Covalent versus Dative Bonds to Main Group Metals,a Useful Distinction

Textbooks of inorganic chemistry describe the formation of adducts by coordination of an electron donor to an electron acceptor, often using the amine-boranes, X₃N → BY₃, as examples. In the Lewis (electron dot) formulas of the compounds, the dative bond in H 3 N → BH₃ and the covalent bond in H₃C?CH₃ are both represented by a shared electron pair. In the simple molecular orbital or valence bond models the wave functions of both electron pairs would be constructed in the same manner from the appropriate sp³ type atomic orbitals on the bonded atoms; the difference between the covalent and the dative bond becomes apparent only after the orbital coefficients have been analyzed. This may be the reason why many structural chemists seem reluctant to distinguish between the two types of bonds. The object of this article is to remind the reader that the physiocochemical properties of covalent and dative bonds may be – and often are – quite different, and to show that a distinction between the two provides a basis for understanding the structures of a wide range of main group metal compounds.     

A theoretical investigation of the interaction between substituted carbonyl derivatives and water: Open or cyclic complexes?

The structures and binding energies of complexes between substituted carbonyl bases and water are the B3LYP/6‐311++G(d,p) computational level. The calculations also include the proton affinity (PA) of the O of the C?O group, the deprotonation enthalpies (DPE) of the CH bonds along a natural bond orbital analysis. The calculations reveal that stable open C?O···H_wO_w as well as cyclic CH···O_wH_w···O?C complexes are formed. The binding energies for the open complexes are linearly related to the PAs, whereas the binding energies for the cyclic complexes depend on both the PA and DPE. Different indicators of hydrogen bonds strength such as electron charge density, intramolecular and intermolecular hyperconjugation energy, occupation of orbitals, and charge transfer show significant differences between open and cyclic complexes. The contraction of the CH bond of the formyl group and the corresponding blue shift of the ν(CH) vibration are explained by the classical trans lone pair effect. In contrast, the elongation or contraction of the CH₃ group involved in the interaction with water results from the variation of the orbital interaction energies from the σ(CH) bonding orbital to the σ* and π* antibonding orbitals of the C?O group. The resulting blue or red shifts of the ν(CH₃) vibrations are calculated in the partially deuterated isotopomers. © 2012 Wiley Periodicals, Inc.     

New insight into the electronic structure of iron(IV)‐oxo porphyrin compound I. A quantum chemical topological analysis

The electronic structure of iron‐oxo porphyrin π‐cation radical complex Por^·+Fe^IV?O (S? H) has been studied for doublet and quartet electronic states by means of two methods of the quantum chemical topology analysis: electron localization function (ELF) η(r) and electron density ρ(r). The formation of this complex leads to essential perturbation of the topological structure of the carbon–carbon bonds in porphyrin moiety. The double C?C bonds in the pyrrole anion subunits, represented by pair of bonding disynaptic basins V_i=1,2(C,C) in isolated porphyrin, are replaced by single attractor V(C,C)_i=1–20 after complexation with the Fe cation. The iron–nitrogen bonds are covalent dative bonds, N→Fe, described by the disynaptic bonding basins V(Fe,N)_i=1–4, where electron density is almost formed by the lone pairs of the N atoms. The nature of the iron–oxygen bond predicted by the ELF topological analysis, shows a main contribution of the electrostatic interaction, Fe^δ+···O^δ?, as long as no attractors between the C(Fe) and C(O) core basins were found, although there are common surfaces between the iron and oxygen basines and coupling between iron and oxygen lone pairs, that could be interpreted as a charge‐shift bond. The Fe? S bond, characterized by the disynaptic bonding basin V(Fe,S), is partially a dative bond with the lone pair donated from sulfur atom. The change of electronic state from the doublet (M = 2) to quartet (M = 4) leads to reorganization of spin polarization, which is observed only for the porphyrin skeleton (?0.43e to 0.50e) and S? H bond (?0.55e to 0.52e). © 2012 Wiley Periodicals, Inc.     

Polysulfonylamine. LVII. Zwei Silber(I)-di(organosulfonyl)-amide mit einer Silber-η2-Aryl- beziehungsweise einer Silber-Silber-Wechselwirkung: Kristallstrukturen von Silberdi(benzolsulfonyl)-amid-Wasser (1/0,5) und von wasserfreiem Silberdi(4-toluolsulfonyl)-amid

Polysulfonyl Amines. LVII. Two Silver(I) Di(organosulfonyl)-amides with Silver-η²-Aryl or Silver-Silver Interactions: Crystal Structures of Silver Di(benzenesulfonyl)amide-Water (1/0.5) and of Anhydrous Silver Di(4-toluenesulfonyl)-amide Crystals of [(PhSO₂)₂NAg(μ-H₂O)AgN(SO₂Ph)₂]_n ( 5 ) and [(4-Me? C₆H₄SO₂)₂NAgAgN(SO₂C₆H₄-4-Me)₂]_n ( 6 ) were obtained from aqueous solutions. The crystallographic data are for 5 (at ?95°C): monoclinic, space group C2/c, a = 2 743.8(5), b = 600.49(12), c = 1 664.5(3) pm, β = 101.143(15)°, V = 2.6908 nm³, Z = 8, D_x = 2.040 Mg m^?3; for 6 (at ?130°C): monoclinic, space group P2₁/n, a = 1 099.8(5), b = 563.7(3), c = 2 487.7(13) pm, β = 99.68(4)°, V = 1.5203 nm³, Z = 4, D_x = 1.888 Mg m^?3. In both crystals, the silver atom has a fivefold coordination. The structure of 5 displays [(RSO₂)₂N? Ag(μ-H₂O)Ag′? N(SO₂R)₂] units with Ag? N 226.9 pm, Ag? O 236.7 pm and Ag? O? Ag′ 95.3°; the water oxygen lies on a crystallographic twofold axis. These units are extended to two fused six-membered rings by intramolecular dative bonds (S)O → Ag′ and S(O)′ → Ag (249.3 pm). One phenyl group from each (PhSO₂)₂N moiety is η²-coordinated with its p-C and one m-C atom to a silver atom of a neighbouring bicyclic unit related by a glide plane to form infinite parallel strands (p-C? Ag 252.2, m-C? Ag 263.9 pm). The strands are interconnected into parallel layers through hydrogen bonds between H₂O and sulfonyl oxygens [O …? O(S) 276.1 pm]. These layers consist of a hydrophilic inner region containing metal ions, N(SO₂)₂ fragments and water molecules, and hydrophobic surfaces formed by phenyl groups. The structure of 6 features centrosymmetric [(RSO₂)₂N? Ag? Ag′? N(SO₂R)₂] units with two intramolecular dative bonds (S)O → Ag′ and (S)O′ → Ag (Ag? Ag′ 295.4, Ag? N 226.0, Ag? O 229.4 pm). These bi-pentacyclic units are associated by translation parallel to y into infinite strands by two dative (S)O → Ag bonds per silver atom (Ag? O 243.2 and 253.3 pm).     

Photoelectron spectra,penning ionization electron spectra,and character of canonical molecular orbitals

When canonical molecular orbitals are expanded in terms of a set of localized molecular orbital building blocks, called bond orbitals, the character of the canonical molecular orbitals can be characterized according to the component bond orbitals resembling the core, lone pair, and localized bond building blocks in an intuitive Lewis structure. Weinhold's natural bond orbital method can produce a unique Lewis structure with total occupancy of its occupied bond orbitals exceeding 99.9% of the total electron density for simple molecules. Two useful indices, Lewis bond order and weight of lone pair orbitals, can be defined according to the weights of the bonding and lone pair components of this unique Lewis structure. Calculation results for molecules N₂, CO, CS, NO, HCN, C₂H₂, H₂O, and H₂S show that the former index can account for the vibrational structures of photoelectron spectroscopy, whereas the latter index can account for the band intensity enhancement of Penning ionization electron spectroscopy. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 882–892, 1998     

Two new phosphinic amides: Synthesis,crystal structure,and theoretical study of hydrogen bonding

Two novel phosphinic amides, (C₆H₅)₂P(O)(NH?cyclo?C₇H₁₃) (I) and (C₆H₅)₂P(O)(NH?cyclo?C₆H₁₁) (II) were synthesized and characterized by spectroscopic methods and X-ray crystallography. Both compounds crystallize in the orthorhombic chiral space group P2₁2₁2₁ and in both structures, the N—H···O hydrogen bonds lead to one-dimensional arrangements along the a axis. The molecular geometries and vibrational frequencies of I and II were investigated with quantum chemical calculations at the B3LYP/6–311G^** level of theory. Furthermore, the hydrogen bonds were studied by means of the Bader theory of atoms in molecules (AIM) and natural bond orbital (NBO) analysis.     

Using (FH)2 and (FH)3 to Bridge the σ‐Hole and the Lone Pair at P in Complexes with H2XP,for X=CH3, OH,H, CCH,F, Cl,NC, and CN

Ab initio MP2/aug′‐cc‐pVTZ calculations are used to investigate the binary complexes H₂XP:HF, the ternary complexes H₂XP:(FH)₂, and the quaternary complexes H₂XP:(FH)₃, for X=CH₃, OH, H, CCH, F, Cl, NC, and CN. Hydrogen‐bonded (HB) binary complexes are formed between all H₂XP molecules and FH, but only H₂FP, H₂ClP, and H₂(NC)P form pnicogen‐bonded (ZB) complexes with FH. Ternary complexes with (FH)₂ are stabilized by F?H???P and F?H???F hydrogen bonds and F???P pnicogen bonds, except for H₂(CH₃)P:(FH)₂ and H₃P:(FH)₂, which do not have pnicogen bonds. All quaternary complexes H₂XP:(FH)₃ are stabilized by both F?H???P and F?H???F hydrogen bonds and P???F pnicogen bonds. Thus, (FH)₂ with two exceptions, and (FH)₃ can bridge the σ‐hole and the lone pair at P in these complexes. The binding energies of H₂XP:(FH)₃ complexes are significantly greater than the binding energies of H₂XP:(FH)₂ complexes, and nonadditivities are synergistic in both series. Charge transfer occurs across all intermolecular bonds from the lone‐pair donor atom to an antibonding σ* orbital of the acceptor molecule, and stabilizes these complexes. Charge‐transfer energies across the pnicogen bond correlate with the intermolecular P?F distance, while charge‐transfer energies across F?H???P and F?H???F hydrogen bonds correlate with the distance between the lone‐pair donor atom and the hydrogen‐bonded H atom. In binary and quaternary complexes, charge transfer energies also correlate with the distance between the electron‐donor atom and the hydrogen‐bonded F atom. EOM‐CCSD spin‐spin coupling constants ^2hJ(F–P) across F?H???P hydrogen bonds, and ^1pJ(P–F) across pnicogen bonds in binary, ternary, and quaternary complexes exhibit strong correlations with the corresponding intermolecular distances. Hydrogen bonds are better transmitters of F–P coupling data than pnicogen bonds, despite the longer F???P distances in F?H???P hydrogen bonds compared to P???F pnicogen bonds. There is a correlation between the two bond coupling constants ^2hJ(F–F) in the quaternary complexes and the corresponding intermolecular distances, but not in the ternary complexes, a reflection of the distorted geometries of the bridging dimers in ternary complexes.     

Can a Single Molecule of Water be Completely Isolated Within the Subnano‐Space Inside the Fullerene C60 Cage? A Quantum Chemical Prospective

Based on an experimental observation, it has been controversially suggested in a study (Kurotobi et al., Science 2011 , 33, 613) that a single molecule of water can completely be localized within the subnano‐space inside the fullerene C₆₀ cage and, that neither the H atoms nor the O lone‐pairs are linked, either via hydrogen bonding or through dative bonding, with the interior C‐framework of the C₆₀ cage. To resolve the controversy, electronic structure calculations were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population and bond orbital analyses, and the results were analyzed by using varieties of recommended diagnostics often used to interpret noncovalent interactions. The present results reveal that the mechanically entrapped H₂O molecule is not electronically innocent of the presence of the cage; each H atom of H₂O is weakly O? H???C₆₀ bonded, whereas the O lone‐pairs are O???C₆₀ bonded regardless of the conformations investigated. Exploration of various featured properties suggests that H₂O@C₆₀ may be regarded as a unique system composed of both inter‐ and intramolecular interactions.     

The role of the sulfur 3d orbitals in bond formation in sulfur-containing compounds

The role of the sulfur 3d orbitals in bond formation is discussed by taking into account the influence of the environment on the orbitals of the sulfur atom in the molecules. The calculation results of a series of prototype molecules containing sulfur such as SF₂ SF₄, NSF₃, SF₀, H₂S are reported. It is convincingly shown that in highly electronegative environment the energy levels of the sulfur 3d orbitals are reduced to the vicinity of those of the ligand valence orbitals and their spatial distributions are contracted to the bonding area, and therefore they can participate in bond formation to a certain extent, which is enhanced by the formation of the d-p π back bonds. It seems that the result reported in this paper is helpful for the solution of the long-standing debate about the sulfur 3d orbital participation in bond formation.     

Correlation between electron delocalization and structural planarization in small water rings

The discovery of the covalent‐like character of the hydrogen bonding (H‐bonding) system [Science 342 , 611(2013)] has promoted a renewal of our understanding of the electronic and geometric structures of water clusters. In this work, based on density functional theory calculations, we show that the preferential formation of a stable quasiplanar structure of (H₂O)_n(n = 3–6) is closely related to three kinds of delocalized molecular orbitals (MOs; denoted as MO‐I, II, and III) of water rings. These originate from the 2p lone pair electrons of oxygen (O), the 2p bond electrons of O and the 1s electrons of H and the 2s electrons of O and 1s electrons of H, respectively. To maximize the orbital overlaps of the three MOs, geometric planarization is needed. The contribution of the orbital interaction is more than 30% in all the water rings according to our energy decomposition analysis, highlighting the considerable covalent‐like characters of H‐bonds. © 2015 Wiley Periodicals, Inc.     

