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This paper introduces for the first time the preparation of cobalt aluminate (CoAl2O4) nanoparticles through a solution combustion method using a Mentha piperita leaves extract. The active constituents present in the mentha leaves extract act as both a chelating and a reducing agent. The isolated precursor was characterized by FTIR, UV–Vis, thermal analysis and XPS. Various techniques (XRD, SEM and TEM, XPS, FTIR and UV–Vis) were also used to characterize the cobalt aluminate spinel from the point of view of structure, morphology and surface chemistry. XRD confirmed the formation of a single-phase, crystalline cubic spinel structure with mean crystalline domain size of 19.5 nm. The TEM analysis showed rhombic and rectangular CoAl2O4 nanoparticles with unimodal particle size distribution and average particle size of about 35 nm. The characteristic peaks of the CoAl2O4 spinel were highlighted by the FTIR spectrum. The tetrahedral configuration of Co2+ ions in the CoAl2O4 spinel structure was illustrated by the absorbance and XPS spectra. Furthermore, XPS spectra reveal both tetrahedral and octahedral configurations of Al3+ ions. To evaluate the catalytic properties of the cobalt aluminate, the photocatalytic degradation of methylene blue (MB) was carried out under visible light irradiation.

This paper describes for the first time two processing routes—the precursor method and the two-step wet chemical process—for the synthesis of magnetic cobalt ferrite using the Tamarindus indica fruit extract. These green approaches are eco-friendly, safe and efficient alternatives to classical chemical methods. The aqueous extract from tamarind fruit contains numerous metabolites (organic acids, aminoacids). All these bioactive components are able to chelate metal ions leading to the formation of the multimetallic complex (precursor of cobalt ferrite). The obtained precursor was characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis, X-ray diffraction analysis (XRD) and magnetic measurements. The structure, morphology and magnetic behavior of the cobalt ferrite samples prepared through both synthesis routes were investigated by various characterization techniques: FTIR, XRD, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), Mossbauer spectroscopy and magnetic measurements. XRD data confirmed that a cubic spinel structure was obtained for both ferrite powders with average crystallite size of 13 and 5 nm, respectively. The microstructure study by SEM revealed the formation of nanocrystallites assemblies using the precursor method and carbon-rich particles forming granulated micron-sized agglomerates, embedding ferrite nanocrystallites obtained through the two-step wet chemical process. Mossbauer spectroscopy results evidenced relaxation processes in the CoFe2O4 samples at room temperature, and the main characteristics of the involved sublattices were derived. The magnetic investigation revealed a typical magnetic behavior for a spinel, with CoFe2O4 nanoparticles ferrimagnetic at low temperature and superparamagnetic at room temperature.

The nanostructured cobalt aluminate (CoAl2O4) was obtained through an eco-friendly precursor method using aqueous extract of tamarind fruit. The use of plant extracts is a simple and effective approach for the preparation of CoAl2O4 nanoparticles. The polynuclear complex precursor was characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–VIS) and thermal analysis. The cobalt aluminate was investigated by: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FTIR, UV–VIS and colour measurements by reflectance spectroscopy (RS). X-ray diffraction patterns confirmed the formation of cubic CoAl2O4 spinel phase with good crystallinity. The average particle size from TEM is about 71 nm. Chromatic coordinates indicate that the bluest colour was obtained for the cobalt aluminate obtained by subsequent heat treatment.

Chromium substituted cobalt ferrites CoFe2−xCrxO4 (x = 0; 1; 1.5) were synthesized through a soft chemistry method—the gluconate precursor route. The gluconate precursors were characterized by infrared spectroscopy (IR), ultraviolet–visible spectroscopy and thermal analysis. The spinel oxide powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mossbauer spectroscopy and Brunauer–Emmett–Teller N2 adsorption–desorption analyses. XRD indicated the formation of the spinel-type phase with good crystallinity. The mean crystalline domains size decreased from 23.8 to 17.8 nm with the increase in the chromium content. SEM revealed faceted particles for which the particle sizes varied significantly with the chromium content. The chromium substituted cobalt ferrites were found to have high catalytic performance.

