D-orbital Splitting Research Articles

Strong Ligand Field Effects of Blue Phosphorescent Ir(III) Complexes with Phenylpyrazole and Phosphines

In the paper, we describe new Ir complexes for achieving efficient blue phosphorescence. New blue-emitting mixed-ligand Ir complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dppz)(PPh3)2(H)(L) (Ll= Cl, NCMe+, CN), [dppz = 3,5-Diphenylpyrazole] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To gain insight into the factors responsible for the emission color change and the variation of luminescence efficiency, we investigate the electron-withdrawing capabilities of ancillary ligands using DFT and TD-DFT calculations on the ground and excited states of the complexes. To achieve deep blue emission and increase the emission efficiency, (1) we substitute the phenyl group on the 3-position of the pyrazole ring that lowers the triplet energy enough that the quenching channel is not thermally accessible and (2) change the ancillary ligands coordinated to iridium atom to phosphine and cyano groups known as very strong field ligands. Their inclusion in the coordination sphere can increase the HOMO-LUMO gap to achieve the hypsochromic shift in emission color and lower the HOMO and LUMO energy level, which causes a large d-orbital energy splitting and avoids the quenching effect to improve the luminescence efficiency. The maximum emission spectra of Ir(dppz)(PPh3)2(H)(CI) and Ir(dppz)(PPh3)2(H)(CN) were in the ranges of 439, 432 nm, respectively.

A Comparative Investigation on the JT Effect in Triangular Compounds of NaMnO2, NaNiO2 and NaTiO2

We present a study on the Jahn—Teller (JT) distortions of the TiO6, NiO6 and MnO6 complexes in NaTiO2, NaNiO2 and NaMnO2 triangular compounds with a C2/m structure. The JT vibronic normal modes are found to be Q3, Q′4 and Q6 by the group symmetry on the C2/m structure. The magnitude of the normal coordinates (Q3, Q′4, Q6) and the structural parameters of distorted octahedra MO6 (M=Ti, Ni, Mn) are obtained and in good agreement with experimental data. The energy level splitting of 3d orbitals and the highest occupied molecular orbital (HOMO) character in the MO6 complex are also calculated in accordance with the JT distortions. These results provide a first insight into the groundstate and magnetic properties of distorted triangular compounds AMO2.

Forward molecular design for highly efficient OLED emitters: A theoretical analysis of photophysical properties of platinum(ii) complexes with N-heterocyclic carbene ligands

The electronic structures and photophysical properties of eight Pt-complexes with different N-heterocyclic carbene ligands and potential to serve as light emitting diode materials were investigated by density functional theory and time-dependent density functional theory, employing the BP86 functional for geometry optimisations, SAOP potential for excited state calculations and all-electron TZ2P basis set throughout. Non-radiative and radiative decay rate constants were determined for each system through analyses of the geometric relaxations, d-orbital splitting and spin-orbit couplings at the optimised S(0) and T(1) geometries. Three Pt-systems bound to two N-heterocyclic carbenes were shown to be nonemissive, while a fourth was shown to be emissive from the T(1) excited state. Similar T(1)-initated emission was observed for three other Pt-systems investigated, each bound to four N-heterocyclic carbenes, while a fourth similarly tetra-ligated system showed T(2)-initation of emission. The results highlight the coupling of ligand-identity to photophysical properties and more importantly, the potential for rational optimisation and tuning of emission wavelengths and phosphorescent efficiencies. Encouragingly, two of the tetra-N-heterocyclic carbene ligated systems show strong potential to serve as highly-efficient blue and green light emitting materials, respectively.

Cu deep level center in CdTe solar cell

Cu would be doped and form deep level centers easily in CdTe solar cells. The deep level centers in ZnTe back contact and graphite back contact CdTe solar cells were studied by deep level transient spectroscopy(DLTS). The electronic density of states on zinc blende CdTe，VCd system and CdTe doping Cu were analyzed with density functional theory. The d-orbital splitting of Cu2+ in C3v and Td fields was obtained. The results show that two deep centers Ev+0206 eV and Ev+0122 eV，respectively，are attributed to substitutional Cu，energy of CdTe is reduced after Cu doping，and Cu could replace Cd.

