A Remarkable Solvent Effect on the Nuclearity of Neutral Titanium(IV)‐Based Helicate Assemblies

The spontaneous self‐assembly of a neutral circular trinuclear Ti^IV‐based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The trimeric ring helicate was obtained after diffusion of n‐pentane into a solution with dichloromethane. The circular helicate has been characterized by using single‐crystal X‐ray diffraction study, ¹³C CP‐MAS NMR and ¹H NMR DOSY solution spectroscopic, and positive electrospray ionization mass‐spectrometric analysis. These analytical data were compared with those obtained from a previously reported double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double‐stranded helicates was characterized by ΔH(toluene)=?30 kJ mol^?1 and ΔS(toluene)=+357 J K^?1 mol^?1, whereas these values were ΔH(CH₂Cl₂)=?75 kJ mol^?1 and ΔS(CH₂Cl₂)=?37 J K^?1 mol^?1 for the ring helicate. The transformation of the ring helicate into the double‐stranded helicate was a strongly endothermic process characterized by ΔH(CH₂Cl₂)=+127 kJ mol^?1 and ΔH(n‐pentane)=+644 kJ mol^?1 associated with a large positive entropy change ΔS=+1115 J K^?1?mol^?1. Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to n‐pentane. Suggestions for increasing the stability of the ring helicate are given.     

Dynamic changes in composition of extracts of natural products as monitored by in situ NMR

The direct in situ NMR observation and quantification, based on the aldehyde –CH chemical shift region, of the inter‐conversion of secoiridoid derivatives due to temperature and solvent effects is demonstrated in complex extracts of natural products without prior isolation of the individual components. The equilibrium between the aldehyde hydrate form and the dialdehyde form of the oleuropein aglycon of an olive leaf aqueous extract in D₂O was shown to be temperature dependent. The resulting thermodynamic values of the Van't Hoff plot with ΔH^o = ?26.34 ± 1.00 kJ mol^?1 and TΔS° (298 K) = ?24.70 ± 1.00 kJ mol^?1 demonstrate a significant entropy term which nearly compensates the effect of enthalpy at room temperature. The equilibrium between the two diastereomeric hemiacetal forms and the dialdehyde form of the oleuropein 6‐O‐β‐d ‐glucopyranoside aglycon of an olive leaf aqueous extract in CD₃OD was also shown to be strongly temperature dependent again because of the significant entropy term (TΔS° (298 K) = ?26.50 ± 1.39 kJ mol^?1) compared with that of the enthalpy term (ΔH^o = ?36.64 ± 1.46 kJ mol^?1). This is the first demonstration of the significant role of the entropy parameter in determining the equilibrium of chemical transformations in complex mixtures of natural products due to solvent and temperature effects. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and Properties of [Cd(HTRTR)2(H2O)4](HTNR)2 as an Energetic Complex

The energetic complex, [Cd(HTRTR)₂(H₂O)₄](HTNR)₂ {HTRTR = 4‐[3‐(1,2,4‐triazol‐yl)‐1,2,4‐triaozle; HTNR^– = styphnic acid anion) was synthesized and characterized by FT‐IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. It crystallizes triclinic in space group P$\bar{1}$ [a = 8.156(2) Å, b = 8.374(2) Å, c = 13.267(4) Å, α = 84.925(11)°, β = 87.016(11)°, γ = 63.683(5)°, V = 808.9(4) ų, ρ = 1.940 g · cm^–3]. The Cd^II ion is six‐coordinate with two HTRTRs and four water molecules. The thermal stabilities were investigated by differential scanning calorimetry (DSC). Non‐isothermal reaction kinetic parameters were calculated by Kissinger's and Ozawa‐Doyle's methods to obtain E_K = 144.0 kJ · mol^–1, lgA_K = 14.22, and E_O = 144.3 kJ · mol^–1. The values of thermodynamic parameters, the peak temperature while β→0 (T_p0), free energy of activation (ΔG^≠), entropy of activation (ΔS^≠), and enthalpy of activation (ΔH^≠) were obtained. Additionally, the enthalpy of formation was calculated by Hess's law on the basis of the experimental constant‐volume heat of combustion measured by bomb calorimetry, obtaining Δ_fH°₂₉₈ = 4985.5 kJ · mol^–1. Finally, the sensitivities toward impact and friction were assessed according to relevant methods. The result indicates it as an insensitive energetic material.     

