Angular Overlap Research Articles

Theoretical analysis of the three-dimensional structure of tetrathiolato iron complexes.

The three-dimensional structures of a number of [M(SR)(4)](n-) complexes, where M is a 3d transition metal and R is an alkyl or aryl group, have been analyzed using density functional theory (DFT). Special attention is paid to the Fe(II)/Fe(III) mimics of rubredoxin. The Fe(II) model complex [Fe(SCH(3))(4)](2-) has an equilibrium conformation with D2d symmetry. The DFT energy has been decomposed into contributions for ligand-ligand and metal-ligand interactions. The latter contribution is analyzed with the angular overlap model (AOM) and constitutes the dominant stereospecific interaction in the Fe(II) complex. The sulfur lone-pair electrons exert anisotropic pi interactions on the 3d(6) shell of Fe(II), which are controlled by the torsion angles, omega(i), for the rotations of the S(i)-C(beta) bonds around the Fe-S(i) axes. In contrast, the pi interactions acting on the high-spin 3d(5) shell of Fe(III) are isotropic. As a consequence, the stereochemistry of the Fe(III) complexes is determined by the Coulomb repulsions between the ligands and has S(4) symmetry. The electrostatic repulsions between the lone pairs of the sulfurs are an essential component of the ligand-ligand interaction. The lone-pair repulsions distort the 90 degree angle SFeS' angles (delta + delta(t)) and give rise to a correlation between delta and omega, which is confirmed by crystallographic data. Both the Fe(II) and Fe(III) complexes exhibit structural bistability due to the presence of low-lying equilibrium conformations with S(4) symmetry in which the complex can be trapped by the crystalline host.

Single-molecule magnets of ferrous cubes: structurally controlled magnetic anisotropy.

Tetranuclear Fe(II) cubic complexes were synthesized with Schiff base ligands bridging the Fe(II) centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4].2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4].2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4].MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1-6, the alkoxo groups of the Schiff base ligands bridge four Fe(II) ions in a mu3-mode forming [Fe4O4] cubic cores. The Fe(II) ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4-6 are shorter than those in 1-3. Dc magnetic susceptibility measurements for 1-6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, -0.64, -0.66, and -0.67 cm(-1) for 1-6, respectively. Ac magnetic susceptibility measurements for 4-6 showed both frequency dependent in- and out-of-phase signals, while 1-3 did not show out-of-phase signals down to 1.8 K, meaning 4-6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4-6. The bridging ligands R-sap2- in 1-3 and R-sae2- in 4-6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn-Teller distortions at Fe(II) centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry.

Magnetic properties of bridged azido complexes

It was shown on the basis of the generalized angular overlap model that specific features of the electronic structure of the N3– anion in polynuclear complexes with the M(μ1,1-N32M magnetic fragment should result in strong ferromagnetism. The μ1,3-N3 coordination mode favors antiferromagnetic properties. The theoretical results agree with experimental magnetostructural correlations.

Are gas-phase reactions of five-coordinate divalent metal ion complexes affected by coordination geometry?

