On the electronic structure and spectroscopic properties of a pseudo-tetrahedral cationic cobalt(II) tetraamine complex -([35] adamanzane)cobalt(II)

The electronic structure and spectrum of the unusual pseudo-tetrahedral cobalt(II) coordination compound formed with the bicyclic tetraamine ligand 1,5,9,13-tetraazabicyclo[7.7.3]nonadecane ([35]adz) has been investigated. The ligand-field absorption spectrum of the quartet ground state of the [Co([35]adz)]2+ cation was resolved into five components, which were assigned by application of angular overlap model (AOM) calculations. Furthermore, density functional theory (DFT) and time-dependent DFT (TD-DFT) were applied to investigate the structure and absorption spectrum of the cation using the B3LYP functional in combination with various basis sets. The DFT calculations provided a geometry for the cation in excellent agreement with the crystal structure of [Co([35]adz)]ZnCl4. The theoretical investigation of the electronic spectrum of the cation shows that TD-DFT can successfully be applied to open shell transition metal compounds, although only spin-allowed, single electron transitions are accounted for.