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Large uniaxial magnetic anisotropy, expressed by a negative value of the axial zero-field splitting parameter D, has been achieved in a series of trigonal prismatic Co(II) complexes with the general formula [Co(L)X]Y, where L = 1,5,13,17,22-pentaazatricyclo[15.2.2.17,11]docosa-7,9,11(22)-triene, X = Cl−(1a,b), Br−(2), N3−(3), NCO−(4), NCS−(5), NCSe−(6), and Y = Cl−(1), Br−(2), NCS−(4), NCSe−(5), ClO4−(3,6). Complexes 1–6 are six-coordinate with the distorted trigonal prismatic geometry imparted by the pentadentate pyridine-/piperazine-based macrocyclic ligand L and by one monovalent coligand X−. Based on magnetic studies, all complexes 1–6 exhibit strong magnetic anisotropy with negative D-values ranging from about −20 to −41 cm−1. This variation in D (i.e. the increase of magnetic anisotropy) parallels the trend obtained by theoretical calculations and the lesser distortion of the coordination sphere with respect to the trigonal prismatic reference geometry. AC magnetic susceptibility investigations revealed field-induced single-molecule magnet behaviour for all complexes except Cl− derivative 1. The series investigated represents a rare example of Co(II) complexes with a robust trigonal prismatic geometry. [ABSTRACT FROM AUTHOR]

A new 15-membered pyridine-based macrocyclic ligand containing one acetate pendant arm (N-carboxymethyl-3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1(18),14,16-triene, L1) was synthesized and its Mn(II) complex MnL1 was investigated in the context of MRI contrast agent development. The X-ray molecular structure of MnL1 confirmed a coordination number of seven with an axially compressed pentagonal bipyramidal geometry and one coordination site available for an inner-sphere water molecule. The protonation constants of L1 and the stability constants of Mn(II), Zn(II), Cu(II) and Ca(II) complexes were determined by potentiometry, and revealed higher thermodynamic stabilities in comparison with complexes of 15-pyN3O2, the parent macrocycle without an acetate pendant arm. The MnL1 complex is fully formed at physiological pH 7.4, but it shows fast dissociation kinetics, as followed by relaxometry in the presence of an excess of Zn(II). The short dissociation half-life estimated for physiological pH (ca. 3 minutes) is related to fast spontaneous dissociation of the non-protonated complex. At lower pH values, the proton-assisted dissociation pathway becomes important, while the Zn(II) concentration has no effect on the dissociation rate. 17O NMR and 1H NMRD data indicated the presence of one inner-sphere water molecule with a rather slow exchange (k 298ex = 4.5 × 106 s−1) and provided information about other microscopic parameters governing relaxation. The relaxivity (r1 = 2.45 mM−1 s−1 at 20 MHz, 25 °C) corresponds to typical values for monohydrated Mn(II) chelates. Overall, the acetate pendant arm in L1 has a beneficial effect with respect to 15-pyN3O2 in increasing the thermodynamic stability and kinetic inertness of its Mn(II) complex, but leads to a reduced number of inner-sphere water molecules and thus lower relaxivity. [ABSTRACT FROM AUTHOR]

A heptadentate macrocyclic ligand, H2L (3,12,18‐triaza‐6,9‐dioxabicyclo[12.3.1]octadeca‐1,14,16‐triene‐3,12‐diacetic acid) with two acetate pendant arms, and its complexes [FeIIIL]ClO4 (1), [FeIIL]·H2O (2), [CoIIL]·H2O (3), and [NiIIL]·H2O (4) were synthesized. The complexes possess an axially compressed pentagonal bipyramidal geometry with the coordination numbers of 7 for 2 and 3, and 6 + 1 for 4. The magnetic susceptibility measurements revealed magnetic anisotropy for compounds 1–4 expressed by axial zero‐field splitting (ZFS) parameters (D = –1.3 cm–1 for 1, –9.6 cm–1 for 2, 29.1 cm–1 for 3, and –8.5 cm–1 for 4), with a rhombic ZFS (E/D = 0, 0.006, 0, and 0.193, respectively). Field‐induced slow relaxation of magnetization was observed for the CoII complex 3 only. The structural and magnetic features of 1–4 were compared with those of similar complexes containing ligand with two 2‐pyridylmethyl pendant arms. Magnetic features of the complexes were also evaluated using theoretical calculations (DFT, CASSCF/NEVPT2). The Fe(II/III), CoII and NiII complexes with a heptadentate 15‐membered pyridine‐based macrocyclic ligand (H2L) were prepared and thoroughly characterized. The complexes possess an axially compressed pentagonal bipyramidal geometry and exhibit a field‐induced SMM behaviour, with clearly defined maxima on the curves showing frequency dependence of the out‐of‐phase component of magnetic susceptibility for the CoII complex 3 only. [ABSTRACT FROM AUTHOR]

Three mononuclear lanthanide complexes of a 2-pyridylmethyl pendant-armed 15-membered ligand {(3,12-bis(2-pyridylmethyl)-3,12,18-triaza-6,9-dioxabicyclo-[12.3.1]octadeca-1,14,16-triene); L} with general formula [Ln(L)(H2O)(NO3)](NO3)2 (Ln = Tb (1), Dy (2), and Er (3)) are reported. Based on X-ray diffraction analysis of 1 and 2, the central lanthanide atoms are nine-coordinated with the N5O4 donor set originating from the ligand L and one coordinated water molecule and one monodentate-bonded nitrato ligand. The coordination geometry of the [LnN5O4] cores can be described as a muffin-like shape. Magnetic measurements revealed that all three compounds show field-induced single-molecule magnet behaviour, with estimated energy barriers U≈ 44–82 K. The experimental study was complemented by CASSCF calculations showing a trend of an increasing first excited energy gap (Tb → Dy → Er) within the muffin-like geometry with the lowest magnetization tunnelling probability for the DyIII complex 2. [ABSTRACT FROM AUTHOR]

