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A series of cocrystals of tetrachloro- and tetrabromoquinone with organic iodide salts has been prepared and structurally characterised. Derivatives N-methylpyridinium were chosen as cations, due to their planarity and similar size to the quinones, while their electronic properties are radically different. While the iodide usually acts as an electron donor, reducing the quinone into the semiquinone radical, sometimes the co-crystals of the neutral quinone and the iodide appear. In the studied crystals, the common motive, or supramolecular synthon, has been identified: a sandwich-like I-∙∙∙quinone∙∙∙I- moiety with close contacts between the iodide anion and carbon skeleton of the quinoid ring. Distances between the iodide and the ring centroid range between 3.6 and 3.85 Å, which is slightly shorter than sum of van der Waals radii for C and I. Interactions between π system aromatic ring and an anion are rarely observed, since aromatics are usually electron-rich ; in the case of electron-depleted quinoid rings, anion∙∙∙π contacts are more likely to form. In the studied cases, however, there is also a partial electron transfer between the iodide and the quinone which is noted by a change of colour: the neutral quinone is yellow, while the co-crystals and the semiquinone crystals are black.

Ferrocene-containing derivatives with only one ferrocene unit and two small peptide chains attached to each cyclopentadienyl ring show a great potential for formation of intra- or interchain hydrogen bonds because of a restricted rotation of these rings. An engagement of two ferrocene units imposes additional conformational flexibility in comparison to the mononuclear ferrocenes. The first oxalamide-bridged dinuclear ferrocene compound with acetyl groups did not show any preference for intramolecular hydrogen bonding. In addition, these compounds did not exhibit any self-assembly and gelation properties, although some of the mononuclear ferrocene- containing and bis(amino acid)-oxalamide derivatives have already been proven as gelators. If we want to predict the self-assembly and gelation properties of oxalamide-bridged dinuclear ferrocene peptides, firstly we need to fully understand the supramolecular structure and its relationship with molecular structure of single molecules. In order to make a clear distinction between affinities of potential hydrogen bond donor and acceptor sites toward inter- or intramolecular hydrogen bonding we performed a detailed conformational study by means of computational chemistry methods (DFT, QTAIM). The results were compared with those obtained by previously conducted experiments. In the course of this research, an improved procedure for syntheses of higher analogues of oxalamide-bridged dinuclear ferrocene compounds is described. In comparison with the first oxalamide-bridged compound these analogues differ in spacer length and sizes of the oppositely attached peptide chains. The total number of potential hydrogen bond donors and acceptor sites increases in both compounds, thus resulting in the formation of multiple intramolecular hydrogen bonds. Nevertheless, some of these sites remain free and able to trigger unidirectional self-assembly and gelation behavior due to intermolecular hydrogen bonding.

Heteropolynuclear metal complexes have been widely investigated for their ability to form different architectures and topologies, and also due to their interest for applications in catalysis, photoluminescence, gas storage and separation, magnetism and multifunctional molecular materials. In the last few decades, the chemistry of oxalate-containing complexes has become an active area of research – the oxalate moiety, C2O42−, acts as a linker between metal centres with vario us possibilities of bridiging modes . It is particularly interesting due to its ability to mediate electronic effects between paramagnetic metal ions. Stable mononuclear anionic oxalate complexes are often used as ligands toward another metal ion. The use of the [Cr(C2O4)3]3− anion in the reactions with organic and inorganic cations results in different structure types, from discrete polynuclear metal compounds to polymeric one- (1D), two-(2D) or threedimensional (3D) assemblies, featuring a range of distinct magnetic properties. Applying the layering technique i.e. slow liquid diffusion, the turquoise stick-like crystals of compounds {; ; ; ; ; ; [ACrCu2(C2O4)4(bpy)2]·H2O}; ; ; ; ; ; n [A = K+(1) and NH4+(2)] were grown from the reaction of an aqueous solution of A3[Cr(C2O4)3]·3H2O and methanol solution of CuCl2·H2O and 2, 2'-bipyridine (bpy), in the molar ratio of 1 : 1 : 1. Structural analysis has showed that compounds 1 and 2 contain oxalate-bridged [Cu(bpy)(μ-C2O4)Cu(bpy)]2+ units mutually connected through oxalate groups from [Cr(C2O4)3]3–, forming ladder -like 1D chains (Figure 1a). Interestingly, in each of these complexes three different bridging modes of the oxalate ligand are observed. The change of N-donor aromatic ligand from bpy to 1, 10-phenanthroline (phen) in the same reaction mixture influenced greatly the reaction outcome. Unusually, the [Cr(C2O4)3]3– anions present in the starting solution have transformed to the Cr2O72–, accompanied by oxidation of CrIII to CrVI in an almost neutral solution. The obtained compound, yellow polyhedra of formula {; ; ; ; ; ; [Cu2(C2O4)(phen)2(Cr2O7)]}; ; ; ; ; ; n (3), contains ladder-like 1D chains, in which copper(II) ions from [Cu(phen)(μ-C2O4)Cu(phen)]2+ units are bridged through four oxygen atoms of Cr2O72– anions (Figure 1b). This is the first known example of such extraordinary bridging mode of Cr2O72– . In addition to the single crystal X- ray diffraction study, characterization of the new complexes has been accomplished by means of the IR spectroscopy and thermal analysis.