Un-doped and doped strontium aluminates (Sr 3 Al 2 O 6 , Sr 3 Al 2 O 6 :Tb 3+ , Sr 3 Al 2 O 6 :Tb 3+ ,Eu 3+ and Sr 3 Al 2 O 6 :Tb 3+ ,Eu 3+ /Eu 2+ ) were synthesized through a soft chemical method – the tartarate precursor route. The tartarate precursors were characterized by infrared spectroscopy (IR) and thermal analysis. The strontium aluminates were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR). The XRD patterns confirmed the formation of single-phase cubic structure Sr 3 Al 2 O 6 with average crystallite size of 18 nm. SEM micrographs showed porous polycrystalline powder microstructures and EDX analysis confirmed the incorporation of the dopant in the Sr 3 Al 2 O 6 powders. The photoluminescence spectrum recorded on Sr 3 Al 2 O 6 : Tb 3+ ,Eu 3+ (obtained from tartarate precursor calcined in air) showed the typical f-f luminescences of the RE-ions. Subsequent calcination of this sample in reducing atmosphere is accompanied by new photoluminescence and thermoluminescence features associated to the Eu 2+ ions.

Silver-cobalt ferrite nanocomposites (Ag-CoFe 2 O 4 ) were synthesized through wet ferritization process and self-propagating combustion method. The structure, morphology, surface chemistry and magnetic properties of the nanocomposites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). X-ray diffraction patterns confirmed the formation of CoFe 2 O 4 and Ag nanoparticles with cubic symmetry. The average crystallite size of CoFe 2 O 4 by wet ferritization ranged between 60 A and 87 A; for those obtained by self-propagating combustion was in the range 232–290 A. SEM micrographs revealed different morphological features of nanocomposites. Ag-CoFe 2 O 4 obtained by wet ferritization exhibited typical superparamagnetic behaviour. The antimicrobial and anti-biofilm properties of all silver-cobalt ferrites were evaluated. The results revealed that the Ag-CoFe 2 O 4 nanocomposites exhibited good microbicidal and anti-biofilm features.

Un-doped and Tb 3+ -doped calcium and strontium aluminates (CaAl 2 O 4 , CaAl 2 O 4 :Tb 3+ , SrAl 2 O 4 , SrAl 2 O 4 :Tb 3+ ) were synthesized by a new soft chemical method—the precursor route via the thermal decomposition of tartarate compounds. The complex precursors have been characterized by elemental chemical analysis, infrared spectroscopy (IR), luminescence spectroscopy and thermal analysis. X-ray diffraction (XRD), scanning electron microscopy (SEM), IR and Raman spectroscopy (RS) were used for the structural and morphological characterization of un-doped and doped alkaline-earth aluminate powders. Photoluminescence (PL) and Thermoluminescence (TL) properties of the aluminates were also investigated. The XRD patterns confirmed the formation of low-temperature structures: hexagonal structure for CaAl 2 O 4 and monoclinic structure for SrAl 2 O 4 , with average crystallite size of 64 nm and 46 nm for CaAl 2 O 4 and SrAl 2 O 4 , respectively. Microstructural analysis by SEM showed the homogeneous microstructure and fine particle size of the powder obtained by precursor method.

The nanocrystalline cobalt ferrites (CoFe 2 O 4 ) were obtained through self-combustion and wet ferritization methods using aqueous extracts of sesame ( Sesamum indicum L) seeds. The multimetallic complex compounds were characterized by Fourier transform infrared spectroscopy (FTIR), UV-VIS spectroscopy and thermal analysis. Phase identification, morphological evolution and magnetic properties of the obtained cobalt ferrites were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), FTIR and magnetic measurements. FE-SEM investigations revealed the particle size of CoFe 2 O 4 obtained by wet ferritization method ranged between 3 and 20.45 nm. Their antimicrobial, anti-biofilm and cytotoxic properties were evaluated.

Chromium substituted cobalt ferrites (CoFe2–xCrxO4, 0 ≤ x ≤ 2) were synthesized through solution combustion method using glycine as fuel, named glycine-nitrates process (GNP). As evidenced by X-ray diffraction data (XRD), single cubic spinel phase was formed for all CoFe2–xCrxO4 (0 ≤ x ≤ 2) series. The cubic lattice parameter (a) decreases with increasing chromium content. Room temperature 57Fe Mössbauer spectra revealed the Fe3+ and Cr3+ site occupancy, the local hyperfine magnetic fields and the substitution of Fe3+ by Cr3+ in the lattice. Scanning electron microscopy (SEM) showed a refinement of particle size with the increase of Cr3+ content. Magnetic measurements from 5 K to 120 K have shown a dropping in the saturation magnetization as the chromium content increases. This behaviour has been explained in terms of substitution of Fe3+ by Cr3+ in the cubic lattice of cobalt ferrite.

