Alkali Tin Halides: Exploring the Local Structure of A<sub>2</sub>SnX<sub>6</sub> (A = K, Rb; X = Cl, Br, I) Compounds Using Solid-State NMR and DFT Computations
Bibliographic record
Abstract
Metal-halide perovskites have both interesting structural characteristics and strong potential for applications in devices such as solar cells and light-emitting diodes. While not true perovskites, A 2 SnX 6 materials are relatives of traditional ABX 3 perovskites that commonly adopt the K 2 PtCl 6 structure type. Herein, we use solid-state nuclear magnetic resonance (NMR) spectroscopy to explore the influence of group 1 (alkali metal) and group 17 (halogen) substitutions on octahedral tilting and spin–orbit (SO) coupling in A 2 SnX 6 (A = K +, Rb +; X = Cl –, Br –, or I – ) materials. For the monoclinic K 2 SnBr 6 and tetragonal Rb 2 SnI 6 compounds, the impact of static octahedral tilting on A-site environments is evident in the form of chemical shift anisotropy (CSA) and sizeable quadrupole coupling constants ( C Q s) for 39 K and 87 Rb. Ultrahigh-field NMR analysis combined with periodic density functional theory (DFT) calculations enables successful determination of the relative orientation between the electric field gradient (EFG) and CSA tensors for 39 K in K 2 SnBr 6 . The B-site polyhedral environments are probed throughout the compositional range via 119 Sn NMR spectroscopy, demonstrating that the 119 Sn chemical shift follows a normal halogen dependence (NHD). Quantum chemical modeling using scalar relativistic and SO DFT on cluster models shows that the NHD is driven by the SO term of the magnetic shielding. Consistent with SO heavy atom effects on NMR chemical shifts, the NHD can be explained in terms of the frontier molecular orbitals and the involvement of Sn and X atomic orbitals in Sn–X bonds. The importance of proper relativistic treatment of heavy atoms is also highlighted by comparing calculations of 119 Sn chemical shifts at different levels of theory.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".