Covalent versus ionic bonding in alkalimetal fluoride oligomers

The most polar bond in chemistry is that between a fluorine and an alkalimetal atom. Inspired by our recent finding that other polar bonds (C--M and H--M) have important covalent contributions (i.e., stabilization due to bond overlap), we herein address the question if covalency is also essential in the F--M bond. Thus, we have theoretically studied the alkalimetal fluoride monomers, FM, and (distorted) cubic tetramers, (FM)4, with M=Li, Na, K, and Rb, using density functional theory at the BP86/TZ2P level. Our objective is to determine how the structure and thermochemistry (e.g., F--M bond lengths and strengths, oligomerization energies, etc.) of alkalimetal fluorides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital theory. The analyses confirm the extreme polarity of the F--M bond (dipole moment, Voronoi deformation density and Hirshfeld atomic charges), and they reveal that bond overlap-derived stabilization (ca. -6, -6, and -2 kcal/mol) contributes only little to the bond strength (-136, -112, and -114 kcal/mol) and the trend therein along Li, Na, and K. According to this and other criteria, the F--M bond is not only strongly polar, but also has a truly ionic bonding mechanism. Interestingly, the polarity is reduced on tetramerization. For the lithium and sodium fluoride tetramers, the F4 tetrahedron is larger than and surrounds the M4 cluster (i.e., F--F>M--M). But in the potassium and rubidium fluoride tetramers, the F4 tetrahedron is smaller than and inside the M4 cluster (i.e., F--F相似文献   

Synthesis,structure, and dynamic behavior of cyclopentadienyl-lithium, -sodium,and -potassium annelated with bicyclo[2.2.2]octene units: a systematic study on site exchange of alkali metals on a cyclopentadienyl ring in tetrahydrofuran

Novel cyclopentadienyl (Cp)-alkali metal complexes 1-M and 2-M (M = Li, Na, K), in which the Cp ring is annelated with two bicyclo[2.2.2]octene units and substituted with a phenyl group for 1 and a tert-butyl group for 2, were synthesized, and their structures and dynamic behaviors were investigated by means of X-ray crystallography, dynamic (13)C NMR, and DFT calculations. The X-ray crystallography results indicated that 1-Li, 1-Na, and 2-Na form monomeric contact ion pairs (CIP) with three THF molecules coordinated to the metal atom. Also, in THF-d(8), all of the 1-M and 2-M form monomeric CIP in the ground state. However, variable-temperature (13)C NMR measurements of 1-M and 2-M in THF-d(8) demonstrated dynamic behavior in which the metal ion exchanges positions between the upper and lower faces of the Cp ring. From a study of the concentration dependence of the dynamic behavior, the exchange was found to proceed principally as an intramolecular process at concentration ranges lower than 0.2 M. The experimentally observed deltaG values for the intramolecular exchange process for all the 1-M and 2-M (except for 2-Li, whose intramolecular process was too slow to observe) were found to be quite similar in THF-d(8) solution and to fall within the range of 12-14 kcal mol(-)(1). Within this range, a tendency was observed for the deltaG values to increase as the size of the metal decreased. Theoretical calculations (B3LYP/6-31G(d)) afforded considerably large values as the gas-phase dissociation energy for 1-M (162.7 kcal mol(-)(1) for M = Li; 131.6 kcal mol(-)(1) for M = Na; 110.9 kcal mol(-)(1) for M = K) and for 2-M (170.0 kcal mol(-)(1) for M = Li; 137.5 kcal mol(-)(1) for M = Na; 115.4 kcal mol(-)(1) for M = K). These values should be compensated for by a decrease in the solvation energies for the metal ions with increasing size, as exemplified by the calculated solvation energy for M(+)(Me(2)O)(4), which serves as a model for metal ions solvated with four molecules of THF (-122.9 kcal mol(-)(1) for M = Li; -94.7 kcal mol(-)(1) for M = Na; -67.7 kcal mol(-)(1) for M = K). This compensation results in a small difference in the overall energy for dissociation of 1-M or 2-M in ethereal solutions, thus supporting the similar deltaG values observed for the intramolecular metal exchange.     

