Elissa A. Ukraintseva

Vapour pressure of 4-methylpyridine (MePy) over [Ni(MePy)4(NCS)2]·y(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy) clathrates during their dissociation

Strain measurement and quasiequilibrium thermogravimetry were used to study the dissociation processes of two clathrates, [Ni(MePy)4(NCS)2]·(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy), accompanied by the liberation of MePy into the gaseous phase. In the Ni clathrate dissociation process in the temperature range 298–368 K the liberated MePy was redistributed between the solid clathrate and gaseous phases; the MePy vapour pressure over the clathrate is a function of temperature and the guest contenty, which agrees with the presence in the MePy-[Ni(MePy)4(NCS)2] system of a wide range of β-clathrate solutions, [Ni(MePy)4(NCS)2]·y(MePy). The same methods used to study the Cu clathrate dissociation resulted in conclusions different from those obtained for the dissociation process of the above clathrate: the process is described by the equation [Cu(MePy)4(NCS)2]·2/3(MePy)solid =[Cu(MePy)2(NCS)2]solid+22/3(MePy)gas; the temperature dependence of the Mepy vapour pressure over the solid sample does not depend on its composition, which points to the absence from the system of solid solutions based on the clathrate. Standard changes of the enthalpy, entropy, and isobaric-isothermal reaction potential for the temperature range 292–325 K are equal to 178.6±1.7 kJ (mole of clathrate)−1, 463±5.6 J (mole of clathrate)−1 K−1, and 40.4±2.4 kJ (mole of clathrate)−1, respectively.

Thermodynamic Dissociation Constants for [MPy4(NO3)2]*2Py Clathrates (M=Mn, Co, Ni, Cu)

Abstract Stoichiometry and thermodynamic parameters of the title clathrates dissociation have been studied with thermoanalytical and strain method techniques. The [MPy4(NO3)2]*2Py (M = Mn, Co, Ni) clathrates dissociate with collapsing clathrate porous phase and destruction of the host complex to give the respective tripyridine complexes and gaseous pyridine. The [CuPy4(NO3)2]*2Py dissociates with collapsing clathrate phase but giving the host [CuPy4(NO3)2] complex as individual phase, with the tripyridine complex forming in further course of decomposition. The comparison of the thermodynamic dissociation parameters for the [MPy4(NO3)2]*2Py series with M = Mn, Co, Ni, Cu, Zn and Cd shows that the differences in the stability of the compounds do not correlate with structural parameters of the clathrates but depend on the nature of the metal cation in the host complex. Thermodynamic stability of these clathrate phases follows the general sequence of stabilty for complexes of the 3d transition metals known as Irwing-Williams sequence: MnZn. These results disclose the main issue of instability of the [MPy4(NO3)2]*2Py clathrates as instability of the respective host complexes.

Thermodynamic Stability of the (M(Pyridine)4X2) ∗ 2G Clathrates as a Function of the Host Components (M, X) and Included Guest (G)

This study compares thermodynamic stability of clathrate compounds belonging to three isomorphous series: [Mpy4(NCO)2]*2Py (M = M(II) = Mn, Fe, Co, Ni), [Mpy4(NO3)2]*2Py (M = Mn, Co, Ni, Cu, Zn), and [CuPy4(NO3)2]*2G (G = pyridine, benzene, THF, chloroform). Thermodynamic parameters (Δ Hav0, Δ Sav0 and Δ G2980 of the dissociation of the clathrates were determined from the dependences of the guest equilibrium pressure over the clathrates versus temperature (tensimetric method). Clathrate phases, when differed only in the host formula, demonstrated the same order of thermodynamic stability as one expected for the host complexes in solution: Mn < Fe < Co < Ni < Cu > Zn for M and NCO > NO3 for X. The influence of the host complex formulation was comparable to the effect of guest template, the effect observed in the third series with the variation of the guest component. This study illustrates a dramatic impact of the stability of the host molecule on the overall stability of the clathrate phases, the impact being comparable to a contribution arising from the host–guest complementarity.