Structural study of glasses in the binary system NaPO 3–MoO 3 by X-ray absorption spectroscopy at the Mo K and L 3 edges

Glasses were prepared in the binary system (100 − x)NaPO 3– xMoO 3 with x varying from 0 to 50 mol%. An increase in the MoO 3 concentration promotes a strong absorption in the visible and near infrared attributed to Mo reduction during glass synthesis. X-ray absorption measurements were performed at the Mo K and L 3 edges to investigate both the coordination number and oxidation state of Mo in these glasses. The evolution of the pre-peak observed at the K edge suggests that Mo atoms are six-fold coordinated in these glasses. This hypothesis was confirmed by data obtained at the Mo–L 3-absorption edge. Since the final electronic states at the L 3-absorption edge are mostly orbitals of d-character which are splitted by the ligand field, the amplitude of the d-orbital splitting could be estimated and the related coordination number of Mo obtained. Finally, the oxidation state of Mo could be related with a change of the white line intensity at the Mo–L 3 edge. These results confirm that the optical absorption in the visible is due to Mo reduction and that transparent samples prepared by slow cooling contain less reduced Mo species.

Playing the Quantum Chemical Slot Machine: An Exploration of ABX2 Compounds

The structures and electronic properties of a number of real and hypothetical ABX(2) compounds sharing (or evolving from) a single P4/mmm structural type are examined. These include the known CaCuO(2) and SrFeO(2) phases. A number of variations of this P4/mmm ABX(2) framework, some obvious, some exotic, all with a chemical motivation, were investigated: A = alkali metal, alkaline earth metal or La, B = Ti, Fe, Cu, or Pt, and X = C, O, S, C(2), H(2), or F. Careful attention was given to the d-orbital splitting patterns and magnetic states (ferromagnetic or antiferromagnetic) of these compounds, as well as their stability gauged by phonon dispersions and energetics. The most interesting as yet unmade compounds that emerged were (a) a carbide SrFe(C(2))(2), containing C(2) units with a C-C distance of 1.267 A, (b) an AeTiO(2) series, with Ti-Ti bonding, part sigma, part pi, tuned by the Ae(2+) cation size, and (c) NaPtF(2), for which a second structure was found, containing a hexagonal layering of (PtF(2))(-) molecules.

The d-Hamiltonian – A new approach for evaluating optical spectra of transition metal complexes

The full multicentre molecular Hamiltonian in local density approximation for a mononuclear transition metal complex is transformed into a single-centre Hamiltonian explicitly including overlap, covalency and ligand-field effects. The orbital interactions of the metal d-orbitals with the ligand orbitals appear as a repulsive pseudopotential yielding the dominant contribution to the ligand-field splitting. This repulsive pseudopotential exhibits the same angular dependence as the electrostatic potential from the ligands entering the Hamiltonian of ligand-field theory. For this reason, ligand-field theory very often yields the correct splitting pattern of the d-orbitals. The radial part, however, is considerably different from the simple expression of ligand-field theory. In particular, there is no general theoretical justification for a R − 5-dependence of the ligand-field splitting even for complexes of cubic symmetry. The reliability and capability of this new approach is demonstrated by calculating the d-orbital splitting pattern for a number of selected systems.

Reverse Photochromic Behavior of an Iron−Magnesium Complex

We have obtained a novel heterobimetallic iron-magnesium complex, (THF)4Mg(mu-Br)2FeBr2 (THF = tetrahydrofuran), which showed reverse photochromism in THF. The response exhibited in this system is associated with d-orbital splitting of the Fe atom and a change in the molecular aggregation state (dimerization).

