| Abstract |
We systematically investigated the tuning of the reduction potentials (E0) for the first row transition metal (M = Cr, Mn, Fe, Co, Ni) complexes with the functionalized 1,4,7-Triazacyclononane-N,N',N芒聙聺-triacetate (TCTA) ligands by means of DFT calculations. To predict reliable E0, the modified UB3LYP functional and equilibrium concept between high and low spin states were utilized. The functional groups single bondNH2, single bondCN, 芒聢聮F, and single bondNO2 were attached to the carbon atoms carefully selected by considering the LUMO and steric hindrance. Based on firmed accuracy of DFT calculations, finally we obtained the calculated E0 for a series of complexes. It was found that electron donating group such as single bondNH2 will cause a negative shift of E0 while electron withdrawing groups have the opposite effect. The overall trend of the calculated E0s according to ligand modifications were predicted to have the order as 芒聢聮NH2 < Pristine < 芒聢聮F 芒聣聢 芒聢聮CN < 芒聢聮NO2. In addition, optimized geometries, LUMO, vertical electron attachment and energy components constituting E0 were discussed in detail to assist the further understanding for E0s. Consequently, we suggested that 16 complexes can play a role as an electrolyte in aqueous redox flow battery. They can be classified into 5 groups having similar E0 ranges: Group I (- 0.6 V 芒聢录 芒聢聮 0.7 V), Group II (around 0.0 V), Group III (around 0.3 V), Group IV (0.6 芒聢录 0.8 V) and Group V (1.1 芒聢录 1.2 V). Especially, it is expected that [MnLF], [MnLCN] and [NiLNH2] can be used as promising catholyte candidates possibly possessing high E0s which almost reach to the reduction potential limitation 1.25 V in aqueous redox flow battery. Our systematic approach to tune E0 can be applied to the design of other complexes via rational ligand modification. |
Mindanao State
University - Iligan Institute of Technology