Experimental and Quantum Mechanical Characterization of an Oxygen-Bridged Plutonium(IV) Dimer

We report the synthesis and characterization of K₄{[PuCl₂(NO₃)₃]₂(μ₂-O)}⋅H₂O, which contains the first known μ₂-oxo bridge between two Pu^IV metal centers. Adding to its uniqueness is the Pu−(μ₂-O) bond length of 2.04 Å, which is the shortest of other analogous compounds. The Pu−(μ₂-O)−Pu bridge is characterized by the mixing of s-, d-, and p-orbitals from Pu with the p-orbitals of O; the 5f-orbitals do not participate in bonding. Natural bond orbital analysis indicates that Pu and O interact through one 3c-2e σ_Pu-O-Pu and two 3c-2e π_Pu-O-Pu bonding orbitals and that the electron density is highly polarized on the μ₂-O. Bond topology properties analysis indicates that the Pu−(μ₂-O) bond shares both ionic and covalent character. Quantum mechanical calculations also show that the dimer has multiconfigurational ground states, where the nonet, septet, quintet, triplet, and singlet are close in energy. This work demonstrates the interplay between experimental and computational efforts that is required to understand the chemical bonding of Pu compounds.     

The Heat of Formation of the Uranyl Dication: Theoretical Evaluation Based on Relativistic Density Functional Calculations

By using a set of model reactions, we estimated the heat of formation of gaseous UO₂²⁺ from quantum‐chemical reaction enthalpies and experimental heats of formation of reference species. For this purpose, we performed relativistic density functional calculations for the molecules UO₂²⁺, UO₂, UF₆, and UF₅. We used two gradient‐corrected exchange‐correlation functionals (revised Perdew–Burke–Ernzerhof (PBEN) and Becke–Perdew (BP)) and we accounted for spin‐orbit interaction in a self‐consistent fashion. Indeed, spin‐orbit interaction notably affects the energies of the model reactions, especially if compounds of U^IV are involved. Our resulting theoretical estimates for Δ_f (UO₂²⁺), 365±10 kcal mol^?1 (PBEN) and 370±12 kcal mol^?1 (BP), are in quantitative agreement with a recent experimental result, 364±15 kcal mol^?1. Agreement between the results of the two different exchange‐correlation functionals PBEN and BP supports the reliability of our approach. The procedure applied offers a general means to derive unknown enthalpies of formation of actinide species based on the available well‐established data for other compounds of the element in question.     

反式-双(二甲基苯膦)铂配合物二阶非线性光学性质的密度泛函理论研究

采用密度泛函理论B3LYP方法,在6-31G(d)的水平上对两种反式-双(二甲基苯膦)铂配合物的几何构型进行优化,在获得稳定构型基础上,利用TD-B3LYP方法得到体系的UV-Vis吸收光谱,并用有限场(FF/B3LYP)方法探讨体系的二阶非线性光学性质(NLO).结果表明,此类铂配合物具有较大的二阶极化率,以及在可见光范围内透明等优点,是具有很好应用前景的非线性光学材料.     

Synthesis and structural features of α-acyloxy-(η-allyl)palladium complexes

α-Acetoxy (η³-allyl)palladium complexes were prepared from acyloxy functionalized allylsilanes under mild conditions and in good isolated yields. The substituent and ligand effects of the acetoxy group on the palladium-allyl bonding were studied by X-ray diffraction. These studies show that the acetoxy group generates a strongly deformed bonding between the metal atom and the allyl moiety. This unsymmetrical bonding is modulated by the σ-donor/π-acceptor properties of the ligands. The ¹³C NMR studies indicated that the shift values correlate with the carbon-palladium bond lengths and the inductive effects of the acetoxy group.     

