Crystal Structures of New Lanthanide Hydroxybenzoates and Different Roles of LMCT State in the Excitation Energy Transfer to Eu³⁺ Ions

Abstract

A series of europium and terbium hydroxybenzoates [Eu(2-OH-Benz) 3 (H 2 O)] (1), [Eu(3-OH-Benz) 3 (H 2 O) 3 ] 2 ·2H 2 O (2), TbNa 3 (2-OH-Benz) 3 ·3H 2 O (3), [Tb 2 (3-OH-Benz) 6 (H 2 O) 4 ]·2H 2 O·0.5(3-OH-HBenz) (4), [Tb(4-OH-Benz) 3 ]·H 2 O (5) has been prepared and investigated using X-ray diffraction and luminescence spectroscopy. Two methoxysalicylates Ln 2 (2-OH-5-OCH 3 -Benz) 3 ·6H 2 O (Ln= Eu, Tb) are also under consideration. A dimeric crystal structure of 2 and polymeric structures of 4 and 5 were first determined by single crystal X-ray analysis. Low-energy ligand-metal charge transfer (LMCT) states caused by a particular binding of the ligands with Ln 3 + ion were identified in the europium compounds. Different roles of the LMCT states located under and above the lowest triplet state of the ligand in the excitation energy transfer in europium hydroxybenzoates are discussed. The lifetimes of 5 D 0 (Eu 3 + ) and 5 D 4 (Tb 3 + ) states at 77 K are consistent with the number of water molecules and other quenchers containing in the compounds. A qualitative correlation is observed between the luminescence brightness of hydroxybenzoates and an efficiency of nonradiative processes caused by the LMCT state and directly the multiphonon relaxation. Nonradiative processes due to the LMCT state are the most efficient at the location of this state lower the lowest triplet of 2hydroxybenzoate ligand in complex 1.[a] K. P. Zhuravlev, Prof. V. I. Tsaryuk, Dr. V. A. Kudryashova

4-Hydroxybenzoato-rare earth(iii) complexes – syntheses, a structural goldmine from coordination diversity and improved corrosion inhibition behaviour

“…4) crystallized as a mixture with the type b dimer, [Y 2 (4hob) 6 (H 2 O) 4 ]·2H 2 O , from a hydrothermal reaction at 120 °C and was separated by hand-picking. The species is isomorphous with a reported terbium complex formed between 70–80 °C 18 (Table S2, ESI†). Numerous attempts to replicate the literature experiment at a range of temperatures gave isomorphous dimer type b (RE = Tb, Dy, Y) or type c (RE = Tb, Er).…”

“…aChelating.bUnidentate.cBridging. CCDC code: I BEMCUU; 18 II BEWBAG; 20 III DUPWUH; 19 IV ELIPAS, 28 ELIPEW, 28 ELINUK. 28 …”

“…It was of interest to see if this coordination diversity extends to rare earth 4-hydroxybenzoate (4hob) complexes, where chelation of OH and carboxyl groups – a feature of light rare earth salicylate polymers 17 – is excluded. The few reported aqua 4hob RE complexes show a surprising range of structural types – a linear polymer, 18 a dimer, 19 and a dimer of dinuclear units, 20 stimulating further interest. Accordingly, we have mounted a detailed study into the structures of rare earth 4-hydroxybenzoates to investigate their coordination and structural diversity.…”

Preparation, Structure and Spectroscopic Properties of NH4[Ln(S2CNH2)4] ⋅ H2O (Ln=La, Eu)

“…Although there is still no definitive and detailed understanding of how ligand properties lead to (LMCT) states of low energies in trivalent lanthanide compounds, many systems reported in the literature present ligands with soft donor sites. Furthermore, several studies have shown that electronic and structural features play an essential role in the electron density delocalization towards the donated site, increasing its polarizability, and consequently changing the position of the LMCT states [19] . In this vein, dithiocarbamate and their derivative compounds have been used as a well‐defined platform for validating experimental and theoretical methodologies in investigating the intramolecular LMCT in the lanthanide complexes containing such states of low energy [16,20] .…”

“…Furthermore, several studies have shown that electronic and structural features play an essential role in the electron density delocalization towards the donated site, increasing its polarizability, and consequently changing the position of the LMCT states. [19] In this vein, dithiocarbamate and their derivative compounds have been used as a well-defined platform for validating experimental and theoretical method-ologies in investigating the intramolecular LMCT in the lanthanide complexes containing such states of low energy. [16,20] It is noteworthy that all lanthanide dithiocarbamate complexes mentioned so far contain relatively large substituent moieties (R).…”