Excited States of the Nickel Carbonyls Ni(CO) and Ni(CO)4: Challenging Molecules for Electronic Structure Theory.

We apply a wide range of correlated electronic structure approaches to the excited states of Ni(CO)4 and Ni(CO) as model complexes of saturated and unsaturated transition metal carbonyls respectively to understand the performance of each method, in addition to setting benchmark data for these metal carbonyls. In particular, we apply the coupled-cluster linear response hierarchy, complete-active-space self-consistent field theory, N-electron valence state multireference perturbation theory, Monte Carlo configuration interaction, and time-dependent density functional theory with a range of functionals and basis sets. We find that although the systems can qualitatively be described by a single configuration, electron correlation effects are sufficiently strong to give large single amplitudes in cluster expansions, which cause spurious solutions to the response equations for the intermediate CCn methods. DFT also performs well if care is taken to choose an appropriate functional, although for Ni(CO) several popular functionals give the incorrect ground spin-state, depending on the amount of Hartree-Fock exchange.

Toward Understanding of the Lower Rim Binding Preferences of Calix[4]arene.

Calixarenes form polymetallic clusters with many first row transition metals and lanthanides via binding at the lower rim. A detailed theoretical study of the relative binding preferences for calix[4]arene (C[4]) toward the first row transition metals is presented. In order to do this, the binding energies of C[4] with transition metals displaying a range of common oxidation states, and a variety of potential spin states of the bound cations were investigated using density functional theory. A known diagnostic test, B1, is employed as a measure to gauge the multireference nature of each compound and is used as justification for the choice of different DFT functionals employed.

Ultrafast photo-induced ligand solvolysis of cis-[Ru(bipyridine)2(nicotinamide)2](2+): experimental and theoretical insight into its photoactivation mechanism.

Mechanistic insight into the photo-induced solvent substitution reaction of cis-[Ru(bipyridine)2(nicotinamide)2](2+) (1) is presented. Complex 1 is a photoactive species, designed to display high cytotoxicity following irradiation, for potential use in photodynamic therapy (photochemotherapy). In Ru(II) complexes of this type, efficient population of a dissociative triplet metal-centred ((3)MC) state is key to generating high quantum yields of a penta-coordinate intermediate (PCI) species, which in turn may form the target species: a mono-aqua photoproduct [Ru(bipyridine)2(nicotinamide)(H2O)](2+) (2). Following irradiation of 1, a thorough kinetic picture is derived from ultrafast UV/Vis transient absorption spectroscopy measurements, using a 'target analysis' approach, and provides both timescales and quantum yields for the key processes involved. We show that photoactivation of 1 to 2 occurs with a quantum yield ≥0.36, all within a timeframe of ~400 ps. Characterization of the excited states involved, particularly the nature of the PCI and how it undergoes a geometry relaxation to accommodate the water ligand, which is a keystone in the efficiency of the photoactivation of 1, is accomplished through state-of-the-art computation including complete active space self-consistent field methods and time-dependent density functional theory. Importantly, the conclusions here provide a detailed understanding of the initial stages involved in this photoactivation and the foundation required for designing more efficacious photochemotherapy drugs of this type.

A time-dependent density functional theory study of the structure and electronic spectroscopy of the group 7 mixed-metal carbonyls: MnTc(CO)10, MnRe(CO)10, and TcRe(CO)10.

A detailed study of the structure, infrared, and electronic spectra of the mixed-metal group 7 carbonyls MnTc(CO)(10), MnRe(CO)(10), and TcRe(CO)(10) is presented using density functional theory, and time-dependent density functional theory, with a variety of modern density functionals. Long-range corrected density functionals are needed to accurately model the transitions in such complexes, and through calibration with data for known bimetallic carbonyls, DFT and TD-DFT can be used to predict the behavior of their as yet elusive counterparts.