GEOMETRIA DESCRIPTIVA II (Examen )

Grup T2. 1a prov

Cooperativity in Tetrel Bonds

A theoretical study of the cooperativity in linear chains of (H₃SiCN)_<i>n</i> and (H₃SiNC)_<i>n</i> complexes connected by tetrel bonds has been carried out by means of MP2 and CCSD­(T) computational methods. In all cases, a favorable cooperativity is observed, especially in some of the largest linear chains of (H₃SiNC)_<i>n</i>, where the effect is so large that the SiH₃ group is almost equidistant to the two surrounding CN groups and it becomes planar. In addition, the combination of tetrel bonds with other weak interactions (halogen, chalcogen, pnicogen, triel, beryllium, lithium, and hydrogen bond) has been explored using ternary complexes, (H₃SiCN)₂:XY and (H₃SiNC)₂:XY. In all cases, positive cooperativity is obtained, especially in the (H₃SiNC)₂:ClF and (H₃SiNC)₂:SHF ternary complexes, where, respectively, halogen and chalcogen shared complexes are formed

Complexes between Dihydrogen and Amine, Phosphine, and Arsine Derivatives. Hydrogen Bond versus Pnictogen Interaction

A theoretical study of the complexes between dihydrogen, H₂, and a series of amine, phosphine, and arsine derivatives (ZH₃ and ZH₂X, with Z = N, P, or As and X = F, Cl, CN, or CH₃) has been carried out using ab initio methods (MP2/aug-cc-pVTZ). Three energetic minima configurations have been characterized for each case with the H₂ molecule in the proximity of the pnictogen atom (Z). In configuration A, the σ-electrons of H₂ interact with σ-hole region of the pnictogen atom generated by the of X–Z bond. These complexes can be ascribed as pnictogen bonded. In configuration C, the lone electron pair of Z acts as the Lewis base, and H₂ plays the role of the Lewis acid. Finally, configuration B presents a variety of noncovalent interactions depending on the binary complex considered. The atoms-in-molecules theory (AIM), natural bond orbitals (NBO) method as well as the density functional theory–symmetry adapted perturbation theory (DFT-SAPT) approach were used in this study to deepen the nature of the interactions considered

Properties of cationic pnicogen-bonded complexes F_4-<i>_n</i>H<i>_n</i>P⁺:N-base with H–P···N linear and <i>n</i> = 1–4

<div><p>ABSTRACT</p><p><i>Ab initio</i> MP2/aug'-cc-pVTZ calculations have been carried out to investigate the pnicogen-bonded complexes F_4-<i>_n</i>H<i>_n</i>P⁺:N-base, for <i>n</i> = 1–4, each with a linear or nearly linear H_ax–P···N alignment. The sp³-hybridised nitrogen bases include NH₃, NClH₂, NFH₂, NCl₂H, NCl₃, NFCl₂, NF₂H, NF₂Cl, and NF_3, and the sp bases are NCNH₂, NCCH₃, NP, NCOH, NCCl, NCH, NCF, NCCN, and N₂. Binding energies increase as the P–N distance decreases, with an exponential curve showing this relationship when complexes with sp³ and sp hybridised bases are treated separately. However, the correlations are not as good as they are for the complexes F_4-<i>_n</i>H<i>_n</i>P⁺:N-base for <i>n</i> = 0–3 with F–P···N linear. Different patterns are observed for the change in the binding energies of complexes with a particular base as the number of F atoms in the acid changes. Thus, the particular acid–base pair is a factor in determining the binding energies of these complexes.</p><p>Three different charge-transfer interactions stabilise these complexes, namely N_lp→σ*P–H_ax, N_lp→σ*P–F_eq, and N_lp→σ*P–H_eq. Unlike the corresponding complexes with F–P···N linear, N_lp→σ*P–H_ax is not always the dominant charge-transfer interaction, since N_lp→σ*P–F_eq is greater in some complexes. N_lp→σ*P–H_eq makes the smallest contribution to the total charge-transfer energy. The total charge-transfer energies of all complexes increase exponentially as the P–N distance decreases in a manner very similar to that observed for the series of complexes with F–P···N linear.</p><p>Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) spin–spin coupling constants ^1pJ(P–N) across the pnicogen bond vary with the P–N distance, but different patterns are observed which depend on the nature of the acid, and for some acids, on the hybridisation of the nitrogen base. ^1pJ(P–N) values for complexes of F₃HP⁺ initially increase as the P–N distance decreases, reach a maximum, and then decrease with decreasing P–N distance as the P···N bond acquires increased covalent character. ^1pJ(P–N) for complexes with H–P···N linear and those with F–P···N linear exhibit similar distance dependencies depending on the number of F atoms in equatorial positions and the hybridisation of the base. Complexation may increase, decrease, or leave the P–H_ax distance unchanged, but ¹J(P–H_ax) always decreases relative to the corresponding isolated ion. Decreasing ¹J(P–H_ax) can be related to decreasing intermolecular P–N distance.</p></div

