It has been argued that some small newly discovered all-metal clusters may be consideredas aromatic. This would make them the first aromatic chemical systems with no carbon content at all. The initial report was on the ionic aluminum cluster, Al42-, which exhibits a planar square structure and has two delocalized π-electrons, thus satisfying Hückel's rule for aromatic systems. It also shows a relatively high chemical and structural stability. By means of quantum chemical calculations, Kuznetsov et al. have shown that the square structure is preserved when the Al cluster reacts to form some bimetallic clusters with various chemical compositions: MAl4- and M2Al4 (where M = Li+, Na+, and Cu+) and that the aromatic nature is apparently preserved. In this paper, we report a density functional theory (DFT) study, using the hybrid functional B3LYP and a 6-31+G(d) basis set, which allows us to rationalize and to quantify the aromatic nature of MAl4- species and to extend our study to other bimetallic clusters which have not yet been reported. These clusters have the general formula MA14n(M = Li+, Na+, K+, Be2+, Mg2+, Ca2+, Sc3+, Al3+, B3+, Ga3+, and Ti4+) where n = - 1, 0, +1, +2. We also evaluate the stability as a function of charge and discuss different properties to assess the aromaticity of these systems, namely through reactivity indices such as the DFT absolute hardness, nucleus-independent chemical shift (NICS), and delocalization indexes (DIs).
|Title of host publication||Theoretical Aspects of Chemical Reactivity|
|Number of pages||16|
|Publication status||Published - 2007|
|Name||Theoretical and Computational Chemistry|
Bibliographical noteFunding Information:
We are grateful to Jesus Hernández–Trujillo from Facultad de Química, UNAM, for very helpful comments and fruitful discussion. JR acknowledges support from CONACYT through project SEP-2003-C02-43453 from Fondo Sectorial SEP-CONACYT. We are also grateful for SGI Series 2000 computer time from Depto. de Supercómputo, DGSCA, UNAM. PG is grateful for a scholarship from CONACYT during her Masters Thesis work, this work partially fulfilling requirements for this degree. MS and JP thank the Spanish MCyT for financial support through projects nos. BQU2002-0412-C02-02 and BQU2002-03334, and the DURSI of the Generalitat de Catalunya through project No. 2001SGR-00290. MS is indebted to the DURSI for financial support through the Distinguished University Research Promotion awarded in 2001. JP also acknowledges the DURSI for the postdoctoral fellowship 2004BE00028.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry