Krishna K. Pandey

Structure and Bonding Energy Analysis of M−Ga Bonds in Dihalogallyl Complexes trans-[X(PMe3)2M(GaX2)] (M = Ni, Pd, Pt; X = Cl, Br, I)

Geometry, electronic structure, and bonding analysis of the terminal neutral dihalogallyl complexes of nickel, palladium, and platinum trans-[X(PMe(3))(2)M(GaX(2))] (M = Ni, Pd, Pt; X = Cl, Br, I) were investigated at the BP86 level of theory. The calculated geometries of platinum gallyl complexes trans-[X(PMe(3))(2)Pt(GaX(2))] (X = Br, I) are in excellent agreement with structurally characterized platinum complexes trans-[X(PCy(3))(2)M(GaX(2))]. In the gallyl complexes of nickel and palladium, the M-Ga sigma bonding orbital is slightly polarized toward the gallium atom, while in the platinum gallyl complexes, the M-Ga sigma bonding orbital is slightly polarized toward the platinum atom. It is significant to note that gallium atoms along the M-Ga sigma bonds have large p character, which is always >51% of the total AO contributions, while along the Ga-X sigma bonds, the p character varies from 72% to 73%. The short M-Ga bond distances, in spite of the significantly small M-Ga pi bonding, are due to the large s character of gallium (approximately 45-48%) along the M-Ga bonds. The calculated NPA charge distributions indicate that the metal atom carries negative charge and the Ga atom carries significantly large positive charge. The contributions of the electrostatic interaction terms, DeltaE(elstat), are significantly larger in all gallyl complexes than the covalent bonding DeltaE(orb) term. Thus, the [M]-GaX(2) bond in the studied gallyl complexes of Ni, Pd, and Pt has a greater degree of ionic character (65.7-72.5%). The pi-bonding contribution is, in all complexes, significantly smaller than the sigma bonding contribution. In the GaX(2) ligands, gallium dominantly behaves as a sigma donor. The interaction energy increases in all three sets of complexes via order of Ni < Pd < Pt, and the absolute value of DeltaE(Pauli), DeltaE(int), and DeltaE(elstat) contributions to the M-Ga bonds decreases via X = Cl < Br < I in all three sets of complexes.

Nature of Bonding in Terminal Borylene, Alylene, and Gallylene Complexes of Vanadium and Niobium [(η5-C5H5)(CO)3M(ENR2)] (M = V, Nb; E = B, Al, Ga; R = CH3, SiH3, CMe3, SiMe3): A DFT Study

Density functional theory calculations have been performed for the terminal borylene, alylene, and gallylene complexes [(η(5)-C(5)H(5))(CO)(3)M(ENR(2))] (M = V, Nb; E = B, Al, Ga; R = CH(3), SiH(3), CMe(3), SiMe(3)) using the exchange correlation functional BP86. The calculated geometry parameters of vanadium borylene complex [(η(5)-C(5)H(5))(CO)(3)V{BN(SiMe(3))(2)}] are in excellent agreement with their available experimental values. The M-B bonds in the borylene complexes have partial M-B double-bond character, and the B-N bonds are nearly B═N double bonds. On the other hand, the M-E bonds in the studied metal alylene and gallylene complexes represent M-E single bonds with a very small M-E π-orbital contribution, and the Al-N and Ga-N bonds in the complexes have partial double-bond character. The orbital interactions between metal and ENR(2) in [(η(5)-C(5)H(5))(CO)(3)M(ENR(2))] arise mainly from M ← ENR(2) σ donation. The π-bonding contribution is, in all complexes, much smaller. The contributions of the electrostatic interactions ΔE(elstat) are significantly larger in all borylene, alylene, and gallylene complexes than the covalent bonding ΔE(orb); that is, the M-ENR(2) bonding in the complexes has a greater degree of ionic character.