Structure of cationized arginine (arg.m, m = h, li, na, k, rb, and cs) in the gas phase: further evidence for zwitterionic arginine

The gas-phase structures of cationized arginine, Arg.M(+), M = Li, Na, K, Rb, and Cs, were studied both by hybrid method density functional theory calculations and experimentally using low-energy collisionally activated and thermal radiative dissociation. Calculations at the B3LYP/LACVP++** level of theory show that the salt-bridge structures in which the arginine is a zwitterion (protonated side chain, deprotonated C-terminus) become more stable than the charge-solvated structures with increasing metal ion size. The difference in energy between the most stable charge-solvated structure and salt-bridge structure of Arg.M(+) increases from -0.7 kcal/mol for Arg.Li(+) to +3.3 kcal/mol for Arg.Cs(+). The stabilities of the salt-bridge and charge-solvated structures reverse between M = Li and Na. These calculations are in good agreement with the results of dissociation experiments. The low-energy dissociation pathways depend on the cation size. Arginine complexed with small cations (Li and Na) loses H(2)O, while arginine complexed with larger cations (K, Rb, and Cs) loses NH(3). Loss of H(2)O must come from a charge-solvated ion, whereas the loss of NH(3) can come from the protonated side chain of a salt-bridge structure. The results of dissociation experiments using several cationized arginine derivatives are consistent with the existence of these two distinct structures. In particular, arginine methyl esters, which cannot form salt bridges, dissociate by loss of methanol, analogous to loss of H(2)O from Arg.M(+); no loss of NH(3) is observed. Although dissociation experiments probe gas-phase structure indirectly, the observed fragmentation pathways are in good agreement with the calculated lowest energy isomers. The combination of the results from experiment and theory provides strong evidence that the structure of arginine-alkali metal ion complexes in the gas phase changes from a charge-solvated structure to a salt-bridge structure as the size of the metal ion increases.     

Bonding analysis of metal-metal multiple bonds in R3M-M'R3 (M, M' = Cr, Mo, W; R = Cl, NMe2)

The bonding situation of homonuclear and heteronuclear metal-metal multiple bonds in R(3)M-M'R(3) (M, M' = Cr, Mo, W; R = Cl, NMe(2)) is investigated by density functional theory (DFT) calculations, with the help of energy decomposition analysis (EDA). The M-M' bond strength increases as M and M' become heavier. The strongest bond is predicted for the 5d-5d tungsten complexes (NMe(2))(3)W-W(NMe(2))(3) (D(e) = 103.6 kcal/mol) and Cl(3)W-WCl(3) (D(e) = 99.8 kcal/mol). Although the heteronuclear molecules with polar M-M' bonds are not known experimentally, the predicted bond dissociation energies of up to 94.1 kcal/mol for (NMe(2))(3)Mo-W(NMe(2))(3) indicate that they are stable enough to be isolated in the condensed phase. The results of the EDA show that the stronger R(3)M-M'R(3) bonds for heavier metal atoms can be ascribed to the larger electrostatic interaction caused by effective attraction between the expanding valence orbitals in one metal atom and the more positively charged nucleus in the other metal atom. The orbital interaction reveal that the covalency of the homonuclear and heteronuclear R(3)M-M'R(3) bonds is due to genuine triple bonds with one σ- and one degenerate π-symmetric component. The metal-metal bonds may be classified as triple bonds where π-bonding is much stronger than σ-bonding; however, the largest attraction comes from the quasiclassical contribution to the metal-metal bonding. The heterodimetallic species show only moderate polarity and their properties and stabilities are intermediate between the corresponding homodimetallic species, a fact which should allow for the experimental isolation of heterodinuclear species. CASPT2 calculations of Cl(3)M-MCl(3) (M = Cr, Mo, W) support the assignment of the molecules as triply bonded systems.     

