Consequences of Substitution in the Photoelectron Spectra of [2, 2]Paracyclophanes: Separation of ‘through-space’ and ‘through-bond’ interactions as a consequence of fluorosubstitution

The PE. spectra of [2, 2]paracyclophane ( 1 ), 4-amino[2, 2]paracyclophane ( 2 ) and 1, 1, 2, 2, 9, 9, 10, 10-octafluoro[2, 2]paracyclophane ( 3 ) are presented. The bands corresponding to ejection of the photoelectron from the five highest occupied π-orbitals have been assigned. The ‘observed’ orbital energies (i.e. the negative ionization potentials) are discussed in terms of ‘through space’ and ‘through-bond’ interactions between the semi-localized π-orbitals ( e_1g ) of the benzene moieties and the C, C-σ-orbitals of the ethylene bridges. The PE. spectrum of 3 shows that the fluorine-induced lowering of the C, C-σ-orbital energy effectively ‘turns-off’ the ‘through-bond’ interaction. The resulting pattern of the first four bands confirms the assignment given for 1 . Finally the band shifts induced by an amino group in position 4 are again in agreement with this assignment. Attention is drawn to the phenomenon of ‘orbital switching’ as a consequence of substitution in loosely coupled systems such as 1 .     

DFT and IsoStar Analyses to Assess the Utility of σ- and π-Hole Interactions for Crystal Engineering

The interpretation of 36 charge neutral ‘contact pairs’ from the IsoStar database was supported by DFT calculations of model molecules 1 – 12 , and bimolecular adducts thereof. The ‘central groups’ are σ-hole donors (H₂O and aromatic C−I), π-hole donors (R−C(O)Me, R−NO₂ and R−C₆F₅) and for comparison R−C₆H₅ (R=any group or atom). The ‘contact groups’ are hydrogen bond donors X−H (X=N, O, S, or R₂C, or R₃C) and lone-pair containing fragments (R₃C−F, R−C≡N and R₂C=O). Nearly all the IsoStar distributions follow expectations based on the electrostatic potential of the ‘central-’ and ‘contact group’. Interaction energies (ΔE^BSSE) are dominated by electrostatics (particularly between two polarized molecules) or dispersion (especially in case of large contact area). Orbital interactions never dominate, but could be significant (∼30 %) and of the n/π→σ*/π* kind. The largest degree of directionality in the IsoStar plots was typically observed for adducts more stable than ΔE^BSSE≈−4 kcal⋅mol⁻¹, which can be seen as a benchmark-value for the utility of an interaction in crystal engineering. This benchmark could be met with all the σ- and π-hole donors studied.     

Inverted Hyperconjugation in Symmetrical 1,4-Dihalocubanes

The σ-orbital manifold of cubane 1 , as suggested by its PE spectrum, is divided into two sets separated by a 3 eV gap extending from ～ -10.5 eV to ～ -13.5 eV. Halogen substituents with np AO basis energies falling into this gap (e.g. Cl or Br) will, therefore, hyperconjugate appreciably with both sets. Interaction with the lower-lying set will lead to the usual destabilization (‘normal’ hyperconjugation), whereas interaction with the set above will necessarily lead to a ‘stabilization’ (‘inverted’ hyperconjugation). As a result the lone-pair ionization energies of Cl or Br substituted cubanes (derived from PE spectra) are much larger than naively expected for an alkyl halide containing as much as 8 C-atoms. In particular no significant shift of the e lone-pair bands in the PE spectra of 1,4-dichloro- and 1,4-dibromocubane can be detected with respect to the first ionization energies of the free atoms Cl and Br, or of HCl and HBr.     

