Mössbauer spectroscopic studies of spin crossover in tris(N, N′-dialkyldithiocarbamato) iron (III) complexes: effect of alkyl substituents

Spin crossover behavior in tris(N,N′-dialkyldithiocarbamato) iron(III) complexes with varying alkyl groups has been studied by variable temperature magnetic moment and Mössbauer spectral studies. All the complexes may be divided into three broad groups; high spin (μ _eff > 4.8 BM), intermediate spin (μ _eff?=?3.5???4.6 BM) and low spin (μ _eff?< 3.2 B.M). Room temperature (RT) Mössbauer spectra exhibit an asymmetric doublet resolved into two doublets corresponding to high and low spin states. Estimated % contributions of HS and LS states and calculated μ _eff were comparable with the experimentally determined values. It has been shown that some complexes undergo spin crossover, ⁶A₁g→²T₂g whereas others exhibit spin transitions ⁶A₁g →⁴T₁g or ⁴T₁g → ²T₂g. IR spectra show characteristic ν _(Fe???S) bands in the region 208–285 (HS) and 311–380 cm^???1 (LS). Nature of alkyl groups affects the spin state.     

M?ssbauer spectroscopic study on valence-detrapping and trapping of mixed-valence trinuclear iron(III, III, II) fluorine-substituted benzoate complexes

Magnetorheological (MR) fluids are new iron-based materials, whose applications include brakes, dampers, clutches, shock absorbers systems and polishing of optical surfaces (lens and mirrors). They are dependent on the size and shape of particles as the magnetic properties. Interested in the possibility of using iron-rich powders, commonly used in nondestructive testing, ranging in size from a few μm to about 200?μm and lower cost than those commercially used for MR fluids, a study of the structural and magnetic properties of iron-rich metallic particles by X-ray diffraction (XRD) and M?ssbauer spectroscopy (MS) at room temperature has been done. Powders, as received, were separated into particle sizes smaller than 20?μm (sample A) and in the range of 20–38?μm (sample B) because these are the sizes generally required for applications in MR fluids. The particles whose sizes exceed the above values were ground in a high energy planetary mill for 3?h, using different values of rotational speed/time: 200?rpm for one hour, a pause of 10?s, 140?rpm for one hour, pause 10?s and then 175?rpm during the last hour. These powders were sieved to obtain particles smaller than 20?μm (sample C). According XRD results, in all samples, only α-Fe (lattice parameter a = 2,867(2) ?) and Fe₂O₃ (lattice parameter a = 5,037(1) ? and c = 13,755(8) ?) were present. The M?ssbauer spectra were fitted with two sextets. The hyperfine parameters values allowed us to assign the highest relative area spectrum (sextet) corresponding to α-Fe and the second one to Fe₂O₃ in accord to the XRD results. Thus, the preparation method using mechanical milling for diminishing the size of the metallic particles allowed us to get particles with size and magnetic properties that could lead to potentially MR fluids applications.     

Mössbauer spectroscopic study of the early crystallization stage of iron(III) hydroxide particles

Mössbauer spectroscopy was used to investigate the early aging stage of iron(III) hydroxide sols prepared by oxidation of Fe(CO)₅ in ethanolic solution, followed by vacuum drying at room temperature. One sample was composed of amorphous particles, while two other samples were partially crystallized, either as a result of solvent change or of spontaneous aging. The main results of Mössbauer measurements in the 80–320 K temperature range are: (a) partially crystallized particles exhibit a strong, S-shaped temperature dependence of the quadrupole splitting, in contrast to a weak and linear variation for amorphous particles; (b) the recoilless fraction temperature dependence is affected by vibration of the particles as a whole, with an effective force constant which is smaller for crystallized particles than for amorphous ones. Furthermore, the former exhibit anf-factor discontinuity near 0°C, which is attributed to melting of a surface layer built up during the crystallization process.     

Synthesis of (E)-2-amino-N′-benzylidenehexahydroquinoline-3-carbohydrazide

Molecular Diversity - A one-pot, multi-component protocol for the synthesis of a new class of functionalized quinoline carbohydrazide derivatives via reaction of various anilines, dimedone,...     

