Isolation of a Perfectly Linear Uranium(II) Metallocene

Reduction of the uranium(III) metallocene [(η⁵‐C₅ⁱPr₅)₂UI] ( 1 ) with potassium graphite produces the “second‐generation” uranocene [(η⁵‐C₅ⁱPr₅)₂U] ( 2 ), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground‐state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f³ 6d¹. Appreciable covalent contributions to the metal‐ligand bonds were determined from a computational study of 2 , including participation from the uranium 5f and 6d orbitals. Whereas three unpaired electrons in 2 occupy orbitals with essentially pure 5f character, the fourth electron resides in an orbital defined by strong 7s‐6d mixing.     

EPR-Untersuchungen am 4d5-“low-spin”-Komplex [Tc(bipy)3](PF6)2 (bippy = α,α′-Bipyridyl)

EPR studies on the 4D⁵ “low-spin” Complex [Rc(bipy)₃](PF₆)₂ (bipy = α, α′- bipyridyl) An EPR study of the trigonally distorted octahedral 4d⁵ “low-spin” (S =1/2) complex [Tc(bipy)₃](PF₆)₂ is reported. The spin-Hamiltonian parameters are used to estimate the ligand-field splitting within the ²T₂ manifold; the unpaired electron occupies the d_xy orbital (E′state). From the ⁹⁹Tc hyperfine interactions it is found that extensive metal-ligand covalent interactions reduce the spin-orbit coupling constant to about 49% Using an axially symmetric model a consistent parameter set is obtained for positive value of g∥?, A∥?^Tc, A⊥^Tc and a negative value of g⊥.     

Probing Multiconfigurational States by Spectroscopy: The Cerium XAS L3-edge Puzzle

The Ce L₃ edge XAS spectra of CeO₂ and cerocene [Ce(C₈H₈)₂] were calculated with relativistic ab-initio multireference wavefunction approaches capable of reproducing the observed spectra accurately. The study aims to resolve the decades-long puzzle regarding the relationship between the number and relative intensities of the XAS peaks and the 4f electron occupation in the ground state (GS) versus the core-excited states (ESs). CeO₂ and cerocene exemplify the different roles of covalent bonding and wavefunction configurational composition in the observed intensity patterns. Good agreement is found between the calculated GS 4f-shell occupations and the value derived from XAS measurements using peak areas (n_f). The identity of the two-peaked Ce L₃ edge is fully rationalized from the perspective of the relaxed wavefunctions for the GS and core ESs. The states underlying the different peaks differ from each other in a surprisingly simple way that can be associated with 4f¹ vs. 4f⁰ sub-configurations. Furthermore, part of one of the cerocene spectral peaks is associated with 4f² sub-configurations. The pattern therefore reveals excited states that can be interpreted in terms of Ce IV and III oxidation numbers, as long assumed, with Ce II states additionally appearing in the cerocene spectrum. While this work demonstrates the rough accuracy of the conventional approach to determining n_f from Ce L₃-edge XAS, limitations are highlighted in terms of the ultimate accuracy of this approach and the potential of observing new types of excited states. The need to determine the sources of n_f by calculations, is stressed.     

On the Bond Length Change upon 4f 1 → 5d 1 Excitations in Eightfold Coordination: CaF2:Ce3+ Cubic Defects

The bond lengths of 4f ¹ and 5d ¹ electronic states of cubic (CeF₈)⁵⁻ defects in fluorite have been calculated using quantum mechanical embedding, spin-free relativistic Hamiltonian, and dynamic electron correlation through second-order perturbation theory. The results predict the bond length between Ce and the surrounding eight F to shorten upon 4f ¹ → 5d ¹ excitation. This result coincides with previous findings for lanthanide and actinide ions in sixfold octahedral complexes where the ligand field splitting of the 5d (6d) orbitals is inverted with respect to the eightfold cubic field splitting. Altogether, the results of sixfold and eightfold coordination indicate that the bond shrinkage experienced upon 4f ⁿ to 4f ^n-15d ¹ excitations (5f ⁿ to 5f ^n-16d ¹ in the actinides) seems to be a general result of f-element complexes. These theoretical results contradict a widespread assumption according to which the bond length increases upon f→ d excitation and, therefore, experimental measurements of the sign of the bond length distortion that either validate or refute the quantum chemical predictions are most desirable.     