CuFe 2− x Cr x O 4 spinel (0≤ x ≤2) powders were synthesized by a soft chemistry method—the gluconate multimetallic complex precursor route. The complex precursors were characterized by elemental chemical analysis, infrared (IR) and ultraviolet–visible (UV–vis) spectroscopy, thermal analysis and Mossbauer spectroscopy. The oxide powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), IR, Raman and Mossbauer spectroscopy. It was shown that the structure, morphology and magnetic properties of the obtained spinel powders depend on the concentration of Cr 3+ ion. The XRD of the chromium substituted copper ferrite powders calcined at 700 °C/1 h indicated the formation of a cubic spinel type structure for x =0.5, 1.0 and a tetragonal structure for x =0, 0.2, 2. The crystallite size ranged from 19 nm to 39 nm. The Mossbauer spectroscopy revealed the site occupancy of iron ions, relative abundance and internal hyperfine magnetic fields in both tetrahedral and cubic CuFe 2− x Cr x O 4 spinels.

Cobalt chromite (CoCr2O4) was synthesized through the precursor method. The precursors: (NH4)3[CoCr2(C4O6H4)4(OH)3]·4H2O, (NH4)3[CoCr2(C6O7H10)4(C6O7H9)]·5H2O were characterized by elemental chemical analysis, infrared (IR) and ultraviolet–visible (UV–vis) spectroscopy, and thermal analysis. The final oxides were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), UV–vis, IR, Raman spectroscopy (RS), magnetic measurements, N2 adsorption–desorption analyses and X-ray photoelectron spectroscopy (XPS). XRD confirmed the cubic CoCr2O4 phase only and determined average crystallite sizes between 14 and 21 nm. Electron microscopy revealed morphology corresponding to the complete crystallization into cubic CoCr2O4. All the samples presented ferrimagnetic ordering below the Currie temperature (Tc), and a phase transition at Ts ∼26 K attributed to the onset of long-range spiral magnetic order. The CoCr2O4 nanoparticles generated through the gluconate route following calcination at 700 °C for 1 h were found to have the best catalytic activity in the total oxidation of methane.

Cobalt chromites (CoCr2O4) powders have been synthesized via thermal decomposition of oxalate precursor compounds (NH4)4[CoCr2(C2O4)4(OH)4]·7H2O (I) and (NH4)12[CoCr2(C2O4)8(OH)4]·(NH4)2C2O4·12H2O (II). The oxalate precursors have been characterized by infrared (IR) and ultraviolet–visible spectroscopy (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. The structure, morphology and magnetic properties of CoCr2O4 powders have been investigated by XRD, SEM, IR and Raman spectroscopy (RS), UV–vis and magnetic measurements. XRD patterns confirmed the formation of spinel-type cobalt chromite, with average crystallite sizes calculated from XRD patterns of 38 nm and 58 nm, for spinel chromites from precursors I and II, respectively. SEM micrographs revealed particle sizes between 30 and 130 nm, with a low degree of aggregation of primary nanocrystallites. Both CoCr2O4 powders presented ferrimagnetic ordering below the Currie temperature (Tc) and a phase transition at Ts~20 K attributed to the onset of long-range spiral magnetic order.

Eu3+,Tb3+-doped Sr3Al2O6 powder phosphor was synthesized via a precursor route and subjected to a subsequent thermal treatment in reducing atmosphere. Photoluminescence and thermoluminescence properties of Sr3Al2O6:Eu3+/Eu2+,Tb3+ were investigated. The structure and morphology of oxides were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used for the nanocrystals surface composition analysis. X-ray diffraction patterns confirmed the formation of the cubic structure specific to Sr3Al2O6 with space group Pa3 and lattice parameter a = 15.8322 A, while SEM investigations revealed equiaxial, polycrystalline particles, with sizes in the submicronic range, for both Sr3Al2O6:Eu3+,Tb3+ and Sr3Al2O6:Eu3+/Eu2+,Tb3+ samples. The photoluminescence spectra showed the typical f-f luminescence lines of the Tb3+ and Eu3+ - ions, accompanied by a broad Eu2+ luminescence band at 510 nm (after calcination in reducing atmosphere). The “after-glow” luminescence signal and the thermoluminescence were assigned to the recombination of close neighbor partners (electron and Eu2+ - hole centers) within the same complex of defects.