Effect of the donor–acceptor properties of ligands on the spectroscopic and electrochemical properties of mixed-ligand complexes of Pt(II) and Ir(III) with cyclometalated 2-phenylbenzothiazole

The results of the spectroscopic NMR (¹H, ¹³C, and ¹⁹⁵Pt), infrared, optical, and voltammetric characteristics of the mixed-ligand complexes of Pt(II) and Ir(III) with metalated 2-phenylbenzothiazole and tert-butylisocyanide (tBuNC), acetonitrile (AN), ethylenediamine (En), O-ethyldithiocarbamate (Exn^–), and diethyldithiocarbamate (Dtc–) ions are presented. It is demonstrated that the change in donor–acceptor interaction of ligands tBuNC, AN, En, Exn^–, and Dtc^– with metal leads to an increase in the energy of the highest occupied molecular orbital of the complexes and is accompanied by a shift of the cathode potential of the metal-centered oxidation, a bathochromic shift of the spin-allowed and spin-forbidden metal-tocyclometalated ligand optical charge transfer transitions, and an increase the degree of mixing of the ¹MLCT and triplet intraligand states, responsible for the phosphorescence of the complexes.     

Synthesis and characterization of phosphorescent iridium complexes of 6-chloro-3-phenylpyridazine and 3-chloro-6-(3′-methoxy-phenyl)-4-methyl-pyridazine

The preparation and photophysics of organometallic Ir(III) complexes with 3-phenylpyridazine (H6Clppdz) and its derivative are reported. IrCl₃ · nH₂O reacts with H6Clppdz, and 3-chloro-6-(3^′-methoxyphenyl)-4-methyl-pyridazine (MCOMppdz) to give the corresponding chloride-bridged dimers, (6Clppdz)₂Ir(μ-Cl)₂Ir(6Clppdz)₂ and (MCOMppdz)₂Ir(μ-Cl)₂Ir(MCOMppdz)₂ in good yields. These chloride-bridged dimers are cleaved with 2-pyrazinecarboxylic acid (Hpyzc), 2-picolinic acid (Hpic), acetylacetone (Hacac), and 2,2,6,6-tetramethyl-3,5-heptanedione (Htmd) to give the corresponding monomer, (6Clppdz)₂Ir(pyzc), (6Clppdz)₂Ir(pic), (6Clppdz)₂Ir(acac), (6Clppdz)₂Ir(tmd), (MCOMppdz)₂Ir(acac), and (MCOMppdz)₂Ir(tmd), respectively. The complexes show bright orange to red luminescence at room temperature and the emission wavelenghts are affected by the ancillary ligands as well as cyclometalating ligands (593–664 nm).     

The characterization of electroplex generated from the interface between 2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole] zinc and N,N′-diphenyl-N,N′- bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine

The electroplex between (2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole) zinc [Zn(4-TfmBTZ)₂] as an electron-acceptor and N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) as an electron-donor was characterized by bilayer, blend, and multilayer quantum-well (MQW) device, respectively. The blend composition and quantum-well number are effective parameters for tuning electroluminescence color. White light with high color purity and color rendering index (CRI) was observed from these devices based on Zn(4-TfmBTZ)₂/NPB. Moreover, the blend and MQW devices all exhibit high operation stability, hence excellent color stability. For the device with 5 mol% NPB in blend layer, its Commission International Del’Eclairage (CIE) coordinate region is x=0.28–0.31, y=0.33–0.35 and CRI is 83.3–91.2 at 5–9 V. For MQW structure device with NPB of 60 nm thickness, its CIE coordinate region is x=0.29–0.32, y=0.31–0.34 and CRI=87.9–92.5 at 10–15 V. Such high color stability and purity and CRI, being close to ideal white light, are of current important for white OLED.     

