Ligand Field Calculations Research Articles

Zeeman effects in the NIR luminescence of Ti 2+-doped MgCl 2

High-resolution Zeeman luminescence experiments in the near-infrared spectral region were performed on a single crystal of the title compound. With the magnetic field parallel to the principal axis of the crystal ( H∥ z), first-order Zeeman splittings of the 1E g excited state and the 3A 2g trigonal component of the ground state were observed and g ∥-values of 1.66 and 1.99 were determine for excited and ground state, respectively. With the magnetic field perpendicular to the axis ( H⊥ z) no splitting was observed in the excited 1E g and a second-order splitting found in the 3A 2g ground state. Theoretical spectra obtained from a full ligand field calculation were shown to agree with the observed spectra.

Ligand field calculation of the lower electronic energy levels of the lanthanide monoxides

Abstract The ligand field theory applied to the lanthanide monoxides predicts that the lower electronic states of these molecules are due to the configuration 4 f N −1 6 s (4 f N for EuO and YbO) of the divalent lanthanide ion Ln 2+ . We present here the results of a ligand field calculation of the energies of the lower electronic states for all the stable rare-earth monoxides.

Bonding parameters of vanadyl ion in humic acid from the Jucu river estuarine region, Brazil

Natural and synthetized complexes of vanadyl ion with humic acid from a sediment of Rio Jucu's estuarine region have been studied by electron spin resonance (ESR) spectroscopy. ESR spectra of natural samples show, besides the VO 2+ ion in an axially symmetric environment, lines attributed to Mn 2+ and Fe 3+. Photoacoustic and ESR spectroscopies data and a LCAO-MO ligand field calculation were used to evaluate the bonding parameters for the synthesized vanadyl-humic acid complex. The values of the parameters suggest that VO 2+ groups in the humic acid molecules are at salycilate-type sites. A comparison of the position of the lines in the ESR spectra of natural and synthesized complexes suggests that the binding sites for vanadyl ions in the natural complex may also be of the salycilate type.

Pentaamminechromium(III) t2g3 Level Properties as Determined from Vibronic Spectra and Crystal Field Calculations

Abstract Low temperature (∼5 K) absorption and emission spectra of various halogenopentaamminechromium(III) salts have been recorded at high sensitivity in the intercombination region from pure microcrystalline powders and doped into corresponding rhodium complexes. Zero phonon and vibrational side bands are better resolved than reported in earlier investigations. They depend on the crystal lattice and allow a more detailed analysis of the vibrational fine structure. For carrying out reliable assignments to vibronic energy levels, the influence of the crystalline environment in different salts is found to be of major importance. Ligand field and angular overlap calculations are very helpful for solving the assignment problem, they can reproduce the proposed energy level scheme if symmetry adapted π-orbital expansion coefficients are introduced into the electron repulsion terms.

A re-interpretation of the recorded electronic spectrum and crystal structure of bis[2-(2-aminoethyl)aminoethanol]nickel(II) nitrate using the ULFM and calculated Racah parameters

The electronic spectrum of the bis[2-(2-aminoethyl)aminoethanol]nickel(II) nitrate complex was measured. An X-ray analysis revealed a C 1 symmetry. Application of the Unified Ligand Field Model and calculation of the Racah parameter B explained the similarity between the observed spectrum and those of octahedral high-spin Ni(II) complexes, and resulted in adjustments to the assignment of the spectrum. Effective ligand charges were calculated and explained. The symmetry, electronic spectrum and B value for bis(2,2′-oxybisethanamine)nickel(II) nitrate were anticipated.

The electronic structure of LaF: A multiconfiguration ligand field calculation

A zero-free-parameter ligand field model is used to account for the observed low-lying (E<10 000 cm−1) electronic states of LaF. The electronic structure of LaF is represented as the effect of a nonpolarizable point F− ligand on the two valence electrons of a free La+ atomic ion. Free-ion configuration interaction (CI) effects (represented by a parametric fit of the free La+ energy levels to Fk,Gk Slater–Condon electrostatic and ζ spin–orbit parameters) and ligand-driven CI (treated by Bk0 ligand field radial integrals evaluated using Hartree–Fock La+ orbitals) are included in the model. A series of calculations is described, from the simplest ‘‘primitive LFT model’’ which includes the three lowest-lying and most important configurations (6s2, 5d6s, 5d2) to the most elaborate ‘‘balanced s-polarized LFT model’’ which includes six configurations (6s2, 5d6s, 5d2, 6s6p, 5d6p, and 6p2) in order to account properly for s–p polarization effects. The inclusion of ligand-driven CI (metal-centered orbital polarization) effects shows that simple electrostatic atomic-ion-in-molecule models are capable of accounting for the electronic structure of many highly polar diatomic molecules having more than a single metal-centered valence electron.

