Synthesis, structure determination, NBO analysis and vibrational/ electronic spectroscopic study of Iron(II) Bis(diethyldithiocarbamate) [Fe (DDTC)₂]

This work deals with the synthesis, computational molecular modeling, and vibrational/electronic spectroscopic analysis of the coordination complex [Fe(DDTC)2]. The complex was synthesized according to the guidelines provided by the graphical method. The optimization of the molecular structure was performed using Density Functional Theory with the exchange functional B3LYP and basis set 6-311G(d,p). The experimental FT-IR and Raman spectra of the complex were recorded in the range of 4000-0 cm(-1) to correlate them with the calculated spectra. Most of the DFT calculated frequencies agreed with the experimental results, and complete vibrational assignments (including metal-ligand) were made. To investigate the internal electronic mobility of the complex, we performed natural bond orbital analysis (NBO), which provided information regarding intramolecular charge transfer interactions resulting from the overlapping of bonding and antibonding orbitals. The NBO analysis also provided information about the electronic distribution between the HOMO and LUMO orbitals due to charge transfers. We found that the NBO analysis provided the main charge transfers between donor and acceptor atoms, and the HOMO-LUMO energy gap revealed that the complex has high kinetic stability. We also correlated the calculated and experimental UV-Vis spectra to investigate the configurations of several excited states of the complex that involve intra-ligand transitions. The charge transfer and D-d (Laporte Forbidden) bands were assigned. The results also corroborate the existence of several Ligand to Metal Charge Transfer (LMCT) and Metal to Ligand Charge Transfer (MLCT) transitions, as well as D-d transitions. We found that the experimental vibrational spectra agreed with the theoretical ones.