Cu 2 In 2 O 5 with orthorhombic structure and CdIn 2 O 4 spinel oxide have been synthesized by the precursor method via the tartarate route. The complex precursors, (NH 4 ) 12 [Cu 2 In 2 (C 4 O 6 H 4 ) 2 (C 4 O 6 H 3 ) 6 ]·6H 2 O( I ) and ( NH 4 ) 4 [CdIn 2 (C 4 O 6 H 4 ) 4 (OH) 4 (H 2 O) 2 ] ( II ), have been characterized by infrared spectroscopy (IR), ultraviolet–visible spectroscopy (UV–Vis), luminescence spectroscopy, magnetic measurements and thermal analysis. Indium-based oxides have been investigated and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectroscopy and magnetic measurements. Both indates are nanocrystalline powders. The average crystallite size is around 40–60 nm.

Zinc chromite (ZnCr 2 O 4 ) nanocrystalline powders were obtained by two different chemical routes: the precursor method and the solution combustion method involving glycine-nitrates. The complex compound precursors, [ZnCr 2 (NH 2 CH 2 COO) 8 ]·9H 2 O and [ZnCr 2 (NH 2 CH 2 COOH) 4.5 ]·(NO 3 ) 8 ·6H 2 O, were characterized by chemical analysis, infrared spectroscopy (IR), ultraviolet–visible spectroscopy (UV–vis) and thermal analysis. The structure, morphology, surface chemistry and magnetic properties of ZnCr 2 O 4 powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), infrared and Raman spectroscopy (RS), ultraviolet–visible spectroscopy (UV–vis) and magnetic measurements. X-ray diffraction patterns indicated the chromite spinel phase with good crystallinity and an average crystallite size of approximately 18–27 nm. The band gap values ranged between 3.31 and 3.33 eV. The magnetic measurements indicated an antiferromagnetic transition at T N ∼ 17.5/18 K.

Zinc chromites (ZnCr 2 O 4 ) have been synthesized via thermal decomposition of (NH 4 ) 2 [ZnCr 2 (C 4 O 6 H 4 ) 4 (OH) 2 ]∙9H 2 O and (NH 4 ) 3 [ZnCr 2 (C 6 O 7 H 11 ) 4 (OH) 7 ]∙H 2 O precursors. The complex precursors have been characterized by infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV–vis), thermal analysis and scanning electron microscopy (SEM). ZnCr 2 O 4 samples have been investigated and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible (UV–vis) and photolumininescence (PL) spectroscopy and Brunauer–Emmett–Teller (BET) N 2 adsorption–desorption analyses. Nanoscaled (∼60 nm) single-phase zinc chromites were obtained by heating the precursors at 900 °C for 1 h. The influence of thermal treatment of tartarate precursor on structural, morphological and textural properties of ZnCr 2 O 4 is discussed.

The CoxZn1−xGa2O4 spinels (x = 0.25, 0.5, 0.75, 1) were synthesized by a wet chemistry method–the precursor route via tartarate decomposition. The complex precursors have been characterized by IR, UV–Vis, magnetic measurements and luminescence spectroscopy. XRD, SEM, IR, UV–Vis and luminescence spectroscopy were used for the structural and morphological investigation of CoxZn1−xGa2O4 spinels; magnetic susceptibilities of the spinel were also measured. The X-ray diffraction patterns confirmed the formation of gallate spinel phase, CoxZn1−xGa2O4.

Cobalt-aluminate spinel, CoAl2O4, has been synthesized by two synthesis variants of the complexation method: tartarate and gluconate routes. The complex precursors have been characterized by IR, UV–vis spectroscopy and thermal analysis. The cobalt-aluminate spinel has been investigated by XRD, IR, UV–vis and luminescence spectroscopy and TEM. The results indicated that in both cases the single-phase nanocrystalline CoAl2O4 spinel was formed. The average crystallite size from TEM images was in the range 50–60 nm. The emission spectra of CoAl2O4 in the visible region confirmed the presence of tetrahedral coordinated Co2+ ion.