X-Ray Photoelectron Study of Thorium Silicate ThSiO4 · nH2O and Uranium Silicate USiO4·nH2O

The naturally occurring compounds of thorium ThSiO₄, ThSiO₄· nH₂O, and (Th, Fe)SiO₄ and uranium USiO₄· nH₂O have been studied by X-ray photoelectron spectroscopy in the range of electron binding energies from 0 to 1200 eV. The oxidation state of Th in the natural compounds is close to that in Th(OH)₄; for uranium, it is similar to that in UO₂. Based on the structure of the low-energy electron spectra it is assumed that the electrons of the filled Th6p- and O2s-atomic orbitals take an active part in chemical bonding. Fine structure was observed in the Th(U)6s-, 5d-, 5p-, 4f-, 4d-, and 4p _3/2 electron spectra of all substances under study. Mechanisms of fine structure formation are discussed and the fine structure parameters are correlated with the physicochemical properties of the compounds.     

Hyperfine structure in the configurations4f 4 6s 2 and4f 4 5d 6s of Nd I

The high resolution laser-atomic-beam technique was used to investigate the hyperfine structure in Nd I 4f ⁴6s ^{2 5} I,⁵ F,⁵ S and 4f ⁴5d6s ⁷ L,⁷ K,⁷ I,⁷ H. The metastable states were populated by an arc discharge burning in the atomic beam. The measured hyperfine constantsA andB of the levels of 4f ⁴6s ² and 4f ⁴5d6s allow a parametric analysis to be performed using the effective tensor operator formalism. The experimental radial integrals of the 4f and 5d electrons fit with those of the other lanthanides. The 4f radial integrals are in agreement with values of optimized Hartree-Fock-Slater calculations. The spectroscopic quadrupole moments of¹⁴³Nd and¹⁴⁵Nd are deduced from the 4f parameters:Q _I =?0.610(21) b and ?0.314(12) b, respectively. TheQ _I resulting from the 5d parameter are in satisfactory agreement with these values. The hyperfine anomaly due to thes electron in 4f ⁴5d 6s amounts to about 1%.     

Synthesis,structures and magnetic properties of a series of polynuclear copper(II)‐lanthanide( III) complexes assembled with carboxylate and hydroxide ligands

Heterometallic copper(II)‐lanthanide(III) complexes have been made with a variety of exclusively O‐donor ligands including betaines (zwitterionic carboxylates) and chloroacetate, which are dinuclear CuLn, tetranuclear Cu₂Ln₂, pentanuclear C_u3Ln₂, and octadecanuclear C_u12 complexes. The results show that subtle changes in both the carboxylates and acidity of the reaction solution can cause drastic changes in the structures of the products. Magnetic studies exhibit that shielding of the Ln³⁺ 4f electrons by the outer shell electrons is very effective to preclude significant coupling interaction between the Ln³⁺ 4f electrons and Cu²⁺ 3d electrons in either a mono‐atomic hydroxide‐bridged, or a carboxylate‐bridged system.     

Element-specific probe of the magnetic and electronic properties of Dy incar-fullerenes

The magnetic and electronic properties of a single atom and a pair of Dy atoms encapsulated inside fullerene carbon cages have been examined using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) as well as resonant photoelectron spectroscopy (RESPES) across the Dy M(4,5)-edge. The comparison of the measured XAS spectra with multiplet calculations indicates that the encaged Dy has a 4f( 9) configuration. The presence of Dy 5d spectral weight in the valence band is not detected by RESPES, indicating that Dy is in a formally trivalent state. The evolution of the encaged Dy orbital and spin moments of the 4f orbitals as a function of the applied magnetic field and temperature has been obtained from XMCD measurements. At 6.9 T and 4 K, both the orbital and the spin magnetic moments of the encaged Dy 4f electrons are dramatically smaller than those expected for the free Dy(3+) at saturation.     

