High-order Cu(II) chloro-complexes in LiCl brines: Insights from density function theory and molecular dynamics. (15th September 2015)

• Record Type: Journal Article
• Authors: Li, Hui-Ji; Yi, Hai-Bo; Xu, Jia-Jia
• Is Part Of: Geochimica et cosmochimica acta. Volume 165(2015:Sep. 15)
• Page Start: 1
• Page End: 13
• Publication Date: 2015-09-15
• Subjects: Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2015.05.018
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Cu(II) complexation by chloride is relevant to the transport of copper in near-surface geologic environments, yet the existence of high-order Cu(II) chloro-complexes still remains in dispute. In this study, the structure characteristics and stabilities of [CuCl x ] 2− x aq ( x = 3, 4, 5) complexes have been investigated using density functional theory (DFT) methods and molecular dynamics (MD) simulations. [CuCl3 ] − and [CuCl4 ] 2− species can both be tracked, while the [CuCl5 ] 3− aq complex cannot be recorded during MD simulations of trace Cu 2+ in chloride-rich brines. DFT calculations indicate that contact ion pair (CIP) conformers of [CuCl3 ] − species are less stable than its solvent separated ion pair (SSIP) conformers, in which one Cl − stays in the second coordination sphere of the centered Cu 2+ . MD simulations also reveal that the SSIP conformer is apt to appear in the aqueous solution than its CIP conformer. It seems that the third Cl − is more likely in the second coordination shell of center Cu 2+ in [CuCl3 ] − . Meanwhile, the characteristic peak around 385 nm resolved in UV–Vis spectra experiments, which was attributed to the [CuCl3 ] − complex, could also be resulted from some SSIP structures of the [CuCl3 ] − complex. In MD simulations, the complex [CuCl4 ] 2− aq is found more stable than [CuCl3 ] − aq . The surrounding water molecules around [CuCl x ] 2− x aq ( x = 3, 4) enhance their stabilities in Cl − brines, especially for [CuCl4 ] 2− aq . The hydration shell of [CuCl4 ] 2− aq species is more intact than that of [CuCl3 ] 2− aq, and the residence time of a water molecule in the second coordination sphere of Cu ion in the [CuCl4 ] 2− aq complex is also obviously longer than that of [CuCl3 ] − aq . The [CuCl4 ] 2− aq complex can even be recorded in the less concentrated (6.33 m) Cl − solution, while the [CuCl3 ] − aq complex is tracked only in the 16.32 m Cl − brine. Meanwhile, the possibilities of [CuCl3 ] − aq and [CuCl4 ] 2− aq complexes found in 16.32 m Cl − solutions both decrease with increasing temperature, [CuCl3 ] − aq cannot be recorded during our simulations at 373 K and 423 K, and only few [CuCl4 ] 2− aq at 423 K.