Case study presenting the use of quantum-mechanical "zone criterion" as a clue in assigning the electronic transitions exhibited by a complex compound

As quantum-mechanical criteria are extremely useful in investigating the molecular structure of a newly synthesized chemical compound (in particular, in assigning its electronic transitions), this paper aims to present the results obtained by using "zone criterion" as a clue in interpreting the UV-Vis spectrum of a complex compound that we dealt with, which was formed by the coordination to Ni(II) of a 1,4-naphthalenedione derivate (namely, 2-mercapto-3-niacinamido-1,4-naphthalenedione). So, by taking into account the fact that an electronic transition extremely unlikely occurs between two quantum-mechanical states involving spatially separated parts of a certain molecule (which we simply called "zone criterion"), we used a specialized software package in order to perform a molecular modeling that was able to lead us (through specific semi-empirical calculation) to the assignment of all the recorded electronic transitions. The results thus obtained proved themselves to be in a very good accordance with the classical interpretation of the UV-Vis spectrum (which we already had reported), showing, once again, that quantum-mechanical analysis can serve as an useful clue and represents a powerful tool in characterizing the structure of a new complex compound.