Leaching behavior of iron from simulated landfills with different operational modes

The aim of the present study was to investigate the leaching behavior of iron from simulated landfills with different operation modes, with an emphasis on the variation of iron in different oxidation state, ferrous Fe(II) and ferric Fe(III) percentage and the distribution of iron content in different landfill leachate fractions. The leaching behavior and accumulated amounts of iron leached out by leachate from conventional landfill (CL) and leachate recirculated landfill (RL) exhibited decidedly different trends except for the initial 28 days. In addition, the percentage of iron leached from CL and RL accounted 1.00% and 0.14% for the total amount in landfills, respectively. No correlations between iron and selected characteristics in leachate were found were observed in the two simulated landfills. Significant positive correlations between particulate bound iron and Fe(III) were found in the leachates from RL (R² = 0.748) and CL (R² = 0.833).     

Oxidation of thiocyanate by iron(V) in alkaline medium

The oxidation of thiocyanate by iron(V) (Fe(V)) was studied as a function of pH in alkaline solutions by a premix pulse radiolysis technique. The rates decrease with an increase in pH. The rate law for the oxidation of SCN⁻ by Fe(V) was obtained as −d[Fe(V)]/dt = k₁₀{[H⁺]²/([H⁺]² + K₂[H⁺] + K₂K₃)}[Fe(V)][SCN⁻], where k₁₀ = 5.72 ± 0.19 × 10⁶ M⁻¹ s⁻¹, pK₂ = 7.2, and pK₃ = 10.1. The reaction precedes via a two-electron oxidation, which converts Fe(V) to Fe(III). Thiocyanate reacts approximately 10³× faster with iron(V) than does with iron(VI).     

Functional model for intradiol-cleaving catechol 1,2-dioxygenase: Synthesis, structure, spectra, and catalytic activity of iron(III) complexes with substituted salicylaldimine ligands

A series of mononuclear iron(III) complexes with containing phenolate donor of substituted-salicylaldimine based ligands [Fe(L¹)(TCC)] · CH₃OH (1), [Fe(L²)(TCC)] · CH₃OH (2), [Fe(L³)(TCC)] (3), and [Fe(L⁴)(TCC)] (4) have been prepared and studied as functional models for catechol dioxygenases (H₂TCC = tetrachlorocatechol, or HL¹ = N′-(salicylaldimine)-N,N-diethyldiethylenetriamine, HL² = N′-(5-Br-salicylaldimine)-N,N-diethyldiethylenetriamine, HL³ = N′-(4,6-dimethoxy-salycyl-aldimine)-N,N-diethyl-diethylenetriamine, HL⁴ = N′-(4-methoxy-salicylaldimine)-N,N-diethyl-diethylenetriamine). They are structural models for inhibitors of enzyme-substrate adducts from the reactions of catechol 1,2-dioxygenases. Complexes 1-4 were characterized by spectroscopic methods and X-ray crystal structural analysis. The coordination sphere of Fe(III) atom of 1-4 is distorted octahedral with N₃O₃ donor set from the ligand and the substrate TCC occupying cis position, and Fe(III) is in high-spin (S = 5/2) electronic ground state. The in situ prepared iron(III) complexes without TCC, [Fe(L¹)Cl₂], [Fe(L²)Cl₂], [Fe(L³)Cl₂], and [Fe(L⁴)Cl₂] are reactive towards intradiol cleavage of the 3,5-di-tert-butylcatechol (H₂DBC) in the presence of O₂ or air. The reaction rate of catechol 1,2-dioxygenase depends on the redox potential and acidity of iron(III) ions in complexes as well as the substituent effect of the ligands. We have identified the reaction products and proposed the mechanism of the reactions of these iron(III) complexes with H₂DBC with O₂.     

