Thermochemical Studies on Metal Complexes. I. Free Energy, Enthalpy, and Entropy Changes for Stepwise Formation of Cadmium(II) Halide Complexes in Aqueous Solution at 25 degrees C.

Gerding, Per; Wennerbeck, Ingegerd; Pedersen, C. Th.; Svanholm, Ulla; Brunvoll, J.; Bunnenberg, E.; Djerassi, Carl; Records, Ruth

doi:10.3891/acta.chem.scand.20-0079

Cited by 33 publications

(17 citation statements)

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“…The sharp decrease of AH: with increasing softness of the acceptor means that the formation of an essentially covalent bond is accompanied by a large evolution of heat, as has also been inferred by ROSSOTTI [B] (p. 27) and by GERDING [30].…”

Section: Agosupporting

confidence: 55%

Enthalpy and Entropy Changes by Formation of Different Types of Complexes

Ahrland¹

1967

Helvetica Chimica Acta

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Ligands coordinated to acceptors termed ( a ) , or hard, are generally held by bonds of an essentially electrostatic character, while the less numerous group of acceptors termed (b), or soft, form bonds which are markedly covalent.The facts supporting this statement may be summarized as follows [l]: With a certain group of ligands of the same charge, e.g. the halide ions, the complexes formed by (a)-acceptors are invariably stronger, the smaller the ligand. The complexes also become stronger the higher the charge and the smaller the radius of the acceptor involved. For (b)-acceptors on the other hand, the strongest complex is not formed by the smallest ligand of a series, but by a succeeding one. Strong complexes are often formed with uncharged ligands of low polarity, or even no polarity at all, such as olefins. For several elements, the (b)-character increases with decreasing charge of the acceptor, and even becomes most pronounced in the zero oxidation state.For typical (b)-acceptors, the bonds become strongly covalent, especially when the ligands are also very soft, i. e. very prone to covalent bonding. Such ligands as a rule exert only weak electrostatic attraction, and are therefore not coordinated by hard acceptors. Hard ligands on the other hand, i . e . those held mainly by electrostatic forces, are coordinated to all acceptors surrounded by a sufficiently strong field, irrespective of whether they are hard or soft.

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Section: Agosupporting

confidence: 55%

Enthalpy and Entropy Changes by Formation of Different Types of Complexes

Ahrland¹

1967

Helvetica Chimica Acta

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“…Again, the values from the Swedish group [66GEb,68GJc] show an ionic strength dependence distinctly smaller than that of the Russian group [67MFa,72FKc]. We assign uncertainties accordingly as: ± 2.0 and ± 3.0 kJ mol -1 , respectively.…”

Section: The CD 2+ + Cl -Systemmentioning

confidence: 99%

“…Reaction enthalpies for the formation of CdCl + have been published by many authors, using direct calorimetry [66GEb,67MFa,68GJc,72FKc] and the temperature variation of the stability constants [49KIa, 53VDa, 62BDc, 69SPa, 81MBa]. As the former technique generally gives more reliable results [58SIL], and as the reaction enthalpies are very small and therefore have large uncertainties, the latter have been rejected.…”

Section: The CD 2+ + Cl -Systemmentioning

confidence: 99%

“…The data from these groups are broadly consistent, although the ionic strength dependence reported by the latter group is larger. Due to the very detailed description of the experimental procedures by [66GEb,68GJc], we give their values a higher weighting in the regression analysis (an assigned uncertainty of ±1.0 kJ mol -1 , compared with ±1.5 kJ mol -1 for the results from [67MFa,72FKc]). The uncertainties assigned to the accepted values include our estimates of possible systematic errors.…”

Section: The CD 2+ + Cl -Systemmentioning

confidence: 99%

“…As the former technique generally gives more reliable results [58SIL], and as the reaction enthalpies are very small and therefore have large uncertainties, the latter have been rejected. The accepted values are presented in Table A2-13. Direct calorimetric determinations have been reported by Swedish [66GEb,68GJc] and Russian [67MFa,72FKc] groups. The data from these groups are broadly consistent, although the ionic strength dependence reported by the latter group is larger.…”

