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A 3D heterometallic oxalate‐bridged coordination polymer [CuIIFeII2(H2O)(terpy)(C2O4)3]n (terpy = 2,2′:6′,2″‐terpyridine) (1) was investigated both as photocatalyst for the organic dye removal and as a single‐source precursor for the preparation of the copper ferrite (CuFe2O4) nanocrystals by thermal processing. The dual functionality of 1 was supported by the degradation of aqueous solutions of rhodamine B (RhB) and methylene blue (MB) solutions under visible (Vis) and ultraviolet (UV) light irradiation, powder X‐ray diffraction data collection at room temperature, and the optical and scanning electron microscopy analyses. A close inspection of the X‐ray diffraction patterns unveiled qualitative and quantitative information on the phase composition obtained after the single‐source molecular precursor route to spinel oxide. By optimizing the temperature levels and setting the controlled heating rate at 6 h of holding time, the phase composition of thermal processing of 1 was evaluated—thermal treatment of 1 at 950°C for 6 h and a heating/cooling rate of 10°C min−1 resulted in the formation of solely tetragonal spinel phase of CuFe2O4, whereas the formation of both tetragonal and cubic CuFe2O4 phases was observed at 950°C by the heating rate of 30°C min−1. To obtain the high‐temperature cubic CuFe2O4 oxide, compound 1 was heated and then quenched at 925°C, which led to the formation of the cubic spinel ferrite as the main crystalline oxide phase. Moreover, the photocatalytic properties of the t‐CuFe2O4 spinel were investigated under the same conditions as for 1. The optical bandgap energies were estimated from UV–Vis absorption spectra for both metal oxide and precursor powder. [ABSTRACT FROM AUTHOR]

[Display omitted] • Air humidity serves as a dewetting agent in surface pattering of soft metal–organic thin films. • Non-covalent interactions at the molecular level govern the growth of films in specific crystal direction. • Vibrational and optical properties of films are comparable to bulk. • Dense thin films show stable ferroelectric switching at a low operating voltage. • Randomly distributed holes on the surface of metal–organic thin films enhance resistive methanol sensing. Molecular ferroelectrics with low power consumption offer environmental and economic advantages over conventional ferroelectrics and could lead to next-generation microelectronic devices. To this end, it is of great importance to understand the conditions under which molecules can be engineered to form large-area, highly oriented thin films, as their electrical properties depend on orientation. In the research field of molecular ferroelectrics, homochiral multifunctional organic molecules are often used to induce the self-assembly of molecules through non-covalent interactions to form polar crystal packings and consequently ferroelectric properties. Here, molecular ferroelectric thin films based on the natural Cinchona alkaloid, cinchoninium cation and chlorocobaltate(II) anion were prepared by a dip-coating technique without post-thermal treatment and assisted stabilization process. The deposition parameters (relative humidity, temperature, concentration and withdrawal speed) were modified to produce either completely dense or fully patterned films with randomly distributed holes on the surfaces. While non-covalent interactions are the main factor in determining the structure of cinchoninium-trichloro-cobalt(II) thin films, relative humidity is a key parameter in the simultaneous self-organization happening at the mesoscale, acting as a dewetting agent. Dense cinchoninium-trichloro-cobalt(II) films exhibit a stable ferroelectric switching at a low operating voltage, and patterned films were tested as resistive methanol sensors. [ABSTRACT FROM AUTHOR]

The synthesis and the structural, spectroscopic, thermal, magnetic and electrical properties of a new heterodinuclear [Cr(bpy)2(H2O)(μ-O)V(C2O4)2]2·9H2O (1) complex, which contains terminal and unsupported oxo-bridge CrIII–O–VV, isolated for the first time in a molecular compound, are reported. Oxo-bridged metal units as functional intramolecular motifs exhibit interesting properties in complexes, and the discovery of new combinations of metals with different electronic configurations and redox potentials is important for the design of new materials. The reaction for the preparation of 1, involving an aqueous solution of CrIII precursor [Cr(bpy)2(H2O)2]3+ cations and VV precursor [VO2(C2O4)2]3− anions, was monitored by UV/vis spectroscopy. New absorbance bands in the 400–600 nm region can be recognized in the electronic spectrum of 1 that could originate from metal-to-metal charge transfer (MMCT). The assignment of MMCT was further supported by ATR spectroscopy under visible light irradiation. Upon exposure to visible light, a change in the intensities and positions of the absorptions bands related to vibrations of the oxo-bridged Cr–O–V moiety is observed. X-band ESR spectroscopy and magnetic susceptibility measurements point to paramagnetic behaviour of 1. The electrical response of complex 1 was studied by impedance measurements over a temperature range of −90 to 50 °C, revealing its semiconducting nature and the absence of a dielectric anomaly. [ABSTRACT FROM AUTHOR]

