Cesar Morales-Verdejo

Toward the synthetic control of the HOMO-LUMO gap in binuclear systems: insights from density functional calculations.

Computational methods based on density functional theory have been applied to address the design of tailored HOMO-LUMO gap bimetallic complexes. We focus our attention on the [Cp*Fe-(L)-FeCp*] system, where two ferrocenyl units are linked through the dianion of fused ring ligands such as pentalene, s-indacene, dicyclopenta-[b,g]-naphthalene, dicyclopenta-[b,i]-anthracene and dicyclopenta-[b,l]-tetracene. Our DFT calculations on the title organometallic complexes suggest a controlled decrease in the HOMO-LUMO gap, which is desirable for studies on electron-transfer phenomena, as well as the design potential devices for molecular electronic purposes.

Computational Study of 13C NMR Chemical Shift Anisotropy Patterns in C20H10 and [C20H10]4-. Insights into Their Variation upon Planarization and Formation of Concentric Aromatic Species in the Smaller Isolated-Pentagon Structural Motif

Corannulene, C20H10, exhibits a concave surface in the ground state that is able to experience a bowl-to-bowl inversion through a planar conformation. Such a structure is the smaller example resembling an isolated-pentagon motif, as a relevant fragment in fullerene chemistry. Here, we explored the differences between bowl and planar conformations involving both energetic and 13C NMR properties, for the neutral and tetraanionic species by using density functional theory (DFT) methods. This allows us to understand the variation of the chemical environment at the carbon atoms upon planarization of this representive motif. Our results reveal that the variation of the chemical shift comes about from the variation of different main components of the shielding tensor, according to the relative position of the carbon atoms in the structure (i.e., rim, hub, and protonated), which is more relevant for both hub and protonated sites, in contrast to the rim carbon remaining almost unshifted. Interestingly, the planar transition state exhibits a more favorable bonding situation than the bowl-shaped conformation; however, the higher strain is enough to overcome this extra stabilization. Upon reduction to the tetraanionic counterpart (C20H104-), a lesser strain in the planar conformation is observed, decreasing the inversion barrier. In addition, the formation of the concentric aromatic ring systems in C20H104-, results in a more axially symmetric chemical shift anisotropy (CSA) tensor for the hub carbons, accounting in a local manner, for the concentric aromatic behavior in such structure in contrast to the neutral parent. These observations can be useful to evaluate the aromatic behavior of teh isolated-pentagon rule (IPR) motif in fullerene cages.

Effect of the homo- and heterobimetallic compounds derived from s-indacene on the thermal decomposition of ammonium perchlorate

This contribution describes an approaching about the catalytic activity of the homo- and heterobimetallic complexes derived from s-indacene on the thermal decomposition of ammonium perchlorate (abbreviate AP). The complexes, anti-[Cp*Fe-s-Ic′-FeCp*] (1), anti-[Cp*Fe-s-Ic′-CoCp*] (2), anti-[Cp*Fe-s-Ic′-NiCp*] (3) and anti-[Cp*Fe-s-Ic′-Mn(CO)3] (4) (with s-Ic′: 2,6-diethyl-4,8-dimethyl-s-indaceneiide), were compared with the catalytic activity of the catocene (cat) complex previously reported. Furthermore, in order to clarify the mechanism of the bimetallic compounds, it was tested ferrocene (Fc) compound as burning rate (BR) catalyst on the thermal decomposition of AP. These compounds shown a shift on the peak temperature to left and an increase released heats during thermal decomposition of AP. The burning rate catalytic activity of Fc, 1, 2, 3 and 4 on thermal decomposition of AP was examined by thermogravimetry and differential scanning calorimetry techniques.

Photophysics of tungsten–benzylidyne complexes derived from s-indacene: synthesis, characterization and DFT studies

The photophysics of the mono- and homobimetallic complexes of tungsten–benzylidyne derived from s-indacene have been examined by using absorption and emission. Theoretical calculations of these compounds were carried out to gain further understanding of these novel molecular systems. Consistent with this prediction, each of the complexes displays a weak, mid-visible absorption band which is attributed to the d → π* transition. The tungsten complexes also exhibit luminescence with a lifetime in the 5–6 ns regime.

Influence of Ag+ on the Magnetic Response of [2.2.2]Paracyclophane: NMR Properties of a Prototypical Organic Host for Cation Binding Based on DFT Calculations

The complexation of metal cations into a host–guest situation is particularly well exemplified by [2.2.2]paracyclophane and AgI, which leads to a strong cation–π interaction with a specific face of the host molecule. Through this study we sought a deeper understanding of the effects the metal center has on the NMR spectroscopic properties of the prototypical organic host, generating theoretical reasons for the observed experimental results with an aim to determine the role of the cation–π interaction in a host–guest scenario. From an analysis of certain components of the induced magnetic field and the 13C NMR shielding tensor under its own principal axis system (PAS), the local and overall magnetic behavior can be clearly described. Interestingly, the magnetic response of such a complex exhibits a large axis-dependent behavior, which leads to an overall shielding effect for the coordinating carbon atoms and a deshielding effect for the respective uncoordinated counterparts, evidence that complements previous experimental results. This proposed approach can be useful to gain further insight into the local and overall variation of NMR shifts for host–guest pairs involving both inorganic and organic hosts.