Characterising Lone‐Pair Activity of Lead(II) by <sup>207</sup>Pb Solid‐State NMR Spectroscopy: Coordination Polymers of [N(CN)<sub>2</sub>]<sup>−</sup> and [Au(CN)<sub>2</sub>]<sup>−</sup> with Terpyridine Ancillary Ligands
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Bibliographic record
Abstract
A series of lead(II) coordination polymers containing [N(CN)(2)](-) (DCA) or [Au(CN)(2)](-) bridging ligands and substituted terpyridine (terpy) ancillary ligands ([Pb(DCA)(2)] (1), [Pb(terpy)(DCA)(2)] (2), [Pb(terpy){Au(CN)(2)}(2)] (3), [Pb(4'-chloro-terpy){Au(CN)(2)}(2)] (4) and [Pb(4'-bromo-terpy)(μ-OH(2))(0.5){Au(CN)(2)}(2)] (5)) was spectroscopically examined by solid-state (207)Pb MAS NMR spectroscopy in order to characterise the structural and electronic changes associated with lead(II) lone-pair activity. Two new compounds, 2 and [Pb(4'-hydroxy-terpy){Au(CN)(2)}(2)] (6), were prepared and structurally characterised. The series displays contrasting coordination environments, bridging ligands with differing basicities and structural and electronic effects that occur with various substitutions on the terpyridine ligand (for the [Au(CN)(2)](-) polymers). (207)Pb NMR spectra show an increase in both isotropic chemical shift and span (Ω) with increasing ligand basicity (from δ(iso) = -3090 ppm and Ω = 389 ppm for 1 (the least basic) to δ(iso) = -1553 ppm and Ω = 2238 ppm for 3 (the most basic)). The trends observed in (207)Pb NMR data correlate with the coordination sphere anisotropy through comparison and quantification of the Pb-N bond lengths about the lead centre. Density functional theory calculations confirm that the more basic ligands result in greater p-orbital character and show a strong correlation to the (207)Pb NMR chemical shift parameters. Preliminary trends suggest that (207)Pb NMR chemical shift anisotropy relates to the measured birefringence, given the established correlations with structure and lone-pair activity.
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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 | 0.003 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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 it