Article pubs.acs.org/JPCA
Bridging a Knowledge Gap from Siloxanes to Germoxanes and Stannoxanes. A Theoretical Natural Bond Orbital Study Ionuţ-Tudor Moraru, Petronela M. Petrar, and Gabriela Nemeş* Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University, Arany János Street No. 11, RO-400082 Cluj-Napoca, Romania
Downloaded via UNIV OF ALABAMA BIRMINGHAM on July 2, 2018 at 09:57:29 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
S Supporting Information *
ABSTRACT: Explaining the nature of the E−O chemical bond (E = Si, Ge, Sn) has been a great challenge for theoretical chemists during the last decades. Among the large number of models used for this purpose, the one based on hyperconjugative interactions sheds more light on the nature of chemical bonding in siloxanes. Starting from this concept, this study aimed to evaluate the impact of siloxane type hyperconjugative effects on the structural features of germoxanic and stannoxanic species and in addition to assess if p−d-like back-bonding interactions can also play important roles in determining the particular structures of these heavier analogues of ethers. Natural bond orbital deletion (NBO DEL) optimizations, carried out at the DFT level of theory, revealed that hyperconjugative effects dictate to a large extent the structural behavior of these species. Furthermore, this study points out that p−d backbonding interactions also influence the equilibrium geometry of these species, although acting as a secondary electronic effect within the E−O−E moieties (E = Si, Ge, Sn).
■
INTRODUCTION
Several decades after, experiments carried out on low-quartz led to new insights concerning the bonding within siloxanic species,9 and a covalent character was proposed for Si−O.10,11 The unusual short bond length was rationalized as a consequence of pO → dSi back-bonding.12,13 Subsequent computational studies questioned the accuracy of the backbonding model,14,15 the contribution of d orbitals being considered merely a polarization function. This observation was generally accepted not only for siloxanic derivatives but also for analogue derivatives of heavier main group elements,16−19 though other studies20 emphasized the need for d orbitals in computing accurate geometries and also reasonable energies. However, for anionic species, d orbitals seem to play a more significant role in the chemical bonding.21,22 Studies on this topic also suggested that the ionic behavior14,23−25 is more appropriate in explaining the structural features of Si−O−Si moieties. Electron densities26,27 or the enhanced steric effects of silyl groups28,29 were also evaluated. In addition, the strength of Si−O was compared to similar chemical bonds containing second row elements,30,31 calculations succeeding to explain the geometrical parameters of some alumosilicates or their affinity toward some cations, by analyzing the Si−Al exchange energies within Si−O−Si linkages. The concept of vicinal hyperconjugative interactions is well documented for sylil groups and siloxanic derivatives,32−36 but
The study of oxanic derivatives containing E−O−E moieties (E = heavy group 14 element) has been of great interest in the last period, from both a fundamental and an applicative point of view. These compounds are mostly used in the synthesis of new materials with controlled properties,1,2 and a full understanding of the chemical bonding within the precursors should allow for a better design of the targeted materials. Siloxanes, germoxanes, and stannoxanes have molecular structures exhibiting large E−O−E bond angles and short E− O bond lengths, unlike C−O−C fragments in analogue ethers. Experimental values for Si−O−Si angles, measured by electron diffraction in the gaseous phase,3,4 range between 144.1° in (H3Si)2O and 148.0° in the permethylated derivative, (Me3Si)2O. Large Ge−O−Ge bond angles have also been reported in (H3Ge)2O (126.5°)5 and (Me3Ge)2O (around 141°).6 The Sn−O−Sn angle in (H3Sn)2O has not yet been determined by experimental methods, but in (Me3Sn)2O, a Sn−O−Sn angle of around 140° has been measured.6 E−O bond lengths range from 1.631 to 1.634 Å in siloxanes3,4 and from 1.766 to 1.770 Å in germoxanes.5,6 The Sn−O distance in hexamethyldistannoxane6 is 1.940 Å. These bonds are noticeably shorter than the sum of the covalent radii7 (1.77 Å for Si− O, 1.86 Å for Ge−O, and 2.05 Å for Sn−O). A great number of literature studies aimed to explain the structural particularities of siloxanic units, and most of them employed computational methods. A first theoretical model of the Si−O bonding was developed by Linus Pauling in the third decade of last century, who classified the chemical bond as predominantly ionic8 based on differences in electronegativity. © 2017 American Chemical Society
Received: February 7, 2017 Revised: March 8, 2017 Published: March 10, 2017 2515
DOI: 10.1021/acs.jpca.7b01208 J. Phys. Chem. A 2017, 121, 2515−2522
Article
The Journal of Physical Chemistry A much less is known about their heavier analogues. The development of computational chemistry enabled a better awareness of these issues,37−42 but the most important contribution regarding the clarification of the hyperconjugative phenomena within disiloxanic derivatives belongs to Weinhold and West,33,44 whose work led to new perspectives in the field.45 This paper presents a comprehensive computational study investigating vicinal hyperconjugative interactions of the type LPO → σ*E−R (E = Si, Ge, Sn; R = H, C) in heavier analogues of ethers. This study also investigated the role of p → d-like interactions in determining the structural features of siloxanic, germoxanic, and stannoxanic derivatives. Natural bond orbital (NBO)46−48 techniques in conjunction with DFT calculations were employed to extensively investigate all of these interactions.
