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U ovom radu istraživano je magnetsko ponašanje mješovitog metalnog oksida CaCr2O4 koji postoji u a- i b-fazi. Helikoidno magnetsko uređenje a-faze općenito ne pogoduje feroelektričnom uređenju, međutim teorijski se predviđa mogučnost magnetoelektričnih vezanja višega reda. U b-fazi poznato namreškanje spinskih ljestvi objašnjava se Dzyaloshinskii- Moriya interakcijom, što ukazuje na moguću magnetoelektričnu vezu[1 ; 2]. Zbog svih tih neispitanih mogučnosti detaljno smo istražili magnetska svojstva CaCr2O4 pri različitim uvjetima. Termičkom razgradnjom novog kompleksa [CaCr2(bpy)2(C2O4)4]n nH2O (bpy = 2, 2’- bipiridin) pri 1100^0C u struji dušika, u jednom koraku, bez dugotrajnih i višestrukih postupaka grijanja i usitnjavanja, pri temperaturama nižim u odnosu na standardne postupke u čvrstoj fazi[2], priređen je mješoviti metalni oksid b CaCr2O4. Ako se temperatura grijanja povisi na 1400^0C, produkt termičke obrade prekursora je smjesa dvaju polimorfa: a- i b-CaCr2O4[3]. Izvršena su magnetska mjerenja SQUID magnetometrom na čiji je nosač nadograđena mogučnost primjene električnog polja. Dobiveni rezultati pokazuju vrlo složeno magnetsko ponašanje s prijelazima u različita magnetska uređenja te je ispitana mogućnost utjecaja električnog polja na magnetizaciju. [1] F. Damay, C. Martin, V. Hardy, A. Maignan, G. André, K. Knight, S, R. Giblin, L. C. Chapon, Phys. Rev. B 81, 214405, (2010) [2] S. E. Dutton, E. Climent- Pascual, P. W. Stephens, J .P. Hodges, A. Huq, C. L. Broholm, R. J. Cava, Phys. Rev. B 83, 024409 (2011) [3] L. Androš, M. Jurić, J. Popović, D. Pajić, K. Zadro, K. Molčanov, D. Žilić, P. Planinić, European Journal of Inorganic Chemistry 33 ; 5703- 5713 (2014)

The oxo-bridged metal units are interesting intramolecular motifs appearing in several bioinorganic molecules such as metalloproteins (Fe–O–Fe core) and in various inorganic systems, especially as polyoxometallates, materials with outstanding properties and functions.[1, 2] Recently, unusual behaviour that causes the changes in material color and magnetic properties has been observed in structures with Cr–O–Cr bridges, referred as metal-to-metal-charge transfer (MMCT).[3] Even though there are several reports of light- and heat-induced MMCT, the occurrence of this intriguing phenomena is hard to predict and the relationship between electron transfer and molecular structure is not jet understood.[4] In the recent years our research group has been involved in intensive studies related to tris(oxalato)oxotantalate(V) anion, with the aim of obtaining new metal-organic coordination systems with specific (electrical, optical, catalytic and/or magnetic) properties. It was found that this type of anion is prone to form heterometallic complexes with different topologies and nuclearities.[5] Depending on reaction conditions and reagents, the oxo group in [TaO(C2O4)3]3– can be protonated or replaced with other ligand in the coordination sphere of tantalum.[6] Reaction of water solutions of complex [Cr(bpy)2(OH2)]3+ cations and [TaO(C2O4)3]3– anions yielded compound with new bonding topology of this anion – dinuclear oxo-bridged complex [Cr(bpy)2(OH2)(μ-O)Ta(C2O4)3]2·7H2O (1) (bpy = 2, 2´-bipyridine). Compound 1 was characterized by single-crystal X-ray diffraction, IR and UV/Vis spectroscopy. Figure 1 shows dinuclear [Cr(bpy)2(OH2)(μ-O)Ta(C2O4)3] unit, with chromium in octahedral geometry and tantalum in distorted pentagonal bipyramidal geometry. Single crystal measurements at room temperature and at 100 K have shown some differences in the unit cell parameters, as well as in the M–(O, N) bond lengths, which my indicate the change of oxidation state of metal centres. Further magnetic and MMCT studies of 1 are in progress.