Nature of M−Ga Bonds in Cationic Metal-Gallylene Complexes of Iron, Ruthenium, and Osmium, [(η5-C5H5)(L)2M(GaX)]+: A Theoretical Study

Density Functional Theory calculations have been performed for the cationic half-sandwich gallylene complexes of iron, ruthenium, and osmium [(η(5)-C(5)H(5))(L)(2)M(GaX)](+) (M = Fe, L = CO, PMe(3); X = Cl, Br, I, NMe(2), Mes; M = Ru, Os: L = CO, PMe(3); X = I, NMe(2), Mes) at the BP86/TZ2P/ZORA level of theory. Calculated geometric parameters for the model iron iodogallylene system [(η(5)-C(5)H(5))(Me(3)P)(2)Fe(GaI)](+) are in excellent agreement with the recently reported experimental values for [(η(5)-C(5)Me(5))(dppe)Fe(GaI)](+). The M-Ga bonds in these systems are shorter than expected for single bonds, an observation attributed not to significant M-Ga π orbital contributions, but due instead primarily to high gallium s-orbital contributions to the M-Ga bonding orbitals. Such a finding is in line with the tenets of Bents Rule insofar as correspondingly greater gallium p-orbital character is found in the bonds to the (more electronegative) gallylene substituent X. Consistent with this, ΔE(σ) is found to be overwhelmingly the dominant contribution to the orbital interaction between [(η(5)-C(5)H(5))(L)(2)M](+) and [GaX] fragments (with ΔE(π) equating to only 8.0-18.6% of the total orbital contributions); GaX ligands thus behave as predominantly σ-donor ligands. Electrostatic contributions to the overall interaction energy ΔE(int) are also very important, being comparable in magnitude (or in some cases even larger than) the corresponding orbital interactions.

Nature of M-Ga bonds in dihalogallyl complexes (η5-C5H5)(Me3P)2M(GaX2) (M = Fe, Ru, Os) and (η5-C5H5)(OC)2Fe(GaX2) (X = Cl, Br, I): a DFT study.

Density functional theory (DFT) calculations have been performed on the terminal dihalogallyl complexes of iron, ruthenium, and osmium (η(5)-C(5)H(5))(Me(3)P)(2)M(GaX(2)) (M = Fe, Ru, Os; X = Cl, Br, I) and (η(5)-C(5)H(5))(OC)(2)Fe(GaX(2)) (X = Cl, Br, I) at the BP86/TZ2P/ZORA level of theory. On the basis of analyses suggested by Pauling, the M-Ga bonds in all of the dihalogallyl complexes are shorter than M-Ga single bonds; moreover, on going from X = Cl to X = I, the optimized M-Ga bond distances are found to increase. From the perspective of covalent bonding, however, π-symmetry contributions are, in all complexes, significantly smaller than the corresponding σ-bonding contribution, representing only 4-10% of the total orbital interaction. Thus, in these GaX(2) complexes, the gallyl ligand behaves predominantly as a σ donor, and the short M-Ga bond lengths can be attributed to high gallium s-orbital character in the M-Ga σ-bonding orbitals. The natural population analysis (NPA) charge distributions indicate that the group 8 metal atom carries a negative charge (from -1.38 to -1.62) and the gallium atom carries a significant positive charge in all cases (from +0.76 to +1.18). Moreover, the contributions of the electrostatic interaction terms (ΔE(elstat)) are significantly larger in all gallyl complexes than the covalent bonding term (ΔE(orb)); thus, the M-Ga bonds have predominantly ionic character (60-72%). The magnitude of the charge separation is greatest for dichlorogallyl complexes (compared to the corresponding GaBr(2) and GaI(2) systems), leading to a larger attractive ΔE(elstat) term and to M-Ga bonds that are stronger and marginally shorter than in the dibromo and diiodo analogues.

Structure and bonding energy analysis of cationic metal-ylyne complexes of molybdenum and tungsten, [(MeCN)(PMe3)4M≡EMes]+ (M = Mo, W; E = Si, Ge, Sn, Pb): a theoretical study.

The molecular and electronic structures and bonding analysis of terminal cationic metal-ylyne complexes (MeCN)(PMe(3))(4)M≡EMes](+) (M = Mo, W; E = Si, Ge, Sn, Pb) were investigated using DFT/BP86/TZ2P/ZORA level of theory. The calculated geometrical parameters for the model complexes are in good agreement with the reported experimental values. The M-E σ-bonding orbitals are slightly polarized toward E except in the complex [(MeCN)(PMe(3))(4)W(SnMes)](+), where the M-E σ-bonding orbital is slightly polarized toward the W atom. The M-E π-bonding orbitals are highly polarized toward the metal atom. In all complexes, the π-bonding contribution to the total M≡EMes bond is greater than that of the σ-bonding contribution and increases upon going from M = Mo to W. The values of orbital interaction ΔE(orb) are significantly larger in all studied complexes I-VIII than the electrostatic interaction ΔE(elstat). The absolute values of the interaction energy, as well as the bond dissociation energy, decrease in the order Si > Ge > Sn > Pb, and the tungsten complexes have stronger bonding than the molybdenum complexes.