Clathrate Formation and Phase Equilibria in the Pyridine-Cadmium Nitrate System

Preparative, thermal (DTA, TGA), solubility, strain and spectral (Raman) techniques were used to study clathrate and complex formation in the pyridine (Py)-cadmium nitrate system. Three compounds have been isolated and studied: the clathrate compound [CdPy4(NO3)2] · 2Py (I), the complex [CdPy3(NO3)2] (II) and a compound of composition ‘Cd(NO3)2·7/4Py’ (III), of unknown nature. The phase diagram of the system has been determined for the concentration and temperature range 0–66 mass-% Cd(NO3)2 and −100 to +200 °C, respectively. ClathrateI undergoes polymorphous conversion at −51.8(4) °C and melts incongruently at 106.0(5) °C, forming complexII. CompoundsII andIII melt congruently at 165.5(4) and 191(1) °C, respectively. The complexes [CdPy4(NO3)2] (the host phase) and [CdPy2(NO3)2] are not observed in the system. The nature and thermodynamic parameters of the dissociation of clathrate I have been determined. For the process 1/13[CdPy4)NO3)2] · 2Pysolid = 1/3[CdPy3(NO3)2]solid + Pygas in the range 290–360K δHo = 54.9(3) kj/mole, ΔS298o = 142(1) J/(mole K), ΔG298o = 12.5(5) kJ/mole.

Benzene sorption by a microporous coordination polymer based on a zinc carboxylate

Benzene vapor sorption by the organometallic coordination polymer [Zn2(bdc)2(dabco)] (H2bdc = benzene-1,4-dicarboxylic acid, dabco = diazabicyclo[2.2.2]octane) is reported. The [Zn2(bdc)2(dabco)] polymer has a high C6H6 sorption capacity of up to 3.8 mol of benzene per formula unit. The heat of sorption has been determined, and its dependence on the composition of the inclusion compound has been investigated. Included benzene molecules are nonequivalent in terms of the energy of their interaction with the metal-organic framework.

Phase Diagram of the Benzene–Dinitratotetrapyridinecopper(II) (Guest–Host) System and Thermodynamic Parameters for the Hostβ2Guest Clathrate Dissociation

In the first part of the work, thephase diagram of the benzene -ndash;[CuPy4(NO3)2] system has beendetermined in the -100 to +200 °C temperaturerange using DTA and solubility techniques. The onlycompound found in the system is the[CuPy4(NO3)2]β 2C6H6clathrate. It is stable up to a temperature of+104.2(5) °C at which it melts incongruently togive liquid and the solid [CuPy4(NO3)2]host phase. At 146.1(5) °C exfoliation into twoliquid phases is observed, with the composition of themonotectic point being close to that of the clathrate.In the second part of the work, thermodynamicparameters of the clathrate dissociation have beendetermined from benzene vapour pressure strainmeasurements. For the process1/2 [CuPy4(NO3)2]β2C6H6(solid) = 1/2 [CuPy4(NO3)2] (solid) +C6H6 (gas) Δ H° = 45.3(3) kJ/mole;Δ S298° = 126(1) J/(mole K);Δ G298° = 7.7(5) kJ/mole.

The thermodynamic stability of inclusion compounds of Zinc(II) and Nickel(II) coordination polymers with chlorobenzene as a guest: The determination of guest vapor pressure by the tensimetric method

The static membrane method was used to study the temperature dependences of equilibrium guest vapor pressure over inclusion compounds of two coordination polymers with chlorobenzene, [M(bipy)(DBM)2] · 2C6H5Cl, where M = M(II) = Zn and Ni, bipy = 4,4′-dipyridyl, and DBM = C6H5COCHCOC6H5− is the dibenzoylmethanate anion. The data obtained were used to calculate the thermodynamic parameters of dissociation of these compounds. The regions of their existence and the stoichiometry and character of phase transitions were determined by thermogravimetric and differential thermal analyses.