Spectroscopic and theoretical studies of the unusual EPR parameters of distorted tetrahedral cupric sites: correlations to x-ray spectral features of core levels

X-ray spectral data and self-consistent field-Xa-scattered wave (SCF-Xa-SW) calculations are presented for D4h and D u CuC12in order to evaluate specific contributions to the small hyperfine in distorted tetrahedral copper sites and to compare the mechanism of hyperfine reduction in these complexes with that for the blue copper site in plastocyanin. Comparison of the 2p3,2 XPS data for the two geometries indicates that the extent of delocalization of the d,z+ ground state in the D u salt is slightly less than in the D4h complex. Multiplet splitting of satellite structure from Cu 3s photoemission shows no change going from D4h to D u CuCIz-, indicating that the indirect Fermi contact contribution to the hyperfine from the core Cu 3s level does not change between the two complexes. Analysis of X-ray edge data for Cs2CuC14 ( D u ) indicates that there is at most 5.8% 4p, mixed into the ground-state wave function, an amount that is insufficient to explain the reduced hyperfine in this distorted Td complex. SCF-Xa-SW calculations performed with sphere radii adjusted so that the ground-state wave function fits the experimental g values indicate that -70% of the reduction in All between D4h and D2d comes from increased orbital angular momentum in the ground state of the Du salt arising from decreased ligand field transition energies. In contrast, increased delocalization relative to D4h CUCI,~accounts for most of the reduction in the blue copper proteins. The remaining 30% of the reduction in All is associated with a -50 X lo4 cm-I reduction in Fermi contact between the two salts. Xa calculations of a number of Cu complexes with < D u symmetry indicate that this reduction is not associated with direct 4s mixing into the half-occupied ground state but is most likely due to increased polarization of the filled totally symmetric valence levels in DZd CuCI,” resulting from increased 4s mixing as compared with D,,, CuCIt-. These studies are then extended to include copper sites exhibiting rhombically split g and A values. Single-crystal optical and EPR studies on copper-doped bis( 1,2-dimethylimidazole)zinc(II) dichloride (Zn[Cu] (dmi),C12) combined with ligand field and SCF-Xa-SW calculations indicate that the rhombic features in these complexes can be explained through admixture of -3% d,z character in the ground-state wave function. Finally, the structurally uncharacterized blue copper protein stellacyanin, which also shows a rhombic EPR spectrum similar to that in Zn[C~](dmi)~Cl~, is considered. In contrast to the C, effective symmetry found in the structurally defined site in plastocyanin, stellacyanin is predicted to have C, effective symmetry. A ligand field calculation using the plastocyanin site as a starting point indicates that stellacyanin requires a stronger field ligand along the Cu-methionine coordinate to produce the observed dzz mixing.

An a b i n i t i o study of low-lying 5f→5f excitations in PuF6

The excited electronic states of PuF6 below 3 eV arise from 5f→5f transitions. These states have been investigated using ab initio wave functions based on a relativistic effective core potential (RECP) for plutonium and nonrelativistic ECP for the fluorines and double-zeta quality basis sets. The effects of electron correlation were included by configuration interaction, and the effects of spin-orbit coupling were included by diagonalizing the correlated wave function over an effective spin-orbit operator. The only previous calculations on PuF6 that include both the effects of configuration interaction (CI) and of spin-orbit (SO) coupling are the semiempirical ligand field calculations of Kugel et al. The agreement between the present work and that of Kugel et al. is truly remarkable, with the average difference in excitation energies being less than 0.03 eV for the nine lowest transitions. Both sets of results are in general agreement with recent gas-phase and matrix spectroscopic studies of PuF6.

Molecular Structure Determination Inferred from Highly Resolved 4A2g ↔ 2Eg, 2T1g Spectra and Ligand Field Calculations of Trigonally Distorted Hexaamminechromate(III)

AbstractHighly resolved vibronic spectra were measured at helium temperatures due to spin‐forbidden 4A2g ↔ 2Eg, 2T1g d—d transitions of hexaamminechromate(III) salts. Almost complete assignments of the detailed vibrational structure are presented including the band positions of all five spin‐orbit electronic origins of S6. The electronic level schemes can be rationalized by conventional ligand field calculations because for NH3‐ligands no π‐bonding is involved. From the electronic level splittings polar angles of trigonal distortions from CrN6 octahedra were determined to be Δα = 0.19° for the CdC‐salt, and 0.23° for the analogous copper compound. The phosphorescence spectra exhibit progressions mainly in the Jahn‐Teller active mode ν2(eg); from relative band intensities, bond length changes of the emitting excited state by a few mÅ are calculated.