Determination of uric acid in human urine and serum by capillary electrophoresis with chemiluminescence detection

A simple and sensitive method based on capillary electrophoresis (CE) with chemiluminescence (CL) detection has been developed for the determination of uric acid (UA). The sensitive detection was based on the enhancement effect of UA on the CL reaction between luminol and potassium ferricyanide (K₃[Fe(CN)₆]) in alkaline solution. A laboratory-built reaction flow cell and a photon counter were deployed for the CL detection. Experimental conditions for CL detection were studied in detail to achieve a maximum assay sensitivity. Optimal conditions were found to be 1.0 × 10⁻⁴ M luminol added to the CE running buffer and 1.0 × 10⁻⁴ M K₃[Fe(CN)₆] in 0.2 M NaOH solution introduced postcolumn. The proposed CE-CL assay showed good repeatability (relative standard deviation [RSD] = 3.5%, n = 11) and a detection limit of 3.5 × 10⁻⁷ M UA (signal/noise ratio [S/N] = 3). A linear calibration curve ranging from 6.0 × 10⁻⁷ to 3.0 × 10⁻⁵ M UA was obtained. The method was evaluated by quantifying UA in human urine and serum samples with satisfactory assay results.     

Design of novel iron compounds as potential therapeutic agents against tuberculosis

In the search for new therapeutic tools against tuberculosis two novel iron complexes, [Fe(L-H)₃], with 3-aminoquinoxaline-2-carbonitrile N¹,N⁴-dioxide derivatives (L) as ligands, were synthesized, characterized by a combination of techniques, and in vitro evaluated. Results were compared with those previously reported for two analogous iron complexes of other ligands of the same family of quinoxaline derivatives. In addition, the complexes were studied by cyclic voltammetry and EPR spectroscopy. Cyclic voltammograms of the iron compounds showed several cathodic processes which were attributed to the reduction of the metal center (Fe(III)/Fe(II)) and the coordinated ligand. EPR signals were characteristic of magnetically isolated high-spin Fe(III) in a rhombic environment and arise from transitions between m_S = ± 1/2 (g_eff ~ 9) or m_S = ± 3/2 (g_eff ~ 4.3) states. Mössbauer experiments showed hyperfine parameters that are typical of high-spin Fe(III) ions in a not too distorted environment. The novel complexes showed in vitro growth inhibitory activity on Mycobacterium tuberculosis H₃₇Rv (ATCC 27294), together with very low unspecific cytotoxicity on eukaryotic cells (cultured murine cell line J774). Both complexes showed higher inhibitory effects on M. tuberculosis than the “second-line” therapeutic drugs.     

Plant-derived phenolic compounds impair the remediation of acid mine drainage using treatment wetlands

The use of wetlands to remediate acid mine drainage has expanded rapidly since the realisation that acid coal mine drainage running into natural sphagnum wetlands undergoes an increase in pH and a precipitation of metals. However, our study suggests that the inclusion of plants in the acid mine drainage treatment system may be questionable, due to inefficiencies caused by exudation of dissolved organic carbon (DOC), and in particular its phenolic constituents. They complex with iron, causing increased solubility, the exact opposite of what is required to facilitate amelioration. The addition of minewater to planted wetland mesocosms initially caused a decline in Fe concentrations, typically from over 1100 to a low of 75 mg L⁻¹. However, it increased higher than 300 mg L⁻¹ after 15 days. The rise in iron occurred concurrently with DOC and phenolic increases; 15-69 and 5-15 mg L⁻¹, respectively, for Eriophorum angustifolium. Removal of DOC by precipitation with calcium lowered the DOC abundance, but without a simultaneous decrease in iron concentration. The concentration of one fraction of the DOC, phenolic compounds, did not decline, and we propose that the Fe was complexed with that phenolic DOC pool. The proposal was confirmed by enzymic depletion of the phenolic compounds using phenol oxidase. Our findings suggest that phenolic complexation represents a potent constraint on wetland-based bioremediation of iron in acid mine drainage.     

A three-stage experimental constructed wetland for treatment of domestic sewage: First 2 years of operation