Semiquinones are a class of stable organic radicals with a great potential for design of novel organic electronics and multifunctional materials. Since the radicals are planar, they typically form π-stacks, which stabilise crystal packing and determine magnetic and electrical properties of the crystals. Stronger π interactions thus imply stronger exchange interactions and lower energy barrier for electron transfer. Two types of stacks π-have been described: 1) Peierls-distorted with alternating short (< 3.1 Å) and long (> 3.35 Å) [1] interplanar distances (i.e. comprising dimers of radicals with paired spins), which are diamagnetic and isolators and 2) stacks of equidistant radicals which are 1D antiferromagnetic and semiconductors. Despite its importance, π-stacking of planar organic radicals has been little studied from the fundamental point of view. Here we present a detailed study of different factors which influence (semi)conductivity of semiquinone systems in the solid state: 1) type of stack (Peierls-distorted or equidistant), 2) induction effect of electron-withdrawing substituents, 3) interplanar distance and 4) orientation of the stacked rings. As suitable systems we chose series of salts of three semiquinones (5, 6-dichloro-2, 3-dicyanosemiquinone, tetrachloro- and tetrabromosemiquinone [1]) with planar organic cations derived from N-methylpyridinium. Since only antiferromagnetic compounds with equidistant radicals are good semiconductors, we focused our attention to this type of stacks. Electronegativity (i.e. electron-withdrawing) of the substituents plays a double role: i) it stabilises the radical by enhancing delocalisation of π electrons and ii) lowers the energy of the HOMO orbital, thus increasing band gap related to electronic transport. Therefore, the most stable radicals (5, 6-dichloro-2, 3-dicyanosemiquinone, DDQ) are the least conductive, while less stable ones (tetrabromosemiquinone) are the best conductors. This effect is far more pronounced than increasing of the band gap by increasing interplanar separation, while orientation of the rings in the stacks apparently does not influence electrical conductivity.

The search for new molecule-based magnets is a very active area in advanced materials, since they offer unique design possibilities, from a wise selection of the molecular building blocks, crystal structures exhibiting cooperative magnetism and even the combination of magnetism with a second property of interest. In the design and synthesis of heteropolynuclear complexes, as potentially new functional materials, an important role belongs to the oxalate ion, C2O42−, because of its various possibilities of coordination to metal centers as well as its ability to mediate magnetic interactions between paramagnetic metal ions. Stable mononuclear anionic oxalate complexes as tris(oxalato)metalate anions, [MIII(C2O4)3]3−, are often used as ligands toward another metal ion for the preparation of extended multifunctional systems. The most effective way to tune the magnetic properties of oxalate-based compounds is to act directly on the exchange pathways within the chains/layers. This can be done either by varying metal centres or by modifying the bridging oxalate ligand, by the use of larger bis(bidentate) bridging ligands as the dianion of 2, 5-dihydroxy-1, 4-benzoquinone (H2dhbq) and its derivatives (C6O4X22− = X2An2−). They show coordination modes similar to the oxalate group and present three additional advantages: (i) they are easy to modify or functionalize in order to tune the exchange coupling through them by simply changing the X group (X = H, F, Cl, Br, I, NO2, OH, CN, etc.) ; (ii) their modification does not affect their coordination mode ; (iii) they are able to provide an effective pathway for the exchange interaction. Also, in the 3, 6-dihalo derivates, halogen atom can play a multifuncional role, either at the electronic or at the supramolecular level, on the physical properties of supramolecular system arising from specific XB-oriented organizations. Thus, our recent (magneto)structural studies on oxalate-based metal complexes have been extended to the reactions of the similar, but more stretched, chloranilate dianion and transition metals [1, 2]. Applying the layering technique, using K3[Cr(C2O4)3]·3H2O and [(n-Bu)4N]3[Cr(Cl2An)3] as building blocks in reactions with CuCl2·H2O and 2, 2'-bipyridine, 1D heterometallic oxalate- and chloranilate-bridged {; ; ; [KCrCu2(C2O4)4(bpy)2]·H2O}; ; ; n (1) and {; ; ; [(n-Bu)4N][CrCu(Cl2An)3(bpy)]}; ; ; n (2) chains have been prepared and characterized, respectively.

