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Four novel manganese(II) complexes with 2,2′-dipyridylamine (dipya) and various benzenedicarboxylate, BDC, ligands as anions of phthalic (pht), isophthalic (ipht) and terephthalic (tpht) acids were hydrothermally synthesized, namely, [Mn(dipya)(pht)(H2O)]2 (1), [Mn(dipya)(ipht)]n (2), [Mn(dipya)2(tpht)]n (3), and [Mn(dipya)(H2O)4](tpht) (4). All complexes were characterized by single-crystal X-ray diffraction, TG/DSC analysis and IR spectroscopy. The obtained complexes display a plenty of different structural features, including geometry of central metal atoms, BDC coordination modes and crystal packing. The coordination numbers of Mn(II) are different: 5 (in 2), 6 (in 3 and 4) and 7 (in 1). 3D networks in 1–4 are determined by strong non-covalent interactions. A survey of the Cambridge Structural Database for BDC complexes was performed in order to analyze orientation of COO groups. The energies of various BDC conformers were calculated by the second order Moller–Plesset perturbation theory and three hybrid HF/DFT methods with 6-311G∗∗ basis set. To explain different behavior, BDC ions were also examined by Localized Molecular Orbital Energy Decomposition and Natural Bond Orbital analyses. Experimental and calculated geometries are in agreement, showing that tpht and ipht anions prefer the planar conformation, while in pht anions COO groups are inclined and make complementary angles relative to the aromatic rings.

Binuclear [Ni2(en)2(H2O)6(pyr)]·4H2O complex undergoes dehydration in 325–400 K temperature region, which is accompanied by polymerization. Polymerized product is characterized by chelate coordination of carboxylate group to Ni, as identified by vibrational spectroscopy. XRD and spectroscopic measurements suggest that the resulting dehydration product is two-dimensional layered polymer with weak interconnectivity between the polymer layers. A combination of experimental measurements and DFT calculations was used to identify two reaction mechanisms, as well as the factors determining the change from one mechanism to the other. Reaction mechanism changes with increase in the heating rate, due to slow diffusion of released water inhibiting the polymerization. Polymerization occurs in parallel with dehydration at lower heating rates, while it follows dehydration at higher heating rates, leading to an increase in overall enthalpy of the reaction of around 50 kJ mol−1 and decrease in crystallinity of the polymeric product. Determined isokinetic temperature of the dehydration reaction corresponds to the vibrational frequency of Ni OH2 bond.

Thermally activated 3D to 2D structural transformation of the binuclear [Ni 2 (en) 2 (H 2 O) 6 (pyr)]·4H 2 O complex was investigated using a combination of theoretical and experimental methods. Step-wise thermal degradation (dehydration followed by release of ethylene diamine) results in two layered flexible coordination polymer structures. Dehydration process around 365 K results in a conjugated 2D structure with weak interlayer connectivity. It was shown to be a reversible 3D to 2D framework transformation by a guest molecule, and rehydration of the dehydration product occurs at room temperature in saturated water vapor. Rehydrated complex exhibits lower dehydration temperature, due to decreased average crystalline size, with higher surface area resulting in easier release and diffusion of water during dehydration. Thermal degradation of dehydration around 570 K, results in loss of ethylene diamine, producing a related 2D layered polymer structure, without interconnectivity between individual polymer layers.

The coordination polymer [Cd(N-Boc-gly)2(H2O)2]n undergoes thermally induced degradation in temperature region between 60 and 900oC. Kinetic parameters were determined for dehydration (63-123oC) and further degradation processes (123-461°C) using different isoconversional and non-isoconversional methods. Due to appearance of kinetic “compensation effect”, isokinetic temperatures were determined for individual degradation processes and correlated with resonant vibrational frequencies ascribed to Cd-OH2 coordination bond, Cd-O (O from N-Boc-glyH ligand) coordination bond and C-O covalent bond. [Projekat Ministarstva nauke Republike Srbije, br. 172015]

