Theoretical Analysis Of ECD Spectra Of Ni-salen Complexes

Chirality has always played an important role in chemical and biological field.Despite there have been many researches of Salen complexes,theoretical research based on first principle level theory could be realized,untill the end of the 20 century.Although there has been many researches on Schiff-base complexes,relations of the crystal structure,ECD spectrum and calculation together is still rare.There is still no clear answer whether the first absorption band symbol of longwave region as well as exciton coupling can be a criteria for Co and Ni Salen complexes.Accordingly,using density functional theory(DFT),We contucted a theoretical analysis on electronic structures,as well as the chiroptical properties of Ni-salen complexes.The main work is as follows:1 Using density functional theory(DFT)at the B3LYP level of theory with the basis set of 6-311+G(2d,p)to optimize the geometries of nickel complex[Ni(sal-R,R-chxn)](no virtue frequency).Based on this,optimizing the geometries of the nickel complexes[Ni(hacp-R,R-dpen],[Ni(dha-R,R-dpen)],[Ni(hacp-S,S-chxn)],[Ni(dha-S,S-chxn)],[Ni(hacp-S-pn)],[Ni(dha-S-pn)]in methanol solution.2 Then using the time-dependent density functional theory(TDDFT)with the same functional and basis set to caculate their excitation energy,oscillator,rotational strength.The solvent effects were included in these calculations,by using the polarized continuum model(PCM).Accordingly,drawing out the corresponding ECD.And analysis their transition Properties3 The calculated ECD spectras have a good match with the observed ones.It reveals that the first circular dichroism(CD)band in the long wavelength region of Ni-Salen complex is dominated by the ligand-to-metal charge transfer transition??d mainly rather than d?d transition as reported.For the complex of Ni-dha,though the first circular dichroism(CD)band in the long wavelength region is dominated by d?d transition mainly,but the metal-to-ligand charge transfer transition d??do exists.The chiral carbon atom has Less impact,the third ligand bound instead of changing the group has no influence on the sign of CD bands,but it indeed have a significant influence on the shape and intensity of the CD spectra,not the traditional view of almost no effect.when the absolute configuration of the central metal is?,the first CD absorption band is positive.However when the absolute configuration of the central metal is?,then the first CD absorption band would be negativetive.These has nothing to do with the change of ethylenediamine side-chain substituents.4 For the complexes of Ni-Salen,the shortwave region is dominated by the Ligand to ligand charge transfer transition???*mainly,mixed with??d and d-?ingredients.For the complexes of Ni-dha,the the shortwave region is dominated by the metal to ligand charge transfer transition d??*mainly.The former have two exciton coupling features,but were affected by the neighborhoods.The banding pattern changes drastically.The latter were affect by solvent effects.So,taking the exciton coupling as a criterion was not a good idea.The rule also applies to other closed-shell[M(salen)]complexs alike.These findings make a good sense to coordination stereochemistry,electronic structures,as well as the chiroptical properties of such complexes.