Jose A. R. Cheda

Luminescent lead(II) complexes: new three-dimensional mixed ligand MOFs

Two new lead(II) butyrate-based compounds with formulae [Pb2(but)4(4,4′-bipy)(H2O)]n (1) and [Pb2(but)4(bpe)(H2O)]n (2) [with but = butyrate; 4,4′-bipy = 4,4′-bipyridine and bpe = 1,2-bis(4-pyridyl)ethene] have been synthesized and characterized, with the aim of obtaining different three-dimensional (3D) structures from the typical two-dimensional (2D) lamellar one of most of metal alkanoates, and enhancing the properties of the products synthesized, using these two different N bridging ligands (4,4′-bipy and bpe). Both new complexes show a similar 3D (42638)-sra network in a monoclinic lattice (C2/c) and present interesting photophysical properties. The two compounds have been fully characterized by single crystal X-ray diffraction (synchrotron radiation), thermogravimetric analysis, differential scanning calorimetry, UV-Vis absorption spectroscopy, and steady-state fluorescence and lifetime measurements.

DSC thermophysics on some lower thallium(I) N-alkanoates

Five of the lower members of thallium(I) n-alkanoates were synthesized and recrystallized until their purity, as determined by DSC, was considered appropriate to undertake thermodynamic studies on the polymorphic and mesomorphic transitions they exhibit and thermodynamic data are reported. Heat capacity measurements by DSC are also given between 320 and 500 K.

A novel rotator glass in lead(II) pentanoate: calorimetric and spectroscopic study.

Lead(II) pentanoate was studied by DSC, XRD, and FTIR and solid state CP/MAS-NMR spectroscopies. A transition from the crystal to the intermediate phase, at T(ss) = 328.2 +/- 0.6 K, with delta(ss)H = 8.8 +/- 0.1 kJ x mol(-1), and a melting at T(f) = 355.6 +/- 0.3 K, with delta(f)H = 12.6 +/- 0.1 kJ x mol(-1), were observed on first heating. The thermal and structural behavior of the lead(II) pentanoate shows as a link between those of the shorter and longer members of the previously studied lead(II) alkanoate series. The optical microscopy and FTIR vs temperature studies show structural changes from the crystal to the intermediate phase and its solid state nature. Moreover, X-ray diffraction and C-13 and Pb-207 CP/MAS-NMR studies confirm the rotator nature of the intermediate phase in this compound. Two different glass states, one from the isotropic liquid and another from the rotator phase, were obtained by quenching at high and low rates, respectively. The glass transition temperatures (measured at 5 K x min(-1)) were 322.9 and 275.7K, respectively.

Thermodynamics of thallium alkanoates III. Heat capacity and thermodynamic functions of thallium(I) n-tetradecanoate from 7 to 450 K

The thermal behavior of thallium(I) n-dodecanoate was studied by adiabatic calorimetry from 6 to 350 K and by d.s.c. from 230 through 470 K. The agreement between the results (temperature and thermal functions of transitions and heat capacity) from both methods was within the experimental error over the common temperature range. Several phases were observed in the sample. Four of the five solid-to-solid transitions appeared in the common temperature range of both techniques. The two lowest-temperature transitions appear as a bifurcated pair (at 282.65 and 284.8 K) with (Cp,mR) ≈ 250 and 450, respectively. The third and fourth occur at 293.1 and 312.1 K with (CpmR) ≈ 250 and 14000. Above 350 K three more transitions were measured by d.s.c.: solid-to-solid, solid-to-mesophase, and mesophase, and mesophase-to-isotropic-liquid transformations at 356.6, 400.1, and 471.5 K. The corresponding values of ΔtrsSmoR for the seven transitionswere 0.910, 1.111, 0.710, 2.075, 0.69, 1.64, and 0.50. Smoothed thermodynamic values are tabulated at selected temperatures through the “clearing” point.

Lithium–thallium(I) butyrates binary system: an intermediate salt and liquid crystal from non-mesogenic compounds.

The binary system between lithium and thallium(I) butyrates, [xLiC3H7CO2 + (1 − x) TlC3H7CO2], where x = mole fraction, has been carefully analyzed, solving the temperature and enthalpy vs. composition phase diagrams. The formation of an intermediate salt or complex with a composition (2 : 1), an ionic liquid crystal phase and a metastable solid solution has been detected. The complex melts incongruently at Tfus = 494.7 K, with ΔfusHm = 7.70 kJ per mol of mixture. Its low temperature crystal structure (monoclinic, P21/c) has been solved and refined using X-ray synchrotron radiation and has been found to be bilayered, as is typical from pure metal alkanoates and, as it happens, for other two analogous intermediate salts studied recently by our group. The liquid crystal phase detected is formed from two non-mesogenic pure compounds, appearing in the binary system between 394.1 and 436.6 K and for x = 0.10 up to x = 0.29. Binary phase diagrams are shown to be a powerful tool to detect and predict the formation of liquid crystal phases and mixed crystals.

