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. 2024 May 27;63(21):9434-9450.
doi: 10.1021/acs.inorgchem.3c02752. Epub 2023 Nov 28.

Expanding the Coordination of f-Block Metals with Tris[2-(2-methoxyethoxy)ethyl]amine: From Molecular Complexes to Cage-like Structures

Sergely Steephen Bokouende  1 , D Nuwangi Kulasekara  1 , Sara A Worku  1 , Cassandra L Ward  2 , Aravind B Kajjam  1 , Jacob C Lutter  1 , Matthew J Allen  1
Affiliations

Expanding the Coordination of f-Block Metals with Tris[2-(2-methoxyethoxy)ethyl]amine: From Molecular Complexes to Cage-like Structures

Sergely Steephen Bokouende et al. Inorg Chem. .

Abstract

Low-valent f-block metals have intrinsic luminescence, electrochemical, and magnetic properties that are modulated with ligands, causing the coordination chemistry of these metals to be imperative to generating critical insights needed to impact modern applications. To this end, we synthesized and characterized a series of twenty-seven complexes of f-metal ions including EuII, YbII, SmII, and UIII and hexanuclear clusters of LaIII and CeIII to study the impact of tris[2-(2-methoxyethoxy)ethyl]amine, a flexible acyclic analogue of the extensively studied 2.2.2-cryptand, on the coordination chemistry and photophysical properties of low-valent f-block metals. We demonstrate that the flexibility of the ligand enables luminescence tunability over a greater range than analogous cryptates of EuII in solution. Furthermore, the ligand also displays a variety of binding modes to f-block metals in the solid state that are inaccessible to cryptates of low-valent f-block metals. In addition to serving as a ligand for f-block metals of various sizes and oxidation states, tris[2-(2-methoxyethoxy)ethyl]amine also deprotonates water molecules coordinated to trivalent triflate salts of f-block metal ions, enabling the isolation of hexanuclear clusters containing either LaIII or CeIII. The ligand was also found to bind more tightly to YbII and UIII in the solid state compared to 2.2.2-cryptand, suggesting that it can play a role in the isolation of other low-valent f-block metals such CfII, NpIII, and PuIII. We expect that our findings will inspire applications of tris[2-(2-methoxyethoxy)ethyl]amine in the design of light-emitting diodes and the synthesis of extremely reducing divalent f-block metal complexes that are of interest for a wide range of applications.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1.
Figure 1.
Chemical structures of 2.2.2-cryptand (1) and tris[2-(2-methoxyethoxy)ethyl]amine (2) showing the similarity in the donoratom arrangement between 1 and 2.
Figure 2.
Figure 2.
Molecular structures and corresponding coordination polyhedron in the crystals of [Eu1(NO3)]I0.83[NO3]0.17 (left), Eu1(OTf)2 (middle), and Eu1(NCS)2 (right). The outer-sphere nitrate and iodide in [Eu1(NO3)]I0.83[NO3]0.17 have occupancies of 0.17 and 0.83, respectively. The outer-sphere nitrate in [Eu1(NO3)]I0.83[NO3]0.17 and hydrogen atoms are removed for clarity. Atom colors: red = oxygen; mint green = europium; gray = carbon; yellow = sulfur; purple = iodine; and lime green = fluorine. Crystallographic data are available free of charge at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2279300 ([Eu1(NO3)]I0.83[NO3]0.17), 2246685 (Eu1(OTf)2), and 2278423 (Eu1(NCS)2).
Figure 3.
Figure 3.
Synthesis, solid-state structures, and coordination polyhedrons of EuII2. Thermal ellipsoids are drawn at 50% probability. Disordered components, noncoordinating solvents, and hydrogen atoms are omitted for clarity. Atom colors: red = oxygen; purple = iodide; gold = bromide; light-peach = boron; lime green = fluorine; mint green = europium; light green = chloride; gray = carbon; sky-blue = amine; dark gray = zinc; and yellow = sulfur. Crystallographic data for all complexes are available free of charge at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2245099 (Eu2(NO3)2), 2209280 ([Eu2(H2O)2]I2), 2209286 ([Eu2(CH3OH)I]I), 2242192 (Eu2(NCS)2), ^2209285 (Eu2Br(CH3OH)]Br), 2209282 ([Eu2I(THF)][BPh4]), 2209284 ((CH3OH)2Eu(μ-Cl)ZnCl3), and 2209281 (Eu2(OTf)2).
Figure 4.
Figure 4.
Solid-state structures and coordination polyhedron of YbII2. Thermal ellipsoids are drawn at 50% probability. All disordered components and hydrogen atoms have been omitted for clarity. Atom colors: red = oxygen; purple = iodide; green = ytterbium; gray = carbon. Crystallographic data for all complexes are available free of charge at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2269084 ([Yb2I]I), 2209288 ([Yb2I][Yb2(H2O)]I3), and 2209283 ([Yb2(H2O)]I2).