Recent research related to the multicomponent Nb-containing oxide materials revealed their very appealing structural and physical properties, leading to their development for a wide range of technological applications, such as ferroelectric and piezoelectric materials, ion conductors, and also as promising catalysts in several highly challenging processes.[1] Lately, metal−organic coordination systems have been used as single-source precursors for the preparation of mixed-metal oxides through thermal decomposition. This method, 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 oxides are formed under significantly milder conditions ; (iii) there is much greater control of the metal stoichiometry in the final products ; and (iv) there are no long-term and repeated grinding procedures. The oxalate anion, C2O42− easily decomposes to the vapor phases CO2 and CO, through the low-temperature routes, and hence, the heterometallic oxalate-based compounds are suitable for the use as molecular precursors for mixed oxides .[1–3] Hence, due to the growing need for Nb-based oxides, further investigation of the Nb-containing heterometallic oxalate compounds that could serve as single-source precursors is of great importance. As a continuation of our studies, [1–3] novel compound [Cr(bpy)2(μ-O)2Nb(C2O4)2]2·3H2O (1) (bpy = 2, 2’-bipyridine) was synthesized and characterized by single-crystal X-ray diffraction, IR and UV/Vis spectroscopy and thermal analysis. The molecular structure of 1 exhibits a square shaped {; ; ; Cr2Nb2(μ-O)4}; ; ; core in which oxo-bridged Cr3+ and Nb5+ ions reside in alternate corners (Figure 1). Both metal ions display the octahedral coordination geometry. Thermal treatment of 1 at 1000 °C leads to molecular precursor-to-material conversion that yields the mixed-metal CrNbO4 oxide, explored by powder X-ray diffraction. [1] M. Jurić, J. Popović, A. Šantić, K. Molčanov, N. Brničević, P. Planinić, Inorg. Chem., 2013, 52, 1832−1842 ; [2] L. Androš, M. Jurić, J. Popović, A. Šantić, P. Lazić, M. Benčina, M. Valant, N. Brničević, P. Planinić, Inorg. Chem., 2013, 52, 14299–14308 ; [3] J. Habjanič, M. Jurić, J. Popović, K. Molčanov, D. Pajić, Inorg. Chem., 2014, 53, 9633−9643.

The book of abstracts - MECAME 2018 contains abstracts of plenary and invited lectures, as well as oral and poster presentations presented during the 4rd Mediterranean Conference on the Applications of the Moessbauer Effect - MECAME 2018. It was held in Zadar, Croatia, from 27th to 31st May 2018. MECAME 2018 is being organized in the honour of Professor Frank J. Berry (University of Birmingham, UK) to celebrate his eminent scientific contributions to Moessbauer Spectroscopy. The objectives of MECAME 2018 were to promote the mutual understandings of the researchers, who are using Mossbauer technique and related techniques in material science, solid state chemistry and physics, coordination chemistry, environmental sciences and earth and planetary sciences.