Enormous efforts are made in synthesizing of new heterometallic coordination polymers of one-, two-, and threedimensionl structures. Incorporation of both organic and inorganic components in these compounds has created a new dimension in searching for functional materials that have desired structures and properties. The chemistry of oxalate-containing complexes has become an active area of research – the oxalate moiety, C2O42−, acts as a linker between metal centres with various possibilities of bridging modes. A property of oxalate ions that has been of specific interest is their ability to mediate electronic effects between paramagnetic metal ions. A frequently used approach for the synthesis of oxalate-based polynuclear coordination systems consists in using mononuclear anionic oxalate complexes as ligands towards other transition-metal complex cations. The introduction of organic ligands containing N-donors into the metal–oxalate systems further stabilizes their solid-state structures. Weak non-covalent interactions such as π-stacking and hydrogen bonding may adjust the dimensionality and lead to new topologies and desired functions of these supramolecular assemblies. Applying the layering technique, the turquoise stick-like crystals of oxalate-bridged compounds {; ; ; ; [KCrCu2(µ-C2O4)4(bpy)2]·H2O}; ; ; ; n (1) have been grown from the reaction of an aqueous solution of K3[Cr(C2O4)3]·3H2O and methanol solution of CuCl2·H2O and 2, 2'-bipyridine (bpy). Interestingly, in this complex three different bridging modes of oxalate ligands are observed. The change of aromatic N-donor ligand from bpy to 1, 10-phenanthroline (phen) in the same reaction mixture, influenced greatly the reaction outcome – yellow polyhedra of formula {; ; ; ; [Cu2(µ-C2O4)(phen)2(µ-Cr2O7)]}; ; ; ; n (2), containing, beside oxalate-bridge units, bridging Cr2O72– anions. Using tridentate 2, 2′:6′, 2′′-terpyridine (terpy) instead of bidentate ligands in similar procedure, green prismatic crystals of hetrometallic chloro-bridged complex salt [Cu4(µ-Cl)3Cl2(terpy)4][Cr(C2O4)3]·9H2O (3) have been isolated.

Reverse turns are structural features of proteins and peptides in which a polypeptide chain changes its direction enabling a protein to fold back on itself.[1] Besides the role in protein folding, turns are involved in molecular recognition processes.[1, 2] Ferrocene-1, 1'-diamine was established as molecular template for the design of turns in symmetricaly disubstituted derivatives.[3] Herein we report the DFT-predicted effect of the backbone chirality on the solid-state conformational properties of orthogonally protected asymmetric peptides containing homo- (1) and heterochiral (2) amino acids. Also, the crystal structure of the conjugate 1 is determined

Semiquinones are a class of stable organic radicals with a great potential for design of novel organic electronics and multifunctional materials. Since the radicals are planar, they typically form π-stacks, which stabilise crystal packing and determine magnetic and electrical properties of the crystals. Stronger π interactions thus imply stronger exchange interactions and lower energy barrier for electron transfer. Two types of stacks π-have been described: 1) Peierls-distorted with alternating short (< 3.1 Å) and long (> 3.35 Å) interplanar distances (i.e. comprising dimers of radicals with paired spins), which are diamagnetic and isolators and 2) stacks of equidistant radicals which are 1D antiferromagnetic and semiconductors. Despite its importance, π-stacking of planar organic radicals has been little studied from the fundamental point of view. Here we present a detailed X-ray charge density study of two types of semiquinone stacks and correlate them with magnetic and (semi)conductive properties of the crystals. As a convenient model system we chose N-methylpyridinium salt of tetrachlorosemiquinone radical anion, which forms stable, well-developed crystals and contains no heavy atoms. Two polymorphs of the studied salt are known: a diamagnetic one with Peierls-distorted stacks and an antiferromagnetic one with stacks of equidistant radicals.

A series of cocrystals of tetrachloro- and tetrabromoquinone with organic iodide salts has been prepared and structurally characterised. Derivatives N-methylpyridinium were chosen as cations, due to their planarity and similar size to the quinones, while their electronic properties are radically different. While the iodide usually acts as an electron donor, reducing the quinone into the semiquinone radical, sometimes the co-crystals of the neutral quinone and the iodide appear. In the studied crystals, the common motive, or supramolecular synthon, has been identified: a sandwich-like I-∙∙∙quinone∙∙∙I- moiety with close contacts between the iodide anion and carbon skeleton of the quinoid ring. Distances between the iodide and the ring centroid range between 3.6 and 3.85 Å, which is slightly shorter than sum of van der Waals radii for C and I. Interactions between π system aromatic ring and an anion are rarely observed, since aromatics are usually electron-rich ; in the case of electron-depleted quinoid rings, anion∙∙∙π contacts are more likely to form. In the studied cases, however, there is also a partial electron transfer between the iodide and the quinone which is noted by a change of colour: the neutral quinone is yellow, while the co-crystals and the semiquinone crystals are black.

Application of X-ray charge density to study of interesting chemical problems is illustrated on several examples involving electron delocalisation and charge transfer. Semiquinone radicals are stabilised by delocalisation of the unpaired electron and negative charge, and their electron structure is somewhere between aromatic (fully delocalised π electrons) and quinoid (distinguishable single and double bonds). In the solid state they form extended π-stacks, and the spin coupling can be diamagnetic (high electron density between the rings) or antiferromagnetic (low electron density between the rings). The border line between a weak covalent bond and a strong intermolecular interaction (such as a hydrogen or a halogen bond) is often a fuzzy one, and the borderline cases are illustrated on an H2O-H-OH2 fragment (Zundel ion) and N-Br-N fragment.

