Structure and stability of cadmium chloride complexes in hydrothermal fluids

Fe isotope fractionation during phase separation in the NaCl–H2O system: An experimental study with implications for seafloor hydrothermal vents

“…An example of this is provided by XAS studies at supercritical conditions of cobalt chloro-complexes, which indicate that at a similar high temperature (440 • C), the water rich [CoCl 2 (H 2 O) 2 ] 0 complex is predominant at low salinity (<0.5 mol/kg dissolved Cl), whereas [CoCl 4 ] 2− exists at high salinity (Liu et al, 2011). Similar spectroscopic studies for the NiCl 2 -, CdCl 2 -, and MnCl 2 -H 2 O-NaCl systems (Bazarkina et al, 2010;Migdisov et al, 2011;Tian et al, 2012Tian et al, , 2014 also exhibit increasing degrees of stability for tetrahedrally coordinated metal aquo-chloro-complexes at elevated temperatures with analogous changes in coordination chemistry as a function of dissolved chloride concentration. We infer from previous spectroscopic efforts that the chloride-rich liquid phase is dominated by [FeCl 4 ] 2− at all times of the experiment, whereas the vapor phase is susceptible to changes in the relative abundance of [FeCl 2 (H 2 O) 2 ] 0 and [FeCl 4 ] 2− upon progressive phase separation.…”

Speciation and thermodynamic properties for cobalt chloride complexes in hydrothermal fluids at 35–440°C and 600bar: An in-situ XAS study

“…For example, under which conditions (T, P, salinity) is the metal bonded with four halide ions (e.g., FeCl 4 2À , Testemale et al, 2009; ZnCl 4 2À , Mayanovic et al, 1999), or with both halide ions and water molecules (e.g., NiBr 3 (H 2 O) À , Hoffmann et al, 1999)? A similar coordination change from octahedral to tetrahedral-like upon increasing temperature and/or salinity was described by Bazarkina et al (2010) for Cd 2+ , with aqueous speciation at high temperature (>300°C) dominated by the tetrahedral complexes CdCl 2 (H 2 O) 2(aq) and CdCl 3 (H 2 O) À .…”

Speciation and thermodynamic properties of zinc in sulfur-rich hydrothermal fluids: Insights from ab initio molecular dynamics simulations and X-ray absorption spectroscopy

“…Compared to some other divalent metal ions such as Cd (II) (Bazarkina et al, 2010), Fe(II) (Testemale et al, 2009), Mn(II) (Tian et al, 2014), Ni(II) and Co (II) (Liu et al, 2011), a unique feature of Zn(II) bisulfide and chloride complexing is that the only octahedral complex in the system is the aqua Zn(H 2 O) 6 2+ complex; i.e., substitution of a chloride or bisulfide ligand causes the complex to attain a tetrahedral geometry. For example, in the simulations that started with octahedral [Zn(HS) (H 2 O) 5 ] + (simulation 1a, 2a, 4a), this octahedral complex rapidly (within less than 1 ps) lost two water molecules to form tetrahedral [Zn(HS)(H 2 O) 3 ] + .…”