Coupling Constants In Complexes Research Articles

The performance and efficiency of twelve range-separated hybrid DFT functionals for calculation of the magnetic exchange coupling constants of di-nuclear first row transition metal complexes

The performance and efficiency of twelve range-separated hybrid functionals are compared with each other in calculating magnetic exchange coupling constant (J) data on eleven di-nuclear first-row transition metal complexes having di-copper (Cu) and di-vanadium (V) as their central atoms. The J values are then compared with the experimental findings. In addition to that we also computed the B3LYP results of these complexes. We compared them with the results obtained from range-separated functionals as well as with the experimental results to understand their performances in predicting the magnetic exchange coupling constant. When computing, we reoptimized all the structures of the complexes taken from the crystal data, and then the values of Js were determined. The performances are predicted in terms of four statistical error matrices, namely, the mean absolute error (MAE), mean fractional error (MFE), mean signed error (MSE), root mean square error (RMSE) in cm−1.

Spin state and magnetic coupling in polynuclear Ni(II) complexes from density functional theory: is there an optimal amount of Fock exchange?

Reliable prediction of the ground-state spin and magnetic coupling constants in transition-metal complexes is a well-known challenge for density functional theory (DFT). One popular strategy for addressing this long-standing issue involves the modification of the fraction of Fock exchange in a hybrid functional. Here we explore the viability of this approach using three polynuclear metal-organic complexes based on a Ni4O4 cubane motif, having different ground state spin values (S = 0, 2, 4) owing to the use of different ligands. We systematically search for an optimum fraction of Fock exchange, across various global, range-separated, and double hybrid functionals. We find that for all functionals tested, at best there only exists a very narrow range of Fock exchange fractions which results in a correct prediction of the ground-state spin for all three complexes. The useful range is functional dependent, but general trends can be identified. Typically, at least two similar systems must be used in order to determine both an upper and lower limit of the optimal range. This is likely owing to conflicting demands of minimizing delocalization errors, which typically requires a higher percentage of Fock exchange, and addressing static correlation, which typically requires a lower one. Furthermore, we find that within the optimal range of Fock exchange, the signand relative magnitude of Ni-Ni magnetic coupling constants are reasonably well reproduced, but there is still room for quantitative improvement in the prediction. Thus, the prediction of spin state and magnetic coupling in polynuclear complexes remains an ongoing challenge for DFT.

DFT analysis of hyperfine couplings in d and f metal complexes with tetrahydro borate ligands

Metal complexes with BH4- ligands show extravagant structural and dynamic properties, and possess many important and applicable qualities (potent reducing agents and catalysts, materials for hydrogen storage). Electron paramagnetic resonance (EPR) is very important for the characterization of complex compounds, the determination of their electronic configuration and geometry. Also, Density Functional Theory (DFT) can predict EPR parameters and explain them more profoundly. Hence, in this paper hyperfine coupling constants of d and f metal complexes with BH4- ligands have been determined by DFT calculations, and analyzed in detail. Of particular importance is the analysis and prediction of hyperfine coupling constants for lanthanide complexes with BH4- ligands, given that there is not much data in the literature. Calculations predicted that proton hyperfine coupling constants are very small in the case of complexes of f elements, and are present only due to weak polarization. The increase of covalence and the number of unpaired electrons does not significantly affect the change of constants of BH4- ligands, but only of protons that are bound by σ bonds.

Complexes H2 CO:PXH2 and HCO2 H : PXH2 for X=NC, F, Cl, CN, OH, CCH, CH3 , and H: Pnicogen Bonds and Hydrogen Bonds.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate H2 CO : PXH2 pnicogen-bonded complexes and HCO2 H : PXH2 complexes that are stabilized by pnicogen bonds and hydrogen bonds, with X=NC, F, Cl, CN, OH, CCH, CH3 , and H. The binding energies of these complexes exhibit a second-order dependence on the O-P distance. DFT-SAPT binding energies correlate linearly with MP2 binding energies. The HCO2 H : PXH2 complexes are stabilized by both a pnicogen bond and a hydrogen bond, resulting in greater binding energies for the HCO2 H : PXH2 complexes compared to H2 CO : PXH2 . Neither the O-P distance across the pnicogen bond nor the O-P distance across the hydrogen bond correlates with the binding energies of these complexes. The nonlinearity of the hydrogen bonds suggests that they are relatively weak bonds, except for complexes in which the substituent X is either CH3 or H. The pnicogen bond is the more important stabilizing interaction in the HCO2 H : PXH2 complexes except when the substituent X is a more electropositive group. EOM-CCSD spin-spin coupling constants 1p J(O-P) across pnicogen bonds in H2 CO:PXH2 and HCO2 H : PXH2 complexes increase as the O-P distance decreases, and exhibit a second order dependence on that distance. There is no correlation between 2h J(O-P) and the O-P distance across the hydrogen bond in the HCO2 H : PXH2 complexes. 2h J(O-P) coupling constants for complexes with X=CH3 and H have much greater absolute values than anticipated from their O-P distances.