Primary-particle-beam-induced reduction of silver acetate in glycerol solutions to form a silver mirror

The liquid SIMS mass spectra of silver acetate dissolved in a glycerol matrix is discussed, with emphasis on the formation of a ‘silver mirror’ on the surface of the glycerol droplet owing to reduction of the silver acetate. Silver clusters containing up to three silver atoms have been observed from this mirrored surface; Ag₃⁺ cluster ions are not observed in the spectrum when conditions are such that the mirror is not formed. For example, use of a slightly oxidizing matrix (o-nitrophenyl octyl ether or m-nitrobenzylalcohol) prevents formation of the ‘mirror’; only Ag⁺ is sputtered from this surface.     

Die Photoelektronen-Spektren des Tricyclo[4.2.1.02,5]nonadiens und seines 3,4-Diaza-Analogons. Ein Beitrag zur Kenntnis der Wechselwirkung zwischen den einsamen Elektronenpaaren der cis-konfigurierten Azogruppe

A comparative photoelectron spectroscopical investigation of the title compound ( 11 ) and its 3,4- and 7,8-dihydro derivatives ( 9 and 10 ) indicates that a considerable ‘through bond’ interaction exists between the π-orbitals in 11 . The PE. spectra of the 3,4-diaza-analogue of 10 and 11 , which contain a cis azo group in a four-membered ring, yield a splitting Δ_n (4-memb. ring) = 1.55–1.60 eV between the nitrogen lone-pair orbital energies. This value contrasts with those obtained for a three-membered ring analogue (3,3-dimethyldiazirine ( 5 ), Δ_n (3-memb. ring) = 3.55 eV) and for a five-membered ring analogue (2,3-diazanorbornene ( 7 ) Δ_n(5-memb. ring) = 3.10 eV). The sequence Δ_n (3-memb. ring) > Δ_n (4-memb. ring) Δ_n (5-memb. ring) is satisfyingly reproduced by MINDO/2- and EHT-calculations for the model systems with n = 3,4,5. A similar trend can be deduced from MINDO/2-calculations for cis-diimid where Δ_n becomes minimal for a N?N? H angle φ ≈ 100°, whereas Δ_n for the corresponding trans-structure goes through a maximum in this region. The experimental finding as well as the calculated results confirm the predictions made by Gimarc [15] who attributes the behaviour of Δ_n for cis-azo groups to a ‘through-bond’ interaction of the n ₊-orbital with a lowerlying N? N σ-orbital; this interaction becomes maximal for N?N? R angles of the size present in a fourmembered ring, e.g. in 12 or 13 .     

A theoretical approach to substituent effects: Interaction between directly bonded groups in the isoelectronic series XNH3+, XCH3, and XBH3−

Ab initio molecular orbital theory including full geometry optimization at the 4-31G level is used to examine the interactions between substitutents X(X = Li, BeH, BH₂, CH₃, NH₂, OH and F) and substrates Y(Y = NH₃⁺, CH₃, BH₃^?) in the isoelectronic series XNH₃⁺, XCH₃ and XBH₃^?. The results indicate that the interaction energies are dominated by σ-effects. NH₃⁺ is found to interact favorably with the σ-donors (e.g. Li, BeH and BH₂) and unfavorably with the σ-acceptors (e.g. F, OH, NH₂). The reverse pattern a observed for XBH₃^?. The range of interaction energies for XCH₃ is considerably smaller than for XNH₃⁺ and XBH₃^?.     

Influence of the Axial Alkyl Ligand on the Reduction Potential of Alkylcob(III)alamins and Alkylcob(III)yrinates