Figure 5.
Figure 5.
Synthesis, solid-state structures, and coordination polyhedrons of [Yb2(CH3OH)X]I (X = Br or Cl). Hydrogen atoms have been omitted for clarity. Atom colors: red = oxygen; purple = iodide; gold = bromide; lime green = fluorine; green = ytterbium; light green = chloride; and gray = carbon. Crystallographic data for all complexes are available free of charge at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2210580 ([Yb2Br(CH3OH)]I) and 2211516 ([Yb2(CH3OH)Cl]I).
Figure 6.
Figure 6.
Solid-state structures and coordination polyhedrons of SmII2 and SmIII2. Hydrogen atoms are omitted for clarity. Atom colors: red = oxygen; purple = iodide; gold = bromide; light green = samarium; green = chloride; sky-blue = amine; and gray = carbon. Crystallographic data for all complexes are available free of charge at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2209279 ([2Sm(μ-Br)2Sm2]I2), 2209291 ([Sm2(CH3CN)(THF)][Sm2(CH3CN)2]2[BPh4]6), 2240326 ([2Sm(μ-Cl)2Sm2]I2), 2265224 ([Sm2(CH3CN)(THF)][BPh4]2), and 2238827 ([Sm2(DMF)2]I3).
Figure 7.
Figure 7.
Synthesis, solid-state structures, and coordination polyhedrons of UIII2. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms and an outer-sphere molecule of THF in [U2I2]I·(THF) have been omitted for clarity. Atom colors: red = oxygen; purple = iodide; light-peach = boron; blue = uranium; light-blue = lanthanum; sky-blue = amine; gray = carbon; and yellow = sulfur. Crystallographic data for all complexes are available free of charge at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2258563 ([La2(OTf)3]), 2209294 ([U2(OTf)3]), 2209293 ([U2I2]I), and ;2209295 ([U2I2][BPh4]).
Figure 8.
Figure 8.
Molecular structure of (A) LaIII cluster in crystals of [H2]2[Ln6(OH)8(OTf)12(THF)6], (B) a hexanuclear LaIII-containing cluster with omission of noncoordination sulfur and oxygen atoms of triflate ions, and (C) coordination polyhedron and (D) rhombic dodecahedron cage-like structure of the LaIII-cluster. Hydrogen, fluorine, and selected carbon atoms (of THF and OTf) have been omitted for clarity. Atom colors: red = oxygen; gray = carbon; yellow = sulfur; and blue = lanthanum. The structure of the CeIII-cluster—which is isomorphous to the LaIII-cluster—is included in the Supporting Information. Crystallographic data for all complexes are available free of charge at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2236824 ([H2]2[La6(OH)8(OTf)12(THF)6]) and 2231607 ([H2]2[Ce6(OH)8(OTf)12(THF)6]).
Figure 9.
Figure 9.
(A) UV–visible and (B) excitation (dashed line) and emission (solid line) spectra of [H2]2[Ce6(OH)8(OTf)12(THF)6] (1 mM) in acetonitrile. X-ray photoemission spectra of 3d5/2 and 3d3/2 orbitals of (C) CeIII and (D) LaIII in crystalline powders of [H2]2[Ln6(OH)8(OTf)12(THF)6] (Ln = Ce or La). Shape and color code for lines in C and D: experimental (O); fitted (red); background (green); and residual (blue).
Figure 10.
Figure 10.
UV–visible spectra of solutions (2 mM) of EuII1 and EuII2 in acetonitrile. Color code: red = [Eu1 (NO3)]I0.83[NO3]0.17; green = Eu1 (OTf)2; dark-purple = [Eu1I]I; cyan = Eu1 (NCS)2; blue = Eu2 (NO3)2; black = Eu2 (OTf)2; orange = Eu2 (NCS)2; purple = [Eu2I(CH3OH)]I; brown = [Eu2Br(CH3OH)]Br; gray = (CH3OH) 2Eu(μ-Cl)ZnCl3.
Figure 11.
Figure 11.
Photophysical properties of solutions of EuII1 and EuII2 (2 mM) in acetonitrile. (A) excitation spectra of EuII1, (B) excitation spectra of EuII2, (C) emission spectra of EuII1, and (D) emission spectra of EuII2. Color code for EuII1 and EuII2 in A−D: red = [Eu1(NO3)]I0.83[NO3]0.17; green = Eu1 (OTf)2; dark-purple = [Eu1I]I; cyan = Eu1 (NCS)2; blue = Eu2 (NO3)2; black = Eu2(OTf)2; purple = [Eu2I(CH3OH)]I; brown = [Eu2Br(CH3OH)]Br; gray = (CH3OH)2Eu(μ-Cl)ZnCl3.
Figure 12.
Figure 12.
UV–visible spectra of [Sm1I]I (2 mM) and YbII2 (4.0–4.7 mM) in acetonitrile. Color code for SmII (solid lines): brown = [2Sm(μ-Br)2Sm2]I2; purple = [Sm2I(CH3OH)]I; black = Sm2 (OTf)2; blue = [Sm1I]I. Color code for YbII (dashed lines): brown = [Yb2Br(CH3OH)]I; light-green = [Yb2Cl(CH3OH)]I.
Figure 13.
Figure 13.
UV–visible spectra of UIII2 (0.39–0.88 mM) and UI3 (0.74 mM) in acetonitrile. Color code: purple = [U2I2]I; green = U2 (OTf)3; black = UI3; red = [U2I2]I.
Scheme 1.
Scheme 1.
Resonance Structures of the Thiocyanate Ion
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