Hybrid constructed wetland systems have recently been used to treat wastewaters where high demand for removal of ammonia is required. However, these systems have not been used too often for small on-site treatment systems. This is because in many countries ammonia is not limited in the discharge from small systems. Hybrid systems have a great potential to reduce both ammonia and nitrate concentrations at the same time. In our study we employed a three-stage constructed wetland system consisting of saturated vertical-flow (VF) bed (2.5 m², planted with Phragmites australis), free-drained VF bed (1.5 m², planted with P. australis) and horizontal-flow (HF) bed (6 m², planted with Phalaris arundinacea) in series. All wetlands were originally filled with crushed rock (4-8 mm). However, nitrification was achieved only after the crushed rock was replaced with sand (0-4 mm) in the free-drain wetland. Also, original size of crushed rock proved to be too vulnerable to clogging and therefore, in the first wetlands the upper 40 cm was replaced by coarser fraction of crushed rock (16-32 mm) before the second year of operation started. The system was fed with mechanically pretreated municipal wastewater and the total daily flow was divided into two batches 12 h apart. The evaluation of the results from the period 2007 to 2008 indicated that such a system has a great potential for oxidation of ammonia and reduction of nitrate. The ammonia was substantially reduced in the free-drained VF bed and nitrate was effectively reduced in the final HF bed. The inflow mean NH₄-N concentration of 29.9 mg/l was reduced to 6.5 mg/l with the average removal efficiency of 78.3%. At the same time the average nitrate-N concentration rose from 0.5 to only 2.7 mg/l at the outflow. Removal of BOD₅ and COD amounted to 94.5% and 84.4%, respectively, with respective average outflow concentrations of 10 and 50 mg/l. Phosphorus was removed efficiently despite the fact that the system was not aimed at P removal and therefore no special media were used. Phosphorus removal amounted in 2008 to 65.4%, but the average outflow concentration of 1.8 mg/l is still high. The results of the present study indicate very efficient performance of the hybrid constructed wetlands, but optimal loading parameters still need to be adjusted. The capital cost of the experimental system is comparable to the conventional on-site treatment plant but the operations and maintenance costs are about one third of the conventional plant.     

Typha latifolia and Cladium jamaicense litter decay in response to exogenous nutrient enrichment

The role of nutrient availability in the decay of Typha latifolia and Cladium jamaicense litter and associated microbial responses were studied under controlled experimental conditions. The experimental setup consisted of three 14 m² mesocosms: (i) an experimentally enriched (N&P) mesocosm containing organic soil, (ii) a mesocosm with organic soil but no external enrichment, and (iii) a mesocosm with no external nutrient inputs and a mineral soil, each equally divided into two areas predominated by T. latifolia and C. jamaicense. Air dried senesced material of each plant species from the three units were placed in litterbags and were introduced back into their respective communities on the soil and water interface. Litter from T. latifolia degraded significantly faster than that of C. jamaicense. The half life of T. latifolia litter averaged approximately 274 days, C. jamaicense litter half life was extrapolated to approximately 377 days. Nutrient enrichment significantly increased the decay rates of T. latifolia, the nutrient effect on C. jamaicense decomposition was less apparent. The microbial biomass carbon in T. latifolia and C. jamaicense litter increased significantly as the litter decomposed. No significant differences between the litter types or amongst mesocosms were found. The relative activities of the extracellular enzymes acid phosphatase and β-glucosidase were significantly (P < 0.001 and P = 0.0284, respectively) affected by litter type and mesocosm over time. Litter associated alkaline phosphatase activity was largest in the mineral mesocosm, followed by the organic control and then organic enriched irrespective of litter type, β-glucosidase activity showed an inverse effect, enriched organic > organic control > mineral. The litter CO₂ and CH₄ microbial production rates showed a significant litter type and mesocosm effect (P = 0.0003 and 0.001, respectively). T. latifolia litter had larger associated methanogenic and microbial respiration rates than C. jamaicense litter. Nutrient enrichment enhanced both forms of microbial metabolic activities (CO₂ and CH₄ production). The effect of nutrient enrichment was primarily evident in the initial (3–6 months) period of decay, extracellular enzyme activities and the litter associated microbial metabolic activities showed most response during this decay stage.     

Methane emissions from freshwater riverine wetlands

To better understand methane emissions from freshwater riverine wetlands, seasonal and spatial patterns of methane emissions were measured over a 1-year period from created freshwater marshes and a river division oxbow, and at a river-floodplain edge (riverside) in central Ohio, USA. Plots were distributed from inflow to outflow and from shallow transition edges to deep water zones in the marshes and oxbow. Median values of CH₄ emissions ranged from 0.33 to 85.7 mg-CH₄-C m⁻² h⁻¹, at the riverside sites and 0.02-20.5 mg CH₄-C m⁻² h⁻¹ in the created marshes. The naturally colonizing marsh had more methane emissions (p = 0.047) than did the planted marsh, probably due to a history of higher net primary productivity in the former. A significant dry period and lower productivity in the oxbow may explain its low range of methane emissions of −0.04 to 0.09 mg CH₄-C m⁻² h⁻¹. There were significantly higher rates of methane emissions in deep water zones compared to transition zones in the created marshes. Overall CH₄ emissions had significant relationships with organic carbon and soil temperature and appear to depend on the hydroperiod and vegetation development. Riparian wetlands can be designed to minimize greenhouse gas emissions while providing other ecosystem services.     

Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

The effect of bicarbonate ion (HCO₃⁻) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10 mM HCO₃⁻ (−Fe+Bic and −Fe, respectively). After 21 d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO₃⁻ (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO₃⁻ upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H⁺-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15 d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO₃⁻ prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.     

Crystal structure and magnetic behaviour of a five-coordinate iron(III) complex of pyridoxal-4-methylthiosemicarbazone

The crystal structure and magnetic properties of a penta-coordinate iron(III) complex of pyridoxal-4-methylthiosemicarbazone, [Fe(H₂mthpy)Cl₂](CH₃C₆H₄SO₃), are reported. The synthesised ligand and the metal complex were characterised by spectroscopic methods (¹H NMR, IR, and mass spectroscopy), elemental analysis, and single crystal X-ray diffraction. The complex crystallises as dark brown microcrystals. The crystal data determined at 100(1) K revealed a triclinic system, space group (Z = 2). The ONSCl₂ geometry around the iron(III) atom is intermediate between trigonal bipyramidal and square pyramidal (τ = 0.40). The temperature dependence of the magnetic susceptibility (5-300 K) is consistent with a high spin Fe(III) ion (S = 5/2) exhibiting zero-field splitting. Interpretation of these data yielded: D = 0.34(1) cm⁻¹ and g = 2.078(3).     

Synthesis, structure, magnetic and electrochemical properties of an oxydiacetate iron(II) complex

Compound [{Fe(oda)(H₂O)₂} · H₂O]_n (1) [oda=O(CH₂COO)₂ ²⁻] has been obtained by reaction of FeCl₂ · 4H₂O with a 1:1 mixture of O(CH₂COOH)₂ and Na₂CO₃ in water. The structure is polymeric with concatenated {Fe(oda)(H₂O)₂} units extended in one direction. Each iron centre is six-coordinated by the tridentate planar oda ligand, two mutually trans water molecules and one oda oxygen atom from an adjacent {Fe(oda)(H₂O)₂} unit. Complex 1 is isomorphous with cobalt and zinc analogues. Magnetic susceptibility measurements down to 2 K showed high-spin non-correlated Fe(II) ions with a typical Curie-Weiss behaviour. Differential-pulse voltammetry establishes a value of 0.488 V versus NHE for the Fe(III)/Fe(II) redox potential of this iron complex in 0.25 mol dm⁻³ NaNO₃.     

New assembled Fe-trans-1,2-bis(4-pyridyl)ethylene-NCS(NCSe) complexes - hydrogen bonded and π-π interacted structure and grid structure enclathrating ligand

Reaction of FeSO₄ · 7H₂O with trans-1,2-bis(4-pyridyl)ethylene (tvp) and NaNCS in the mixed solvent of water and ethanol gave rise to the formation of different coordination polymers. One (Fe(tvp)₂(NCS)₂(H₂O)₂) is hydrogen bonded and π-π interacted structure, while the other ([Fe(tvp)₂(NCS)₂][0.5(tvp · 2EtOH)]) is 2D grid structure, which enclathrates tvp · 2EtOH. This enclathrated tvp · 2EtOH interacts with the two 2D grid sheets to form 3D structure. The same reaction was carried out with KNCSe instead of NaNCS (Fe(tvp)₂(NCSe)₂(H₂O)₂). ⁵⁷Fe Mössbauer spectra revealed that all the present assembled complexes are in the Fe^II high-spin state. The dissociation behavior of enclathrated molecule and ligand was investigated by TG, and the resultant electronic state of iron atom was studied by ⁵⁷Fe Mössbauer spectroscopy.     