Single Electron Pnicogen Bonded Complexes

A theoretical study of the complexes formed by monosubstituted phosphines (XH₂P) and the methyl radical (CH₃) has been carried out by means of MP2 and CCSD­(T) computational methods. Two minima configurations have been obtained for each XH₂P:CH₃ complex. The first one shows small P–C distances and, in general, large interaction energies. It is the most stable one except in the case of the H₃P:CH₃ complex. The second minimum where the P–C distance is large and resembles a typical weak pnicogen bond interaction shows interaction energies between −9.8 and −3.7 kJ mol^–1. A charge transfer from the unpaired electron of the methyl radical to the P–X σ* orbital is responsible for the interaction in the second minima complexes. The transition state (TS) structures that connect the two minima for each XH₂P:CH₃ complex have been localized and characterized

Pnicogen-Bonded Cyclic Trimers (PH₂X)₃ with X = F, Cl, OH, NC, CN, CH₃, H, and BH₂

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to determine the structures and binding energies of cyclic trimers (PH₂X)₃ with X = F, Cl, OH, NC, CN, CH₃, H, and BH₂. Except for [PH₂(CH₃)]₃, these complexes have <i>C</i>_3<i>h</i> symmetry and binding energies between −17 and −63 kJ mol^–1. Many-body interaction energy analyses indicate that the two-body terms are dominant, accounting for 97–103% of the total binding energy. Except for the trimer [PH₂(OH)]₃, the three-body terms are stabilizing. Charge transfer from the lone pair on one P atom to an antibonding σ* orbital of the P atom adjacent to the lone pair plays a very significant role in stabilization. The charge-transfer energies correlate linearly with the trimer binding energies. NBO, AIM, and ELF analyses have been used to characterize bonds, lone pairs, and the degree of covalency of the P···P pnicogen bonds. The NMR properties of chemical shielding and ³¹P–³¹P coupling constants have also been evaluated. Although the ³¹P chemical shieldings in the five most strongly bound trimers increase relative to the corresponding isolated monomers, there is no correlation between the chemical shieldings and the charges on the P atoms. EOM-CCSD ³¹P–³¹P spin–spin coupling constants computed for four (PH₂X)₃ trimers fit nicely onto a plot of ^1pJ­(P–P) versus the P–P distance for (PH₂X)₂ dimers. A coupling constant versus distance plot for the four trimers has a second-order trendline which has been used to predict the values of ^1pJ­(P–P) for the remaining trimers

Pnicogen-Bonded Complexes H_<i>n</i>F_5–<i>n</i>P:N-Base, for <i>n</i> = 0–5

Ab initio MP2/aug′-cc-pVTZ calculations have been carried out on the pnicogen-bonded complexes H_<i>n</i>F_5–<i>n</i>P:N-base, for <i>n</i> = 0–5 and nitrogen bases NC^–, NCLi, NP, NCH, and NCF. The structures of these complexes have either <i>C</i>_4<i>v</i> or <i>C</i>_2<i>v</i> symmetry with one exception. P–N distances and interaction energies vary dramatically in these complexes, while F_ax–P–F_eq angles in complexes with PF₅ vary from 91° at short P–N distances to 100° at long distances. The value of this angle approaches the F_ax–P–F_eq angle of 102° computed for the Berry pseudorotation transition structure which interconverts axial and equatorial F atoms of PF₅. The computed distances and F_ax–P–F_eq angles in complexes F₅P:N-base are consistent with experimental CSD data. For a fixed acid, interaction energies decrease in the order NC^– > NCLi > NP > NCH > NCF. In contrast, for a fixed base, there is no single pattern for the variations in distances and interaction energies as a function of the acid. This suggests that there are multiple factors that influence these properties. The dominant factor appears to be the number of F atoms in equatorial positions, and then a linear F_ax–P···N rather than H_ax–P···N alignment. The acids may be grouped into pairs (PF₅, PHF₄) with four equatorial F atoms, then (PH₄F, PH₂F₃) with F_ax–P···N linear, and then (PH₃F₂ and PH₅) with H_ax–P···N linear. The electron-donating ability of the base is also a factor in determining the structures and interaction energies of these complexes. Charge transfer from the N lone pair to the σ* P–A_ax orbital stabilizes H_<i>n</i>F_5–<i>n</i>P:N-base complexes, with A_ax either F_ax or H_ax. The total charge-transfer energies correlate with the interaction energies of these complexes. Spin–spin coupling constants ^1p<i>J</i>(P–N) for (PF₅, PHF₄) complexes with nitrogen bases are negative with the strongest bases NC^– and NCLi but positive for the remaining bases. Complexes of (PH₄F, PH₂F₃) with these same two strong bases and H₄FP:NP have positive ^1p<i>J</i>(P–N) values but negative values for the remaining bases. (PH₅, PH₃F₂) have negative values of ^1p<i>J</i>(P–N) only for complexes with NC^–. Values of ¹<i>J</i>(P–F_ax) and ¹<i>J</i>(P–H_ax) correlate with the P–F_ax and P–H_ax distances, respectively

