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- Title
The Supramolecular and Coordination Chemistry of Cobalt(II) Extraction by Phosphinic Acids.
- Authors
Carson, Innis; Tasker, Peter A.; Love, Jason B.; Moser, Michael; Fischmann, Adam J.; Jakovljevic, Boban; Soderstrom, Matthew D.; Morrison, Carole A.
- Abstract
A combination of mass spectrometry, DFT calculations and 31P{1H} NMR spectroscopy has been used to define the mode of action of the commercial cobalt extractant, bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX®272, L¹H) in Co recovery. The nature of the CoII complexes formed in the water-immiscible phase is determined largely by the propensity of phosphinates to form strong interligand H-bonds in the outer coordination sphere and also to form stable µ2-Co-O-P-O-Co bridges. At low Co loading levels, the predominant species is the 4:1 complex, [Co(L¹·L¹H)2], in which coordinated neutral phosphinic acid ligands form strong H-bonds to adjacent anionic phosphinates. At higher Co loading, oligomers such as [(L¹·L¹H)Co(L¹ 2Co)n(L¹·L¹H)] are formed with µ2-phosphinate bridging, resulting in a substantial increase in the viscosity of the water-immiscible phase. The presence of tris(2,4,4-trimethylpentyl) phosphine oxide (L²) in the commercial formulation reduces the viscosity because its incorporation into oligomeric complexes such as [(L²)Co{L¹ 3CoL¹CoL¹ 3Co}mL¹] can terminate chains, resulting in a lower average molecular weight. The uptake of Zn by L¹H shows a very similar dependence of viscosity on loading, and DOSY spectra and mass spectrometry demonstrate that higher molecular weight species are present at high Zn loading.
- Subjects
PHOSPHINIC acid; COBALT; COORDINATION compounds; MASS spectrometry; DENSITY functional theory
- Publication
European Journal of Inorganic Chemistry, 2018, Vol 2018, Issue 13, p1511
- ISSN
1434-1948
- Publication type
Article
- DOI
10.1002/ejic.201701473