RESUMO
Ultrasmall ligand-protected clusters are prototypical species for evaluating the variation at the bottom of the nanoscale range. Here we explored the ultrasmall gold-phosphine M13(dppe)6 cluster, as a prototypical framework to gain insights into the fundamental similarities and differences between Au, Ag, and Cu, in the 1-3 nm size range, via relativistic DFT calculations. Different charge states involving 8- and 10-cluster electron (ce) species with a 1S21P6 and 1S21P61D2 configuration, leading to structural modification in the Au species between Au13(dppm)65+ and Au13(dppm)63+, respectively. Furthermore, this structural distortion of the M13 core is found to occur to a lower degree for the calculated Ag and Cu counterparts. Interestingly, optical properties exhibit similar main patterns along with the series, inducing a blue-shift for silver and copper, in comparison to the gold parent cluster. For 10-ce species, the main features of 8-ce are retained with the appearance of several weak transitions in the range. The ligand-core interaction is enhanced for gold counterparts and decreased for lighter counterparts resulting in the Au > Cu > Ag trend for the interaction stabilization. Hence, the Ag and Cu counterparts of the Au13(dppm)6 cluster appear as useful alternatives, which can be further explored towards different cluster alternatives for building blocks for nanostructured materials.
RESUMO
Host-guest chemistry is a relevant issue in materials science, which encourages further development of versatile host structures. Here the particular features of coinage-metal pillarplexes are evaluated towards formation of host-guest aggregates by the inclusion of 1,8-diaminooctane, as characterized for [M8(LMe)2]4+ (M = Ag, and, Au). The obtained results denotes the main contribution from van der Waals type interaction (50%), followed by a contribution from orbital polarization and electrostatic nature (20% and 30%), involving both orbitalary and electrostatic terms. Throughout the different coinage-metal based hosts (M = Cu, Ag, and Au), a similar interaction energy is found given by the large contribution of the π-surface from the organic ligand backbone to both van de Waals and electrostatic interactions. This suggests that a similar host structure can be obtained for the lighter copper counterpart, retaining similar how-guest features. Moreoves, the [Au8(LMe)2]4+ host exhibits inherent luminescent properties, involving the shortening of Au(i)-Au(i) contacts at the excited state, which is partially avoided when the guest is incorporated, accounting for the observed quenching from titration experiments. This results encourages further exploration of coinage metal hosts in the formation of inclusion complexes.
RESUMO
The bonding properties of phosphazenes and spirocyclophosphazenes containing tris-2,2'-dioxybiphenyl groups and their derivatives were investigated by means of different computational techniques. Electronic delocalization and phosphazene-ligand bonding were studied in terms of natural bond orbitals (NBOs) and energy decomposition (EDA) analysis in combination with the natural orbital for chemical valence (NOCV), which showed the dependency of the charge transfer with the electron delocalization. TD-DFT calculations were employed to study the absorption profile of the studied molecules and to contrast the redshift and change in intensities of the λmax. An assessment of second-order stabilization energies, ΔE2, within the NBO analysis revealed clear differences between the cyclic-phosphazene arrays. The EDA-NOCV showed that the ligand-phosphazene charge transfer is stronger in phosphazene with amine substituents (4c), which is due to the donor character of the substituent over the phenyl ring. The NBO analysis confirmed either the inflow or outflow of charge due to the influence of the electron donor or electron withdrawing groups.