Ab Initio Study of Ternary Complexes X:(HCNH)⁺:Z with X, Z = NCH, CNH, FH, ClH, and FCl: Diminutive Cooperative Effects on Structures, Binding Energies, and Spin–Spin Coupling Constants Across Hydrogen Bonds

Ab initio calculations have been performed on a series of complexes in which (HCNH)⁺ is the proton donor and CNH, NCH, FH, ClH, and FCl (molecules X and Z) are the proton acceptors in binary complexes X:HCNH⁺ and HCNH⁺:Z, and ternary complexes X:HCNH⁺:Z. These complexes are stabilized by C–H⁺···A and N–H⁺···A hydrogen bonds, where A is the electron-pair donor atom of molecules X and Z. Binding energies of the ternary complexes are less than the sum of the binding energies of the corresponding binary complexes. In general, as the binding energy of the binary complex increases, the diminutive cooperative effect increases. The structures of these complexes, data from the AIM analyses, and coupling constants ¹<i>J</i>(N–H), ^1h<i>J</i>(H–A), and ^2h<i>J</i>(N–A) for the N–H⁺···A hydrogen bonds, and ¹<i>J</i>(C–H), ^1h<i>J</i>(H–A), and ^2h<i>J</i>(C–A) for the C–H⁺···A hydrogen bonds provide convincing evidence of diminutive cooperative effects in these ternary complexes. In particular, the symmetric N···H⁺···N hydrogen bond in HCNH⁺:NCH looses proton-shared character in the ternary complexes X:HCNH⁺:NCH, while the proton-shared character of the C···H⁺···C hydrogen bond in HNC:HCNH⁺ decreases in the ternary complexes HNC:HCNH⁺:Z and eventually becomes a traditional hydrogen bond as the strength of the HCNH⁺···Z interaction increases

Characterizing Traditional and Chlorine-Shared Halogen Bonds in Complexes of Phosphine Derivatives with ClF and Cl₂

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out on the halogen-bonded complexes H₂XP:ClF and H₂XP:Cl₂, with X = F, Cl, OH, NC, CN, CCH, CH₃, and H. H₂XP:ClF complexes are stabilized by chlorine-shared halogen bonds with short P–Cl and significantly elongated Cl–F distances. H₂XP:Cl₂ complexes with X = OH and CH₃ form only chlorine-shared halogen bonds, while those with X = H, NC, and CN form only traditional halogen bonds. On the H₂FP:Cl₂, H₂(CCH)­P:Cl₂, and H₂ClP:Cl₂ potential surfaces small barriers separate two equilibrium structures, one with a traditional halogen bond and the other with a chlorine-shared bond. The binding energies of H₂XP:ClF and H₂XP:Cl₂ complexes are influenced by the electron-donating ability of H₂XP and the electron accepting ability of ClF and ClCl, the nature of the halogen bond, other secondary interactions, and charge-transfer interactions. Changes in electron populations on P, F, and Cl upon complex formation do not correlate with changes in the chemical shieldings of these atoms. EOM-CCSD spin–spin coupling constants for complexes with chlorine-shared halogen bonds do not exhibit the usual dependencies on distance. ^2X<i>J</i>(P–F) and ^2X<i>J</i>(P–Cl) for complexes with chlorine-shared halogen bonds do not correlate with P–F and P–Cl distances, respectively. ^1X<i>J</i>(P–Cl) values for H₂XP:ClF correlate best with the Cl–F distance, and approach the values of ¹<i>J</i>(P–Cl) for the corresponding cations H₂XPCl⁺. Values of ^1X<i>J</i>(P–Cl) for complexes H₂XP:ClCl with chlorine-shared halogen bonds correlate with the binding energies of these complexes. ¹<i>J</i>(F–Cl) and ¹<i>J</i>(Cl–Cl) for complexes with chlorine-shared halogen bonds correlate linearly with the distance between P and the proximal Cl atom. In contrast, ^2X<i>J</i>(P–Cl) and ^1X<i>J</i>(P–Cl) for complexes with traditional halogen bonds exhibit more normal distance dependencies

Fostering the Basic Instinct of Boron in Boron–Beryllium Interactions

A set of complexes L₂HB···BeX₂ (L = CNH, CO, CS, N₂, NH₃, NCCH₃, PH₃, PF₃, PMe₃, OH₂; X = H, F) containing a boron–beryllium bond is described at the M06-2X/6-311+G­(3df,2pd)//M062-2X/6-31+G­(d) level of theory. In this quite unusual bond, boron acts as a Lewis base and beryllium as a Lewis acid, reaching binding energies up to −283.3 kJ/mol ((H₂O)₂HB···BeF₂). The stabilization of these complexes is possible thanks to the σ-donor role of the L ligands in the L₂HB···BeX₂ structures and the powerful acceptor nature of beryllium. According to the topology of the density, these B–Be interactions present positive laplacian values and negative energy densities, covering different degrees of electron sharing. ELF calculations allowed measuring the population in the interboundary B–Be region, which varies between 0.20 and 2.05 electrons upon switching from the weakest ((CS)₂HB···BeH₂) to the strongest complex ((H₂O)₂HB···BeF₂). These B–Be interactions can be considered as beryllium bonds in most cases