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This paper explores the ligand field picture applied to organometallic compounds. Given the dearth of experimental data, the high-level ab initio ligand field theory (aiLFT) method is deployed as a surrogate for experiment and the necessary d orbital sequences and relative energies are obtained computationally. These are fitted to local cellular ligand field (CLF) σ, π and δ bonding parameters. Results are reported for planar [Cu(CR3)4]−, (R = F, H), octahedral M(CO)6n (M = Fe, Mn, Cr, V, Ti; n = +2, +1, 0, −1, −2), and the sandwich compounds M(Cp)2 (Cp = cyclopentadienyl, M = Fe, Ni, V), [Ni(Cp)2]2+ and Cr(C6H6)2. With respect to the aiLFT framework, these organometallic systems behave just like coordination complexes and most maintain the integrity of their formal dn configurations. Both [Cu(CR3)4]− compounds are formulated as low-spin d8 CuIII species and have normal ligand fields consistent with their planar geometries. The metal carbonyls reveal a new way of counting valence electrons which only requires the CLF d orbital energy level diagram to rationalise the 18-electron rule as well as its many exceptions. The bonding in sandwich compounds shows a remarkable variation. In ferrocene, Cp− behaves as a strong field ligand, comparable to [CN]− in [Fe(CN)6]4−. Fe(Cp)2 is low spin as is Cr(C6H6)2. Cp− in Fe(Cp)2 is a weak σ donor, strong π donor and weak δ acceptor while benzene in Cr(C6H6)2 is also a weak σ and strong π donor but is a much better δ acceptor. In contrast, Cp− is weak field in high spin, 20-electron Ni(Cp)2 but 'ultra-covalent' in [Ni(Cp)2]2+. The formal IV oxidation state is too high for the ligand set and the integrity of the d6 configuration is lost. Similarly, [V(CO)6]− and [Ti(CO)6]2− are ultra-covalent except now the formal metal oxidation states are too negative. Both mechanisms relate to the breaching of the metal's 3s23p6 'Pauli shield' and these ultra-covalent systems lie outside the ab initio ligand field regime. However, within the ligand field regime, the bonding in 'coordination complexes' and 'organometallic compounds' has the same conceptual footing and the nature of the local σ, π and δ interactions can be extracted from analysing the ligand field d orbitals. [ABSTRACT FROM AUTHOR]

Organometallic compounds offer broad scope for the design of therapeutic agents, but this avenue has yet to be widely explored. A key concept in the design of anticancer complexes is optimization of chemical reactivity to allow facile attack on the target site (e.g., DNA) yet avoid attack on other sites associated with unwanted side effects. Here, we consider how this result can be achieved for monofunctional 'piano-stool' ruthenium(II) arene complexes of the type [[([[eta].sup.6]-arene)Ru(ethylenediamine)(X)].sup.n+]. A potentially important activation mechanism for reactions with biomolecules is hydrolysis. Density functional calculations suggested that aquation (substitution of X by [H.sub.2]O) occurs by means of a concerted ligand interchange mechanism. We studied the kinetics and equilibria for hydrolysis of 21 complexes, containing, as X, halides and pseudohalides, pyridine (py) derivatives, and a thiolate, together with benzene (bz) or a substituted bz as arene, using UV-visible spectroscopy, HPLC, and electrospray MS. The x-ray structures of six complexes are reported. In general, complexes that hydrolyze either rapidly (e.g., X = halide [arene = hexamethylbenzene (hmb)]) or moderately slowly [e.g., X = azide, dichloropyridine (arene = hmb)] are active toward A2780 human ovarian cancer cells, whereas complexes that do not aquate (e.g., X = py) are inactive. An intriguing exception is the X = thiophenolate complex, which undergoes little hydrolysis and appears to be activated by a different mechanism. The ability to tune the chemical reactivity of this class of organometallic ruthenium arene compounds should be useful in optimizing their design as anticancer agents. anticancer | bioorganometallic | hydrolysis | kinetics | ruthenium complexes

The model correctly predicts that the regiochemistry for R = OMe, Me and CN is the same for neutral and cationic Pd complexes while for R = CH2OH the regiochemistry reverses. The regiochemistry is thus implicit in the electronic structure of the precursor complex.