Table 1. Selected Geometrical Parameters for the Global Minima of (R3E)2O Species (E = C, Si, Ge, Sn; R = H, Me) E−O−E (deg) E C Si Ge Sn
R H CH3 H CH3 H CH3 H CH3
B3LYP 112.9 128.1 152.9 159.5 129.7 136.9 134.5 138.9
E−O (Å)
PBE0
expt.a
112.2 127.1 147.7 150.5 127.8 133.9 132.5 134.4
58
111.8 130.859 144.13,4 148.03 126.55 141.06 140.86
B3LYP
PBE0
expt.a
1.411 1.444 1.637 1.643 1.784 1.790 1.969 1.976
1.400 1.430 1.634 1.641 1.774 1.780 1.956 1.963
1.41558 1.42059 1.6343,4 1.6313 1.7665 1.7706 1.9406
a
Experimental values were measured by gaseous-phase electron diffraction.
■
data in the gaseous phase was observed. However, B3LYP seemed to slightly overestimate the Si−O−Si and Ge−O−Ge angles in the siloxanic and germoxanic species, in comparison with PBE0 and experimental data. Better agreement was observed between B3LYP and experimental values for Sn−O− Sn, while PBE0 tended to underestimate these angles. While the calculated C−O−C angle in dimethyl ether was close to 109°, the computed E−O−E angles in species of the type (H3E)2O (E = Si, Ge, Sn) were much wider (Table 1). The C−O−C angle increased with the bulkiness of the substituents; calculated values reached 128.1° (B3LYP) and 127.1° (PBE0) in di-tert-butyl ether. In contrast, the widening of the E−O−E angles (E = Si, Ge, Sn) from (H3E)2O to (Me3E)2O derivatives was less important. The calculated values of Si−O, Ge−O, and Sn−O were significantly shorter than the sum of the covalent radii of the atoms, with values of 0.14−0.15 Å for the disiloxanic derivatives and 0.08−0.09 Å for the digermoxanic and distannoxanic ones (Table 1). The most stable conformations for the (H3E)2O derivatives were found to be those in which the hydrogen atoms are in eclipsed orientations (see Table S1 in the Supporting Information). In (Me3E)2O derivatives, the calculated values of the C−E−E−C dihedrals ranged between 30 and 45° (Table S1). The molecular structures of (H3O)2E derivatives were also optimized using smaller (Def2-SV(P)) and larger (Def2QZVPPD) basis sets. The calculated E−O−E angles and E− O bond lengths obtained using these basis sets were in good agreement with those delivered by the triple-ζ one (Tables S2 and S3). Constrained geometry optimizations, with the E−O−E angles fixed at 180°, were performed to estimate the linearization potentials for the E−O−E units in all investigated compounds (E = C, Si, Ge, Sn), which were calculated as the difference between the energy of the constrained molecular geometry and the global minimum (Table S4). Larger potentials were calculated for the C−O−C units in ethers than for the E−O−E moieties in siloxanic, germoxanic, and stannoxanic species. The calculated linearization potential for the C−O−C moiety was >33 kcal/mol in dimethyl ether and >20 kcal/mol in the hexamethylated derivative. The lowest potentials were obtained for the Si−O−Si fragments in all siloxanic derivatives, with values 0.1 kcal/mol identified, several vicinal hyperconjugative interactions of the type LPO → σ*E−H and back-bonding LPO → RyE effects were detected for each of the (H3Si)2O, (H3Ge)2O, and (H3Sn)2O species (Scheme 2). The total hyperconjugation energy computed as the sum of all LPO → σ*E−R interactions (∑ LPO → σ*E−R) for each of the investigated species is presented in Table 