Five-coordinate metal complex ions of the type [ML](2+) [where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and L= 1,9-bis(2-pyridyl)-2,5,8-triazanonane (DIEN-(pyr)(2)) and 1,9-bis(2-imidazolyl)-2,5,8-triazanonane (DIEN-(imi)(2)] have been reacted with acetonitrile in the gas phase using a modified quadrupole ion trap mass spectrometer. The kinetics and thermodynamics of these reactions show that the reactivity of these complexes is affected by metal electronic structure and falls into three groups: Mn(II) and Ni(II) complexes are the most reactive, Fe(II) and Co(II) complexes exhibit intermediate reactivity, and Cu(II) and Zn(II) complexes are the least reactive. To help explain the experimental trends in reactivity, theoretical calculations have been used. Due to the relatively large size of the metal complexes involved, we have utilized a two-layered ONIOM method to perform geometry optimizations and single point energy calculations for the [ML](2+) and [ML + CH(3)CN](2+) systems. The calculations show that the reactant five-coordinate complexes ([ML](2+)) exhibit structures that are slightly distorted trigonal bipyramidal geometries, while the six-coordinate complexes ([ML + CH(3)CN](2+)) have geometries that are close to octahedral. The Delta G values obtained from the ONIOM calculations roughly agree with the experimental data, but the calculations fail to completely explain the trends for the different metal complexes. The failure to consider all possible isomers as well as adequately represent pi-d interactions for the metal complexes is the likely cause of this discrepancy. Using the angular overlap model (AOM) to obtain molecular orbital stabilization energies (MOSE) also fails to reproduce the experimental trends when only sigma interactions are considered but succeeds in explaining the trends when pi interactions are taken into account. These results indicate that the pi-donor character of the CH(3)CN plays a subtle, yet important, role in controlling the reactivity of these five-coordinate complexes. Also, the AOM calculations are consistent with the experimental data when the [ML](2+) complexes have high-spin trigonal bipyramidal configurations. Generally, these results suggest that ion-molecule reactions can be very sensitive to metal complex coordination geometry and thus may have some promise for providing gas-phase coordination structure.

Early interaction with C.K. Jørgensen

A personal account is given of interactions in the 1950s and 1960s with Christian Klixbüll Jørgensen (CKJ). These cover his analysis of the absorption spectra of several rare-earth ions, in which he was the first to use Racah’s 1949 tables, and his construction with two colleagues of the angular overlap model. Its role in the later extension to two-electron operators in the crystal-field Hamiltonian is described. Recollections of Jørgensen the man and of his vision of chemistry are included.

Crystal-field splitting of the Cr 4+ terms in LiAlO 2 oxide crystal

The absorption and excitation spectra of the tetrahedrally coordinated Cr 4+ ions doped in LiAlO 2 oxide crystal were measured by Kück and Hartung at room temperature (Chem. Phys. 240 (1999) 387). These spectra have provided evidence of the occurrence of transitions from the 3 A 2( 3 F) ground state to the crystal-field split levels 3 T 2( 3 F), 3 T 1( 3 F) and 3 T 1( 3 P) (levels are assigned to the T d symmetry, i.e., ideal tetrahedron CrO 4). The splitting of each band of the T d symmetry is due to the distortion of the ideal tetrahedron. Using the experimentally determined data from the absorption and excitation spectra, a theoretical calculation for the crystal-field levels of Cr 4+:LiAlO 2 was performed by Kück and Hartung, based on the angular overlap model theory. The calculation reveals a good agreement between the mean values of the bands, while it underestimates the splitting of each band. A detailed crystal-field analysis of electronic energy levels of Cr 4+ doped in LiAlO 2 oxide crystal based on the Racah theory is proposed in this work. The observed crystalline-field splitting of the Cr 4+ terms was accounted for by using a C 2 symmetric Hamiltonian. In turn, reliable crystal-field and Racah parameters have been obtained. This theoretical analysis confirms the observed crystalline-field splittings of the 3 F and 3 P terms of the Cr 4+ ion doped in the oxide crystal LiAlO 2.

Inclusion of the ligand field contribution in a polarizable molecular mechanics: SIBFA-LF.

To account for the distortion of the coordination sphere that takes place in complexes containing open-shell metal cations such as Cu(II), we implemented, in sum of interactions between fragments ab initio computed (SIBFA) molecular mechanics, an additional contribution to take into account the ligand field splitting of the metal d orbitals. This term, based on the angular overlap model, has been parameterized for Cu(II) coordinated to oxygen and nitrogen ligands. The comparison of the results obtained from density functional theory computations on the one hand and SIBFA or SIBFA-LF on the other shows that SIBFA-LF gives geometric arrangements similar to those obtained from quantum mechanical computations. Moreover, the geometric improvement takes place without downgrading the energetic agreement obtained from SIBFA. The systems considered are Cu(II) interacting with six water molecules, four ammonia or four imidazoles, and four water plus two formate anions.