The structure of new cis-dichloro[(E)-ethyl-2-(2-((8-hydroxyquinolin-2-il)methylene)hidrazinyl)acetate-κ2 N]-palladium(II) complex was determined using a combination of XRD and IR measurements and DFT calculations. Inherent flexibility of its structure is evident from the complexity of its IR spectrum, which could only be theoretically reproduced as a combination of several closely related structures, involving rotation around C–O bond and changes in hydrogen interactions of its –OH group. Its thermal stability and decomposition were studied non-isothermally, and the thermal decomposition mechanism was proposed using correlation with DFT calculations at the molecular level. It was determined that the initial degradation step consists of the release of Cl free radical, which then reacts with both the initial compound and the degradation products. Besides the endothermic steps, there are exothermic ones, contributing to the complex shape of the DSC curve, consisted of overlapping endothermic and exothermic peaks. Deconvolution of DTG curve allowed identification of primary fragments of the initial degradation process and, in conjunction with DFT calculations, construction of the most likely reaction mechanism.

Thermal degradation of ternary transition metal complex containing tetraanion of pyromellitic acid, pyr, and ethylenediamine, en, [Ni-2(en)(2)(H2O)(6)(pyr)]center dot 4H(2)O, 1, was investigated under non-isothermal conditions. The mechanism of thermal degradation, which occurs in three steps, was clarified by TG/DSC measurements in conjunction with FT-IR spectroscopy and XRPD analysis. The complexity of all degradation steps has been revealed using isoconversional methods. Dehydration comprises the loss of ten water molecules in a relatively narrow temperature interval, resulting in a very complicated reaction mechanism. In addition, density functional theory calculations have been applied for better understanding of dehydration. The second degradation step, related to loss of en, was separated into two single-step processes with Fraser-Suzuki function. The obtained individual steps were described by Johnson-Mehl-Avrami A2 model and estak-Berggren model, respectively. Validation of the proposed kinetic triplets for individual steps was performed using master plot and P,rez-Maqueda criteria. The third degradation step is related to the fragmentation of pyr ion most likely followed with the release of a number of gaseous products.

[Ni2(btc)(en)2]n coordination polymer exhibits a layered two-dimensional structure with weak interaction between the layers. Correlation of experimental measurements, DFT calculations and molecular simulations demonstrated that its structural features, primarily the inherent flexibility of the layered polymeric structure, lead to improved hydrogen storage performance at room temperature, due to significant enhancement in isosteric heats of hydrogen adsorption. Volumetric measurements of hydrogen adsorption at room temperature show up to 0.3 wt.% hydrogen absorbed at 303 K and 2.63 bar of hydrogen pressure, with isosteric heats of adsorption of about 12.5 kJ mol−1. Predicted performance at room temperature is 1.8 wt.% at 48 bar and 3.5 wt.% at 100 bar, better than both MOF-5 and NU-100, with calculated values of isosteric heats for adsorption of hydrogen in 8–13 kJ mol−1 range at both 77 K and 303 K. Grand canonical Monte Carlo calculations show that this material, at 77 K, exhibits gravimetric hydrogen densities of more than 10 wt.% (up to 8.3 wt.% excess) with the corresponding volumetric density of at least 66 gL−1, which is comparable to MOF-5, but achieved with considerably smaller surface area of about 2500 m2 g−1. This study shows that layered two-dimensional MOFs could be a step towards MOF systems with significantly higher isosteric heats of adsorption, which could provide better room temperature hydrogen storage capabilities. This is the peer reviewed version of the following article: Blagojević, V.A., Lukić, V., Begović, N.N., Maričić, A.M., Minić, D.M., 2016, “Hydrogen storage in a layered flexible [Ni2(btc)(en)2]n coordination polymer”, International Journal of Hydrogen Energy, http://dx.doi.org/10.1016/j.ijhydene.2016.08.203

Naturally occurring flavonoids, delphinidin, pelargonidin and malvin, were investigated experimentally and theoretically for their ability to scavenge hydroxyl and nitric oxide radicals. Electron spin resonance (ESR) spectroscopy was used to determine antiradical activity of the selected compounds and M05-2X/6- 311+G(d, p) level of theory for the calculation of reaction enthalpies related to three possible mechanisms of free radical scavenging activity, namely HAT, SET-PT and SPLET. The results obtained show that the molecules investigated reacted with hydroxyl radical via both HAT and SPLET in the solvents investigated. These results point to HAT as implausible for the reaction with nitric oxide radical in all the solvents investigated. SET-PT also proved to be thermodynamically unfavourable for all three molecules in the solvents considered.

