ABSTRACT
Results of the neutron powder diffraction measurements carried out for R5Pt2In4 (R = Tb-Tm) are reported. The compounds crystallize in an orthorhombic crystal structure of the Lu5Ni2In4-type with the rare earth atoms occupying three different sublattices. Neutron diffraction data reveal that at low temperatures the rare earth magnetic moments order below the critical temperature equal to 105, 93, 28, 12 and 3.8â K for R = Tb, Dy, Ho, Er and Tm, respectively. With decreasing temperature the rare earth magnetic moments at the 2a and 4g2 sites order first, while the moments at the 4g1 site order at lower temperatures. Ferrimagnetic order along the c axis, described by the propagation vector k1 = [0,â 0,â 0], develops in Tb5Pt2In4 below the Curie temperature (TC = 105â K). At lower temperatures, an antiferromagnetic component in the ab plane appears. The component is incommensurate with the crystal structure (k2 = [0, 0.66, ½]), but it turns into a commensurate one (k3 = [0, 0, ½]) with decreasing temperature. Antiferromagnetic order along the c axis, described by k4 = [½, 0, 0], is found in Dy5Pt2In4 below the Néel temperature (TN = 93â K). The k4-related component disappears below 80â K and the magnetic structure transforms into a ferro/ferrimagnetic one described by k1 = [0,â 0,â 0]. Further decrease in temperature leads to the appearance of an incommensurate antiferromagnetic component within the ab plane below 10â K (k2 = [0, 0.45, ½]), which finally turns into a commensurate one (k5 = [0, ½, ½]). In Ho5Pt2In4, a sine-modulated magnetic structure with moments parallel to the c axis (k6 = [â ,0,0]) is observed below 28â K. With a decrease in temperature, new components, related to k1 = [0,â 0,â 0] (bc plane) and k4 = [½, 0, 0] (c axis), appear. The coexistence of two orderings - in the ab plane (k1 = [0,â 0,â 0]) and a modulated one with moments along the b axis (k7 = [kx,â 0,â 0]) - is found in Er5Pt2In4 below 12â K. Decreasing temperature leads to the order-order transformation of the k1-related component to another one with magnetic moments still constrained to the ab plane and preserved value of the propagation vector (i.e. k1 = [0,â 0,â 0]). Tm5Pt2In4 orders antiferromagnetically below TN = 3.8â K. Thulium magnetic moments lie in the ab plane, while the magnetic structure is described by k5 = [0, ½ , ½]. The direction of magnetic moments depends on the rare earth element involved and indicates an influence of single ion anisotropy resulting from interaction with the crystalline electric field.
ABSTRACT
Crystal and magnetic structures of R2Ni2In (R = Tb and Ho) have been studied using powder neutron diffraction at low temperatures. The compounds crystallize as orthorhombic crystal structures of the Mn2AlB2 type. At low temperatures, the magnetic moments localized solely on the rare earth atoms form antiferromagnetic structures. The Tb magnetic moments, equal to 8.8â (4)â µB and parallel to the c axis, form a collinear magnetic structure described by the propagation vector k = [½ , ½ , ½]. This magnetic structure is stable up to the Néel temperature TN = 40â K. For Ho2Ni2In a complex, temperature-dependent magnetic structure is detected. In the temperature range 6.1-8.6â K, an incommensurate sinusoidal magnetic structure, described by the propagation vector k1 = [0.24,â 1,â 0.52] is observed, while in the temperature interval 2.2-2.5â K a square-modulated magnetic structure, related to k2 = [0.17,{{5} \over {6}},{{1} \over {2}}] (the component along the a axis slightly differs from the commensurate value) and its third harmonics 3k2 = [0.50,{{5} \over {2}},{{3} \over {2}}] is found. At 3.1-3.7â K as well as below 2â K, a coexistence of both detected magnetic structures is observed. The Ho magnetic moments remain parallel to the c axis in both the sine- and square-modulated magnetic structures. The low-temperature heat capacity data confirm a first-order transition near 3â K.
ABSTRACT
Complementary methods are applied to investigate the phase transitions and crystallization kinetics of the liquid crystalline compound denoted as 3F5FPhH6. Two crystal phases are confirmed, and one of them is the conformationally disordered (CONDIS) phase. Complexity of the melt crystallization process is revealed by the analysis with Friedman's isoconversional method. The melt crystallization of 3F5FPhH6 shows different mechanisms depending on temperature, which is explained by the relation between the thermodynamic driving force and the thermal energy of translational degrees of freedom. The studied compound crystallizes even during fast cooling (30 K/min), unlike similar compounds with different fluorosubstitutions of the benzene ring, which form the smectic glass for moderate cooling rates. The tendency to vitrification of the smectic phase decreases apparently with the decreasing stability width of the SmCA* phase and the increasing relaxation time of the collective relaxation process in this phase, at least for homologues differing from 3F5FPhH6 only by the type of fluorosubstitution.