Mixed-metal oxides are an important class of advanced materials, due to their stability, low cost, low toxicity, useful photophysical properties and wide range of technological applications. They are mostly utilized as catalysts and structural ceramics, but recently, the use of mixed-metal oxides as sensors, actuators, and smart materials has also been explored. It is known that the effect of crystallinity, particle size, structure and morphology of these materials could highly affect their properties. These can be tuned in part by changing the synthesis methods. The possibility of using coordination polymers through the thermal decomposition process as molecular precursors in the synthesis of nanomaterials with high surface and specific morphology has been considered only recently. This method of obtaining oxide materials, compared with conventional methods, has several advantages: (i) the obtained material is more homogeneous because the metals are mixed at the molecular level ; (ii) the resulting materials have relatively high specific surface areas because the crystalline oxides are formed under significantly milder conditions than those in, for instance, solid-state reaction processes ; (iii ) the existence of bridging or chelating ligands in the precursors prevents metal separation during oxide formation ; (iv) the re is much greater control of the metal stoichiometry in the final oxide. The C2O42− group easily decomposes to gaseous CO2 and CO at low temperatures, and hence, the oxalate-based solids can serve as a convenient source of oxides [1]. Utilizing the preparation of the oxide materials via thermal decomposition, several oxalate-based compounds were tested as molecular precursors. Discrete heterotetranuclear oxo -bridged compound [Cr2(bpy)4(μ-O)4Nb2(C2O4)4]·3H2O (1 ; bpy = 2, 2'-bipyridine) showed to be a good candidate for molecular precursor-to-material conversion, yielding the rutile-type CrNbO4 oxide after heat treatment at 900°C. The thermal processing of heterodimetallic one-dimensional (1D) compound {; ; ; ; ; ; [CaCr2(bpy)2(C2O4)4]·0.83H2O}; ; ; ; ; ; n(2) proved to be a simple, one-step synthesis route for the preparation of the β-CaCr2O4 phase at 1100 °C in nitrogen flow. The r.t. structure of β-CaCr2O4 is isomorphic with calcium ferrite, unlike most chromate structures, which usually crystallize as spinel oxides. A three-dimensional (3D) oxalate-based coordination polymer {; ; ; ; ; ; [Co(bpy)3][Mn2(C2O4)3]·H2O}; ; ; ; ; ; n(3) was used as a single-source precursor for the formation of spinel oxide CoMn2O4 heating at 800 °C. The conversion via thermal decomposition of compounds 1–3 was explored by thermal analysis (TGA and DTA), IR spectroscopy and powder X-ray diffraction (PXRD). References [1] M. Jurić, J. Popović, A. Šantić, K. Molčanov, N. Brničević and P. Planinić, Inorg. Chem. 52 (2013) 1832-1842.

Radikale, kemijske vrste s nesparenim elektronima, obično se smatra vrlo nestablinima, tako da ih se može pri - praviti samo pod posebnim uvjetima i proučavati samo pomoću posebnih, vrlo skupih, instrumenata. Također ih se smatra štetnima te neprimjerenima za pokuse u školi. Ipak, radikali imaju ključnu ulogu u biološkim susta - vima. Zahvaljujući nesparenim elektronima, obično su živo obojani, tako da se njihovo nastajanje često može opaziti golim okom. Ovdje je opisano nekoliko jednostavnih reakcijâ s biološki najvažnijim radikalom, semikinonom. Lako ih je izvesti u školskom laboratoriju uporabom male količine jeftinih i bezopasnih tvari. Jednostavnim promatranjem tih reakcijâ dade se naučiti mnogo toga o kemiji (slob odnih) radikala

Stacking of aromatic rings is a well-known type of intermolecular interaction and has found its way into textbooks on supramolecular chemistry. It is usually considered as rather weak (typically

Chloranilic acid is a quinoid compound with very diverse chemical behaviour: it is a good ligand, proton donor and acceptor, and also able to form unusually strong π-interactions. The reason for its versatility is its especially malleable π-electron system, which can adopt various degrees of delocalisation, depending on ionisation and molecular environment. Therefore, its neutral form is a typical para-quinone, while its dianion has two delocalised systems separated by two single C-C bonds. The mono anion, however, has a delocalised system over a half of the ring, while the other half has distinguishable single and double bonds. It can also bind to metals either as a bridging (bis)bidentate ligand, which has a dianion-like structure or as a terminal bidentate ligand with an ortho-quinoid structure. Differences in molecular geometry, related to changes of electronic structure, affect significantly IR spectra: its C-C and C-O stretching bands display a variety of red- and blue-shifts. Herein, we present a detailed X-ray charge density study of the electron delocalisation in all five different forms of the chloranilic acid. Electron density at the bond critical points is a more accurate measurement of bond order (and therefore electron delocalisation) which complements previous data on bond lengths and IR bands. Also, mapping of the electrostatic potential indicates electron-rich and electron-poor areas in the molecule, corresponding to single (electron-poor), double and delocalised bonds (electron-rich).