Thermochemical properties of free radicals from G3MP2B3 calculations

For a set of 32 selected free radicals, energy minimum structures, harmonic vibrational wave numbers ω_e, principal moments of inertia I_A, I_B, and I_C, heat capacities C°_p(T), entropies S°(T), thermal energy contents H°(T) ? H°(0), and standard enthalpies of formation Δ_fH°(T) were calculated at the G3MP2B3 level of theory in the temperature range 200–3000 K. In this article, thermodynamic functions at T = 298.15 K are presented and compared with recent experimental values. The mean absolute deviation between calculated and experimental Δ_fH°(298.15) values resulted in 3.91 kJ mol^?1, which is close to the average experimental uncertainty of ± 3.55 kJ mol^?1. The influence of hindered rotation on thermodynamic functions is studied for isopropyl and tert‐butyl radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 550–560, 2002     

Synthesis and Properties of [Ba(CHZ)(BT)(H2O)2]n as a New Energetic Coordination Compound

In order to enhance the thermal stability of the barium salt of 5,5′‐bistetrazole (H₂BT), carbohydrazide (CHZ) was used to build [Ba(CHZ)(BT)(H₂O)₂]_n as a new energetic coordination compound by using a simple aqueous solution method. It was characterized by FT‐IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. The crystal belongs to the monoclinic P2₁/c space group [a = 8.6827(18) Å, b = 17.945(4) Å, c = 7.2525 Å, β = 94.395(2)°, V = 1126.7(4) ų, and ρ = 2.356 g · cm^–3]. The Ba^II cation is ten‐coordinated with one BT^2–, two shared carbohydrazides, and four shared water molecules. The thermal stabilities were investigated by differential scanning calorimetry (DSC) and thermal gravity analysis (TGA). The dehyration temperature (T_dehydro) is at 187 °C, whereas the decomposition temperature (T_d) is 432 °C. Non‐isothermal reaction kinetics parameters were calculated by Kissinger's method and Ozawa's method to work out E_K = 155.2 kJ · mol^–1, lgA_K = 9.25, and E_O = 158.8 kJ · mol^–1. The values of thermodynamic parameters, the peak temperature (while β → 0) (T_p0 = 674.85 K), the critical temperature of thermal explosion (T_b = 700.5 K), the free energy of activation (ΔG^≠ = 194.6 kJ · mol^–1), the entropy of activation (ΔS^≠ = –66.7 J · mol^–1), and the enthalpy of activation (ΔH^≠ = 149.6 kJ · mol^–1) were obtained. Additionally, the enthalpy of formation was calculated with density functional theory (DFT), obtaining Δ_fH°₂₉₈ ≈ 1962.6 kJ · mol^–1. Finally, the sensitivities toward impact and friction were assessed according to relevant methods. The result indicates the compound as an insensitive energetic material.     

Study on the Interaction of Nd3+ with Human Serum Albumin at Molecular Level

Neodymium is applied widely in agriculture to improve crop nutrition and incidentally in fertilizers, yet little is known of its effect on the biological function of human serum albumin (HSA). The interaction of Nd³⁺ to HSA has been investigated mainly by fluorescence spectra, UV–vis absorption spectra and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of HSA by Nd³⁺ was a static quenching process and the binding constant is 5.71 × 10⁴ L mol^‐1 and the number of binding sites is 1 at 292 K. The thermodynamic parameters (ΔH⁰ = ‐20.79 kJ mol^‐1, ΔG⁰ = ‐26.58 kJ mol^‐1, and ΔS⁰ = 19.85 J mol^‐1 K^‐1) indicate that electrostatic effect between the protein and Nd³⁺ is the main binding force. The distance r = 2.91 nm between donor (HSA) and acceptor (Nd³⁺) was obtained according to Förster's nonradiative energy transfer. In addition, UV–vis, CD and synchronous fluorescence results showed that the addition of Nd³⁺ changed the conformation of HSA.     