Crystal-field analysis of the Cr4+absorption and excitation spectrum in LiGaO2oxide crystal

The absorption and excitation spectra of the tetrahedrally coordinated Cr 4+ ions doped in LiGaO 2 oxide crystal are measured by Kiick and Hartung at room temperature. Using the experimentally determined data from these spectra, a theoretical calculation for the crystal-field levels of Cr 4+ .LiGaO 2 was performed by Kiick and Hartung, based on the angular overlap model theory (AOM). The calculation reveals an important discrepancy between the theoretical and the experimental energies. A detailed crystal-field analysis of electronic energy levels of Cr 4+ doped in LiGaO 2 oxide crystal based on the Racah theory is proposed in this work. The observed crystalline-field splitting of the Cr 4+ terms was accounted for using a C 1 symmetric Hamiltonian. In turn, reliable crystal-field and Racah parameters have been obtained. This theoretical analysis confirms the observed crystalline-field splittings of the 3 F and 3 P terms of the Cr 4+ ion doped in the oxide crystal LiGaO 2 .

Spectroscopic and structural characterization of the [Fe(imidazole)(6)](2+) cation.

Spectroscopic, structural, and magnetic data are presented for Fe(C(3)H(4)N(2))(6)(NO(3))(2), which facilitate a precise definition of the electronic and molecular structure of the [Fe(Im)(6)](2+) cation. The structure was determined at 120(1) K by X-ray diffraction methods. The salt crystallizes in the trigonal space group R3 with unit-cell parameters a = 12.4380(14) A, c = 14.5511(18) A, and Z = 3. All the imidazole ligands are equivalent with an Fe-N bond distance of 2.204(1) A. Variable-temperature inelastic neutron scattering (INS) measurements identify a cold magnetic transition at 19.4(2) cm(-1) and a hot transition at 75.7(6) cm(-1). The data are interpreted using a ligand field Hamiltonian acting in the weak-field (5)D basis, from which the diagonal trigonal field splitting of the (5)T(2g) (O(h)) term is estimated as approximately 485 cm(-1), with the (5)A(g) (S(6)) component lower lying. High-field multifrequency (HFMF) EPR data and measurements of the magnetic susceptibility are also reported and can be satisfactorily modeled using the energies and wave functions derived from analysis of the INS data. The electronic and molecular structures are related through angular overlap model calculations, treating the imidazole ligand as a weak pi-donor.

Magnetism of the praseodymium halide thiosilicates Pr 3X[SiS 4] 2 (X=Cl, Br, I)

The magnetism of the three compounds Pr 3X[SiS 4] 2 (X=Cl, Br, I) has been measured in the temperature range between 1.7 and 300 K. For the theoretical calculations to interpret the magnetic behavior the angular overlap model was employed to reproduce the ligand field influence and the molecular field approach to take magnetic interaction into account.

Crystal-field analysis, upconversion, and excited-state dynamics for(U4+,U3+):Ba2YCl7single crystals

Single crystals of $({\mathrm{U}}^{4+},{\mathrm{U}}^{3+}):{\mathrm{Ba}}_{2}{\mathrm{YCl}}_{7}$ were grown by the Bridgman-Stockbarger technique. The ${\mathrm{U}}^{4+}$ and ${\mathrm{U}}^{3+}$ ions substitute for ${\mathrm{Y}}^{3+}$ and have ${C}_{1}$ site symmetry in ${\mathrm{Ba}}_{2}{\mathrm{YCl}}_{7}.$ Sixty energy levels of ${\mathrm{U}}^{4+}$ were assigned to $40000{\mathrm{cm}}^{\ensuremath{-}1}$ from absorption, excitation, and luminescence spectra, which encompasses all but the ${}^{1}{S}_{0}$ multiplet. A crystal-field analysis was performed by fitting 8 atomic and 19 crystal-field parameters to the experimental Stark levels. The values obtained from the fit had a standard deviation of $36.6{\mathrm{cm}}^{\ensuremath{-}1}$ and agreed with those calculated from the angular overlap model. Efficient luminescence was observed at 7 K from ${\mathrm{the}}^{4}{G}_{7/2}$ and ${}^{4}{F}_{9/2}$ levels of the ${\mathrm{U}}^{3+}$ ions and from the ${}^{1}{D}_{2}$ and ${}^{1}{I}_{6}$ of the ${\mathrm{U}}^{4+}$ ions with decay times of 0.5, 0.55, 9.2, and 4.3 $\ensuremath{\mu}\mathrm{s},$ respectively. For the ${\mathrm{U}}^{4+}$ ions, a very strong anti-Stokes emission was observed due to energy-transfer processes. The emission of the ${\mathrm{U}}^{3+}$ ions is strongly quenched by temperature in contrast to that of the ${\mathrm{U}}^{4+}$ ions for which emission was observed even at room temperature. Energy transfer between the ${\mathrm{U}}^{3+}$ and ${\mathrm{U}}^{4+}$ ions has been shown to occur in the $({\mathrm{U}}^{4+},{\mathrm{U}}^{3+})$ doped ${\mathrm{Ba}}_{2}{\mathrm{YCl}}_{7}.$

