Synthesis of four different antimony(III) O,O′-dialkyldithiophosphates: Characterization by 31P CP/MAS NMR, single-crystal X-ray diffraction, and adsorption at a stibnite surface (Sb2S3)

doi:10.1016/j.jcis.2011.10.064

Journal of Colloid and Interface Science

Volume 368, Issue 1, 15 February 2012, Pages 488-495

https://doi.org/10.1016/j.jcis.2011.10.064 Get rights and content

Abstract

Four different dialkyldithiophosphate (DTP) ions, (RO)₂PSS⁻ (R = C₃H₇, iso-C₃H₇, iso-C₄H₉, and cyclo-C₆H₁₁), have been adsorbed on the surface of synthetically prepared stibnite, Sb₂S₃, and studied by means of ³¹P CP/MAS NMR. Corresponding individual [Sb{S₂P(OR)₂}₃] complexes have also been synthesized and used for comparison with the surface-adsorbed DTP species. The results show that a low concentration of collector at the surface leads to a chemisorbed monolayer of DTP on the mineral surface. At high concentration of DTP, a surface precipitate of Sb(DTP)₃ is formed. ³¹P CP/MAS NMR and chemical shift anisotropy data indicate that the S single bond PS bite angle of the chemisorbed DTP groups on the surface is larger than in the corresponding precipitated complexes and the coordination of the ligands differs. Using single-crystal X-ray diffraction technique, the molecular structure of a solvated form of crystalline O,O′-di-cyclo-hexyldithiophosphate antimony(III) complex has been resolved. In this novel molecular structure, the central antimony atom S,S′-anisobidentately coordinates three structurally non-equivalent DTP groups, and therefore, the geometry of the [SbS₆] chromophore can be approximated by a distorted octahedron. Besides that, useful correlations between ³¹P CSA parameters and structural data on this complex were also established.

Graphical abstract

Highlights

► Crystal structure determination of [Sb{S₂P(O-cyclo-C₆H₁₁)₂}₃]·1/3 C₂H₅OH. ► ³¹P CP/MAS NMR chemical shift anisotropy parameters for [Sb{(S₂P(OR)₂}₃] complexes are determined. ► ³¹P CP/MAS NMR data on dithiophosphate ligands surface adsorbed on synthetic stibnite suggest a bridging coordination.

Introduction

Antimony and its compounds have many important applications, e.g., in alloys, in batteries, as flame-retardants, semiconductors, and pigments [1], [2], [3], [4], [5], [6], [7], [8], [9]. Antimony trisulfide (Sb₂S₃) has found use, e.g., in various optical and photosensitive applications, for radiolabeling, and as a lubricant [1], [2], [3], [4], [5], [6], [7], [8], [9]. The principal source of antimony is the natural mineral stibnite, Sb₂S₃. In the froth flotation of sulfide minerals, ionic O,O′-dialkyldithiophosphates (DTP) are frequently used reagent collectors. One of the important questions in flotation theory is connected with the fixation modes of ionic dithioreagent collectors (such as dialkyldithiophosphates, alkyldithiocarbonates (i.e., xanthates), and dialkyldithiocarbamates) on the surfaces of sulfide minerals. Previously, using both liquid and solid-state ³¹P NMR techniques, we have established principally different fixation modes of DTP ions on the surface of both synthetic sphalerite (ZnS) [10] and galena (PbS) [11]. The bridging coordination of DTP groups to two neighboring zinc atoms was suggested in the case of surface zinc(II) complexes on a ZnS surface [10], while there is mainly terminal S,S′-chelating coordination of DTP ions to one lead atom on a PbS surface [11]. To get an efficient flotation of Sb₂S₃, it is meaningful to understand the interaction between mineral surface and ionic dialkyldithiophosphate collectors.

In this study, we have characterized four different potassium O,O′-dialkyldithiophosphates adsorbed on the surface of synthetically prepared Sb₂S₃. It is known that Sb(III) is starting to oxidize to Sb(V) at pH above 4 [9]. In order to avoid oxidation, the adsorption experiments were performed at pH 3. ³¹P CP/MAS NMR was used to study the coordination of DTP groups to the mineral surface. For comparison, Sb(DTP)₃ complexes with the same ligands were synthesized and ³¹P and ¹³C CP/MAS NMR measurements were taken. Both ³¹P chemical shifts and chemical shift anisotropy (CSA) were used to characterize the surface coordination.

