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. 2023 May 9;52(18):6152-6165.
doi: 10.1039/d3dt00184a.

Multi-technique structural analysis of zinc carboxylates (soaps)

Molly Wagner  1   2   3 , Roberta Pigliapochi  1   4   5 , Valeria Di Tullio  6 , Jaclyn Catalano  7 , Nicholas Zumbulyadis  1 , Silvia A Centeno  4 , Xiaoling Wang  8 , Kuizhi Chen  8 , Ivan Hung  8 , Zhehong Gan  8 , Michael R Dworzak  1 , Glenn P A Yap  1 , Cecil Dybowski  1
Affiliations

Multi-technique structural analysis of zinc carboxylates (soaps)

Molly Wagner et al. Dalton Trans. .

Abstract

A series of medium- and long-chain zinc carboxylates (zinc octanoate, zinc nonanoate, zinc decanoate, zinc undecanoate, zinc dodecanoate, zinc pivalate, zinc stearate, zinc palmitate, zinc oleate, and zinc azelate) was analyzed by ultra-high-field 67Zn NMR spectroscopy up to 35.2 T, as well as 13C NMR and FTIR spectroscopy. We also report the single-crystal X-ray diffraction structures of zinc nonanoate, zinc decanoate, and zinc oleate-the first long-chain carboxylate single-crystals to be reported for zinc. The NMR and X-ray diffraction data suggest that the carboxylates exist in three distinct geometric groups, based on structural and spectroscopic parameters. The ssNMR results presented here present a future for dynamic nuclear polarization (DNP)-NMR-based minimally invasive methods for testing artwork for the presence of zinc carboxylates.

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Conflict of interest statement

There are no conflicts of interest to declare.

Figures

Fig. 1
Fig. 1. X-ray-derived molecular structures of (A) zinc nonanoate, (B) zinc decanoate, and (C) zinc oleate, with 30% probability ellipsoids. H-atoms are depicted with standard bond lengths.
Fig. 2
Fig. 2. Structures of group I represented by ZnC9 (A) and ZnZ-C18 (B), and group II represented via ZnC10 (C) highlighting the arrangement of tetrahedron about the zinc in each crystal type. Hydrogens have been removed for visual clarity.
Fig. 3
Fig. 3. FTIR spectra of the zinc carboxylates, highlighting the νs COO (∼1540–1520 cm−1) highlighted in red and νas COO (1410–1395 cm−1) region highlighted in blue. Δν for all samples is characteristic of bidentate ligands. The splitting of the resonances is indicative of asymmetric zinc centers.
Fig. 4
Fig. 4. 13C NMR spectra for the zinc carboxylate series.
Fig. 5
Fig. 5. 13C NMR data for the carboxylate series, focusing on the carboxylate region.
Fig. 6
Fig. 6. 67Zn spectra for ZnC8. (Top, Black) Ssnake fitting parameters visualized in TopSpin; (Bottom, Blue) WURST-QCPMG spectrum at 15 625 Hz MAS. B0 35.2 T.
Fig. 7
Fig. 7. 67Zn spectra for ZnC10. (Top, Black) Ssnake fitting parameters visualized in TopSpin; (Bottom, Blue) WURST-QCPMG spectrum at 15 625 Hz MAS. B0 19.6 T.
Fig. 8
Fig. 8. 67Zn spectra for ZnPIV. (Top, Black) Ssnake fitting parameters visualized in TopSpin; (Bottom, Blue) WURST-QCPMG spectrum at 16 000 Hz MAS. Sideband regions denoted with asterisks. B0 35.2 T.
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