ABSTRACT
The synthesis of molecular materials with magnetic properties, in particular ferromagnetic properties, has been the subject of interest in coordination chemistry for decades. In the last three decades, research has accelerated, as it has emerged that creating bridging systems based on cyanido ligands is a good and relatively simple way to create complex polymer structures exhibiting magnetic properties. Based on many years of personal experience in the field of the synthesis of polycyanido systems, supported by comprehensive structural analysis, a simple method of transforming cyanido complexes into soft ferromagnetic materials with a Curie temperature (TC) higher than the thermal decomposition temperature, usually above 150 °C has been developed. Two soft ferromagnetic materials based on zinc and cadmium hexacyanido salts in the system with [W(CN)6(bpy)]2-/- anions are presented. The crystal structures (X-ray single crystal as well as XRD) of the precursors and the properties of the ferromagnetic materials are discussed. Most importantly, a patented method of synthesizing this type of material, based on which we obtain more than 80 soft, high-temperature ferromagnetic compounds, which proves the wide spectrum of this method, is also presented.
ABSTRACT
Magnetic molecules known as molecular nanomagnets (MNMs) may be the key to ultra-high density data storage. Thus, novel strategies on how to design MNMs are desirable. Here, inspired by the hexagonal structure of the hardest intermetallic magnet SmCo5, we have synthesized a nanomagnetic molecule where the central lanthanide (Ln) ErIII is coordinated solely by three transition metal ions (TM) in a perfectly trigonal planar fashion. This intermetallic molecule [ErIII(ReICp2)3] (ErRe3) starts a family of molecular nanomagnets (MNM) with unsupported Ln-TM bonds and paves the way towards molecular intermetallics with strong direct magnetic exchange interactions-a promising route towards high-performance single-molecule magnets.
ABSTRACT
The magnetic structure in Er3Cu4Sn4 has been determined using high-resolution powder neutron diffraction, supported by symmetry analysis. At low temperatures, Er3Cu4Sn4 assumes a crystal structure of the Tm3Cu4Sn4 type (in the monoclinic space group C2/m). The Er atoms occupy two distinct Wyckoff sites: 2c and 4i. It has been found that the Er magnetic moments on the 2c site form a commensurate antiferromagnetic structure (k1 = [0, 0, ½]) below 6â K. The magnetic moments reach 8.91â (8)â µB at 1.4â K and are parallel to the b axis. The Er magnetic moments on the 4i site order below 2â K and form an incommensurate antiferromagnetic sine-modulated structure (k2 = [1, 0.4667â (1), ½]), with magnetic moments lying in the ac plane and perpendicular to the a axis. The amplitude of modulation equals 8.7â (1)â µB at 1.4â K.
ABSTRACT
Propeller-like lanthanide complexes with suitable chiral ligand scaffolds are highly desired as they combine chirality with possible magnetic bistability. However, the library of relevant chiral lanthanide-based molecules is quite limited. Herein we present the preparation, structures, magnetic behavior as well as EPR studies of a series of propeller-shaped lanthanide Single Ion Magnets (SIMs). Coordination of the smallest helicene-type molecule 1,10-phenanthroline-N,N'-dioxide (phendo) to LnIII ions results in the formation of homoleptic complexes [LnIII(phendo)4](NO3)3·xMeOH (Ln = Gd, Er, Yb) Gd, Er and Yb, where four phendos encircle the metal center equatorially in a four-bladed propeller fashion. The magnetization dynamics in these systems is studied by magnetic measurements and EPR spectroscopy for non-diluted as well as solid state dilutions of Er and Yb in a diamagnetic [YIII(phendo)4](NO3)3·xMeOH (Y) matrix. Careful analysis of the slow magnetic relaxation in the diluted samples can be described by a combination of Raman and Orbach relaxation mechanisms. The most important finding concerns the identical power law τ≈T-3 describing the anomalous Raman relaxation for all three reported compounds diluted in the Y matrix. This identical power law strongly suggests that the exponent of the Raman relaxation process in the series of solid-state diluted isostructural compounds is practically independent of the metal ion (as long as the molar mass changes are negligible) and highlights a possible experimental strategy towards reliable Raman relaxation determination.