This paper presents solid state synthesis and characterization of tetra-oxy iron(iv) and iron(v) species in their salt forms (Na4FeO4–FeIV and K3FeO4–FeV). Stability of the synthesized salts, commonly called ferrates, in water was determined by applying the 57Fe Mössbauer spectroscopy technique. Within 2 s in water, FeIV converted into FeIII while FeV transformed into FeVI and FeIII at pH = 8.2. Comparatively, FeVI (bought as K2FeO4) remained stable in aqueous solution during the short time period. The oxidative removal efficiency of the high-valent iron species was then tested against five environmentally important estrogenic hormones (estron (E1), 17-β-estradiol (E2), estriol (E3), 17-α-ethinylestradiol (EE2), and diethylstibestrol (DES)) in effluent water of a wastewater treatment plant. Three dosages of iron species (1, 10, and 100 mg L−1) were applied to the effluent water. An increase in the concentration of dosages enhanced the removal of estrogens. Both FeV and FeVI were effective in degrading estrogens, but FeIV showed limited oxidation capacity to transform estrogens. The oxidized products of the estrogens were analyzed using Raman spectroscopy and high-performance liquid chromatography-mass spectrometry (HPLC-MS) techniques. Results demonstrated the transformation of estrogens into low molecular weight oxygenated compounds such as quinone-like and opened-aromatic ring species. A detailed study on E1 by using excess FeVI showed the mineralization of the parent compound. The results demonstrate great potential of high-valent iron species in the degradation of endocrine disruptor chemicals like estrogens with several superior aspects including fast reactions, complete degradation and/or formation of benign organic species, and environmentally-acceptable iron oxide by-products. [ABSTRACT FROM AUTHOR]

A novel positively charged surfactant N-dodecyl- N, N-dimethyl-(1,2-propandiol) ammonium chloride was used for the dynamic coating of the inner wall of a silica capillary. This paper covers the evaluation of dynamic coating and study of the influence of the analysis conditions for the magnitude and direction of electroosmotic flow as well as for the effective and selective separation of chosen proteins (ribonuclease A, cytochrome c, lysozyme, and myoglobin). The concentration of 0.1 mM of N-dodecyl- N, N-dimethyl-(1,2-propandiol) ammonium chloride enabled the reversal of the electro-osmotic flow, however, to separate basic as well as neutral proteins the higher concentration of the studied surfactant was necessary. The final conditions for the separation of studied proteins were set at 100 mM sodium acetate pH 5.5 with 10.0 mM of the studied surfactant. The results were also compared with those of two commercially available cationic surfactants, cetyltrimethylammonium bromide and dodecyltrimethylammonium bromide. Additionally, the developed method for protein separation was applied for the determination of lysozyme in a cheese sample. The limits of detection and quantification of lysozyme were 0.9 and 3.0 mg/L, respectively. The mean concentration of lysozyme found in the cheese sample was 167.3 ± 10.3 mg/kg. [ABSTRACT FROM AUTHOR]

Background: The Prussian blue analogues represent well-known and extensively studied group of coordination species which has many remarkable applications due to their ion-exchange, electron transfer or magnetic properties. Among them, Co-Fe Prussian blue analogues have been extensively studied due to the photoinduced magnetization. Surprisingly, their suitability as precursors for solid-state synthesis of magnetic nanoparticles is almost unexplored. In this paper, the mechanism of thermal decomposition of [Co(en)3][Fe(CN) 6] ⋅ 2H2O (1a) is elucidated, including the topotactic dehydration, valence and spins exchange mechanisms suggestion and the formation of a mixture of CoFe2O4-Co3O4 (3:1) as final products of thermal degradation. Results: The course of thermal decomposition of 1a in air atmosphere up to 600°C was monitored by TG/DSC techniques, 57Fe Mössbauer and IR spectroscopy. As first, the topotactic dehydration of 1a to the hemihydrate [Co (en) 3][Fe(CN) 6] ⋅ 1/2H2O(1b) occurred with preserving the single-crystal character as was confirmed by the X-ray diffraction analysis. The consequent thermal decomposition proceeded in further four stages including intermediates varying in valence and spin states of both transition metal ions in their structures, i.e. [FeII (en) 2 (µ-NC) CoIII (CN) 4], FeIII (NH2CH2CH3)2 (µ-NC) 2Co (CN) 3] and Fe [CoII (CN) 5], which were suggested mainly from Fe Mössbauer, IR spectral and elemental analyses data. Thermal decomposition was completed at 400°C when superparamagnetic phases of CoFe2O4 and Co3O4 in the molar ratio of 3:1 were formed. During further temperature increase (450 and 600°C), the ongoing crystallization process gave a new ferromagnetic phase attributed to the CoFe2O4-Co3O4 nanocomposite particles. Their formation was confirmed by XRD and TEM analyses. In-field (5 K / 5 T) Mössbauer spectrum revealed canting of Fe(III) spin in almost fully inverse spinel structure of CoFe2O4. Conclusions: It has been found that the thermal decomposition of [Co(en) 3][Fe(CN) 6] ⋅ 2H2O in air atmosphere is a gradual multiple process accompanied by the formation of intermediates with different composition, stereochemistry, oxidation as well as spin states of both the central transition metals. The decomposition is finished above 400°C and the ongoing heating to 600°C results in the formation of CoFe2O4-Co3O4 nanocomposite particles as the final decomposition product. [ABSTRACT FROM AUTHOR]