Stability and electronic properties of isoelectronic heteroatomic analogs of
Graphical abstract
Research highlights
► Ga2, In2, and In2 are isoelectronic to the Zintl ion . ► Photoelectron spectra and theoretical studies reveal similar electronic structures. ► HOMO–LUMO gaps and stability of isomers depend on size and location of heteroatoms.
Introduction
Materials in which atomic or molecular clusters serve as the building blocks motivate our desire to understand and manipulate cluster properties [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Since the characteristics of clusters change with size, composition, and charge state, cluster assembled materials offer the prospect of nanoscale materials with atomic control. This is different from top-down approaches that reside primarily in the ‘scaling regime’ of nanoscience. Here, properties vary less dramatically than in the cluster regime where every atom and every electron matters [12]. One important class of cluster assembled materials, the Zintl phases, were discovered almost 70 years ago [13]. The building blocks of Zintl phases are the multiply anionic, post-transition metal clusters that are stabilized by alkali or alkali-based countercations [14], [15], [16], [17], [18], [19], [20]. A viable strategy to synthesize such Zintl phases from new clusters is to conduct experiments on Zintl analogs (clusters that are isoelectronic with species already known to form Zintl assemblies). One way to accomplish this is to study gas phase clusters, since numerous gas phase studies have established that the Zintl analog clusters appear as the most abundant species in mass spectra [4], [21], [22], [23]. As the gas phase synthesis of such a series of clusters is straightforward it offers a viable pathway to compare a large range of candidates for Zintl phases [21], [22], [23], [24], [25], [26], [27], [28].
In the current study, we have examined the properties of a series of isoelectronic heteroatomic clusters. Heteroatomic clusters offer an additional degree of freedom by which the properties of nanoscale materials may be manipulated [29], [30], [31], [32], [33], [34], [35], [36]. This is possible because heteroatomic substitutions allow the size and charge state of the components to be easily varied. We choose the five-atom analogs of for this study because the parent ion forms cluster assemblies [37], and because five-atom clusters provide more options for substitution than the traditional tetrahedral or distorted tetrahedral four-atom clusters. The cluster is a well known Zintl anion, whose stability is attributed to Wade–Mingos rules, as it has five atoms and 12 valence p-electrons with a trigonal bipyramidal geometry [38], [39]. Previous studies in our group have pointed out that Ga2, which is isoelectronic with , is a very stable species that displays a high abundance in the mass spectrum, high adiabatic electron detachment energy (AEDE), and a large gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO–LUMO gap) [29]. In another communication, similar results were found [30] for In2, an analog of ; another species isoelectronic with is In2. Here, we perform a comparative study of these three clusters and show how the size of the atoms and point of substitution affects the electronic structure and stability of the clusters. We employ photoelectron spectroscopy experiments to give a fingerprint of the electronic structure and allow for a comparison of stability. Our theoretical investigations allow control over the substitution, and reveal the evolution of electronic structure with the choice of heteroatomic dopants and point of substitution.
Section snippets
Methods
The experimental details for the current study are provided elsewhere [40]. In brief, Inx, Gax, and Inx clusters were formed by using ¼′′ 50:50 molar ratio In-Bi, Ga-Bi, and In-Sb molded rods in a laser vaporization source. Helium was used as a carrier gas and the clusters were mass analyzed using Wiley McLaren time-of-flight mass spectrometry [41]. The photoelectron spectra for the clusters were obtained using a magnetic bottle time-of-flight photoelectron spectrometer [42],
Results
The photoelectron spectrum of In2 is shown in Figure 1 and is compared with the spectra of Ga2 and In2. The adiabatic electron detachment energy (AEDE) is assigned by extrapolating the leading edge of the first peak. This method may provide a valid estimation of the true AEDE when the vibrational progression is not well-resolved. The clusters studied here have rigid trigonal bipyramid structures that do not substantially change upon electron addition, yielding a good Frank–Condon
Conclusions
The present studies have examined the effects of substitution in a series of IIIV gas phase clusters that are isoelectronic with . These heteroatomic clusters are singly charged and demonstrate enhanced stability as seen through the AEDE, R.E., A.E., and HOMO–LUMO gap. The ground state geometry in all three cases is that in which the Group V atoms form the equatorial triangle, while the Group III atoms cap the trigonal bipyramid. This enhances the bonding within the equatorial triangle,
Acknowledgement
We gratefully acknowledge financial support from the US Department of the Army through a MURI Grant No. W911NF-06-1-0280.
References (49)
- et al.
Chem. Phys. Lett.
(2009) - et al.
ACS Nano
(2009) - et al.
J. Phys. Chem. C
(2009) ACS Nano
(2010)Nano Lett.
(2007)ACS Nano
(2010)- et al.
J. Phys. Chem. C
(2009) - et al.
Nature
(2006) - et al.
J. Am. Chem. Soc.
(2008) - et al.
J. Am. Chem. Soc.
(2009)
Science
J. Phys. Chem. A
P. Nat. Acad. Sci. USA
Angew. Chem.
Chem. Rev.
Organometallics
Chem. Phys. Chem.
Inorg. Chem.
Inorg. Chem.
J. Am. Chem. Soc.
Inorg. Chem.
J. Chem. Phys.
Z. Physik D: At. Mol. Clusters
J. Am. Chem. Soc.
Cited by (6)
Dicarboxylic acid as a linker to improve the content of amorphous drug in drug-in-polymer film: Effects of molecular mobility, electrical conductivity and intermolecular interactions
2020, Journal of Controlled ReleaseCitation Excerpt :Furthermore, the HOMO-LUMO energy band gap (ΔE) of all OLN salts was calculated to compare the intrinsic stability (Table 3). Lower ΔE reflected lower chemical reactivity of the OLN salt, which indicated higher energy needed to break down the interactions inside the OLN salts [60]. OLN·Mal showed the highest ΔE, while OLN·Fum showed the lowest ΔE.
Structural transitions of tin clusters: Sn <inf>n</inf> (n = 34-44)
2012, Chemical Physics LettersComparison of Sn<inf>n</inf>(n=2-15) neutral and ionic structures
2013, Chemical Research in Chinese UniversitiesPalladium in the gap: Cluster assemblies with band edges localized on linkers
2012, Journal of Physical Chemistry C