title: Octacoordinate metal carbonyls of scandium and yttrium: theoretical calculations and experimental observation.
abstract: BACKGROUND
  The transition metal carbonyls are among the most important complexes in coordination chemistry. The maximum coordination number in these complexes is seven. Because the cations Sc(+) and Y(+) have empty second outermost d orbital subshells, they can possibly bond eight CO ligands, forming the 18-electron d(10)s(2)p(6) noble gas configuration. The aim of this study is to determine whether the octacoordinate metal carbonyls of Sc(+) and Y(+) exist.
  
  
  METHODS
  The structures and bonding of M(CO)n(+) (M = Sc and Y, n = 7-9) were studied using Density Functional Theory (DFT) calculations with the functionals of B3LYP and BP86. The cationic complexes from laser ablation of Sc and Y in CO gas were analyzed by time-of-flight mass spectrometry.
  
  
  RESULTS
  The structures of M(CO)n(+) (M = Sc and Y, n = 7-9) and the bond dissociation energies for the last CO ligand in M(CO)n(+) (M = Sc and Y, n = 8 and 9) were obtained using DFT calculations. The products in the experiment for both metals include the series MO(CO)n(+), MO(H2O)(CO)n(+) and M(CO)n(+) (M = Sc or Y). The intensities of the MO(CO)n(+) and MO(H2O)(CO)n(+) ions change gradually with the number of CO ligands, while most M(CO)n(+) ions are very weak except for three intense ones, Sc(CO)7(+), Sc(CO)8(+) and Y(CO)8(+).
  
  
  CONCLUSIONS
  Comparisons between the theoretical calculations and the experimental observations indicate that eight CO ligands are chemically bonded on the central atom in the singlet state of Sc(CO)8(+) ((1)A1 state of D(4d) symmetry) and the singlet and triplet states of Y(CO)8(+) ((1)A1 state of D(4d) symmetry and (3)A(1g) state of O(h) symmetry). The (1)A1 states of both Sc(CO)8(+) and Y(CO)8(+) have the 18-electron d(10)s(2)p(6) noble gas configuration. In M(CO)9(+) (M = Sc or Y), the ninth CO is weakly adsorbed on the external shell.
authors.affiliation: University of Chinese Academy of Sciences, College of Materials Sciences and Opto-Electronic Technology, Beijing 100049, China.
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Xing
authors.forename: Jie
authors.initials: J
authors.lastname: Wang
authors.forename: Hua
authors.initials: H
authors.lastname: Xie
authors.forename: Zhiling
authors.initials: Z
authors.lastname: Liu
authors.forename: Zhengbo
authors.initials: Z
authors.lastname: Qin
authors.forename: Lijuan
authors.initials: L
authors.lastname: Zhao
authors.forename: Zichao
authors.initials: Z
authors.lastname: Tang