Millennium Nucleus
Molecular Engineering for Catalysis and Biosensors

What we learned...


Coinage Metal Superatomic Cores: Insights into Their Intrinsic Stability and Optical Properties from Relativistic DFT Calculations
Franck Gam, Dayan Paez-Hernandez, Ramiro Arratia-Perez, C. W. Liu, Samia Kahlal, Jean-Yves Saillard, Alvaro Muñoz-Castro
Chem. Eur. J. 2017, [5.317, 2016]
DOI:   10.1002/chem.201701673
Coinage-metal atomically precise nanoclusters are made of a well-defined metallic core embedded in a ligand- protecting outer shell. Whereas gold derivatives are particu- larly well documented, examples of silver nanoclusters are somewhat limited and copper species remain particularly scare. Our DFT relativistic calculations on superatomic metal- lic cores indicate that copper species are almost as stable as gold clusters and more stable than their silver counterparts. Thus, for silver superatomic cores, the role of the stabilizing ligands is more crucial in the stabilization of the overall structure, in comparison to copper and gold. Hence, the chemistry of the earlier counterparts of gold, especially copper, should grow quickly with at least characterizations of species related to that found in the heavier elements in the triad, which requires tackling synthetic challenges. Time- dependent (TD)-DFT calculations show that with an increase of the cluster core nuclearity, the absorption bands are red- shifted, allowing us to differentiate between the clusters types. Moreover, the optical properties of the silver cores are fairly different from that of their Cu and Au relatives.

The origin of phosphorescence in Iridium (III) complexes. The role of relativistic effects
Plinio Cantero-López, Dayan Páez-Hernández, Ramiro Arratia-Pérez
Chem. Phys. Lett. 2017, 685, 60–68 [1.815, 2016]
DOI:   10.1016/j.cplett.2017.07.006
A series of luminescent Ir(III) complexes of the type [Ir(F2ppy)2L] (where L = Lpytz, LOMe, Lbut) have been studied using relativistic two-component density functional theory considering the spin-orbit coupling. The absorption spectra of the three complexes were determined. The most important transition appears in the region between 250 and 350 nm, which is in good agreement with the experimental reports. The three complexes show phosphorescent properties due to a metal-ligand charge transfer (MLCT) process, where the spin-orbit coupling (SOC) plays a key role due to the introduction of a zero field splitting (ZFS) and the mixing of states with different spins which contributes to modify the emission selection rule. The lifetimes of the emission processes were calculated, and the values are in the same order of the experimental reports.

Inclusion of [H3PW12O40] and [H4SiW12O40] into a silica gel matrix via “sol-gel” methodology
Matías Reyes-López, Alejandro Pizarro-Luna, Ignasi Mata, Elies Molins, Desmond Macleod-Carey
J. Chil. Chem. Soc. 2017, 62, 3322-3324 [, 0]
Here we report the inclusion of two Keggin Polyoxometalates (POMs), [H3PW12O40] and [H4SiW12O40], into silica gels by integrating them during the preparation of the SiO matrix via “sol-gel” methods. Aerogels were produced by supercritical drying of the wet gels impregnated with the POMs, and lyogels were obtained by means of a lyophilization process. These materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR) spectroscopy and thermoanalytical techniques (TGA-DSC). We found that a large fraction of POMs are lost during the aging time, and solvent exchange for lyophilization. However the thermal stability of the bare matrix is modified by the inclusion of POMs. Some aggregates with a high content of POMs were found via SEM-EDX.

X-ray diffraction and relativistic DFT studies on the molecular biomarker fac-Re(CO)3(4,4’-dimethyl-2,2’-bpy)(E-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol)(PF6)
Alexander Carreño, Manuel Gacitúa, Elies Molins, Ramiro Arratia-Pérez
Chem. Pap. (2017) [1.326, 2016]
DOI:   10.1007/s11696-017-0196-6
The fac-[Re(CO)3(4,4’-dimethyl-2,2’-bpy)L]PF6 (C2) complex have been recently reported as a useful fluorophore 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 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) Å; Re1–C25, 1.58(12) Å and Re1–C26, 1.90(8) Å. The distorted octahedral geometry observed in the C2 structure is due to the C(CO)–Re1–N1(imine) angle for the three carbonyls that are significantly different. The Re–N1 bond distance of 2.16(4) Å 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 Å) 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.