Low symmetry distortions of hexahalo anions of Re(IV) and Os(IV) investigated by polarized absorption spectra and ligand field calculations

Polarized absorption spectra of intraconfigurational transitions of Re4+ and Os4+ in trigonal environments (D 3d site symmetry of host lattices) were measured at low temperature (110 K to 1·9 K). The vibronic side bands and electronic origins arising from electric and magnetic dipole transitions are assigned to appropriate term symbols. The vibrational fine structure is explained by normal vibrations with quanta closely related to those of the ground state. Some of the complex octahedra of doped species do not adopt the type of distortion (stretched or squeezed) to which they are predisposed by the host crystals. In the case where the space provided is not adequate for the doped compound, additional local distortions are present which are different for Re and Os. The degree of splitting due to the trigonal symmetry on octahedral Re4+ energy levels has been found always larger for the ground state, even though it has only spin degeneracy, than for the excited states. Ligand field theory is able to explain ...

Hochaufgelöste vibronische Spektren von Al(acac)3 : Cr3+/Highly Resolved Vibronic Spectra of Al(acac)3: Cr3+

Abstract Highly resolved emission spectra of Cr3+ doped Trisacetylacetonatoaluminum(III) have been measured at various temperatures. By comparison with absorption spectra of dilute crystals the three most intense peaks have been assigned to the same molecular zero phonon transition according to three inequivalent Cr3+ sites in the low temperature phase of the host crystal. The usually unobserved ground state splitting has been resolved (1.0 cm-1) in emission spectra at T = 1.9 K. Band assignments are confirmed by ligand Field calculations using complete trigonal perturbation matrices including spin-orbit coupling. From the obtained parameters K = 725 cm-1 and K′ = - 600 cm-1 the trigonal distortion of the chromium complex in the Al-crystal is determined. This indicates that the phase transition of the host crystal leads to rotations of rigid molecules while the molecular geometry remains.

Electronic Spectrum of the Co(II) Ion in the Columbite CoNb2O6 Host Lattice at 4.2 K

AbstractThe polarized absorption spectrum of the Co(II) ion in CoNb2O6 at 4.2 K in the range 5000 to 28000 cm−1 with the electric vector E parallel to all three crystallographic axes is reported. After a careful examination of the excited states and of the site symmetry, the bands are assigned as “ligand field bands”. As far as the intensity is concerned, the most contribution is due to the effect of the local distortion, but the effects of the spin–orbit coupling and vibronic interaction are also taken into consideration. The assignments are confirmed from the behaviour of the intensity of the polarized bands and from a ligand field calculation that fits the band energies very well.

Linear polarized absorption spectra of ReX 2−6 in trigonal crystals

Low-temperature single-crystal absorption spectra of ReX 2− 6 (X = F, Cl, Br) in different Sn host crystals of trigonal symmetry are recorded using polarized light. From symmetry selection rules band assignments are obtained. Ligand-field calculations can explain the type and degree of trigonal-field splitting. Low-symmetry ligand-field parameters obtained indicate that trigonally compressed or expanded ReX 2− 6 octahedra are present in different host lattices.

Spin-orbit electronic states of octahedral Pt-group d 6 complexes as derived from reflectance spectra and ligand field calculations

The 90 K diffuse reflectance spectra of some octahedral Rh(III), Ir(III) and Pt(IV) complex compounds with chloride, thiocyanate and amine ligands are reported. The spectra show in the visible and near ultraviolet distinct bands due to spin-orbit components of singlet-triplet d-d transitions which are explained by ligand field calculations including spin-orbit coupling considering all possible d-electron configurations. Model parameter sets are obtained by fitting the measured band peaks to possible transitions between calculated energy levels. For some of the bands the vibrational structure could be resolved which is assigned to metal-ligand stretching vibrations of the electronically excited complex octahedra with vibrational fundamentals lower than those of the ground state.

Relativistic calculation of the electronic structure of IrCl 63−

Relativistic MSXα calculations have been performed on a IrCl 6 3− cluster and compared with non-relativistic MSXα results obtained with identical sets of parameters. The impact of the relativistic effects on the photoionization energies is demonstrated; better agreement with the experimental spectrum is obtained. The variation of the spin—orbit parameters with the eigenvalues is discussed and the absorption spectrum is compared with both experimental results and ligand field calculations.

