Density Functional And Ab Initio MO Study On The Electrionic Structure And Carbonyls' Fluxionality Of The Triosmium Carbonyl Clusters

The characteristic spectra of the triosimum carbonyl clusters have been extensively studied by quantum chemistry due to the clusters are of importance to both theory and application, but the carbonyls' fluxional behaviour in the clusters have hardly been studied by same method. It is well known that the carbonyls' fluxional behaviour have something to do with some catalytic reactions, So in order to look inside that we tried to use density functional theory and ab injtio method to study these clusters so as to obtain some reasonable results.Considering the big molecules as well as the expensive of the theoretical calculations, we use the density functional theory to optimize the geometries of clusters, and then, on the basis of the geometric optimizations, the ab initio method has been used to do their natural bond orbitals' calculations. All the conclusion can be summaried as follow:(1)It has been verifed that the transference of CO^<sup> procede CO in 0s3(CO)2:but the transference of defferent CO.,. or CO.,, of the same Os atom is a quasi-coupled transformation.(2)The Mulliken Populations indicated that, in clusters0s3 (CO) ^{i -H}2.,( ii -L)n (n0, 1, 2, L11, CW, OCI-L, Br), each atom Os lost 0. 3e charge which are obtained terminal CO. In addition, the Mulliken Populations also show that there are charge transference between molecular fragments Os(CO)4 and Os (CO)3, where each Os (CO)4 get charge from two fragments Os (CO)3(3)All the lengths of C-O bonds are longer in optimized geometries than in the result of experimentation. In Os(CO)4 fragment , the C..-O,, are longer than C&O. bonds. As to the clusters containing the hybride ligands , the Os-Os bonds with two bridging L ligands are longer in the experimentation, while those without bridging L ligand are shorter. The Os-Os bonds in Os.(CO)o(Li-Br)2 clusters are longer in the calculation. Every Os-C bond is longer in the calculation ,and it is longer in Os(CO)4 fragment than in Os(CO): fragment , it makes carbonyl move in proper sequence: the carbonyl in Os (CO)1 fragment forego than the horizontal ones in Os(CO)4 fragment . As to 0s3(CO)o(u-BrY clusters, the average length of OsC bonds is shorter than the longest one in Os (CO): fragment. So it makes the carbonyl in Os(CO)3 fragment forego than that in Os(CO)1, while the axile carbonylIIIforego than horizontal ones in Os(CO)4 fragment . Sum up, as to the kind of clusters like 0s3(CO)( p.-Ll)( i'-L2), the moving of earbonyl is parted, it is decided by the substitute ligand.(4)On describing the composing of orbitals , all the metal atoms' orbitals of Os-Os bonds and Os-C bonds in triosimum carbonyl clusters are basically composed by 6s orbitals and 5d orbitals , and the latter makes the central contribution, while all the Os atoms' 5d orbitals in Os (CC) . fragment mostly can be concerned in the composing. While in the Os (CC) fragment of Os (CC) 'o ( i -H) (u -L) (LH, 0db, Br) and Os3(COY0(p- Br)2, the orbitals' composing of o bonds and 't bonds also have some rules: the two it bonds of horizontal carbonyl are composed by 2pz or 2pz and 2py ,while the o bond is composed by 2s and 2px and 2py orbitals, the two it bonds of the axile carbonyls are composed by 2px 2py orbitals, the a bond is composed by 2s and 2pz orbitals, the carbonyl in Os (COY fragment, no matter for it bonds or for a bonds , it's every orbital of 2p orbitals is capable to appear in the composings.