Theoretical Analysis Of The IR Frequency Shift Of C-O Stretching Frequency In Metal Carbonyls

The bond between metal cation (atom) and small molecular plays a special role in thestructure and properties, and metal complexes are one of the most important areas inchemistry, bioscience and material science. Metal complexes developed rapidly inrecent years, and have a bright future. An increasing number of researchers studymetal complexes, some devote to practical application, and some have found specialcharacter, like catalytic activity, biological activity and conductivity. Some scientistsemphasize in structure and theoretical research. It is very helpful for understandingthe nature of the bond and complexes.Metal carbonyls have been widlely studied in experimental researches. The IRfrequency in C-O bond shifts is observed as blue or red shift. The thereotical analysisemphasizes the electron density change using Dewar-Chatt-Duncanson (DCD) model.This model is useful in studying the origin of red shift, but is not available in studyingthe origin of blue shift. Another model proposed by Frenking suggests therepolarization is the main reason of the origin in the blue shift, which is useful instudying blue shift. Based on these two models and our previous studies, the maingoal of this article is to find an available unified explanation for the frequency shift inmetal carbonyls. Whether the electron density redistribution and rehybridization isalso available in metal carbonyls. This article will be useful in understanding thechemical origin in theretical chemistry.We study the interactions and vibrational frequency in the metal complexes throughtheoretical study using density functional theory. We also use Natural Bond Orbital(NBO) method to analyze the influence of electron redistribution and rehybridization on chemical bond and vibrational frequency. In addition, we use Atoms in Molecule(AIM) to study the nature of the bond between metal cation and ligand. Our workfocuses on the following aspects:Chapter one: Natural Bond Orbital (NBO) method and Atoms in Molecules (AIM)theory are used to study the chemical origin in the direction and trend of C-Ofrequency shift, and the Cu+…C bond nature in copper carbonyl cations Cu+(CO)n(n=1-8). NBO analyses show that the interplay of two competing factors, involvingπ-back-donation and rehybridization, are responsible for both the direction and trendof C-O stretching frequency shift in Cu+(CO)n(n=1-8) complexes. Our studyemphasizes the role of π-back-donation in explaining the C-O blue shift. In addition,Cu+…C interactions are interesting because optimized Cu+(CO)n(n=1-4) structure hadone sphere CO ligands, and Cu+(CO)n(n=5-8) had two sphere CO ligands.Topological analyses of the electron density are applied to characterize the Cu+…Cinteractions between first/second sphere CO with Cu+, and to explore Cu+…Cinteractions in nature.Chapter two: Natural Bond Orbital (NBO) method is used to study the chemicalorigin in the direction and trend of C-O frequency shift. NBO analyses show that theinterplay of two competing factors, involving π-back-donation and rehybridization, isresponsible for both the direction and trend of C-O stretching frequency shift inAu+(CO)n(n=1-4) complexes. Our study emphasizes the role of π-back-donation inexplaining the C-O blue shift.Chapter three: Natural Bond Orbital (NBO) method and Atoms in Molecules (AIM)theory are used to study the chemical origin in the direction and trend of C-Ofrequency shift, and the Fe-…C bond nature in copper carbonyl cations Fe-(CO)n(n=1-8). NBO analyses show that the interplay of two competing factors, involvingπ-back-donation and rehybridization, are responsible for both the direction and trendof C-O stretching frequency shift in studied complexes. Charge transfer and rehybridization during complexation lead to change in geometricstructure and vibrational frequency. NBO analyses indicate the interplay of electrondensity redistribution and rehybridization determines the frequency shift uponcomplexation. Topological analyses of the electron density are applied to characterizethe nature of Fe-…C bond.