A thermophysical study of the melting process in alkyl chain metal n-alkanoates: The thallium (I) series

The peculiar thermal behavior of the thallium(I) n-alkanoates series (consisting in several transitions between polymorphic and mesomorphic phases) in comparison with other metallic n-alkanoates series is stated. The allowance of highly accurate adiabatic heat capacity data permits a study of the CH2 contributions to the lattice heat capacity curve at low temperature. Moreover, in this series an anomalous gradual enhancement of the lattice heat capacity has been interpreted from vibrational spectroscopy results as a noncooperative effect due to the internal hindered rotation of the alkyl chain (formation of gauche defects, even in the solid state). The thermodynamics of the “stepwise melting process” from the totally ordered solid at low temperature to the isotropic liquid is based on a revised lattice heat-capacity curve. This was used to evaluate the energy and entropy not only of the clear first order transitions present in the series but also of the described noncooperative effect. The CH2 enthalpy an...

Thermophysics of thallium alkanoates IV. Heat capacity and thermodynamic functions of thallium(I) n-dodecanoate from 7 to 470 K

The thermal behavior of thallium(I) n-dodecanoate was studied by adiabatic calorimetry from 6 to 350 K and by d.s.c. from 230 through 470 K. The agreement between the results (temperature and thermal functions of transitions and heat capacity) from both methods was within the experimental error over the common temperature range. Several phases were observed in the sample. Four of the five solid-to-solid transitions appeared in the common temperature range of both techniques. The two lowest-temperature transitions appear as a bifurcated pair (at 282.65 and 284.8 K) with (Cp,mR) ≈ 250 and 450, respectively. The third and fourth occur at 293.1 and 312.1 K with (CpmR) ≈ 250 and 14000. Above 350 K three more transitions were measured by d.s.c.: solid-to-solid, solid-to-mesophase, and mesophase, and mesophase-to-isotropic-liquid transformations at 356.6, 400.1, and 471.5 K. The corresponding values of ΔtrsSmoR for the seven transitionswere 0.910, 1.111, 0.710, 2.075, 0.69, 1.64, and 0.50. Smoothed thermodynamic values are tabulated at selected temperatures through the “clearing” point.

DSC thermophysics on some medium chain thallium(I) n-alkanoates: Phase transitions, thermal functions and heat capacity

Abstract Four members of the series of anhydrous thallium(I) n -alkanoates with medium chain-length ( n -octanoate, n -nonanoate, n -undecanoate and n -tridecanoate) have been prepared, purified, and studied by differential scanning calorimetry between 200 and 500 K. Their polymorphic and mesomorphic behaviour has also been investigated by polarization microscopy. The temperatures and enthalpy changes for the phase transitions have been measured and the corresponding entropy changes calculated. Heat capacity measurements by DSC between 300 and 500 K are also reported.

Thermodynamics of thallium alkanoates V. Heat capacity and thermodynamic functions of thallium(I) n-decanoate from 6 to 480 K

Abstract The heat capacity of thallium(I) n -decanoate was measured by adiabatic calorimetry from 6 to 350 K and by d.s.c. from 200 through 480 K. Excellent overlap occurs over the common temperature range of both techniques. Four solid-to-solid transitions were found; at 232.9 K, at 288.3 K, and two more at 305.6 K (very sharp with a for the maximum of about 1700 R ), and at 327.6 K. The corresponding values of Δ trs H m o are 352 R ·K, 83.8 R ·K, and 1026 R ·K (for the set of two transitions), respectively, and of Δ trs S m o are 1.46 1 R , 0.28 3 R , and 3.19 R (for the set of two), respectively. The compound melts to a liquid-crystal phase at 450.0 K: Δ trs H m o = 682 R ·K, Δ trs S m o = 1.68 R . Finally, “clearing” occurs at 484.0 K: Δ trs H m o = 307 R ·K, Δ trs S m o = 0.63 R . Smoothed thermophysical functions are tabulated through “clearing” at selected temperatures.

{Thallium(I) n-tetradecanoate + n-tetradecanoic acid} phase diagram: formation of a molecular complex

The mixture { x C 13 H 27 CO 2 Tl + (1 − x )C 13 H 27 CO 2 H} has been investigated by d.s.c. and hot-stage polarizing-light microscopy over the whole range of x . The main features of this phase diagram, determined by measuring the temperatures of transition and plotting the corresponding Δ trs H m against x are: a eutectic at x ≈ 0.12 and a temperature 2 K below the melting temperature of the pure acid; the formation of a 1-1 molecular complex between the salt and the acid, which undergoes a solid-to-solid phase transition at about 338 K and melts incongruently at about 340 K (peritectic); and a region at T > 374 K and x ⩾ 0.70 in which the mixture shows lyotropic mesomorphism.