Search results for "Field Theory"
showing 10 items of 1188 documents
SIMPRE: A software package to calculate crystal field parameters, energy levels, and magnetic properties on mononuclear lanthanoid complexes based on…
2013
This work presents a fortran77 code based on an effective electrostatic model of point charges around a rare earth ion. The program calculates the full set of crystal field parameters, energy levels spectrum, and wave functions, as well as the magnetic properties such as the magnetization, the temperature dependence of the magnetic susceptibility, and the Schottky contribution to the specific heat. It is designed for real systems that need not bear ideal symmetry and it is able to determine the easy axis of magnetization. Its systematic application to different coordination environments allows magneto-structural studies. The package has already been successfully applied to several mononucle…
Effect of the metal dilution on the thermal and light-induced spin transition in [FexMn1−x(bpp)2](NCSe)2: When T(LIESST) reaches T1/2
2008
International audience; The thermal and light-induced spin transition in [FexMn1−x(bpp)2](NCSe)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) has been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal spin transition and exhibit the light-induced excited spin state trapping (LIESST) effect at low temperature. For each mixed-crystal system, the thermal spin transition temperature, T1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T1/2 decreases with the metal dilution while T(LIESST) remains unchanged, suggesting that the two interco…
EXTENDED HÜCKEL MOLECULAR ORBITAL CALCULATION OF THE TEMPERATURE DEPENDENCE OF THE QUADRUPOLE SPLITTING OF [Fe(H2O)6] SiF6 AND KFeCl3
1976
A number of papers have appeared in which the temperature dependence of the quadrupole splitting has been treated, whereby covalency effects have been considered by introducing the orbital reduction factor k, with k ranging from 1.-0.7. There are, however, two problems : (1) k is unisotropic if the symmetry is lower than cubic, (2) the spin orbit coupling of the ligand electrons are usually neglected. These two problems have been treated here by using SCCEHMO [1] calculations on two examples, [Fe(H2O)6]SiF6 and KFeCl3, which have been previously delt with by other authors using ligand field theory [2, 3]. For both compounds the differences between the measured and the calculated quadrupole …
ChemInform Abstract: Crystal Structure and Spectroscopic Studies of Bis(N-2-pyridinylcarbonyl-2-pyridinecarboximidato)copper(II) Monohydrate. Local B…
1989
Abstract The crystal and molecular structure of bis(N-2- pyridinylcarbonyl-2-pyridinecarboximidato)copper(II) monohydrate, Cu(BPCA)2·H2O, has been determined from single crystal X-ray data. It crystallizes in the monoclinic space group P21/c with four formula units in a cell of dimensions: a = 8.917(1), b = 8.932(1), c = 28.794(17) A, β= 95.49(2)°.Least- squares refinement of 2754 reflections with I > 2.5σ(I) and 379 parameters gave a final R = 0.037 (Rw = 0.036). The structure consists of discrete neutral Cu(BPCA)2 entities linked two by two through water molecules hydrogen bonded to ligand carbonyl groups. The coordination geometry around copper ions can approximately be described as orth…
Crystal Structure and Magnetic Properties of 3,5-Pyridinedicarboxylate-Bridged Re(Ii)M(Ii) Heterodinuclear Complexes (M = Cu, Ni and Co)
2021
Abstract The use of the mononuclear rhenium(II) precursor NBu4[Re(NO)Br4(H2pydc)]·i-PrOH (1) (H2pydc = 3,5-pyridinedicarboxylic acid) as a metalloligand towards Cu(II), Ni(II) and Co(II) afforded three new heterobimetallic complexes [Re(NO)Br4(μ-Hpydc)Cu(4,4′-dmbipy)2]·(CH3)2CO·0.25MeCN (2), [Re(NO)Br4(μ-Hpydc)Ni(dmphen)2]·MeCN (3) and [Re(NO)Br4(μ-Hpydc)Co(dmphen)2]·2H2O (4), respectively [4,4′-dmbipy = 4,4′-dimethyl-2,2′-bipyridine, dmphen = 2,9-dimethyl-1,10-phenanthroline and Bu4N+ = tetra-n-butylammonium]. The crystal structures of 1 and 2 are reported herein together with the cryomagnetic investigation of 1–4 in the temperature range of 2.0–300 K. 1 is a mononuclear compound whose str…
