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Research has been conducted on the alkyl-cobalt(III) complexes. The synthesis and characterization of these complexes have been carried out in investigating the role of the tridentate ligand in the alkylation reaction and the results are reported.

Research has been conducted on the dinuclear complexes with Me and H. The synthesis and the solution and solid-state characterization of the [MeCo-(DH)(DB(OMe)(4-Py))] (sub)2 compound which is a molecular box (the metal unit walls formed by a bifunctional ligand) have been investigated and discussed.

Research has been conducted on the organocobalt complexes. The X-ray structure and formation mechanisms of these complexes have been investigated and the results are reported.

The analysis of the electronic spectra of adenosylcobalamin (AdoCbl) and its derivative in which the trans axial base was replaced by a water molecule (AdoCbi–H2O) has been performed by means of time-dependent density functional theory (TDDFT). The latter corresponds to the situation encountered in strongly acidic conditions. The TDDFT electronic transitions and oscillator strengths were calculated at the optimized B3LYP and BP86 ground state equilibrium geometries. A comparison of the orbital energy diagrams obtained with the B3LYP and BP86 functionals reveals a different orbital order and composition of the highest occupied and lowest unoccupied molecular orbitals. In B3LYP the lowest-energy transitions are of π/d→π*, π/d→σ*, and π/d→d characters while in the case of BP86 they are mainly d/π→π* and d→π*. The long range charge transfer transitions involving excitations from adenine π orbitals to antibonding corrin π* orbital can be observed at low energies, especially in BP86 results. Calculated electronic excitations were used to simulate the absorption spectra for a direct comparison with the absorption spectra recorded for AdoCbl at different pH values. As previously found for methylcobalamin [see Andruniów et al., J. Chem. Phys. 129, 085101 (2008)] also for AdoCbl the two-parameter scaling technique is required to obtain a satisfactory agreement between theoretical and experimental spectra. Both functionals correctly predict the shifting of the lowest intense transition toward blue by approximately 13 nm upon changing pH from 7 to 1. [ABSTRACT FROM AUTHOR]

Time-dependent density functional theory (TDDFT) has been applied to the analysis of the electronic spectra of methylcobalamin (MeCbl) and its derivative in which the trans axial base was replaced by a water molecule (MeCbi[Single_Bond]H2O). The latter corresponds to the situation encountered in strongly acidic solutions. The study primarily focuses on the accuracy of two functionals, the hybrid B3LYP and the gradient corrected BP86, in dealing with the electronic excitations. The high resolution crystal structure of MeCbl was the source of the initial coordinates. To generate the initial structures, the full MeCbl was simplified by replacing the corrin side chains by H atoms. The vertical excitation energies, together with the corresponding oscillator strengths, were calculated at the optimized BP86 and B3LYP structures of the ground electronic state of the complexes. The NBO analysis shows that the B3LYP functional gives a bonding description of the ground state as a more polarized covalent bond compared to that given by BP86. The latter functional has more covalent bonding and is thus more appropriate for modeling the axial bonding properties. To validate the accuracy of the present TDDFT analysis, the computed excitations were directly compared to the absorption spectra of MeCbl. In order to obtain a reliable agreement between experiment and theory, the two-parameter scaling technique was introduced, which compensates differently the low-energy and high-energy excitations. Electronic excitations strongly depend on the choice of the functional. Transitions involving corrin π→π* excitations are better described by the B3LYP functional while transitions associated with metal-to-ligand (d/π→π*/d) excitations are better described by BP86. These differences can be associated with the different bonding descriptions obtained by B3LYP and BP86. [ABSTRACT FROM AUTHOR]

The reaction of a cis beta folded organacobalt derivative, a racemeric compound of the delta and lambda enantiomers, with L-tyrosine afforded a mixture of two disastereoisomers delta and lambda. The successive isomerization reaction is negligible for L-trysine but goes practically to completion for trans-4 hydroxy-L-proline.

Research has been conducted on beta cis folded organocobalt derivatives with a salen-type ligand. The authors report the modification of equatorial ligand in organocobaloxime-type complexes.

Research has been conducted on 1,4-phenylenebisboronic acid and methylcobaloxime. The authors describe the guest-induced synthesis of the molecular box from these compounds with pyrazine as guest.

The reduction of (Co(III)(LE-py)2)ClO4 (LE-py = 2(2(2-pyridyl)ethyl)imino-3- butanone oximoto) with subsequent alkylation of the resulting nucleophile generates dinuclear complex (mu-OH)(RCo(III)(LE-py)(sub 2)(ClO4) (R = Me, Et). X-ray crystallography indicates that the complex contains ClO4 anions, (MeCo(LE-py))2OH) cations, and H2O hydration molecules. Each Co(III) in the cation exhibits a distorted octahedral geometry with the LE-py occupying three equatorial positions. Methyl and the oxime O occupy the axial position.