Confirming the Molecular Basis of the Solvent Extraction of Cadmium(II) Using 2-Pyridyl Oximes through a Synthetic Inorganic Chemistry Approach and a Proposal for More Efficient Extractants

Abstract

The present work describes the reactions of CdI2 with 2-pyridyl aldoxime (2paoH), 3-pyridyl aldoxime (3paoH), 4-pyridyl aldoxime (4paoH), 2-6-diacetylpyridine dioxime (dapdoH2) and 2,6-pyridyl diamidoxime (LH4). The primary goal was to contribute to understanding the molecular basis of the very good liquid extraction ability of 2-pyridyl ketoximes with long aliphatic chains towards toxic Cd(II) and the inability of their 4-pyridyl isomers for this extraction. Our systematic investigation provided access to coordination complexes [CdI2(2paoH)2] (1), {[CdI2(3paoH)2]}n (2), {[CdI2(4paoH)2]}n (3) and [CdI2(dapdoH2)] (4). The reaction of CdI2 and LH4 in EtOH resulted in a Cd(II)-involving reaction of the bis(amidoxime) and isolation of [CdI2(L’H2)] (5), where L’H2 is the new ligand 2,6-bis(ethoxy)pyridine diimine. A mechanism of this transformation has been proposed. The structures of 1, 2, 3, 4.2EtOH and 5 were determined by single-crystal X-ray crystallography. The complexes have been characterized by FT-IR and FT-Raman spectra in the solid state and the data are discussed in terms of structural features. The stability of the complexes in DMSO was investigated by 1H NMR spectroscopy. Our studies confirm that the excellent extraction ability of 2-pyridyl ketoximes is due to the chelating nature of the extractants leading to thermodynamically stable Cd(II) complexes. The monodentate coordination of 4-pyridyl ketoximes (as confirmed in our model complexes with 4paoH and 3paoH) seems to be responsible for their poor performance as extractants.

Reactions of Cadmium(II) Halides and Di-2-Pyridyl Ketone Oxime: One-Dimensional Coordination Polymers

“…For example, the Cd1-N1 and Cd1-N3** [1 − x , 1 − y , 1 − z ] bond lengths in 3 are 2.375(6) and 2.503(7) Å, respectively ( Figure S1 , Table 2 ). The Cd II -N pyridyl and Cd II -N oxime bond lengths are typical for 6-coordinate metal cadmium(II) centers in 2-pyridyl oxime complexes [ 16 , 22 , 23 , 24 , 25 , 26 , 27 ].…”

“…Typical examples are the various 2-pyridyl oximes ( Figure 1 , left; R = a non-donor group). These ligands have been used among other purposes, including the following: (i) the linking (by coordination bonds) of smaller clusters to supramolecular entities [ 12 ]; (ii) the synthesis of single-chain magnets (SCMs) [ 13 ]; (iii) the isolation of 3d/4f-metal dinuclear and polynuclear complexes [ 14 ]; (iv) the “switching on” of single-molecule magnetism (SMM) properties [ 15 ]; and (v) the modeling of solvent extraction of Cd(II) from aqueous media using 2-pyridyl ketoxime extractants [ 16 ].…”

“…The complex [Cd(O 2 CMe) 2 (2-pyaoH) 2 ] [ 27 ] has a similar structure to that of [Cd(HClO 2 ) 2 (2-pyaoH) 2 ] [ 26 ], the two monodentate carboxylate ligands being in cis positions. Our group has also contributed to the Cd(II)/pyridyl ald oxime chemistry by isolating and characterizing the mononuclear complex [CdI 2 (2-pyaoH) 2 ] and the 1D chain compounds {[CdI 2 (3-pyaoH) 2 ]} n and {[CdI 2 (4-pyaoH) 2 ]} n [ 16 ], where 3-pyaoH is pyridyl-3-aldoxime; the 2-pyaoH molecules behave as N pyridyl and N oxime -bidentate chelating ligands, whereas 3-pyaoH and 4-pyaoH act in a monodentate manner coordinating via their pyridyl nitrogen atom.…”

Conversion of corn shell as biomass solid waste into carbon species for efficient decontamination of wastewater via heavy metals adsorption

“…Wastewater treatment becomes a vital issue for developing countries in regards to the water as well as environmental securities. Conventional techniques such as solid-liquid extraction [8,9], liquid-liquid extraction [10,11], precipitation [12,13], and sorption [14,15] have been applied for heavy metals removal from aqueous solution. Although these technologies are frequently used, they have intrinsic disadvantages, e.g., high-energy requirements, byproduct formation, and high sludge production [3][4][5][6][7][8].…”

Anion–pyridine-n-oxime interplay to control metal–metal separations in a series of Cu(ii) coordination polymers

“…[12][13][14][15] The studies from Prof. S. P. Perlepes' group confirm the excellent extraction ability of 2-pyridyl ketoximes as chelating agents for Cd(II) contrary to the poor performance of 4-pyridyl ketoximes as extractants, most probably due to their monodentate coordination. 16 The magnetic properties of polynuclear oximate or hydroxamate complexes of 3d metals are governed by the exchange interactions in the polynuclear building blocks and can be predetermined by the appropriate choice of starting compound. 6,15,17 Dicarboxylic acids, both aromatic and aliphatic ones, as ligands demonstrate their excellent bridging functions in metal-organic networks.…”