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In ferroelectric materials, spontaneous electric polarization can be reversibly switched under the external electric field. While homochirality provides an important bridging effect between structure and ferroelectric properties, the discovery of new ferroelectrics is often random rather than strategically designed.[1] Here we report on the targeted synthesis of two metal- organic complex salts containing bicyclic amine cations and bis(oxalato)chromium(III) anions: (DABCO)[Cr(phen)(C2O4)2]2·9H2O (DABCO = 1, 4- diazabicyclo[2.2.2]octane ; phen = 1, 10- phenanthroline) and (COOH-OH-ABCO)[Cr(bpy) (C2O4)2]·H2O (COOH-OH-ABCO = 3-hydroxy-1- azabicyclo[2.2.2]octane-3-carboxylic acid ; bpy = 2, 2′-bipyridine). Complex salts were prepared using the mechanochemical synthesis and recrystallized from aqueous solutions to give single crystals. Structural and dielectric properties of these compounds were studied by combination of single-crystal X-ray diffraction, thermal analysis, infrared and impedance spectroscopy, and polarization−voltage measurements. Newly prepared azabicyclic cation COOH-OH-ABCO+ was characterized using 1H and 13C NMR spectroscopy. Interesting optical phenomena of pleochroism was observed in (DABCO)[Cr(phen) (C2O4)2]2·9H2O, where crystals change color from pink to orange if rotated under plane-polarized light.

Solid–solid phase transition compounds with electric, magnetic, and thermally switchable states usually provide an effective strategy for the design of functional materials such as ferroelectric materials, nonlinear-optical switches, and switchable dielectric devices. Among these properties, ferroelectric behaviour is particularly desirable because it is possible to switch rapidly between different states by an external electric field. The most widely used materials for ferroelectric applications are mainly pure inorganic oxides such as BaTiO3, LiNbO3, and PbZr1–xTixO3, due to their superior electric properties, high thermal stability and phase transition temperature. Recent studies have shown that ferroelectric metal-organic molecule based materials are a promising candidates to replace the predominant lead-based ferroelectrics. [1, 2] The strategy in design of molecular ferroelectrics frequently relies on rotating polar globular ionic molecules, such as 1- azabicyclo[2.2.2]octane (ABCO), as they can be readily reoriented in response to an applied electric field and induce ferroelectric polarization. In attempt to prepare new molecular ferroelectric systems different bicyclic amine cations, including simple derivatives of globular ABCO molecule (O-ABCO = 1-azabicyclo[2.2.2]octan- 3-one ; COOH-OH-ABCO = 3-hydroxy-1- azabicyclo[2.2.2]octane-3-carboxylic acid) and more complex chiral natural alkaloids with ABCO fragment (Q= quinine ; Cnd = cinchonidine) have been used in reactions with chlorocobaltate(II) anions. A series of complexes of the formula ACoCl3 (A = O-ABCO, COOH-OH-ABCO, Q, Cnd) has been prepared. By using the combined techniques of variable-temperature powder X-ray structural analyses, differential scanning calorimetry, impedance spectroscopy, and polarization-voltage measurements, we revealed exciting structural and electric properties in this series of compounds.

Ferroelectrics are ubiquitous materials used in daily life and industrial production, as memories, transducers, capacitors, sensors, and so forth. The main feature of ferroelectrics is spontaneous polarization that can be reversed by the application of an electric field larger than the coercive field. By far the most studied and used electroceramic with ferroelectric properties is lead zirconate titanate, which is nowadays becoming an increasingly serious problem in terms of the environment, costs, and energy.[1] Due to the overall superior performance of lead-based ferroelectrics finding alternatives has proven to be challenging. Herein preparation of two new lead-free ferroelectric systems will be presented, both based on chemical solution synthesis. First, the block copolymer–templated mesostructured LiNbO3 thin films prepared by evaporation induced self-assembly will be presented and their ferroelectric performance will be discussed in terms of different device construction, ie. top and bottom electrodes.[2] The efficiency of ferroelectric materials is related to the way they are prepared because characteristics such as chemical purity, crystallinity, and morphology are important in the obtained materials. Porous electroceramics typically exhibit lower polarizability than their dense counterparts, but they offer much more possibilities for structuring, especially when it comes to producing multifunctional and multicomponent systems and tuning/tailoring of properties. Another approach for the preparation of new ferroelectric systems relies on the chemical design of molecular compounds. Chirality that certain molecules possess is a very convenient feature especially important for the design of polar structures. Using this strategy we have chosen naturally occurring chiral alkaloids of the Cinchona plants: quinine and cinchonidine, in reactions with chlorocobaltate(II) anions to prepare complexes of the formula ACoCl3 (A = alkaloid), that reveal exciting structural and electric properties.