2. However, individual interactions contribute to the total energy in different ratios, depending on several factors, such as the spatial orientation or the nature of the atomic orbitals (OAs) involved. Among the investigated structures, the total hyperconjugation energy from interactions occurring within the E−O−E moiety (E = Si, Ge, Sn) decreased with the increase of the atomic number of E and the bulkiness of the substituent on the E atom (Table 2). The higher hyperconjugation energy within the permethylated species is due to a better orbital overlap between the LPs and σ*E−C when compared with the LPs and σ*E−H overlap. Moreover, the NBO analysis led to similar results for both B3LYP and PBE0 functionals, with differences of less than 2 kcal/mol in each case. NBOs involved in the identified hyperconjugative interactions for one of the two bonds from the E−O−E unit in disiloxanes, digermoxanes, and distannoxanes are presented in Figure 1; similar interactions were of course observed along the other bond. NBO calculations showed that the electron donor behavior of the two LPs on the oxygen atom within the hyperconjugative interactions is not identical. While one of the lone pairs (LPO1) (Figure 1a1−a3, b1−b3, and c1−c3) presents a certain extent of s character, the other lone pair, LPO2 (Figure 1a4,a5, b4,b5, and c4,c5) behaves as a pure p AO (Table S5). The amount of s character in the LPO1 increases from disiloxane (8−11%) to distannoxane (40−41%). Similar trends were observed for the oxygen LPs in the permethylated species even though the s character of LPO1 is less pronounced than that for each of the corresponding (H3E)2O (Table S5). The electron acceptor antibonding orbitals σ*E−R (R = H, C) have contributions from E (60−70%) and R (30−40%) AOs. AOs from the E atom have in all of the cases around 25% s and 75% p character, while H atoms contribute to σ*E−H with pure s orbitals. For σ*E−C, the s/p ratio in E AOs was found to be also around 1/3 (Tables S6 and S7), with no contribution from d AOs. Both σ*E−H and σ*E−C exhibit an elongated shape along E−H and E−C chemical bonds, the main difference between 2518
DOI: 10.1021/acs.jpca.7b01208 J. Phys. Chem. A 2017, 121, 2515−2522
Article
The Journal of Physical Chemistry A
Table 3. Calculated Values for the E−O−E Angles and E−O Bond Lengths According to NBO DEL Unconstrained Optimizations Following the Removal of LPO → σ*E−R Interactions and Differences between the NBO DEL Optimization Calculated Values and the Ones Corresponding to Equilibrium Geometries B3LYP NBO DEL opt ∑ (LPO → σ*E−R)
PBE0
Δ(NBO DEL − equilibrium geom.)
NBO DEL opt ∑ (LPO → σ*E−R)
Δ(NBO DEL − equilibrium geom.)
E
R
E−O−E (deg)
E−O (Å)
ΔE−O−E (deg)
ΔE−O (Å)
E−O−E (deg)
E−O (Å)
ΔE−O−E (deg)
ΔE−O (Å)
Si Ge Sn
H H H
124.2 117.4 121.9
1.706 1.841 2.015
−28.7 −12.3 −12.6
0.069 0.057 0.046
120.9 115.6 119.9
1.702 1.829 1.999
−26.8 −12.2 −12.6
0.068 0.055 0.043
Table 4. Calculated Values for the E−O−E Angles and E−O Bond Lengths According to Unconstrained NBO DEL Optimizations Following the Removal of LPO → σ*E−R and LPO → RyE Interactions and Differences between the Values Obtained Using NBO DEL Optimizations and the Ones Computed for the Equilibrium Geometries B3LYP NBO DEL opt ∑ (LPO → σ*E−R + LPO → RyE)
PBE0
Δ(NBO DEL − equilibrium geom.)