Atom transfer as a preparative tool in coordination chemistry. Synthesis and characterization of Cr(V) nitrido complexes of bidentate ligands.

The transfer of a terminal nitrido ligand from Mn(V)(N)(salen) to Cr(III) complexes is explored as a new preparative route to Cr(V) nitrido complexes. Reaction of Mn(V)(N)(salen) with labile CrCl(3)(THF)(3) in acetonitrile solution precipitates [Mn(Cl)(salen)].(CH(3)CN) and yields a solution containing a mixture of Cr(V) nitrido species with only labile auxiliary ligands. From this solution Cr(V) nitrido complexes with bidentate monoanionic ligands can be obtained in high yields. Five coordinate complexes of 8-hydroxoquinolinate (quin), 1,3-diphenylpropane-1,3-dionate (dbm), and pyrrolidinedithiocarbamate (pyr-dtc) have been structurally characterized: Cr(N)(quin)(2) (1) crystallizes as compact orange prisms in the triclinic space group P with cell parameters a = 7.2450(6) A, b = 8.1710(4) A, c = 13.1610(12) A, alpha = 80.519(6) degrees, beta = 75.721(7) degrees, gamma = 75.131(5) degrees, V = 725.47(10) A(3), Z = 2. Cr(N)(dbm)(2) (2) crystallizes as green rhombs in the orthorhombic space group Pbca with cell parameters a = 14.6940(6) A, b = 16.4570(18) A, c = 19.890(3) A, V = 4809.8(8) A(3), Z = 8. Cr(N)(pyr-dtc)(2) (3) crystallizes as orange prisms in the monoclinic space group P21/c with cell parameters a = 14.8592(14) A, b = 8.5575(5) A, c = 11.8267(12) A, beta = 106.528(7) degrees, V = 1441.7(2) A(3), Z = 4. Complexes 2 and 3 represent new coordination environments for first row transition metal nitrido complexes. The d-orbital energy splitting in these systems with relatively weak equatorial donors differs significantly from the pattern in vanadyl and the previously known first row transition metal nitrido complexes. The d(x)2(-)(y)2 orbital in 2 and 3 is lower in energy and well resolved from the M-N pi orbitals [d(zx),d(yz)].

Spin-State Alteration from Sterically Enforced Ligand Rotation in Bis(indenyl)chromium(II) Complexes1

The rotational orientation of cyclopentadienyl rings usually has no effect on d-orbital energy levels and splitting in transition metal complexes. With related but less symmetrical carbocyclic ligands, however, the magnetic properties of the associated complexes can be altered by the alignment of the ligands. Examples of this effect are found in substituted organochromium(II) bis(indenyl) complexes. The monosubstituted compounds (1-RC(9)H(6))(2)Cr (R = t-Bu, SiMe(3)) are prepared from the substituted lithium indenides and CrCl(2) in THF; they are high-spin species with four unpaired electrons. Their spin state likely reflects that in the unknown monomeric (C(9)H(7))(2)Cr, which is calculated to have a high-spin (S = 2) ground state in the staggered configuration (180 degrees rotation angle). However, the analogous bis(indenyl) complexes containing t-Bu or SiMe(3) groups in both the 1 and 3 positions on the indenyl ligands ((1,3-R(2)C(9)H(5))(2)Cr) are low-spin compounds with two unpaired electrons. X-ray diffraction results indicate that [1-(t-Bu)C(9)H(6)](2)Cr exists in a staggered conformation, with Cr-C (av) = 2.32(4) A. In contrast, the average Cr-C distances in [1,3-(t-Bu or SiMe(3))(2)C(9)H(5)](2)Cr are 2.22(2) and 2.20(2) A, respectively, and the rings are in a gauche configuration, with rotation angles of 87 degrees. The indenyl conformations are sterically imposed by the bulk of the t-Bu and SiMe(3) substituents. The change from a staggered to a gauche indenyl orientation lowers the symmetry of a (C(9)H(7))(2)M complex and allows greater mixing of metal and ligand orbitals. Calculations indicate that previously nonbonding pi orbitals of the indenyl anion are able to interact with the chromium d orbitals, producing bonding and antibonding combinations. The latter remain unpopulated, and the resulting increase in the HOMO-LUMO gap forces the complexes to adopt a low-spin configuration. The possibility of using sterically imposed ligand rotation as a means of spin-state manipulation makes indenyl compounds a potentially rich source of magnetically adjustable molecules.