Guidelines to design new spin crossover materials
2010
International audience; This review focuses on new families of spin crossover (SCO) complexes based on polynitrile anions as new anionic ligands or on polyazamacrocycles as neutral macrocyclic ligands. We have shown that the structural and electronic characteristics (original coordination modes and high electronic delocalization) of the polynitrile anions can be tuned by slight chemical modifications such as substitution of functional groups or variation of the negative charge to design new discrete or polymeric SCO systems.In our ongoing work on the design of new molecular systems based on new ligands that can be fine-tuned via chemical modifications, another promising way which has been r…
Cyanido-bridged {FeIIILnIII} heterobimetallic chains assembled through the [FeIII{HB(pz)3}(CN)3]−complex as metalloligand: synthesis, crystal structu…
2021
A new series of cyanido-bridged {FeIIILnIII} heterobimetallic chains of general formula {[(NC)FeIII{HB(pz)3}(μ-CN)2LnIII(bpdo)(NO3)2(H2O)]·CH3CN}n [HB(pz)3− = hydrotris(pyrazol-1-yl)borate, bpdo = 2,2′-bipyridine-N,N′-dioxide and Ln = Gd (1), Tb (2), Dy (3) and Ho (4)], were obtained by using the low-spin [Fe{HB(pz)3}(CN)3]− complex as a metalloligand towards the preformed [Ln(bdpo)(NO3)2(H2O)]+ species. Single-crystal X-ray diffraction shows that 1–4 are isostructural compounds that crystallize in the monoclinic P21/c space group. Their crystal structure consists of neutral 1D coordination polymers where the [Fe{HB(pz)3}(CN)3]− fragment adopts a bis-monodentate coordination mode, through t…
Anionic Cyclometalated Iridium(III) Complexes with a Bis-Tetrazolate Ancillary Ligand for Light-Emitting Electrochemical Cells
2017
none 10 si A series of monoanionic Ir(III) complexes (2-4) of general formula [Ir(C^N)2(b-trz)](TBA) are presented, where C^N indicates three different cyclometallating ligands (Hppy = 2-phenylpyridine; Hdfppy = 2-(2,4-difluoro-phenyl)pyridine; Hpqu = 2-methyl-3-phenylquinoxaline), b-trz is a bis-tetrazolate anionic N^N chelator (H2b-trz = di(1H-tetrazol-5-yl)methane), and TBA = tetrabutylammonium. 2-4 are prepared in good yields by means of the reaction of the suitable b-trz bidentate ligand with the desired iridium(III) precursor. The chelating nature of the ancillary ligand, thanks to an optimized structure and geometry, improves the stability of the complexes, which have been fully char…
Synthesis and Magnetic Properties of Novel Azamacrocyclic LnIII, CuII, FeIII, and SrII Complexes and Conformational Analysis of the Ligands
2008
Hexaalkoxy-substituted azamacrocyclic metal complexes 1 · MXn [MXn = FeCl3, CuCl2, SrCl2, Ln(NO3)3; Ln = La, Pr, Eu, Ho, Er] with various chain lengths were prepared by a convergent approach using 1,2-bisalkoxy-4,5-diamines 3 and 4-alkoxy-pyridine-2,6-dicarbaldehydes 4 as key building blocks for template-assisted cyclocondensation. Metal complexes 1 · MXn were considered as potential metallomesogens. However, differential scanning calorimetry and optical polarizing microscopy of 1 · MXn did not reveal any mesomorphism. The magnetic susceptibility shows deviation from Curie-like behavior. Due to ligand field effects the effective magnetic moments are a function of the temperature. In order t…
Coordination isomerism in spin crossover (SCO) materials
2021
International audience; A new series of three spin crossover (SCO) Fe(II) complexes based on a cyanocarbanion and on the neutral quinolin-8-amine (aqin) ligands, [Fe(aqin)2(tcnsme)2] (1), [Fe(aqin)2(tcnset)2] (2), and [Fe(aqin)2(tcnspr)2] (3), has been studied. The three complexes display similar molecular structures consisting of discrete [Fe(aqin)2(tcnsR)2] complexes [R = Me (1), Et (2), and Pr (3)]. Infrared spectroscopy and magnetic studies, performed on the three complexes, revealed the presence of similar SCO behaviors which strongly differ by their transition temperatures [234 K (1) < 266 K (2) < 360 K (3)]. The increase of the transition temperatures when passing from 1 to 3 may be …