International audience; Herein, we present a detailed X-ray charge density study of the electron delocalisation in five species of the chloranilic acid: neutral molecule, mono- and dianion, and two chelating modes – bidendate and (bis) bidentate. The experiments provide the electron density at the bond critical points, which yields an accurate measure of bond order (and therefore electron delocalisation), and complements previous literature and our data on bond lengths extracted from crystal structures and infrared spectra. 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) that can explain stacking interactions of quinoid rings in crystal packing.

Beside their applications in catalysis, photoluminescence, magnetism, gas storage and separation, metal-organic coordination systems have recently been used as molecular precursors for the preparation of the mixed metal oxides by their thermal decomposition. It has been observed that the use of a well-defined heterometallic precursor can produce crystalline oxide materials under conditions that are significantly milder than those applied in traditional solid-state synthesis. Moreover, the single-source precursors provide better control over the stoichiometry of the metal ions in the final products as well as the homogeneity of the materials due to the mixing of the metals at the molecular level. The existence of bridging or chelating ligands in the precursors prevents metal separation during oxide formation. The C2O42− anion easily decomposes to the vapour phases CO2 and CO, by the low- temperature routes, and hence, heterometallic oxalate complexes are very convenient for the preparation of mixed metal oxides [1]. Heterometallic oxalate complexes do not always contain the appropriate stoichiometry for the formation of the desired single phase mixed-metal oxide. So, we have tested whether the multimetallic oxides could be prepared by mixing two or more different oxalate precursor in various ratios prior to thermal decomposition [2]. A highly crystalline materials Ba2CrNbO6 were obtained after thermal decomposition of the mixture of the well-defined and structurally characterized oxalate-based compounds {; ; ; Ba2(H2O)5[NbO(C2O4)3]HC2O4}; ; ; ·H2O [3] and (NH4)3[Cr(C2O4)3]·3H2O taken in equimolar ratio and grinded in agate mortar prior to heating treatment. Following the same strategy, oxide NiNb2O6 was prepared from the mixture of [Ni(bpy)3]2[NbO(C2O4)3]Cl·12H2O [4] and (NH4)3[NbO(C2O4)3]·H2O [3] complexes, taken in a 1 : 3 ratio. The phase formation and structural ordering of oxides obtained by modified molecular precursor-to-material method has been investigated through a combination of thermal analysis (TGA and DTA) and powder X-ray diffraction.