The Zundel ion, H5O2+, occupies a central place in the theory of hydrogen bonding and proton transfer. It is formed as an intermediate during the proton transfer processes in aqueous solutions (and all other protic solutions, too) and biologial systems. One can hardly imagine fundamental biological reactions, such as enzyme kinetics, respiration and photosynthesis without transfer of protons and/or electrons. However, it is an ultrafast process, with a timescale of pico- and femtoseconds, which can be directly studied only by the most advanced time-resolved spectroscopic methods (femtosecond laser UV/vis and IR/Raman) and femtosecond X-ray diffraction using an X-ray free-electron lasers (XFEL). Zundel-like states, with dynamic proton disorder, can be 'trapped' in otherwise 'static' crystals, extending their lifetime by a dozen orders of magnitude - from pico- and femtoseconds to days and months. Then it becomes possible to focus on a single hydrogen bond, using a variety of experimental and theoretical methods.[1] An ideal system for study of the proton dynamics in a Zundel ion is nitranilic acid hexahydrate.[1] It is a small molecule which contains only light atoms (C, N, O), elliminating the problem of absorption and allowing accurate location of hydrogen atoms. Moreover, its crystals comprise H5O2+ cations located in the general position, thus artificial centrosymmetricity (which is usually the case with Zundel ions in the crystal state) can be avoided.[1] Thus, nitranilic acid hexahydrate is an ideal system for X-ray charge density study of a Zundel ion. We present the first X-ray charge density study of a Zundel ion, which reveals electron density and bond order of its central O∙∙∙H∙∙∙O group. To accurately model low electron density on the protons, we have combined X-ray and neutron diffraction (experiment was performed at Laboratoire Léon Brillouin in Saclay, France, with support by prof. Alexandre Bataille): position and anisotropic displacement parameters of the protons used in the refinement of charge density are taken from the structure determined by neutron diffraction.

Over the past few decades, there has been a constant growing interest for novel metal−organic coordination polymers due to their potential applications as functional materials in diverse fields such as hydrogen storage and gas separation, heterogeneous catalysis, luminescence and ion exchange, sensors, or supramolecular magnetism. In the design and synthesis of heteropolynuclear complexes an important role belongs to the oxalate C2O42− anion because of its various possibilities of coordination to metal centers and the ability to mediate magnetic interactions between paramagnetic metal ions. In the search for suitable synthetic routes leading to novel and promising polynuclear species, it has been of considerable importance to find convenient mononuclear complexes that could be used as ligands toward other metal ions. The tris(oxalato)metalate anions [M(C2O4)3]3− (M = trivalent metal) have been widely used as ligands toward metal ions in the preparation of extended multifunctional systems. The dimensionality and nuclearity of these oxalate- bridged compounds are controlled by a templating counterion, namely its size, charge and geometry as well as synthetic conditions (Jurić et al., 2013). In general, metal–organic coordination systems have recently been used as molecular precursors for the preparation of the mixed-metal oxides by their thermal decomposition. This method of obtaining oxide materials, compared with conventional methods, has several advantages. The C2O42− anion easily decomposes to the vapour phases CO2 and CO, by the low-temperature routes, and hence, heterometallic oxalate complexes have already been used for the single-step preparation of mixed metal oxides (Androš et al., 2013). As a continuation of our magneto- structural studies concerning the polynuclear transition-metal complexes, new heterometallic 3D oxalate-bridged coordination polymers {; ; ; ; [M(bpy)3] [Mn2(C2O4)3]·H2O}; ; ; ; n [M = Co2+ (1), Cu2+ (2) ; bpy = 2, 2′-bipyridine] have been prepared and, in addition to the single-crystal X-ray study, characterized by magnetization measurements. The ability of compounds 1 and 2 to act as the single-source precursors for the formation of the spinel oxides was investigated by the thermal analysis (TGA and DTA) and X-ray powder diffraction. References: Jurić, M., Popović, J., Šantić, A., Molčanov, K., Brničević, N. & Planinć, P. (2013). Inorg. Chem. 52, 1832-1842. Androš, L., Jurić, M., Popović, J., Šantić, A., Lazić, P., Benčina, M., Matjaz, V., Brničević, N., & Planinić, P. (2013). Inorg. Chem. 52, 14299-14308.

The simultaneous presence of ferromagnetism and ferroelectricity in a single phase and possible spin-phonon couplings in these systems offers the appealing opportunity to design unconventional devices, such as multiple-state memory elements and electric-field controlled magnetic sensors. Mixed double perovskites, due to its structural diversity, represent a very promising platform in a quest for new multiferroics. A new synthesis route for the preparation of mixed metal oxides crystallizing in the double perovskite structural type will be presented and discussed. This procedure includes the thermal decomposition of the mixture containing two heterometallic molecular precursors (Ba-Nb oxalate- and Ni-Ta oxalate-based complexes!), in a specific ratio. A detailed X-rays powder diffraction study has been carried out in order to examine structural features of prepared oxide material containing two metals on both crystallographic sites (A and B) within perovskite lattice. The effect of thermal decomposition temperature on the microstructural parameters will be discussed as well.

