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 [Ln 3 L 3 (μ 2 -F) 4 (NO 3 ) 2 ](NO 3 ) 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-μ 2 -F bridges. The detailed analysis of the photophysical properties of the [Eu 3 L 3 (μ 2 -F) 4 (NO 3 ) 2 ](NO 3 ) 3 ·2H 2 O and [Tb 3 L 3 (μ 2 -F) 4 (NO 3 ) 2 ](NO 3 ) 3 ·3H 2 O 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 [Eu 1.5 Tb 1.5 L 3 (μ 2 -F) 4 (NO 3 ) 2 ](NO 3 ) 3 ·3H 2 O are in accordance with the ratiometric luminescent thermometer behavior. Measurements of the direct-current (dc) magnetic susceptibility of the [Dy 3 L 3 (μ 2 -F) 4 (NO 3 ) 2 ](NO 3 ) 3 ·2H 2 O 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 U eff = 12.3 cm -1 (17.7 K) with a pre-exponential relaxation time, τ 0 of 7.3 × 10 -6 s. A similar reaction of mononuclear macrocyclic complexes with a higher number of fluoride equivalents results in polymeric {[Ln 3 L 3 (μ 2 -F) 5 ](NO 3 ) 4 } n 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.