Bruce E. Bursten

Ab initio relativistic effective potentials with spin-orbit operators. VII. Am through element 118

Ab initio averaged relativistic effective core potentials (AREP) and spin-orbit (SO) operators are reported for the elements Am through element 118. Two sets have been calculated for certain elements to provide AREPs with varying core/valence space definition, thereby permitting the treatment of core/valence correlation interactions. The AREPs and SO operators are tabulated as expansions in Gaussian-type functions (GTF). GTF valence basis sets are derived for the lowest energy state of each atom. The reliability of the AREPs and SO operators is gauged by comparing calculated atomic orbital eigenvalues and SO splitting energies with all-electron relativistic values.

Molecular orbital studies on cyclobutadienemetal complexes: the concept of metalloaromaticity

Nonempirical molecular orbital calculations have been performed on a variety of cyclobutadienemetal complexes. For C4H4Fe(CO),, a detailed analysis of the frontier orbitals indicates that the molecule is best described as a C4H4Fe fragment perturbed by the carbonyls rather than as an Fe(C0)3 moiety perturbed by the C4H4 ring. This description is more consistent with the photoelectron spectrum of C4H4Fe(C0)3 than the Hartree-Fock description of the molecule. The C4H4-Fe bond is highly covalent resulting in a delocalization of six electrons in metal-ring a orbitals, a phenomenon which shall be referred to as metalloaromaticity. These concepts are extended to C4H4Cr(C0)4 and C4H4Ni(CO),. The former species has been synthesized but the latter has not. Correlation of these facts with the calculations will be presented. Finally, a comparison will be made of C4H4 to C5H5 and C6H6 as ligands

Electronic structure of f1 lanthanide and actinide complexes. Part 2. Non-relativistic and relativistic calculations of the ground state electronic structures and optical transition energies of [Ce(η-C5H5)3], [Th(η-C5H5)3] and [Pa(η-C8H8)2]

Abstract Non-relativistic and relativistic discrete variational-X α calculations have been performed on [Ce( η -C 5 H 5 ) 3 ], [Th( η -C 5 H 5 ) 3 ] and [Pa( η -C 8 H 8 ) 2 ]. Metal—ligand covalent interactions in [Ce( η -C 5 H 5 ) 3 ] and [Th( η -C 5 H 5 ) 3 ] are dominated by metal d-orbital participation in the ( η -C 5 H 5 ) π 2 -based 2e and 3e molecular orbitals, and an f-orbital contribution to the la 2 level. The non-relativistic calculations predict formal ground configurations of 4f 1 and 5f 1 for [Ce( η -C 5 H 5 ) 3 ] and [Th( η -C 5 H 5 ) 3 ] respectively, while the destabilisation of the n f and slight stabilisation of the ( n + 1)d σ level on the incorporation of relativistic effects result in a 6d 1 electronic configuration for [Th( η -C 5 H 5 ) 3 ]. [Pa( η -C 8 H 8 ) 2 ] is found to have a 5f 1 ground configuration in both non-relativistic and relativistic calculations, and both the 6d and 5f metal orbitals participate significantly in metal-ligand covalent bonding. The 4f-based molecular orbitals of [Ce( η -C 5 H 5 ) 3 ] are found to be little altered from those of free Ce(III), and show a three-below-four ( j = 5/2 below j = 7/2) spin—orbit coupling pattern. The greater radial extension of the 5f atomic orbitals and their closer energy match with vacant carbocyclic ring levels destroys this splitting pattern in [Th( η -C 5 H 5 ) 3 ] and [Pa( η -C 8 H 8 ) 2 ]. The electronic absorption spectra of all three molecules have been calculated using the transition state method. In [Ce( η -C 5 H 5 ) 3 ] and [Pa( η -C 8 H 8 ) 2 ], the transitions are principally f → f in nature, although a low-lying f → d σ shift is predicted in both cases. In [Ce( η -C 5 H 5 ) 3 ], the calculated f → d σ transition is in good agreement with that found experimentally for [Ce( η -C 5 H 3 (SiMe 3 ) 2 ) 3 ]. The calculated spectrum of [Th( η -C 5 H 5 ) 3 ] consists of a series of d → f transitions, in agreement with the intense peaks observed in the experimental spectrum of [Th( η -C 5 H 3 (SiMe 3 ) 2 ) 3 ]. Comparison of the calculated transitions of [Pa( η -C 8 H 8 ) 2 ] with the experimental spectrum of [Pa( η -C 8 H 4 (CH 3 ) 4 ) 2 ] suggests that the latter is due to charge transfer transitions and that the f → d σ shift has not yet been experimentally observed.

Density functional calculations of dinuclear organometallic carbonyl complexes. Part I: metalmetal and metalCO bond energies

Abstract One of the most fundamental properties in chemistry is the bond dissociation energy (BDE), the energy required to break a specific bond of a molecule. In this paper we apply gradient-corrected density functional theory (DFT) to the calculation of the BDEs of three prototypical organometallic complexes, Mn 2 (CO) 10 , Fe 2 (CO) 9 , and Co 2 (CO) 8 , along with the CO-loss products Mn 2 (CO) 9 and Mn 2 (CO) 8 . We consider the dissociation of both the metalmetal bond and a metalcarbonyl bond. For Mn 2 (CO) 10 and Fe 2 (CO) 9 , the calculated metalmetal BDE is within the error of the experimental measurements. However, the calculated metalmetal BDE for Co 2 (CO) 8 is not within the errors of the measurements, but is improved greatly with an unrestricted wavefunction compared with a restricted wavefunction. For the first carbonyl BDE, the calculations agree within a few kcal mol −1 for each complex.