Spectroscopic Behavior of Iron(III) in Silicate Glass

The coordination of ferric iron was studied in lead silicate and lead‐sodium silicate glasses by optical spectroscopy in the region 11000 to 28500 cm−1.There is clear evidence from the spectra ofFe3+ octahedral and tetrahedral coordination, which is also supported by ligand field calculations.

Intraconfigurational absorption and magnetic circular dichroism spectra of Os4+ in Cs2ZrCl6 and in Cs2ZrBr6

Electronic d-d transitions within the t 2g 4 configuration of Os4+ doped into cubic crystals of Cs2ZrCl6 and Cs2ZrBr6 were studied by means of low temperature absorption and magnetic circular dichroism (MCD) spectroscopy. The direct observation of the complete manifold of states in both host systems is reported and leads to a reinterpretation of earlier work. Vibronic analysis and MCD allow assignment of all the electronic origins of this configuration. Their energies are compared to results of a ligand field calculation.

Metalloprotein models, location of the magnetic axes in low-symmetry complexes. Single crystal electron paramagnetic resonance, magnetic susceptibility anisotropy, and angular overlap ligand field calculations on a complex containing the distorted tetrahedral Co IIN 2O 2 coordination unit, bis(N-isopropylsalicyclaldiminato)cobalt(II)

Single-crystal and powder electron paramagnetic resonance (epr) spectra of bis(N-isopropylsalicylaldiminato)cobalt(II), Co(iPr-sal) 2, doped into the isomorphous zinc complexes were obtained at liquid helium temperatures. Principal molecular g-values of g x, 7.09; g y 0.57; and g z, <0.3, were obtained. The orientation of the principal magnetic axes with respect to the distorted tetrahedral Co IIN 2O 2 coordination unit of approximate C 2 symmetry was determined from the angular variation of the single-crystal epr signals using the method of Schonland. The x-axis approximately bisects the NCoO angles of the individual bidentate ligands, the y-axis is the approximate bisector of the NCoO angles formed between different ligands, while the z-axis is taken as the approximate molecular C 2 axis. Ligand field calculations employing the angular overlap model (AOM) predict principal molecular magnetic axis directions in excellent agreement with experiment. Principal crystal magnetic susceptibility anisotropies were measured by the critical torque method. The derived molecular susceptibilities were used to evaluate dipolar nuclear magnetic resonance shifts of ligand nuclei. When dipolar contributions to the observed shifts are accounted for, the unpaired electron spin delocalization patterns of the Co(iPr-sal) 2 and Ni(iPr-sal) 2 are quite similar. The relevance of these results to the problem of achieving a detailed understanding of the properties of cobalt(II)-substituted zinc metalloproteins is stressed.

ChemInform Abstract: LOW‐TEMPERATURE MAGNETIC PROPERTIES OF THREE VANADIUM(III) AND MANGANESE(III) β‐DIKETONATE COMPLEXES

The low-temperature (2-100 K) polycrystalline magnetic properties of V ( a ~ a c )M~ ,n ( a ~ a c )a~n,d Mn(trop)3 are reported [Hacac = 2,4-pentanedione and Htrop = tropolone]. For V(acac), the zero-field splitting (D) is 7.7 cm-', gI1 = 1.96 and g , = 1.78, all compatible with the reinterpreted optical spectrum. The magnetic data for Mn ( a ~ a c h) a~v e been interpreted with D = 3.1 cm-' and g = 2.00 and are also compatible with ligand field calculations based on the reinterpreted optical spectrum. In Mn(trop), there appears to be a very weak intermolecular coupling through the tropolonate ligands, the magnetic parameters being D = -2.6 cm-], g = 2.00, and J = -0.18 cm-l.

Low-temperature magnetic properties of three vanadium(III) and manganese(III) .beta.-diketonate complexes

The low-temperature (2-100 K) polycrystalline magnetic properties of V ( a ~ a c )M~ ,n ( a ~ a c )a~n,d Mn(trop)3 are reported [Hacac = 2,4-pentanedione and Htrop = tropolone]. For V(acac), the zero-field splitting (D) is 7.7 cm-', gI1 = 1.96 and g , = 1.78, all compatible with the reinterpreted optical spectrum. The magnetic data for Mn ( a ~ a c h) a~v e been interpreted with D = 3.1 cm-' and g = 2.00 and are also compatible with ligand field calculations based on the reinterpreted optical spectrum. In Mn(trop), there appears to be a very weak intermolecular coupling through the tropolonate ligands, the magnetic parameters being D = -2.6 cm-], g = 2.00, and J = -0.18 cm-l.