Properties of the mixed-metal oxides could be highly affected by the effect of crystallinity, particle size, phase composition and morphology. These can be tuned in part by changing the synthesis methods. The possibility of using metal– organic coordination systems through the thermal decomposition process as molecular precursors in the synthesis of nanomaterials with high surface and specific morphology has been considered only recently. It has been observed that the use of a well-defined heterometallic precursor can produce crystalline oxide materials under conditions that are significantly milder than those applied in traditional solid-state synthesis. Also, the single-source precursors provide better control over the stoichiometry of the metal ions in the final products as well as the homogeneity of the materials due to the mixing of the metals at the molecular level. The existence of bridging or chelating ligands in the precursors prevents metal separation during oxide formation. For example, the C2O42− anion easily decomposes to the vapour phases CO2 and CO, by the low-temperature routes, and hence, heterometallic oxalate complexes are very convenient for the preparation of mixed metal oxides.[1] Most of the perovskite compounds that have potential technological interests are not simple systems, but rather ternary oxides such as A(B'B'')O3. Heterometallic oxalate complexes do not always contain the appropriate stoichiometry for the formation of the desired single phase oxide. So, we have tested whether the multimetallic oxides containing two or more metals could be prepared by mixing two or more different oxalate precursor in various ratios prior to thermal decomposition.[2] A highly crystalline materials Ba(M1/3−xMx'NbV2/3)O3 [M = NiII, M' = CoII ; x = 0−1/3] were obtained after thermal decomposition of the mixture of the well-defined and structurally characterized heterometallic oxalate-based compounds Ba2(H2O)5[NbO(C2O4)3]HC2O4}; ; ; ; ; ·H2O, [1] [Ni(bpy)3]2[NbO(C2O4)3]Cl·12H2O[3] and [Co(bpy)3]2[NbO(C2O4)3]Cl·12H2O, [3] grinded in an agate mortar in different ratios. The phase formation and structural ordering of the tri- or tetrametallic perovskite oxides obtained by this modified molecular precursor route have been characterized by powder X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The magnetic properties of newly prepared materials which adopt the disordered cubic structure (Pm3 ̅m space group) with random distribution of B' and B'' ions, have been also investigated.

Magnetic behavior of novel heterotetranuclear compound [Cr2(bpy)4(μ-O)4Nb2(C2O4)4]·3H2O (1 ; bpy = 2, 2’-bipyridine) was investigated by magnetization measurements, EPR (X-, Q-band and and high-field) spectroscopy and DFT calculations. Results of M(T) measurements show antiferromagnetic interaction of CrIII ions through two diamagnetic bridges -O-NbV -O- with parameter of interaction J = −12.77cm−1 and ZFS parameter D = −0.17cm−1. The EPR spectra simulations and DFT calculations reveal the presence of a single-ion anisotropy that is close to being uniaxial, D = −0.31cm−1 and E = 0.024cm−1. [1] [1] Project FerMaEl (UIP-2014-09- 8276) financed by the Croatian Science Foundation

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.

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).

Iron oxides and oxyhydroxides are common and widespread compounds in nature. Goethite (α- FeOOH) and hematite (α-Fe2O3) are the most stable and the most ubiquitous iron oxyhydroxide and iron oxide, respectively. A number of favourable properties (nontoxicity, stability, low cost, band gap in the visible range, etc.) make these compounds promising candidates for different applications (catalysts, photocatalysts, gas sensors, battery electrodes, supercapacitors, etc.). Properties of goethite and hematite can be enhanced by modification of particle size and shape, as well as by incorporation of different metal cations into their crystal structure. For example, elongated (1D) hematite nanoparticles (nanorods) showed higher visible-light photocatalytic activity compared to hematite nanoplates (2D) or nanocubes (3D). Substitution of Fe3+ ions with other metal ions can also significantly modify different properties. Ni-doped goethite (α-FeOOH) nanorods were synthesized from mixed Fe(III)-Ni(II) nitrate aqueous solutions by a hydrothermal treatment in a highly alkaline medium using a strong organic alkali tetramethylammonium hydroxide (TMAH). Small amounts of Ni-containing ferrihydrite and Ni ferrite were present as minor phases in samples with 10 mol% Ni and more. Ni-doped hematite (α- Fe2O3) nanorods were obtained by calcination of Ni-doped goethite nanorods at 400 °C. Ni-for-Fe substitution in the structure of goethite and hematite was confirmed by the determination of the unit cell expansion using XRPD and by the measurement of the hyperfine magnetic field (HMF) reduction using Mössbauer spectroscopy. Ni-doped goethite and hematite nanorods were smaller compared to reference samples for 5 mol % Ni but significantly larger for higher Ni contents. Electrochemical measurements showed significant increase in oxygen evolution reaction (OER) catalytic activity of Ni-doped goethite and Ni-doped hematite nanorods compared to pure phase.