Ground-State Reversal by Matrix Interaction: Electronic States and Vibrational Frequencies of CUO in Solid Argon and Neon

The reactions of laser-ablated metal atoms with small molecules during their condensation in frozen noble gas matrices have led to a remarkable number of fundamental small molecules that provide new insights into the structures of and bonding in metal complexes.

Spin-Orbit Coupling versus the VSEPR Method: On the Possibility of a Nonplanar Structure for the Super-Heavy Noble Gas Tetrafluoride (118)F4

When relativistic considerations are taken into account it seems likely that the tetrafluoride of the noble gas element 118 does not favor a square-planar geometry like the lighter homologues XeF4 and RnF4, but rather a tetrahedral geometry as a result of large spin-orbit effects (see picture).

Metathesis of nitrogen atoms within triple bonds involving carbon, tungsten, and molybdenum.

(ButO)3Mo triple bond N and W2(OBut)6(M triple bond M) react in hydrocarbons to form Mo2(OBut)6(M triple bond M) and (ButO)3W triple bond N via the reactive intermediate MoW(OBut)6(M triple bond M). (ButO)3W triple bond N and CH3C triple bond N15 react in tetrahydrofuran (THF) at room temperature to give an equilibrium mixture involving (ButO)3W triple bond N15 and CH3C triple bond N. The (ButO)3W triple bond N compound is similarly shown to act as a catalyst for N15-atom scrambling between MeC13 triple bond N15 and PhC triple bond N to give a mixture of MeC13 triple bond N and PhC triple bond N15. From studies of degenerate scrambling of N atoms involving (ButO)3W triple bond N and MeC13 triple bond N in THF-d8 by 13C(1H) NMR spectroscopy, the reaction was found to be first order in acetonitrile and the activation parameters were estimated to be DeltaH = 13.4(7) kcal/mol and DeltaS = -32(2) eu. A similar reaction is observed for (ButO)3Mo triple bond N and CH3C triple bond N15 upon heating in THF-d8. The reaction is suppressed in pyridine solutions and not observed for the dimeric [(ButMe2SiO)3W triple bond N]2. The reaction pathway has been investigated by calculations employing density functional theory on the model compounds (MeO)3M triple bond N and CH3C triple bond N where M = Mo and W. The transition state was found to involve a product of the 2 + 2 cycloaddition of M triple bond N and C triple bond N, a planar metalladiazacyclobutadiene. This resembles the pathway calculated for alkyne metathesis involving (MeO)3W triple bond CMe, which modeled the metathesis of (ButO)3W triple bond CBut. The calculations also predict that the energy of the transition state is notably higher for M = Mo relative to M = W.

Relativistic density functional investigation of Pu(H2O)n3+ clusters

The solvation of the Pu{sup 3+} ion in water was investigated using relativistic density functional theory including generalized gradient corrections. Binding energies and optimized geometries for different coordination numbers of water molecules [Pu(H{sub 2}O){sub n}{sup 3+}, n=6, 8, 9, 10, 12] around the ion were calculated. The results indicate that the first solvation shell of Pu{sup 3+} is likely to contain eight or possibly nine waters with a Pu-O bond length of 2.51-2.55 {angstrom}. The theoretical results are compared with two recent EXAFS experiments on the Pu{sup 3+} aqueous system.

The bonding in tris(η5-cyclopentadienyl) actinide complexes IV: Electronic structural effects in AnCl3 and (η5-C5H5)3An (An ≡ Th — Cf) complexes☆

Abstract The cp3An (cp ≡ η5-C5H5; An ≡ actinide element) framework is the most ubiquitous one in organoactinide chemistry. Cp3An (or modified cp) compounds have been synthesized for An  Th, U, Np, Pu, Am, Cm, Bk, and Cf, and in some cases represent the only known organometallic complex for the given element. The electronic structures of these cp3An complexes have been investigated via Xα-SW molecular orbital calculations that include quasirelativistic corrections. A comparison of the cp-metal bonding interactions as a function of the metal will be presented, with an emphasis on the relative roles of the actinide 5f and 6d atomic orbitals. The radial extension of the 5f orbitals as a function of the metal will be discussed, and the possibility of these orbitals participating in the bonding of a fourth ligand will be considered.

An analysis of the bonding in some ‘nonclassical’ d0 and d10 metal carbonyl complexes

Abstract The bonding in nonclassical carbonyl complexes, those with unusually high CO stretching frequencies, is analyzed via Fenske-Hall molecular orbital calculations. The systems analyzed include nonclassical carbonyl complexes of d10 Ag(I) and of d0 Zr(IV); these are compared to classical carbonyl complexes of Zr(II) and Mo(O). The Cotton-Kraihanzel CO-stretch force constants are correlated to the Mulliken populations of the 5σ and 2π molecular orbitals of the CO ligands.