Frontispiece: Relativistic DFT Calculations of Hyperfine Coupling Constants in 5d Hexafluorido Complexes: [ReF6]2− and [IrF6]2−

Frontispiece: Relativistic DFT Calculations of Hyperfine Coupling Constants in 5d Hexafluorido Complexes: [ReF₆]²⁻ and [IrF₆]²⁻

Relativistic DFT Calculations of Hyperfine Coupling Constants in 5d Hexafluorido Complexes: [ReF6 ]2- and [IrF6 ]2.

The performance of relativistic density functional theory (DFT) methods has been investigated for the calculation of the recently measured hyperfine coupling constants of hexafluorido complexes [ReF6]2− and [IrF6]2−. Three relativistic methods were employed at the DFT level of theory: the 2‐component zeroth‐order regular approximation (ZORA) method, in which the spin–orbit coupling was treated either variationally (EV ZORA) or as a perturbation (LR ZORA), and the 4‐component Dirac–Kohn–Sham (DKS) method. The dependence of the results on the basis set and the choice of exchange‐correlation functional was studied. Furthermore, the effect of varying the amount of Hartree–Fock exchange in the hybrid functionals was investigated. The LR ZORA and DKS methods combined with DFT led to very similar deviations (about 20 %) from the experimental values for the coupling constant of complex [ReF6]2− by using hybrid functionals. However, none of the methods were able to reproduce the large anisotropy of the hyperfine coupling tensor of complex [ReF6]2−. For [IrF6]2−, the EV ZORA and DKS methods reproduced the experimental tensor components with deviations of ≈10 and ≈5 % for the hybrid functionals, whereas the LR ZORA method predicted the coupling constant to be around one order of magnitude too large owing to the combination of large spin–orbit coupling and very low excitation energies.

The mutual influence of Y···N and H···H interactions in XHY···NCH···HM complexes (X = F, Cl, Br; Y = S, Se; M = Li, Na, BeH, MgH): tuning of the chalcogen bond by dihydrogen bond interaction

The equilibrium structures, interaction energies, and bonding properties of ternary XHY···NCH···HM complexes are studied by ab initio calculations, where X = F, Cl, Br, Y = S, Se, and M = Li, Na, BeH, MgH. The ab initio calculations are carried out at the MP2/aug-cc-pVTZ level. The results indicate that all optimized Y···N and H···H binding distances in the ternary complexes are smaller than the corresponding values in the binary systems. The calculated cooperative energies (Ecoop) are between −0.20 kcal/mol in BrHS···NCH···HBeH and −3.29 kcal/mol in FHSe···NCH···HNa. For a given Y and M, the estimated Ecoop values increase as X = F > Cl > Br. In addition, the selenium-bonded complexes exibit larger Ecoop values than those of the sulfur-bonded counterparts. The cooperativity between Y···N and H···H interactions is further analyzed by quantum theory of atoms in molecules and natural bond orbital methods. Cooperative effects make an increase in the J(Y–N) and J(H–H) spin–spin coupling constants of the ternary complexes with respect to the binary systems.