Theoretical investigation of different reactivities of Fe(IV)O and Ru(IV)O complexes with the same ligand topology

The structures and mechanisms for hydrogen abstraction from isopropylbenzene for four high-valence complexes, cis-β-[Fe^IV(O)(BQCN)]²⁺ (Fe-2b and Fe-2b-2) and cis-β-[Ru^IV(O)(BQCN)]²⁺ (Ru-2b and Ru-2b-2) (BQCN = N,N′-dimethyl-N,N′-bis(8-quinolyl)-cyclohexanediamine), were investigated using density functional theory. Of the two iron complexes, Fe-2b-2 has more exposed FeO units than Fe-2b, with iron being further out of the equatorial plane because of the steric interaction of the same ligand topologies with the iron-oxo group trans to a quinolyl or amine nitrogen. The contribution of BQCN to Fe-2b is higher than the contribution to Fe-2b-2 as shown by the density-of-states spectra. The iron isomers can abstract hydrogen from isopropylbenzene via two-state reactivity patterns, whereas the ruthenium isomers react with isopropylbenzene via a single-state mechanism. In the gas phase, the relative reactivity exhibits the trend Fe-2b > Fe-2b-2, whereas with the addition of the ZPE correction and the SMD model, the relative reactivity follows Fe-2b-2 > Fe-2b. For the ruthenium complexes, the relative reactivity follows the trend Ru-2b-2 > Ru-2b in both the gas phase and solvent. Thus, the same ligand topologies with the metal-oxo group trans to a different nitrogen affect the reactivities of the iron and ruthenium complexes.     

Titanocene(IV) and vanadocene(IV) complexes of dicyanomethanidobenzoate

The new titanocene and vanadocene complexes of the non-linear pseudohalides Cp₂Ti(dcmb)₂, Cp₂VCl(dcmb), (η⁵-C₅H₄Me)₂VCl(dcmb) and Cp₂V(dcmb)₂ were prepared by reaction of titanocene dichloride (Cp₂TiCl₂) and vanadocene dichlorides (Cp₂VCl₂, (η⁵-C₅H₄Me)₂VCl₂) with dicyanomethanidobenzoic acid (dcmbH, PhC(OH)C(CN)₂). These reactions have proven that the dcmb ligand could be coordinated to the central metal by oxygen or nitrogen donor atoms. The bonding mode of the dcmb ligand reflects properties of the central metal. The strongly oxophilic titanium(IV) shows the bonding through oxygen atom while bonding through nitrogen atom was observed for less oxophilic vanadium(IV). The bonding fashion of the dcmb ligands was determined by spectroscopic methods. X-ray diffraction analysis was used for the structure determination of the compounds dcmbH·H₂O, Cp₂Ti(dcmb)₂·CH₂Cl₂, (η⁵-C₅H₄Me)₂VCl(dcmb) and [Cp₂V(OC(Ph)C(CN)C(OMe)NH)][dcmb].     

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

The coordination of tBuNC and CO with the diarsenido complexes (C₅Me₅)₂An(η²-As₂Mes₂), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of Th^IV and U^IV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the Th^IV and U^IV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon An^IV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(C−O) orbitals relative to the An−As bond.     

Theoretical Study of Intradimer Mechanism for Diamond Growth over Diamond (100)

The study of the energetics of the accepted intradimer diamond growth mechanism over (100) diamond surface is presented. The calculations were made in a density functional approach with the DGauss code using a DZVP2 basis set and a BLYP interchange and correlation potential. A simple 9-carbon cluster modeling the (100) diamond surface was used; its validity is discussed in relation with other calculations that used larger model clusters. The mechanism, presented in six steps, is based in the Harris and Garrison's work that considers the methyl radical as the main growth precursor agent and the breaking of the dimer surface bond with the corresponding methylene radical formation as a prior step to the formation of a CH₂-bridge structure, which is a feasible step; in contrast to these molecular dynamics results, Huang and Frenklach, using semiempirical methods, consider the breaking of the dimer surface bond and the formation of a CH₂-bridge structure as one step and this step as the energetically determinant of the mechanism. They also found an activation energy barrier for the interaction between a radical surface center with a H and CH₃. The present work tries to discern between these two ideas by calculating the activation barriers and the reaction energies for each step of the Harris and Garrison's mechanism in a density functional approach and comparing them to the results of Huang and Frenklach. The energy calculations point toward the scission of the dimer bond (step 4) as the determinant step; this step is endothermic, with an energy barrier of 50.43 kcal-mol^–1. On the other hand, the formation of the CH₂-bridge structure (step 5) is a feasible step with an energy barrier of 13.57 kcal-mol^–1. The adsorption of CH₃ (step 2) and H (step 6) species over radical surface sites did not involve any energy barriers, as it would be hoped. These steps were strongly exothermic and are close to the thermodynamic values for C—C and C—H bond energies. The removal of methylic hydrogen (step 3) did not show any problem because the activation barrier is only 3.68 kcal-mol^–1 less than the removal of a surface hydrogen (step 1), which has an energy barrier of 19.59 kcal-mol^–1. All steps, except number 4, were exothermic.     