Research has been conducted on oxygen atom transfer reactions. The use of density functional theory calculations in investigating these reactions from the biological oxygen atom donors trimethylamine N-oxide and dimethyl sulfoxide to the molybdenum(IV) complexes is described.

Research has been conducted on cobalt in +2 oxidation state. The compound's relative energies of low and high spin configurations have been investigated when the compound is bound to H(sub)2 O and NH (sub)3 ligands in the effort to determine whether ligands' coordination chemistry would change the spin state of Co (super)2+ and the results are reported.

Kinetics and a mechanism for the reaction of cis-Pt(SiMePh2)2(PMe2Ph)2 with the chelating bis(diphenylphosphino)ethane (dppe) in dichloromethane and for the phosphine exchange in toluene, together with a series of quantum chemical density functional theory (DFT) calculations is reported. DFT calculations show that the distortion is due to the rehybridization that takes place when two strongly binding silyl ligands are in cis configuration.

The Hg(super 2+)- and HgCl(super +)- assisted aquations of a series of platinum(II) chloride complexes and the reverse chloride transfer from HgCl2 and HgCl(super +) to platinum are assessed. Transient metal-metal bonded Pt-Hg adducts characterized by their stability constants and electronic spectra are observed for Hg(super 2+) but not for HgCl(super +) and these adducts are probably not intermediates along the reaction coordinate.

The oxidation of HSO3- by [MoVIO2(mnt)2]2- (mnt2- = 1,2-dicyanoethylenedithiolate) was examined through density functional techniques and extended Huckel computations. Findings showed that the favored pathway requires the attack of the sulphur atom of HSO3- on one of the oxo groups of the molybdenum dioxo unit with concomitant hydrogen atom transfer to the other oxo group.

The possible presence of hydroxide at the active site of xanthine oxidase is investigated by local density approximation of density functional theory. As such, optimized structures are computed for four-, five- and six-coordinate model active sites. Two experimentally confirmed singly bonded sulfur ligands are shown by thiolate (CH3S)- and dithiolene (SRCCRS)2-, where R = H, CH3. However, both exhibit nearly the same data as the related models. A comparative analysis between recently available data and the calculated M-L distances reveals the futility of four- and six-coordination.

The activation energy barriers governing water exchange reaction on (Pd H2O 4)2+, (Pt H2O 4)2+, and trans-(PtCl2 H2O 2) is calculated using density functional theory. Optimization of geometries at the local density approximation level and relativistically corrected LDA are strongly consistent with the reported data. The energy deviations of the actual transition states from the model trigonal pyramidal systems, which are of importance to associative activation processes, are not large.

An electronic energy term for transition metals (copper and nickel complex) was constructed for extending Molecular Mechanics (MM) to open-shell, Werner-type coordination compounds. Cellular Ligand Field Stabilization (CLFSE) was computed by calculating the d-orbital energies generated from a ligand field. Copper complexes are intrinsically flexible and with the Jahn-Teller effect can undergo large geometrical changes from relatively minor crystal packing effects.

The dielectric response of spin-crossover (SCO) materials is a key property facilitating their use in next-generation information processing technologies. Solid state hybrid density functional theory calculations show that the temperature-induced and strongly hysteretic SCO transition in the Cs+Fe2+[Cr3+(CN-)6] Prussian blue analogue (PBA) is associated with a large change (Δ) in both the static, Δϵ0(HS - LS), and high frequency, Δϵ ∞(HS - LS) dielectric constants. The SCO-induced variation in CsFe[Cr(CN)6] is significantly greater than the experimental Δϵ values observed previously in other SCO materials. The phonon contribution, Δϵphon(HS - LS), determined within a lattice dynamics approach, dominates over the clamped nuclei term, Δϵ ∞(HS - LS), and is in turn dominated by the low-frequency translational motions of Cs+ cations within the cubic voids of the Fe[Cr(CN)6]- framework. The Cs+ translational modes couple strongly to the large unit cell volume change occurring through the SCO transition. PBAs and associated metal-organic frameworks emerge as a potentially fruitful class of materials in which to search for SCO transitions associated with large changes in dielectric response and other macroscopic properties. [ABSTRACT FROM AUTHOR]