Formation of Metal Oxyfluorides from Specific Metal Reactions with Oxygen Difluoride: Infrared Spectroscopic and Theoretical Investigations of the OScF2 Radical and OScF with Terminal Single and Triple Sc?O Bonds

The scandium oxydifluoride free radical, OScF₂, is produced by the spontaneous, specific reaction of laser ablated Sc atoms with OF₂ in solid argon and characterized by using matrix infrared spectroscopy and theoretical calculations. The OScF₂ molecule is predicted to have C_2v symmetry and a ²B₂ ground state with an unpaired electron located primarily on the terminal oxygen atom, which makes it a scandium difluoride molecule coordinated by a neutral oxygen atom radical in forming the Sc? O single bond. The closed shell singlet OScF molecule with an obtuse bent geometry has a much shorter Sc? O bond of 1.682 Å than that of the OScF₂ radical (1.938 Å) on the basis of B3LYP calculations. The Sc? O bond in OScF consists of two covalent bonds and a dative bond in which the oxygen 2p_π lone pair donates electron density into an empty Sc 3d orbital thus forming a triple oxo bond. Density functional calculations suggest it is highly exothermic for fluorine transfer from OF₂ to scandium, which favors the formation of the OScF₂ radical species as well as the OScF molecule after fluorine loss.     

Cluster calculations of the H2O/Pt(111) system

The electronic interaction between water and a Pt(111) surface as evaluated for different Pt_x(H₂O)_y clusters is discussed. Hartree–Fock–Slater (HFS ) one-electron ground state energies, ionization potentials, partial densities of states, and Mulliken occupation numbers are related to bonding shifts, as well as initial and final state screening for different orientations of the molecule. The formation of Pt? H₂O bonds are sensitive to the orientation since surface oriented H atoms bridge the spatial separation between O 2p and Pt 5d orbitals and thus increase the intermixing of metal and adsorbate orbitals. The dipole moment and the net charge of the H₂O molecule is also discussed. Finally, approximations of the metal–H₂O potential for use in statistical models of the liquid–metal interface are suggested.     

Theoretical Characterisation of Phosphinyl Radicals and Their Magnetic Properties: g Matrix

The g matrices (g tensors) of various phosphinyl radicals (R₂P^.) were calculated using the DFT and multireference configuration interaction (MRCI) methods. The g matrices were distinctly dependent on the molecular structure of the radical. To thoroughly examine this dependence, the contributions from individual atoms and excited states were calculated. The former revealed the gain from the phosphorus atom to be preeminent unless P?O or P?S bonds are present in the radical molecule. The contributions owing to excited states arising from electronic transitions between doubly occupied molecular orbitals and the SOMO were clearly positive, as in the case of semiquinone and niroxide radicals. The transitions from the phosphorus lone pair were of paramount importance. Surprisingly, unlike for semiquinones and nitroxides, a significant negative contribution was observed from excitations from the SOMO to unoccupied molecular orbitals. For radicals with P?O bonds, this contribution to the g₂ component was dominant.     

A radial probability density function for analysis of canonical molecular orbitals

A one‐dimensional probability density function, analogous to the atomic radial density for the hydrogen atom, r²R_nl(r), is defined for an arbitrary three‐dimensional density. It is obtained numerically by taking the derivative of a cumulative probability distribution with respect to the cubic root of the volume enclosed by each in a series of isosurfaces. Each point in the function is associated with a unique isosurface, and the isosurface associated with the maximum of the defined function represents the most probable isosurface with respect to the putative radius. This function therefore provides an objective selection criterion for a single isosurface to represent a three‐dimensional density. This technique is applied to set of canonical molecular orbitals. The selected threshold value varies from orbital to orbital, but the enclosed probability falls in the range of 20% to 55% for the reported orbitals. In all cases, the enclosed probability is much smaller than the common choices found in the literature. The concomitant smaller volume often makes possible a more localized interpretation and helps to clarify the conventional delocalized interpretation of molecular orbitals. For example, the isosurface plots selected by this method distinguish the formally bonding orbital in He₂ from the true bonding orbital in H₂. Examples from N₂, F₂, HF, H₂O, C₂H₆, and Ni(CO)₄ are also presented. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 310–321, 2000     

(2‐Hydro­xy‐5‐methyl­phenyl)­di­phenyl­phosphine oxide

Pairs of individual mol­ecules of the title compound, C₁₉H₁₇O₂P, (I), containing tetrahedrally coordinated P atoms are connected across crystallographic inversion centres via complementary O—H?O=P hydrogen bonds.     

