The Metal (ion) And Complex Organic Molecules, The Nature Of The Bonding And Spectroscopic Properties Of Theoretical Research

Organometallic ion complex has been a long-standing topic for its important role in biology and chemistry. A theoretical study on the nature of binding and characters such as geometries, interaction energies and vibrational frequencies will provide a theoretical basis for the relevant studies.In this thesis, we have studied the binding between metal cation and ligand as well as its effect on the vibrational frequency; the (natural bond orbital) NBO analysis has been carried to study the effects of electron density redistribution and rehybridization on the strength and vibrational frequencies of some bond. In the last section, we attempted to study the dihydrogen bonded system. Our work will focus on four aspects:Chapter one: The structures, vibrational frequencies and interaction energies of acetone and its complexes with various metal cations were determined using the hybrid three-parameter B3LYP density functional method. For all the studied complexes, the interaction between metal cation and the C=O group of acetone is mainly electrostatic in nature, and the carbonyl (C=O) stretch vibration is red-shifted with respect to the C=O vibrational frequency in free acetone. The NBO analyses show that electron density redistribution and rehybridization are responsible for the red shift of the C=O stretch in all the studied complexes, and that electron density redistribution and rehybridization can be used to explain the extent as well as the trend of the red shift of the C=O stretch in all the studied complexes. Lee's explanation fails in some complexes, such as Mg²⁺/Ca²⁺/Al+/Mg+/Ca+- acetone.Chapter two: M+-C2H2 (M=V, Fe, Co, Ni) and M+-C6H6 (M=V, Si, Ni) complexes were studied by using density functional theory (DFT) at B3LYP/6-311+G** and B3LYP/6-311++G** levels,respectively. In M+-C2H2 complexes, the C-H bond length displays an increase with a concomitant red shift of C-H stretching frequencies, compared with C-H stretching vibration in free C2H2, while in M+- C6H6 complexes, the C-H bonds exhibit contraction accompanied by the blue shift of C-H stretching frequencies. These frequency shifts are well consistent with experimental results. To account for the interesting changes of C-H vibrations in M+-C2H2/C6H6 complexes, the natural bond orbital (NBO) analysis was carried out. The NBO results suggest that both the red and blue shifts are attributed to changes of electron density inσ*CH and s-character of carbon atom in C-H bond. The conclusion of our research is that electron density redistribution and rehybridization are the chemical origin of these two types of frequency shifts in M+-C2H2/C6H6 complexes.Chapter three: The structures, vibrational frequencies and binding energies of CO and its complexes with Au+ have been determined using the B3LYP method. For Au+ (CO) and Au+ (CO)2 complexes, their structures are linear. Au+ (CO)3 has a trigonal planar structure and Au+(CO)4 is tetrahedral. For all the studied complexes, the CO bond length displays contraction accompanied by blue shifts of CO stretching frequencies, with respect to the free CO stretching frequency (2143 cm-1). The NBO analyses show that the blue-shifting effect resulting from rehybridization in all complexes is much larger than the red-shifting effect due to ED redistribution, as a result these CO stretch frequencies are blue-shifted. This means that the blue shift can also be attributed to the whole effect of electron density redistribution and rehybridization.Chapter four: The structures and vibrational frequencies of dihydrogen bonded complexes LiH-C2HX (X=H, F, Cl) and C6H5OH-BTMA have been determined. In C6H5OH-BTMA complex, the O-H stretching frequency is red-shifted with respect to the O-H vibrational frequency in benzene monomer. And for LiH-C2HX (X=H, F, Cl) complexes, the Li-H bond and C-H bond of LiH-C2HX are blue-shifted and red-shifted respectively. In order to explain the red and blue shifts of C-H, O-H and Li-H bonds, the NBO analysis was carried. And the corresponding results show that, both the red shifts of O-H and C-H bonds and the blue shift of Li-H bond are the results of electron density redistribution and rehybridization.Charge is transferred between metal cations and ligands upon the formation of complex. And this charge transfer can result in the formation of a new electronic structure and changes in geometry and vibrational frequencies of the ligands. The NBO analysis shows that both the red and blue shifts in the complexes studied here are the results of electron density redistribution and rehybridization.