The irreversible-reduction potentials of 26 alkylcob(III)alamins (RCbl^III 1a – z ) and 26 alkylcob(III)yrinates (R‘Cby’^III; 2a – z ) (E_p 1a – z and E_p 2a – z , resp.) have been measured in situ by single-scan voltammetry of hydroxocob(III)alamin hydrochloride (vitamin B_12b- HCl; 1 ) or heptamethyl cob(II)yrinate perchlorate (ClO₄‘Cby’^II; 2 ) in presence of the corresponding alkyl halides (RX; 3a – z ) in DMF. The reduction potentials of alkylcobalt complexes exhibiting half-life times as short as a few seconds become measurable by this technique. Thermodynamic cycles prove that the observed reduction potentials are closely related to the standard reduction potentials E°(R? Co^III + e^??R? + Co^I). Electron-withdrawing groups and/or an increased degree of substitution at the Co-bound C-atom in RCbl^III and, R‘Cby’^III shift E_p( 1a – z ) and E_p ( 2a – z ) towards positive potentials. Linear correlations have been found between E_p( 1a – z ) (E_p( 2a – z )) of RCbl^III (R‘Cby’^III) and the pK_a of RH (or the Taft σ*- or the Hammett σ-values of R) within each class of R, i. e. MeCbl^III (Me‘Cby’^III), primary RCbl^III (R‘Cby’^III) and secondary RCbl^III (R‘Cby’^III). The correlations allow to distinguish between electronic effects of the Co-bound alkyl residues and their steric interactions with the corrin side chains. The correlations have further been used to visualize the light-induced formal insertion of an olefin into the Co, C-bond of an alkylcobalamin (Scheme 2, 1a → 1u ), a key step in the vitamin-B₁₂-catalized C, C-bond formation.     

Dosimetry in photochemistry

Abstract— A method of dosimetry which is useful in analyzing complex photochemical reactions involving more than one photoproduct is described. This involves determining a photochemical cross section for each of the products, σ_B, σ_c…., and an absorption cross section σ. for the reacting species. The ratio σ_B/σ_a is the quantum yield for production of product B. Where a number of photoproducts are produced simultaneously, it is convenient to express ‘dose’ in terms of the average number of photons per cm²‘seen’ by each molecule in the vessel. This average can be calculated from the number of incident photons, the volume of the liquid, the absorbance and the path length. Experimental details of the irradiation facility which is convenient for such studies are presented. The method of dosimetry is illustrated using photochemical data for uracil and orotic acid in solution.     

Transition-Metal Complexes with Bidentate Ligands Spanning trans-Positions. III. Preparation and solution studies of complexes [MX(1)] (M = Cu,Ag and Au; X = anionic ligand; 1 = 2, 11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene)

The preparation of monomeric complexes [MX( 1 )] is reported where M = Cu, Ag, Au; X = I, Cl, NO₃, BF₄ and 1 = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene. The solution structure of the complexes is discussed on the basis of molecular weight, conductivity and NMR. measurements. In acetonitrile and nitromethane, the nitrate and fluoroborate complexes exist as ionic species [M( 1 )]⁺X^? whereas the halo-complexes are present as equilibrium mixtures of ‘covalent’ and ‘ionic’ forms. All the complexes are associated in CH₂Cl₂-solutions. The values of ¹J show that this association in [Ag(NO₃) ( 1 )] and [Ag(BF₄) ( 1 )] is best described in terms of ion-pairing while that for species [AgX( 1 )] (X = Cl, Br and I) is mainly ‘covalent’ in nature. Evidence is presented for the formation of the complex ion [Ag(CH₃CN)_n( 1 )]⁺ in acetonitrile solution.     

STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—VI. AB INITIO CONFIGURATION INTERACTION CALCULATIONS ON THE GROUND AND LOWER EXCITED SINGLET AND TRIPLET STATES OF ETHYL BACTERIOCHLOROPHYLLIDE-a AND ETHYL BACTERIOPHEOPHORBIDE-a‡

