Synthesis, structure and electrochemistry of isomeric nickel(ii) complexes of a [9]ane fused cyclam macrotricycle: evidence for a stable trans-IV and a redox induced rearrangement in a trans-I conformation
Bibliographic record
Abstract
The macrotricyclic ligand, 1,11-dithia-4,8,14,18-tetraaza-[5,2,2,5]-eicosane, L3 has been synthesized from cyclam. Both the cis- and the trans- isomers of the Ni(ii) complexes have been prepared and characterized by single crystal X-ray crystallography. In the cis-[Ni(trans-I, syn-L3)](Cl(2))·4H(2)O, the syn-isomer of L3 is present in which the cyclam ring adopts a trans-I stereochemistry. Crystal structure data (Pna2(1), tetragonal, a = 17.450(3), b = 12.188(2), c = 11.897(2) Å, V = 2530.2(8) Å(3), R(1) = 0.032 and wR(2) = 0.078) indicate that two of the Ni-N distances, Ni-N(4) = 2.164(3) Å and Ni-N(2) = 2.179(3) Å are longer than Ni-N(1) = 2.100(3) Å and Ni-N(3) = 2.101(3) Å. The Ni-S distances, 2.4265(11) Å and 2.4512(11) Å, are similar to lengths observed in many thioether complexes. The cyclic voltammogram for the Ni(2+/3+) redox couple of the cis-complex is scan rate dependent. Although quasi-reversible at a scan rate of 1000 mV s(-1), when the scan rate is lowered below 100 mV s(-1) the redox couple shows chemical irreversibility. There is evidence for rearrangement of the inner coordination sphere and adsorption of the oxidized species onto the Pt electrode. However, there is no evidence to suggest that isomerization of the cis- to the trans-complex occurs. Consistent with this electrochemical behavior, a time-dependent change in the ESR spectrum for the Ni(iii) species was also observed. A mechanism is proposed where through dissociation of a thioether donor and subsequent substitution of a solvent CH(3)CN, the trans-I conformation changes from a cis-type coordination to a trans-mode. In the trans-[Ni(trans-IV, anti-L3)](ClO(4))(2) complex, the anti-form of L3 is present where the cyclam moiety adopts the rare trans-IV stereochemistry. The trans-complex (C(2)/(c), monoclinic, a = 22.382(9), b = 10.118(2), c = 14.300(3) Å, V = 2493.3(13) Å(3), R(1) = 0.051 and wR(2) = 0.142) is a minor product with all Ni-N distances at 2.124(4) Å and Ni-S distances at 2.5321(13) Å. The trans-complex shows a reversible cyclic voltammogram for the Ni(2+/3+) couple and an axial ESR spectrum for the Ni(iii) species that is expected for such a symmetrical system. That there are no changes in the ESR spectroscopic features following redox cycles is consistent with the structural rigidity expected in an encapsulated system.
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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) | 0.001 | 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".