Ab initio quasirelativistic calculations on electronic transitions in ICl by the multireference many‐body perturbation theory

A quasirelativistic perturbative method of ab initio calculations on ground and excited molecular electronic states and transition properties within the relativistic effective core potential approximation is presented and discussed. The method is based on the construction of a state‐selective many‐electron effective Hamiltonian in the model space spanned by an appropriate set of Slater determinants by means of the second‐order many‐body multireference perturbation theory. The neglect of effective spin–orbit interactions outside of the model space allows the exploitation of relatively high nonrelativistic symmetry during the evaluation of perturbative corrections and therefore dramatic reduction of the cost of computations without any contraction of the model‐space functions. One‐electron transition properties are evaluated via the perturbative construction of spin‐free transition density matrices. Illustrative calculations on the X0⁺ ? A1, B0⁺, and (ii)1 transitions in the ICl molecule are reported. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Electronic structure and coordination chemistry of phenanthridine ligand in first‐row transition metal complexes: A DFT study

The geometric parameters, electronic structures, and haptotropic migration of a series of hypothetical compounds of general formula CpM(C₁₃H₉N) and (CO)₃M(C₁₃H₉N) (M = fist row transition metal, Cp = C₅H₅, and C₁₃H₉N = phenanthridine ligand) are investigated by means of the density functional theory. The phenanthridine ligand can bind to the metal through η¹ to η⁶ coordination mode, in agreement with the electron count and the nature of the metal, showing its capability to adapt itself to the electronic demand of the metal as well as to the polycyclic aromatic hydrocarbons. In the investigated species, the most favored closed‐shell count is 18‐electron except for the Ti and V models which are deficient open‐shell 16‐electron configuration. This study has shown the difference in coordination ability of this heteropolycyclic ligand: the coordination of the central C₅N ring is less favored than the terminal C₆ rings, in agreement with the π‐electron density localization. Most of the investigated complexes are expected to exhibit a rich fluxional behavior. This flexibility favors the possibility for the existence of several isomers as well as their interconversion through haptotropic shifts. © 2012 Wiley Periodicals, Inc.     

三(芳氧基)芳烃络合低价锕系离子的结构和还原性质理论探索

由于具有特殊的电子结构和独特的反应性,低价锕系配合物已得到广泛关注.目前,实验中得到的可分离、晶体结构确定的+2锕系元素配合物少之又少.本工作通过相对论密度泛函理论探索了低价[AnL]^z(An=Ac～Pu;L=[(^Me,MeAr OH)₃Ar]^3–;z=0和-1)的结构和氧化还原性质.计算发现,在[AnL]→[AnL]–还原过程中An-C_Ar和An-Arcent距离缩短,这是由于还原电子进入到An和Ar共享区域,增强了δ(An-Ar)成键作用所致.还原时,配合物[AcL]和[ThL]的Ar基团捕获了大部分还原电子,而Pa～Pu配合物的则更多地定域在金属周围.因此,还原产物中Ac和Th仍为+3,而Pa～Pu则为+2、具有5fn电子组态.得到的还原电势值随着Ac～Pu整体呈上升趋势,在U和Np处出现相对Pa和Pu的低点.这一趋势与电子亲和能和An-CAr/Arcent距离变化有很好的相关性.     

