UV-visible spectroscopy of macrocyclic alkyl, nitrosyl and halide complexes of cobalt and rhodium. Experiment and calculation

Abstract

Transition metal complexes (NH3)5CoX(2+) (X = CH3, Cl) and L(H2O)MX(2+), where M = Rh or Co, X = CH3, NO, or Cl, and L is a macrocyclic N4 ligand are examined by both experiment and computation to better understand their electronic spectra and associated photochemistry. Specifically, irradiation into weak visible bands of nitrosyl and alkyl complexes (NH3)5CoCH3(2+) and L(H2O)M(III)X(2+) (X = CH3 or NO) leads to photohomolysis that generates the divalent metal complex and ˙CH3 or ˙NO, respectively. On the other hand, when X = halide or NO2, visible light photolysis leads to dissociation of X(-) and/or cis/trans isomerization. Computations show that visible bands for alkyl and nitrosyl complexes involve transitions from M-X bonding orbitals and/or metal d orbitals to M-X antibonding orbitals. In contrast, complexes with X = Cl or NO2 exhibit only d-d bands in the visible, so that homolytic cleavage of the M-X bond requires UV photolysis. UV-Vis spectra are not significantly dependent on the structure of the equatorial ligands, as shown by similar spectral features for (NH3)5CoCH3(2+) and L(1)(H2O)CoCH3(2+).

The metallic thread in a patchwork thesis

“…In developing a Slater determinant based direct CI approach, Ruedenberg and Ivanic 51,52 found that approximately 50% of configurations in CISD were non-significant contributors to the energy. The picture was worse for CISDT and CISDTQ with some 90% of configurations being non-significant deadwood 52 .…”

“…and CISDTQ (including quadruples excitations) 98% for most systems 26,51,52 . While CI methods are introduced in computational chemistry textbooks previously referenced, the review article by Sherrill and Shaefer 26 is invaluable for gaining a good understanding of the method.…”

The metallic thread in a patchwork thesis

“…TDDFT calculations 51 on this system indicated that this photochemistry is mostly due to interactions between TDDFT natural orbitals 100 and 101. Those TDDFT calculations were previously performed 51 with GAMESS 19,20 and NWCHEM 52 using the Stuttgart small core ECP 31,32,53 for the rhodium, and the cc-pVDZ 23 basis set for the remaining atoms. Currently VVO calculations require all-electron basis sets, so for the VVO calculation, the all electron Sapporo [54][55][56] augmented double zeta basis sets were chosen for computational efficiency.…”