Jasminka Popović

Long cycle life of CoMn2O4 lithium ion battery anodes with high crystallinity

CoMn2O4 nanomaterials are prepared by a low temperature precipitation route employing metal acetates and NaOH. Structural changes, induced by different annealing temperatures, are comprehensively analyzed by X-ray powder diffraction and Raman spectroscopy. With rising annealing temperature the crystal lattice of CoMn2O4 undergoes changes ; AO4 tetrahedra expand due to thermally induced substitution of Co2+ by larger Mn2+ metal ions on the A-site of the spinel structure, while in contrast, BO6 octahedra shrink since the B-site becomes partially occupied by smaller Co3+ metal ions on account of the migrated Mn ions. CoMn2O4 particle sizes are easily fine-tuned by applying different annealing temperatures ; the particle size increases with increasing annealing temperature. During the battery operation, pulverization and reduction of particle sizes occurs regardless of the initial size of the particles, but the degree of division of the particles during the operation is dependent on the initial particle properties. Thus, contrary to the common assumption that nanostructuring of the anode material improves the battery performance, samples with the largest particle sizes exhibit excellent performance with a capacity retention of 104% after 1000 cycles (compared to the 2nd cycle).

Chiral Hexa- and Nonamethylene-Bridged Bis(L-Leu-oxalamide) Gelators: The First Oxalamide Gels Containing Aggregates with a Chiral Morphology

Chiral amino acid- and amino alcohol-oxalamides are well-known as versatile and efficient gelators of various lipophilic and polar organic solvents and water. To further explore the capacity of the amino acid/oxalamide structural fragment as a gelation-generating motif, the dioxalamide dimethyl esters 1(6)Me and 1(9)Me, and dicarboxylic acid 2(6)OH/2(9)OH derivatives containing flexible methylene bridges with odd (9; n=7) and even (6; n=4) numbers of methylene groups were prepared. Their self-assembly motifs and gelation properties were studied by using a number of methods (FTIR, (1)H NMR spectroscopy, CD, TEM, DSC, XRPD, molecular modeling, MMFF94, and DFT). In contrast to the previously studied chiral bis(amino acid or amino alcohol) oxalamide gelators, in which no chiral morphology was ever observed in the gels, the conformationally more flexible 1(6)Me, 1(9)Me, 2(6)OH, and 2(9)OH provide gelators that are capable of forming diverse aggregates of achiral and chiral morphologies, such as helical fibers, twisted tapes, nanotubules, straight fibers, and tapes, in some cases coexisting in the same gel sample. It is shown that the differential scanning calorimetry (DSC)-determined gelation enthalpies could not be correlated with gelator and solvent clogP values. Spectroscopic results show that intermolecular hydrogen-bonding between the oxalamide units provides the major and self-assembly directing intermolecular interaction in the aggregates. Molecular modeling studies reveal that molecular flexibility of gelators due to the presence of the polymethylene bridges gives three conformations (zz, p1, and p2) close in energy, which could form oxalamide hydrogen-bonded layers. The aggregates of the p1 and p2 conformations tend to twist due to steric repulsion between neighboring iBu groups at chiral centers. The X-ray powder diffraction (XRPD) results of 1(6)Me and 1(9)Me, xerogels prove the formation of p1 and p2 gel aggregates, respectively. The latter results explain the formation of gel aggregates with chiral morphology and also the simultaneous presence of aggregates of diverse morphology in the same gel system.

Effect of the Cation Distribution and Microstructure on the Magnetic Behavior of the CoMn2O4 Oxide

The sizes of CoMn2O4 nanoparticles can easily be tuned, from 40 to 8 nm, depending on the temperature of decomposition of the single-source molecular precursor {[Co(bpy)3][Mn2(C2O4)3]·H2O}n. The structural features of the CoMn2O4 spinel are also affected by the heat treatment temperature, showing a pronounced expansion of unit cell parameters as a consequence of thermally induced cation redistribution between tetrahedral and octahedral sites. Moreover, the magnetic behavior of CoMn2O4 was successfully tailored as well; depending on the heat treatment, it is possible to switch between the superparamagnetic and ferrimagnetic ordering and to tailor the magnetic transition temperatures, i.e., the boundaries between the hard and soft magnetic behavior.

Aquabromo(6-carboxypyridine-2-carboxylato- O , N , O ')mercury(II)

The title compound, [HgBr(C7H4NO4)(H2O)], was obtained by the reaction of an aqueous solution of mercury(II) bromide and pyridine-2,6-dicarboxylic acid (picolinic acid, dipicH(2)). The shortest bond distances to Hg are Hg-Br 2.412 (1) A and Hg-N 2.208 (5) A; the corresponding N-Hg-Br angle of 169.6 (1) degrees corresponds to a slightly distorted linear coordination. There are also four longer Hg-O interactions, three from dipicH(-) [2.425 (4) and 2.599 (4) A within the asymmetric unit, and 2.837 (4) A from a symmetry-related molecule] and one from the bonded water molecule [2.634 (4) A]. The effective coordination of Hg can thus be described as 2+4. The molecules are connected to form double-layer chains parallel to the y axis by strong O-H.O hydrogen bonds between carboxylic acid groups of neighbouring molecules, and by weaker hydrogen bonds involving both H atoms of the water molecule and the O atoms of the carboxylic acid groups.