Absorption spectrophotometric study of berkelium(III) and (IV) fluorides in the solid state

Absorption spectrophotometry has been used to study the dimorphic BkF₃ system and BkF₄ in the solid state. LaF₃-type trigonal BkF₃ can be distinguished from YF₃-type orthorhombic BkF₃ by subtle, but reproducible, differences in their corresponding absorption spectra. This ability emphasizes the sensitivity of absorption spectrophotometric analysis, since both crystal modifications of BkF₃ have the same metal ion coordination number of nine. The absorption spectrum of BkF₄ (UF₄-type monoclinic structure) is reported for the first time.     

Phospha(III)guanidinate complexes of titanium(IV) and zirconium(IV) amides

Two procedures for the synthesis of group 4 phosphaguanidine compounds M(R₂PC{NR′}₂)(NR″₂)₃ (M = Ti, Zr; R = Ph, Cy; R′ = ⁱPr, Cy; R″ = Me, Et) are described. Spectroscopic characterization indicated symmetrical bonding of the phosphaguanidinate ligand in solution for the P-diphenyl derivatives whereas the P-dicyclohexyl analogs adopt a more rigid geometry with inequivalent N_amidine substituents within the phosphaguanidinate ligand. X-ray diffraction studies show exclusively monomeric tbp metal centers for a series of derivatives, with a chelating phosphaguanidinate ligand that spans an axial and an equatorial position. Two different conformers have been identified in the solid-state that differ in the relative orientation of the phosphorus R₂P–C substituents with respect to the equatorial plane of the tbp metal. The synthetic protocol was extended to the bimetallic complex, [PhP(C{NⁱPr}₂Ti{NMe₂}₃)CH₂–]₂, which was characterized by crystallography as the meso-form.     

Theoretical study on phosphorescence efficiency and color tuning from orange to blue-green of Ir(III) complexes based on substituted 2-phenylimidazo[1,2-a]pyridine ligand

The geometrical structures, phosphorescence quantum yields, and electroluminescence (EL) efficiency of six iridium(III) complexes containing 2-phenylimidazo[1,2-a]pyridine ligand are investigated by density functional theory (DFT), which show a wide color tuning of photoluminescence from orange (λ(em) = 550 nm) to blue-green (λ(em) = 490 nm). The calculated results shed some light on the reasons of the remarkably manipulated excited-state and EL properties through substitution effect. The Mulliken charge calculation reveals that attached -CF(3) groups on phenyl and imidazo[1,2-a]pyridine (impy) moieties (4) can make both of them as electron-deficient region, which will lead to the contraction of the whole coordination sphere and strengthen the metal-ligand interaction. While attaching two -CF(3) groups on phenyl ring can make it more electron-deficient, which will induce electron transferring from acac and impy fragment to phenyl ring, and also result in the contracted structure. The largest metal-to-ligand charge transfer ((3)MLCT) character and the smaller S(1)-T(1) energy gap (ΔE(S(1)-T(1))) value increase the emission quantum yields of 4 and 6 than other complexes. For EL efficiency, because of the similar highest occupied molecular orbital (HOMO) levels of 4 and 6 to that of holes injection material poly(N-vinylcarbazole) (PVK) and the larger dipole moments, majority hole will be accumulated on the HOMO of 4 and 6. Combination with the lower lowest unoccupied molecular orbital energy levels compared with PVK, the recombination zones of 4 and 6 can be well confined within emitting material layer (EML) and lead to the higher EL efficiency.     

Theoretical and Crystallographic Study of Lead(IV) Tetrel Bonding Interactions

The ability of tetrahedral lead(IV) to establish noncovalent σ-hole tetrel bonding interactions with electron-rich atoms (ElRs; anions and Lewis bases) has been studied at the PBE0-D3/def2-TZVPD level of theory. An analysis of the Cambridge Crystallographic Database (CSD), which is a convenient storehouse of geometric information, has been performed to investigate the existence of tetrel bonding interactions involving tetrahedral lead(IV) derivatives. Several examples of tetrel bonding interactions that are crucial in crystal packing, ranging from 0D to 2D assemblies, have been found. In addition to the energetic and theoretical study of several XPb(CH₃)₃⋅⋅⋅ElR complexes (X=F, CN, CF₃, and CH₃), Bader's theory of atoms in molecules has also been used to further analyze and characterize the noncovalent interactions described herein.