Inclusion of chlorophenols by 4,4′‐(cyclohexane‐1,1‐diyl)diphenol: structures and kinetics of decomposition

The structures of the inclusion compounds 4,4′‐(cyclohexane‐1,1‐diyl)diphenol–3‐chlorophenol (1/1) and 4,4′‐(cyclohexane‐1,1‐diyl)diphenol–4‐chlorophenol (1/1), both C₁₈H₂₀O₂·C₆H₅ClO, are isostructural with respect to the host molecule and are stabilized by extensive host–host, host–guest and guest–host hydrogen bonding. The packing is characterized by layers of host and guest molecules. The kinetics of thermal decomposition follow the R2 contracting‐area model, kt = [1 − (1 − α)^½], and yield activation energies of 105 (8) and 96 (8) kJ mol⁻¹, respectively.     

Formation and Stability of Gaseous WS2Cl2, WS2Br2 and WS2I2 – A Combined Experimental and Theoretical Study

Gaseous WS₂Cl₂ and WS₂Br₂ are formed by the reaction of solid WS₂ with chlorine resp. bromine at temperatures of about 1000 K. This could be shown by mass spectrometric measurements. The heats of formation and entropies of WS₂Cl₂ and WS₂Br₂ have been determined by means of mass spectrometry (MS) and quantum chemical calculations (QC). WS₂I₂ could not be detected by experimental methods. This is in line with the quantum chemically determined equilibrium constant of the formation reaction. The following values are given:, Δ_fH⁰₂₉₈(WS₂Cl₂) = –230.8 kJ · mol^–1 (MS), Δ_fH⁰₂₉₈(WS₂Cl₂) = –235.0 kJ · mol^–1 (QC),, S⁰₂₉₈(WS₂Cl₂) = 370.7 J · K^–1 · mol^–1 (QC) and, c_p⁰_T(WS₂Cl₂) = 103.78 + 7.07 × 10^–3 T – 0.93 × 10⁵ T^–2 – 3.25 × 10^–6 T² (298.15 K < T < 1000 K) (QC). Δ_fH⁰₂₉₈(WS₂Br₂) = –141.9 kJ · mol^–1 (MS), Δ_fH⁰₂₉₈(WS₂Br₂) = –131.5 kJ · mol^–1 (QC),, S⁰₂₉₈(WS₂Br₂) = 393.9 J · K^–1 · mol^–1 (QC) and, c_p⁰_T(WS₂Br₂) = 104.84 + 5.32 × 10^–3 T – 0.75 × 10⁵ T^–2 – 2.45 × 10^–6 T² (298.15 K < T < 1000 K) (QC). Δ_fH⁰₂₉₈(WS₂I₂) = –18.0 kJ · mol^–1 (QC), S⁰₂₉₈(WS₂I₂) = 409.9 J · K^–1 · mol^–1 (QC) and, c_p⁰_T(WS₂I₂) = 105.17 + 4.77 × 10^–3 T – 0.67 × 10⁵ T^–2 – 2.19 × 10^–6 T² (298.15 K < T < 1000 K) (QC). These molecules have the expected C_2v‐symmetry.     

Studies on Thermodynamics Features of the Interaction between Imidacloprid and Bovine Serum Albumin

At different temperatures, the interactions between imidacloprid （IMI） and bovine serum albumin （BSA） were investigated with a fluorescence quenching spectrum, a synchronous fluorescence spectrum, a three-dimensional fluorescence spectrum and an ultraviolet-visible spectrum. The average values of bonding constants （KLB： 3.424 × 10^4 L,mol^-1）, thermodynamic parameters （△H： 5.188 kJ,mol^-1, △G^（○—）：-26.36 kJ,mol^-1, △S： 103.9 J,K^-1,mol^-1） and the numbers of bonding sites （n： 1.156） could be obtained through Stern-Volmer, Lineweaver-Burk and ther- modynamic equations. It was shown that the fluorescence of BSA could be quenched for its reactions with IMI to form a certain kind of new compound. The quenching belonged to a static fluorescence quenching, with a non-radiation energy transfer happening within a single molecule. The thermodynamic parameters agree with △H〉 0, △S〉0 and△G^（○-）〈0, suggesting that the binding power between IMI and BSA should be mainly a hydrophobic interaction.     