NBO DEL opt ∑ (LPO → σ*E−R + LPO → RyE)
Δ(NBO DEL − equilibrium geom.)
E
R
E−O−E (deg)
E−O (Å)
ΔE−O−E (deg)
ΔE−O (Å)
E−O−E (deg)
E−O (Å)
ΔE−O−E (deg)
ΔE−O (Å)
Si Ge Sn
H H H
114.5 115.6 121.2
1.769 1.861 2.039
−38.4 −14.3 −13.3
0.132 0.077 0.070
111.5 113.9 119.8
1.760 1.847 2.021
−36.2 −13.9 −12.7
0.126 0.073 0.065
bonding ones. The interaction energies decreased with the increase of the atomic number of E and the bulkiness of the substituent on the E atom. The RyE orbitals had mainly d character, which decreased in the group (from ∼95% in siloxanes to ∼60% in stannoxanes; see Tables S11 and S12). Considering that the LPs behave as almost pure p AOs while RyE contains high amounts of d orbitals, the LPO → RyE interactions can be approximated as classical pO → dE backbonding effects, especially for the siloxanic species. The back-bonding interaction energies and the contribution of d AOs in RyE orbitals, calculated using Def2-SV(P) and Def2-QZVPPD basis sets are presented in the Supporting Information (Tables S13−S16). According to the results obtained, the choice of basis set influenced the energy of LPO → RyE interactions to some extent. Thus, the total backbonding energy computed for the disiloxane molecule by using the double-ζ and quadruple-ζ basis sets was around 3 kcal/mol smaller and 3 kcal/mol higher, respectively, compared to the ones delivered by the triple-ζ one; for digermoxane and distannoxane, the calculated energy differences between these basis sets were smaller. While d orbitals are considered rather polarization functions, more complete basis sets should lead to a decrease of the back-bonding effect. However, the greatest interaction energies were obtained for the Def2-QZVPPD basis set, a fact that is opposite of this general accepted statement and thus supports, even though in a smaller ratio, the participation of d orbitals in the E−O chemical bond. In order to evaluate the impact gained by the corroboration of all LPO → σ*E−R and LPO → RyE interactions, NBO DEL optimizations were also performed, removing in this case all of these effects. Following the unconstrained DEL procedures for (H3E)2O species (Table 4), the Si−O−Si and Ge−O−Ge angles were lowered down to the C−O−C values of their analogue ethers. Furthermore, the Si−O and Ge−O distances were significantly elongated, to values very close to the sum of the covalent radii. The widening of the Sn−O−Sn angle was less influenced by the removal of LPO → RySn interactions, while the Sn−O bond lengths increased after the extra deletion
Table 3 presents the calculated values of the E−O−E angles and E−O bond lengths for the (H3E)2O species using unconstrained NBO DEL optimizations and calculated differences with respect to the global minima. Optimizations in the absence of LPO → σ*E−H interactions led to a consistent decrease of the E−O−E angles while the length of the E−O chemical bonds increased (Table 3). Furthermore, these NBO DEL unconstrained optimizations showed that the H−E−E−H dihedrals were strongly influenced by LP O → σ* E−H interactions. The removal of these effects (Table S9) led to a change in the orientation of H atoms from an eclipsed to an anti orientation. The calculated values for E−O−E angles and E−O bond lengths in (Me3E)2O species, according to the constrained NBO DEL optimizations, are presented in Table S10. In addition, for a better comparison, the (H3E)2O species have also been optimized with the same constraints used for (Me3E)2O derivatives. Comparisons between constrained and unconstrained DEL optimizations for the (H3E)2O derivatives showed that the constrained calculations can be used as a relevant approach in estimating the manner in which the hyperconjugative effects impact the widening of the E−O−E angles and the length of the E−O bonds. By optimizing the molecular structures in the absence of LPO → σ*E−R interactions, the E−O−E angles were lowered by comparison to the equilibrium values, while the E−O bonds were elongated. However, the calculated E−O−E angle for each derivative was still wider than the C−O−C ones contained in the analogue ethers, while the lengths of the E−O bonds remained shorter than the sum of the covalent radii of the constituent atoms, even in the absence of these adjacent hyperconjugative interactions. Therefore, we have further assessed the cumulative effect of the vicinal LPO → σ*E−R interactions and LPO → RyE back-bonding ones. The total energy of the identified back-bonding interactions (∑ LPO → RyE) is presented in Tables S11 and S12 together with the amount of d character in RyE. However, the sum of the hyperconjugative interactions was higher than that of the back2519
DOI: 10.1021/acs.jpca.7b01208 J. Phys. Chem. A 2017, 121, 2515−2522
Article
The Journal of Physical Chemistry A Author Contributions
of these back-bonding effects, getting closer to the sum of the their covalent radii (Table 4). In addition, the cumulative removal of LPO → σ*E−R and LPO → RyE effects led also to an anti orientation of the H−E−E−H dihedrals (Table S17). For the constrained DEL optimizations performed on the (Me3E)2O species (Table S18), the impact of LPO → RyE interactions on the E−O−E angles was not as pronounced as that for the (H3E)2O derivatives, in good agreement with the decrease in energy of these effects from (H3E)2O to (Me3E)2O. However, the DEL calculated E−O−E angles within the hexamethyl derivatives dropped below the C−O−C value in ditert-buthyl ether.