ABSTRACT
Crystal engineering of magnetic relaxation in supramolecular networks based on almost isotropic cyanido-bridged {Mn9[W(CN)8]6L8(solv)8} clusters decorated by bulky 4,4'-di-tert-butyl-2,2'-bipyridine (But2bpy) and 4,7-diphenyl-1,10-phenanthroline (Ph2phen) ligands is presented. The three new compounds {MnII9[WV(CN)8]6(But2bpy)8(MeOH)8}·Pri2O·13MeOH (1), {MnII9[WV(CN)8]6(But2bpy)8(MeOH)6(H2O)2}·4Pri2O·2H2O (1a), and {MnII9[WV(CN)8]6(Ph2phen)8(MeOH)8}·29MeOH·6H2O (2) were characterized structurally and magnetically. Compound 1 exhibits unequivocal domination of repulsive intercluster contacts operating between the side But groups leading to intercluster distances exceeding 10 Å in all three dimensions. Compound 1a reveals a 1-dimensional (1D) supramolecular chain structure with very close intercluster distances of 6.7 Å realized through the direct W-CNHO-Mn hydrogen bonds along the chain, further isolated by the above repulsive ButBut synthons. Compound 2 shows significant separation in all three directions with the intercluster distances close to 10, 12 and 13.5 Å. However, in contrast to 1, these separations are accompanied by indirect hydrogen bond arrays and local π-π interactions of potential to assist in the transfer of weak magnetic interactions. The dc magnetic data show the signature of S = 39/2 in the ground state, which is typical in this group of compounds. The high-spin clusters are accompanied by different intercluster interactions, illustrated by the effective zJ' values of +0.010 cm-1 (1), +0.008 cm-1 (1a) and +0.001 cm-1 (2). The low temperature ac susceptibility measurements revealed a temperature- and field-dependent magnetic relaxation time for all 1, 1a and 2 compounds (τ1, τ1a-fast, and τ2-fast in the range 10-3-10-4 s). In contrast and only in the case of 1a and 2, an additional temperature independent slow process was detected (τ1a-slow and τ2-slow located between 0.1 s and 1 s). The magnetic relaxations were correlated with the obtained supramolecular networks, indicating the significant role of dipolar fields, weak non-covalent interactions, hydrogen bonds and π-π interactions.
ABSTRACT
Cyanide-bridged {MnII9[WV(CN)8]6} clusters with the ground state spin SSG = 39/2 were connected by a 4,4'-dipyridyl disulfide (4,4'-dpds) linker into 2-D double-connected coordination layers of the I0O2 type, {MnII9(4,4'-dpds)4(MeOH)16[WV(CN)8]6}·12MeOH (1). The intercluster contacts are controlled by the bridging MnII-(4,4'-dpds)-MnII coordination modes and direct hydrogen bonds W-CN···HOMeOH-Mn in three crystallographic directions, with the vertex-to-vertex contact unprecedented in {Mn9W6}-based networks dominating over the typical edge-to-edge contacts. The resulting 3D supramolecular network of high-spin clusters was subjected to a thorough magnetic characterization in context of two critical issues. First, the intracluster WV-CN-MnII exchange coupling and intercluster interaction were successfully modeled through the combination of dc measurements, Quantum Monte Carlo simulations, and mean-field calculations, yielding a reasonable Jap = -8.0 cm-1, Jeq = -19.2 cm-1 (related to apical and equatorial CN bridges, depending on the angle they form with the S4 axis of dodecahedral [W(CN)8]3- units, respectively), and zJ' = 0.014 cm-1 with the average gW = gMn = 2.0 parameter set. Continuing this approach, we simulated the magnetocaloric effect (MCE) and compared it to the experimental result of ΔSmax = 7.31 J kg-1 K-1 for fields >5.0 T. Second, two relaxation processes were induced by a relatively weak magnetic field, Hdc = 500 Oe, at an Hac field frequency range of up to 10 kHz, which are related to dipole-dipole interactions between high-spin (39/2) moieties. The observed relaxation times significantly differ from each other, the slow process with τslow at tenths of a second being temperature independent and the faster process being 3-5 orders of magnitude faster with the effective energy barrier Δeff = 17.6 K. These dynamic properties are surprising, since the compound is made up of isotropic high-spin molecules.
ABSTRACT
The aim of the present study was an evaluation of the influence of the addition of different sewage sludge doses on the uptake of polycyclic aromatic hydrocarbons from fertilized soil. Sewage sludge was introduced into the soil in the following doses: 30, 75, 150, 300, and 600 Mg/ha. The content of polycyclic aromatic hydrocarbons (PAH) was determined by means of HPLC-UV method. The addition of increasing doses of sludge into the soil resulted in a gradual increase in the amount of the polycyclic aromatic hydrocarbons contained therein. During the period of the study, continuous changes in the content of all the compounds studied were found in all the experimental variants. Finally, on the last day of the study, the highest degree of degradation (73%) of 16 PAHs' sum (US EPA) was noted for sludge doses of 30 and 300 Mg/ha. In the case of individual PAHs, the change in their content differed and clearly depended on the sewage sludge dose. The introduction of sewage sludge into the soil influenced the increase of the sum of 16 PAHs in the plants grown in this soil. The influence mentioned above depended on the sewage sludge dose and the plant species grown, as well as the PAH content in the soil. The evaluation of individual PAHs in plants showed an increase in their content with the increase of the amount of sewage sludge. A statistically significant increase in their content was most often observed for sewage sludge doses above 150 Mg/ha. Moreover, it was found that fertilization of the soil with sewage sludge resulted in pollution of the plants with PAHs of high molecular weight.