Variationally determined electronic states for the theoretical analysis of intramolecular interaction. II. Qualitative nature of the P?O bond in phosphine oxides

We have developed a space‐restricted wave function (SRW) method for the analysis of various types of intramolecular interactions. In this study, we demonstrate the applicability of our SRW method to the analysis of the nature of the P? O bond in phosphine oxide (R₃PO), one of the hypervalent molecules. An interesting character of this bond has been extensively studied by focusing on the negative hyperconjugation of the O lone pair (n_O) with the R₃P group. We reinvestigated the nature of the bond in terms of a change in total energy to produce evidence for the validity of our method. The electronic states without the interaction involving three n_O orbitals (R₃P⁺?O^?) produced by the method were used as reference states in the assessment of the effects of this n_O–R₃P interaction. The result confirms that this interaction plays an essential role in the nature of the bond and occurs between the n_O orbitals and the P? R antibonding orbitals, in agreement with previous studies. A molecular orbital (MO)‐pair analysis technique shows that the n_O–R₃P interaction is decomposed into the negative hyperconjugation and the Pauli repulsion. Considering a reference state where the P? O bond is completely broken (R₃P²⁺···O^2?) at an interacting distance, P? O bond formation is attributed to one σ bond plus two 0.5 π bonds. This is equivalent to three banana bonds highly polarized to the O atom. Consequently, the SRW method suggested improved explanations of the nature of the P? O bond. © 2012 Wiley Periodicals, Inc.     

The Analysis of Electronic Structures,NBO, EDA,and QTAIM of trans‐(H3P)2(η2‐BH4 )W(≡C‐para‐C6H4X)(CO) Complexes

In the present research, the impact of substitution on the dipole moment, electronic structure, and frontier orbital energy in trans ‐(H₃P )₂(η²‐BH₄ )W(≡C‐para ‐C₆H₄X )(CO ) complexes (X = H, F, SiH₃ , CN , NO₂ , SiMe₃ , CMe₃ , NH₂ , NMe₂ ) was studied with mpw1pw91 quantum chemical computations. The nature of the chemical bond between the trans‐[Cl(η²‐BH₄ )(H₃P ) ₂W ]⁻ and [C‐para ‐C₆H₄X ]⁺ fragments was demonstrated through energy decomposition analysis (EDA ). The percentage composition in terms of the specified groups of frontier orbitals was examined for these complexes to investigate the feature in metal–ligand bonds. Quantum theory of atoms in molecules (QTAIM ) and natural bond orbital (NBO ) analysis were applied to elucidate these complexes’ metal–ligand bonds.     

Localized orbitals based on the fermi hole

The Fermi hole provides a direct (non-iterative) method for tansforming canonical SCF molecular orbitals into localized orbitals. Except for simple overlap integrals required to maintain orthogonality, this method requires no integrals over orbitals or basis functions. This method is demonstrated by application to a furanone (C₄H₄O₂), methylacetylene, and boron trifluoride. The results of these calculations are compared to those determined by the orbital centroid criterion of localization.     

The kinetics of the chlorine isotopic exchange between chloride ion at O,O-diarylphosphorochloridates or O,O-diarylphosphorochloridothionates

The kinetics of the chlorine isotopic exchange reaction between tetraethylammonium chloride-³⁶Cl and O,O-diarylphosphorochloridates (p-RC₆H₄O)₂POCl or O,O-diarylphosphorochloridothionates (p-RC₆H₄O)₂PSCl has been studied in acetonitrile solution. Good Hammett's correlations of the rate constants with Taft's σ⁰ constants were obtained. The values of the reaction constants ρ were found identical for phosphoryl and thiophosphoryl compounds. In comparison with oxygen in the phosphoryl group, the sulfur atom exhibits an electron-donating effect (Δσ⁰ ～ 0.80). No correlation has been found for the enthalpy and entropy of activation. The effect of the substituents aryloxy groups, oxygen, or sulfur atoms in the phosphoryl group on the kinetics of the S_N2-P reaction is discussed. The reactivity of the investigated compounds is determined by the extent of the positive charge localized on the phosphorus atom. The positive charge is formed by the direct interactions of the substituents with the reaction center and the indirect–intramolecular interactions revealed in the structure of the compound.