Half-Sandwich Silane σ-Complexes of Ruthenium Supported by NHC Carbene

Reactions of carbene complex [Cp(IPr)Ru(pyr)2][BF4] (6, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with excess acetonitrile and LiCl in THF afford complexes [Cp(IPr)Ru(NCCH3)2][PF6] (7) and Cp(IPr)RuCl (8), respectively. Complex 8 was characterized by NMR and X-ray diffraction analysis. Addition of hydrosilanes to 8 results in silane σ-complexes Cp(IPr)Ru(η2-HSiR3)Cl (4), which were characterized by NMR and X-ray studies of Cp(IPr)Ru(η2-HSiMeCl2)Cl (4b) and Cp(IPr)Ru(η2-H3SiPh)Cl (4d). The hydrogen–silicon coupling constants of complexes 4 show an unusual trend in that the J(H–Si) values increase from the less-chlorinated complex Cp(IPr)Ru(η2-HSiMe2Cl)Cl (4c) to the trichloro derivative Cp(IPr)Ru(η2-HSiCl3)Cl (4a). Reaction of Cp(IPr)RuCl (8) with two equivalents of HSiCl3 gave the ruthenate complex [IPrH]+[CpRuCl(H) (SiCl3)2]−, characterized by NMR and X-ray study. Addition of hydrosilanes to the cationic complex [Cp(IPr)Ru(NCCH3)2][BArF4] (9) furnished very unstable cationic silane σ-comple...

Structure and magnetic properties of Saturn-shaped fullerenol complexes with ferrocene and nickelocene dicarboxylic acids: DFT simulation

DFT simulations of the electron and spin structure of fullerenol derivatives C60(OH)24·2Fe(C5H4COOH)2 and C60(OH)24·2Ni(C5H4COOH)2 have shown that these compounds form stable complexes with intermolecular hydrogen bonds. Calculated exchange coupling constants for the last complexes indicate that they can possess ferromagnetic properties. If this is true, then compounds will have a great potential for medical application as drug delivers under the control of external magnetic field.

Spin-flip non-orthogonal configuration interaction: a variational and almost black-box method for describing strongly correlated molecules.

In this paper, we report the development, implementation, and assessment of a novel method for describing strongly correlated systems, spin-flip non-orthogonal configuration interaction (SF-NOCI). The wavefunction is defined to be a linear combination of independently relaxed Slater determinants obtained from all possible spin-flipping excitations within a localized orbital active-space, typically taken to be the singly occupied orbitals of a high-spin ROHF wavefunction. The constrained orbital optimization of each CI basis configuration is defined such that only non-active-space orbitals are allowed to relax (all active space orbitals are fixed). A number of simplifications and benefits arise due to the fact that only a restricted number of orbital rotations are permitted, (1) basis states cannot coalesce during SCF, (2) basis state optimization is better conditioned due to a larger effective HOMO-LUMO gap, (3) smooth potential energy surfaces are easily obtained, (4) the Hamiltonian coupling between two basis states with non-orthogonal orbitals is greatly simplified. To illustrate the advantages over a conventional orthogonal CI expansion, we investigate exchange coupling constants of bimetallic complexes, the avoided crossing of the lowest singlet states during LiF dissociation, and ligand non-innocence in an organometallic complex. These numerical examples indicate that good qualitative agreement can be obtained with SF-NOCI, but dynamical correlation must be included to obtain quantitative accuracy.

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)J(P-F) and (2X)J(P-Cl) for complexes with chlorine-shared halogen bonds do not correlate with P-F and P-Cl distances, respectively. (1X)J(P-Cl) values for H2XP:ClF correlate best with the Cl-F distance, and approach the values of (1)J(P-Cl) for the corresponding cations H2XPCl(+). Values of (1X)J(P-Cl) for complexes H2XP:ClCl with chlorine-shared halogen bonds correlate with the binding energies of these complexes. (1)J(F-Cl) and (1)J(Cl-Cl) for complexes with chlorine-shared halogen bonds correlate linearly with the distance between P and the proximal Cl atom. In contrast, (2X)J(P-Cl) and (1X)J(P-Cl) for complexes with traditional halogen bonds exhibit more normal distance dependencies.

A successful DFT calculation of carbon-13 NMR chemical shifts and carbon–fluorine spin–spin coupling constants in (η6-fluoroarene)tricarbonylchromium complexes

Carbon-13 isotropic shielding constants and C–F spin–spin coupling constants for fluorobenzene, 3- and 4-dimethylaminofluorobenzene as well as for their tricarbonylchromium complexes have been calculated using DFT methods.