The mechanisms of the carboxylations of lithium, potassium, rubidium, and cesium phenoxides are investigated by means of the DFT method with the LANL2DZ basis set. It is shown that the reactions of all alkali metal phenoxides with carbon dioxide occur via very similar reaction mechanisms. The reactions can proceed in the ortho and para positions. The exception is lithium phenoxide which yields only salicylic acid in the Kolbe-Schmitt reaction. It is found that the yield of the para substituted product increases with increasing the ionic radius of the alkali metal used. An explanation for this experimental and theoretical observation is proposed.

Some new experimental evidence of complex irregular oscillations in the Belousov-Zhabotinsky reaction realized in a batch reactor is presented. The results were obtained under relatively low cerium and malonic acid concentrations. One-dimensional maps were used for general discussion, and particularly, for the influence of noise on the evolution of the oscillations. Daju se novi eksperimentalni rezultati o kompleksnim neregularnim oscilacijama BŽ sistema ostvarenog u zatvorenom reaktoru, u uslovima relativno niske koncentracije cerijuma i malonske kiseline. Jednodimenzionalne mape su korišćene za generalnu diskusiju rezultata, a posebno za uticaj šuma na oscilatornu evoluciju.

Models for the formation of biogenic iodine in marine aerosols have been proposed in the literature. Here, we analyse the possible species and reactions that could occur in the proposed models. We calculate the enthalpies of formation for the species and the enthalpies of corresponding reactions. We propose a modified model using iodous acid (HOIO) and reactions that are particularly suited to humid conditions.

The theoretical study of hypoiodous and iodous acid isomers, which can be written in the common form HIOn (n = 1,2), is presented. For this purpose, several basis sets and several computational methods are tested. The best fitting with the values known in the literature is achieved using density functional theory at the level of Gill96 exchange and Perdew-Wang91 correlation functional (G96PW91) method, with Lanl2DZ basis set augmented with p and d diffuse and polarization functions for oxygen, relativistic effective core potential of Hay and Wadt combined with Lanl2DZ basis set augmented with diffuse (s and p) and polarization (d and f) functions for iodine, and 6-311++G(3df,3pd) basis set for hydrogen. Using this method for the calculation of bond lengths, vibrations, and energies, the mentioned species are analyzed. The justification of the calculated values is performed by thermochemical calculations of enthalpy of formation of mentioned species. We found that between hypoiodous acid isomers HOI is mor...

The crystallization mechanism and kinetics of Fe40Ni40P14B6 amorphous alloy were studied under non-isothermal conditions. Thermal stabilization of this alloy manifests in DSC through two complex peaks, corresponding to crystallization and recrystallization, respectively. The complex crystallization DSC peak was deconvoluted into individual steps corresponding to crystallization of individual phases, where the results using both Gaussian-Lorentzian cross-product and Fraser-Suzuki function were compared. It was determined that the values of kinetic triplets of the individual steps did not exhibit any significant difference, depending on the deconvolution function. Anisotropic growth was indicated to be the prevailing type of impingement for all crystallization steps. Using the calculated values of the respective kinetic triplets and the mechanisms determined from the value of Avrami exponent, distinct values of activation energies for nucleation and crystal growth for crystallization of each individual phase were calculated, showing significantly higher values for nucleation than those for crystal growth. Alloy samples treated non-isothermally in the DSC cell exhibit inhomogeneous surface morphology with highly granulated structure dependent on heating rate. © 2015 Elsevier B.V. All rights reserved.