Prediction and characterization of a new kind of alkali--superhalogen species with considerable stability: MBeX(3) (M = Li, Na; X = F, Cl, Br)

The geometries of the MBeX(3) (M = Li, Na; X = F, Cl, Br) series with all real frequencies are reported using the B3LYP and MP2 methods with the 6-311+G(d) basis set. The natural bond orbital (NBO) and atom in molecule (AIM) analyses indicate the ionic character of the M-X bonds connecting the alkali atom M and the superhalogen BeX(3). The introduction of a counterion M(+) only slightly affects the geometry of BeX(3)(-), but produces a more stable species. The bond energies (E(b)) and vertical ionization potentials (VIP) of the MBeX(3) species are obtained at the CCSD(T)/6-311+G(3df) level. These alkali-superhalogen species exhibit large E(b) (130.4-222.3 kcal mol(-1)) and VIP values (9.46-14.05 eV) to show considerable stabilities. In addition, both E(b)s and VIPs of MBeX(3) are found to be closely related to the electronegativity of the X ligands and partial atomic charges.     

Experimental and theoretical investigation of alkali metal cation interactions with hydroxyl side-chain amino acids

Absolute bond dissociation energies of serine (Ser) and threonine (Thr) to alkali metal cations are determined experimentally by threshold collision-induced dissociation of M+AA complexes, where M+=Li+, Na+, and K+ and AA=Ser and Thr, with xenon in a guided ion beam tandem mass spectrometer. Experimental results show that the binding energies of both amino acids to the alkali metal cations are very similar to one another and follow the order of Li+>Na+>K+. Quantum chemical calculations at three different levels, B3LYP, B3P86, and MP2(full), using the 6-311+G(2d,2p) basis set with geometries and zero-point energies calculated at the B3LYP/6-311+G(d,p) level show good agreement with the experimental bond energies. Theoretical calculations show that all M+AA complexes have charge-solvated structures (nonzwitterionic) with [CO, N, O] tridentate coordination.     

Competition between pi and non-pi cation-binding sites in aromatic amino acids: a theoretical study of alkali metal cation (Li+, Na+, K+)-phenylalanine complexes

To understand the cation-pi interaction in aromatic amino acids and peptides, the binding of M(+) (where M(+) = Li(+), Na(+), and K(+)) to phenylalanine (Phe) is studied at the best level of density functional theory reported so far. The different modes of M(+) binding show the same order of binding affinity (Li(+)>Na(+)>K(+)), in the approximate ratio of 2.2:1.5:1.0. The most stable binding mode is one in which the M(+) is stabilized by a tridentate interaction between the cation and the carbonyl oxygen (O[double bond]C), amino nitrogen (--NH(2)), and aromatic pi ring; the absolute Li(+), Na(+), and K(+) affinities are estimated theoretically to be 275, 201, and 141 kJ mol(-1), respectively. Factors affecting the relative stabilities of various M(+)-Phe binding modes and conformers have been identified, with ion-dipole interaction playing an important role. We found that the trend of pi and non-pi cation bonding distances (Na(+)-pi>Na(+)-N>Na(+)-O and K(+)-pi>K(+)-N>K(+)-O) in our theoretical Na(+)/K(+)-Phe structures are in agreement with the reported X-ray crystal structures of model synthetic receptors (sodium and potassium bound lariat ether complexes), even though the average alkali metal cation-pi distance found in the crystal structures is longer. This difference between the solid and the gas-phase structures can be reconciled by taking the higher coordination number of the cations in the lariat ether complexes into account.     

The special five-membered ring of proline: An experimental and theoretical investigation of alkali metal cation interactions with proline and its four- and six-membered ring analogues

The interaction of the alkali metal cations, Li+, Na+, and K+, with the amino acid proline (Pro) and its four- and six-membered ring analogues, azetidine-2-carboxylic acid (Aze) and pipecolic acid (Pip), are examined in detail. Experimentally, threshold collision-induced dissociation of the M+(L) complexes, where M = Li, Na, and K and L = Pro, Aze, and Pip, with Xe are studied using a guided ion beam tandem mass spectrometer. From analysis of the kinetic energy dependent cross sections, M(+)-L bond dissociation energies are measured. These analyses account for unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. Ab initio calculations for a number of geometric conformations of the M+(L) complexes were determined at the B3LYP/6-311G(d,p) level with single-point energies calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. Theoretical bond energies show good agreement with the experimental bond energies, which establishes that the zwitterionic form of the alkali metal cation/amino acid, the lowest energy conformation, is formed in all cases. Despite the increased conformational mobility in the Pip systems, the Li+, Na+, and K+ complexes of Pro show higher binding energies. A meticulous examination of the zwitterionic structures of these complexes provides an explanation for the stability of the five-membered ring complexes.     