Ab Initio Study of Cooperative Effects in Complexes X:HBO:Z, with X, Z=LiH, HNC, HF, HCN, HCl, ClF, and HBO: Structures, Binding Energies, and Spin-Spin Coupling Constants across Intermolecular Bonds

Abstract A systematic ab initio investigation has been carried out to determine the structures, binding energies, and spin-spin coupling constants of ternary complexes X:HBO:Z for X, Z= LiH, HNC, HF, HCN, HCl, ClF, and HBO. All complexes X:HBO:Z are linear with C∞ v symmetry, except for HCl:HBO:Z and ClF:HBO:Z which have Cs symmetry, thereby reflecting the structures of the corresponding X:HBO and HBO:Z complexes. Cooperative effects on energies are synergistic in all ternary complexes. The enhanced binding energies of complexes X:HBO:Z correlate with the binding energies of the X:HBO and HBO:Z complexes. Coupling constants 1J(B-H) and 2hJ(B-A) across B-H···sA hydrogen bonds correlate with the B-A distance, and exhibit synergistic effects due to the presence of Z. 1hJ(H-A) indicates that these bonds have little proton-shared character. Coupling constants across D-H···sO hydrogen bonds, H-Li···sO lithium bonds, and F-Cl···sO halogen bonds are also sensitive to the synergistic effects arising from the presence of X. D-H···sO hydrogen bonds in ternary complexes are traditional (normal) hydrogen bonds.

One Ferromagnetic and Two Antiferromagnetic Dinuclear Nickel(II) Complexes Derived from a Tridentate N,N,O‐Donor Schiff Base Ligand: A Density Functional Study of Magnetic Coupling

AbstractThree new dinuclear NiII complexes, [Ni2L2(NO3)2] (1), [Ni2L2(NO2)2] (2), and [Ni2L2(CH3COO)2(H2O)] (3), have been synthesized by using a tridentate Schiff base ligand, 2‐({[3‐(dimethylamino)propyl]imino}methyl)phenol (HL), along with a nitrate, nitrite, or acetate ion, respectively, as co‐ligand. These three complexes were characterized by spectral analysis, X‐ray crystallography, and variable‐temperature magnetic susceptibility measurements. The structural analyses revealed that the NiII ions are coordinated by the deprotonated chelating tridentate Schiff base and possess a distorted octahedral geometry in all three complexes. Complexes 1 and 2 are two di‐μ2‐phenoxido‐bridged species in which the nitrate and nitrite act as chelating co‐ligands. However, in complex 3, in which the acetate anion is monodentate, an additional water bridge is present along with two μ2‐phenoxido bridges making the complex a face‐sharing bi‐octahedron. Magnetic susceptibility measurements indicate an antiferromagnetic intradimer interaction in complexes 1 and 2 with J values of –20.34(5) and –25.25(4) cm–1, respectively, whereas complex 3 shows a dominant ferromagnetic exchange coupling with J = 19.11(9) cm–1. DFT calculations were performed, and the theoretically obtained J values of –19.99 (for 1), –24.19 (for 2) and 18.81 cm–1 (for 3) corroborate very well the experimental results. An attempt has also been made to correlate the effect of Ni···Ni distances and bridging Ni–O–Ni angles on the coupling constants of the NiII complexes through DFT calculations. The relative energy calculations show that the diphenoxido‐bridged complexes are stable at larger bridging angles, and consequently the coupling is antiferromagnetic, whereas with an additional water bridge, the formation of complexes with the Ni–O–Ni bridging angle in the ferromagnetic region is energetically profitable.

Do nitrogen bases form chlorine-shared and ion-pair halogen bonds?

Ab initio calculations have been carried out to investigate the structures, binding energies, and spin–spin coupling constants of complexes with FCl as the Lewis acid and a series of sp, sp2, and sp3 hybridized nitrogen bases. These properties indicate that neutral complexes are stabilized by traditional F–Cl…N halogen bonds, although the chlorine-shared character of the bond is greater with sp2 and sp3 bases. Thus, these complexes are dramatically different from neutral complexes FCl:CNX with sp hybridized carbon bases, which exhibit traditional, chlorine-shared, and ion-pair halogen bonds.