Section: The CD 2+ + Cl -Systemmentioning

confidence: 99%

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Chemical speciation of environmentally significant metals with inorganic ligands. Part 4: The Cd2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)

Powell

Brown

Byrne

et al. 2011

Pure and Applied Chemistry

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Abstract:The numerical modeling of Cd II speciation amongst the environmental inorganic ligands Cl -, OH -, CO 3 2-, SO 4 2-, and PO 4 3-requires reliable values for the relevant stability (formation) constants. This paper compiles and provides a critical review of these constants and related thermodynamic data. It recommends values of log 10 β p,q,r°v alid at I m = 0 mol kg -1 and 25 °C (298.15 K), along with the equations and empirical reaction ion interaction coefficients, Δε , required to calculate log 10 β p,q,r values at higher ionic strengths using the Brønsted-Guggenheim-Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, Δ r H, are reported where available. Unfortunately, with the exception of the Cd II -chlorido system and (at low ionic strengths) the Cd II -sulfato system, the equilibrium reactions for the title systems are relatively poorly characterized.In weakly acidic fresh water systems (-log 10 {[H + ]/c°} < 6), in the absence of organic ligands (e.g., humic substances), Cd II speciation is dominated by Cd 2+ (aq), with CdSO 4 (aq) as a minor species. In this respect, Cd II is similar to Cu II [2007PBa] and Pb II [2009PBa]. However, in weakly alkaline fresh water solutions, 7.5 < -log 10 {[H + ]/c°} < 8.6, the speciation of Cd II is still dominated by Cd 2+ (aq), whereas for Cu II [2007PBa] and Pb II [2009PBa] the carbonato-species MCO 3 (aq) dominates. In weakly acidic saline systems (-log 10 {[H + ]/c°} < 6; -log 10 {[Cl -]/c°} < 2.0) the speciation is dominated by CdCl n (2-n)+ complexes, (n = 1-3), with Cd 2+ (aq) as a minor species. This is qualitatively similar to the situation for Cu II and Pb II . However, in weakly alkaline saline solutions, including seawater, the chlorido-complexes still dominate the speciation of Cd II because of the relatively low stability of CdCO 3 (aq). In contrast, the speciation of Cu II [2007PBa] and Pb II [2009PBa] in seawater is dominated by the respective species MCO 3 (aq). There is scope for additional high-quality measurements in the Cd 2+ + H + + CO 3 2-system as the large uncertainties in the stability constants for the Cd 2+ -carbonato complexes significantly affect the speciation calculations.

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Kontinuierliche Titrationscalorimetrie. Teil II: Anwendungen

Becker

1969

Chemie Ingenieur Technik

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Die bisher bekannt gewordenen Anwendungen der kontinuierlichen Titrationscalorimetrie erstrecken sich auf die Bestimmung von Reaktionsenthalpien in wäßrigen und nichtwäßrigen Medien, auch von heterogenen Prozessen, ferner vor allem auf die Bestimmung der vollständigen thermodynamischen Daten ein‐ und mehrstufiger Gleichgewichtsreaktionen in Lösung sowie schließlich auf die kontinuierliche Bestimmung von Mischungswärmen. Insgesamt wird in diesem Beitrag gezeigt, welche Möglichkeiten die Methode der kontinuierlichen Titrationscalorimetrie bietet, wie sie sich mit anderen physikalischen Methoden koppeln läßt, und wo ihre Vorzüge und Grenzen liegen.

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Thermochemical Studies on Metal Complexes. I. Free Energy, Enthalpy, and Entropy Changes for Stepwise Formation of Cadmium(II) Halide Complexes in Aqueous Solution at 25 degrees C.

Cited by 33 publications

References 0 publications

Enthalpy and Entropy Changes by Formation of Different Types of Complexes

Enthalpy and Entropy Changes by Formation of Different Types of Complexes

Chemical speciation of environmentally significant metals with inorganic ligands. Part 4: The Cd2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)

Kontinuierliche Titrationscalorimetrie. Teil II: Anwendungen

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