The SiSn Chemical Bond: An Integrated Thermochemical and Quantum Mechanical Study of the SiSn Diatomic Molecule and Small Si–Sn Clusters

Abstract

The silicon-tin chemical bond has been investigated by a study of the SiSn diatomic molecule and a number of new polyatomic Si(x)Sn(y) molecules. These species, formed in the vapor produced from silicon-tin mixtures at high temperature, were experimentally studied by using a Knudsen effusion mass spectrometric technique. The heteronuclear diatomic SiSn, together with the triatomic Si(2)Sn and SiSn(2) and tetratomic Si(3)Sn, Si(2)Sn(2), and SiSn(3) species, were identified in the vapor and studied in the overall temperature range 1474-1944 K. The atomization energy of all the above molecules was determined for the first time (values in kJ mol(-1)): 233.0+/-7.8 (SiSn), 625.6+/-11.6 (Si(2)Sn), 550.2+/-10.7 (SiSn(2)), 1046.1+/-19.9 (Si(3)Sn), 955.2+/-26.8 (Si(2)Sn(2)), and 860.2+/-19.0 (SiSn(3)). In addition, a computational study of the ground and low-lying excited electronic states of the newly identified molecules has been made. These electronic-structure calculations were performed at the DFT-B3LYP/cc-pVTZ and CCSD(T)/cc-pVTZ levels, and allowed the estimation of reliable molecular parameters and hence the thermal functions of the species under study. Computed atomization energies were also derived by taking into account spin-orbit corrections and extrapolation to the complete basis-set limit. A comparison between experimental and theoretical results is presented. Revised values of (716.5+/-16) kJ mol(-1) (Si(3)) and (440+/-20) kJ mol(-1) (Sn(3)) are also proposed for the atomization energies of the Si(3) and Sn(3) molecules.

Investigation of New Intermetallic Bonds and Molecules by Knudsen Effusion Mass Spectrometry Integrated with ab Initio Calculations

“…Data from ref. [11]. analogous situation is not favoured in the Sn 3 Si species, where the formation of three Si-Sn bonds is preferred, and a fan-like geometry is found in the ground state.…”

“…However, among the ten intragroup heteronuclaer diatomics, only five (namely, SiC, GeC, SnC, GeSi, and SnGe) were experimentally characterized until five years ago [9]. To fill this gap, in the last few years we undertook a systematic study of these species, which led us to identify and characterize the new SnPb, SiPb, GePb, and SiSn species by KEMS experiments [9][10][11]. After this work, the knowledge of the dissociation energies of Group 14 diatomics is now almost complete (Fig.…”

“…1), with typical temperature differences of 500-700 degrees between the lower crucible (Pb reservoir) and the upper Knudsen cell. The following gaseous equilibria were monitored in the overall temperature range 1420-2300 K: At variance with the Pb-containing molecules, the lower volatility difference between Si and Sn permitted to study the Si-Sn system with a single cell molecular source, by vaporizing a Si-Sn alloy of proper composition [11]. Under the established experimental conditions, it was possibile in this case to identify a series of polyatomic species beside the simple SiSn diatomic, namely Si 2 Sn, SiSn 2 , Si 3 Sn, Si 2 Sn 2 , and SiSn 3 (see the next section).…”

“…Dissociation energy (kJ/mol) of intra-group 14 diatomics. Data from ref.s [24] (C 2 ), [25] (SiC), [26] (Pb 2 ), [27] (GeC), [11] (Si 2 , SiSn, Sn 2 ), [28] (GeSi), [29] (Ge 2 ), [30] (GeSn), [10] (SiPb,GePb), [9] (SnPb).…”

“…The aim of our research [8][9][10][11] is to contribute to the understanding of "novel" chemical bonds; i.e. chemical bonds which come into action between a combination of chemical elements never observed before in "naked" molecules and clusters.…”