Proton NMR spectroscopy was used to monitor behavior of water during the oscillatiory part of the Bray−Liebhafsky (BL) reaction. A series of 1H NMR spectra showed the complex structure of the water signal with periodic changes of the chemical shift and line splitting, which were in agreement with the periodicity of the BL reaction obtained by potentiometric measurements. An analysis of known intermediates in the BL reaction indicated that oxygen formation both as dissolved and in form of bubbles has the dominant effect on NMR spectra. In addition, certain restructuring of water was observed during oscillations, suggesting the subtle role of water in the mechanism of the BL reaction and pointing out to the importance of the NMR techniques in investigation of the chemical oscillators.

The influence of heavy water on the Bray−Liebhafsky (BL) oscillating reaction was investigated for varying amounts of D2O, at three different temperatures. Evolution of the system was monitored potentiometrically. Simultaneous recordings of gaseous oxygen over the reaction solution were also performed. In separate experiments the iodine concentration was monitored spectrophotometrically. Replacement of H2O by D2O progressively intensifies the reactions of oxidation of the iodine species, compared to the reactions of their reduction. As a result there is a critical ratio of D2O/H2O, after which the dynamics of the system is considerably altered. The same effect is observed at all temperatures, but it is more pronounced at lower temperatures. Two possible explanations for the progressively intensified oxidation are discussed: the reverse isotope effect and the selective energy transfer. It is established that the oxidation and reduction of the iodine species in the BL reaction do not proceed through the sa...

The M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d,p) models are used to evaluate scavenging potency of gallic acid. The hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), and single electron transfer followed by proton transfer (SET-PT) mechanisms of gallic acid with some radicals ((•)OO(-), (•)OH, and CH3OO(•)) were investigated using the corresponding thermodynamic quantities: bond dissociation enthalpy (BDE), ionization potential (IP), and proton affinity (PA). Namely, the ΔHBDE, ΔHIP, and ΔHPA values of the corresponding reactions in some solvents (water, DMSO, pentylethanoate, and benzene) are investigated using an implicit solvation model (SMD). An approach based on the reactions enthalpies related to the examined mechanisms is applied. This approach shows that a thermodynamically favored mechanism depends on the polarity of reaction media and properties of free radical reactive species. The most acidic 4-OH group of gallic acid is the active site for radical inactivation. The results of this investigation indicate that the SPLET mechanism can be a favored reaction pathway for all three radicals in all solvents, except for (•)OH in the aqueous solution. In water, gallic acid can inactivate (•)OH by the HAT mechanism.

Thermal stability of a series of palladium(II) complexes with N-heteroaromatic bidentate hydrazone ligands was investigated using a combination of experimental measurements and DFT calculations. All complexes exhibit a reversible second-order transition around 333 K, which can be attributed to structural reorganization of the ligand molecules. Thermal degradation begins in 570-610 K temperature region, with an endothermic peak, followed by exothermic peaks in DSC. TG measurements show a well-defined mass loss corresponding to the initial degradation, while subsequent processes are poorly separated. DFT calculations suggest that the initial degradation step occurs with release of Cl, which then reacts with remaining part of the complex molecule in an exothermic process. This leads to decomposition of the ligand molecule into four fragments corresponding to ethyl chloride, carbon dioxide, methyl amine, and the fragment with the aromatic group. Mass spectrum suggests that creation of these fragments most likely corresponds to the initial degradation, after which some of these coordinate to Pd center, whose coordination sphere is left incomplete by release of Cl. TG measurement to 1123 K indicates that the final degradation product at this temperature is palladium. (C) 2014 Elsevier B.V. All rights reserved.

The resumption of oscillatory trains in the non-oscillatory region subsequent to completion of the last oscillation, as a phenomenon interesting for the stability of any reaction which can reach the oscillatory state in principle, is analyzed here for the case of the Bray-Liebhafsky reaction. It is shown that this effect is affected by temperature, acidity, initial concentration of hydrogen peroxide and quantity of added water.