Structural and optical properties of (Co0.01Zn0.99)Al2O4 and Zn(Al1.99Ln0.01)O4 (where Ln(III) = Eu(III), Tb(III)) spinels obtained by a variant of the complexation method—tartarate route were studied. The tartarate precursors have been characterized by IR, UV–vis and luminescence spectroscopy. The doped aluminium based spinels have been investigated by X-ray diffraction (XRD), transsmision electron microscopy (TEM), infrared spectroscopy (IR), ultraviolet visible spectroscopy (UV–vis) and luminescence spectroscopy. Pure spinel nanometer powders were obtained. Under excitation at 380 nm the nanoparticles exhibits strong luminescence corresponding to 5D0 → 7F2 transition of Eu3+ ions and respectively, to 5D4 → 7Fj (j = 3, 4, 5, 6) transition of Tb3+ ions. No blue emission from the 5D3 state were observed.

Two soft chemistry routes – complexation and solution combustion – are explored to obtain the zinc gallate spinel ZnGa 2 O 4 . Three types of complexes, namely: (NH 4 ) 2 [ZnGa 2 (C 4 O 6 H 4 ) 4 (OH) 2 ]·4H 2 O, [ZnGa 2 (NH 2 CH 2 COOH) 4.5 ](NO 3 ) 8 ·4H 2 O and [ZnGa 2 (CO(NH 2 ) 2 ) 7 ](NO 3 ) 8 ·9H 2 O have been synthesized and characterized by IR and UV–vis spectroscopy. Zinc gallate spinels obtained by decomposition of these compounds have been investigated by XRD spectra, analytic electronic microscopy and photoluminescence spectroscopy. Zinc gallate spinels exhibited blue emission spectra in the wavelength range of 400 nm–450 nm.

Lithium ferrite was prepared by the thermal decomposition of three polynuclear complex compounds containing as ligands the anions of malic, tartaric and gluconic acid: (NH4)2[Fe2.5Li0.5(C4H4O5)3(OH)4(H2O)2]?4H2O (I), (NH4)6[Fe2.5Li0.5(C4H4O6)3(OH)8]?2H2O (II) and (NH4)2[Fe2.5Li0.5(C6H11O7)3(OH)7] (III). The polynuclear complex precursors were characterized by chemical analysis, IR and UV-Vis spectra, magnetic measurements and thermal analysis. The obtained lithium ferrites were characterized by XRD, scanning electron microscopy, IR spectra and magnetic measurements. The single a-Li0.5Fe2.5O4 phase was obtained by thermal decomposition of the tartarate complex annealed at 700?C for 1 h. The magnetization value ? 50 emu g-1 is lower than that obtained for the bulk lithium ferrite due to the nanostructural character of the ferrite. The particle size was smaller than 100 nm.

The nanosized copper ferrite with tetragonal structure was obtained by combustion-reaction of ureate precursors, so called self-propagating synthesis. The ureate complex compounds–precursors were characterized by chemical and physico-chemical measurements. The copper ferrites were investigated by: X-ray diffractometer (XRD), scanning electron microscopy (SEM), IR microscopy and magnetic measurements.

The possibility of obtaining yttrium iron garnet (Y3Fe5O12, YIG) through thermal decomposition of two coordination compounds with malate and gluconate anions as ligands, (NH4)6[Y3Fe5(C4O5H4)6(C4O5H3)6]·12H2O and (NH4)6[Y3Fe5(C6O7H10)6(C6O7H9)6]·8H2O. A mixture of simple oxides, namely Y2O3 and α-Fe2O3, orthorhombic ferrite YFeO3 and small amounts Y3Fe5O12, is generated from the thermolysis of malate compound, while a clean Y3Fe5O12 is obtained from gluconate compound.

The cobalt ferrite (CoFe2O4) and silver-cobalt ferrite (Ag-CoFe2O4) nanoparticles were obtained through self-combustion and wet ferritization methods using aqueous extracts ofHibiscus rosa-sinensisflower and leaf. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and magnetic measurements were used for the characterization of the obtained oxide powders. The antimicrobial activity of the cobalt ferrite and silver-cobalt ferrite nanoparticles against Gram-positive and Gram-negative bacteria, as well as fungal strains, was investigated by qualitative and quantitative assays. The most active proved to be the Ag-CoFe2O4nanoparticles, particularly those obtained through self-combustion using hibiscus leaf extract, which exhibited very low minimal inhibitory concentration values (0.031–0.062 mg/mL) against all tested microbial strains, suggesting their potential for the development of novel antimicrobial agents.