Interactions of free copper (II) ions alone or in complex with iron (III) ions with erythrocytes of marine fish Dicentrarchus labrax

As a consequence of human activity, various toxicants - especially metal ions - enter aquatic ecosystems and many fish are exposed to considerable levels. As the free ion and in some complexes, there is no doubt that copper promotes damage to cellular molecules and structures through radical formation. Therefore, we have investigated the influence of copper uptake by the red blood of the sea bass (Dicentrarchus labrax), and its oxidative action and effects on cells in the presence of complexed and uncomplexed Fe³⁺ ions.Erythrocytes were exposed to various concentrations of CuSO₄, Fe(NO₃)₃, and K₃Fe(CN)₆ for up to 5 h, and the effects of copper ions alone and in the combination with iron determined. The results show that inside the cells cupric ion interacts with hemoglobin, causing methemoglobin formation by direct electron transfer from heme Fe²⁺ to Cu²⁺. Potassium ferricyanide as a source of complexed iron decreases Met-Hb formation induced by copper ions unlike Fe(NO₃)₃. We also found that incubation of fish erythrocytes with copper increased hemolysis of cells. But complexed and uncomplexed iron protected the effect of copper. CuSO₄ increased the level of lipid peroxidation and a protective effect on complexed iron was observed. Incubation of erythrocytes with copper ions resulted in the loss of a considerable part of thiol content at 10 and 20 μM. This effect was decreased by potassium ferricyanide and Fe(NO₃)₃ only after 1 and 3 h of incubation. The level of nuclear DNA damage assayed by comet assay showed that 20 μM CuSO₄ as well as 20 μM Fe(NO₃)₃ and 10 mM K₃Fe(CN)₆ induce single- and double-strand breaks. The lower changes were observed after the exposure of cells to K₃Fe(CN)₆. The data suggest that complexed iron can act protectively against copper ions in contrast to Fe(NO₃)₃.     

Functional model for catecholase-like activity: Synthesis, structure, spectra, and catalytic activity of iron(III) complexes with substituted-salicylaldimine ligands

Four new mononuclear iron(III) complexes with the substituted-salicylaldimine ligands, [Fe(L¹)(TCC)] (1), [Fe(L²)(TBC)] (2), [Fe(L³)(TBC)] (3) and [Fe(L⁴)(TCC)](CH₃CN) (4) (HL¹ = N′-(5-OH-salicylaldimine)-diethylenetriamine, HL² = (N′-(5-Cl-salicylaldimine)-diethylenetriamine, HL³ N′-(5-Br-salicyl-aldimine)-dipropylenetriamine, HL⁴ = (N′-3,5-Br-salicylaldimine)-dipropylenetriamine, H₂TCC = tetrachlorocatechol, and H₂TBC = tetrabromocatechol), were prepared and characterized by XRD, EPR, and Mössbauer spectroscopy. The coordination sphere of the Fe(III) in complexes 1-4 is a distorted octahedral with N₃O₃ donors set which constructed by the Schiff-base ligands and the catecholate substrates of TBC or TCC. The in situ prepared Fe(III) complexes [Fe(L¹)Cl₂], [Fe(L²)Cl₂], [Fe(L³)(Cl₂)], and [Fe(L⁴)Cl₂] in absence of TBC or TCC show a high catecholase-like activity for the oxidation of 3,5-DTBC to the corresponding quinone 3,5-DTBQ.     

Synthesis, crystal structures and magnetic properties of mononuclear tris(croconate)ferrate(III) complexes

A straightforward synthetic method to prepare mononuclear croconato-containing iron (III) complexes, (A)₃[Fe(C₅O₅)₃] [A = tetrabutylammonium = n-Bu₄N⁺ (1) and along with their crystal structures and magnetic properties, are reported. The Fe(III) atom adopts a pseudo-octahedral geometry while magnetic susceptibility measurements, in the 2-300 K temperature range, show the occurrence of a high spin state (S = 5/2) in both complexes.     

A process-orientated design and performance assessment methodology for passive mine water treatment systems

The aim of this paper is the development of a methodology for assessing the iron removal efficiency of passive mine water treatment settling lagoons and reed beds. Previous work in the design and sizing of coal mine drainage lagoons and wetlands has focussed on the use of standard hydraulic residence times or using the 10 g m⁻² d⁻¹ metric, these criteria have been applied without regard to the fundamental physical and chemical processes controlling iron removal in the system, namely the pH dependent rates of Fe(II) oxidation and physical settling of the particulate Fe(III). In this study field water quality data have been collected from lagoons and reed beds. These data are examined alongside data from the UK Coal Authority database and combined with simple mathematical formulations to provide a framework through which to understand passive treatment schemes from a process-orientated perspective. It is demonstrated that for the sites studied reed beds are more efficient for iron removal. This paper recommends that judgements of iron removal performance should be based on a derived treatment efficiency index (?) and that the modelling approach espoused in this paper should be used when designing passive mine water treatment schemes.     

