Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (07): 1637-1644.doi: 10.3866/PKU.WHXB201204111

• THEORETICAL AND COMPUTATIONAL CHEMISTRY • Previous Articles     Next Articles

The Cr—Cr Bonding Character in Metal String Complexes [Cr3(dpa)4LL'] (dpa=dipyridylamide; L, L'=Cl, BF4, CCPh)

MA Hua-Xuan1, ZHENG Yan-Ling1, ZHAN Yi-Shi1, TAN Ying1, HUANG Xiao1, PENG Qi1, XU Xuan1,2,3,4   

  1. 1. School of Chemistry & Environment, South China Normal University, Guangzhou 510006, P. R. China;
    2. Key Laboratory of Theoretical Chemistry of Environment, Ministry of Education, Guangzhou 510006, P. R. China;
    3. Key Laboratory of Electrochemical Technology on Energy Storage and Power Generation in Guangdong Universities, Guangzhou 510006, P. R. China;
    4. Engineering Research Center of Materials and Technology for Electrochemical Energy Storage, Ministry of Education, South China Normal University, Guangzhou 510006, P. R. China
  • Received:2012-02-23 Revised:2012-04-10 Published:2012-06-07
  • Contact: XU Xuan E-mail:xuxuan@scnu.edu.cn
  • Supported by:

    The project was supported by the Natural Science Foundation of Guangdong Province, China (9151063101000037), Ministry of Education of Guangdong Province, China (2010B090400184), Program of Talent Introduction of Guangdong Province, China (C10133), Science and Technology Program of Guangzhou City, China (2011J4300063).

Abstract:

To study the configuration, the metal-metal interactions and the influences of axial ligands L and L' on the Cr—Cr bond in metal string complexes Cr3(dpa)4LL' (L, L'=Cl, BF4, CCPh), the structures of complexes Cr3(dpa)4Cl2 (1), Cr3(dpa)4(BF4)2 (2), Cr3(dpa)4Cl(BF4) (3), Cr3(dpa)4(CCPh)2 (4) and Cr3(dpa)4Cl(CCPh) (5) were investigated by density functional theory UBP86 method. The conclusions can be drawn as follows: (1) The complex with longer average Cr—Cr distance tends to form a symmetrical configuration, while it tends to form a asymmetric configuration with shorter average Cr—Cr distance. The most stable spin states, quintet states, with the longest average Cr—Cr distance tend to form a symmetrical configuration, while septuplet states with shortest Cr—Cr distance tend to form asymmetrical one; (2) For quintet states of all complexes, there is only a 3-center-3-electron σ bond in Cr36+ chain. Furthermore, except the σ bond, there are weak π Cr—Cr interactions in complex 2 and 3. For septuplet states, there is a triple bond in the short Cr—Cr bond of complexes 1-3 and 5, while there is only a 3-center-3-electron σ bond in complex 4. Not only in symmetrical configuration but also in asymmetric configuration, there are σ delocalizations in Cr36+ chain, suggesting the asymmetrical metal string complexes are still the potential molecular wire species; (3) The interactions between axial ligand L and Cr atom mainly correspond to the nL→4sCr and nL→3dz2Cr delocalizations. In addition, for stronger σ donor CCPh- ligand, there are σC—C→4sCr delocalizations as well. The order of the bond strength of axial ligand L and Cr atom is 2<3<1<5<4. The strongest bonding between CCPh- ligand and Cr atom weakens the Cr—Cr bond and lengthens the Cr—Cr distance. Therefore, every spin state of 4 tends to form a symmetrical configuration.

Key words: Metal string complexes, Density functional theory, Natural bond orbital, Metal-metal interaction

MSC2000: 

  • O641