Structure and bonding analysis of dimethylgallyl complexes of iron, ruthenium, and osmium [(η5-C5H5)(CO)2M(GaMe2)] and [(η5-C5H5)(Me3P)2M(GaMe2)].

Density functional theory calculations have been performed for the dimethylgallyl complexes of iron, ruthenium, and osmium [(η(5)-C(5)H(5))(L)(2)M(GaMe(2)] (M = Fe, Ru, Os; L = CO, PMe(3)) at the DFT/BP86/TZ2P/ZORA level of theory. The calculated geometry of the iron complex [(η(5)-C(5)H(5))(CO)(2)Fe(GaMe(2))] is in excellent agreement with structurally characterized complex [(η(5)-C(5)H(5))(CO)(2)Fe(Ga(t)Bu(2))]. The Pauling bond order of the optimized structures shows that the M-Ga bonds in these complexes are nearly M-Ga single bond. Upon going from M = Fe to M = Os, the calculated M-Ga bond distance increases, while on substitution of the CO ligand by PMe(3), the calculated M-Ga bond distances decrease. The π-bonding component of the total orbital contribution is significantly smaller than that of σ-bonding. Thus, in these complexes the GaX(2) ligand behaves predominantly as a σ-donor. The contributions of the electrostatic interaction terms ΔE(elstat) are significantly smaller in all gallyl complexes than the covalent bonding ΔE(orb) term. The absolute values of the ΔE(Pauli), ΔE(int), and ΔE(elstat) contributions to the M-Ga bonds increases in both sets of complexes via the order Fe < Ru < Os. The Ga-C(CO) and Ga-P bond distances are smaller than the sum of van der Waal radii and, thus, suggest the presence of weak intermolecular Ga-C(CO) and Ga-P interactions.

Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of EUX3 (E = N, P, CH; X = H, F, Cl)

Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [EUX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of UN bond in [NUF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate UN vibrational frequencies follows the order BLYP>revPBE>BP86>PW91>TPSS>PBE>M06-L. The BLYP functional gives accurate value of the UE bond distances. The uranium atom in the studied compounds [EUX3] is positively charged. Upon going from [EUF3] to [EUCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for UE bonds ranges from 2.90 to 3.29. The UE bond dissociation energies vary with different density functionals as M06-L<TPSS<BLYP<revPBE<BP86<PBE≈PW91. The orbital interactions ΔEorb, in all studied compounds [EUX3] are larger than the electrostatic interaction ΔEelstat, which means the UN bonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The UE σ-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [PUX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimmes D3(BJ) corrections, the Corminboeufs dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals.

Theoretical insights into structure, bonding, reactivity and importance of ion-pair interactions in Kirby's tetrafluoroboric acid salts of twisted amides

The geometries of the amides 1-azatricyclo [3.3.1.13,7] decan-2-one, tetrafluoroboric acid salt (1), 3-methyl-1-azatricyclo [3.3.1.13,7] decan-2-one, tetrafluoroboric acid salt (2), and 3,5,7-trimethyl-1-azatricyclo [3.3.1.13,7] decan-2-one, tetrafluoroboric acid salt (3) have been calculated at the DFT-D3 (BJ) level using density functionals PBE, PBE0, TPSS and TPSSH. The optimized structure of (1) at the DFT/PBE0-D3(BJ) level of theory in methanol is in excellent agreement with the experimental structure. The geometries of the hydrolyzed products (4–7) have been optimized with PBE and PBE0 functionals. In the studied compounds (1–3), the [BF4]− anion interacts with cationic fragments [1]+, [2]+ and [3]+ through the N–H⋯F hydrogen bond. The ion-pair interactions affect the C–N–H bond angles which are relatively smaller (110.3° in 1, 109.9° in 2, 110.0° in 3) than those for cationic fragments (104.8° in 1+, 104.8° in 2+, 105.1° in 3+). The charge analysis formulates the salts (1–3) as [cation]q+[BF4]q− with q = ∼0.81. The high stability of ion-pairs is due to significant flow of charge from the BF4− anion to the cation. There is significant hydrogen bonding (H⋯F) interaction in 1–3. Salt 1 has the lowest ion pair dissociation energy of ΔE = 5.46 kcal mol−1 in methanol and 4.91 kcal mol−1 in acetonitrile. The hydrolysis reaction of 1 is most exothermic (ΔE = −11.84 kcal mol−1) and thus it is more favourable. The hydrolysis of amides 2 and 3 with a bridgehead methyl is relatively less favourable. Hydrolysis reactions of amides 1 and 3 at the DFT/PBE-D3(BJ) level in acetonitrile have been investigated. The calculated enthalpies of the hydrolysis product formation are 4, 41.61 kcal mol−1 and 7, 32.43 kcal mol−1.