The thermorchemistry of the di-η5-cyclopentadienyl derivatives of the first transition series and their unipositive ions

The heats of formation [△H⁰f(MCp₂, c, 298)] have been determined for the di-η⁵-cyclopentadienyl derivatives of magnesium, vanadium, chromium, manganese, iron, cobalt and nickel, by static-bomb calorimetry. They are (in kJ mol^-1) (M =) Mg, 77.0 ± 3; V, 123 ± 4; Cr, 186 ± 3; Mn, 198 ± 2; Fe, 158 ± 4; Co, 205 ± 4; and Ni, 262 ± 3.the heats of formation [△H⁰_f(M(CO)_xCp, c, 298)] of tricarbonylcyclopentadienylmanganese and dicarbonylcyclopentadienylcobalt have also been determined as —478 ± 1 and —169 ± 10 kJ mol^?1, respectively.By using the measured heats of formation of the metallocenes of the first transition series and other enthalpy values from the literature in Hess's law cycles, the feasibility of the process MCp₂ → MCp⁺₂ + e (obtained from the photoelectron ionisation energies) has been analysed and shown to be the result of the interplay of exchange energy and ligand-field stabilisation energy terms in these low-spin complexes. The feasibility order, V < Cr > Mn > Fe < Co > Ni is associated with the special stability associated with half-filled and filled shelss, which, because of the large ligand-field splitting, occur at d³, d⁶, d⁸ and d¹⁰.It is shown that bond energy additivity does not occur for the above cyclopentadienylmetal carbonyls.     

Theory of spin triplet ground states ind 6 transition metal compounds and the effect of high-energy states on the nature of the ground state

The formation of spin triplet, quintet, and singlet ground states within the 3d ⁶ electron configuration is investigated inD _4h , andD _3d symmetries employing irreducible tensor operator methods. Significant differences in the possible ground states are encountered between a complete CI and spin-orbit interaction treatment and an approximate calculation within the cubic⁵ T ₂,¹A₁,³ T ₁, and³ T ₂ parents.     

Valence Fluctuation of Uranium Ions in Uranium Sesquinitride Revealed by Dynamical Mean-field Theory Merged with Density Functional Theory

The electronic properties, in particular, the occupation number of 5f electrons and the valence state of U ions in uranium sesquinitride (U₂N₃) are studied by using density functional theory (DFT) calculations merged with dynamical mean-field theory (DMFT). The results demonstrate that j=5/2 and j=7/2 manifolds are in the weakly correlated metallic and weakly correlated insulating regimes, respectively. The quasi-particle weights indicate that LS coupling scheme is more feasible for 5f electrons, which are not in the orbital-selective localized state. The weighted summation of the occupation probabilities of 5fⁿ (n=0,1,2,3,4) atomic configurations suggests that 5f electrons have the inter-configuration fluctuation, or the mixed-valence state for U ions, together with an average occupation number of 5f electrons n_5f∼2.234, which is in good agreement with the electron localization function (ELF) and occupation analysis based on other DFT-based calculations. The 5fⁿ-mixing-driven inter-configuration fluctuation might originate from the dual nature of 5f electrons, and the flexible electronic configuration of U ions. Finally, the so-called quasiparticle band structure is also discussed.     

Second-order isotope shifts in the ground configuration of Nd I

The isotope shift between all stable neodymium isotopes has been measured for 21 transitions in the Nd I spectrum by means of laser-atomic-beam absorption spectroscopy. A parametric analysis of the observed shifts in all the levels of the terms⁵ I,⁵ F, and⁵ S of the ground configuration 4f ⁴6s ² yields not only the magnetic parameterz _4f but, for the first time, also the effective electrostatic parametersa,b, andc. A more accurate value of the nuclear parameter ^148,150 (Nd)=0.369(20) fm² is obtained from the investigation of a 4f ³5d6s ²–4f ³5d6s6p transition. The comparison of non-relativistic Hartree-Fock calculations with the experimental data yields a scaling factorS _I ^* (Nd)=1.50(9) that agrees with the corresponding one from the hyperfine structure analysis.     

