Modulating Electronic Coupling Using O- and S-donor Linkers.
Structures of compounds having two dimolybdenum units Mo2(DAniF)3+ (DAniF = N,N'-di-p-anisylformamidinate) connected by unsubstituted oxamidate (1) and dithiooxamidate (2) linkers are isomorphous, and the cores of the molecules are planar because of two intramolecular hydrogen bonds within the linkers. Molecular mechanics calculations show a barrier of rotation along the C-C bond of approximately 10 kcal x mol(-1), which suggests that planar conformations are also expected in solution. Changing the two oxygen atoms in the linker of 1 to sulfur atoms results in a significant enhancement of the electronic coupling between the dimetal units (Delta(E1/2) = 204 mV for 1 and 407 mV for 2). The electronic spectrum of 2 shows an intense low energy (600 nm) metal-to-ligand charge transfer (MLCT) band, whereas that for 1 shows only a weak absorption band at 460 nm. DFT calculations on models 1' and 2', in which the anisyl groups were replaced by hydrogen atoms, show that the energy of the pi* orbital of the linker is much lower for 2'. This allows dpi-ddelta interactions from the electrons in the delta orbitals of the Mo2 unit to the sulfur atom that in turn facilitates an electron hopping pathway.
Cotton
F Albert
FA
Department of Chemistry and Laboratory for Molecular Structure and Bonding, P.O. Box 3012, Texas A&M University, College Station, Texas 77842-3012, USA.
Li
Zhong
Z
Liu
Chun Y
CY
Murillo
Carlos A
CA
D003198:Computer Simulation; D018360:Crystallography, X-Ray; D019281:Dimerization; D004583:Electrons; D008956:Models, Chemical; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D013057:Spectrum Analysis; D013455:Sulfur / Q000737:chemistry*
D009942:Organometallic Compounds; D013455:Sulfur; D008982:Molybdenum; D010100:Oxygen