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. 2025 Apr 17:13:1536383.
doi: 10.3389/fchem.2025.1536383. eCollection 2025.

In situ monitoring of ligand-to-metal energy transfer in combination with synchrotron-based X-ray diffraction methods to elucidate the synthesis mechanism and structural evolution of lanthanide complexes

Ban H Al-Tayyem  1 , Philipp Müscher-Polzin  1 , Kanupriya Pande  2 , Oleksandr Yefanov  2 , Valerio Mariani  2 , Anja Burkhardt  3 , Henry N Chapman  2   4   5 , Christian Näther  1 , Michael Braun  1 , Marvin Radke  1 , Steve Waitschat  1 , Kenneth R Beyerlein  2 , Huayna Terraschke  1
Affiliations

In situ monitoring of ligand-to-metal energy transfer in combination with synchrotron-based X-ray diffraction methods to elucidate the synthesis mechanism and structural evolution of lanthanide complexes

Ban H Al-Tayyem et al. Front Chem. .

Abstract

Despite wide application of lanthanide complexes in solar cells, light-emitting diodes and sensors, their crystallization mechanisms have not been studied in detail. Further investigations of this kind can lead to the development of targeted synthesis protocols and tailoring of their structure-related physical properties. In this work, the structural evolution during the synthesis of the luminescent [Tb (bipy)2(NO3)3] (bipy = 2,2'-bipyridine) complex is studied by monitoring the ligand-to-metal energy transfer through in situ luminescence measurements combined with synchrotron-based X-ray diffraction (XRD) analysis. These experiments reveal an interesting crystallization pathway involving the formation of a reaction intermediate that is dependent on parameters such as ligand-to-metal molar ratios. In addition, the structure of [Tb (bipy)2(NO3)3] is solved from serial crystallography data collected at a microfocused synchrotron X-ray beamline. This is an emerging technique that can be used to interrogate individual crystallites and overcome beam damage effects. The resulting structure is found to correspond to that determined by classical single crystal XRD, and a perspective on realizing future in situ measurements of this type is given. This work therefore describes multiple advancements combining crystallite-specific diffraction probes and in situ techniques to track the synthesis kinetics of luminescent materials.

Keywords: In situ luminescence; crystal structure; lanthanide complexes; ligand-to-metal energy transfer; small-molecule serial crystallography; synchrotron radiation.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Serial crystallography measurement using polyimide tape drive. The red X-ray beam is focused onto a yellow polyimide tape that is strung between two rollers and contains green [Tb (bipy)2(NO3)3] crystals affixed to it. The diffraction from a crystal is measured in transmission on a large grey 2D detector. A microscopic image of such a tape that was used for the measurement is shown.
FIGURE 2
FIGURE 2
[Tb (bipy)2(NO3)3] Serial Structure Solution. (A) The distributions of orthorhombic unit cell parameters found by indexing frames without symmetry input are shown. (B) The trend of Rsplit for the merged intensities is shown along with a dashed line denoting the cutoff used on the reflection list. (C) A cross-section of the merged reflections through the h-k plane of reciprocal space, generated using the CrystFEL render_hkl program. Each spot represents an hkl reflection with the color representing the structure factor [sqrt(I)] according to the normalized color scale shown. (D) Structure comparison. The atomic anisotropic displacement isosurfaces obtained from serial crystallography (pastel colors) are overlayed onto those obtained from of the single crystal structure refinement (RGB colors).
FIGURE 3
FIGURE 3
View of the Tb3+ coordination in the crystal structure of [Tb (bipy)2(NO3)3].
FIGURE 4
FIGURE 4
Synthesized [Tb (bipy)2(NO3)3] illuminated with ambient (left) and UV light (right).
FIGURE 5
FIGURE 5
Optical reflectance of 2,2′-bipyridine (blue curve), excitation (λem = 542 nm, red curve) and emission (λex = 330 nm, black curve) spectra of [Tb (bipy)2(NO3)3] crystals.
FIGURE 6
FIGURE 6
(A) 3D representation of the in situ luminescence spectra (λex = 365 nm) recorded during the synthesis of [Tb (bipy)2(NO3)3] at a ligand addition rate of 0.5 mL/min. (B) Respective time-dependence of the addition volume of the 2,2′-bipyridine to Tb3+ solutions (black), the pH value (blue), the ionic conductivity (grey) and the normalized emission intensity of the 5D4→7F5 Tb3+ transition (green) (Exp. 2, Table 1).
FIGURE 7
FIGURE 7
(A) In situ XRD patterns recorded at the P08 DESY beamline (λ = 0.4959 Å) are (B) compared to calculated diffraction patterns for [Tb (bipy)2(NO3)3] (ratio bipy:Tb = 2:1, Exp. 4). (C) Time-dependence of light transmission intensity at 367 nm (blue curve) and emission intensity of the Tb3+ 5D4→7F4 transition at 545 nm (green curve) are compared to simultaneous in situ XRD measurements at, e.g. 3.99° 2θ {violet doted curve, [Tb (bipy)2(NO3)3]} and 4.07°2θ (orange doted curve, intermediate) as well as the addition rate of the bipy solution to the reactor containing terbium (III) nitrate at 0.5 mL/min (red curve).
FIGURE 8
FIGURE 8
(A) In situ emission intensity (λex = 365 nm) recorded during the synthesis of [Tb (bipy)2(NO3)3] at 300% reactant concentration with the addition rate of 2,2′-bipyridine at 0.5 mL/min (Experiment 4). (B) Time-dependent changes in 5D4→7F5 splitting pattern recorded during the synthesis of [Tb (bipy)2(NO3)3] (ratio bipy:Tb3+ = 2:1, Experiment 4).
FIGURE 9
FIGURE 9
Time dependence of (A) the addition of bipy to the Tb3+ solution as well as intensity of the synchrotron-based Bragg peak assigned to (B) the intermediate at 4.07°2θ and to (C) the [Tb (bipy)2(NO3)3] product at 3.99°2θ.
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