Thermal behavior of novel catanionic cholates XRPD technique in solving problems

In this article, we bring new insight into room temperature structure of catanionic cholates and complement their thermal behavior given by the conventional thermal techniques with the XRPD technique. The comparative study of the addition of each dodecyl chain and ammonium group is made bearing in mind the complete architecture of synthesized cholates. The examined samples are crystal smectic phases at room temperature, with proposed sandwich-type structure, promoted by cholates architecture. For most of the studied compounds, thermal behavior is characterized as formation of structural varieties and/or polymorphs as low-temperature phases and formation of high-temperature mesomorphic, lamellae-like phases. The exception is dimeric dicholate, which only forms SmA phase before its decomposition. The dependence of the isotropization temperatures, enthalpy and entropy changes, on the increasing ammonium headgroup number, points to the fact that thermal stability of these catanionics depends on the structure of cationic component that is its constituent, where cholate anion shows minor effect. The chemistry of amphiphiles, their supramolecular behavior and thermotropic affinity is at the frontier of the contemporary research and design of the new functional materials, because this is simple but effective way to control the nature and location of reactions. From that point of view, the systematic analysis of physico-chemical properties of various catanionic amphiphiles brings new findings of their chemical structure–properties relationship, therefore enabling simpler and reliable way of new materials synthesis with desired properties.

Mystique world of acrobatic molecular crystals

Everybody enjoys mystique and mystery that goes along with it, but they are hard to find outside the brother Grimm’s fairy tales. But upon a travel to a nanoworld, not unlike Gulliver’s voyage to Lilliput, in certain cases we can witness a truly fascinating and mystique phenomenon – a thermosalient effect. Thermosalient crystals, or more colloquially called jumping crystals, are intriguing materials that during heating/cooling exhibit joyful acrobatics in the form of hopping. These jumps are exhibited during the topotactic polymorphic phase transitions which are extremely fast and energetic so the crystals are balistically projected to heights several hundred times larger than their own dimensions. Thermosalient materials are also exhibiting huge technological potential because they are very promising candidates for fabrication of actuators on the microscopic level, such as nanoswitches, thermal sensors, artificial muscles, etc [1, 2]. In the past several years, a large number of experimental studies was performed with the to unveil the origin of the thermosalient effect, but still today the real reason for this phenomenon remains foggy and mysterious. It is becoming obvious that the experimental methods solely are not enough to successfully tackle this challenge so it seems opportune to try to complement these results with the theoretical studies, employing the highly developed DFT calculations. We present the results of such, to the best of our knowledge, first collaboration between experimental and theoretical studies performed on one of the thermosalient systems – N’-2-propylidene- 4-hydroxybenzohydrazide. This system experiences even three polymorphic thermosalient transition, one of them being irreversible and the other two reversible. As with the large majority of thermosalient compounds, it is also characterised with anisotropic thermal expansion. It shows immense negative uniaxial thermal expansion (along b direction), which we suspect is the governing force for the thermosalient phenomenon in this system. Our first principle electronic structure calculations prove that it is a direct consequence of the negative uniaxial compressibility. Elastic properties are also shown to be the origin of the reversibility or irreversibility of the thermosalient phase transitions. And finally, our DFT calculations suggest that excitations of the low-energy phonons provide a necessary trigger for the thermosalient effect in N’-2- propylidene-4-hydroxybenzohydrazide, propelling the system over the energy barrier between the thermosalient phases. [1] Skoko, Ž. et al. (2010). J. Am. Chem. Soc. 132, 14191-14202. [2] Nath, N. K. et al. (2014). CrystEngComm 2014, 1850-1858.

Educational and outreach projects of the Croatian Association of Crystallographers