Experimental and theoretical study of the vibrational spectra of 12-crown-4-alkali metal cation complexes

The vibrational, Raman, and IR, spectra of the five 12-crown-4 (12c4) complexes with Li+, Na+, K+, Rb+, and Cs+ alkali metal cations were measured. Except for a small shift of the position of some bands in the vibrational spectra of the Li+ complex, the vibrational spectra of the five complexes are so similar that it is concluded that the five complexes exist in the same conformation. B3LYP/6-31+G* force fields were calculated for six of the eight predicted conformations in a previous report (J. Phys. Chem. A 2005, 109, 8041) of the 12c4-Li+, Na+, and K+ complexes that are of symmetries higher than the C1 symmetry. These six conformations, in energy order, are of C4, Cs, Cs, C(2v), C(2v), and Cs symmetries. Comparison between the experimental and calculated vibrational frequencies assuming any of the above-mentioned six conformations shows that the five complexes exist in the C4 conformation. This agrees with the fact that the five alkali metal cations are larger than the 12c4 ring cavity. The B3LYP/6-31+G* force fields of the C4 conformation of the Li+, Na+ and K+ complexes were scaled using a set of eight scale factors and the scale factors were varied so as to minimize the difference between the calculated and experimental vibrational frequencies. The root-mean-square (rms) deviations of the calculated frequencies from the experimental frequencies were 7.7, 5.6, and 5.1 cm(-1) for the Li+, Na+, and K+ complexes, respectively. To account for the earlier results of the Li+ complex that the Cs conformation is more stable than the C4 conformation by 0.16 kcal/mol at the MP2/6-31+G* level, optimized geometries of the complex were calculated for the C4 and Cs conformations at the MP2/6-311++G** level. The C4 conformation was calculated to be more stable than the Cs conformation by 0.13 kcal/mol.     

On Bonding,Structure, and Stability of Ternary Hydrides A2MH2 (A = Li,Na; M = Pd,Pt)

Bonding, structure, and stability of solid A₂MH₂ with A = Li, Na; M = Pd, Pt were investigated with a relativistically corrected density-functional approach, which reliably describes the trends among these four compounds. In order to examine the influence of the ligands (A) and of the crystalline environment, calculations were also made for free A₂MH₂ molecules and MH₂^2– ions. The free MH₂^2– complex is held together by strong bonds between formally closed shell atomic units because of strong M-d,s hybridization. The M–H bonds are further stabilized by the alkali metal ion ligands and by the crystal surrounding. The crystal field expands the H–A distance and enhances the H–A polarity. Relativistic effects contribute to M–H bonding in the solid state. The experimentally determined bond lengths and their trends are in accordance with theory. Due to relativistic and lanthanide effects, the Pt–H bond length becomes nearly as short as the Pd–H one. The small Li ion causes a distortion of the Li₂PtH₂ crystal resulting in an even shorter Pt–H bond length. In the gas-phase, A₂PtH₂ is more stable against dissociation than A₂PdH₂. The stability of the solid compounds is strongly influenced by the cohesive energy of the metal M, and also by the nature of the alkali metal. The evaluated enthalpies of formation favor increasing stability of solid A₂MH₂ against disproportionation into M and AH from Pt to Pd and from Li to Na. This is in agreement with experimental findings. The assignment of the experimental vibrational excitations should be reconsidered.     