Tris(pyrazolyl)methanesulfonates: More Than Just Analogues of Tris(pyrazolyl)borate Ligands; N,N,N‐, N,N,O‐, and Other Coordination Modes

AbstractThe thallium(I) salts of tris(pyrazolyl)methanesulfonate (Tpms) and tris(3‐tert‐butylpyrazolyl)methanesulfonate (TpmstBu) have been used to prepare the following complexes: [(TpmstBu)ZnX] [X = Cl (1a), Br (1b), I (1c), Et (3), OAc (5a)], [(TpmstBu)NiX] [X = Cl (2a), Br (2b)], [(TpmstBu)CoCl(HpztBu)] (3), [(TpmstBu)Zn(μ‐OAc)(μ‐OH)Zn(TpmstBu)] (5b), [(TpmstBu)Cu(CO)] (6a), and [(Tpms)Cu(CO)] (6b). The solid‐state structures of 1b, 2a, 3, and 5b have been determined by X‐ray analysis. The optical spectra of 2a and 3 were investigated by means of the angular overlap model to elucidate their electronic structures in view of the underlying molecular geometries. Variable‐temperature NMR and IR spectroscopic studies show that Tpms and TpmstBu can act as N,N,N and N,N,O ligands. Both coordination modes are present in solution for the zinc complexes 1a,b and the copper carbonyl complexes 6a,b. The N,N,O bonding mode is entropically favoured in solution. For the nickel complexes 2a,b, the TpmstBu ligand acts as a tripodal nitrogen ligand in the solid state and in solution. For the dinuclear zinc complex 5b, one of the TpmstBu ligands acts as an N,N,O ligand and one as an N,O ligand. Complex 5b is one of the very few structural models of the dinuclear zinc enzymes phospholipase C and phosphotriesterase. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Diastereomers of copper(II) complexes exhibiting difference in coordination geometry by R- or S-1-phenylethylamine ligands in the solid state and structural conversion of crystals into solutions

Crystal structures of meso and optically active trans-bis(5,5-diphenylhydantoinato) bis(1-phenylethylamine)copper(II) complexes were determined. Distortion of [CuN 4] coordination geometries in the crystals was induced by chirality of 1-phenylethylamine ligands and their structural distortion in the solutions was estimated by angular overlap model on the basis of circular dichroism spectrum.