Dispersion-Corrected Relativistic Density Functional Theory (DFT) Calculations of Structure and 119Sn Mössbauer Parameters for M≡SnR Bonding in Filippou’s Stannylidyne Complexes of Molybdenum and Tungsten

(119)Sn Mössbauer isomer shift (IS) and quadrupole splitting (ΔEQ) for M≡SnR bonding in metal-stannylidyne complexes trans-[Cl(PMe3)4Mo≡Sn-R] (1), trans-[Cl(PMe3)4W≡Sn-R] (2), trans-[Cl(dppe)2Mo≡Sn-R] (3), trans-[Cl(dppe)2W≡Sn-R] (4), [(dppe)2Mo≡Sn-R](+) (5), [(dppe)2W≡Sn-R](+) (6) (R = C6H3-2,6-Mes2) have been investigated for the first time. Calculations of optimized structures and (119)Sn Mössbauer parameters were carried out at the DFT/TPSS-D3(BJ)/TZVPP/ZORA level of theory. The calculated geometry parameters of stannylidyne complexes of molybdenum and tungsten (1-6) are in good agreement with experimental values of W-Sn and Sn-C bond distances. The calculated values of the isomer shift for the complexes (1-6) are almost same to the experimental values (within ±0.1 mm/s). Experimental values (ISexptl, 2.38-2.50 mm/s) and calculated values (IScalcd, 2.37-2.49 mm/s) of isomer shifts indicate that the oxidation state of tin in the studied complexes with M≡Sn-R bonding is Sn(II). The variations of ISexptl, as a function of Sn s electrons (Ns(Sn)), also exhibit a linear trend. (IS = 0.477Ns(Sn) - 1.888, R(2) = 0.9973). Calculated values of isomer shift (IScalcd) using the linear regression with the Ns(Sn) electron density are in excellent concord with the ISexptl.The calculated values of nuclear quadrupole splitting parameters (ΔEQ(calcd)) of (119)Sn using the relation ΔEQ(calcd) = (0.540 + 0.28) V are in agreement with the experimental values.

Insights into the nature of ME bonds in [(PMe3)4ME(Mes)]+ (M = Mo, W) and [(PMe3)5WE(Mes)]+: a dispersion-corrected DFT study

Structures and bonding energy analysis of terminal cationic metal–ylidyne complexes [(PMe3)4ME(Mes)]+ (M = Mo, W) and [(PMe3)5WE(Mes)]+ (E = Si, Ge, Sn, Pb) were investigated by DFT, DFT-D3 and DFT-D3(BJ) methods using BP86, PBE and PW91 functionals. The Nalewajski–Mrozek (N–M) bond orders and Pauling bond orders show that the M–E bonds in the studied cationic complexes are essentially ME triple bonds. Atomic orbital populations reveal that the out-of-plane π-bonding in all complexes is stronger than the in-plane π-bonding. The bonding of the M–E σ-bond is quite strong, as is the total M–E π-bond strength, and increases upon going from molybdenum to tungsten. The contribution of the orbital interactions ΔEorb is significantly larger (58–63%) than the electrostatic contributions ΔEelstat in all the complexes studied. The absolute values of the bond dissociation energies decrease in the order Si > Ge > Sn > Pb. The D3-dispersion energies with zero-damping are in the range 13.0–17.9 kcal mol−1 (BP86), 7.1–10.6 kcal mol−1 (PBE) and 7.7–10.6 kcal mol−1 (PW91), which are smaller than the corresponding DFT-D3(BJ) energies of 21.0–24.6 kcal mol−1 (BP86), 9.9–13.6 kcal mol−1 (PBE) and 10.6–13.6 kcal mol−1 (PW91). The percentage dispersion-corrections to the bond dissociation energies increase as E becomes heavier. The effects of relativistic core contractions in heavier nuclei, i.e. tungsten and lead, are also evaluated.