Chromium niobate and tantalate (CrNbO4 and CrTaO4) were synthesized by pyrolysis of the oxalate‐based heterometallic complexes [Cr2(bpy)4(μ‐O)4Nb2(C2O4)4]·3H2O (Cr‐Nb) and [Cr(bpy)2(H2O)(μ‐O)Ta(C2O4)3]2·3.5H2O (Cr‐Ta) (bpy = 2,2'‐bipyridine). Compared to conventional solid‐state synthesis, herein studied oxides are prepared at lower temperatures, in one step without repeating grinding procedures. The structure, morphology, and optical properties of the as‐synthesized oxides were characterized using powder X‐ray diffraction (PXRD), field emission scanning electron microscopy (SEM), the thermogravimetric and differential thermal analysis (TG/DTA) and UV‐vis diffuse reflectance spectroscopy (UV‐vis DRS). The determined band gap energies of CrNbO4 and CrTaO4 are 2.39 and 2.82 eV, respectively, which prompted us to investigate photocatalytic activity of these oxides in degradation of dyes. Microscopy studies show that the particles of both oxides began to aggregate into bigger particles, leading to an increase in grain size. Additionally, magnetization measurements on both oxides revealed spin‐glass behavior at low temperatures. [ABSTRACT FROM AUTHOR]

Heterodinuclear complexes [Cr(bpy)2(H2O)(μ-O)Ta(C2O4)3]2·3.5H2O (1) and [H2(terpy)][Cr(terpy)(C2O4)(μ-O)Ta(C2O4)3]·0.5H2C2O4·2.5H2O (2) (bpy = 2,2′-bipyridine; terpy = 2,2′:6′,2′′-terpyridine) have been synthesised through a reaction of a tris(oxalate)oxotantalate(v) anion and a complex chromium(iii) cation with corresponding aromatic N-donor ligands. These are the first examples of a Cr–O–Ta bridge in molecular compounds, and the first report of heterodinuclear complexes prepared from a tris(oxalate)oxotantalate(v) anion as a building block. Structural analysis of both compounds revealed that TaV in pentagonal bipyramid geometry is connected through a slightly bent μ-O bridge to CrIII having a distorted octahedral environment. The geometry optimization performed with density functional theory (DFT) calculations gave very good agreement with the experimentally obtained structure of 1. Room temperature solid state UV-Vis spectra were recorded for both compounds and compared to those of starting reagents, in order to test for possible new electronic transitions attributed to the metal-to-metal charge transfer between CrIII and TaV through the oxo-bridge. Infrared (IR) spectroscopy supported with DFT calculations was used to assign vibrational modes to all spectral features, especially those coming from the molecular μ-oxo bridge. Temperature dependence of magnetic properties of 1 and 2 were probed with magnetic susceptibility measurements on a SQUID magnetometer. Additionally, zero-field splitting parameters were determined from electron paramagnetic resonance (EPR) spectra of compound 1 and experimentally obtained values were confirmed by DFT calculations. [ABSTRACT FROM AUTHOR]

Newly synthesized amino acid hydrazide ligands (L1 = N,N′-di-l-leucine hydrazide; L2 = N,N′-di-l-phenylalanine hydrazide) have shown excellent reactivity and stability, as well as extraordinary coordination ability. Reactions of L1/L2 with copper(ii) ions and 4,4′-bipyridine (4,4′-bpy) as a secondary spacer yielded new coordination polymers {Cu(L1)0.5(4,4′-bpy)(H2O)(NO3)}n·1.5nH2O (1) and {Cu3(L2)2(4,4′-bpy)(H2O)2}n(NO3)2n·3nH2O (2). UV/vis spectroscopy together with structural analysis showed that the deprotonated ligands L12−/L22− with six available donor atoms per ligand have the ability for strong chelation to copper(ii) ions, acting as bis-bidentate (L12−) and bridging bi + tridentate (L22−) ligands. Compound 1 contains copper(ii) ions simultaneously bridged with short hydrazide bridges (4.725 Å) and long 4,4′-bpy spacers (11.144 Å) forming a two-dimensional coordination network. In compound 2, a pair of L22− molecules bridges three copper(ii) ions, which are further interconnected with 4,4′-bpy into an overall one-dimensional chain-like structure. Although bulkier, the phenylalanine ligand (L2) was found to be more flexible compared to the leucine ligand (L1), exhibiting additional intramolecular contact: cation–π interaction. In both compounds, the hydrazide (–N–N–) bridge mediates the antiferromagnetic interaction between copper(ii) ions. Hydrogen bonds have a strong influence on the crystal packing and physical (magnetic) properties. The reported compounds are first examples of hydrazide-bridged metal centres featuring amino acid-based ligands. [ABSTRACT FROM AUTHOR]

