Why Do the Heavy-Atom Analogues of Acetylene E₂H₂ (E = Si−Pb) Exhibit Unusual Structures?

Abstract

DFT calculations at BP86/QZ4P have been carried out for different structures of E(2)H(2) (E = C, Si, Ge, Sn, Pb) with the goal to explain the unusual equilibrium geometries of the heavier group 14 homologues where E = Si-Pb. The global energy minima of the latter molecules have a nonplanar doubly bridged structure A followed by the singly bridged planar form B, the vinylidene-type structure C, and the trans-bent isomer D1. The energetically high-lying trans-bent structure D2 possessing an electron sextet at E and the linear form HEEH, which are not minima on the PES, have also been studied. The unusual structures of E(2)H(2) (E = Si-Pb) are explained with the interactions between the EH moieties in the (X(2)Pi) electronic ground state which differ from C(2)H(2), which is bound through interactions between CH in the a(4)Sigma(-) excited state. Bonding between two (X(2)Pi) fragments of the heavier EH hydrides is favored over the bonding in the a(4)Sigma(-) excited state because the X(2)Pi --> a(4)Sigma(-) excitation energy of EH (E = Si-Pb) is significantly higher than for CH. The doubly bridged structure A of E(2)H(2) has three bonding orbital contributions: one sigma bond and two E-H donor-acceptor bonds. The singly bridged isomer B also has three bonding orbital contributions: one pi bond, one E-H donor-acceptor bond, and one lone-pair donor-acceptor bond. The trans-bent form D1 has one pi bond and two lone-pair donor-acceptor bonds, while D2 has only one sigma bond. The strength of the stabilizing orbital contributions has been estimated with an energy decomposition analysis, which also gives the bonding contributions of the quasi-classical electrostatic interactions.

Hydrogen and silyl bridges in group 13 and 14 atom containing molecules

“…Tables III, IV (and also Tables SI3, SI4) show the optimized geometries, calculated electronic properties and bond orders of Si 2 H 2 ( 5m , 5d ), Ge 2 H 2 ( 6m , 6d ), SiGeH 2 ( 7m ( a ), 7m ( b ), 7d ), Si 2 H 4 ( 8m , 8d ( cis ), 8d ( trans )), Ge 2 H 4 ( 9m , 9d ( cis ), 9d ( trans )) and SiGeH 4 ( 10m ( b ), 10d ( cis ), 10d ( trans )). The geometries are in agreement with previous theoretical calculations 4(a), 5(a).…”

Hydrogen and silyl bridges in group 13 and 14 atom containing molecules

“…Tables III, IV (and also Tables SI3, SI4) show the optimized geometries, calculated electronic properties and bond orders of Si 2 H 2 ( 5m , 5d ), Ge 2 H 2 ( 6m , 6d ), SiGeH 2 ( 7m ( a ), 7m ( b ), 7d ), Si 2 H 4 ( 8m , 8d ( cis ), 8d ( trans )), Ge 2 H 4 ( 9m , 9d ( cis ), 9d ( trans )) and SiGeH 4 ( 10m ( b ), 10d ( cis ), 10d ( trans )). The geometries are in agreement with previous theoretical calculations 4(a), 5(a).…”

Topochemical Transformations of CaX 2 (X=C, Si, Ge) to Form Free‐Standing Two‐Dimensional Materials

“…For CaGe 2 and CaSi 2 , the fully hydrogenated layered two‐dimensional silicane (SiH) n and germanane (GeH) n are computed to be substantially more stable than the molecular units Si 2 H 2 and Ge 2 H 2 . Among the various possible structures of these molecules, such as the trans ‐bent, cis ‐bent, and bridged structures, the bridged structures are computed to be the most stable, which is in excellent agreement with previous reports,38, 39 and they are considered in Table 2. The relative energies of different structures of Si 2 H 2 and Ge 2 H 2 are tabulated in the Supporting Information, Table S2.…”

“…[15] The computed reaction energies for transformation of CaX 2 (X = C, Si, Ge) into their respective layered materials and molecular units are given in Ta ble 2. For CaGe 2 and CaSi 2 ,t he fully hydrogenated layered two-dimensional silicane (SiH) n and germanane (GeH) n are computed to be substantially more stable than the molecular units Si 2 H 2 and Ge 2 H 2 .A mong the various possible structures of these molecules, such as the trans-bent, cis-bent, and bridged structures, the bridged structuresa re computed to be the mosts table, which is in excellent agreement with previous reports, [38,39] and they are considered in Ta ble 2. The relative energies of different structures of Si 2 H 2 and Ge 2 H 2 are tabulated in the Supporting Information, Ta ble S2.A mong the layered products, the two-dimensional buckled "up-down X-H" structures are the most stable forms for all systems.F igure 3a shows the structureo fs uch layered systems( form B-I).…”

Comparative Study of Neutral and Cationic Sn2H2: Toward Laboratory Detection of the Cation

“…All HOMO, LUMO, SOMO, bonding, and important interaction orbitals are shown in Supporting Information . Overall, the NBO orbital analysis agrees with the research of Frenking and co-workers 59 for the neutral species, with the exception of the trans and monobridged structures. In the butterfly structure ( Figure 7 ), there are a Sn–Sn single bond ( Figure 7 a), two Sn–H single bonds Figure 7 b,c, two donor–acceptor bonds formed between an empty π orbital ( Figure 7 d,e), and a Sn–H bond on an adjacent Sn atom.…”

