-Decker Hexaazamacrocyclic Lanthanide(III) Complexes: Structure, Magnetic Properties, and Temperature-Dependent Luminescence

The reaction of fluoride anions with mononuclear rare-earth (III) complexes of the hexaazamacrocycle derived from 2, 6-diformylpyridine and ethylenediamine affords trinuclear coordination compounds Ln3L3 (μ2-F) 4 (NO3) 2 (NO3) 3. The X-ray crystal structures of these complexes show triplex cationic complexes where the three roughly parallel macrocyclic lanthanide (III) units are linked by bis-μ2-F bridges. The detailed analysis of the photophysical properties of the Eu3L3 (μ2-F) 4 (NO3) 2 (NO3) 3·2H2O and Tb3L3 (μ2-F) 4 (NO3) 2 (NO3) 3·3H2O complexes reveals different temperature dependence of luminescence intensity and luminescence decay time of the Eu (III) and Tb (III) derivatives. The spectra of mixed species of average composition Eu1. 5Tb1. 5L3 (μ2-F) 4 (NO3) 2 (NO3) 3·3H2O are in accordance with the ratiometric luminescent thermometer behavior. Measurements of the direct-current (dc) magnetic susceptibility of the Dy3L3 (μ2-F) 4 (NO3) 2 (NO3) 3·2H2O complex indicate possible ferromagnetic interactions between the Dy (III) ions. Alternating current (ac) susceptibility measurements of this complex indicate single-molecule magnet behavior in zero dc field with magnetic relaxation dominated by Orbach mechanism and an effective energy barrier Ueff = 12. 3 cm–1 (17. 7 K) with a pre-exponential relaxation time, τ0 of 7. 3 × 10–6 s. A similar reaction of mononuclear macrocyclic complexes with a higher number of fluoride equivalents results in polymeric Ln3L3 (μ2-F) 5 (NO3) 4n complexes. The X-ray crystal structure of the Nd (III) derivative of this type shows trinuclear units that are additionally linked by single fluoride bridges to form a linear coordination polymer.