Optical properties of bicyclometalated Ir(III) and Rh(III) complexes of benzo[h]quinoline with (N∧S)− and (N∧O)− chelating ligands

[M(bzq)₂(N∧X)] complexes (M = Rh(III), Ir(III); (bzq)^? is the deprotonated form of benzo[h]quinoline, and (N∧X)^? are 2-thiolpyridine, 2-hydroxypyridine, and 2-thiolbenzothiazole ions) are studied by absorption and emission spectroscopy and voltammetry. The long-wavelength absorption bands of [Rh(bzq)₂(N∧X)] in the range of 420–424 nm are attributed to the optical metal-to-ligand charge transfer (MLCT) transitions, while the low-temperature (77 K) phosphorescence in the range of 490–610 nm is assigned to the intraligand (IL) transition of the {Rh(bzq)₂} metal-complex fragment. The phosphorescence of the [Ir(bzq)₂(N∧X)] complexes in liquid solutions in the range of 585–675 nm is assigned to the radiative MLCT transition, while the low-temperature (77 K) phosphorescence occurs from the thermally nonequilibrium MLCT and IL excited states of the {Ir(bzq)₂} metal-complex fragment.     

Structural,luminescence and biological studies of trivalent lanthanide complexes with N,N′-bis(2-hydroxynaphthylmethylidene)-1,3-propanediamine Schiff base ligand

New eight lanthanide metal complexes were prepared. These complexes were characterized by elemental analysis, molar conductivity measurements, spectral analysis (¹H NMR, FT-IR, UV–vis), luminescence and thermal gravimetric analysis. All Ln(III) complexes were 1:1 electrolytes as established by their molar conductivities. The microanalysis and spectroscopic analysis revealed eight-coordinated environments around lanthanide ions with two nitrate ligands behaving in a bidentate manner. The other four positions were found to be occupied with tetradentate L_III ligand. Tb–L_III and Sm–L_III complexes exhibited characteristic luminescence emissions of the central metal ions and this was attributed to efficient energy transfer from the ligand to the metal center. The L_III and Ln–L_III complexes showed antibacterial activity against a number of pathogenic bacteria.     

EPR investigations of Cu(II) complexes with 5′-CMP and 5′-GMP

Electron paramagnetic resonance investigation of the Cu(II) complexes with guanosine-5′-monophosphate (5′-GMP) and cytidine-5′-monophosphate (5′-CMP) shows the affinity of the Cu(II) ion to interact with the base and the phosphate group. The different modes of the coordination of the metal ion at the nucleotide and the water molecules lead to octahedral species, distorted by dynamical Jahn-Teller effect (g₀ = 2.106) for the Cu(II)-5′-CMP complex and rhombically distorted (g₁ = 2.358, g₂ = 2.126, g₃ = 2.068) or tetragonally distorted (g_∥^′ = 2.299, g_⊥^′ = 2.126) for the Cu(II)-5′ -GMP complex. The compound with 5′-CMP presents also a more stable in time square-planar species (g_∥ = 2.265, A_∥ = 162 G, g_⊥ = 2.076). The local symmetry changes in aqueous solution by coordination of water molecules.     

Quantitative analysis of iron nitrides (γ′-Fe4 and ϵ-Fe2−3N) using auger electron spectroscopy

The investigation and development of tribologically important transition metal nitride surface layers rely on the accurate quantitative analysis of light elements used in conjunction with a suitable depth profiling technique. This paper describes the quantitative AES analysis of iron nitrides (γ′-Fe₄N and ϵ-Fe₂₋₃N) by comparison with reference materials and by applying correction factors for ionization by backscattered primary electrons, atom number density and inelastic mean free paths of the Auger electrons in the matrix. It is shown that the nitrogen contents of these iron nitrides may be determined to within 10% accuracy, and it is also shown that this accuracy depends firstly on the correct calculation of the abovementioned correction factors, and secondly on the correct determination of the Auger electron yield. The Auger electron yield should be determined by measuring the area below the Auger peak on the N(E)E spectrum, after removal of the background electron spectrum to ensure that details of the relatively small nitrogen peaks are not overlooked.     

