Outer-Sphere Charge-Transfer Effects on the Spectroscopy of the [Ru(NH3)5(py)]2+ Complex

Abstract

We repon here the results of a theoretical analysis of the [Ru- (NHMpy)]'+ absorption spectrum. which is known to be sensitive to media effects.' The intermediate neglect of differential overlap (INDO) model parametrized for spectroscopy at the configuration interaction (CI) level of theory has been used in these studies.? We demonstrate here that the absorption spectrum of the above complex can be reproduced only if specific outer-sphere effects are considered and, in particular. that the solvent-to-complex charge transfer is essential in lowering the energy of the metal-to-ligand charge transfer (MLCT) excitations to positions that agree with experiment.' A simple point-charge model we utilize in this work is shown to be a successful substitute for the explicit solvent modeling. The proposed procedure reproduces the experimental energies and provides a correct assignment of the absorption bands at substantially reduced computational cost.In this work we examine the spectroscopy of [Ru(NHs)s-(py)]'-. whose structure is shown in Figure 1. Although the electronic spectra of such complexes have been known for over 25 years to he sensitive to the nature of the solvent, the reasons for this sensitivity have remained elusive.'.' The bond lengths we use for the model structure shown in Figure I are taken from X-ray experiments.-' The INDO parametrization' used for the ruthenium 4d orbitals (/&) was obtained to reproduce the observed d-d spectrum of [Ru(NH&,]~+. I The j ? , , thus obtained is -13.0 eV. The value for /3 for the s and p electrons has been modified slightly from that used for the firs-row transition series, from /?. = /j --1 .O eV to , 9\ = / 3, , = -2.0 eV.The molecular orbital (MO) diagram for the frontier orbitals of [Ru(NH&,l'+ and [Ru(NH3)5(py)l'+ is given in Figure 2.The pyridine-dominated n* orbitals were found in the d-d gap as expected from the spectroscopy of similar Ru compounds and previous theoretical work.5-n The loCalion of the occupied ; r pyridine orbitals varies slightly with the geometry and is typically 0.1 au ( I au = 27.21 eV) below the occupied Ru d orbitals. labeled in Figure 2 as d,.As one can expect from the MO diagram in Figure 2. the absorption spectrum of [Ru(NHz)5(py)]'+ should contain contributions from weak d-d excitations and from the more intense d -x* MLCT and intraligand n -n* transitions. The symmeq-forbidden d-d transitions are not expected to compete 0 I Ford. P.: Rudd. De F. P.: Gaunder. R.: Tauhe. H. J . Am. Clzm#. SO<.

X-ray absorption spectroscopy to analyze nuclear geometry and electronic structure of biological metal centers?potential and questions examined with special focus on the tetra-nuclear manganese complex of oxygenic photosynthesis

“…To obtain insights in the electronic basis of the changes described above and in the relation between the multiplescattering picture, on the one hand, and the molecular-orbital picture, on the other hand, we carried out MO calculations using the semi-empirical approach of Zerner [40,41,42]; for details see "Materials and methods". Again, standard parameters were used and no efforts were made to obtain improved agreements with the experimental results by varying calculation parameters.…”

Solvent Effects on Molecular and Ionic Spectra IX: The Change in Dipole Moment Accompanying Metal to Ligand Charge Transfer Absorption in Pentaaminopyridylruthenium(II)

“…The general nature of chargetransfer electronic transitions in inorganic complexes is of considerable current theoretical interest. [11][12][13][14] In general, [15][16][17][18] the molecular parameter that can be most reliably extracted from electroabsorption spectroscopy is the change in dipole moment on excitation, ∆µ. None of the properties are straightforward to calculate a priori, but ∆µ and the absorption band frequency ν are perhaps the simplest.…”

“…This will lead 11,16 to improved understanding of the properties of inorganic and other charge-transfer systems and will allow the investigation of possible additional effects such as charge-transfer to solvent. 12 …”

Hybrid Ab initio/EFP approach for calculating d‐d absorption spectrum of hexaammineruthenium(II) ion in aqueous solutions

“…Actually, there is some uncertainty with the predicted hydrogen bond lengths for this and related complexes in water solution [15][16][17]. Despite that we have found only a single local minimum among numerous ones corresponding to structures with different H-bond networking on the potential surface of the solvated complex, our estimated NOH.…”