Mononuclear iron(III) complexes supported by tripodal N3O ligands: Synthesis, structure and reactivity towards DNA cleavage

A new synthetic route to the known tripodal tetradentate N₃O ligand L¹ (HL¹ = [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine) is reported. The related compounds HLⁿ (n = 2, 3) were prepared by a similar procedure. Treatment of HLⁿ (n = 1-3) with FeCl₃·6H₂O in hot methanol led to the mononuclear iron(III) complexes [Fe(Lⁿ)Cl₂] (1: n = 1, 2: n = 2, 3: n = 3). The solid-state structures of complexes 1 and 2 were determined by X-ray crystallography. [Fe(L¹)Cl₂] (1) showed effective nuclease activity in the presence of hydrogen peroxide, converting supercoiled plasmid DNA to its linear form.     

Synthesis, spectroscopic and structural characterization of the high-spin Fe(II) cyanato-N and thiocyanato-N “picket fence” porphyrin complexes

Two new iron(II) five-coordinated porphyrin complexes [Na(2,2,2-crypt)] [Fe^II(TpivPP)(NCO)] (1) (TpivPP = α,α,α,α-tetrakis(o-pivalamidophenyl) porphyrin known as picket fence porphyrin and 2,2,2-crypt is the cryptand-222) and [K(2,2,2-crypt)][Fe^II(TpivPP)(NCS)] (2) have been prepared and characterized. The UV-Vis and IR spectroscopic data are consistent with a cyanato-N and thiocyanato-N ferrous porphyrinates. The Mössbauer data and the X-ray structural analysis indicate that the Fe(II) cation in 1 and 2 is high-spin (S = 2) and has the (d_xy)²(d_xz)¹(d_yz)¹(d_z²)¹(d_x²-y²)¹ ground state electronic configuration.For complex 1, the average equatorial iron-pyrrole N bond length (Fe-N_p = 2.120(2) Å), the distance between the iron and the 24-atom mean plane of the porphyrin ring (Fe-P_C = 0.6805(7) Å) and the distance between the iron and the plane made by the four pyrrole nitrogens (Fe-P_N = 0.5923(12) Å) are longer than those of complex 2 and similar five-coordinated Fe(II) high-spin porphyrinates. This is probably due to the significant electronic repulsion of the d_x²-y² and d_xy orbitals by the negative charge of the pyrrole N atoms in case of 1.     

New polymeric thiocyanatoiron(II) complex with N,N′-diethylnicotinamide - Synthesis, structure, magnetic and spectral properties

The iron(II) compound of formula [Fe(NCS)₂(dena)₂]_n (dena = N,N′-diethylnicotinamide) has been prepared by the reaction between iron(III) thiocyanate and dena in ethanol solution. The complex was characterized by elemental analysis, spectral and magnetic measurements. Single-crystal X-ray diffraction methods show that the complex, crystallizing in the triclinic space group, undergoes a phase transition between 220 K and 230 K, connected with the doubling of cell volume. Crystal structures at 230 K (1a; HT phase) and 150 K (1b; LT phase) are described and a transition mechanism is discussed. In both phases the compound has an extended chain structure, in which the neutral molecule of N,N′-diethylnicotinamide acts as a bridging ligand binding through pyridine N atom to one centre and through amide O atom to the neighbouring Fe centre. The Fe²⁺ ion has a slightly distorted trans-octahedral environment with FeO₂N₄ chromophore, and all Fe-O and Fe-N bonds in the typical for high-spin iron(II) compounds range. Variable-temperature magnetic susceptibility data in the temperature range 1.8-300 K show that iron(II) is high-spin S = 2(⁵T_2g) and as a result effects due to zero-field splitting are anticipated at low temperatures. The IR spectrum suggested the coordination of N,N′-diethylnicotinamide to the central atom of iron(II) as a bridging ligand and NCS group as a monodentate ligand.