In recent years, iron oxide nanoparticles have been interested in various applications, such as magnetic storage media, drug delivery, MRI contrast medium and hyperthermia. It is known that iron oxide nanoparticles are produced in the pores of the silica matrices, which is possible to control the size of iron oxide nanoparticles homogeniously, using sol-gel method. In this study, iron oxide nanoparticles in amorphous silica matrix (Fe2O3 :SiO2 = 40 : 60 in mass%, abbreviated as 40Fe60Si) were prepared by sol-gel method and investigated by powder X-ray diffractometry (XRD), transmission electron microscopy (TEM), 57Fe Mössbauer spectroscopy at room temperature (57Fe MS), and magnetic susceptibility. Only a halo was detected from the XRD patterns of 40Fe60Si heat treated at 400 and 600 oC for 2 h. Based on the fringes of the observed TEM images, the averaged crystalline size of iron oxide nanoparticles in 40Fe60Si heat treated at 400 and 600 °C were estimated to be 4 and 5 nm, respectively. Mössbauer spectra of 40Fe60Si recorded before (Fig. 1(a)) and after heat treatment at 400 oC (Fig. 1(b)) and 600 °C (Fig. 1(c)) for 2 h consisted of a doublet. The Mössbauer parameter of 40Fe60Si heat treated at 400 °C was similar to that heat treated at 600 °C. As the obtained value of the isomer shift was 0.32 mm s-1 at room temperature, it was determined that 40Fe60Si contained only Fe3+. From the temperature dependence of dc magnetic susceptibility under zero field cooling, the highest magnetic susceptibility of 40Fe60Si after heat treatment at 400 and 600 °C were recorded at the blocking temperature of 33 and 37 K, respectively. In ac magnetic susceptibility measurements, the blocking temperatures became higher with increase in magnetic field frequency. From the relationship between blocking temperature and relaxation time, in the case of 40Fe60Si heated at 400 °C, the value of microscopic relaxation time and the dynamical exponent were estimated to be 9.8 ns and 9.1, respectively, of which the magnetic property was ascribed to superparamagnetism.

Oxide glasses shows some characteristic behavior at low temperature region. However, there are only few reports about the chemical states of magnetic ions effecting the magnetic properties of oxide glass because structure of oxide glass is amorphous. In this study, the relationship between the local structure and magnetic properties of iron phosphate glass (50Fe2O3·50P2O5 glass, composition in mass%) prepared by sol-gel method was investigated by measuring 57Fe Mössbauer spectra, X-ray diffraction pattern (XRD), dc and ac magnetic susceptibility. Only a halo patterns were detected in the XRD diffractograms of 50Fe2O3·50P2O5 glass annealed (HT) at 200, 300 and 400 oC for 2 h. After the isothermal annealing at 500 oC for 2 h, in contrast, diffraction peaks due to α-Fe2O3 and FePO4 were detected. Mössbauer spectra of 50Fe2O3·50P2O5 glass, recorded before the annealing (Fig. 1(a)), consisted of a doublet with isomer shift (IS) and quadrupole splitting (QS) of 0.33 and 0.63 mm s-1, respectively, reflecting the presence of distorted FeIIIO4 tetrahedra. On the other hand, Mössbauer spectra of 50Fe2O3·50P2O5 glass annealed at higher than 200 oC for 2 h (Fig. 1(b)-(d)) consisted of two doublets. In case of the glass HT at 200 oC, one doublet with IS and QS of 1.0 and 2.6 mm s-1, respectively, was ascribed to FeIIO6 octahedra, and the other with IS and QS of 0.31 and 0.76 mm s-1, respectively, was ascribed to FeIIIO4 tetrahedra. The Mössbauer parameters of the glass HT at 300 oC were similar to that of the glass HT at 200 oC. However, the FeIII/FeII ratio of the glass HT at 200 oC was higher than that of the glass HT at 300 oC. From the temperature dependency of dc magnetic susceptibility under zero field cooling, the value of magnetic moment was the highest around 5 K. In measurements of ac magnetic susceptibility, this peak shifted towards higher temperatures with increasing in frequency of magnetic field. From the relationship between cusp temperature and relaxation time, the value of microscopic relaxation time and the dynamical exponent were estimated 0.22 ns and 13.9, respectively, in the case of the glass heat treated at 200 oC, when the magnetic property was ascribed to spin glass[1]. On the other hand, the value of the dynamic exponent decreased with heat treatment at higher temperature, of which the magnetic properties changed spin glass to superparamagnetism with heat treatment at higher temperature.

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.

