Mauricio Barrera

New oxovanadium complexes coordinated to a fac-tridentate organometallic ligand and X-ray crystal structure of [η-CpCo{P(O)(OC2H5)2}3VO(acac)]: Their role in oxidative catalysis

Abstract Treatment of VO(acac) 2 with the facial-tridentate organometallic ligand [η-CpCo{P(O)(OEt) 2 } 3 ] − affords a new binuclear compound [η-CpCo{P(O)(OEt) 2 } 3 VO(acac)] (I). This compound undergoes protonation with HPF 6 in the presence of 1,10-phenanthroline (phen), or 2,2′-bipyridyl (bipy), to yield binuclear cationic derivatives [η-CpCo{P(O)(OEt) 2 } 3 VO(phen))] + PF 6 − (II), and [η-CpCo{P(O)(OEth) 2 } 3 VO(bipy)] + PF 6 − (III). The X-ray crystal structure determination and full characterization of I has been performed. The catalytic oxygenation and oxygen transfer to 3,5-di-t-butylcatechol in the presence of I, II + , or III + complexes is reported.

Photochemistry and emission behaviour of the iron(II) mixed metallocene complexes [C5R5Fe(arene)]PF6(R = H or Me)

Mixed metallocenes of general formula [(η5-C5R5)Fe+(η6-arene)](R = H or Me), irradiated at long wavelengths (> 320 nm) show a fluorescence band centred at 520 nm. Fluorescence yields are strongly dependent upon the arene, and range from 1.2 × 10–3 for [CpFe+(p-dimethoxybenzene)](Cp = C5H5), to less than 0.2 × 10–4 when the arene is benzene, toluene, mesitylene, or pentamethylbenzene. The fluorescence quantum yields obtained upon irradiation of [CpFe+(p-xylene)] increase when hexamethylbenzene (HMB) is added, and approach, at high HMB concentrations, a value of 8 × 10–4, similar to that obtained when [CpFe+(HMB)] is irradiated. These results are explained in terms of an efficient ligand exchange on the excited surface. Hexamethyl(dewar benzene)(HMDB) increases the fluorescence of [CpFe+(p-xylene)] and decreases the fluorescence emitted by [CpFe+(p-dimethoxybenzene)]. In both systems the fluorescence yields can be extrapolated, at high [HMDB], to the value observed when [CpFe+(HMB)] is irradiated. These results are compatible with both the occurrence of an efficient valence isomerization of HMDB and ligand exchange on the excited surface.

ANOMALOUS BEHAVIOR OF Ir(III) CYCLOMETALATED COMPLEXES: APPLICATION IN LIGHT-EMITTING ELECTROCHEMICAL CELLS

The cationic Ir(III) complex with 7,8-benzoquinoline (bzq) as cyclometalating ligand and 4,4´-diterbutyl-2,2´-bipyridine (tBuB) as ancillary ligand, [Ir(bzq) 2 (tBuB)](PF 6 ) (1), was utilized in the fabrication of a light-emitting electrochemical cell (LEC). The photophysical properties and the characterization of the LEC device with this complex was compared with literature data for the analogous complex with 2-phenylpyridine (ppy), [Ir(ppy) 2 (tBuB)](PF 6 ) (2). Complex 1 showed blue shifted emission compared to complex 2. Surprisingly, complex 1 shows lower luminance, efficiency and stability in regard to 2. This behavior correlated well with the low values of quantum yield and lifetime, registered for complex 1 in solution. The performance observed is unexpected, taking into account the emission wavelengths recorded for each complex, and the lesser non radiative deactivation processes expected for a complex with a more rigid ligand as bzq. A possible explanation of this behavior is given in terms of the predominance of a fluorescent emission in the case of the complex 1 instead of a phosphorescent emission, as observed for complex 2.

Photo-activated valence isomerization of hexamethyl(Dewar benzene)(HMDB) assisted by arene–iron(II) complexes: luminescence properties of [HMDB ⋯(η5-C5R5)Fe(η6-arene)]* adducts

Hexamethyl(Dewar benzene)(HMDB) isomerizes to hexamethylbenzene (HMB) under light irradiation in the presence of stoicheiometric or catalytic amounts of the cationic complexes [(η5-C5R5)Fe(η6-arene)]+X–, (R = H, Me; X = BF4–, PF6–), (1a–e) and (2), in dichloromethane solutions at 273 K; mixtures of HMDB and (1b–e) or (2) in dichloromethane exhibit a luminescence band at 530–540 nm probably due to formation of the corresponding exciplex.

ELECTRONIC PROPERTIES OF ATOMS AND COVALENT RADIUS DETERMINED BY MEANS OF AN EXCHANGE POTENTIAL NEW MODEL CONTAINING SELF INTERACTION AND GRADIENT CORRECTIONS

Within the Density Functional Theory a new model of exchange potential containing corrective terms for self interaction and long range behavior is proposed . This potential model contains three constants: a , b and g. The first two are determined through experimental data while the third is calculated by means of a polynomial function of six degrees depending on the total number of electrons. When this potential is introduced in the effective potential and Kohn-Sham equations are solved by iterations, calculated total energies and eigen values reproduce with high accuracy the experimental values. Total electronic densities obtained with this scheme are employed to find numerically the point where the derivatives of the kinetic energy respect to the total electronic density equal either the exchange correlation potential or half the effective Kohn-Sham potential. Solutions of this equality come as a singular point in the radial mesh and are correlated with atomic and covalent radius