Inorganic and Theoretical Chemistry

  • Lists of Publications:

  • -1995    1996-2000      2001-2005      2006-2010      2010-

  • Luminescence and LEDs

  • Boron chelate complexes, [BPh2(iminopyrrolyl)], exhibit photophysical properties dependent on the substituents present on the bidentate ligand. The fluorescence emission may go from high energy (blue) and high quantum yield to a green shift with much lower quantum yields, while 2,6-aryl bulky substituents induce a shift in the emission to the violet region and a significant decrease in quantum yield by restricting ring rotation. DFT and TDDFT calculations showed that the excited singlet state with a planar aryliminopyrrolyl ligand is a condition for a good emitter. The lowest energy absorption results in general from a HOMO to LUMO excitation, assigned to a transition between π and π* orbitals (mainly ILCT) of the iminopyrrolyl ligand, more or less delocalized depending on the substituent.

  • Spectroelectrochemistry of Transition Metal Complexes

  • Osmium complexes mer-[Os(CO)(bpy)Cl3] and trans-[Os(CO)(PrCN)(bpy)Cl2] can be reduced to mer-[Os(CO)(bpy.-)Cl3]2- and trans-[Os(CO)(PrCN)(bpy.-)Cl2]-, respectively, which react to afford Os(0) species. In THF, mer-[Os(CO)(bpy)Cl3] leads to an Os-Os bonded polymer, probably [Os(CO)(THF)(bpy)]n, in PrCN to the well soluble, probably mononuclear [Os(CO)(PrCN)(bpy)] species, and in MeCN (as in THF) to the [Os(CO)(MeCN)(bpy)]n polymer. The Os(0) species convert CO2 into CO or CO and formate. DFT and TDDFT calculations assisted in the identification of the square planar Os(0) complex, based on the electronic spectrum (experimental one in the inset; PrCN, 293 K).

  • Reaction Mechanisms - Ring-opening Polymerization (ROP) of Lactide

  • Click to Enlarge Zn-NHC alkoxide complexes are present in solution as binuclear [(S,CNHC)ZnCl(OBn)]2 (NHC = N-heterocyclic carbene) species, as confirmed by DFT calculations and catalyze the ring-opening polymerization (ROP) of lactide to produce chain-length-controlled polylactide (PLA) or in the presence of MeOH the controlled degradation of PLA to afford methyl lactate as the major product. DFT calculations showed the operation of the coordination insertion mechanism involving the assistance of the second Zn center.

  • Organometallic Electrochemistry

  • The anodic electrochemical oxidation of ReCp(CO)2(PPh3) (2) leads to the radical cation (2+), which dimerizes (222+), as happened with ReCp(CO)3. DFT calculations (ADF) lead to very good estimates of the oxidation potentials. The E01(2/2+) of 0.49 V is calculated as 0.54 V in dichloromethane (relative to Fc/Fc+), while ΔGf for the reaction 2+ + 2+ → 22+ was calculated as -3.12 kcal mol-1 in dichloromethane (as ΔHf, since entropy effects were not considered).

  • Reaction Mechanisms - Hydrogenation and Transfer Hydrogenation

  • Click to Enlarge RuCl(CNN)(dppb) reacts with NaOEt in EtOH to give Ru(OEt)(CNN)(dppb), and rapidly equilibrates with the hydride RuH(CNN)(dppb). The ethoxide Ru(OEt)(CNN)(dppb) reacts reversibly with H2 in solution leading also to the hydride EtOH via dihydrogen splitting. NMR studies reveal that Ru-X (X = H, OR), the NH2 functionality and EtOH are involved in hydrogen bond interactions and exchange processes. DFT calculations were performed to understand the mechanism of the catalytic transfer hydrogenation and hydrogenation reactions and the role of the alkoxide complex in this system, which procedes by the catalytic cycles shown.

  • Self-assembly: copper(II) picolinamide building blocks

  • [Cu(N3)2(piaH)2] (1) and [Cu(NCO)2(piaH)2] (2) yield the square planar [Cu(pia)2] • 2H2O (3) upon recrystallization, along with deprotonation of the piaH ligand. DFT calculations confirmed the octahedral coordination of Cu(II) in 1 and 2, as the trans isomer. Using suitable models, it was shown that 1 and 2 underwent stepwise transfer of two hydrogen atoms from the piaH ligands to the two axial ligands N3- or NCO- that were released yielding 3. Complex [Cu(pia)(piaH)(ClO4)]2 (4) was formed in the presence of perchlorate, which is so weak a base that it cannot deprotonate the piaH ligand. After the first hydrogen transfer assisted by available acetate the dimer 4 is formed.

  • Organometallic Intercalators

  • 1,10-phenanthroline Mo(II) complexes were found to be effective in vitro against different tumor cell lines and to act as intercalators. In order to understand their binding mode, a computational study was initiated, starting from simple systems (the 1,10-phenanthroline ligand and two DNA base pairs, one in each side), but extending published reports (the ligand over one pair of bases). Geometrical changes and energy contributions are analyzed by means of Density Functional Theory (DFT), with M06-2X functional, although M05-2X, M06, M06-L, B97D, and ΩB97XD functionals, which take also into account dispersion contributions, are also tested for comparison. The results are expressed in terms of polarizability, dipole moments, electronic density, energy of frontier orbitals, charge transfer, and molecular electrostatic potential maps, as the one shown in the figure.

  • Catalysis and Catalysts

  • The synthesis of 80% of the industry compounds requires a catalytic reaction. Activity and selectivity, namely enantioselectively, are important features in catalyst development. Supported organometallic catalysts combine the advantages of the homogeneous catalysts (high activity) with the ones of the simple heterogeneous catalysts (high selectivity, easy separation, high thermal stability). Mo(II) precursors [MoX(η3-C3H5)(CO)2L] ( X = Cl, Br; L = bidentate ligands) proved to be active catalysts for olefin oxidation with TBHP, the outcome of the reaction depending on the support (silica, MCM type mesoporous materials, clays).
    Recently we started to address the role of different ionic liquids as solvents (biphasic catalysis) and catalysts.

  • Multifunctional Magnetic Materials

  • Binary data storage functions by switching between two stable states under the same ambient conditions and information is written by application of a stimulus to switch between them. The goal is to store binary information via the orientation of individual electron spins. Magnetic compounds with good potential for incorporation into spintronic materials include spin crossover (SCO) transition metal complexes. These molecules can switch between two magnetic states with a simple stimulus such as heat, pressure, light or magnetic field, and the switch is often accompanied by a considerable hysteretic window.
    The Fe(III) complex (perchlorate salt) undergoes a spin transition at room temperature with some hysteresis.

  • Antimicrobial Fluid Filtration on Biocidal Coated Ceramic Surfaces. (SFRH/BPD/88135/2012, FCT Sponsor)

  • In compliance with the objective of combatting biofouling, this project aims at developing an alternative solution to mitigate filters biofouling by providing coatings for ceramic based surfaces. Synthesis and functionalization of bioactive compounds in order to be able to be immobilized in polymeric matrices, compatible with water contacted surfaces is the main activity. Other applications, such as metal based surfaces for cooling systems, are also pursued in the study.