Spectroscopic studies of Pyrococcus furiosus superoxide reductase: implications for active-site structures and the catalytic mechanism.

The combination of UV/visible/NIR absorption, CD and variable-temperature magnetic circular dichroism (VTMCD), EPR, and X-ray absorption (XAS) spectroscopies has been used to investigate the electronic and structural properties of the oxidized and reduced forms of Pyrococcus furiosus superoxide reductase (SOR) as a function of pH and exogenous ligand binding. XAS shows that the mononuclear ferric center in the oxidized enzyme is very susceptible to photoreduction in the X-ray beam. This observation facilitates interpretation of ground- and excited-state electronic properties and the EXAFS results for the oxidized enzyme in terms of the published X-ray crystallographic data (Yeh, A. P.; Hu, Y.; Jenney, F. E.; Adams, M. W. W.; Rees, D. C. Biochemistry 2000, 39, 2499-2508). In the oxidized state, the mononuclear ferric active site has octahedral coordination with four equatorial histidyl ligands and axial cysteinate and monodentate glutamate ligands. Fe EXAFS are best fit by one Fe-S at 2.36 A and five Fe-N/O at an average distance of 2.12 A. The EPR-determined spin Hamiltonian parameters for the high-spin (S = (5)/(2)) ferric site in the resting enzyme, D = -0.50 +/- 0.05 cm(-1) and E/D = 0.06, are consistent with tetragonally compressed octahedral coordination geometry. UV/visible absorption and VTMCD studies facilitate resolution and assignment of pi His --> Fe(3+)(t(2g)) and (Cys)S(p) --> Fe(3+)(t(2g)) charge-transfer transitions, and the polarizations deduced from MCD saturation magnetization studies indicate that the zero-field splitting (compression) axis corresponds to one of the axes with trans-histidyl ligands. EPR and VTMCD studies provide evidence of azide, ferrocyanide, hydroxide, and cyanide binding via displacement of the glutamate ligand. For azide, ferrocyanide, and hydroxide, ligand binding occurs with retention of the high-spin (S = 5/2) ground state (E/D = 0.27 and D < 0 for azide and ferrocyanide; E/D = 0.25 and D = +1.1 +/- 0.2 cm(-1) for hydroxide), whereas cyanide binding results in a low-spin (S = 1/2) species (g = 2.29, 2.25, 1.94). The ground-state and charge-transfer/ligand-field excited-state properties of the low-spin cyanide-bound derivative are shown to be consistent with a tetragonally elongated octahedral coordination with the elongation axis corresponding to an axis with trans-histidyl ligands. In the reduced state, the ferrous site of SOR is shown to have square-pyramidal coordination geometry in frozen solution with four equatorial histidines and one axial cysteine on the basis of XAS and UV and NIR VTMCD studies. Fe EXAFS are best fit by one Fe-S at 2.37 A and four Fe-N/O at an average distance of 2.15 A. VTMCD reveals a high-spin (S = 2) ferrous site with (Cys)S(p) --> Fe(2+) charge-transfer transitions in the UV region and (5)T(2g) --> (5)E(g) ligand-field transitions in the NIR region at 12400 and <5000 cm(-1). The ligand-field bands indicate square-pyramidal coordination geometry with 10Dq < 8700 cm(-1) and a large excited-state splitting, Delta (5)E(g) > 7400 cm(-1). Analysis of MCD saturation magnetization data leads to ground-state zero-field splitting parameters for the S = 2 ground state, D approximately +10 cm(-1) and E/D approximately 0.1, and complete assessment of ferrous d-orbital splitting. Azide binds weakly at the vacant coordination site of reduced SOR to give a coordination geometry intermediate between octahedral and square pyramidal with 10Dq = 9700 cm(-1) and Delta (5)E(g) = 4800 cm(-1). Cyanide binding results in an octahedral ferrous site with 10Dq = 10,900 cm(-1) and Delta (5)E(g) = 1750 cm(-1). The ability to bind exogenous ligands to both the ferrous and ferric sites of SOR is consistent with an inner-sphere catalytic mechanism involving superoxide binding at the ferrous site to yield a ferric-(hydro)peroxo intermediate. The structural and electronic properties of the SOR active site are discussed in relation to the role and bonding of the axial cysteine residue and the recent proposals for the catalytic mechanism.