Three heterometallic oxo-bridged compounds, [Cr2(phen)4(μ-O)4Nb2(C2O4)4]·2H2O (1; phen = 1,10-phenanthroline), [Cr2(terpy)2(H2O)2(μ-O)4Nb2(C2O4)4]·4H2O (2; terpy = 2,2′;6′,2′′-terpyridine) and [Cr(terpy)(C2O4)(H2O)][Cr2(terpy)2(C2O4)2(μ-O)2Nb(C2O4)2]·3H2O (3), have been synthesized using a building block approach and characterized by IR spectroscopy, single-crystal and powder X-ray diffraction, magnetization measurements, and DFT calculations. The molecular structures of 1 and 2, crystallizing in P42212 and P21/n space groups, respectively, contain a square-shaped {CrIII2(μ-O)4NbV2} unit, while that of complex salt 3 (P1̅ space group) consists of a mononuclear cation containing CrIII and trinuclear anions in which two CrIII ions are bridged by a –O–NbV–O– fragment. Besides hydrogen-bonding patterns resulting in a 1D- or 3D-supramolecular arrangement in 1–3, an unusual intermolecular contact has been noticed between parallel oxalate moieties occurring due to the electrostatic attraction of electron-rich carbonyl oxygen and severely electron-depleted carbon atoms in the crystal packing of 2. The antiferromagnetic coupling observed in all three compounds, determined from magnetization measurements (J = −13.51(2), −8.41(1) and −7.44(4) cm−1 for 1, 2 and 3, respectively) and confirmed by DFT calculations, originates from two CrIII ions with spin 3/2 interacting through diamagnetic –O–NbV–O– bridge(s). [ABSTRACT FROM AUTHOR]

Mixed-valence manganese oxides with a perovskite structure are promising candidates for next-generation electronic devices, among others, because of the combination of ferromagnetism with other technologically important properties. Herein we report the block copolymer-templating synthesis, structural characterization and magnetic properties of thermally stable thin films of cubic mesoporous praseodymium calcium manganite (PCMO), Pr1−xCaxMnO3 with x≈ 0.3. This novel sol–gel derived material is one of the rare examples of a complex mixed-metal oxide with both uniform and ordered nanoscale porosity. Calcination in air at 750 °C produces the desired crystallinity without compromising the pore-solid architecture. The data acquired from superconductive quantum interference device magnetometry confirm the phase purity and high degree of crystallinity. Below around 115 K, the films show clear signs of ferromagnetic behavior, with large low-temperature coercivity. Collectively, the results unequivocally demonstrate the quality of the polymer-templated mesostructured PCMO thin films, whose unique morphology makes them attractive for a variety of applications and further provides an opportunity for designing tailored and multifunctional (host/guest) nanocomposites. [ABSTRACT FROM AUTHOR]

The reaction of bis(phenanthroline)metal(ii) cations (M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) with bis(oxalato)chromium(iii) anions in a water/ethanol solution gives rise to a series of compounds with oxalate-bridged cations, [{M(phen)2}2(μ-C2O4)][Cr(phen)(C2O4)2]2·4H2O [Mn2Cr2 (1), Co2Cr2 (2), Ni2Cr2 (3), Cu2Cr2 (4) and Zn2Cr2 (5)]. Their structural analysis reveals that all the prepared compounds crystallize in the triclinic system, space group P1̅, having similar unit cell parameters, molecular structures and crystal packing features. All metal centres in 1–5 are octahedrally coordinated: M2+ in homodinuclear cations are coordinated with two phen molecules and one bridging oxalate ligand; Cr3+ in anions is coordinated with one phen ligand and two bidentate oxalate groups. The copper atom in Cu2Cr2 (4) exhibits a Jahn–Teller-distorted octahedral coordination. Owing to the considerable number of pyridyl groups present in 1–5 (from phen ligands) the crystal packing of cations and anions is driven by stacking interactions appearing in offset-face-to-face (OFF) and edge-to-face (EF) orientations. The hydrogen bonds between the anions and water molecules of crystallization form 1D ladder-like motifs. In addition to the single crystal X-ray diffraction studies, the characterization of the new complexes was accomplished by means of IR and UV/Vis spectroscopy and magnetization measurements on a SQUID magnetometer. The temperature dependence of magnetic susceptibility reveals different magnetic super exchange interactions taking place in homodinuclear oxalate-bridged cations depending on the transition metal centre (Mn2+, Co2+, Ni2+ and Cu2+). Oxalate ligands mediate the ferromagnetic coupling of Cu2+ metal cations in Cu2Cr2 (4), whereas in Mn2Cr2 (1), Co2Cr2 (2) and Ni2Cr2 (3), antiferromagnetic interactions are observed between Mn2+, Co2+ and Ni2+ cations, respectively. Also, relatively large zero-field splitting parameters for Cr3+ ions (from mononuclear anions), D≈ 1 cm−1, were observed. [ABSTRACT FROM AUTHOR]