Molecular switch triggered by solvent polarity: synthesis,Acid-base behavior,alkali metal ion complexation,and crystal structure

The synthesis and characterization of the new tetraazamacrocycle L, bearing two 1,1'-bis(2-phenol) groups as side-arms, is reported. The basicity behavior and the binding properties of L toward alkali metal ions were determined by means of potentiometric measurements in ethanol/water 50:50 (v/v) solution (298.1+/-0.1 K, I=0.15 mol dm(-3)). The anionic H(-1)L(-) species can be obtained in strong alkaline solution, indicating that not all of the acidic protons of L can be removed under the experimental conditions used. This species behaves as a tetraprotic base (log K(1)=11.22, log K(2)=9.45, log K(3)=7.07, log K(4)=5.08), and binds alkali metal ions to form neutral [MH(-1)L] complexes with the following stability constants: log K(Li)=3.92, log K(Na)=3.54, log K(K)=3.29, log K(Cs)=3.53. The arrangement of the acidic protons in the H(-1)L(-) species depends on the polarity of the solvents used, and at least one proton switches from the amine moiety to the aromatic part upon decreasing the polarity of the solvent. In this way two different binding areas, modulated by the polarity of solvents, are possible in L. One area is preferred by alkali metal ions in polar solvents, the second one is preferred in solvents with low polarity. Thus, the metal ion can switch from one location to the other in the ligand, modulated by the polarity of the environment. A strong hydrogen-bonding network should preorganize the ligand for coordination, as confirmed by MD simulations. The crystal structure of the [Na(H(-1)L)].CH(3)CN complex (space group P2(1)/c, a=12.805(1), b=20.205(3), c=14.170(2) A, beta=100.77(1) degrees, V=3601.6(8) A(3), Z=4, R=0.0430, wR2=0.1181), obtained using CH(2)Cl(2)/CH(3)CN as mixed solvent, supports this last aspect and shows one of the proposed binding areas.     

Effect of the complexant shape on the large first hyperpolarizability of alkalides Li+(NH3)4M-.

The effect of complexant shape effect on the first hyperpolarizability beta(0) of alkalides Li(+)(NH(3))(4)M(-) (M=Li, Na, K) was explored. At the MP2/6-311++G level, Li(+)(NH(3))(4)M(-) (M=Li, Na, K) have considerable beta(0) values due to excess electrons from chemical doping and charge transfer. By comparison with the alkalides Li(+)(calix[4]pyrrole)M(-), a complexant shape effect in Li(+)(NH(3))(4)M(-) is detected. The beta(0) values of Li(+)(NH(3))(4)M(-) with the "smaller", inorganic, T(d)-symmetric (NH(3))(4) complexant are more than four times larger than those of Li(+)(calix[4]pyrrole)M(-) with the "larger", organic C(4v)-symmetric calix[4]pyrrole complexant. The ratios of the beta(0) values of Li(+)(NH(3))(4)M(-) and Li(+)(calix[4]pyrrole)M(-) are 6.57 (M=Li ), 6.55 (M=Na), and 5.17 (M=K). In the Li(+)(NH(3))(4)M(-) systems, the NBO charge and oscillator strength are found to monotonically depend on the atomic number of the alkali metal anion. The order of the NBO charges of the alkali anions M(-) is -0.667 (M=Li )>-0.644 (M=Na)>-0.514 (M=K), while the order of the oscillator strengths in the crucial transition is 0.351 (M=Li )<0.360 (M=Na)<0.467 (M=K). This indicates that complexant shape effects are strong, and consequently the beta(0) values of Li(+)(NH(3))(4)M(-) are found to be beta(0)=70 295 (M=Li )<96 780 (M=Na)<185 805 a.u. (M=K). This work reveals that the use of a high-symmetry complexant is an important factor that should be taken into account when enhancing the first hyperpolarizability of alkalides by chemical doping.     

Pnicogen-hydride interaction between FH2X (X = P and As) and HM (M = ZnH, BeH, MgH, Li, and Na)

A pnicogen-hydride interaction has been predicted and characterized in FH(2)P-HM and FH(2)As-HM (M = ZnH, BeH, MgH, Li, and Na) complexes at the MP2/aug-cc-pVTZ level. For the complexes analyzed here, P(As) and HM are treated as a Lewis acid and a Lewis base, respectively. This interaction is moderate or strong since, for the strongest interaction of the FH(2)As-HNa complex, the interaction energy amounts to -24.79 kcal/mol, and the binding distance is equal to about 1.7 ?, much less than the sum of the corresponding van der Waals radii. By comparison with some related systems, it is concluded that the pnicogen-hydride interactions are stronger than dihydrogen bonds and lithium-hydride interactions. This interaction has been analyzed with natural bond orbitals, atoms in molecules, electron localization function, and symmetry adapted perturbation theory methods.     

