Structure of highly concentrated aqueous electrolyte solutions of transition metal chlorides and bromides
(2025) In Dalton Transactions- Abstract
The structures of the complexes dominating in highly concentrated and 1.0 mol dm−3 aqueous solutions of first-row transition metal chlorides and bromides have been studied using large angle X-ray scattering (LAXS) and/or EXAFS. Of these systems, only zinc(ii) chloride and bromide form inner-sphere complexes in dilute aqueous solutions. No inner-sphere complexes corresponding to dilute aqueous perchlorate solutions and [M(H2O)6](ClO4)2 solids were formed in 1.0 mol dm−3 aqueous solutions of the cobalt(ii), nickel(ii) and copper(ii) chloride and bromide systems, according to the superimposing EXAFS spectra of these samples. A cis-dibromo complex dominates in a highly... (More)
The structures of the complexes dominating in highly concentrated and 1.0 mol dm−3 aqueous solutions of first-row transition metal chlorides and bromides have been studied using large angle X-ray scattering (LAXS) and/or EXAFS. Of these systems, only zinc(ii) chloride and bromide form inner-sphere complexes in dilute aqueous solutions. No inner-sphere complexes corresponding to dilute aqueous perchlorate solutions and [M(H2O)6](ClO4)2 solids were formed in 1.0 mol dm−3 aqueous solutions of the cobalt(ii), nickel(ii) and copper(ii) chloride and bromide systems, according to the superimposing EXAFS spectra of these samples. A cis-dibromo complex dominates in a highly concentrated aqueous manganese(ii) bromide solution, as that found in the solid state. In highly concentrated solutions of cobalt(ii) and nickel(ii) chloride and bromide and copper(ii) chloride, one inner-sphere complex is formed, while the remaining halide ions are in the second coordination shell. In an almost saturated copper(ii) bromide solution (5.67 mol dm−3), a polynuclear complex based on hydrated cis-CuBr2 units is formed with a significantly different structure than that observed in the solid state, trans-[CuBr2(H2O)2]. In a highly concentrated zinc chloride solution, 11.81 mol dm−3, with less than two water molecules per ZnCl2 formula unit, a [Zn2Cl4] complex is formed, where the zinc ions are three-coordinated in a triangular fashion. In a 5.60 mol dm−3 zinc bromide solution, a dimeric [Zn2Br4(H2O)2] complex is formed, where the coordination around the zinc ions is distorted tetrahedral. These structures are different from those precipitated from saturated aqueous zinc chloride and bromide solutions, [Zn(H2O)6][ZnCl4], [(H2O)5Zn-Cl-ZnCl3] or [Cl3ZnClZn(H2O)4ClZnCl]n and [Zn(H2O)6][Zn2Br6]. An increased stability of high-symmetry complexes is observed in the solid state, while in aqueous solution, complexes with maximized hydration seem to be favored.
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- author
- Bajnóczi, Éva G. ; Sigfridsson Clauss, Kajsa G.V. LU and Persson, Ingmar
- organization
- publishing date
- 2025
- type
- Contribution to journal
- publication status
- epub
- subject
- in
- Dalton Transactions
- publisher
- Royal Society of Chemistry
- external identifiers
-
- scopus:105018677139
- pmid:40986374
- ISSN
- 1477-9226
- DOI
- 10.1039/d5dt01840d
- language
- English
- LU publication?
- yes
- additional info
- Publisher Copyright: © 2025 The Royal Society of Chemistry.
- id
- 809dd08f-d308-4ddb-8a20-6b4515e72eae
- date added to LUP
- 2026-01-26 09:47:54
- date last changed
- 2026-01-26 09:48:18
@article{809dd08f-d308-4ddb-8a20-6b4515e72eae,
abstract = {{<p>The structures of the complexes dominating in highly concentrated and 1.0 mol dm<sup>−3</sup> aqueous solutions of first-row transition metal chlorides and bromides have been studied using large angle X-ray scattering (LAXS) and/or EXAFS. Of these systems, only zinc(ii) chloride and bromide form inner-sphere complexes in dilute aqueous solutions. No inner-sphere complexes corresponding to dilute aqueous perchlorate solutions and [M(H<sub>2</sub>O)<sub>6</sub>](ClO<sub>4</sub>)<sub>2</sub> solids were formed in 1.0 mol dm<sup>−3</sup> aqueous solutions of the cobalt(ii), nickel(ii) and copper(ii) chloride and bromide systems, according to the superimposing EXAFS spectra of these samples. A cis-dibromo complex dominates in a highly concentrated aqueous manganese(ii) bromide solution, as that found in the solid state. In highly concentrated solutions of cobalt(ii) and nickel(ii) chloride and bromide and copper(ii) chloride, one inner-sphere complex is formed, while the remaining halide ions are in the second coordination shell. In an almost saturated copper(ii) bromide solution (5.67 mol dm<sup>−3</sup>), a polynuclear complex based on hydrated cis-CuBr<sub>2</sub> units is formed with a significantly different structure than that observed in the solid state, trans-[CuBr<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]. In a highly concentrated zinc chloride solution, 11.81 mol dm<sup>−3</sup>, with less than two water molecules per ZnCl<sub>2</sub> formula unit, a [Zn<sub>2</sub>Cl<sub>4</sub>] complex is formed, where the zinc ions are three-coordinated in a triangular fashion. In a 5.60 mol dm<sup>−3</sup> zinc bromide solution, a dimeric [Zn<sub>2</sub>Br<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>] complex is formed, where the coordination around the zinc ions is distorted tetrahedral. These structures are different from those precipitated from saturated aqueous zinc chloride and bromide solutions, [Zn(H<sub>2</sub>O)<sub>6</sub>][ZnCl<sub>4</sub>], [(H<sub>2</sub>O)<sub>5</sub>Zn-Cl-ZnCl<sub>3</sub>] or [Cl<sub>3</sub>ZnClZn(H<sub>2</sub>O)<sub>4</sub>ClZnCl]<sub>n</sub> and [Zn(H<sub>2</sub>O)<sub>6</sub>][Zn<sub>2</sub>Br<sub>6</sub>]. An increased stability of high-symmetry complexes is observed in the solid state, while in aqueous solution, complexes with maximized hydration seem to be favored.</p>}},
author = {{Bajnóczi, Éva G. and Sigfridsson Clauss, Kajsa G.V. and Persson, Ingmar}},
issn = {{1477-9226}},
language = {{eng}},
publisher = {{Royal Society of Chemistry}},
series = {{Dalton Transactions}},
title = {{Structure of highly concentrated aqueous electrolyte solutions of transition metal chlorides and bromides}},
url = {{http://dx.doi.org/10.1039/d5dt01840d}},
doi = {{10.1039/d5dt01840d}},
year = {{2025}},
}