Hydrogen and silyl bridges in group 13 and 14 atom containing molecules

“…Tables III, IV (and also Tables SI3, SI4) show the optimized geometries, calculated electronic properties and bond orders of Si 2 H 2 ( 5m , 5d ), Ge 2 H 2 ( 6m , 6d ), SiGeH 2 ( 7m ( a ), 7m ( b ), 7d ), Si 2 H 4 ( 8m , 8d ( cis ), 8d ( trans )), Ge 2 H 4 ( 9m , 9d ( cis ), 9d ( trans )) and SiGeH 4 ( 10m ( b ), 10d ( cis ), 10d ( trans )). The geometries are in agreement with previous theoretical calculations 4(a), 5(a).…”

Topochemical Transformations of CaX 2 (X=C, Si, Ge) to Form Free‐Standing Two‐Dimensional Materials

“…For CaGe 2 and CaSi 2 , the fully hydrogenated layered two‐dimensional silicane (SiH) n and germanane (GeH) n are computed to be substantially more stable than the molecular units Si 2 H 2 and Ge 2 H 2 . Among the various possible structures of these molecules, such as the trans ‐bent, cis ‐bent, and bridged structures, the bridged structures are computed to be the most stable, which is in excellent agreement with previous reports,38, 39 and they are considered in Table 2. The relative energies of different structures of Si 2 H 2 and Ge 2 H 2 are tabulated in the Supporting Information, Table S2.…”

“…[15] The computed reaction energies for transformation of CaX 2 (X = C, Si, Ge) into their respective layered materials and molecular units are given in Ta ble 2. For CaGe 2 and CaSi 2 ,t he fully hydrogenated layered two-dimensional silicane (SiH) n and germanane (GeH) n are computed to be substantially more stable than the molecular units Si 2 H 2 and Ge 2 H 2 .A mong the various possible structures of these molecules, such as the trans-bent, cis-bent, and bridged structures, the bridged structuresa re computed to be the mosts table, which is in excellent agreement with previous reports, [38,39] and they are considered in Ta ble 2. The relative energies of different structures of Si 2 H 2 and Ge 2 H 2 are tabulated in the Supporting Information, Ta ble S2.A mong the layered products, the two-dimensional buckled "up-down X-H" structures are the most stable forms for all systems.F igure 3a shows the structureo fs uch layered systems( form B-I).…”

Comparative Study of Neutral and Cationic Sn2H2: Toward Laboratory Detection of the Cation

“…All HOMO, LUMO, SOMO, bonding, and important interaction orbitals are shown in Supporting Information . Overall, the NBO orbital analysis agrees with the research of Frenking and co-workers 59 for the neutral species, with the exception of the trans and monobridged structures. In the butterfly structure ( Figure 7 ), there are a Sn–Sn single bond ( Figure 7 a), two Sn–H single bonds Figure 7 b,c, two donor–acceptor bonds formed between an empty π orbital ( Figure 7 d,e), and a Sn–H bond on an adjacent Sn atom.…”

Hydrogen and silyl bridges in group 13 and 14 atom containing molecules

“…Tables III, IV (and also Tables SI3, SI4) show the optimized geometries, calculated electronic properties and bond orders of Si 2 H 2 ( 5m , 5d ), Ge 2 H 2 ( 6m , 6d ), SiGeH 2 ( 7m ( a ), 7m ( b ), 7d ), Si 2 H 4 ( 8m , 8d ( cis ), 8d ( trans )), Ge 2 H 4 ( 9m , 9d ( cis ), 9d ( trans )) and SiGeH 4 ( 10m ( b ), 10d ( cis ), 10d ( trans )). The geometries are in agreement with previous theoretical calculations 4(a), 5(a).…”

Topochemical Transformations of CaX 2 (X=C, Si, Ge) to Form Free‐Standing Two‐Dimensional Materials

“…For CaGe 2 and CaSi 2 , the fully hydrogenated layered two‐dimensional silicane (SiH) n and germanane (GeH) n are computed to be substantially more stable than the molecular units Si 2 H 2 and Ge 2 H 2 . Among the various possible structures of these molecules, such as the trans ‐bent, cis ‐bent, and bridged structures, the bridged structures are computed to be the most stable, which is in excellent agreement with previous reports,38, 39 and they are considered in Table 2. The relative energies of different structures of Si 2 H 2 and Ge 2 H 2 are tabulated in the Supporting Information, Table S2.…”

“…[15] The computed reaction energies for transformation of CaX 2 (X = C, Si, Ge) into their respective layered materials and molecular units are given in Ta ble 2. For CaGe 2 and CaSi 2 ,t he fully hydrogenated layered two-dimensional silicane (SiH) n and germanane (GeH) n are computed to be substantially more stable than the molecular units Si 2 H 2 and Ge 2 H 2 .A mong the various possible structures of these molecules, such as the trans-bent, cis-bent, and bridged structures, the bridged structuresa re computed to be the mosts table, which is in excellent agreement with previous reports, [38,39] and they are considered in Ta ble 2. The relative energies of different structures of Si 2 H 2 and Ge 2 H 2 are tabulated in the Supporting Information, Ta ble S2.A mong the layered products, the two-dimensional buckled "up-down X-H" structures are the most stable forms for all systems.F igure 3a shows the structureo fs uch layered systems( form B-I).…”

Comparative Study of Neutral and Cationic Sn2H2: Toward Laboratory Detection of the Cation

“…All HOMO, LUMO, SOMO, bonding, and important interaction orbitals are shown in Supporting Information . Overall, the NBO orbital analysis agrees with the research of Frenking and co-workers 59 for the neutral species, with the exception of the trans and monobridged structures. In the butterfly structure ( Figure 7 ), there are a Sn–Sn single bond ( Figure 7 a), two Sn–H single bonds Figure 7 b,c, two donor–acceptor bonds formed between an empty π orbital ( Figure 7 d,e), and a Sn–H bond on an adjacent Sn atom.…”