Abstract— Ab initio quantum mechanical calculations on ethyl bacteriochlorophyllide-a (Et-BChl-a) and ethyl bacteriopheophorbide-a (Et-BPheo-a) are presented, including self-consistent-field (SCF) molecular orbital studies on the ground states using the molecular fragment procedure, and configuration interaction (CI) calculations on the low-lying singlet and triplet states and absorption spectra. A characterization and comparison of many of the higher-lying molecular orbitals obtained from the SCF studies is presented. The estimated first ionization potentials are 5.66 and 5.97 eV for Et-BChl-a and Et-BPheo-a, respectively. Excited state calculations show that the visible spectrum of both molecules consists of an intense, y-polarized S₁← S₀ transition and a weakly-allowed, x-polarized S₂← S₀ transition. Both S₁ and S₂ states are ¹(π, π*) in character, and are described by a four-orbital model. Transitions to the remaining calculated states, S₃-S₁₂, appear in the Soret region of the spectrum of both molecules. However, only transitions to S₉(‘x’), S₁₀(‘x’) and S₁₁(‘y’) of Et-BChl-a, and S₇(‘x’) and S₁₀(‘y’) of Et-BPheo-a are of high intensity. The composition of the high intensity Soret states is ¹(π, π*) and strongly “four-orbital” in nature. The lowest triplet state, T₁, is predicted to lie 9752 cm^-1 and 7880 cm^-1 above S₀ for Et-BPheo-a and Et-BChl-a, respectively. In each molecule T₂ and S₁ are nearly degenerate, suggesting a favorable pathway for intersystem crossing. Calculated T_n← T₁ transitions indicate that the y-polarized T₁₂← T₁ transition in Et-BChl-a corresponds to the observed intense 24,400 cm^-1 absorption in the triplet-triplet spectrum of BChl-a. A similar type spectrum is also predicted for BPheo-a.     

The effect of basis set superposition error on the convergence of interaction energies

 For the intermolecular interaction energies of ion-water clusters [OH⁻(H₂O) _n (n=1,2), F⁻(H₂O), Cl⁻(H₂O), H₃O⁺(H₂O) _n (n=1,2), and NH₄ ⁺(H₂O) _n (n=1,2)] calculated with correlation-consistent basis sets at MP2, MP4, QCISD(T), and CCSD(T) levels, the basis set superposition error is nearly zero in the complete basis set (CBS) limit. That is, the counterpoise-uncorrected intermolecular interaction energies are nearly equal to the counterpoise-corrected intermolecular interaction energies in the CBS limit. When the basis set is smaller, the counterpoise-uncorrected intermolecular interaction energies are more reliable than the counterpoise-corrected intermolecular interaction energies. The counterpoise-uncorrected intermolecular interaction energies evaluated using the MP2/aug-cc-pVDZ level is reliable. Received: 14 March 2001 / Accepted: 25 April 2001 / Published online: 9 August 2001     

Bildung ionischer NO- und NO2-Komplexe von aromaten in der Gasphase

The Production of NO⁺- and NO₂⁺- intermediate complexes formed by nitration of aromatic compounds by means of ion-molecule reactions in the gas phase were attempted. The experiments were performed with benzene, pyridine and toluene respectively and with NO⁺, NO₂⁺ CH₃NO₂⁺ and CH₂ONO₂⁺ als ‘nitration’ ions. Aromatic NO+-as well as NO₂⁺-complexes were observed with varying reaction cross-sections. The determined lower limit of bonding energy of 16 kcal/mol for to be σ-complexes. This fact was regarded as additional support for the analogy between electrophilic substitution reactions and ion-molecule reactions.     

Synthesis of macrocyclic tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane in carbonic acid solution

The possibility to synthesize stereoregular tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane (tris-cis-tris-trans-[PhSi(O)OH]12) in an inorganic liquid medium – aqueous carbonic acid solution – was shown. The interaction of polyhedral phenylcoppersodiumsiloxane, {[(C₆H₅Si(O)O^?]₁₂(Cu₂⁺)₄(Na⁺)₄}*(L)_m (L?=?Buⁿ OH, H₂O), with carbonic acid can be considered as a new ‘green’ method to obtain functional organosiloxane macrocycles. In contrast to the known methods, no organic solvents were used during the reaction. The identification of the structure of the end compound was performed by means of NMR and Infrared spectroscopy as well as X-ray crystallography.     

