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<p>This study focuses on the analysis of the absorption spectra of cobalt(II) nitrate and cobalt(II) bromide complexes in the <i>x</i>Ca(NO<sub>3</sub>)<sub>2</sub>–(1 − <i>x</i>)NH<sub>4</sub>NO<sub>3</sub>–H<sub>2</sub>O system. Measurements were conducted within the wavelength range of 400–800&#xa0;nm, at a constant temperature of <i>T</i> = 328.15&#xa0;K and atmospheric pressure of <i>p</i> = 101.3&#xa0;kPa. The spectra were recorded for systems with a fixed salt composition of 0.3Ca(NO<sub>3</sub>)<sub>2</sub>–0.7NH<sub>4</sub>NO<sub>3</sub>–H<sub>2</sub>O, but with varying water content, described by the mole ratio of water to salt (<i>R</i> = H<sub>2</sub>O/salt), where <i>R</i> was set to 1.0, 1.2, and 1.6. Additionally, the study investigated systems with varying calcium nitrate-to-ammonium nitrate ratios, represented as <i>x</i>Ca(NO<sub>3</sub>)<sub>2</sub>–(1 − <i>x</i>)NH<sub>4</sub>NO<sub>3</sub>–H<sub>2</sub>O, where <i>x</i> takes the values 0.3, 0.4, and 0.6. In these systems, the mole ratio of water to total salt was kept constant at <i>R</i> = 1.6. For systems with <i>x</i> = 0.7 and 0.9, a higher water-to-salt mole ratio of <i>R</i> = 3.6 was used. The analysis of absorption spectra revealed a shift of the maximum absorption peak toward shorter wavelengths (blue shift) as the water content (<i>R</i>) increased. This behavior suggests that both water molecules and nitrate ions participate in the coordination around the cobalt(II) ion. Based on the spectral data, the presence of the following complexes was confirmed: [Co(NO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>2−</sup>, [Co(NO<sub>3</sub>)<sub>2</sub>Br<sub>2</sub>]<sup>2−</sup> and [CoBr<sub>4</sub>]<sup>2−</sup>. The overall stability constants of these complexes were calculated, and the corresponding resolved spectra of the species were determined at <i>T</i> = 328.15&#xa0;K.</p>

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Influence of Water on the Stability of Cobalt Bromide Complexes in Aqueous Calcium Nitrate–Ammonium Nitrate Melts at T = 328.15 K: A Spectrophotometric Approach

  • 期刊论文

  • 发表日期：

    2025年4月24日

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  • Milan B. Vraneš,
  • Snežana M. Papović

摘要

This study focuses on the analysis of the absorption spectra of cobalt(II) nitrate and cobalt(II) bromide complexes in the xCa(NO3)2–(1 − x)NH4NO3–H2O system. Measurements were conducted within the wavelength range of 400–800 nm, at a constant temperature of T = 328.15 K and atmospheric pressure of p = 101.3 kPa. The spectra were recorded for systems with a fixed salt composition of 0.3Ca(NO3)2–0.7NH4NO3–H2O, but with varying water content, described by the mole ratio of water to salt (R = H2O/salt), where R was set to 1.0, 1.2, and 1.6. Additionally, the study investigated systems with varying calcium nitrate-to-ammonium nitrate ratios, represented as xCa(NO3)2–(1 − x)NH4NO3–H2O, where x takes the values 0.3, 0.4, and 0.6. In these systems, the mole ratio of water to total salt was kept constant at R = 1.6. For systems with x = 0.7 and 0.9, a higher water-to-salt mole ratio of R = 3.6 was used. The analysis of absorption spectra revealed a shift of the maximum absorption peak toward shorter wavelengths (blue shift) as the water content (R) increased. This behavior suggests that both water molecules and nitrate ions participate in the coordination around the cobalt(II) ion. Based on the spectral data, the presence of the following complexes was confirmed: [Co(NO3)4(H2O)2]2−, [Co(NO3)2Br2]2− and [CoBr4]2−. The overall stability constants of these complexes were calculated, and the corresponding resolved spectra of the species were determined at T = 328.15 K.