Trans-[CrX2([15]aneN4)]+(X=F,CI)의 전자분광학과 리간드장 해석

trans-<TEX>$[CrX_2([15]aneN_4)]ClO_4 ([15]aneN_4=1,4,8,12-tetraazacyclopentadecane; X=F, Cl)$</TEX>의 전자흡수 스펙트럼을 리간드장 이론으로 해석하였다. AOMX 프로그램을 사용하여 관측한 스핀허용 전이와 계산값을 최적화시켰다. 결정한 CFT 파라미터를 AOM, NSH 및 여러 가지 다른 파라미터와 관련시켜 구하고, 이를 화학적 견지에서 논의하였다. 리간드장 해석으로부터 이들 착물에서는 F 리간드가 강한<TEX>${\sigma}-$</TEX> 및 <TEX>${\pi}-$</TEX>주개인 반면에 Cl 원자는 Cr(III) 이온에 약한 <TEX>${\sigma}-$</TEX> 및 <TEX>${\pi}-$</TEX>주개 성질이 있음을 확인할 수 있었다. The electronic absorption spectra of trans-<TEX>$[CrX_2([15]aneN_4)]ClO_4\;([15]aneN_4$</TEX>=1,4,8,12-tetraazacyclopentadecane; X=F, Cl) complexes have been interpreted using the ligand field theory. An AOMX program is used to optimize the differences between the calculated and the observed positions for the spin-allowed transition bands. The crystal field theory(CFT) parameter is directly related to the angular overlap model(AOM), normalized spherical harmonic hamiltonians(NSH), and semiempirical parameters. The various ligand field parameters are discussed in terms of their chemical significances. According to the ligand field analysis, we can confirm that the fluoride ligand is a very strong <TEX>${\sigma}-$</TEX> and <TEX>${\pi}-$</TEX>donor while the chloride has weak <TEX>${\sigma}-$</TEX> and <TEX>${\pi}-$</TEX>donor properties toward chromium(III) ion.

Computer-Simulation Study of the Orthorhombic−Hexagonal Phase Change in Lanthanide Manganates (LnMnO3)

Static lattice simulation techniques are applied to modeling the structures of the lanthanide manganates (LnMnO3). New interatomic potentials are developed based on the Born model of the ionic solid supplemented by the angular overlap model to describe the nonspherical components of the Mn3+−O2- interactions. The new model correctly predicts the greater stability of hexagonal compared with orthorhombic structures for the system containing the smaller lanthanide ions. A detailed comparison of the simulated structures with experiment is presented.

Aqua Ions. 1. The structures of the [Ru(OH(2))(6)](3+) and [V(OH(2))(6)](3+) cations in aqueous solution: an EPR and UV-Vis study.

Spectroscopic data are presented for the [V(OH(2))(6)](3+) and [Ru(OH(2))(6)](3+) cations, from which inferences are drawn regarding their structures in aqueous solution. EPR and absorption spectra of solutions and glasses are supplemented by spectra of the aqua ions in various crystalline environments, and the electronic and molecular structures inter-related through elementary angular overlap model calculations. It is concluded that in aqueous solution the [Ru(OH(2))(6)](3+) cation is localized in the all-horizontal D(3)(d)geometry, whereas the structure of the [V(OH(2))(6)](3+) cation is close to T(h) symmetry. These results are consistent with the most energetically favored geometries predicted by ab initio calculations.

Reaction of Coordinated Ligands. III. Synthesis and Characterization of Some Lanthanide Complexes of 2,6‐Diacetylpyridine‐2‐thenoylpicolinoyl Dihydrazone

A new ligand, 2,6‐diacetylpyridine‐2‐thenoylpicolynoyl dihydrazone (H2dapthph), has been prepared. Complexes of the type [Ln(H2dapthph)Cl2]Cl (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb and Dy) have been synthesized and characterized by analytical, molar conductance, FAB mass, IR, NMR, electronic and emission spectral data. The bonding sites of the hydrazone are deduced from IR and NMR spectra and the ligand is found to bond to the metal ion in a hexadentate fashion. Electronic spectra of the complexes have been analyzed and the spectral parameters viz. nephelauxetic ratio (β), bonding parameter (b1/2), Sinha parameter (δ%), angular overlap covalency (η) and oscillator strength (P) were calculated and discussed. The symmetry around the Ln(III) ions is indicated from emission spectra of the Eu(III) complex.

