title: Filling a void: isolation and characterization of tetracarboxylato dimolybdenum cations.
abstract: Dimolybdenum tetracarboxylato cations have been prepared and structurally characterized for the first time. The reactions of the new, quadruply bonded compound, Mo(2)(TiPB)(4), where TiPB = 2,4,6-triisopropylphenyl carboxylate, with NOPF(6) and NOBF(4) give the ionic compounds [Mo(2)(TiPB)(4)]PF(6) and [Mo(2)(TiPB)(4)]BF(4), respectively. Each product crystallizes in space group P2(1)/n and displays an elongation of the Mo-Mo bond of 0.060 and 0.068 A, respectively, over that of the parent compound (2.076(1) A). Each complex displays a characteristic EPR signal, showing hyperfine coupling to the spin active isotopes (95)Mo and (97)Mo, with g( parallel) = g( perpendicular) = 1.936, that is consistent with the presence of an unpaired electron. Electronic spectroscopy indicates the expected red shift in the delta --> delta(*) transition for the cations, due to the loss of exchange energy in going from the two-electron to one-electron system. We have also obtained a small amount of crystalline [Mo(2)(O(2)CC(4)H(9))(4)]PF(6) from the reaction of Mo(2)(O(2)CC(4)H(9))(4) with AgPF(6). This product crystallizes in the space group C2/c, and the Mo-Mo bond is elongated by 0.063 A over that of the neutral parent compound. These ionic compounds have the first isolated and characterized [Mo(2)(O(2)CR)(4)](+) cationic species.
authors.affiliation: Department of Chemistry and Laboratory for Molecular Structure and Bonding, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012, USA. cotton@tamu.edu
authors.forename: F Albert
authors.initials: FA
authors.lastname: Cotton
authors.forename: Lee M
authors.initials: LM
authors.lastname: Daniels
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Hillard
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Murillo