The presented review on chirality is dedicated to the centennial birth anniversary of Nobel laureate Vladimir Prelog and 160 years of Pasteur's discovery of chirality on tartrates. Chirality has been recognized in nature by artists and architects, who have used it for decorations and basic constructions, as shown in the Introduction. The progress of science through history has enabled the gathering of knowledge on chirality and its many ways of application. The key historical discoveries about the rotation of polarized light as a consequence of molecular chirality and findings of Pasteur and Lord Kelvin are described. Chirality can be found in physics of elementary particles and in many fields of chemistry: analytical and organic chemistry, chemistry of natural compounds, medicinal and pharmaceutical chemistry, biochemistry and biotechnology, and molecular biology. The development of knowledge about chirality and its physical background are briefly described. Definitions for geometrical, topological, and conformational chirality are given accompanied by numerous examples of molecules exhibiting such features. The relations between symmetry and chirality in crystallography are exposed. X-ray crystallography is a method of choice for unambiguous determination of molecular architecture, including the absolute configuration of the molecule using Bijvoet's approach. Two methods of determination of absolute configuration by X-ray diffraction and circular dichroism are briefly discussed. To mark two significant jubilees, the essay is dedicated to the role of chirality in stereochemistry. Stereochemistry is not a branch of chemistry but rather a view at chemistry, as considered by E. L. Eliel; this approach is respected in the essay presented. This very approach leads to various aspects of chirality and brings to the consistency of many definitions. The future will bring us knowledge on the role of chirality in communications among molecules, which guide our life processes. The synthesis of various dynamically chiral supramolecules from achiral molecules and preparations of conjugated homochiral polymers will offer new types of biosensors, artificial enzymes and some sophisticated materials. Theresearch of isotopic chirality by quantum-chemical methods reveals some parity-violating effects and shed more light on the physical bases of molecular chirality.

Povodom obilježavanja 2014. godine kao Svjetske godine kristalografije, Hrvatska udruga kristalografa i Hrvatska kristalografska zajednica u suradnji s PLIVOM i Kemijskim odsjekom Prirodoslovno-matematičkog fakulteta u Zagrebu, osmislila je i realizirala prvo hrvatsko natjecanje u rastu kristala, pod nazivom Ljepota kristalnih ploha. Kako bi se osiguralo minimalno poznavanje kemije potrebno za natjecanje, u istom su sudjelovali učenici koji su se već susreli s nastavom kemije, odnosno učenici sedmih i osmih razreda osnovnih škola, te učenici srednjih škola. Zadatak natjecatelja temeljen je na pripravi kristala anorganske soli, organske tvari ili kristala unutar kristala ; što veće mase, bistrine i pravilnosti ploha, iz unaprijed dostavljene količine materijala. Za kristalizaciju su odabrane tvari s kojima su se učenici susreli tijekom ranijeg školovanja – modra galica, limunska kiselina, te kromova i aluminijeva stipsa. Vrijeme kristalizacije bilo je ograničeno na dva mjeseca. Pored temeljnih ciljeva natjecanja, upoznavanja učenika s kristalima, kristalnim rastom i kristalografijom, kao i povećanja njihovog interesa za bavljenje kemijom i znanošću općenito, postignuto je upoznavanje učenika s osnovama laboratorijskog rada, odnosno korištenjem laboratorijskog pribora i kemikalija, vođenjem detaljnih bilješki i opisa pokusa u laboratorijskom dnevniku, kao i važnosti kritičkog razmišljanja i vrednovanja vlastitih rezultata. Postignut je neočekivano dobar odaziv. Na natjecanje je prijavljeno više od 100 škola s ukupno 465 natjecatelja podijeljenih u 155 timova. To je pokazatelj velikog interesa učenika prema kemiji i izvođenju pokusa, što je osnovni preduvjet za donošenje zaključaka na temelju vlastitih rezultata. Ovo je također pokazatelj spremnosti mentora na proširivanje nastavnih sadržaja, u cilju boljeg usvajanja gradiva i proširivanja znanja učenika. Za objektivnu valorizaciju podataka razrađena je metodologija koja je uključivala ocjenu kvalitete dobivenih kristala uz poseban osvrt na vođenje laboratorijskih dnevnika.

Semiquinones are a class of stable organic radical anions ; especially stable are ones with four electronegative substituents, which enhance delocalisation of the unpaired electrons. Therefore, they are potential candidates for design of functional materials with fine-tuned magnetic properties. Semiquinoid anions in crystals are usually stacked by π-interactions, and their magnetic properties depend on their interplanar distance. Most often, the radicals form closely bound dimers with coupled spins [1, 2], which result in diamagnetic properties. However, in smartly designed crystals the distance can be increased, so stacks with equidistant rings will appear, which may be antiferromagnetic [3] or paramagnetic. Therefore, we varied substituents on the semiquinone ring - tetrachloro- (CA), tetrabromo- (BA) and 2, 3-dicyano-5, 6-dichlorosemiquinone (DDQ) were used as anions ; aromatic, approximately planar organic cations (pyridinium, N-methylpyridinium and diquat) were used to check for possible π-interactions between cations and anions. The goal of our research was design novel stable (in air, at room temperature) semiquinone systems with fine-tuned magnetic properties by crystal engineering: we varied size of substituents on the quinoid ring and aromatic organic cations. A combination of crystallographic, magnetic (EPR, SQUID), electrical (impedance spectroscopy) and thermal (TG/DTA, DSC) methods was used to obtain data on stability and magnetic properties of the crystalline compounds. To gain further insight into spin coupling/decoupling, impedance spectroscopy was used to measure band gap between radicals (or dimers of radicals) ; measurement was done on single crystals with electrical contacts applied in the direction of stacking. A pair of analogous salts, N-MePy∙CA and N-MePy∙BA is especially interesting, and be described in detail. In triclinic polymorphh of CA salt closely bound radical dimers occur, similar to previously known alkali salts of semiquinones [1, 2], and the crystals are diamagnetic due to spin pairing. In its triclinic polymorph and isostructural BA salt radicals are equdistant leading to different spin ordering, similar to high-temperature polymorph of K∙CA∙MeCOEt [3]. All crystals were found to be good semiconductors and stable in air at room temperature. [1] K. Molčanov, B. Kojić-Prodić, D. Babić, D. Žilić, B. Rakvin, CrystEngComm, 13 (2011), 5170-5178 ; [2] K. Molčanov, D. Babić, B. Kojić-Prodić, J. Stare, N. Maltar-Strmečki, L. Androš, Acta Crystallogr. B, 70 (2014), 181-190 ; [3] K. Molčanov, B. Kojić-Prodić, D. Babić, D. Pajić, N. Novosel, K. Zadro, CrystEngComm, 14 (2012), 7958-7964.