Thermodynamic investigation of several natural polyols

The low-temperature heat capacity C _p,m of erythritol (C₄H₁₀O₄, CAS 149-32-6) was precisely measured in the temperature range from 80 to 410 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=390.254 K from the experimental C _p-T curve. The molar enthalpy and entropy of this transition were determined to be 37.92±0.19 kJ mol⁻¹ and 97.17±0.49 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions [H _T-H _298.15] and [S _T-S _298.15], were derived from the heat capacity data in the temperature range of 80 to 410 K with an interval of 5 K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined: Δ_c H _m⁰(C₄H₁₀O₄, cr)= −2102.90±1.56 kJ mol⁻¹ and Δ_f H _m⁰(C₄H₁₀O₄, cr)= − 900.29±0.84 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.     

Thermodynamic Properties of Hydrofullerene C60H36 from 5 to 340 K

The temperature dependence of the molar heat capacity (C⁰ _p) of hydrofullerene C₆₀H₃₆ between 5 and 340 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. The experimental data were used for the calculation of the thermodynamic functions of the compound in the range 0 to340 K. It was found that at T=298.15 K and p=101.325 kPa C⁰ _p (298.15)=690.0 J K⁻¹ mol⁻¹,H^o(298.15)−H^o(0)= 84.94 kJ mol⁻¹,S^o(298.15)=506.8 J K⁻¹ mol⁻¹, G^o(298.15)−H^o(0)= −66.17 kJ mol⁻¹. The standard entropy of formation of hydrofullerene C₆₀H₃₆ and the entropy of reaction of its formation by hydrogenation of fullerene C₆₀ with hydrogen were estimated and at T=298.15 K they were Δ_fS^o= −2188.4 J K⁻¹ mol⁻¹ and Δ_rS^o= −2270.5 J K⁻¹mol⁻¹, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vapor Composition over Solid Indium Trichloride and in ­Indium Chloride Unsaturated Vapor

The dependence of indium trichloride saturated and unsaturated vapor pressure on temperature was studied in the range of 630–950 K by static methods using a quartz membrane zero‐manometer and taking into account the volume of its working chamber and substance mass. The thermodynamic data on the process of dissociation of dimeric molecules and sublimation of monomer and dimer from solid indium trichloride were calculated: ΔH⁰_subl InCl₃(g)₂₉₈ = 155.3 ± 6.2 kJ · mol^–1; ΔS⁰_subl InCl₃(g)₂₉₈ = 199.5 ± 7.9 J · mol^–1 · K^–1; ΔH⁰_subl In₂Cl₆(g)₂₉₈ = 159.3 ± 6.2 kJ · mol^–1; ΔS⁰_subl In₂Cl₆(g)₂₉₈ = 207.1±3.8 J · mol^–1 · K^–1; ΔH⁰_dis In₂Cl₆(g)₂₉₈ = 152.6 ± 5.5 kJ · mol^–1 and ΔS⁰_dis In₂Cl₆(g)₂₉₈ = 171.6 ± 5.2 J · mol^–1 · K^–1. The saturated vapor over solid indium trichloride consists mainly of a mixture of monomeric and dimeric molecules (InCl₃ and In₂Cl₆), and the content of the latter is slightly growing with increasing temperature.     

Non-isothermal Kinetics of the Thermal Decomposition of 3-Nitro-1,2,4-triazol-5-one Magnesium Complex

Introduction3 Nitro 1,2 ,4 triazol 5 one (NTO)metalcomplexeshavemanyspecialstructuresandsomepotentialusesinammunition .1 4 Wepreviouslypreparedanddeterminedthecrystalstructureofitsmagnesiumcomplex ,5andinthispaper ,wediscusseditsthermalbehaviorbyDSCandTG/DTGtechniquesandstudieditsnon isothermalkineticsbythemeansoftheKissingermethod ,theOzawamethod ,thedifferentialmethodandtheintegralmethod .ExperimentalSample[Mg(H2 O) 6 ](NTO) 2 ·2H2 Owaspreparedasfollows :AcalculatedamountofMg(OH…     