Molecular and electronic structure of nitridocyanometalates of chromium(V) and manganese(V): a combined experimental and DFT study.

The six-coordinate complexes [M(N)(CN)5]3- (M = Cr, Mn) have been isolated as salts of robust rhodium amine complexes. [Rh(en)3][Mn(N)(CN)5].H2O (1) and [Rh(tn)3] [Cr(N)(CN)5].2H2O (2) have been characterized by single-crystal X-ray crystallography: 1 crystallizes in the hexagonal space group P6(3) with a = b = 15.810(2) A, c = 13.844(3) A, V = 2996.8(8) A3, and Z = 6; 2 crystallizes in the orthorhombic space group Pbcn with a = 9.723(1) A, b = 14.564(2) A, c = 31.498(4) A, V = 4460.3(8) A3, and Z = 8. In 1, all the anions are oriented with their Mn identical to N directions almost coparallel to the crystallographic 3-fold axis. Polarized single-crystal UV-vis spectroscopy of 1 confirms the validity of the Jørgensen-Ballhausen-Gray d-orbital splitting scheme with the lowest energy transition being dxy-->[dyz,dzx]. Single-crystal EPR spectroscopy of [Cr(N)(CN)5]3- diluted into 1 shows the hyperfine (53Cr) and super-hyperfine (14N) tensors to be quite anisotropic with different major axes. For the hyperfine interaction we observe A Parallel > A Perpendicular, whereas, for the super-hyperfine interaction to the terminal nitrido ligand, the reverse ordering is found: A Perpendicular > A Parallel. The complexes [M(N)(CN)5]3-, trans-[M(N)(CN)4(py)]2-, and [M(N)(CN)4]2- (M = Cr, Mn) were investigated by DFT methods. Good reproduction of the molecular structures, vibrational, and UV-vis spectra was obtained. However, pronounced differences between local density and gradient corrected functionals were observed in the description of the weak bonding to the ligands trans to the nitrido ligand. For the five-coordinate [M(N)(CN)4]2- complexes the LUMO is predicted to be a strongly admixed dz2(M)-pz(M) hybrid.

Periodic trends in the diatomic monoxides and monosulfides of the 3d transition metals

Non-local, density functional calculations have been performed on the ground and low-lying excited states of the 3d transition metal monoxide and monosulfide molecules. Periodic trends in properties such as bond lengths, bond energies, vibrational force constants and dipole moments are examined. The variations in the bond lengths and energies are compared to those in the monoxide and monosulfide solids. Analysis of the electronic structures of the molecules reveals the d-orbital splitting to be dπ > dσ ≥ dδ and shows the non-bonding role of the dσ and dδ functions. This sequence mirrors that in the electronically related dichloride molecules and leads to similarities in the periodic trends with those in the solids. Systematic errors in the calculated bond energies and vibrational frequencies are identified. The successful use of a correctly parameterized ligand-field model is reported allowing quantitative reproduction of the ‘d–d’ spectra of the monoxide molecules and the prediction of band positions of unassigned transitions.