Bonding in gold-rare earth [Au2M] (M = Eu, Yb, Lu) ions. A strong covalent gold-lanthanide bond
Dayán Páez-Hernández, Alvaro Muñoz-Castro, Ramiro Arratia-Perez
Chem. Phys. Lett. 2017, 683, 421-424 [1.860, 2015]
DOI:   10.1016/j.cplett.2017.03.074
The electronic structure and bonding nature of a series of intermetallic gold-lanthanide [Au2Ln] molecules, where Ln = Eu, Yb, Lu is predicted via the DFT and CASSCF/CASPT2 calculations. The 2c-2e bond model shows a good description of the intermetallic bonding which have a large covalent component with important contribution from bonding interaction between the 6s-Au and the 6s-Ln shell of orbitals.

Modeling the electronic states and magnetic properties derived from the f1 configuration in lanthanocene and actinocene compounds
Eduardo Solis-Céspedes and Dayán Páez-Hernández
Dalton Trans., 2017,46, 4834-4843 [4.177, 2016]
DOI:   10.1039/C7DT00111H
The electronic structure and magnetic properties of a series of Kramers ions with f1 configuration in axial symmetry have been analyzed with a combination of theoretical methods: ab initio relativistic wavefunction methods as well as a crystal-field (CF) model with parameters extracted from the ab initio calculations. The molecules were treated in an idealized D8h and D7h symmetry and different combinations of active electrons and orbitals were used to describe correctly the nature of the ground and excited states. The spin Hamiltonian parameters for the Kramers doublet derived from the ground multiplet were determined and discussed on the basis of the crystal-field (CF) and spin–orbit interaction. The prime interests were the electron paramagnetic resonance g-factors and their relation to the complex geometry, crystal-field (CF) and spin–orbit coupling. The developed models agree well with the ab initio calculations and experimental reports.

Spin-orbit effect into isomerization barrier of small gold Clusters. Oh ↔ D2h Fluxionality of the Au62+ cluster Investigated by relativistic methods
Alvaro Muñoz-Castro, Dayan Paez-Hernandez, Ramiro Arratia-Perez
Chem. Phys. Lett. 2017, 683, 404-407 [1.860, 2015]
DOI:   10.1016/j.cplett.2017.02.054
The Oh-[Au6]2+ cluster exhibits an open-shell 1s21p2 which trend to a more stable D2h isomer in 31.5 kcal/mol, as observed in the experimental [Au6{P(C6H4Me-o)pH2}6] cluster. By taking into account the spin-orbit coupling (SOC) in Oh-[Au6]2+, a resulting 1s1/221p1/22 closed-shell superatomic configuration is obtained stabilizing such structure by about 14.7 kcal/mol, decreasing the isomerization barrier. Thus, the spin-orbit term favors the Oh ↔ D2h conformation rearrangement depicting a decrease in the calculated energy difference between both conformations, an interesting consequence which is not obtained in the hypothetical lighter counterparts.

Substituted bidentate and ancillary ligands modulate the bioimaging properties of the classical Re(I) tricarbonyl core with yeasts and bacteria
Alexander Carreño, Alejandra E. Aros, Carolina Otero, Rubén Polanco, Manuel Gacitúa, Ramiro Arratia-Pérez,and Juan A. Fuentes
New J. Chem., 2017,41, 2140-2147 [3.277, 2015]
DOI:   10.1039/C6NJ03792E
Rhenium(I) tricarbonyl complexes with heteroaromatic ligands have been intensely investigated with respect to their properties as imaging probes, although they have only recently been tested in vivo. In this context, fac-Re(CO)3(N,N)L complexes (N,N: substituted bidentate ligand; L: ancillary ligand) are the most studied complexes due to their photophysical properties. However, the role of the N,N bidentate ligand in classical fac-Re(CO)3(N,N)L complexes (i.e. where L is a halogen such as Br) has not been explored regarding cytotoxicity and staining capabilities in walled cells (i.e. yeasts and bacteria). In the present study, we tested different rhenium(I) tricarbonyl complexes of type fac-Re(CO)3(N,N)Br [where N,N are 1,10-phenanthroline (phen) (C1); 5,6-dione-1,10-phenanthroline (dione) (C2); 2,2?-bpy (bpy) (C3); 4,4?-dimethyl-2,2?-bpy (dmb) (C4); and 4,4?-diethanoate-2,2?-bpy (deeb) (C5)] in order to characterize the properties of the N,N bidentate ligand in cellular biomarkers. We also compared these classical rhenium(I) tricarbonyl complexes (C1 to C5) with a fac-Re(CO)3(deeb)L+ complex, where L is the Schiff base (E)-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol, with respect to its potential for cell labelling. In our study, we found that both the N,N substituted bidentate ligand and the ancillary ligand L contributed to modulating the suitability in cell bioimaging, showing that it is possible to perform molecular engineering design to obtain improved biomarkers for walled cells, and eventually for other cell types.