Lanthanide Tetrazolate Complexes Combining Single‐Molecule Magnet and Luminescence Properties: The Effect of the Replacement of Tetrazolate N₃ by β‐Diketonate Ligands on the Anisotropy Energy Barrier

Abstract

Three new sets of mononuclear Ln(III) complexes of general formulas [LnL3 ]⋅CH3 OH [Ln(III) =Yb (1), Er (2), Dy (3), Gd (4), and Eu (5)], [LnL2 (tmh)(CH3 OH)]⋅n H2 O⋅m CH3 OH [Ln(III) =Yb (1 b), Er (2 b), Dy (3 b), Gd (4 b)], and [LnL2 (tta)(CH3 OH)]⋅CH3 OH [Ln(III) =Yb (1 c), Er (2 c), Dy (3 c), Gd (4 c)] were prepared by the reaction of Ln(CF3 SO3 )⋅n H2 O salts with the tridentate ligand 2-(tetrazol-5-yl)-1,10-phenanthroline (HL) and, for the last two sets, additionally with the β-diketonate ligands 2,2,6,6-tetramethylheptanoate (tmh) and 2-thenoyltrifluoroacetonate (tta), respectively. In the [LnL3 ]⋅CH3 OH complexes the Ln(III) ions are coordinated to three phenanthroline tetrazolate ligands with an LnN9 coordination sphere. Dynamic ac magnetic measurements on 1-3 reveal that these complexes only exhibit single-molecule magnet (SMM) behavior when an external dc magnetic field is applied, with Ueff values of 11.7 K (1), 16.0 K (2), and 20.2 K (3). When the tridentate phenanthroline tetrazolate ligand is replaced by one molecule of methanol and the β-diketonate ligand tmh (1 b-3 b) or tta (1 c-3 c), a significant increase in Ueff occurs and, in the case of the Dy(III) complexes 3 b and 3 c, out-of-phase χ'' signals below 15 and 10 K, respectively, are observed in zero dc magnetic field. CASSCF+RASSI ab initio calculations performed on the Dy(III) complexes support the experimental results. Thus, for 3 the ground Kramers' doublet is far from being axial and the first excited state is found to be very close in energy to the ground state, so the relaxation barrier in this case is almost negligible. Conversely, for 3 b and 3 c, the ground Kramers' doublet is axial with a small quantum tunneling of the magnetization, and the energy difference between the ground and first Kramers' doublets is much higher, which allows these compounds to behave as SMMs at zero field. Moreover, these calculations support the larger Ueff observed for 3 b compared to 3 c. Additionally, the solid-state photophysical properties of 1, 2, 4, and 5 show that the phenanthroline tetrazolate ligand can act as an effective antenna to sensitize the characteristic Yb(III) , Er(III) , and Eu(III) emissions through an energy-transfer process.

Closing the Circle of the Lanthanide-Murexide Series: Single-Molecule Magnet Behavior and Near-Infrared Emission of the NdIII Derivative

“…However these have been mainly performed on Tb III and Dy III ions because of their efficient SMM behaviors coupled with good emission properties (see ref [54] for full review) [55][56][57][58][59]. The approach has been less developed on NIR emissive Ln-SMM where mainly Er III -SMM [60][61][62][63][64][65] and Yb III -SMM [29,[66][67][68][69][70][71][72][73] have been investigated. The drawback of these ions is that their emission is not always strong enough to allow for reliable magneto-luminescent correlations.…”

New field-induced single ion magnets based on prolate Er(iii) and Yb(iii) ions: tuning the energy barrierUeffby the choice of counterions within an N3-tridentate Schiff-base scaffold

“…Apart from the herein presented compounds, there are only 10 reported unique structures that adopt the ErN 6 O 3 coordination environment (eight of which are monometallic), whereas the YbN 6 O 2 coordination sphere was observed in 26 compounds (fourteen of which are monometallic) (Tables S4 and S5 ‡). From the point of view of molecular similarity, there are only two compounds exhibiting significant structural resemblance to 1 (ITOCUR, ITODIG), 98 which belong to the family of N 3 -tetrazolate/β-diketonate heteroleptic complexes. It is encouraging to see that such a ligand arrangement indeed is responsible for SIM behaviour, which was observed therein; hence additional comparison is possible (cf.…”

“…Magnetization follows the AC magnetic field due to QTM. 98,108 It is well-known that the QTM effect can be suppressed by the application of a small DC field. 99,109,110 Therefore, when the AC measurements were performed in the presence of an external DC field of 0.1 T, the observed dependence of the χ″ M signals on frequency ( Fig.…”

Synthesis of Actinide Materials for the Study of Basic Actinide Science and Rapid Separation of Fission Products

“…The use of a benign transfer agent can facilitate the addition of high-nitrogen ligands to metal centers in a safe way. Lanthanide-tetrazolate complexes have also become more of interest in the literature recently, [191][192][193][194][195][196][197][198][199][200][201] with most of the research focusing on luminescent properties of the 4f tetrazolates. [191][192][193][194][197][198][199] They have also been studied for their ability to behave as single-molecule magnets, due to their strong spin-orbit coupling ability.…”

“…[191][192][193][194][197][198][199] They have also been studied for their ability to behave as single-molecule magnets, due to their strong spin-orbit coupling ability. 196 Very few organometallic lanthanide-tetrazolate complexes have been published, 200,201 and there are no current examples of cerium-tetrazolates. This chapter describes the synthesis and characterization of a novel goldtetrazolate compound, and gives brief insight into its use as a precursor for actinide-tetrazolate synthesis.…”