STUDIES ON COORDINATE BONDS IN POLYNUCLEAR COMPLEXES

1994 Fiscal Year Final Research Report Summary

• Project/Area Number: 05640638
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: Inorganic chemistry
• Research Institution: DAIDO INSTITUTE OF TECHNOLOGY
• Principal Investigator: SAKAI Yoichi DAIDO INSTITUTE OF TECHNOLOGY,DEPARTMENT OF CHEMISTRY ASSOCIATE PROFESSOR, 工学部, 助教授 (00126070)
• Co-Investigator(Kenkyū-buntansha): SUZUKI Takayoshi OKAZAKI NATIONAL INSTITUTES,INSTITUTE FOR MOLECULAR SCIENCE,RESERCH ASSOCIATE, 分子科学研究所, 助手 (80249953) ; YAMATERA Hideo DAIDO INSTITUTE OF TECHNOLOGY,DEPARTMENT OF CHEMISTRY PART-TIME LECTURER, 工学部, 非常勤講師 (70022499)
• Project Period (FY): 1993 – 1994
• Keywords: Polynuclear Complex / Dinuclear Oxoanion / Oxo-bridge / Methy1-bridge / 5-Coordinate Carbon / bond angle / Angular Overlap Model / Linear Coordination Polymer

Research Abstract

The electroinic structure of bridging bonds in polynuclear complexes was cprrelated with their geometrical structure. The two following types of complexes were examined.
1. The relationship between the electronic structure of the bridging bond and the bond angle at the bridging oxygen in R_2O_7^<n->-type dinuclear complexes was examined by using hybridized orbitals, localized molecular orbitals, linear combinations of the localized molecular orbitals, and delocalized molecular orbitals. In every case, the results of calculation showed a tendency that the bond angle increases with decreasing electronegativity of the central (R) atom, in agreement with the observed tendency. The bond angles obtained from calculations with reasonable parameter values were slightly smaller than the experimental bond angles. This deviation was taken as a token of partial ionic character of the bonds. Among the types of orbitals used in the calculation, the localized ones should be preferred at an elementary stage ; with simple delocalized molecular obirtals (without cinfigulation interactions), the bond energy only slightly depended on the bond angle.
2. The peculiar structure of five-coordinate carbon atom observed in the methy1 bridge of linear polymers, [Be(CH_3)_2]_*, [Mg(CH_3)_2]_*, and [LiAl(C_2H_5)_4]_*, was investtigated. Because of unlikeliness of five covalency of carbon, an ionic model with metal ions and CH_3^-(C_2H_5^-)ligands was first examined. In every complex, electrostatic interaction between ions including long-range interactions stabilized the polymer. However, the calculated bond angle of the CH_3-bridge was much greater than the observed. On the other hand, an angular overlap treatment of convalent bond energies (relative values) gave too small bond angles in the Be and Mg complexes, where a molecuar orbital treatment allowing for ionic contribution gave reasonable bond angles. In the Li-Al complex, a model where the C-Al covalent bond is much stronger than the C-Li one, i.e.a model approximated by Li^+[Al(CH_3)_4]_-, gave a bond angle consistent with the observed angle.