Theoretical and Spectroscopic Analysis of Square-Planar Tellurium(II) and Selenium(II) Diphenyl Thiourea Complexes in p2 Electronic Configurations.

In this work, we performed a detailed mathematical ligand field theory analysis of square-planar (D4h) main group complexes in p2 electronic configurations, and the results were subsequently used to generate an energy-level correlation diagram. We synthesized the model p2 tellurium(II) diphenyl thiourea coordination complex for further spectroscopic investigation. Dissolution of TeO2 in concentrated HCl resulted in the formation of a [TeCl6]2- complex in acidic media, and subsequent addition of diphenyl thiourea resulted in the reduction of Te4+ to Te2+ (observed by 125Te NMR spectroscopy) and the formation of a cis-Te(dptu)2Cl2 complex, which was characterized by single-crystal X-ray diffraction (XRD). Using in situ optical/magnetic spectroscopy - specifically, UV-vis and magnetic circular dichroism (MCD) spectroscopy - we observed absorbance bands and polarized transitions consistent with the calculated p-orbital splitting in a square planar (D4h) ligand field. Using the results of our spectroscopic investigation, we generated a molecular orbital (M.O.) diagram for the cis-Te(dptu)2Cl2 complex. We then used the M.O. diagram, in conjunction with the energy level correlation diagram, to assign the electronic transitions observed in the spectra of the cis-Te(dptu)2Cl2 complex. The analogous selenium(II) complex, cis-Se(dptu)2Cl2, was used to elucidate the observed transitions with minimal contribution from spin-orbit coupling. Our work examined how in situ spectroscopy and complementary ligand field theory analysis can be used to elucidate the electronic structures of main group coordination complexes.