Objective: The purpose of this study was to analyse the morphological, chemical and crystallographical changes of bone tissue after osteotomy performed with the erbium:yttrium- aluminium-garnet (Er:YAG) laser and a low speed pilot drill. Materials and methods: The bone blocks were prepared from porcine ribs, and on each block, two tunnel preparations were performed using the Er:YAG laser (pulse energy: 1000 mJ, pulse duration: 300 µs, pulse repetition rate: 20 Hz) or the low-speed surgical pilot drill. The morphological changes of the cortical and the spongiuos surface of the tunnel preparations were analysed under the field emission scanning electron microscopy (FE-SEM) at low and high resolution. The distribution and the level of chemical elements in the treated surfaces was evaluated by qualitative and semi-quantitative energy dispersive x-ray analysis (SEM-EDX). Diffraction x-ray analysis was used to detect any differences and thermally induced modifications of hydroxyapatite crystals. Results: FE-SEM revealed sharp edges of the Er:YAG preparations, with empty intertrabecular spaces and without signs of carbonization. In the drill group, the surface of the preparations was smooth, completely covered with smear layer and microcracks embaded, and the edges were with hairy-like irregularities. SEM-EDX analysis did not reveal any differences in the amount of specific chemical elements between the laser and the drill group. There were no thermally induced modifications of hydroxyapatite crystal structure in the bone tissue in both groups. Conclusion: The Er:YAG laser ablation did not cause any morphological, chemical or crystallographical changes of the bone tissue when compared to the surgical drill.

Prethodno opisana istraživanja ferocenskih peptida I (Y-Fca-Ala-OMe) i II (Y-Ala-Fca-OMe) [Y = di-tertbutildikarbonat (Boc), acetamid (Ac) ; Fca = 1'-aminoferocen-1-karboksilna kiselina]1 nastavljena su sintezom i konformacijskom analizom njihovih prolinskih analoga III (Y-Fca-Pro-OMe) i IV (Y-Pro-Fca- OMe). Utjecaj prolina, dobro poznatoga začetnika okretâ, 2 na konformacijska svojstva i citotoksičnu aktivnost izomernih biokonjugata III i IV ispitali smo spektroskopskim metodama (IR, NMR i CD) i in vitro testom proliferacije na humanoj tumorskoj staničnoj liniji. Pri tomu je u konjugatima III pronađena interlančana vodikova veza NHFca...OCPro (9-člani prsten) dok konjugati IV ostvaruju konformaciju gama- okreta tvorbom intralančane vodikove veze NHFca...OCPro.

The synthesis of nanoparticles has been studied extensively in order to understand physics and chemistry at a ‘small’ scale and because of promising applications due to their size-dependent properties.1 There are two major reasons why nanocrystals and their bulk counterparts differ from each other: (i) in nanocrystals the number of surface atoms is a large fraction of the total, (ii) the size of the nanocrystal interior causes a systematic transformation in the density of electronic energy levels.2 Namely, in any material the surface atoms make a distinct contribution to the free energy, so the changes in thermodynamic properties of the nanocrystals compared to the crystalline bulk material of same composition can appear (e.g. melting temperature depression, solid-solid phase transition elevation). Also, changes in thermodynamic stability associated with size can induce modification of cell parameters and/or structural transformations. To display mechanical or structural stability, a nanoparticle must have a low surface free energy. As a consequence of this requirement, phases that have a low stability in bulk materials can become very stable in nanostructures. This structural phenomenon has been detected in TiO2, VOx, Al2O3 or MoOx oxides. For (semi)conductors, as the particle get smaller an additional effect, the so-called quantum-size effect or confinement effect which essentially arise from the presence of discrete, atom-like electronic states which influences the energy shift of exciton levels and optical band gap3. Therefore, synthesis of nanoparticles with controlled size and shape has been found to be demanding for tailoring the desired materials properties since the thermal, electric, optical, catalytic and magnetic properties are strongly composition-, structure- , but also, size- and shape-dependent4. Our work is focued on development of new synthetic routes for oxide materials preparation, namely, direct molecular-to-materials pathways which include heterometallic complexes as single-molecular precursors. Generally, preparation method from single-molecular precursor5, as compared to conventional methods, has several advantages: (i) the obtained material is more homogeneous because the metals are mixed at the molecular level ; (ii) the resulting materials are characterized by relatively high specific surface areas because the they are usually formed under milder ; and (iii) bridging or chelating ligands in the precursor can prevent unwanted metal separation during the oxide formation. Structural and microstructural characterisation of Ba4Nb2O9, Ba4Ta2O9, CoMn2O4 and CaCr2O4 will be discussed in details.