A series of eight novel complexes of chloranilic acid (CA) with the first-row transition metals (M = Mn, Cr, Ni, Co) were prepared and characterised by single-crystal X-ray diffraction, IR spectroscopy and polycrystalline X-band electron spin resonance (ESR) spectroscopy. All studied complexes revealed distorted octahedral arrangements. Three coordination modes of the chloranilate ligand are observed: bidentate, bis(bidentate) and, a novel one, mono+bidentate bridging, which can easily be distinguished by IR spectra. The size of the metal atom and different modes of chloranilate coordination affect crystal-packing topologies: 0D (mononuclear or dinuclear) and 1D (zig-zag chains or ladder-like chains). However, the ancillary ligands have a minor influence on the topology of the systems studied. [ABSTRACT FROM AUTHOR]

The synthesis of a homochiral building block based on L -tartrate-chromium(III) complex anions is reported. The dinuclear complex anion, which contains two bridging L -tartrate ligands and one aromatic N-donor ligand coordinated to chromium(III) ions, exhibits a boat conformation in which intramolecular resonance-assisted hydrogen bonding is present. The sodium L -tartrate-chromium(III) compound with the formula Na[Cr2(bpy)2(L -tart)2H]·9H2O (1) crystallizes from a methanol–water solution as a high water content material in the monoclinic space group P2. The as-synthesized compound is only stable at high relative humidity and undergoes structural transformations during drying, which are accompanied by water loss. However, these transformations are reversible and upon wetting, the material returns to its high water content structure. Based on a combination of experimental techniques (PXRD, in situ ATR-FTIR and EPR spectroscopy), the structure of the complex anions appears to be insensitive to the humidity variable processes (wetting and drying). Due to the presence of several hydrogen acceptor and donor groups in the L -tartrate-chromium(III) complex anion, we investigated the proton transport properties of a sodium L -tartrate-chromium(III) compound by impedance spectroscopy under dry and wet conditions at different temperatures. Since the relative humidity affects the structural transformations in this system, it also has a large influence on the proton conductivity, which varies by up to four orders of magnitude depending on the degree of hydration. These results confirm that the proton conductivity can be tuned in flexible structures in which non-covalent interactions determine the crystal packing. [ABSTRACT FROM AUTHOR]

The ability of amino acid-based hydrazide ligands to produce polar crystalline materials that could possess technologically important physical properties, such as ferroelectricity, is tested. Two new coordination polymers {Cu3(L1/L2)2(TPA)}n×solvent were prepared in solvothermal reaction of copper(II) ions, terephthalic acid (TPA) and amino acid-based hydrazide ligands (H2L1 = N,N′-di- L -leucine hydrazide; H2L2 = N,N′-di- L -phenylalanine hydrazide). Structural analysis showed that both coordination polymers crystallize in an enantiomorphic polar point group 1 (C1) at room temperature. The assembled coordination polymers are neutral and consist of three copper(II) ions bridged with two amino acid-based hydrazide molecules, which in turn are linked with TPA molecules to form an overall one-dimensional structure. The magnetic order in these compounds is an antiferromagnetic interaction between copper(II) ions bridged by a hydrazide (–N–N–) bridge. Thermal decomposition of the two coordination polymers begins above 480 K, confirming the high thermal stability of the amino acid hydrazide ligands. The DSC shows that both compounds undergo a reversible phase transition around 388 K. The two coordination polymers show electrical conductivities of less than 10−10 S cm−1, with no change in the real part of the dielectric constant throughout the studied temperature range. Since both compounds crystallize in the ferroelectric space group, the occurrence of spontaneous polarization was tested by polarization–voltage hysteresis experiments. [ABSTRACT FROM AUTHOR]