Ligand field and density functional descriptions of the d-states and bonding in transition metal complexes

The d-orbital energy sequences for low symmetry transition metal complexes derived from Kohn-Sham density functional theory and ligand field theory are different due to each model's treatment of interelectron repulsion. The implications for providing a unified description of the underlying metal-ligand bonding are analysed and illustrated using conventional and time-dependent DFT. Previous detailed spectroscopic studies have established the d orbital sequence in planar coordination complexes containing pi-donor halide ligands as dx2-y2 >> dxy > dxz, dyz > dz2 while for a sigma-only system like [Pd(NH3)4]2+, ligand field approaches like the angular overlap model (AOM) or cellular ligand field (CLF) model predict dxz, dyz, and dxy, should be degenerate. However, the energies of the Kohn Sham (KS) 'd' orbitals of [PdCl4]2- and [Pd(NH3)4]2+ place dxy below the dxz/dyz pair. Direct use of the KS orbital eigenvalues in AOM or CLF analyses would imply both ligands are pi acceptors. This result is independent of the choice of functional or whether the calculation is carried out in vacuo or in a polarised continuum representing solvation by water. The origin of the difference between the KS and LFT d orbital sequences derives from their treatments of d-d interelectron repulsion. KS orbitals include interelectron repulsion contributions while LFT d orbitals do not. For a low-spin d8 complex, DFT gives less d-d interelectron repulsion in the xy plane leading to a lowering of dxy relative to dxy/dyz. This differential effect can be reversed qualitatively by progressively removing electron density from dz2 and placing it in dx2-y2. When about 0.6 electrons is rearranged, E(dxy) > E(dxz/dyz) for [PdCl4]2- and the dpi orbitals for [Pd(NH3)4]2+ are virtually degenerate. The wider ramifications of these interelectron repulsion effects are discussed for other symmetries. Excited d state energies for [PdCl4]2- are computed using both time dependent density functional theory (TDDFT) and determinant energies. The latter give the experimental sequence 1A2g < 1Eg < 1B1g while TDDFT gives 1Eg < 1A2g < 1B1g. Both give transition energies up to 30% lower than observed. A DFT analysis of the bonding energies in [PdCl4]2- indicates that the Pd-Cl pi bonding in the molecular plane is about 33% weaker than the out-of-plane pi interaction due to non-zero overlap between ligand orbitals. The normal LFT assumption of linear ligation may not always be valid.

On the electronic structure and spectroscopic properties of a pseudo-tetrahedral cationic cobalt(ii) tetraamine complex ? ([35]adamanzane)cobalt(ii)Electronic supplementary information (ESI) available: Table S1: Cartesian coordinates of the DFT optimized geometry of the [Co([35]adz)]2+ ion. Table S2: Results of experimental and calculated infrared absorption spectra for the [Co([35]adz)]2+ ion. See http://www.rsc.org/suppdata/dt/b3/b305712g/

The electronic structure and spectrum of the unusual pseudo-tetrahedral cobalt(II) coordination compound formed with the bicyclic tetraamine ligand 1,5,9,13-tetraazabicyclo[7.7.3]nonadecane ([35]adz) has been investigated. The ligand-field absorption spectrum of the quartet ground state of the [Co([35]adz)]2+ cation was resolved into five components, which were assigned by application of angular overlap model (AOM) calculations. Furthermore, density functional theory (DFT) and time-dependent DFT (TD-DFT) were applied to investigate the structure and absorption spectrum of the cation using the B3LYP functional in combination with various basis sets. The DFT calculations provided a geometry for the cation in excellent agreement with the crystal structure of [Co([35]adz)]ZnCl4. The theoretical investigation of the electronic spectrum of the cation shows that TD-DFT can successfully be applied to open shell transition metal compounds, although only spin-allowed, single electron transitions are accounted for.

Synthesis, structure, and magnetic behavior of a new chloride thiosilicate with neodymium Nd 3ClS 2[SiS 4

Single crystals of Nd 3ClS 2[SiS 4] were prepared from the elements. Data collection was carried out using a STOE image plate detector at 293 K. The compound crystallizes in the orthorhombic space group Pnma with eight familiar units in a cell of dimension: a=1240.3(2),b=1035.8(2),c=1616.4(3) pm The corresponding residual (all data) for the refined structures is 3.45%. In the crystal structure, the chloride ions form chains along [0 1 0] with trigonal coordination by the lanthanide ions. The magnetic behavior of powdered crystals was interpreted by ligand field calculations where the influence of the ligand field was taken into account by applying the angular overlap model and magnetic exchange by the molecular field approximation.