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 improved and tuned by modification of particle size and shape, as well as by incorporation of various 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). Also, smaller hematite and goethite 1D nanoparticles (nanorods) showed higher visible-light photocatalytic activity compared to larger hematite and goethite 1D particles (microrods). Substitution of Fe3+ ions in iron oxides with divalent metal cations can significantly modify their electronic properties. As a consequence of modified electronic properties, Cu-doped goethite and hematite showed improved catalytic, photocatalytic and gas sensing properties compared to pure phases. In this work Cu-doped goethite and hematite 1D nanoparticles (nanoneedles) were prepared and studied. Cu-doped goethite nanoneedles (with Cu content up to 4 mol%) were synthesized by precipitation in a highly alkaline medium. Cudoped hematite nanoneedles were prepared by calcination of Cu-doped goethite samples at 500 °C. Phase composition of prepared samples was determined using X-ray powder diffraction (XRPD) and Mössbauer spectroscopy. Cu2+-for-Fe3+ substitution in the goethite crystal structure was confirmed by the determination of the unit cell expansion using XRPD and by the measurement of the hyperfine magnetic field reduction using Mössbauer spectroscopy. An increased Cu2+-for-Fe3+ substitution in goethite caused a gradual elongation and narrowing of nanorods with formation of nanoneedles at 3 and 4 mol% Cu. The shape and size of nanoneedles were not changed by goethite to hematite thermal transformation. Thermal analysis showed a decrease in the temperature of goethite dehydroxylation by Cu doping. Cu2+-for-Fe3+ substitution in goethite and hematite affected an increased absorption of visible and near IR radiation compared to pure phases, as well as a decrease in the optical band gap energy.

Hematite (α-Fe2O3) is n-type semiconductor with Eg value of ~ 2.1 eV and this material has various applications in traditional as well as advanced technologies. Recently, it has been extensively investigated as photoanode material in the photoelectrochemical (PEC) devices for water and air purification, waste water remediation, etc. A lot of efforts have been made to improve magnetic, electrical, catalytic, photocatalytic, or other properties of hematite. These properties are highly dependent on its crystal structure, particles size and morphology and can be tuned by controlling the synthesis conditions or/and doping with foreign metal ions There is also the increasing number of studies of nanocomposites of hematite and other metal oxides. These hematite materials are specifically interesting since they may exhibit new physical properties overcoming the failing of the single materials. In the present work the nanofibers of α-Fe2O3/ CuFe2O4 have been synthesized using electrospinning method starting from viscous solution of polyvinylpyrrolidone (PVP) containing appropriate molar ratio of Fe(NO3)3 and Cu(NO3)2 solutions. As synthesized electrospun fibres were calcined in air at 500 °C for 1 hour and additionally at 700 °C for 1 hour. The reference electrospun α-Fe2O3 was synthesized at the same experimental conditions. The microstructural, magnetic and optical properties of the synthesized electrospun fibres were characterized by XRD, FE SEM, 57-Fe Mössbauer, FT-IR, UV-Vis-NIR spectroscopies and magnetometric measurements. A small amount of Fe3O4 was detected in the reference hematite fibres obtained at both calcined temperatures. On the other hand, the electrospun fibers containing copper ions obtained by calcination at 500 °C show the presence of α-Fe2O3, CuFe2O4 and γ-Fe2O3 phases. A small amount of Fe3O4 is also present. Additional heating at 700 °C of these fibres lead to the formation of hematite and cuprospinel composite. The α-Fe2O3/CuFe2O4 composite fibres showed enhanced magnetic and optical properties compared to reference α-Fe2O3 electrospun fibres.

