Isotope effects on the vibrational spectra of the Fe(Phen)2(NCS)2 spin-crossover complex studied by density functional calculations

摘要

A geometry optimization and vibrational frequency calculation has been carried out on the Fe(phen)2(NCS)2(phen=1,10 phenantroline)molecule in both spin states(5=0 and S=2)using the density functional theory(DFT)method with the B3LYP functional and the 6-31G(d)basis set.The frequency shifts upon 54Fe-57Fe and 14N-13N isotope substitutions have been calculated and compared with the experimental frequency shifts as well as with calculated data(DFT/BP86)published in the literature.In the low frequency region(100-600 cm~(-1)),both DFT methods reproduce correctly the measured isotope shifts.The accuracy of the calculated vibrational entropy change upon the spin crossover(SCO)is lower:reasonable errors(~0%)of the calculated frequencies lead to a relatively large error(~0%)of the total entropy change.