Theoretical studies of metallo (Li and Na)-ene reaction mechanisms

The reaction mechanisms of allyl-lithium and allyl-sodium with ethylene were studied by ab initio molecular orbital (MO) methods. The reaction mechanisms were analyzed by a CiLC-IRC method on the basis of ab initio CASSCF MOs. The ene reaction pathways of allyl-Li and allyl-Na with ethylene were located. The complex between allyl-metal and ethylene for both systems is found in the first step of the reaction, and then the metal migration and new C-C bond formation occur synchronously through the transition state. The complexation energies are -13.2 and -9.6 kcal/mol for Li and Na systems, respectively. The activation energy barriers from the reactants are 3.5 kcal/mol for the Li system and 2.0 kcal/mol for the Na system at the MRMP2 calculation level. These barriers are significantly lower than that of the ene reaction of propene with ethylene as the parent reaction. The CiLC-IRC analysis shows that the reaction of allyl-metal with ethylene is a concerted ene reaction mechanism, not a metal catalysis and/or a stepwise reaction.     

Synthesis,structures, and conformational characteristics of calixarene monoanions and dianions

The synthesis, complete characterization, and solid state structural and solution conformation determination of calix[n]arenes (n = 4, 6, 8) is reported. A complete series of X-ray structures of the alkali metal salts of calix[4]arene (HC4) illustrate the great influence of the alkali metal ion on the solid state structure of calixanions (e.g., the Li salt of monoanionic HC4 is a monomer; the Na salt of monoanionic HC4 forms a dimer; and the K, Rb, and Cs salts exist in polymeric forms). Solution NMR spectra of alkali metal salts of monoanionic calix[4]arenes indicate that they have the cone conformation in solution. Variable-temperature NMR spectra of salts HC4.M (M = Li, Na, K, Rb, Cs) show that they possess similar coalescence temperatures, all higher than that of HC4. Due to steric hindrance from tert-butyl groups in the para position of p-tert-butylcalix[4]arene (Bu(t)C4), the alkali metal salts of monoanionic Bu(t)C4 exist in monomeric or dimeric form in the solid state. Calix[6]arene (HC6) and p-tert-butylcalix[6]arene (Bu(t)C6) were treated with a 2:1 molar ratio of M(2)CO(3) (M = K, Rb, Cs) or a 1:1 molar ratio of MOC(CH(3))(3) (M = Li, Na) to give calix[6]arene monoanions, but calix[6]arenes react in a 1:1 molar ratio with M(2)CO(3) (M = K, Rb, Cs) to afford calix[6]arene dianions. Calix[8]arene (HC8) and p-tert-butylcalix[8]arene (Bu(t)()C8) have similar reactivity. The alkali metal salts of monoanionic calix[6]arenes are more conformationally flexible than the alkali metal salts of dianionic calix[6]arenes, which has been shown by their solution NMR spectra. X-ray crystal structures of HC6.Li and HC6.Cs indicate that the size of the alkali metal has some influence on the conformation of calixanions; for example, HC6.Li has a cone-like conformation, and HC6.Cs has a 1,2,3-alternate conformation. The calix[6]arene dianions show roughly the same structural architecture, and the salts tend to form polymeric chains. For most calixarene salts cation-pi arene interactions were observed.     

Relative binding affinities of alkali metal cations to

The binding affinity and selectivity of a new ionophore, [1(8)]starand (1), toward alkali metal cations in methanol were examined through NMR titration experiments and free energy perturbation (FEP) and molecular dynamics simulations. The preference was determined to be K(+) > Rb(+) > Cs(+) > Na(+) > Li(+) in both FEP simulations and NMR experiments. The FEP simulation results were able to predict the relative binding free energies with errors less than 0.13 kcal/mol, except for the case between Li(+) and Na(+). The cation selectivity was rationalized by analyzing the radial distribution functions of the M-O and M-C distances of free metal cations in methanol and those of metal-ionophore complexes in methanol.     