Subject(s)
Crops, Agricultural/metabolism , Fertilizers , Polycyclic Aromatic Hydrocarbons/metabolism , Sewage , Soil Pollutants/metabolism , Brassica rapa/metabolism , Edible Grain/metabolism , Food Contamination , Polycyclic Aromatic Hydrocarbons/analysis , Soil , Soil Pollutants/analysis , Solanum tuberosum/metabolismABSTRACT
The present study evaluates the content of the mild-solvent extracted fraction of the polycyclic aromatic hydrocarbons. Ten compounds from the US EPA list (phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chryzene, benzo[b]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene oraz indeno[1,2,3-cd]pyrene) were chosen. The compounds were extracted with n-butanol from 11 sewage sludges that differed both in the total PAH content and in their physicochemical properties. On the basis of the results obtained, the influence of the properties of the PAH and some properties of selected sludge on the content of the mild-solvent extracted fractions of these compounds was determined. The content of the fraction extracted with n-butanol within the total of 10 PAHs ranged from 12.5 to 83.2% (mean 40.1%) depending on the type of sludge. Similarly, as in the case of the total of the 10 PAHs, significant differences in the content of PAHs extracted with n-butanol were also noted for the individual compounds studied. In the case of most individual PAHs their mean share did not differ statistically in relation to the PAH type and was close to 40%. An evaluation of the relation between the share of the fraction extracted with n-butanol from the different types of sludge and the properties of the PAHs showed that statistically, there existed significant (P < 0.05) correlations between log Koc (in the case of one sewage sludge) and between the nitrogen content, the ratio of C/N, cations Mg2+ and K+ (in the case of a few PAHs). A clear and significant relation was found between the content of and the share of the fraction of n-butanol extracted and the PAH fraction present in the sewage sludge pore water (determined on the basis of an equilibrium partition model).
Subject(s)
Environmental Pollutants/analysis , Polycyclic Aromatic Hydrocarbons/analysis , Sewage/chemistry , Biological Availability , Polycyclic Aromatic Hydrocarbons/chemistry , Waste Disposal, FluidABSTRACT
The study presents the efficiency of sewage sludge sample clean-up with the application of SPE columns with various types of adsorbents. Six columns were tested: C8-octyl, C18 PolarPlus, C18-octadecyl, silicagel (SG), phenyl, cyano. The highest efficiency of recovery was observed for C18-octadecyl. Then, using C18, the method was optimised by changing the following parameters: eluent type and volume, column drying and effect of washing of cartridge.
Subject(s)
Polycyclic Aromatic Hydrocarbons/analysis , Refuse Disposal/methods , Sewage/chemistry , Soil Pollutants/analysis , Osmolar ConcentrationABSTRACT
Impacts of flooding on the soil environment with regard to soil pollution with polycyclic aromatic hydrocarbons and s-triazine (cyanazine, simazine, atriazine, propazine, prometryn) herbicides have been evaluated. No clear differences in the sum of the PAHs content were observed in the present studies. Only changes in the levels of individual PAHs were noted. In soils covered with flooding both at a depth of 0-20 and 20-40 high molecular weight PAHs were predominant (especially mutagenic and carcinogenic 5-rings PAHs) whereas in non-flooded areas, 2- and 3-rings PAHs constituted over 80%. In the case of s-triazine herbicides, no influence of flooding on the changes in their content in agriculturally used soils was noted. On the other hand, clearly lower levels of cyanazine, simazine and atriazine were not in the flooded forest soil as compared to the non-flooded forest soil.
Subject(s)
Herbicides/chemistry , Polycyclic Aromatic Hydrocarbons/chemistry , Soil Pollutants , Triazines , Water Pollutants, Chemical , Biodegradation, Environmental , Disasters , HumansABSTRACT
In the present work the influence of soil fertilization with sewage sludge on the changes in the content of polycyclic aromatic hydrocarbons (PAH) in this soil was studied during a one-year field experiment. The experiment consisted of six plots to which sewage sludge was introduced at doses of 30 (1%), 75 (2.5%), 150 (5%), 300 (10%) and 600 ton/ha (20%) as calculated for dry mass. The PAH content at a depth of 0-20 and 20-40 cm was determined. With time, an increase in the PAH content in the lower soil layer (20-40 cm) and a gradual decrease of the PAH content in the 0-20 cm layer was observed. In most cases, a decrease by half in the PAH content in the soil fertilised with sewage sludge was observed.