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS I.M. thanks Babes-Bolyai University for financial support from the Research Scholarship, being also grateful to the “World Federation of Scientist” Scholarship. Additional computational resources were provided by the high-performance computational facility MADECIP, POSCCE, COD SMIS 48801/1862 co-financed by the European Regional Development Fund of the European Union. The authors thank Professor Romuald Poteau (Université Paul Sabatier, Toulouse) for helpful discussions.
■
CONCLUSIONS This work showed that vicinal hyperconjugative interactions of the type LPO → σ*E−R play an important role in determining the structural features of germoxanes and stannoxanes, similarly to previous observations for siloxanic species. However, DFT calculations and NBO analysis suggested that back-bonding LPO → dE interactions also dictate, albeit to a lesser extent, the structural behavior of all of these derivatives. Assessment of the basis set dependence on LPO → dE effects revealed the implication of these interactions in bonding, although in smaller ratios, as secondary electronic effects. Several geometrical parameters in these species are better explained when taking into account the cumulative effect of both hyperconjugative and back-bonding interactions, according to the NBO DEL optimizations. Thus, in the absence of all of these effects, the E−O−E angles decreased to values similar to C−O−C angles in analogue ethers, or to even lower values. However, the Sn−O−Sn angle was less influenced by the deletion of LPO → RySn effects. The energy of these interactions and also the d character of the Ry orbitals in the investigated E−O−E units decreased with the increase of the atomic number of E. Deletion of hyperconjugative and backbonding effects also impacted the length of the E−O bonds; Si−O and Ge−O distances were elongated to the sum of covalent radii following the NBO DEL optimizations. In addition, the most stable eclipsed conformations of these species were strongly influenced by these interactions.
■
■ ■
ABBREVIATIONS NBO, natural bond orbital; AO, atomic orbital; NBO DEL, natural bond orbital deletion; LP, lone pair; Ry, Rydberg orbital
(1) Silicon Based Polymer Science, Advances in Chemistry 224; Zeigler, J. M., Fearon, F. W. G., Eds.; American Chemical Society: Washington, DC, 1990. (2) King, L.; Sullivan, A. C. Main Group and Transition Metal Compounds with Silanediolate [R2SiO2]2‑ and α-ω-Siloxane Diolate [O(R2SiO)n]2‑ Ligands. Coord. Chem. Rev. 1999, 189, 19−57. (3) Timofeeva, T. V.; Dubchak, I. L.; Dashevsky, V. G.; Struchkov, Yu. T. Flexibility of Siloxane Rings and Rigidity of Ladder-Like Siloxane Polymers: Interpretation on the Basis of Atom-Atom Potential Functions. Polyhedron 1984, 3, 1109−1119. (4) Almenningen, A.; Bastiansen, O.; Ewing, V.; Hedberg, K.; Traetteberg, M. The Molecular Structure of Disiloxane, (SiH3)2O. Acta Chem. Scand. 