Additionally, the crystal and molecular structure of tris(O,O′-di-cyclo-hexyldithiophosphato-S,S′)antimony(III), which is solvated with ethanol, has been determined using the single-crystal X-ray diffraction technique.

Section snippets

Synthesis of Sb₂S₃

Antimony trisulfide, Sb₂S₃, was synthesized in basically the same way as is previously reported [2]. An excess of thioacetamide was added to a 0.1 M solution of SbCl₃ in absolute ethanol. The solution was stirred until the color changed from yellow to red. The mixture was left for 24 h before the precipitate was filtered and washed with ethanol. The red Sb₂S₃ was dried in vacuum at 100 °C until it transformed into the stable black form. The identity of the sample was confirmed by XRD.

Preparation of surface complexes

Surface

Structural description of [Sb{S₂P(O-cyclo-C₆H₁₁)₂}₃]·1/3 C₂H₅OH (III)

Table 1 summarizes selected crystal data for solvated compound III. The unit cell of the compound comprises eighteen molecules of tris(O,O′-di-cyclo-hexyldithiophosphato-S,S′)antimony(III) and six ethanol molecules, [Sb{S₂P(O-cyclo-C₆H₁₁)₂}₃]·1/3 C₂H₅OH.

The central antimony atom exhibits a sixfold coordination with three dithiophosphate groups acting as S,S′-bidentate-chelating ligands (see Fig. 2). Therefore, the coordination polyhedron [SbS₆] can be approximated by a distorted octahedron,

Summary and conclusions

³¹P CP/MAS NMR data show that even if the isotropic chemical shifts of the DTP groups adsorbed at the Sb₂S₃ surface are almost identical to the chemical shifts of the corresponding Sb(DTP)₃ complexes, the chemical shift anisotropy tensors are completely different for these two types of species. The tensors are more spherical for the ³¹P nuclei in the chemisorbed complexes and more prolate for the more crystalline Sb(DTP)₃ complexes, indicating that the S single bond PS bite angle increases when the DTP

Supplementary material

CCDC 833600 contains the supplementary crystallographic data for complex III. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: [email protected].

Acknowledgments

We wish to thank CHEMINOVA AGRO A/S for kindly supplying the potassium dialkyldithiophosphate salts. Part of the study was financed by Agricola Research Centre Multicomponent Mineral Systems (ARC-MMS), through the Strategic Mining Research Program, co-funded by the Swedish mining industry and the Swedish Governmental Agency for Innovation Systems (Vinnova), and Centre for Advanced Mining and Metallurgy (CAMM), financed by strategic funds from the Swedish Government.

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Synthesis of four different antimony(III) O,O′-dialkyldithiophosphates: Characterization by 31P CP/MAS NMR, single-crystal X-ray diffraction, and adsorption at a stibnite surface (Sb2S3)

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Synthesis of Sb2S3

Preparation of surface complexes

Structural description of [Sb{S2P(O-cyclo-C6H11)2}3]·1/3 C2H5OH (III)

Summary and conclusions

Supplementary material

Acknowledgments

Mater. Res. Bull.

Solid State Commun.

Appl. Radiat. Isotopes

Mater. Chem. Phys.

Wear

Inorg. Chim. Acta

J. Coll. Interf. Sci.

Inorg. Chim. Acta

J. Magn. Reson.

J. Magn. Reson.

Solid State Nucl. Mag.

Inorg. Chim. Acta

Inorg. Chim. Acta

J. Magn. Reson.

Inorg. Chim. Acta

Polyhedron

Structure-Property Relations in Nonferrous Metals

D: Appl. Phys.

J. Mater. Chem.

Trans. Instn. Min. Metall. (Sect. C: Miner. Process. Extr. Metall.)

Zhur. Obshch. Khim.

Lubric. Eng.

J. Chem. Phys.

Synthesis of four different antimony(III) O,O′-dialkyldithiophosphates: Characterization by ³¹P CP/MAS NMR, single-crystal X-ray diffraction, and adsorption at a stibnite surface (Sb₂S₃)

Synthesis of Sb₂S₃

Structural description of [Sb{S₂P(O-cyclo-C₆H₁₁)₂}₃]·1/3 C₂H₅OH (III)