Photonics of zinc complexes of 3,3′-bis(dipyrrolylmethenes)

We measure the spectral luminescence characteristics (absorption, fluorescence, lasing, phosphorescence, and luminescence excitation spectra; fluorescence and phototransformation quantum yields; lifetimes of long-lived radiation) and estimate the fluorescence radiation constants and lifetimes for new synthesized binuclear bihelical complexes of zinc(II) with 3,3′-bis(dipyrrolylmethenes) of different structure in liquid and solid solutions. We discuss possible applications of these compounds.     

Mössbauer spectra of iron (III) sulfide particles

Trivalent iron sulfide (Fe₂ S ₃) particles were synthesized using a modified polyol method. These particles exhibited a needle-like shape (diameter =?10-50 nm, length =?350-1000 nm) and generated a clear XRD pattern. Mössbauer spectra of the product showed a paramagnetic doublet at room temperature and distributed hyperfine magnetic splitting at low temperature. The Curie temperature of this material was determined to be approximately 60 K. The data suggest that the Fe₂ S ₃ had a structure similar to that of maghemite (γ-Fe₂ O ₃) with a lattice constant of a =?10.6 Å. The XRD pattern calculated from this structure was in agreement with the experimental pattern and the calculated hyperfine magnetic field was also equivalent to that observed in the experimental Mössbauer spectrum.     

First-order properties and Buckingham birefringence of N2O and OCS – A computational (re)investigation

Prompted by recent experimental reinvestigations of the Buckingham birefringence of CO, CO₂, OCS and N₂O, we have carried out our own reinvestigation of the relevant first- and second-order properties entering the electric-field-gradient-induced birefringence effect of N₂O and OCS by means of state-of-the-art quantum chemical methods. The computed and experimentally derived results remain at significant variance, also in consequence of a remarkable disagreement between the ab initio and the experimental values of the quadrupole moment relative to the centre of the nuclear masses.     

Chemical Synthesis of C3N and BC2N Compounds

A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride （CC14）, boron tribromide （BBr3）, lithium nitride （Li3N） and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively.     

Conformational Studies of 1-(2′-Hydroxythiobenzoyl)piperidine and 4-(2′-Hydroxythiobenzoyl)morpholine by High Resolution N.M.R. Spectroscopy

Abstract

The 220 MHz ¹H nmr spectra of the title compounds (1a) and (2a), respectively, at low temperature in CDCl₃ solution are interpreted in terms of two interconverting chair forms with unequal populations (K_e = 1.17, δG° ～70 cals/mole for 1a and K_e = 1.8, δG° ～0.2 kcal/mole for 2a at ?30°C). A strong intramolecular OH…S hydrogen bond in both compounds reduces the number of degrees of freedom of the bulky N-thiobenzoyl substituent, which nearly eclipses the equatorial α-CH₂ hydrogen atoms in both comformations. Steric interactions between the 6′ phenyl proton and the hetero-ring α-CH₂ protons trans to the thiocarbonyl group are different in the two conformations of la and 2a.     

Theoretical study on the influence of different NˆN ligands on the electronic structures and optoelectronic properties of heteroleptic Iridium(III) complexes

DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and phosphorescence properties of a series of heteroleptic Ir(III) complexes consisting of two N-heterocyclic carbene ligands and a conjugated bicyclic N,N′-heteroaromatic (N?N) ligand. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complex (mpmi)₂Ir(pybi) (1) [Hmpmi = 1-(4-tolyl)-3-methyl-imidazole; Hpybi = 2-(pyridin-2-yl)-1H-benzo[d]imidazole] emits green light with an extremely high-quantum phosphorescence efficiency (Φ _PL ) of 79.3%, while a relatively lower Φ _PL (only 11%) was measured for (fpmi)₂Ir(tfpypz) (2) [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C, C^2′; tfpypz = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato] emitting blue light by tuning the N?N ligands. Besides, we also designed (fpmi)₂Ir(pyN3) (3) [pyN3H = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine] and (fpmi)₂Ir(pyN4) (4) [pyN4H = 2-(1H-tetrazol-5-yl)pyridine] to explore the influence of electron-withdrawing substituents on N?N ligands on the electronic and optical properties of these Ir(III) complexes. The results revealed that electron-withdrawing substituents can stabilise both HOMOs and LUMOs and induce HOMO–LUMO energy gap change. Moreover, the emission properties can be significantly tuned by introducing different N?N ligands. While new insights were gained on structural and electronic properties, the extremely high Φ _PL of 1 was found to be not inherent to spin-orbital coupling effects, but determined by its large transition dipole moment (μ_{S 1}) upon S ₀–S ₁ transition compared with that of 2. On the basis of these results, the designed complexes 3 and 4 are considered to be the promising candidates for blue-emitting phosphorescence materials with higher Φ _PL than the complex 2.     