Bond Characterization of Metal Squarate Complexes [MII(C4O4)(H2O)4; M = Fe, Co, Ni, Zn

Tetraaqua metal squarate complexes, M(C4O4)(H2O)4, (M = Fe, Co, Ni, Zn), are known to have a polymeric chain structure with C4O42- as a bridge (μ-2) ligand between two metal ions in the trans position. Each metal ion is bonded to two C4O42- and four water molecules. They are all isostructural with space group C2/c. A complete Ewald sphere of data is measured at 120 K up to 2θ of 100−120° using Mo Kα radiation for each complex. Such carefully measured intensities are used to investigate the detailed electron density distribution in order to understand the chemical bonding and the d-orbital splitting of the metal ions subjected in such a ligand field. Results on the electron density distribution will be presented in the form of deformation density and of Laplacian maps. Deformation density will be presented in terms of experimental Δρx-x, Δρm-a (multipole model), and of theoretical Δρ derived from the HF and DFT calculations. The interesting bent bond feature on the four-membered ring ligand C4O42- is explicitly demonstrated by the deformation density distribution and the bond path of the cyclic carbon−carbon bond. The asphericity in electron density distribution around the metal ion is also clearly illustrated in these compounds both in the deformation density and in Laplacian of the density. The comparison on the series of 3d-transition metal complexes will be made not only by the deformation density distribution and by the Laplacian of the density but also by the d-orbital population and by the associated topological properties at the bond critical point. The total number of d-electrons from the experiments are 6.05, 6.88, 7.89, and 8.40, respectively, for Fe(II), Co(II), Ni(II), and Zn(II) ions in these compounds. A comparison between experiment and theory is made for the Ni complex.

Ground state properties of a high-spin Mn12O12 molecule in an organic compound

The electronic structure and the magnetism of a Mn12O12 molecule at ground state have been studied by density functional theory with a local spin density approximation. We have found that the magnetic moments of Mn ions in the tetrahedron and those of Mn ions in the crown of the Mn12O12 molecule align antiferromagnetically. The average moment per Mn ion is about 3.07μB in the tetrahedron and 4.07μB in the crown. The total spin amounts to 20.0μB which is in agreement with recent experimental results. The significant difference of magnetic moments between Mn ions at two sites is attributed to the different exchange splitting of 3d orbitals. However, the charge difference between the two kinds of Mn ions is as small as 0.22 electrons. The charge density and the spin density exhibit strong directional dependence, which indicates the strong anisotropy in this molecule.

Charge density studies in NH4[Ti(C2O4)2].2H2O crystals at two wavelengths

The crystal structure of ammonium bis-μ-oxalatotitanate(III) dihydrate, NH4[Ti(C2O4)2].2H2O, is reinvestigated by careful single-crystal X-ray diffraction using Mo Kα (room temperature and 130 K) and Ag Kα radiation (room temperature). It crystallizes in noncentrosymmetric hexagonal space group P6422, with cell parameters a = 8.947 (2), c = 10.898 (1) Å, Z = 3, F(000) = 423, Mr = 278.1, Dx = 1.833, R = 0.035, wR = 0.030 for 2296 observed reflections with I ≥ 2σ(I), on Ag Kα data. Accurate data measurement was applied using two wavelengths (0.7107 Å for Mo Kα and 0.5609 Å for Ag Kα in order to study the charge density distribution and also to investigate the wavelength effect in such investigations. A total of 22650 and 20298 reflections were measured using Mo Kα radiation at room temperature and 130 K, respectively, and 18361 reflections using Ag Kα radiation. The Ti atom is coordinated by four oxalate dianions with coordination number 8 in an approximate symmetry of D 4 geometry. Each oxalato ligand is bridged between two Ti atoms and forms an infinite polymeric spiral column along the c axis. The deformation density maps, Δρ, obtained from all three data sets are consistent and agree well. Although the formal charge of Ti in this complex is 3+, with only one electron on the 3d orbitals expected, the net atomic charge on Ti from this study is, ~2+. Charge asphericity around the Ti atom caused by the splitting of 3d orbitals is clearly observed in the deformation density. The d-orbital populations are evaluated from multipole refinement. The expected d 1 electron is mainly located in the dZ2 orbital.

