X-ray diffraction and relativistic DFT studies

What is it about?

The fac-[Re(CO)3(4,40 -dimethyl-2,20 -bpy)L]PF6 (C2) complex have been recently reported as a useful fluo- rophore for walled cells (yeasts and bacteria) without the need of antibodies. In the present work, we report the structural parameters of the C2 complex, where L is an ancillary ligand E-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol, which presents an intramolecular hydrogen bond (IHB). The C2 crystals were obtained by slow evaporation of a dichloromethane solution, yielding yellow blocks. The crystal structure solution of the complex C2 showed a monoclinic crystal system and discrete organometallic cations and PF6- as the counter ion, with partially occupation of solvent corresponds to the nitrogen coordination of the pyridine fragment of the ancillary ligand L, completing the octahedral geometry. Here we complement the C2 descriptions due to the considerable biological interest of its use as d6 metal fluorophore in walled cells (i.e., yeast and bacteria). DFT calculations were performed including scalar and spin–orbit (SO) relativistic effects with agree often reasonably well with experimental X-ray data. Through frequency calculations we estimated the strength of the intramolecular hydrogen bond ̊(with a OH---N distance of 2.621 A) accounting for near 40 kcal/mol, indicating that is a strong hydrogen bond which contributes to the molecular stability. In addition, we observed the L electron-withdrawing effect on the rhenium core. The agreement between the observed and computed bond distances and angles brings confidence on the choice of the computed models and level of theory. These kind of Rhenium (I) complexes designed to develop novel fluorophores suitable for biological applications. molecules (CH2Cl2). The complex C2 having a fac-geometry of the three carbonyl ligands, possesses the following bond ̊ distances Re–C(CO): Re1–C24, 1.87(8) A; Re1–C25, ̊ and Re1–C26, 1.90(8) A. The distorted octahedral ̊ 1.58(12) A geometry observed in the C2 structure is due to the C(CO)– Re1–N1(imine) angle for the three carbonyls that are signifi- ̊ cantly different. The Re–N1 bond distance of 2.16(4) A

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Why is it important?

Single crystal of C2 was determined by X-ray crystallography, showed a discrete distribution of organometallic cations and PF6- anions with partially occluded molecules of dichloromethane. Also, the structure showed that the rhenium atom adopts a distorted octahedral coordination geometry and it is coordinated by three carbonyl ligands in a fac arrangement, with two nitrogen atoms of the bipyridine ligand (equatorial plane) and the nitrogen atom of L ligand (axial plane) producing the distorted geometry in the rhenium (I) core. The bond angles indicate that the CO ligands are not linearly coordinated by the steric factors between th eheteroaromatic rings of the pyridine ligand and the twist of the phenol ring in L. Experimental bond distances and angles are in good agreement with calculated results. In addition, electrochemical studies revealed that L has an electron-with- drawing effect at the rhenium center as has been corroborated on past studies and the ligand process affect the control mechanism for oxidations, as well. From the chemical point of view, it should be pointed out the interesting properties induced by this kind of Schiff bases ancillary ligand (L) on the electronic properties of C2 when bromide in the C1 complex is exchanged, maintaining the carbonyl facial (fac) isomer arrangement with a local symmetry loss. This assertion suggests that the octahedral geometry could be also relevant to the design of new Re(I) complexes suitable as biomarkers. On the other hand, this kind of Schiff bases as ancillary ligands (L) exhibits aromatic rings and heteroatomic substituents suggesting that C2 is able to interact by covalent and ionic interactions with the walled compositions (C2 is a complex showing a positive charge).

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