Enhancement in electronic communication upon replacement of Mo-O by Mo-S bonds in tetranuclear clusters of the type [Mo2]2(mu-E-E)2 (E = O or S).
A tetranuclear cluster containing two quadruply bonded cis-Mo2(DAniF)2 units (DAniF = N,N'-di-p-anisylformamidinate) linked by four hydroxide groups (1) was obtained by hydrolysis of [Mo2(cis-DAniF)2](mu-OCH3)4. Analogous compounds linked by two bidentate bridges (o-O2C6H4 for 2, o-O2C10H6 for 3, and o-S2C6H4 for 4) were synthesized by direct assembly of the corner species precursor [Mo2(cis-DAniF)2(NCCH3)4](BF4)2 and the respective protonated ligands. All four compounds were characterized by X-ray crystallography. Cyclic voltammograms of the O-linked compound 2 and the S analogue 4 show two reversible one-electron-oxidation processes with potential separations (DeltaE(1/2)) of 474 and 776 mV, respectively. The large increase of about 300 mV in DeltaE(1/2) for the S analogue relative to that of the O compound is consistent with a large increase in electronic communication. This enhancement occurs despite the increase of ca. 0.45 A in nonbonding separation between the midpoints of the Mo2 units, which changes from 3.266 A in 2 to 3.72 A in 4, and the increase of ca. 0.4 A in M-E distances as E changes from O to S. Density functional theory calculations show that the increase in electronic communication between the metal centers in 4 is due to a superexchange pathway involving d and p orbitals in the linker E atoms that is less important in 2.
Cotton
F Albert
FA
Department of Chemistry, Laboratory for Molecular Structure and Bonding, Texas A&M University, College Station, TX 77842-3012, USA.
Li
Zhong
Z
Liu
Chun Y
CY
Murillo
Carlos A
CA
D018360:Crystallography, X-Ray; D004563:Electrochemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013455:Sulfur / Q000737:chemistry*
D010087:Oxides; D013455:Sulfur; D008982:Molybdenum