Resonant emission of UO<Subscript>2</Subscript>, U<Subscript>3</Subscript>O<Subscript>8</Subscript>, and UO<Subscript>2+<Emphasis Type="Italic">x</Emphasis></Subscript> valence electrons under SR excitation near the O<Subscript>4,5</Subscript>(U) absorption edge

The structure of the resonant electron emission (REE) spectra of UO₂ (REE appears under the excitation with synchrotron radiation near the O_4,5(U) absorption edge at ∼100 eV and ∼110 eV) is studied with regard to the X-ray O_4,5(U) absorption spectrum of UO₂ and a quantitative scheme of molecular orbitals based on the X-ray electron spectroscopy data and the results of a relativistic calculation of the electronic structure of UO₂. The structure of the REE spectra of U₃O₈ and UO_2+x is studied for comparison, and the effect of the uranium chemical environment in oxides on it is found. The appearance of such a structure reflects the processes of excitation and decay involving the U5d and electrons of the outer valence MOs (OVMOs, from 0 to ∼13 eV) and inner valence MOs (IVMOs, from ∼13 eV to ∼35 eV) of the studied oxides. It is noted that REE spectra show the partial density of states of U6p and U5f electrons. Based on the structure of REE spectra, it is revealed that U5f electrons directly participate (without losing the f nature) in the chemical bonding of uranium oxides and are delocalized within CMOs (in the middle of the band), which results in the enhancement of the intensity of the REE spectra of CMO electrons during resonances. The U6d electrons are found to be localized near the bottom of the outer valence band and are observed in the REE spectra of the studied oxides as a characteristic maximum at 10.8 eV. It is confirmed that U6p electrons are effectively involved in the formation of IVMOs, which leads to the appearance of the structure in the region of IVMO electron energies during resonances. This structure depends on the chemical environment of uranium in the considered oxides.     

Ab initio calculations on low-lying electronic states of PdH

Potential energy curves for the low-lying electronic states of PdH have been calculated using the MRCI method with scalar relativistic and spin-orbit corrections, and all electronic states correlating to the 4d¹⁰ (¹S), 4d⁹ 5s¹ (³D), 4d⁹ 5s¹ (¹D) and 4d⁸ 5s² (³F) states of Pd were included. Potential energy curves for the individual Ω states have been obtained, and the experimentally observed spectra of both PdH and PdD isotopologues have been assigned appropriately based on the ab initio results. Einstein A coefficients were calculated for other possible transitions from the low-lying electronic states to the X²Σ⁺ ground state. Diagonal and off-diagonal matrix elements of the spin-orbit Hamiltonian were calculated for all vibrational levels of the X²Σ⁺, 1²Δ, 1²Π, 2²Σ⁺ and 3²Σ⁺ states, and it was found from the eigenvectors that the vibrational wavefunctions of the 1²Δ_3/2 and 1²Π_3/2 states are mixed significantly in both PdH and PdD isotopologues.     

Spin-orbit corrections to the indirect nuclear spin-spin coupling constants in XH4 (X = C, Si, Ge, and Sn)

Summary Using the quadratic response function at theab initio SCF level of approximation we have calculated the relativistic corrections from the spin-orbit Hamiltonian,H ^SO, to the indirect nuclear spin-spin coupling constants of XH₄ (X = C, Si, Ge, and Sn). We find that the spin-orbit contributions toJ _X-H are small, amounting only to about 1% forJ _Sn-H. For the geminal H-H coupling constants the relativistic corrections are numerically smaller than forJ _X-H, but in some cases relatively larger compared to the actual magnitude ofJ _H-H. We also investigate the use of an effective one-electron spin-orbit Hamiltonian rather than the fullH ^SO in the calculation of these corrections.     

