Low-temperature heat capacity and the standard molar enthalpy of formation of compound chromium(III) tri(pyrazine-2-carboxylate)

doi:10.1016/j.tca.2012.05.023

Thermochimica Acta

Volume 543, 10 September 2012, Pages 118-124

https://doi.org/10.1016/j.tca.2012.05.023 Get rights and content

Abstract

Low-temperature heat capacities of the coordination compound, chromium(III) tri(pyrazine-2-carboxylate), formulated as Cr(pyza)₃ (pyza = pyrazine-2-carboxylate), were measured by a precision automated adiabatic calorimeter over the temperature range of 78–400 K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least square method. Based on the fitted polynomial equation, the fitted heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated at the interval of 5 K. In accordance with a reasonable thermochemical cycle designed, the standard molar enthalpy of formation of the title complex was determined to be −1207.86 ± 3.39 kJ mol⁻¹ by an isoperibol solution–reaction calorimeter.

Highlights

▸ Low-temperature heat capacities of chromium(III) tri(pyrazine-2-carboxylate) were measured from 78 to 400 K. ▸ Thermodynamic functions of the compound at 298.15 K were calculated based on low-temperature heat capacity. ▸ The standard molar enthalpy of formation of the target was determined to be −1207.86 ± 3.39 kJ mol⁻¹ through a designed thermochemical cycle.

Introduction

The inorganic–organic hybrid materials has become a popular field of research in recent years due to the intriguing diversity of the structures and first for the usefulness in the areas like selective absorption, separation, gas storage, ion exchange, catalysis, optoelectronics and magnetic material [1], [2], [3], [4], [5], [6], [7]. In particular, rational selection of multifunctional ligands containing suitable coordination sites plays a crucial role in adjusting the network structure where the nature of the donor atoms may lead to the desired properties and functions. Multidentate N-/O-donor ligands are commonly used as organic spacers in the construction of coordination polymers. Pyrazine-2-carboxylic acid (Hpyza), a multifunctional heterocycle ligand with carboxylate group having three potential binding sites (one carboxylate group and two pyrazine-N atoms), has been frequently used for the construction of coordination polymers.

Only with thermodynamic data of substances can we quantitatively describe thermal stability and stable states at different temperatures and energy changing in different processes, and so on [8], [9]. Since heat capacity is the fundamental quality from which other thermodynamic functions may be derived, it is clearly important to clarify the microstructure both theoretical and practical purposes from any apparently C_p behavior of compound. Extending our work [10], the coordination compound, chromium(III) tri(pyrazine-2-carboxylate), formulated as Cr(pyza)₃ (pyza = pyrazine-2-carboxylate), was synthesized in the present work, and structurally determined by X-ray crystallography. Low-temperature heat capacities of the title compound were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 390 K, and heat capacities and thermodynamic data were also obtained. In addition, the standard molar enthalpy of formation of the title complex was determined by an isoperibol solution–reaction calorimeter. We expect these results would facilitate the application of the title compound in the urgently needed fields.

Section snippets

Materials and equipments

All reagents were of analytical grade and purchased commercially and used without further purification. The content of Cr³⁺ in Cr(OH)₃·3H₂O was complexometrially titrated, from which the mass fraction of Cr(OH)₃·3H₂O were determined as 99.90%. Elemental analyses (C, H and N) were performed on a Vario EL III analyzer. The precision of the elemental analysis is within 5‰. X-ray diffractions were collected with graphite monochromated Mo KR radiation ((λ) 0.71073 Å) on a Bruker CCD diffractometer

Synthesis and structural analysis

Compared with the previous report [19], the structure of the title compound was not influenced by the nature of the anion, this is to say, the reaction of CrCl₃ or Cr(NO₃)₃ with Hpyza results in the isostructured coordination compounds.

The molecular structure of chromium(III) tri(2-pyrazinecarboxylate) is plotted in Fig. 1. The dimensions of the crystal used for X-ray diffraction data collection are given in Table S1. Selected bond lengths and angles are listed in Table S2.

As shown in Fig. 1,

Conclusions

The paper reported the low temperature heat capacities of chromium(III) tri(2-pyrazinecarboxylate) measured by adiabatic calorimetry. The experimental molar heat capacities were derived from the experimental results. The fitted heat capacities and thermodynamic functions of the title compound were also obtained. In addition, the standard molar enthalpy of formation of the title compound was determined to be −(1207.86 ± 3.39) kJ mol⁻¹.

Acknowledgements

We gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant nos. 21173168 and 21127004) and the Nature Science Foundation of Shaanxi Province (Grant nos. 11JS110, FF10091 and SJ08B09).

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The authors of reference [8] published a set of papers on the thermochemistry of these metal-containing species. These involved enthalpies of formation and heat capacities, e.g. that of Na+ [14] and Cr3+ [15]. As the former quantity involves both solution phase reaction and combustion calorimetry of solid pyrazine-2-carboxylic acid, a new value for the solid phase enthalpy of formation of this species necessarily affects that of these and other metal salts.
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Low-temperature heat capacity and the standard molar enthalpy of formation of compound chromium(III) tri(pyrazine-2-carboxylate)

Abstract

Highlights

Introduction

Section snippets

Materials and equipments

Synthesis and structural analysis

Conclusions

Acknowledgements

Coord. Chem. Rev.

Thermochim. Acta

J. Chem. Thermodyn.

Reticular chemistry: occurrence and taxonomy of nets and grammar for the design of frameworks

Acc. Chem. Res.

Functional porous coordination polymers

Angew. Chem. Int. Ed.

Crystallized frameworks with giant pores: are there limits to the possible?

Acc. Chem. Res.

High-throughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture

Science

A mesh-adjustable molecular sieve for general use in gas separation

Angew. Chem. Int. Ed.

Copper(I) 1,2,4-triazolates and related complexes: studies of the solvothermal ligand reactions, network topologies and photoluminescence properties

J. Am. Chem. Soc.

Low-temperature heat capacities and thermodynamic properties of ethylenediammonium tetrachlorozincate chloride (C2H10N2)2(ZnCl4)Cl2

Thermochim. Acta

Low-temperature heat capacity and standards molar enthalpy of formation of copper l-threonate hydrate Cu(C4H7O5)·0.5H2O

Thermochim. Acta

High-throughput synthesis of zeolitic imidazolate frameworks and application to CO₂ capture

Low-temperature heat capacities and thermodynamic properties of ethylenediammonium tetrachlorozincate chloride (C₂H₁₀N₂)₂(ZnCl₄)Cl₂

Low-temperature heat capacity and standards molar enthalpy of formation of copper l-threonate hydrate Cu(C₄H₇O₅)·0.5H₂O