Our future aim is to ascertain the effects of selected nanoparticles on plants of agricultural importance. In the future study we intend (a) to prepare the nanoparticles containing iron and (b) to obtain data about iron metabolism in the plant(s) and (c) to propose different iron utilization strategies in agriculture. In this sense the experiments involving the plants grown in hydroponics or soil conditions will be conducted. In our previous work [1] we reported about iron(III)-oxyhydroxide and non-stoichiometric magnetite nanoparticles with the aim to use them as possible nutrition source for plants. 57Fe Mössbauer spectra of magnetite nanoparticles synthesized under different preparation conditions at ambient atmosphere showed that the magnetite nanoparticles are highly oxidized. In order to obtain more efficient magnetite nanoparticles with higher FeII content, magnetite nanoparticles were prepared in N2 gas atmosphere. The chemical co-precipitation method was utilized, starting with stoichiometric ratio of FeSO4 and FeCl3 solutions for magnetite formation. Then, ammonia solution was slowly and continuously added to the iron salts solution. After the reaction was completed, the precipitates were filtered, washed several times with deionized water and lyophilized. Citric acid coated nanoparticles were also prepared similarly, but adding the citric acid dissolved in deionized water before the addition of ammonia solution. 57Fe Mössbauer spectra (Fig. 1) of washed and lyophilized nanomagnetite prepared in inert gas atmosphere undoubtedly indicated the presence of considerable fraction of FeII, close to the stoichiometric magnetite composition, both at room temperature (RT) and at 80K. XRD pattern of the same sample corresponded to nanomagnetite crystal structure. Mössbauer spectra in Fig. 1 also showed that after lyophilization the unwashed citric acid coated samples contained some FeII which disappeared when the sample was washed before lyophilisation. The washed samples, however, showed a poorly crystalline character.

In recent years, disposal of general garbage exhausted from households is one of the serious environmental problems. Ishikawa et al. reported that iron-containing glass ceramics prepared from household waste slag denoted as Slag + 10Na2O + xFe2O3 (SlagNaFex) showed photocatalytic effect under visible-light irradiation after the samples were heat treated at 800 °C for 100 min. It was turned out that the photocatalytic effect of SlagNaFex after heat treatment is closely related to the precipitated amount of α-Fe2O3 nanoparticles [1]. In this study, a relation between chemical structure of Fe and photocatalytic effect of Slag + xFe2O3 (SlagFex, x = 0, 5, 10 in mass%) was investigated by means of Mössbauer spectroscopy, XRD, UV-Vis and ESI-MS. SlagFex was prepared by conventional melt-quenching method. Mixture of slag collected from Tamagawa incineration plant and Fe2O3 was placed in a platinum crucible, and was melted at 1400 °C for 1 h in the electric furnace. Dark brown samples were obtained by dipping the bottom of the crucible in ice. Each sample was heat-treated at 800 °C for 100 min or 1000 min after being purverized. Photocatalytic activity of SlagFex before and after heat treatment was evaluated by soaking 40 mg of the powdered samples into 20 mL methylene blue (MB) aqueous solution with the concentration of 20 μmol/L. The MB concentration and decomposition products were detremined by UV-Vis and ESI-MS, respectively. 57Fe Mössbauer spectra (57FeMS) were recorded by constant acceralation method at both room temperature and 80 K, using 57Co(Rh) and -Fe as a source and a reference. X-ray diffraction (XRD) patterns were obtained between 2of 10 and 80 °, by using Cu-K rays ( = 0.1541 nm). As shown in Fig. 1, MB concentration in aqueous solution decreased when it was reacted with SlagFex under the visible-light irradiation. The largest first-order rate constant, k of 1.3×10-3 min-1 was recorded for SlagFe5 after heat treatment at 800 °C for 100 min. According to ESI-MS the MB solution after the degradation test showed a peak at m/z of 257, indicating that MB was decomposed into Azure A. XRD patterns of heat-treated SlagFex showed that the peaks assinged to iron oxides (Fe3O4 andγ-Fe2O3) and CaFeAlSiO6. 57Fe MS of heat treated SlagFex measured at 80 K (Fig. 2) are composed of magnetically relaxated of sextets and doublet peaks of Fe(III). The doublet with quadrupole splitting of 1.00 mms-1 and isomer shift of 0.46 mm s-1 are assinged to paramagnetic CaFeAlSiO6 and the another doublet to superparamagnetic component, γ-Fe2O3. In comparison with previous study, SlagFex showed relatively smaller photocatalytic effect than SlagNaFex containing Na [1]. It is concluded that the smaller nanoparticles of γ-Fe2O3 precipitated in SlagFex is effective to promote photocatalytic effect under visible-light irradiation.