An ab initio study of cooperative effects in ternary complexes X:CNH:Z with X, Z=CNH, FH, ClH, FCl, and HLi: structures, binding energies, and spin–spin coupling constants across intermolecular bonds

A systematic ab initio investigation has been carried out to determine the structures, binding energies, and spin-spin coupling constants of ternary complexes X:CNH:Z and corresponding binary complexes X:CNH and CNH:Z, for X, Z = CNH, FH, ClH, FCl, and HLi. The enhanced binding energies of ternary complexes X:CNH:Z for fixed X as a function of Z decrease in the same order as the binding energies of the binary complexes CNH:Z. In contrast, the enhanced binding energies of the ternary complexes for fixed Z as a function of X do not decrease in the same order as the binding energies of the binary complexes X:CNH, a consequence of the increased stabilities of ternary complexes FCl:CNH:Z due to very strong chlorine-shared halogen bonds. For complexes in which the X···CNH interaction is a D-H···C hydrogen bond for D-H the proton-donor group (N-H, F-H, or Cl-H), spin-spin coupling constants (1)J(D-H) and (2h)J(D-C) in ternary complexes X:CNH:Z decrease in absolute value as the binding energies of binary complexes CNH:Z and the enhanced binding energies of the ternary complexes for fixed X as a function of Z also decrease. However, (2X)J(F-C) increases as the enhanced binding energies of the ternary complexes FCl:CNH:Z decrease, a consequence of the nature of the chlorine-shared halogen bond. The one-bond coupling constants (1)J(N-H) for the CNH···Z interaction in ternary complexes vary significantly, depending on the nature of the X···CNH interaction. The largest values of (1)J(N-H) are found for ternary complexes with FCl as X. Two-bond coupling constants (2h)J(N-A) for A the proton-acceptor atom of Z, and (2d)J(N-H) decrease in absolute value in the order of decreasing enhancement energies of ternary complexes X:CNH:Z for fixed Z as a function of X.

New amino-dithiaphospholanes and phosphoramidodithioites and their rhodium and iridium complexes

New sulfur derivatives of phosphoramidite ligands were synthesized and the impact of the sulfur unit on the spectroscopic properties of their rhodium and iridium complexes was investigated. The new ligands Bn2NPSCH2CH2Sa(P-Sa) (Bn=benzyl, 4), Bn2NPSCHCHSa(CH2)3CaH2(P-Sa)(Ca-Sa) (6) and Bn2NP(4-XC6H4OMe)2 (X=S, 7a; X=O, 7b) were converted to the rhodium and iridium complexes trans-[Rh(CO)Cl(L)2] (L=4, 6, 7), [RhCl(COD)(L)] (L=4, 6, 7), [IrCl(COD)(7a)] and [IrCl2Cp∗(6)]. For comparison, some phosphoramidite complexes of these formulations also were synthesized. The new metal complexes were spectroscopically analyzed. For the carbonyl complexes, the νCO IR stretching frequencies were lower than for the corresponding phosphite and phosphoramidite ligands. The 1JPRh coupling constants for the rhodium complexes with the new ligands were also smaller than for the respective phosphoramidite and phosphite complexes. Finally, the 1JPSe coupling constants of the selenides of the new ligands were lower than those of the phosphoramidite ligands but higher than for PPh3. The spectroscopic data reveal that the new thio ligands 4, 6 and 7a are more electron donating than phosphites and phosphoramidites but less electron donating than PPh3.

Ab Initio Study of Ternary Complexes A···NCH···C with A,C = HCN, HF, HCl, ClF, and LiH: Energetics and Spin−Spin Coupling Constants across Intermolecular Bonds

A systematic ab initio study has been carried out to investigate the structures, binding energies, and spin-spin coupling constants of binary complexes A...NCH and NCH...C and ternary complexes A...NCH...C for A,C = HCN, HF, HCl, FCl, and HLi. These complexes are stabilized by some combination of hydrogen bonds, dihydrogen bonds, halogen bonds, and lithium bonds. The binding energies of the ternary complexes are enhanced relative to those of the corresponding binary complexes, suggesting that A...NCH is a stronger proton-donor acid and NCH...C is a stronger base relative to the isolated monomer HCN. The ternary complexes with the largest enhancement energies are FH...NCH...HLi, HLi...NCH...NCH, and HLi...NCH...HLi, each containing molecules with large dipole moments, and each with a linear head-to-tail arrangement of dipole moment vectors. The equation-of-motion coupled-cluster single and doubles method (EOM-CCSD) has been employed to evaluate spin-spin coupling constants across intermolecular bonds for binary complexes A...NCH and NCH...C and for ternary complexes A...NCH...C. These data are used to investigate how the presence of C influences coupling constants associated with the A...NCH interaction, and how the presence of A influences coupling constants for the NCH...C interaction. Changes in coupling constants in the ternary complexes relative to the binary may be related to the binding energies of corresponding binary complexes and the enhanced binding energies of the ternary complexes. Two-bond coupling constants across X-H...Y hydrogen bonds [(2h)J(X-Y)] are related to changes in intermolecular distances.

