Heteronuclear Eu 2 Pt 2 luminescent arrays: composition???thermometric properties correlations

Lanthanide dinuclear complexes [Ln2(tta)6(μ-pyrzMO)2] (Ln3+ = Eu3+ and Gd3+; Htta = thenoyltrifluoroacetone; pyrzMO = pyrazine-N oxide) can behave as ligands for the synthesis of molecular heterometallic complexes. Fast reactions at room temperature occur with [Pt(μ-Cl)Cl(EPh3)]2 (E = P, As) affording as a single product [Ln2(tta)6(μ-pyrzMOPtCl2EPh3)2] (E = P, Ln = Eu, 1; Ln = Gd, 2); (E = As, Ln = Eu, 3; Ln = Gd, 4). Similarly, the new platinum compound [PtClppy(pyrzMO)], 5, obtained reacting [Pt(μ-Cl)ppy]2 (ppy = 2-phenylpyridine) with pyrzMO and structurally characterized through XRD, has been used to prepare [Ln2(tta)6(μ-pyrzMOPtClppy)2] (Ln = Eu, 6; Ln = Gd, 7) starting from the anhydrous formally unsaturated [Ln(tta)3] fragments. XRD studies on all heterometallic compounds have established a tetranuclear Ln2Pt2 molecular structure with the platinum fragment coordinated to the nitrogen atom of the pyrazine while the N-oxide donor functionality is bridging two lanthanide centres as in the dinuclear lanthanide precursors. PL and thermometric properties of the Eu3+ complexes are strongly correlated with the nature of the ligand coordinated to Pt that is PPh3, AsPh3 and ppy. Upon UV excitation, 1 and 3 exhibit intense red emission, typical of Eu3+ ions, with a luminance of ∼10 cd m−2 significantly higher than that of 6 (∼0.3 cd m−2). Temperature-induced variations in emission intensity have been exploited to develop a series of luminescent thermometers. The integrated intensity of the 5D0 → 7F2 europium transition can be used as the thermometric parameter (Δ). 1 and 3 reach Sr = 1 at around 200 K, while 6 exhibits a steeper decay in Δ, achieving Sr = 1 at approximately 100 K. For 1 and 3, the temperature sensitivity is related to non-radiative deactivation channels involving the platinum-containing fragment and tta ligands. For 6, instead, the interactions are limited only to the Pt-containing fragment.