5-methyl-5-(4’-methylphenyl) hydantoin is a chiral compound whose racemic mixture crystallizes as a conglomerate. This molecule
has two polymorphs: an orthorhombic form (stable form) and a monoclinic form of monotropic character. These forms share extensive
structural analogies (identical 2D periodic fragment) and consistently their lattice energies are quite close. The analyses
of the crystal structures lead to propose an irreversible polymorphic transition based on a destructive/reconstructive mechanism.
Under comparable conditions (mass of solid, temperature, etc.) the conversion is completed within 14 days by means of slurring
in ethanol (10 days if seeded) whereas 5 h only are necessary by means of mechanical activation under wet conditions and 9
h under dry milling. In the latter conditions the resulting materials appears significantly more defective in comparisons
to the other modes of conversion.
Authors:P. Storoniak, J. Rak, P. Skurski, K. Krzymiński, and J. Błażejowski
10-Methylacridinium chloride, bromide and iodide were prepared in crystalline forms (the first two salts as monohydrates)
and subjected to thermogravimetric investigations. Decomposition of the compounds is initially accompanied by the liberation
of water (in case of monohydrates), halomethanes and acridine molecules. As decomposition proceeds, side reactions occur which
are reflected in a complex pattern of thermogravimetric curves. TG traces corresponding to the initial decomposition stage
were used to determine the kinetic characteristics of the thermal dissociation of the salts. MNDO/d, AM1 and PM3 methods were
employed independently to examine reaction pathways and to predict thermodynamic and kinetic barriers for the thermal decomposition
of the compounds. These data were subsequently supplemented with theoretically determined crystal lattice energies, which
enabled the relevant characteristics for the decomposition of crystalline phases to be predicted. The theoretically predicted
characteristics are qualitatively comparable with those originating from thermogravimetric investigations, which allows one
to believe that both are valid.
Authors:W. Guan, L. Li, H. Wang, J. Tong, and J. Yang
A brown and transparent ionic liquid (IL), [C4mim][FeCl4], was prepared by mixing anhydrous FeCl3 with 1-butyl-3-methylimidazolium chloride ([C4mim][Cl]), with molar ratio 1/1 under stirring in a glove box filled with dry argon. The molar enthalpies of solution, ΔsHm, of [C4mim][FeCl4], in water with various molalities were determined by a solution-reaction isoperibol calorimeter at 298.15 K. Considering
the hydrolyzation of anion [FeCl4]− in dissolution process of the IL, a new method of determining the standard molar enthalpy of solution, ΔsHm0, was put forward on the bases of Pitzer solution theory of mixed electrolytes. The values of ΔsHm0 and the sum of Pitzer parameters:
were obtained, respectively. In terms of thermodynamic cycle and the lattice energy of IL calculated by Glasser’s lattice
energy theory of ILs, the dissociation enthalpy of anion [FeCl4]−, ΔHdis≈5650 kJ mol−1, for the reaction: [FeCl4]−(g)→Fe3+(g)+4Cl−(g), was estimated. It is shown that large hydration enthalpies of ions have been compensated by large the dissociation enthalpy
of [FeCl4]− anion, ΔdHm, in dissolution process of the IL.
Although melting is a most familiar physical phenomenon, the nature of the structural changes that occur when crystals melt
are not known in detail. The present article considers the structural implications of the changes in physical properties that
occur at the melting points, Tm, of the alkali halides. This group of solids was selected for comparative examination because the simple crystal lattices
are similar and reliable data are available for this physical change. For most of these salts, the theoretical lattice energies
for alternative, regular ionic packing in 4:4, 6:6 and 8:8 coordination arrangements are comparable. Density differences between
each solid and liquid at Tmare small. To explain the pattern of quantitative results, it is suggested that the melt is composed of numerous small domains,
within each of which the ions form regular (crystal-type) structures (regliq). The liquid is portrayed as an assemblage of
such domains representing more than a single coordination structure and between which dynamic equilibria maintain continual
and rapid transfers of ions. Tmis identified as the temperature at which more than a single (regular) structure can coexist. The interdomain (imperfect and
constantly rearranging) material (irregliq) cannot withstand shear, giving the melt its fluid, flow properties. From the physical
evidence, it is demonstrated that the structural changes on melting are small: these can accommodate only minor modifications
of the dispositions of all, or most, ions or larger changes for only a small fraction. This proposed representation, the set/liq
melt model, may have wider applicability.
Authors:J. Song, R. Hu, B. Kang, Y. Lei, F. Li, and K. Yu
[Cd(NTO)4Cd(H2O)6]4H2O was prepared by mixing the aqueous solution of 3-nitro-1,2,4-triazol-5-one and cadmium carbonate in excess. The single crystal
structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group C2/c with crystal parameters
of a=2.1229(3) nm, b=0.6261(8) nm, c=2.1165(3) nm, β=90.602(7), V=2.977(6) nm3, Z=4, Dc=2.055 gcm−3, μ=15.45 cm−1, F(000)=1824, λ(MoKα)=0.071073 nm. The final R is 0.0282. Based on the results of thermal analysis, the thermal decomposition mechanism of [Cd(NTO)4Cd(H2O)6]4H2O was derived. From measurements of the enthalpy of solution of [Cd(NTO)4Cd(H2O)6]4H2O in water at 298.15 K, the standard enthalpy of formation, lattice energy, lattice enthalpy and standard enthalpy of dehydration
have been determined as -(1747.84.8), -2394, -2414 and 313.6 kJ mol−1 respectively.