The solvent extraction of alkali metal picrates with 4,13-N,N'-dibenzyl-4,13-diaza-18-crown-6

Extraction of alkali metal picrates with N,N'-dibenzyl-18-crown-6 was carried out, with dichloromethane as water-immiscible solvent, as a function [ligand]/[metal cation]. The extractability of metal picrates (Li(+), Na(+), K(+), Rb(+), Cs(+)) was evaluated as a function of [L]/[M(+)]. The extractability of complex cation-picrate ion pairs decreases in this sequence: Li(+)>Rb(+)>Cs(+)>K(+)>Na(+). The overall extraction equilibrium constants (K(ex)) for complexes of N,N'-dibenzyl-18-crown-6 with alkali metal picrates between dichloromethane and water have been determined at 25 degrees C. The values of the extraction constants (logK(ex)) were determined to be 10.05, 6.83, 7.12, 7.83, 6.73 for Li(+), Na(+), K(+), Rb(+) and Cs(+) compounds, respectively. DB186 shows almost 2-fold extractability against Li(+) compared to the other metal picrates, whereas it shows no obvious extractability difference amongst the other metal cations when [L]/[M(+)] is 0.2-1. However, an increasing extractability is observed for Cs(+) when [L]/[M(+)] [1].     

配体数与电子化物的一阶超极化率的碱金属原子序数依赖性

用MP2方法得到单配位电子化物M—X(M=Li, Na, K; X=NH3, NCH, HF)和二配位电子化物M—(FH)2(M=Li, Na, K)的几何结构. 使用高水平的QCISD/6-311++G(3df, 3pd)计算了它们的一阶超极化率β0. 在单配位的电子化物中, 单调的一阶超极化率的碱金属原子序数依赖性未表现出来, 而二配位电子化物 M—(FH)2(M=Li, Na, K)的β0值随着碱金属原子序数的增加而增加, 这与文献报道的四配位相关体系的情况一致. 这表明, 电子化物中配位数与一阶超极化率碱金属原子序数依赖性相关.     

Electronic effect on protonated hydrogen-bonded imidazole trimer and corresponding derivatives cationized by alkali metals (Li(+), Na(+), and K(+))

The electronic effects on the protonated hydrogen-bonded imidazole trimer (Im)(3)H(+) and the derivatives cationized by alkali metals (Li(+), Na(+), and K(+)) are investigated using B3LYP method in conjunction with the 6-311+G( *) basis set. The prominent characteristics of (Im)(3)H(+) on reduction are the backflow of the transferred proton to its original fragment and the remoteness of the H atom from the attached side bare N atom. The proton transfer occurs on both reduction and oxidation for the corresponding hydrogen-bonded imidazole trimer. For the derivatives cationized by Li(+), (Im)(3)Li(+), the backflow of the transferred proton occurs on reduction. The electron detachment from respective highest occupied molecular orbital of (Im)(3)Na(+) and (Im)(3)K(+) causes the proton transferring from the fragment attached by the alkali metal cation to the middle one. The order of the adiabatic ionization potentials of (Im)(3)M(+) is (Im)(3)H(+)>(Im)(3)Li(+)>(Im)(3)Na(+)>(Im)(3)K(+); the order of (Im)(3)M indicates that (Im)(3)H is the easicst complex to be ionized. The polarity of (Im)(3)M(+) (M denotes H, Li, Na, and K) increases on both oxidation and reduction. The (Im)(3)M(+) complexes dissociate into (Im)(3) and M(+) except (Im)(3)H(+), which dissociates preferably into (Im)(3) (+) and H atom, while the neutral complexes [(Im)(3)M] dissociate into (Im)(3) and M. The stabilization energy of (Im)(3)Li(2+), (Im)(3)Na(2+), and (Im)(3)K(2+) indicate that their energies are higher as compared to those of the monomers.