A TG, DTG and DTA study of three polynuclear coordination compounds, containing Al(III)-Mg(II), namely (NH4)4[Al2Mg(C4O5H4)4(OH)4]⋅2H2O, (NH4)4[MgAl2(C4H4O6)4(OH)4]⋅3H2O and (NH4)2[Al2Mg(C6O7H11)5(OH)5]⋅3H2O, has been reported together with the associated thermal decomposition mechanism rationalized in terms of intermediate products. As decomposition end-product, magnesium-aluminum spinel is obtained. The values of MgAl2O4 mean crystallite size depend on the anionic ligand contained by the precursor compound, varying in the order: malate (143 A) ligand contained by the precursor compound, varying in the order: malate (143 A)

Nanoparticles of copper ferrites with tetragonal structure were obtained by two soft chemical methods: a complexation method and a self-propagating combustion. We demonstrated that in both these methods the precursors of copper ferrites were polynuclear coordination compounds. Three polynuclear coordination compounds with glycine as ligands: [Fe(III)2Cu(II)(NH2CH2COO)4(OH)3](NO3)·H2O, [Fe(III)2Cu(II)(NH2CH2COO)6(NH2CH2COOH)2](NO3)2 and [Fe(III)2Cu(II)(NH2CH2COOH)4.5](NO3)8·4H2O were synthesized. The complex compounds were characterized by elemental chemical analysis and physico-chemical measurements (IR, UV–vis, magnetic measurements). The copper ferrites were investigated by XRD, IR spectra and magnetic measurements. The crystallite sizes of the copper ferrites were found in the range 18–29 nm.

The thermal behaviour of three coordination compounds, precursors of copper ferrite, namely [Fe 2 Cu(NH 2 CH 2 COOH) 4.5 ](NO 3 ) 8 ·4H 2 O (I), [Fe 2 Cu(NH 2 CH 2 COO) 4 (OH) 3 ](NO 3 )·H 2 O (II) and [Fe 2 Cu(NH 2 CH 2 COO) 6 (NH 2 CH 2 COOH) 2 ](NO 3 ) 2 (III), has been investigated. For a complete and reliable assignment of the thermal transformations, the isolable intermediates and end products were characterized by IR and X-ray diffraction. The coordination compounds which undergo a stepwise decomposition in the temperature range 60–375 °C are less stable than free glycine (206–375 °C), indicating the occurrence of some self-propagating reactions. The nitrate/glycine ratio contained by the parent coordination compound, affects the final decomposition temperature (decreases as the ratio increases) but not the decomposition mechanism, and the mean particles size of the decomposition end product Fe 2 CuO 4 (an optimum value has to be found in order to avoid local combustion occurrences).

Nickel–zinc ferrites have been synthesized via thermal decomposition of polynuclear coordination compounds containing as ligand the anion of malic acid, namely (NH4)[Fe2NixZn1–x(C4H4O5)(OH)3]·nH2O (x =0.25, 0.5 and 0.75, n=3 and 5). A comparison between the thermal behaviour of the studied polynuclear coordination compounds is inferred. Fe2NixZn1–xO4 (n=0.25, 0.5 and 0.75) ferrites with mean particle sizes of 65–85 A and free from other phases are formed after a heating treatment of only one hour at 500°C.

A new type of complexes compounds (NH 4 ) 6 [M 3 Fe 5 (C 4 O 5 H 4 ) 6 (C 4 O 5 H 3 ) 6 ] 16H 2 O (where M(III) = Y, Eu, Gd, Er), (NH 4 ) 6 [M 3 Fe 5 (C 4 O 6 H 4 ) 6 (C 4 O 6 H 3 ) 6 ]. 16H 2 O (where M(III) = Gd, Er) and (NH 4 ) 6[M 3 Fe 5 (C 6 O 7 H 1 0 ) 6 (C 6 O 7 H 9 ) 6 ] xH 2 O (where M(III) = Y; x = 8; M(III) = Eu, Er; x = 22) [C 4 O 5 H 4 2 = malate anion; C 4 O 4 H 4 2 - = tartaratc anion, C 6 O 7 H 1 1 = gluconate anion] have been synthesized and characterised by elemental chemical analysis and physico-chemical measurements (1R, UV-Vis spectroscopy and magnetic determinations). The synthetic possibilities offered by the use of these new compounds as potential precursors for garnets have been suggested.

