Gallium(iii) hydration in aqueous solution of perchlorate, nitrate and sulfate. Raman and 71-Ga NMR spectroscopic studies and ab initio molecular orbital calculations of gallium(iii) water clustersElectronic supplementary information (ESI) available: Unscaled HF/6-31+G* frequencies, intensities and force constants of the hexaaqua-Ga(iii) ion, octadeca-aqua gallium(iii) and octadeca-aqua gallium(iii) cluster. See http://www.rsc.org/suppdata/cp/b2/b202567c/
Bibliographic record
Abstract
Raman spectra of aqueous Ga(III)- perchlorate, - nitrate and -sulfate solutions were measured. In Ga(III)- perchlorate solutions, a strongly polarized mode of medium intensity at 526 cm−1 and two depolarized modes at 430 cm−1 and 328 cm−1 have been assigned to v1(a1g), v2(eg) and v5(f2g) of the hexaaquagallium(III) ion, [Ga(OH2)63+] (Oh symmetry), respectively. The infrared active mode at 510 cm−1 has been assigned to v3(f1u). The polarized mode v1(a1g) GaO6 has been followed over a temperature range from 25 to 75 °C and band parameters (band maximum, full width of half height and band intensity) have been examined. The position of the v1(a1g) GaO6 mode shifts by only about 2 cm−1 to lower frequencies and broadens by about 10 cm−1 for a 50 °C temperature increase. The Raman spectroscopic data suggest that the hexaaquagallium(III) ion is thermodynamically stable in perchlorate solutions (no inner-sphere complex formation) over the temperature and concentration range measured. In a concentrated Ga(NO3)3 solution, most of the gallium (III) exist in the form of an outer-sphere ion pair, [Ga(OH2)63+ NO3−], except for a few percent of the gallium (III) which occurs as an inner-sphere complex, [Ga(OH2)5ONO2]2+. The nitrato complex is thermodynamically weak and disappears completely upon dilution. Gallium sulfate solutions show a different picture and a thermodynamically stable gallium(III) sulfato complex could be detected using Raman spectroscopy and 71-Ga NMR. The formation of the sulfato complex is favoured with increasing temperature and is thus entropically driven. At higher temperatures a basic gallium(III) sulfate of the alunite type is precipitated and was characterised by wet chemical analysis and X-ray diffraction (XRD). Ab initio geometry optimizations and frequency calculations of [Ga(OH2)n3+] clusters with n = 1 to 6 were carried out at the Hartree–Fock and second order Møller–Plesset levels of theory, using various basis sets up to 6-31+G*. The global minimum structure of the aqua Ga(III) species was reported. The unscaled vibrational frequencies of the [Ga(OH2)63+] cluster were reported and do not correspond well with experimental values because of the missing second hydration sphere. The theoretical binding enthalpy for [Ga(OH2)63+] was calculated and accounts for ca. 62% of the experimental single ion hydration enthalpy for Ga(III). Ab initio geometry optimizations and frequency calculations are also reported for a [Ga(OH2)183+] (Ga[6+12]) cluster with 6 water molecules in the first sphere and 12 water molecules in the second sphere (T symmetry). The calculated v1 GaO6 mode of the gallium [6+12] cluster occurs at 524 cm−1 (HF/6-31G*), in good agreement with the experimental value at 526 cm−1. The other frequencies of the gallium [6+12] cluster also correspond well with the observed frequencies in solution. The theoretical binding enthalpy for [Ga(OH2)183+] was calculated and is slightly underestimated compared to the experimental single ion hydration enthalpy for Ga(III).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.001 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), 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".