1963, 17, 2455−2460. (5) Glidewell, C.; Rankin, D. W. H.; Robiette, A. G.; Sheldrick, G. M.; Beagley, B.; Cradock, S. Molecular Structures of Digermyl Ether and Digermyl Sulphide in the Gas Phase, studied by Electron Diffraction. J. Chem. Soc. A 1970, 315−317. (6) Vilkov, L. V.; Tarasenko, N. A. Electron-Diffraction Study of Hexamethyl Digermoxane [(CH3)3Ge]2O and Hexamethyl Distannoxane [(CH3)3Sn]2O in Vapor. J. Struct. Chem. 1970, 10, 979−979. (7) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Covalent Radii Revisited. Dalton Trans. 2008, 21, 2832−2838. (8) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell Univ. Press: Itacha, NY, 1960. (9) Le Page, Y.; Donnay, G. Refinement of the Crystal Structure of Low-Quartz. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1976, 32, 2456−2459. (10) Pauling, L. The Nature of Silicon-Oxygen Bonds. Am. Mineral. 1980, 65, 321−323. (11) Stewart, R. F.; Whitehead, M. A.; Donnay, G. The Ionicity of the Si-O Bond in Low-Quartz. Am. Mineral. 1980, 65, 324−326. (12) Craig, D. P.; Maccoll, A.; Nyholm, R. S.; Orgel, L. E.; Sutton, L. E. Chemical Bonds Involving d-Orbitals. J. Chem. Soc. 1954, 332−357. (13) Cruickshank, D. W. J. The Role of 3d-Orbitals in π-Bonds between (a) Silicon, Phosphorus, Sulphur, or Chlorine and (b) Oxygen or Nitrogen. J. Chem. Soc. 1961, 0, 5486−5504. (14) Oberhammer, H.; Boggs, J. E. Importance of (p-d)π Bonding in the Siloxane Bond. J. Am. Chem. Soc. 1980, 102, 7241−7244. (15) Ernst, C. A.; Allred, A. L.; Ratner, M. A.; Newton, M. D.; Gibbs, G. V.; Moskowitz, J. W.; Topiol, S. Bond Angles in Disiloxane: A Pseudo-Potential Electronic Structure Study. Chem. Phys. Lett. 1981, 81, 424−429.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.7b01208. Tables containing computed data of several geometrical parameters, potentials to linearization, contribution of the AOs in the NBOs involved in hyperconjugative and p → d-like back-bonding interactions and their corresponding energies, image illustrating the NBOs involved in the hyperconjugative interactions for the permethylated derivatives, and DFT coordinates of the analyzed compounds (PDF)
■
REFERENCES
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Gabriela Nemeş: 0000-0003-4031-594X 2520
DOI: 10.1021/acs.jpca.7b01208 J. Phys. Chem. A 2017, 121, 2515−2522
Article
The Journal of Physical Chemistry A (16) Reed, A. E.; Schleyer, P. v. R. Chemical Bonding in Hypervalent Molecules. The Dominance of Ionic Bonding and Negative Hyperconjugation over d-Orbital Participation. J. Am. Chem. Soc. 1990, 112, 1434−1445. (17) Magnusson, E. The Role of d Functions in Correlated Wave Functions: Main Group Molecules. J. Am. Chem. Soc. 1993, 115, 1051−1061. (18) Gilheany, D. G. No d Orbitals but Walsh Diagrams and Maybe Banana Bonds: Chemical Bonding in Phosphines, Phosphine Oxides, and Phosphonium Ylides. Chem. Rev. 1994, 94, 1339−1374. (19) Galbraith, J. M. On the Role of d Orbital Hybridization in the Chemistry Curriculum. J. Chem. Educ. 2007, 84, 783−787. (20) Mezey, P. G.; Haas, E. C. The Propagation of Basis Set Error and Geometry Optimization in