Acta Phys. -Chim. Sin. ›› 1996, Vol. 12 ›› Issue (01): 59-62.doi: 10.3866/PKU.WHXB19960113

• Communication • Previous Articles     Next Articles

Bonding of Alkali-mercury and Alkanli-lead Clusters

Liao Meng-Sheng   

  1. Department of Chemistry,Xiamen University,Xiamen 361005
  • Received:1995-03-15 Revised:1995-05-22 Published:1996-01-15
  • Contact: Liao Meng-Sheng

Abstract:

Relativistic density-functional calculations on free Hg2, Hg4, Hg8, Pb2 and Pb4 clusters, and those clusters embedded in an alkali (A) atom surrounding are reported. Heavy metal-metal (M-M) distances, binding energies and effective charges have been calculated. The Hg-Hg distance in the weakly bound free clusters is over 330 pm. Upon embedding in an alkali surrounding, the bonding is strengthened; the bond lengths are reduced for square planar Hg4 to below 300 pm. The bonding in the hypothetical tetrahedral alkali-mercury cluster appear to be quite different, where Hg4 will undergo a transition to four Hg1. This explains the strict preference of square over the tetrahedral geometry of Hg4 clusters in amalgams. Pb4 is predicted to be stable in a pure cluster and does not show significantly different bonding feature in the lead-alkali crystal. The effective charges on Hg and Pb are calculated to be -0.4 and -0.6, respectively. The bonding characteristics are also examined by calculation of the M4-An interaction energies. The amalgamation energies lie in the range of 50 to 70 kJ/molHg. The formation energy of alkali-Pb is up to 150 kJ/molPb, much stronger than that of alkali-Hg.

Key words: Alkali-mercury compounds, Alkali-lead compounds, Nature of bonding