Structural and spectroscopic investigation of the N-methylformamide–water (NMF···3H2O) complex

In this work, theoretical studies on the structure, molecular properties, hydrogen bonding, and vibrational spectra of the N-methylformamide–water (NMF···3H₂O) complex will be presented. The molecular geometry was optimised by using Hartree–Fock (HF), second Møller–Plesset (MP2), and density functional theory methods with different basis sets. The harmonic vibrational frequencies are computed by using the B3LYP method with 6-311++G(d,p) as a basis set and then scaled with a suitable scale factor to yield good coherence with the observed values. The temperature dependence of various thermodynamic functions (heat capacity, entropy, and enthalpy changes) was also studied. A detailed analysis of the nature of the hydrogen bonding, using natural bond orbital (NBO) and topological atoms in molecules theory, has been reported.     

Synthesis and Reactivity of Mg(II)–Fe(II)–Fe(III) Hydroxycarbonates

Green rust-like compounds (GRs) were discovered as natural minerals in various hydromorphic soils, where anoxic conditions allow their stability. They may control some redox processes in aquifers and participate to the transformation of various pollutants. Since Mg(II) cations are present in the fields where GRs were discovered, a partial substitution of Mg(II) to Fe(II) leading to intermediate compounds between GRs and usual Mg(II)–Fe(III) hydroxysalts is suspected. Mg(II)–Fe(II)–Fe(II) hydroxycarbonates can be obtained as intermediate oxidation products of (Mg, Fe)(OH)₂ in carbonate-containing aqueous media obeying to [Fe^II _4(1–x)Mg^II _4x Fe^III ₂(OH)₁₂]²⁺ [CO₃ ^2– nH₂O]^–2. TMS spectra at 12 K are similar to those of GRs, i.e., two quadrupole doublets, one due to Fe(II) with a large isomer shift =1.29 mms^–1 (with respect to -iron at room temperature) and quadrupole splitting E _Q=2.76 mms^–1, the other one due to Fe(III) with smaller hyperfine parameters =0.49 mms^–1 and E _Q=0.44 mms^–1. Fe(II) ions oxidise rapidly into Fe(III) with dissolved O₂. The reactivity is similar to that of Fe(II)–Fe(III) hydroxysalts GR, and thus the potential of Mg(II)–Fe(II)–Fe(III) compounds for reducing pollutants.     

Synthesis, Photo-physical and DFT Studies of ESIPT Inspired Novel 2-(2′,4′-Dihydroxyphenyl) Benzimidazole, Benzoxazole and Benzothiazole

Novel ESIPT inspired benzimidazole, benzoxazole and benzothiazole were synthesized from 2,4-dihydroxy benzoic acid and 1,2-phenelenediamine, 2-aminophenol, and 2-aminothiophenol respectively. The synthesized 2-(2′,4′-dihydroxyphenyl) benzimidazole, benzoxazole and benzothiazole are fluorescent and the emission characteristic are very sensitive to the micro-environment. They show a single absorption and dual emission with large Stokes shift originating from excited state intramolecular proton transfer. The absorption-emission characteristics of all these compounds are studied as a function of pH. The change in the electronic transition, energy levels, and orbital diagrams of synthesized compounds were investigated by the molecular orbital calculation and were correlated with the experimental spectral emission. Experimental absorption and emission wavelengths are in good agreement with those predicted using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)].