Homodinuclear Lanthanide Complexes with the Divergent Heterotopic 4,4′‐Bipyridine N‐Oxide (bipyMO) Ligand

Abstract

The synthesis of dinuclear molecular complexes [Eu2(dbm)6(bipyMO)2], 1, [Tb2(dbm)6(bipyMO)2], 2, [Eu2(tta)6(bipyMO)2], 3 [Eu2(hfac)6(bipyMO)3], 4, [Tb2(hfac)6(bipyMO)3], 5 is here reported (bipyMO = 4,4′‐bipyridine N‐oxide, Hdbm = dibenzoylmethane, Htta = thenoyltrifluoroacetone, Hhfac = hexafluoroacetylacetone). The products were obtained in mild conditions and with high yields reacting anhydrous lanthanide β‐diketonates and bipyMO in 1:1 or 1.5 molar ratio in toluene. X‐ray single crystal studies on 2, 3, 4 showed that the heterotopic ligands are hypodentate, bridging the two lanthanide centres exclusively through the oxygen atom. Photoluminescence studies show bright red emissions from europium derivatives with absolute quantum yields up to 44 %.

Composition–Thermometric Properties Correlations in Homodinuclear Eu3+ Luminescent Complexes

“…Since previous studies established the product composition [Ln 2 (β-diketonate) 6 (bipyMO) 2 ] (β-diketonate = tta, dbm) regardless of the [Ln(β-diketonate) 3 ]/bipyMO molar ratio (1/1 or 2/3), 41 the reaction between [Eu(β-diketonate) 3 ] (β-diketonate = tta, dbm) and pyrzMO was carried out with a 1/1 molar ratio in hot anhydrous toluene. The products [Eu 2 (tta) 6 (pyrzMO) 2 ]·C 7 H 8 ( 1 ·C 7 H 8 ) and [Eu 2 (dbm) 6 (pyrzMO) 2 ] ( 2 ) were obtained in satisfactory yields.…”

“…The molecular structures of 1 and 2 closely resemble the related bipyMO structures [Ln 2 (β-diketonate) 6 (bipyMO) 2 ]. 41 …”

“… 36 − 38 Recently, we focused on lanthanide coordination chemistry with the heterotopic divergent N -oxide ligand 4,4′-bipyridine N -oxide (bipyMO). 39 − 41 The different affinities of 4f metal ions toward O- and N-donor ligands afford the synthesis of lanthanide dinuclear complexes with the composition [Ln 2 (β-diketonate) 6 (bipyMO) x ] ( x = 2, 3 depending on the β-diketonate) where the oxygen atom of bipyMO bridges two lanthanide ions and the nitrogen donor atom is not coordinated. 41 − 44 In this context, we developed a family (16 members) of homodinuclear Eu 3+ and Gd 3+ luminescent compounds to study the effect of the β-diketonato and N -oxide ligands on the thermometric properties of the complexes.…”

“… 39 − 41 The different affinities of 4f metal ions toward O- and N-donor ligands afford the synthesis of lanthanide dinuclear complexes with the composition [Ln 2 (β-diketonate) 6 (bipyMO) x ] ( x = 2, 3 depending on the β-diketonate) where the oxygen atom of bipyMO bridges two lanthanide ions and the nitrogen donor atom is not coordinated. 41 − 44 In this context, we developed a family (16 members) of homodinuclear Eu 3+ and Gd 3+ luminescent compounds to study the effect of the β-diketonato and N -oxide ligands on the thermometric properties of the complexes. We used four β-diketonato ligands with different steric and electronic properties commonly used for the synthesis of europium luminescent derivatives: thenoyltrifluoroacetone (Htta), dibenzoylmethane (Hdbm), benzoyltrifluoroacetone (Hbta), and hexafluoroacetylacetone (Hhfac).…”

“… 45 − 47 The studied family is composed of [Ln 2 (tta) 6 (pyrzMO) 2 ] (Ln = Eu ( 1 ·C 7 H 8 ), Gd ( 5 )), [Ln 2 (dbm) 6 (pyrzMO) 2 ] (Ln = Eu ( 2 ), Gd ( 6 )), [Ln 2 (bta) 6 (pyrzMO) 2 ] (Ln = Eu ( 3 ), Gd ( 7 )), [Ln 2 (hfac) 6 (pyrzMO) 3 ] (Ln = Eu ( 4 ), Gd ( 8 )), and their bipyMO-based analogues ( 1b – 8b ). 41 All of the europium complexes showed an intense red emission at room temperature under UV radiation and a strong temperature ( T ) dependence of europium emission intensity between 223 and 373 K. This remarkable variation is exploited to develop a series of luminescent thermometers by using the integrated intensity of the europium 5 D 0 → 7 F 2 transition as a thermometric parameter (Δ). The effect of the different β-diketonato and N -oxide ligands on the shape of thermometer calibration (Δ vs T ) curves is investigated and presented in detail.…”