Electron-density distribution in a crystal of potassium tetrafluoronickelate, K2NiF4

Dipotassium tetrafluoronickelate(II), K 2 NiF 4 , M r =212.90, tetragonal, I4/mmm, a=4.0130 (6), c=13.088 (2) A, V=210.78 (4) A 3 , Z=2, T=300 K, D x =3.36 Mg m -3 , Mo Kα, λ=0.7107 A, μ=656 mm -1 , F(000)=204, final R=0.018 for 698 unique reflections [I>2σ(I)]. Charge asphericity around the Ni atom caused by the splitting of 3d orbitals is clearly observed in the deformation density. Although the exact site symmetry at the Ni atom is D 4h , the local geometry around Ni is practically O h with Ni-F distances of 2.0065 (3) and 2.0062 (8) A

Local site symmetry of dispersed molybdenum oxide catalysts: XANES at the Mo L2,3-edges

The local site symmetry of nanodispersed molybdenum oxide phases have been determined for the first time using X-ray absorption near edge spectroscopy (XANES) at the Mo L[sub 2,3]-edges. Local site symmetries varying between pure tetrahedral coordination through mixed symmetries to pure octahedral coordination were determined for species present at concentrations above and below a submonolayer. X-ray absorption near-edge spectra at the Mo L[sub 2,3]-edges were obtained for a series of supported molybdate catalysts and Mo[sup 6+] reference materials with a range of oxygen coordination types. Basic ligand field concepts can be used to interpret the spectra. Tetrahedral molybdates display d-orbital splitting in the 1.8-2.0-eV range, whereas octahedrally coordinated molybdates display split peaks in the 3.0-4.5-eV range. The direct comparison between a complete set of molybdenum reference compounds and dispersed magnesium oxide-supported molybdate catalysts has been used to determine the detailed symmetries of the dispersed molybdenum phases that are present as amorphous, crystalline, and mixed phases. 26 refs., 5 figs., 1 tab.

Magnetic exchange and zero-field splitting in the d3[Os V Cl6]? ion

The principal magnetic susceptibilities, and magnetisations, of [PPh4][OsVCl6] are reported for temperatures between 4.5 and 300 K at 1.0 T, and between 2.5 and 20 K at 0.25 to 5.0 T respectively. The data are interpreted in terms of zero-field splitting of the ground 4A2g term [D=–16.5(1.5) cm–1], large because of the high spin-orbit coupling constant for the Os5+ ion, with smaller Ising antiferromagnetic exchange [J=–8(2) cm–1], probably of one-dimensional nature, given the constraints of the crystal structure. This appears to be the first observation of one-dimensional magnetic exchange in a heavy transition-metal complex. A DV-Xα calculation on the [OsCl6]– ion in its experimental tetragonal geometry is included, which estimates, inter alia, the overall d-orbital splitting, 10Dq, the low-symmetry energy splitting of the t2g orbitals, and the orbital angular momentum reduction factor, k. Crystal-field calculations, using similar values of these parameters, together with reasonable values for spin-orbit coupling and Racah parameters, agree with the magnetic behaviour and optical spectrum. In particular the large negative, zero-field splitting parameter, D, is reproduced.

The crystal field theory for D2d symmetric complexes and the splitting of d-orbitals of Mo5+ in Mo[S2CN(C2H5)2]4I3

The energy order assignment of the d-orbitals of Mo5+ in Mo[S2CN(C2H5)2]4I3 given by Jasimet al. (1985) is restudied and corrected. It is indicated that, in general, the energy order of the d-orbitals of D2d symmetric complexes is depending on the bond angles and bond lengths of the ligands, thus there cannot be any universal energy order.