Structural stability and evolution of terbium-doped silicon clusters and influence of 4f → 5d electronic transition mechanism on magnetism and appearance of photoelectron spectroscopy for TbSin0/− (n = 6-18) clusters

The global minimal structures of terbium-doped Si clusters and their anions TbSi _n^0/− (n = 6-18) are confirmed by employing the ABCluster unbiased global search technique combined with a B2PLYP double-hybrid density functional and comparing consistency of simulated and experimental photoelectron spectroscopy (PES). The results demonstrated that structural evolution patterns for neutral clusters prefer Tb-substitutional to Tb-encapsulated configuration starting from n = 16. While for the corresponding anionic clusters, the growth pattern adopts Tb-linked structures to encapsulated motif. The Natural Population Analysis revealed that the 4f electrons of Tb atom in TbSi _n^0/− (n = 6-18) clusters participate in bonding. The way to participate in bonding is one 4f electron transition to 5d orbital ([Xe]6s²4f⁹ → [Xe]6s²4f⁸5d¹), which significantly affects the cluster's magnetism and appearance of PES. The total magnetic moments of neutral TbSi _n and the corresponding anions maintain at 7 μB and 6 μB, respectively, which are larger than that of an isolated Tb atom. The HOMO-LUMO energy gap, relative stability, and chemical bonding analysis demonstrated that superatomic TbSi₁₆⁻ cluster is a magic cluster with fine thermodynamic and moderate chemical stability.     

Kristallstrukturen,Normalkoordinatenanalysen und 15N‐NMRund 77Se‐NMR‐Verschiebungen von trans‐[OsO2(NCO)4]2–, trans‐[OsO2(NCS)4]2– und trans‐[OsO2(SeCN)4]2–

Crystal Structures, Normal Coordinate Analyses, and ¹⁵N NMR and ⁷⁷Se NMR Chemical Shifts of trans ‐[OsO₂(NCO)₄]^2–, trans ‐[OsO₂(NCS)₄]^2–, and trans ‐[OsO₂(SeCN)₄]^2– The crystal structures of trans‐(Ph₃PNPPh₃)₂[OsO₂(NCO)₄] ( 1 ) (orthorhombic, space group Pbca, a = 19.278(3), b = 16.674(4), c = 19.982(2) Å, Z = 4), trans(n‐Bu₄N)₂[OsO₂(NCS)₄] ( 2 ) (triclinic, space group P1, a = 12.728(3), b = 12.953(3), c = 16.255(6) Å, α = 97.39(4), β = 105.62(2), γ = 95.25(3)°, Z = 2) and trans‐(n‐Bu₄N)₂[OsO₂(SeCN)₄] ( 3 ) (tetragonal, space group I4/m, a = 13.406(2), c = 12.871(1) Å, Z = 2) have been determined by single‐crystal X‐ray diffraction analysis, showing the bonding of NCO and NCS via the N atom but the coordination of SeCN via the Se atom to osmium. Based on the molecular parameters of the X‐ray determinations the vibrational spectra have been assigned by normal coordinate analyses. The valence force constants are for 1 f_d(OsO) = 6.43, f_d(OsN) = 3.32, f_d(NC) = 14.50, f_d(CO) = 12.80, for 2 f_d(OsO) = 6.56, f_d(OsN) = 1.75, f_d(NC) = 15.00, f_d(CS) = 5.50, and for 3 f_d(OsO) = 6.75, f_d(OsSe) = 0.99, f_d(SeC) = 3.23, f_d(CN) = 15.95 mdyn/Å. The observed NMR shifts are δ(¹⁵N) = –386.6 ( 1 ), δ(¹⁵N) = –294.7 ( 2 ) and δ(⁷⁷Se) = 108.8 ppm ( 3 ).     

Lanthanide chelates of fluorinated β-diketones. Part III. Mass spectra of lanthanide chelates of five fluorinated β-diketones

Summary The mass spectra of sixty lanthanide chelates of the fluorinated -diketones RC(OH)=CHCOCF₃ (R=2-theonyl,p-BrC₆H₄,m-MeC₆H₄,o-MeC₆H₄, and Bu-t) have been obtained. The mass spectra were essentially similar, in contrast to those found ford-block transition metal chelates. Valency change from 3 to 2 occurred with samarium (4f ⁵), europium (4f ⁶), thulium (4f ¹²), and ytterbium (4f ¹³); the intensity of the Met(II)-containing peaks varied: Eu Sm > Yb > Tm, reflecting the decreasing tendency of these lanthanides to display bivalency. Valency change from 4 to 3 was observed with cerium (4f¹) but not with terbium (4f⁸).Part II,Transition Met. Chem., 9, 423 (1984).     