Thermal investigations of two novel coordination compounds, potential precursor of copper sulfides, namely [Cu2(S2O3)2(NH3)4]·5H2O and Na2[Cu4(S2O3)5(NH3)8]·2H2O were performed either in solid state (static air atmosphere), as well as in reaction medium. During both decompositions, Cu2+ reduction occurs. In solid state decomposition, a mixture containing sulfides and sulfates is observed. In the reaction medium, CuSy compounds with sulfur content y (0.66

The thermal behaviour of three coordination compounds, potential precursors of nickel ferrite [Fe2Ni(C4H4O5)2.5(OH)2]NO3·5H2O,[Fe2Ni(C4H8O3N2)4](NO3)8·24H2O and (NH4)[Fe2Ni(C4H4O5)3(OH)3]·3H2O has been investigated to evaluate their suitability as precursors for nickel ferrite. For a complete and reliable assignment of the thermal transformations, the isolable solid intermediates and end products were characterized by IR, X-ray diffraction and Mossbauer investigations. A decomposition scheme is proposed.

The coordinations compounds (NH4)[Fe(C4H4O5)(OH)2]·0.5H2O, [Ni(C4H4O5)]·3H2O and [Zn(C4H4O5)]·5H2O were synthesized by a precipitation method and characterized by chemical analysis, spectral (IR, UV-VIS) and magnetical investigations. In the range 50-600°C stepped thermal decompositions occur with formation of anhydrous malates, malonates, oxoacetates (iron and nickel compounds) and hydroxocarbonate (Zn compound) as intermediates observed by FT-IR spectroscopy. α-Fe2O3, NiO and ZnO constitute the final decomposition products.

The authors present the results concerning the synthesis and the characterisation of some coordination compounds with malic acid as ligand: Co(C 4 H 4 O 5 )·2H 2 O, [Fe 2 (C 4 H 4 O 5 )(OH) 4 ]·4H 2 O and [Fe 2 Co(C 4 H 4 O 5 ) 2 (OH) 4 ]·6H 2 O. The heterometallic compound is a precursor of Co-ferrite. The values of the non-isothermal kinetic parameters for the dehydration reactions were determined. These values obtained by three integrals methods are in a satisfactory agreement.

Oxalates containing various 3d transitional elements and positive NH 4 or negative OH groups were newly synthesized. Each above-mentioned component has directly influenced the structure, the electronic or interaction properties, while some unexpected behaviors were revealed by various magnetic and Mssbauer measurements. The main magnetic parameters, the long-range anti-ferromagnetic couplings observed at very low temperature and, particularly the uncompensated moment are discussed in detail. The induced lower spin states for bivalent ions and especially the anti-parallel arrangement of the spins belonging to trivalent and bivalent iron inside the molecule are also emphasized. © 2010 Elsevier B.V. All rights reserved., The financial support of CNCSIS-UEFISCSU via contract 235/2007 of ‘‘IDEI’’ Romanian National Program and, respectively, MINCYT Spain projectMAT08/1077 are acknowledged, firstly and deeply.

The thermal behaviour of four coordination compounds (NH4)6[Y3Fe5(C4O5H4)6(C4O5H3)6]·12H2O, (NH4)6[Y3Fe5(C6O7H10)6(C6O7H9)6]·8H2O, (NH4)6[Er3Fe5(C4O5H4)6(C4O5H3)6]·10H2O and (NH4)6[Er3Fe5(C4O6H4)6(C4O6H3)6]·22H2O has been studied to evaluate their suitability for garnet synthesis. The thermal decomposition and the phase composition of the resulted decomposition compounds are influenced by the nature of metallic cations (yttrium-iron or erbium-iron) and ligand anions (malate or gluconate).

3 figures, 1 table., Two new hetero tri-nuclear oxalates (NH4)8[Fe2Co(C2O4)8]·6H2O and [Fe2Co(C2O4)2(OH)4]·2H2O have been synthesized. The compound presented opposite behaviour in ac-susceptibility measurements, different frustration level and spin–orbit coupling in magnetization ones. The Mössbauer approach pointed to local interactions governed by metal-oxalate strongly coupled unit. The data were interpreted in terms of role of positive (NH4) or negative (OH) bridging ligands on general magnetic properties.