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A M Macintosh

Publications and source records attributed to A M Macintosh.

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Heterogeneous electron-transfer rate constants for M2(O2CR)4(0)/+, where M = Mo, W, Ru, or Rh and R = alkyl or aryl.

By the use of Nicholson's method, the heterogeneous electron-transfer rate constants (ks) for the oxidation of a series of M2(O2CR)4 complexes have been determined in benzonitrile, where the metal M = Mo, W, Ru, or Rh and R = alkyl or aryl. For R = tBu, the values of ks follow the order M = Mo > W > Ru > Rh. No simple influence of R on ks was observed, although added ligands that are known to reversibly bind to the dinuclear center were shown to influence the E1/2 values in order of their basicity and to suppress the rate of electron transfer. The reported data are compared with those obtained for Cp2Fe0/+, Cp2*Fe0/+, and Ru(bpy)2(2)+/3+ and with earlier work on dirhenium multiply bonded compounds.

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Vitamin K1.

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Dimolybdenum bis((S,S,S)-triisopropanolaminate(3-)): a blue compound with an unusual Mo-Mo triple bond.

Mo2(OtBu)6 and Mo2(NMe2)6 each react with (S,S,S)-triisopropanolamine (2 equiv) in benzene to yield dimolybdenum bis((S,S,S)-isopropanolaminate(3-)), Mo2[(OC-(S)-HMeCH2)3N]2 (M identical to M), as a blue crystalline solid. Cell parameters at -160 degrees C: a = 17.389(6) A, b = 10.843(3) A, c = 10.463(3) A, beta = 125.28(1) degrees, Z = 2 in space group C2. The molecular structure involves an Mo2 unit inside an O6N2 distorted cubic box. The Mo2 axis is disordered about three positions with occupancy factors of ca. 45%, 45%, and 10%. Despite this disorder, the molecular structure is shown to contain a central Mo identical to Mo unit of distance 2.15(3) A coordinated to two triolate ligands which each have two chelating arms and one that spans the Mo identical to Mo bond. The local Mo2O6N2 moiety has approximate C2h symmetry, and the Mo-N distances are long, 2.4 A. The 1H and 13C(1H) NMR spectra recorded in benzene-d6 are consistent with the geometry found in the solid-state structure. The blue color arises from weak absorptions, epsilon approximately 150 dm3 mol-1 cm-1, at 580 and 450 nm in the visible region of the electronic absorption spectrum. Raman spectra recorded in KCl reveal pronounced resonance effects with excitation wavelengths of 488.0, 514.5, and 568.2 nm, particularly for the 322 cm-1 band, which can probably be assigned to nu(Mo identical to Mo). The electronic structure of this compound is investigated by B3LYP DFT calculations, and a comparison is made with the more typical ethane-like (D3d) Mo2(OR)6 compounds is presented. The distortion imposed on the molecule by the triisopropanolaminate(3-) ligands removes the degeneracy of the M-M pi molecular orbitals. The HOMO and SHOMO are both M-M pi and M-O sigma* in character, while the LUMO is M-M pi* and the SLUMO is predominantly M-O sigma* with metal sp character. The calculated singlet-singlet transition energies are compared with those implicit in the observed electronic spectrum.

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