Thermosalient materials, or colloquially commonly called “jumping crystals”, are promising materials for conversion of thermal (or light) energy to mechanical work on nanoscale [1]. These materials, when heated/cooled undergo a sudden and sharp polymorphic single crystal to single crystal phase transition. During this transition the crystals experience a change in their shape, as well as in the size of the unit-cell, and this change is so large that it causes them to jump up to height that is several times their size. This behaviour usually takes place in the time frame of several microseconds. Jumping crystals show high discontinuity in the change of the crystal lattice ; the change can be up to 12% [2]. It was reported [3] that 4-hydroxy-N’- isopropylidenebenzohydrazide shows behaviour somewhat similar to that of jumping crystal. This system was found in three polymorphic modifications (I, II and III), all having the same polar space group Pna21, with the phase transitions I to II, and III to II reported as topotactic (single crystal to single crystal). It was also reported that during irreversible phase transition from I to II, the polar axis undergoes a strong compression (approximately 15%) and single crystals of phase I are violently shuttered into single crystal fragments of the phase II (without jumping), while in the reversible phase transition III to II the polar axis expands (approximately 14%) and the integrity of the single crystals is preserved – and no movement of crystals is observed. Our measurements showed somewhat different behaviour – during the irreversible phase transition from I to II some of the crystals did indeed shutter into smaller fragments, but a large number remained intact and showed a typical jumping crystals behaviour – jumping all around over the large distances (several cm). This is typical of other thermosalient materials [1]. Also, during the reversible phase transition II III (both ways) crystals exhibited jumping behaviour, alas somewhat weaker than during the phase transition I to II. This is in contrast to previously reported behaviour and the new model for jumping crystals phenomenon in this system has to be proposed. References: [1] Skoko, Ž., Zamir, S., Naumov, P. & Bernstein, J. (2010), J. Am. Chem. Soc. 132, 14191. [2] Steiner, T., Hinrichs, W. & Saenger, W. (1993), Acta Crystallogr. B49, 708. [3] Centore, R., Jazbinsek, M., Tuzi, A., Roviello, A., Capobianco, A. & Peluso, A. (2012) CrystEngComm 14, 2645.

New bisprimary and bisquaternary diamantane-1, 6- and -4, 9-diammonium/diaminium salts were synthesized, and characterized by NMR spectroscopy and X-ray crystallography. The impetus for these syntheses were previously reported X-ray crystallographic investigations of adamantane mono- and bisquaternary ammonium ions [3, 5-diMeAda-1-NH3 or Ada-1, 3-di(NMe3)] complexed with cucurbit[n]uril (n = 7, 8). The crystal structures were analyzed with the goal to ascertain possible structural hypotheses for high binding affinity guests bound within various diameter pumpkin-shaped hosts. While Diam-4, 9-di(NMe3I) 5 could be readily prepared from the bisprimary precursor, the corresponding Diam-1, 6-di(NMe3I) 14 could not be obtained even under strong reaction conditions. Stereochemical analysis of this situation suggests very severe steric non-bonding cis-1, 3-diaxial type H…H interactions between the 'axial'-type NMe3 group and neighboring 'axial' proton neighbors. These same interactions are found in Ada-2, 6-di(NMe3I) analogues, but they are alleviated in this smaller polycyclic skeleton via tilting the axial C(methylene)—NMe3 bond away from its axial neighbors. However, similar structural relief for Diam-1, 6-di(NMe3I) is not possible, since the C(methine)—NMe3 bond therein is ligated to the diamondoid's rigid skeleton.

Stacking of quinoid rings which we recently observed is unlike "π-interactions" of aromatic rings: quinoid rings stack face-to-face without offset and with very short interplanar distance, interatomic distances being some 0.3 Å shorter than the sum of van der Waals radii. This indicates unusually strong interactions, which may be comparable to hydrogen bonds, and therefore may be applied in crystal engineering and materials science. The nature of this strong interaction remains to be defined. Therefore, we extended our research of quinoid stacking to a detailed in-depth study of interactions in a well-known model system, potassium hydrogen chloranilate dihydrate using a combination of X-ray charge density determination, quantum chemical methods and electrical conductivity. X-ray charge density study provided us with detailed high-resolution map of electron density. It revealed not just interesting data of electron delocalisation in hydrogen chloranilate anion, but also its electrostatic potential: as expected, single C-C bonds are electron-deficient (positive potential), while delocalised and double ones are electron-rich (negative potential). The mutual orientation of contiguous rings is such that positive and negative parts of the molecules come in a close contact, maximising electrostatic attraction, while minimising repulsion. Therefore, face-to-face stacking of quinoid rings is a dominantly electrostatic interaction. Quantum chemical calculations indicate that the stacking interaction between adjacent rings is notably influenced by dispersion forces ; apparently the dispersion component amounts to several kcal/mol and is slightly dependent on the torsional alignment between the rings. Electric conductivity was measured to assess the degree of charge transfer between the rings. As expected, the conductivity is very low, confirming the electrostatic nature of the interactions.