Zhao, Qinliang (2009-05). Conformation and electronic configuration of complexes with multiple dimetal units. Doctoral Dissertation. Thesis uri icon


  • By using the building blocks Mo2(DAniF)3(O2CCH3) (DAniF = N,N'-di-panisylformamidinate) and [Mo2(cis-DAniF)2(NCCH3)4](BF4)2, a series of complexes with multiple dimolybdenum units, bridged by a variety of linkers and having various oxidation states, has been synthesized and studied by various physical and chemical methods. The isomeric neutral diamidate-bridged molecules, ?- and ?- (DAniF)3Mo2(ArN(O)CC(O)NAr)Mo2(DAniF)3 (Ar = p-anisyl), have been oxidized to give the PF6 salts of the four cations ?1+, ?2+, ?1+, ?2+; all four structures together with supporting evidence show that in ?1+ and ?2+ the unpaired electrons are localized while in ?1+ and ?2+ they are delocalized in the time scale of these experiments. It is also found that a hydroxide bridged complex having a [Mo2](u-OH)2[Mo2] core undergoes a oxidative deprotomation, both in solution and in crystals, to a compound with a [Mo2](u-O)2[Mo2] core. A probable key intermediate with one OH and one O bridge has also been characterized. One electron oxidation of the tetrabridged compounds [Mo2(cis-DAniF)2]2(u-X)4, where X is a halogen atom (Cl, Br, I), produces a decrease of about 0.24 A in the separation between the midpoints of the multiply bonded dimolybdenum units. DFT calculations suggest partial bond formation during the oxidation, which is consistent with NIR, EPR and electrochemical measurements. Additionally, a pair of isomeric cyclic triads containing three [Mo2(cis-DAniF)2]2+ units, bridged by six fluoride anions, have been synthesized and crystallographically characterized. The symmetry of the ? isomer is C2v because the three [Mo2] units are oriented in two orthogonal directions while that of the other isomer is D3h because the three [Mo2] units are parallel. No direct interconversion between isomers has been detected by heating or irradiation of solutions but oxidation of the ? isomer first generates an ?+ species that changes to ?+. Finally, reaction of [Mo2(cis-DAniF)2(NCCH3)4](BF4)2 and Bun 4NBH4 in ether gives [Mo2(cis-DAniF)2]2(u-H)4 (14), a compound whose Mo4H4 core may be described as an elongated tetrahedron in which the four H atoms are along the four long edges and the Mo2 units along the short edges.

publication date

  • August 2007