Authors:S. Jirong, C. Zhaxou, Hu Rongzu, X. Heming, and L. Fuping
The single crystal of lead salt of 3-nitro-1,2,4-triazol-5-one (NTO), [Pb(NTO)2(H2O)] was prepared and its structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, its space group is P21/n with crystal parameters of a=0.7262(1) nm, b=1.2129(2) nm, c=1.2268(3) nm, =90.38(2)°, V=1.0806(2) nm3, Z=4, Dc=2.97 g cm–3, µ=157.83cm–1, F(000)=888. The final R is 0.027. By using SCF-PM3-MO method we obtained optimized geometry for [Pb(NTO)2
H2O] and particularly positions for hydrogen atoms. Through the analyses of MO levels and bond orders it is found that Pb atom bond to ligands mainly with its 6pz and 6py AOs. The thermal decomposition experiments are elucidated when [Pb(NTO)2
H2O] is heated, ligand water is dissociated first and NO2 group has priority of leaving. Based on the thermal analysis, the thermal decomposition mechanism of [Pb(NTO)2
H2O] has been derived. The lattice enthalpy and its lattice energy were also estimated.
Authors:J. Błażejowski, K. Krzymiński, P. Storoniak, and J. Rak
The decomposition of the quaternary salts mentioned in the title was examined at the quantum mechanical Hartree-Fock level
of theory employing pseudopotentials combined with a SBKJ** basis set. This enabled identification of intermediate and transition
state species on the reaction pathway and prediction of the thermodynamic and kinetic barriers to the dissociation of the
compounds in the gaseous phase. Application of classical methods permitted the lattice energies of salts, whose crystal structures
had been established earlier, to be predicted. Combination of these latter characteristics with the heats of formation of
gaseous halide ions (available from the literature) and the relevant cations (obtained at the density functional (B 3LYP)/6-31G**level
of theory) provided heats of formation of the salts. On the basis of these values, the thermodynamic and kinetic barriers
to the dissociation of the compounds were predicted. The characteristics thus obtained compare quite well with those available
in the literature or determined in this work on the basis of TG or DSC measurements. These investigations have shed more light
on the mechanism of the thermal dissociation of quaternary salts, and more generally on thermal processes involving solids.
Hexachlorohafnates of pyridine and its three methyl-substituted derivatives were synthesized and examined by the thermoanalytical
methods. The van't Hoff equation employed for the thermogravimetric αvs. T dependencies enabled evaluation of the heats of the thermal dissociation and subsequently enthalpies of formation and crystal
lattice energies of the salts. Geometry and energy of formation of HfCl
was determined at the ab initio Hartree-Fock SCF level, using all electron MINI basis set augmented with standard polarization
functions (MINI*). Electron correlation was considered at the MP2 level. Thermodynamic characteristics for the latter species were also obtained
combining ab initio results with those of statistical thermodynamics. The usefulness of theoretical methods in examination
of solid state energetics is briefly discussed.
Authors:J. Rulewski, J. Rak, P. Dokurno, P. Skurski, and J. Błażejowski
Crystal lattice energies of several organochlorine compounds—including pesticides, of known crystal structures were calculated
on the basis of a model which takes into account electrostatic, dispersive and repulsive interactions—using three different
sets of empirical parameters. These characteristics compare reasonably with experimental heats of volatilization, and it was
subsequently shown how statistical and classical thermodynamics can be employed to evaluate dependencies of function of states
of gaseous and solid compounds on temperature and how enthalpies and temperatures of sublimation at standard pressure, as
well as vapour pressurevs. temperature dependencies can be predicted.
Authors:B. Zadykowicz, K. Krzymiński, P. Storoniak, and J. Błażejowski
The melting points and melting enthalpies of nine phenyl acridine-9-carboxylates—nitro-, methoxy- or halogen-substituted in
the phenyl fragment—and their 9-phenoxycarbonyl-10-methylacridinium trifluoromethanesulphonate derivatives were determined
by DSC. The volatilisation temperatures and enthalpies of phenyl acridine-9-carboxylates were either measured by DSC or obtained
by fitting TG curves to the Clausius–Clapeyron relationship. For the compounds whose crystal structures are known, crystal
lattice energies and enthalpies were determined computationally as the sum of electrostatic, dispersive and repulsive interactions.
By combining the enthalpies of formation of gaseous phenyl acridine-9-carboxylates or 9-phenoxycarbonyl-10-methylacridinium
trifluoromethanesulphonate ions, obtained by the DFT method, and the corresponding enthalpies of sublimation and/or crystal
lattice enthalpies, the enthalpies of formation of the compounds in the solid phase were predicted. In the case of the phenyl
acridine-9-carboxylates, the computationally predicted crystal lattice enthalpies correspond reasonably well with the experimentally
obtained enthalpies of sublimation. The crystal lattices of phenyl acridine-9-carboxylates are stabilised predominantly by
dispersive interactions between molecules, whilst the crystal lattices of their quaternary salts are stabilised by electrostatic
interactions between ions.