Zur Bedeutung von V2O3(OH)4(g) für den chemischen Transport von V2O5(s) in Anwesenheit von Wasser. Nachweis des Gasteilchens,thermodynamische Daten und Modellrechnungen

V₂O₃(OH)₄(g), Proof of Existence, Thermochemical Characterization, and Chemical Vapor Transport Calculations for V₂O₅(s) in the Presence of Water By use of the Knudsen-cell mass spectrometry the existence of V₂O₃(OH)₄(g) is shown. For the molecules V₂O₃(OH)₄(g), V₄O₁₀(g), and V₄O₈(g) thermodynamic properties were calculated by known Literatur data. The influence of V₂O₃(OH)₄(g) for chemical vapor transport reactions of V₂O₅(s) with water ist discussed. Δ_BH°(V₂O₃(OH)₄(g), 298) = –1920 kJ · mol^–1 and S°(V₂O₃(OH)₄(g), 298) = 557 J · K^–1 · mol^–1, Δ_BH°(V₄O₁₀(g), 298) = –2865,6 kJ · mol^–1 and S°(V₄O₁₀(g), 298) = 323.7 J · K^–1 · mol^–1, Δ_BH°(V₄O₈(g), 298) = –2465 kJ · mol^–1 and S°(V₄O₈(g), 298) = 360 J · K^–1 · mol^–1.     

Non-isothermal Kinetics of the First-stage Decomposition Reaction of the Complex of Terbium p-Methylbenzoate with 1,10-Phenanthroline

The thermal behavior of Tb₂ (p‐MBA)₆(phen)₂ (p‐MBA=p‐methylbenzoate; phen=1,10‐phenanthroline) in a static air atmosphere was investigated by TG‐DTG, SEM and IR techniques. The thermal decomposition of the Tb₂(p‐MBA)₆(phen)₂ occurred in three consecutive stages at T_P of 354, 457 and 595 °C. By Malek method, RO (n<1) was defined as kinetic model for the first‐step thermal decomposition. The activation energy (E) of this step is 170.21 kJ·mol^‐1, the enthalpy of activation (ΔH^≠) 164.98 kJ·mol^‐1, the Gibbs free energy of activation (ΔG^≠) 145.04 kJ·mol^‐1, the entropy of activation (ΔS^≠) 31.77 J·mol^‐1·K^‐1, and the pre‐exponential factor (A) 10^15.21 s^‐1.     

High‐performance liquid chromatographic enantioseparation of isoxazoline‐fused 2‐aminocyclopentanecarboxylic acids on a chiral ligand‐exchange stationary phase

The application of a chiral ligand‐exchange column for the direct high‐performance liquid chromatographic enantioseparation of unusual β‐amino acids with a sodium N‐((R)‐2‐hydroxy‐1‐phenylethyl)‐N‐undecylaminoacetate‐Cu(II) complex as chiral selector is reported. The investigated amino acids were isoxazoline‐fused 2‐aminocyclopentanecarboxylic acid analogs. The chromatographic conditions were varied to achieve optimal separation. The effects of temperature were studied at constant mobile phase compositions in the temperature range 5–45°C, and thermodynamic parameters were calculated from plots of lnk or lnα versus 1/T. Δ(ΔH°) ranged from –2.3 to 2.2 kJ/mol, Δ(ΔS°) from –3.0 to 7.8 J mol^?1 K^?1 and –Δ(ΔG°) from 0.1 to 1.7 kJ/mol, and both enthalpy‐ and entropy‐controlled enantioseparations were observed. The latter was advantageous with regard to the shorter retention and greater selectivity at high temperature. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes. The sequence of elution of the enantiomers was determined in all cases.     

