Neutral rhenium (I) tricarbonyl complex of 1,10-phenanthroline-5,6-diol

What is it about?

we studied through experimental and relativistic DFT (R-DFT) calculations, the neutral complex fac-[Re(CO)3(1,10-phenanthroline-5,6-diol)Cl] (B1) as a potential precursor compound for designing new fluorophores suitable for confocal microscopy specially in walled cells. This work also describes via DFT calculations the electronic and spectroscopic properties of the facial (fac) and meridional (mer) isomers of this compound. The calculations shows that mer-isomer is 17.5 kcal/mol (in vacum) and 21.1 kcal/mol (when the solvent is considered) higher in energy with respect to the fac-isomer. The calculated emission spectra of B1, indicates an emission around 620 nm in acetonitrile in good agreement with the experimental reports for similar molecules. Finally, the Morokuma–Ziegler energy decomposition analysis shows a major lability for Cl ligand which is ideal for designing new compounds replacing this ligand for another ancillary ligand suitable for biological applications.

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Why is it important?

From the present results, we can conclude that the fac-[Re(CO)3(1,10-phenanthroline-5,6-diol)Cl (B1) complex maybe a suitable rhenium(I) tricarbonyl complex precursor to design biomarker for walled cells due to the current emission spectra in the visible region. The neutral fac-[Re(CO)3(1,10-phenanthroline-5,6-diol)Cl (B1) was synthesized, characterized and studied by relativistic DFT (R-DFT) and TD-DFT methods. For a correct assignment of the B1 structure we employed the complete analyses of FTIR and 1HNMR of 1,10-phenantroline-5,6-dione (dione) and 1,10-phenantroline-5,6-diol (diol). For the computational studies, were compared facialB1 with its mer isomer B2 and also neutral fac and mer Re(CO)3(1,10-phenanthroline)Cl classical rhenium(I) tricarbonyl compounds. The calculation method showed that in B1, the rhenium atom adopts a distorted octahedral coordination geometry and it is coordinated by three carbonyl ligands (CO) in a fac arrangement, with two nitrogen atoms of the diol bidentate ligand (equatorial plane) and the corresponding chlorine in the axial plane, producing the distorted geometry in the rhenium (I) core. This facial orientation also was confirmed by both experimental and computed FTIR and UV–vis study. In B1, the bond angles indicate that the CO ligands are linearly coordinated by the steric factors between the twist of the OH groups in the diimine ring (diol) and explain the convolution of the observed antisymmetric mode of the CO ligands. On the other hand, the computed transitions of B1 in acetonitrile solvent are in agreement with experimental data. The nature of the principal electronic transitions assigned are ILCT (HOMS-5 → LUMS) and MLCT (HOMS-2 → LUMS) transitions, respectively. The stability of the hydrogen bond was also confirmed by the character of the absorption band, where the band is located experimentally around at 300 nm. Theoretically this band is associated with HOMS-2 → LUMS transitions, where the OH groups present in the diol ligand are involved. Also, we predicted theoretically the emission spectrum of B1 which is similar to observed emission of other rhenium complexes. The latter is a emission located at the 600 nm region, thus, being suitable for confocal microscopy due to the fact that the microorganism autofluorescence (such as Candida Albicans or Cryptococcus spp.) occurs in the UV region. The Morokuma–Ziegler energy decomposition of B1 found that the interaction with ligands have an ionic character respect to Re-Cl and this ionic interaction represents the 69% of the stabilization energy. That should explain the most common substitution of the Cl ligand for another ancillary ligands. This kind of compounds have the possibility to form an hydrogen bond due to the presence of the hydroxyl groups in the diol ligand, and B1 is a suitable precursor complex that maybe tuned in new designs of rhenium(I) compounds as biomarkers for walled cells (Yeasts and Bacteria).

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