Synthesis and reactivity of rhodium and iridium alkene, alkyl and silyl complexes supported by a phenyl-substituted PNP pincer ligand

New rhodium and iridium complexes supported by the phenyl-substituted PNP pincer ligand PNPPhH (HN(2-PPh2-4-Me-C6H3)2) (1) were synthesized. The reaction of 2 equiv. of 1 with [(COD)IrCl]2 afforded the coordination complex [(PNPPhH)Ir(COD)]Cl (2) featuring hydrogen bonding between the N–H group and the chloride anion, as characterized by NMR spectroscopy and X-ray crystallography. Reaction of 1 with [(COE)2IrCl]2 or [(COE)2RhCl]2 in benzene provided a mixture of complexes including (PNPPhH)MHCl2 (M = Ir (4), M = Rh (7)) and (PNP)M(COE) (M = Ir (5), M = Rh (8)). Alkene complexes of the type (PNPPh)M(L) (M = Ir, L = COD (3) and COE (5); M = Rh, L = COE (8) and L = ethylene (9)) were synthesized by reaction of (PNPPh)Li with the appropriate alkene chloride complexes. Reactions of silanes with 5, 8 or 9 produced silyl hydride complexes (PNPPh)MH(SiR3) (M = Ir, R = Ph (16) and R = Et (17); M = Rh, R = Ph (18), Et (19) and Ph2Cl (20)) via Si–H oxidative addition. The JSiH coupling constants for rhodium complexes 18, 19 and 20 were determined to be ca. 35 Hz, while iridium complexes 16 and 17 exhibited coupling constants less than 10 Hz. X-Ray crystal structures of 16 and 18 reveal isostructural complexes featuring a trigonal bipyramidal geometry about iridium with a mer binding of the PNPPh ligand. A hydride ligand, located from the Fourier map for 18, has a short contact of 1.83(3) Å with the silicon atom. Oxidative addition of iodomethane to 5 and 8 afforded (PNPPh)M(Me)(I)(THF) (M = Rh (14), M = Ir (12)), respectively. Arene C–H activation upon thermolysis of 12 in benzene produced (PNPPh)M(Ph)(I)(THF). Iridium silyl iodide complexes (PNPPh)IrI(SiR3) (SiR3 = SiPh3 (21), SiH2Mes (22) and SiH2Xyl (23)) resulted from addition of organosilanes to 12, via elimination of CH4.

Characterizing Complexes with F−Li···N, H−Li···N, and CH3Li···N Lithium Bonds: Structures, Binding Energies, and Spin−Spin Coupling Constants

Ab initio calculations have been carried out to determine the structures, binding energies, and spin-spin coupling constants of complexes stabilized by X-Li...N bonds with F-Li, H-Li, and CH3Li as the Lewis acids. Complexes of these acids with the nitrogen bases N2, HCN, 1,3,5-triazine, pyrazine, 1,2,3-triazine, pyridine, and NH3 have linear X-Li...N bonds. Methylamine forms a nonlinear lithium bond only when F-Li is the lithium donor. Two bases, HN=CH2 and aziridine, form nonlinear X-Li...N bonds with each acid. Except for complexes with N2, which have small binding energies of about 5 kcal/mol, the binding energies of lithium-bonded complexes are appreciable, varying between 15 and 23 kcal/mol. The one-bond coupling constant 1J(F-Li) may increase or decrease upon complexation, but 1J(H-Li) and 1J(C-Li) decrease significantly. These coupling constants have their smallest values in complexes with nonlinear X-Li...N bonds. No correlations appear to exist between 1J(X-Li) and the X-Li distance and 1liJ(Li-N) and the Li-N distance. Values of the two-bond coupling constants 2liJ(X-N) are extremely small. Comparisons of 2liJ(F-N) with 2hJ(F-N) for coupling across a hydrogen bond and 2xJ(F-N) for coupling across a halogen bond suggest that the extremely small values of 2liJ(X-N) are not due to long X-N distances but to the low valence electron density on Li in lithium-bonded complexes.