Croatian Association of Crystallographers (CAC) [1] is a professional association founded in 2012 with an objective to endorse excellence, encourage co-operation, facilitate international contacts and exchange and support career developments within the Croatian crystallographic community, as well as to promote the achievements and importance of crystallography towards the general public. These goals are being achieved by an intense programme of international workshops, summer schools, seminars, conferences and other scientific and professional gatherings, as well as educational activities oriented towards the school children and promotional activities in the mainstream media. From Sep. 2017 to Sep. 2018 CAC, endorsed by the city of Zagreb, will organize a series of ten monthly seminars under the brand name International crystallographic seminars in Zagreb, where the successful PhD students and postdocs working in the field of crystallography and related disciplines at the universities and public research centres across the region of South Eastern Europe will have the opportunity to present their research. In order to tackle fascinating recent achievements and developments, which put crystallography to the front lines of the natural sciences CAC has developed the a unique concept of a high level workshop under the brand Hot Topics in Contemporary Crystallography [2]. It is intended to the utterly ambitious PhD students and postdocs, as well as to the young crystallographers in the early stages of their autonomous carriers, conducting their research within the broad spectrum of disciplines and sub disciplines related to crystallography. THe first edition, with 6 lecturers and 27 students, was held from May 10th to 15th, 2014 in Šibenik, Croatia and it was a central event to mark the UN proclaimed International year of crystallography in Croatia. The second edition HTCC2017, was held in Poreč, from Apr. 22nd to 26th, 2017 with the participation of 7 lecturers and 25 students. In 2014 and in 2017, CAC has, with the generous support of Pliva Inc. – member of TEVA group, co-organized the school contest in crystal growth called “The beauty of crystal faces” intended to students of elementary and secondary schools across Croatia. Both contests were amazingly popular among the children and young people, as more than 150 schools were involved in both contests. The chemicals were distributed to those who had applied, the school teams were established, led by chemistry or physics teachers, and the experiments were conducted. 3rd European Crystallographic School (ECS3) [3], organized jointly by ECA and CAC, was held in Bol, Croatia, from Sep. 25th to Nov. 2nd, 2016. ECS3 had 116 registered participants. 29th European Crystallographic Meeting (ECM29), organized jointly by CAC and ECA was held under the patronage of the Ministry of science, education and sports of the Republic of Croatia, in Rovinj, Croatia, from Aug. 23rd to Aug. 28th, 2015.

Structural and magentoelectric study of triethylmethylammonium tetrachloroferrate(III)

The novel organic-inorganic hybrids with a perovskite-type structure represent a potentially very attractive platform for interesting electrical and magnetic properties. In contrast to pure inorganic multiferroics, this class of materials exhibit new properties tuned by the nature of metal centers, organic cations and appropriate ligands. It was found that inorganic-organic hybride compounds containing tetrabromoferrate(III) anion exhibit the ferroelectric and magnetic phase transitions resulting in a strong magnetodielectric coupling at ∼360 K [1]. Namely, the combination of disordered cation and magnetic transition metal ion results in formation of a magnetodielectric molecule-based functional material above room temperature. A dark-yellow polycrystalline sample of a triethylmethylammonium tetrachloroferrate(III) compound was produced by the wet chemical synthesis. Detailed high temperature in-situ X-ray powder diffraction in the range from RT to 400 K was utilized in order to follow the temperature-induced structural changes. Title compound crystallizes in hexagonal space group P63mc at RT where the organic cationic part is completely disordered. Both the FeBr4 − anion and the organic cation lie on a hexagonal axis. It was found that structural phase transition of triethylmethylammonium tetrachloroferrate(III) was accompanied with changes in magnetic and electrical behaviour as shown in Figure 1. Since for most multiferroics, the magnetic phase transition temperature is much lower than the ferroelectric phase transition temperature, (finally resulting in a weak coupling between magnetic and ferroelectric orderings) this compound exhibiting transitions at similar temperatures shows potential for further investigations of magnetoelectric coupling. 1. Cai, H.-L., et al., Above-Room-Temperature Magnetodielectric Coupling in a Possible Molecule-Based Multiferroic: Triethylmethylammonium Tetrabromoferrate(III). Journal of the American Chemical Society, (2012)134, 18487-18490.

Facile route for preparation of nanochristalline ZnMn2O4 ; effect of preparation conditions on structure and microstructure

Traditional synthesis of spinel materials such as solid-state route involving grinding and firing of a mixture of oxides, nitrates or carbonates which requires elevated temperatures and prolonged process times have been abandoned. Indeed, majority of papers on manganese spinels are focused on low cost preparation methods which proceed at moderate temperatures (600°C) with enhanced reaction kinetics [1, 2]. Interestingly, Liu et al. reported a room temperature route for preparation of AMn2O4 (A=Zn, Co, Cd) from metal acetates [3]. Although synthetic route proposed by Liu et al. represents a facile and very efficient route for low temperature synthesis of spinel materials, in order to utilize this route for the targeted design of nanomaterials it is necessary to establish, very precisely, correlations between specific preparation conditions(concentration of NaOH, aging period, and temperature of additional heat treatments), structure, microstructure and properties. Detailed structural investigation using X-ray powder diffraction (XRPD) and Raman spectrocopy have been carried out in order to correlate specific structural and microstructural features with changes in preparation conditions. ZnMn2O4 was prepared by precipitation with NaOH (c=0.25-0.8 M) from solution of Zn and Mn acetates. Also, sample obtained by 0.8 M NaOH was additionaly heat treated at T=300, 400 and 500 °C. Pronounced difference in crystallinity was observed with increase in concentration of NaOH. Based on the results of Raman spectroscopy a model described by the formula: [Zn2+1-xMn2+ x]tetra[Zn2+xMn3+2-2xMn4+x]octaO4 has been proposed and tested upon structural data. It was shown, based on Rietveld structure refinement, that unit-cell constants as well as the inversion parameter of spinel lattice increase with the increase in temperature of thermal treatment. 1. L. Hu et al., Sci. Rep., 2, 217-226, 2012. Y. 2. Li et al., Nanoscale, 5, 2045-2054, 2013. 3. Y. Liu et al. RSC Advances, 4, 4727-4731, 2014.