Article ID: 2016-0049
DFT (density functional theory) calculation was performed for various iron(III) chloride complexes, changing the geometry from octahedral to tetrahedral. Four kinds of functionals, BHandHLYP，wB97XD，CAM-B3LYP，LC-wPBE, were used with the basis set of 6-311+G(d,p) or 6-311+G(3df,2pd). Geometry optimization was carried out in water as the solvent employing PCM method. Optimized geometries of various complexes obtained by four kinds of functionals reproduced well each structure of iron(III) chloride. We discussed which isomer is energy stable between octahedral cis-[Fe(III)Cl2(H2O)4]+ and trans-[Fe(III)Cl2(H2O)4]+. Also discussed was the difference of the energy of the trigonal dipyramidal [Fe(III)Cl3(H2O)2] from the tetrahedral [Fe(III)Cl3(H2O)]. Change in stretching frequencies of coordinated water molecule to Fe(III) in various iron(III) chloride complex indicated that the frequency shifted to higher wavenumber as the decrease in the number of coordinated water in the octahedral form. The frequency again shifted to lower wavenumber in the trigonal dipyramidal and the tetrahedral form, indicating that the interaction between the coordinated water molecule and Fe(III) became stronger. The relation between the Fe(III)-H2O distance with the number of coordinated H2O also showed the result similar to the stretching frequency.