Ab Initio Calculations. A Statistical Analysis of the Sulfur d-Orbital Problem. J. Chem. Phys. 1982, 77, 870−876. (21) Hajgató, B.; De Proft, F.; Szieberth, D.; Tozer, D. J.; Deleuze, M. S.; Geerlings, P.; Nyulászi, L. Bonding in Negative Ions: the Role of d Orbitals in the Heavy Analogues of Pyridine and Furan Radical Anions. Phys. Chem. Chem. Phys. 2011, 13, 1663−1668. (22) Cypryk, M.; Chojnowski, J. Silanols and Metasilicates from Negatively Charged = SiO(−) and = SiO2(2−) Precursors. Theoretical Study. J. Organomet. Chem. 2002, 642, 163−170. (23) Gillespie, R. J.; Johnson, S. A. Study of Bond Angles and Bond Lengths in Disiloxane and Related Molecules in Terms of the Topology of the Electron Density and its Laplacian. Inorg. Chem. 1997, 36, 3031−3039. (24) Gillespie, R. J.; Robinson, A. Models of Molecular Geometry. Chem. Soc. Rev. 2005, 34, 396−407. (25) Grabowsky, S. J.; Hesse, M. F.; Paulmann, C.; Luger, P.; Beckmann, J. How to Make the Ionic Si-O Bond More Covalent and the Si-O-Si Linkage a Better Acceptor for Hydrogen Bonding. Inorg. Chem. 2009, 48, 4384−4393. (26) Gibbs, G. V.; D’Arco, P.; Boisen, M. B., Jr. Molecular Mimicry of Bond Length and Angle Variations in Germanate and Thiogermanate Crystals: a Comparison with Variations Calculated for C-, Si-, and SnContaining Oxide and Sulfide Molecules. J. Phys. Chem. 1987, 91, 5347−5354. (27) Gibbs, G. V.; Boisen, M. B.; Hill, F. C.; Tamada, O.; Downs, R. T. SiO and GeO Bonded Interactions as Inferred from the Bond Critical Point Properties of Electron Density Distributions. Phys. Chem. Miner. 1998, 25, 574−584. (28) Grigoras, S.; Lane, T. H. Ab Initio Calculations on the Effect of Polarization Functions on Disiloxane. J. Comput. Chem. 1987, 8, 84− 93. (29) Grigoras, S.; Lane, T. H. Molecular Mechanics Parameters for Organosilicon Compounds Calculated from Ab Initio Computations. J. Comput. Chem. 1988, 9, 25−39. (30) Hass, E. C.; Plath, P. J.; Mezey, P. G. A Non-Empirical Molecular Orbital Study on Loewenstein’s Rule and Zeolite Composition. J. Mol. Struct.: THEOCHEM 1981, 76, 389−399. (31) Hass, E. C.; Plath, P. J.; Mezey, P. G. In Computational Theoretical Organic Chemistry; Csizmadia, I. G., Daudel, R., Eds.; D. Reidel Publ. Co.: New York, 1981; pp 403−408. (32) Pitt, G. Hyperconjugation: an Alternative to the Concept of the pπ-dπ Bond in Group IV Chemistry. J. Organomet. Chem. 1970, 23, C35−C37. (33) Pitt, C. G. Hyperconjugation and its Role in Group IV Chemistry. J. Organomet. Chem. 1973, 61, 49−70. (34) Bock, H.; Mollere, P.; Becker, G.; Fritz, G. Photoelectron Spectra and Molecular Properties. Dimethyl Ether, Methoxysilane, and Disiloxane. J. Organomet. Chem. 1973, 61, 113−125. (35) Pitt, C. G.; Bursey, M. M.; Chatfield, D. A. The Relative GasPhase Proton Affinities and Polarisabilities of Alkyl and Silyl Ethers. J. Chem. Soc., Perkin Trans. 2 1976, 2, 434−438. (36) West, R.; Wilson, L. S.; Powell, D. L. Basicity of Siloxanes, Alkoxysilanes and Ethers Toward Hydrogen Bonding. J. Organomet. Chem. 1979, 178, 5−9.