Spectroscopic studies on the interaction of alpha‐eleostearic acid with calf thymus DNA

Interaction between alpha‐eleostearic acid (α‐ESA) and calf thymus DNA in Tris‐HCl buffer (pH = 7.4) using neutral red (NR) dye as a spectral probe was investigated using UV–Vis absorption and fluorescence spectroscopy. Spectral data matrix of the complexed reaction between α‐ESA and NR with DNA was processed with an alternative least‐squares (ALS) algorithm, the obtained concentration profiles and the corresponding pure spectra for species (NR, DNA–NR, and DNA–NR–ESA) demonstrated three kinds of reactions might occur in the system. The major groove binding between α‐ESA and DNA was further validated using circular dichroism, viscosity, DNA melting, and ionic strength effect measurements. Moreover, the calculated values of thermodynamic parameters, such as enthalpy (ΔH^θ, ?22.04 kJ/mol) and entropy change (ΔS^θ, 91.52 J K^?1 mol^?1), suggested binding between α‐ESA and DNA was mainly driven by hydrophobic interactions and hydrogen bonds without electrostatic force.     

Ligand Dynamics in the Solid: Lithium‐fluorenide and Lithium‐benzo[b]fluorenide N,N,N′,N′‐Tetramethylethylenediamine (tmeda) Complexes

The dynamic behavior of the N,N,N′,N′‐tetramethylethylenediamine (tmeda) ligand has been studied in solid lithium‐fluorenide(tmeda) ( 3 ) and lithium‐benzo[b]fluorenide(tmeda) ( 4 ) using CP/MAS solid‐state ¹³C‐ and ¹⁵N‐NMR spectroscopy. It is shown that, in the ground state, the tmeda ligand is oriented parallel to the long molecular axis of the fluorenide and benzo[b]fluorenide systems. At low temperature (<250 K), the ¹³C‐NMR spectrum exhibits two MeN signals. A dynamic process, assigned to a 180° rotation of the five‐membered metallacycle (π‐flip), leads at elevated temperatures to coalescence of these signals. Line‐shape calculations yield ΔH^?=42.7 kJ mol^?1, ΔS^?=?5.3 J mol^?1 K^?1, and =44.3 kJ mol^?1 for 3 , and ΔH^?=36.8 kJ mol^?1, ΔS^?=?17.7 J mol^?1 K^?1, and =42.1 kJ mol^?1 for 4 , respectively. A second dynamic process, assigned to ring inversion of the tmeda ligand, was detected from the temperature dependence of T_1ρ, the ¹³C spin‐lattice relaxation time in the rotating frame, and led to ΔH^?=24.8 kJ mol^?1, ΔS^?=?49.2 J mol^?1 K^?1, and =39.5 kJ mol^?1 for 3 , and ΔH^?=18.2 kJ mol^?1, ΔS^?=?65.3 J mol^?1 K^?1, and =37.7 kJ mol^?1 for 4 , respectively. For (D₁₂)‐ 3 , the rotation of the CD₃ groups has also been studied, and a barrier E_a of 14.1 kJ mol^?1 was found.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

Thermodynamics of Hydrogen Adsorption on Metal‐Organic Frameworks

Interaction between adsorbed hydrogen and the coordinatively unsaturated Mg²⁺ and Co²⁺ cationic centres in Mg‐MOF‐74 and Co‐MOF‐74, respectively, was studied by means of variable‐temperature infrared (VTIR) spectroscopy. Perturbation of the H₂ molecule by the cationic adsorbing centre renders the H? H stretching mode IR‐active at 4088 and 4043 cm^?1 for Mg‐MOF‐74 and Co‐MOF‐74, respectively. Simultaneous measurement of integrated IR absorbance and hydrogen equilibrium pressure for spectra taken over the temperature range of 79–95 K allowed standard adsorption enthalpy and entropy to be determined. Mg‐MOF‐74 showed ΔH⁰=?9.4 kJ mol^?1 and ΔS⁰=?120 J mol^?1 K^?1, whereas for Co‐MOF‐74 the corresponding values of ΔH⁰=?11.2 kJ mol^?1 and ΔS⁰=?130 J mol^?1 K^?1 were obtained. The observed positive correlation between standard adsorption enthalpy and entropy is discussed in the broader context of corresponding data for hydrogen adsorption on cation‐exchanged zeolites, with a focus on the resulting implications for hydrogen storage and delivering.