A new series of gallium( iii )/lanthanide( iii ) metallacrown (MC) complexes ( Ln-1 ) was synthesized by the direct reaction of salicylhydroxamic acid (H 3 shi) with Ga III and Ln III nitrates in a CH 3 OH/pyridine mixture. X-ray single crystal analysis revealed two types of structures depending on whether the nitrate counterion coordinate or not to the Ln III : [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 4 (NO 3 )](py) 2 (Ln = Gd III , Tb III , Dy III , Ho III ) and [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 5 ](NO 3 )(py) (Ln = Er III , Tm III , Yb III ). The representative Tb-1 and Yb-1 MCs consist of a Tb/YbGa 4 core with four [Ga III –N–O] repeating units forming a non-planar ring that coordinates the central Ln III through the oxygen atoms of the four shi 3− groups. Two H 2 shi − groups bridge the Ln III to the Ga III ring ions. The Yb III in Yb-1 is eight-coordinated while the ligation of the nine-coordinated Tb III in Tb-1 is completed by one chelating nitrate ion. Ln-1 complexes in the solid state showed characteristic sharp f–f transitions in the visible (Tb, Dy) and near-infrared (Dy, Ho, Er, Yb) spectral ranges upon excitation into the ligand-centered electronic levels at 350 nm. Observed luminescence lifetimes and absolute quantum yields were collected and discussed. For Yb-1 , luminescence data were also acquired in CH 3 OH and CD 3 OD solutions and a more extensive analysis of photophysical properties was performed. This work demonstrates that while obtaining highly luminescent lanthanide( iii ) MCs via a direct synthesis is feasible, many factors such as molar absorptivities, triplet state energies, non-radiative deactivations through vibronic coupling with overtones of O–H, N–H, and C–H oscillators and crystal packing will strongly contribute to the luminescent properties and should be carefully considered.
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Lanthanide-mediated tuning of electronic and magnetic properties in heterotrimetallic cyclooctatetraenyl multidecker self-assemblies
The synthesis of a novel family of homoleptic COT-based heterotrimetallic self-assemblies bearing the formula [LnKCa(COT) 3 (THF) 3 ] (Ln( iii ) = Gd, Tb, Dy, Ho, Er, Tm, and Yb) is reported followed by their X-ray crystallographic and magnetic characterization. All crystals conform to the monoclinic P 2 1 / c space group with a slight compression of the unit cell from 3396.4(2) Å 3 to 3373.2(4) Å 3 along the series. All complexes exhibit a triple-decker structure having the Ln( iii ) and K( i ) ions sandwiched by three COT 2− ligands with an end-bound {Ca 2+ (THF) 3 } moiety to form a non-linear (153.5°) arrangement of three different metals. The COT 2− ligands act in a η 8 -mode with respect to all metal centers. A detailed structural comparison of this unique set of heterotrimetallic complexes has revealed consistent trends along the series. From Gd to Yb, the Ln to ring-centroid distance decreases from 1.961(3) Å to 1.827(2) Å. In contrast, the separation of K( i ) and Ca( ii ) ions from the COT-centroid (2.443(3) and 1.914(3) Å, respectively) is not affected by the change of Ln( iii ) ions. The magnetic property investigation of the [LnKCa(COT) 3 (THF) 3 ] series (Ln( iii ) = Gd, Tb, Dy, Ho, Er, and Tm) reveals that the Dy, Er, and Tm complexes display slow relaxation of their magnetization, in other words, single-molecule magnet (SMM) properties. This behaviour is dominated by thermally activated (Orbach-like) and quantum tunneling processes for [DyKCa(COT) 3 (THF) 3 ] in contrast to [ErKCa(COT) 3 (THF) 3 ], in which the thermally activated and Raman processes appear to be relevant. Details of the electronic structures and magnetic properties of these complexes are further clarified with the help of DFT and ab initio theoretical calculations.
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- Award ID(s):
- 2003411
- NSF-PAR ID:
- 10325301
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 13
- Issue:
- 13
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 3864 to 3874
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2SC00631F