Darstellung,Kristallstrukturen, Schwingungsspektren und Normalkoordinatenanalysen der mer‐Trihalogeno‐tris‐Pyridin‐Osmium(III)Komplexe mer‐[OsX3Py3], X = Cl,Br, I

Synthesis, Crystal Structures, Vibrational Spectra, and Normal Coordinate Analyses of the mer ‐Trihalogeno‐tris‐Pyridine‐Osmium(III) Complexes mer‐[OsX₃Py₃], X = Cl, Br, I By reaction of the hexahalogenoosmates(IV) with pyridine and iso‐amylalcohol mer‐trihalogeno‐tris‐pyridine‐osmium(III) complexes are formed and purified by chromatography. X‐ray structure determinations on single crystals have been performed of mer‐[OsBr₃Py₃] (monoclinic, space group P2₁/n, a = 9.098(5), b = 12.864(5), c = 15.632(5) Å, β = 90.216(5)°, Z = 4) and mer‐[OsI₃Py₃] (monoclinic, space group P2₁/n, a = 9.0952(17), b = 13.461(4), c = 15.891(10), β = 91.569(5)°, Z = 4). The pyridine rings are twisted propeller‐like against the N₃ meridional plane with mean angles of 49° (Cl), 46° (Br), 44° (I). Based on the molecular parameters of the X‐ray structure determinations and assuming C₂ point symmetry, the IR and Raman spectra are assigned by normal coordinate analysis. Due to the stronger trans influence of pyridine as compared with the halide ligands for N'–Os–X ^· axes significantly different valence force constants are observed in comparison with symmetrically coordinated octahedron axes: f_d(OsCl) = 1.74, f_d(OsCl^·) = 1.49, f_d(OsBr) = 1.43, f_d(OsBr ^· ) = 1.18, f_d(OsI) = 0.99, f_d(OsI ^· ) = 0.96, f_d(OsN) between 1.96 and 2.07 and f_d(OsN') between 2.13 and 2.32 mdyn/Å.     

Darstellung,Kristallstruktur, Schwingungsspektren und Normalkoordinatenanalyse von (Ph4P)2[OsN(N3)5] und 15N‐NMR‐Verschiebungen von Nitridoosmaten(VI,VIII)

Synthesis, Crystal Structure, Vibrational Spectra, and Normal Coordinate Analysis of (Ph₄P)₂[OsN(N₃)₅] and ¹⁵N NMR Chemical Shifts of Nitridoosmates(VI, VIII) The treatment of (Ph₄P)[OsNCl₄] with NaN₃ yields (Ph₄P)₂[OsN(N₃)₅], which crystal structure has been determined by single crystal X‐ray diffraction analysis (monoclinic, space group P 2₁/a, a = 20.484(6), b = 11.168(1), c = 20.666(4) Å, β = 97.35(3)°, Z = 4). The IR and Raman vibrations were assigned by a normal coordinate analysis based on the molecular parameters of the X‐ray determination. The valence force constants are f_d(Os≡N) = 8.52, f_d(Os–N^α) = 1.99, f_d(N^α–N^β) = 12.42, f_d(N^β–N^γ) = 12.73 and for the azido ligand in trans‐position to the nitrido group f_d(Os–N^{α ·} ) = 1.84, f_d(N^{α ·} –N^{β ·} ) = 11.91, f_d(N^{β ·} –N^{γ ·} ) = 12.18 mdyn/Å. The ¹⁵N NMR spectra of various nitridoosmates reveal the chemical shifts δ(¹⁵N) for K[OsO₃¹⁵N] = 387.6, K₂[Os¹⁵NCl₅] = 446.7, (Ph₄P)[Os¹⁵NCl₄] = 352.9, [(n‐C₆H₁₃)₄N]₂[Os¹⁵N(N₃)₅] = 307.3 and for [(n‐Pr)₄N]₂[Os¹⁵N(¹⁵NCO)₅] = 483,7 (Os≡N), –417,7 (OsNCO_eq) und –392,8 ppm (OsNCO_ax).