(37) Veszprémi, T.; Nagy, J. The Role of Inductive, Hyperconjugative and d-Orbital Effects in Organosilicon Compounds. J. Organomet. Chem. 1983, 255, 41−47. (38) Reed, A. E.; Schade, C.; Schleyer, P. v. R.; Kamath, P. V.; Chandrasekhar, J. Anomeric Effects Involving Silicon Centers: Silanols. J. Chem. Soc., Chem. Commun. 1988, 67−69. (39) Shambayati, S.; Schreiber, S. L.; Blake, J. F.; Wierschke, S. G.; Jorgensen, W. L. Structure and Basicity of Silyl Ethers: A Crystallographic and Ab Initio Inquiry into the Nature of Silicon-Oxygen Interactions. J. Am. Chem. Soc. 1990, 112, 697−703. (40) Bakk, I.; Bóna, Á .; Nyulászi, L.; Szieberth, D. Modelling Extended Systems Containing Siloxane Building Blocks. J. Mol. Struct.: THEOCHEM 2006, 770, 111−118. (41) Cypryk, M.; Apeloig, Y. Ab Initio Study of Silyloxonium Ions. Organometallics 1997, 16, 5938−5949. (42) Cypryk, M. Thermochemistry of Redistribution of Poly[oxymulti(dimethylsilylenes -[(Me2Si)mO]n-, to Polysiloxanes and Polysilanes. Theoretical Study. Macromol. Theory Simul. 2001, 10, 158−164. (43) Weinhold, F.; West, R. The Nature of the Silicon-Oxygen Bond. Organometallics 2011, 30, 5815−5824. (44) Weinhold, F.; West, R. Hyperconjugative Interactions in Permethylated Siloxanes and Ethers: The Nature of the SiO Bond. J. Am. Chem. Soc. 2013, 135, 5762−5767. (45) Huang, N.; Xu, J.; Zhang, H.; Xu, Z. The Origin of the Decreasing Basicity from Monofunctional Alkoxysilane to Tetrafunctional Alkoxysilane: a Combined IR and Theoretical Study. J. Mol. Struct. 2015, 1089, 216−221. (46) Weinhold, F.; Landis, C. R. Valency and Bonding: A Natural Bond Orbital Donor-Acceptor Perspective; Cambridge Univ. Press: Cambridge, U.K., 2005. (47) Weinhold, F.; Landis, C. R. Discovering Chemistry with Natural Bond Orbitals; Wiley-Interscience: Hoboken, NJ., 2012. (48) Weinhold, F.; Landis, C. R.; Glendening, E. G. What is NBO analysis and how is it useful? Int. Rev. Phys. Chem. 2016, 35, 399−440. (49) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al. Gaussian 09, revision E.01; Gaussian, Inc.: Wallingford, CT, 2009. (50) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−788. (51) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648−5651. (52) Adamo, C.; Barone, V. Toward Reliable Density Functional Methods without Adjustable Parameters: The PBE0Model. J. Chem. Phys. 1999, 110, 6158−6170. (53) Rappoport, D.; Furche, F. Property-Optimized Gaussian Basis Sets for Molecular Response Calculations. J. Chem. Phys. 2010, 133, 134105. (54) Feller, D. The Role of Databases in Support of Computational Chemistry Calculations. J. Comput. Chem. 1996, 17, 1571−1586. (55) Schuchardt, K. L.; Didier, B. T.; Elsethagen, T.; Sun, L.; Gurumoorthi, V.; Chase, J.; Li, J.; Windus, T.L. Basis Set Exchange: A Community Database for Computational Sciences. J. Chem. Inf. Model. 2007, 47, 1045−1052. (56) Weinhold, F.; Glendening, E. G. NBO 6.0 Manual Program; Theoretical Chemistry Institute; University of Wisconsin: Madison, WI, 2013. (57) Cypryk, M.; Gostyński, B. Computational Benchmark for Calculation of Silane and Siloxane Thermochemistry. J. Mol. Model. 2016, DOI: 10.1007/s00894-015-2900-1. (58) Tamagawa, K.; Takemura, M.; Konaka, S.; Kimura, M. Molecular Structure of Dimethylether as Determined by a Joint Analysis of Gas Electron Diffraction and Microwave Spectroscopic Data. J. Mol. Struct. 1984, 125, 131−142. (59) Liedle, S.; Mack, H.-G.; Oberhammer, H.; Imam, M. R.; Allinger, N. L. Gas-Phase Structures of di-t-Butyl Ether and t-Butyl Methyl Ether. J. Mol. Struct. 1989, 198, 1−15. 2521
DOI: 10.1021/acs.jpca.7b01208 J. Phys. Chem. A 2017, 121, 2515−2522
Article
The Journal of Physical Chemistry A (60) Durig, J. R.; Flanagan, M. J.; Kalasinsky, V. F. The Determination of the Potential Function Governing the Low Frequency Bending Mode of Disiloxane. J. Chem. Phys. 1977, 66, 2775−2785.
2522
DOI: 10.1021/acs.jpca.7b01208 J. Phys. Chem. A 2017, 121, 2515−2522