Fragmentation of ion–molecule adducts of transition metal ions with aromatic ring-containing nitriles in the gas phase

Gas-phase ion–molecule reactions of transition metal ions, M⁺ (M⁺ = Ni⁺, Co⁺, Fe⁺ and Mn⁺), with six aromatic ring-containing nitriles were investigated in a modified fast atom bombardment (FAB) source. It is shown that the monoadduct, (Ph(CH₂)_nCN)–M⁺, is one of the most abundant ion–molecule reaction products. The main fragments in the FAB source are the [C₇H₇]⁺ and [C₈H₉]⁺ ions, and their formation is shown to involve metal ion insertion into the nitriles rather than direct bond cleavage from the ‘free’ or complexed nitriles after FAB ionization. An intramolecular oxidation–reduction reaction, giving [C₇H₇]⁺, is found in the metastable and collisionally induced dissociations of benzyl nitrile adducts accompanied by neutral MCN formation, but not seen for longer chain samples. An ortho effect is observed in the elimination of HCN from the 2-methylbenzyl nitrile adduct ions. This reaction dominates the metastable ion spectrum of the adduct of Mn⁺, whereas metal detachment is nearly the major process for the other complexes of Mn⁺. The different bond-insertion selectivities of the metal ions are also shown.     

The ESI CAD fragmentations of protonated 2,4,6‐tris(benzylamino)‐ and tris(benzyloxy)‐1,3,5‐triazines involve benzyl–benzyl interactions: a DFT study

The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6‐tris(benzylamino)‐1,3,5‐triazine (1) and 2,4,6‐tris(benzyloxy)‐1,3,5‐triazine (6) show abundant product ion of m/z 181 (C₁₄H₁₃⁺). The likely structure for C₁₄H₁₃⁺ is α‐[2‐methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the ‘N’ analog (1) but low for the ‘O’ analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H‐toluene]⁺ and [M + H‐benzene]⁺ for compounds 1 and 6, respectively. The protonated 2,4,6‐tris(4‐methylbenzylamino)‐1,3,5‐triazine (4) exhibits competitive eliminations of p‐xylene and 3,6‐dimethylenecyclohexa‐1,4‐diene. Moreover, protonated 2,4,6‐tris(1‐phenylethylamino)‐1,3,5‐triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring ‘N’. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H‐shift from ring carbon to ‘O’ generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium‐labeling and CAD experiments combined with DFT calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

Enthalpic pair interaction coefficients in DMF solution

Dissolution enthalpies of NaI in mixtures of N,N-dimethylformamide with urea, formamide, acetamide and N,N-dimethylacetamide were measured. The results were compared with data measured earlier for other DMF — non-electrolyte mixtures. The enthalpic pair interaction coefficients,h _xy (Na⁺I^? — non-electrolyte) in DMF were calculated and analysed together with the appropriate data concerning other Na⁺I^? — non-electrolyte pairs in DMF. The group interaction coefficients illustrating the interactions of Na⁺I^? with the CH₂, OH, O, CO, ‘Pep’ and ‘iPep’ groups were determined and discussed.     

Quantitative Assessment of Ligand Substituent Effects on σ- and π-Contributions to Fe−N Bonds in Spin Crossover FeII Complexes

The effect of para-substituent X on the electronic structure of sixteen tridentate 4- X -(2,6-di(pyrazol-1-yl))-pyridine ( bpp^X ) ligands and the corresponding solution spin crossover [Fe^II( bpp^X )₂]²⁺ complexes is analysed further, to supply quantitative insights into the effect of X on the σ-donor and π-acceptor character of the Fe- N_A (pyridine) bonds. EDA-NOCV on the sixteen LS complexes revealed that neither ΔE_orb,σ+π (R²=0.48) nor ΔE_orb,π (R²=0.31) correlated with the experimental solution T_1/2 values (which are expected to reflect the ligand field imposed on the iron centre), but that ΔE_orb,σ correlates well (R²=0.82) and implies that as X changes from EDG → EWG (Electron Donating to Withdrawing Group), the ligand becomes a better σ-donor. This counter-intuitive result was further probed by Mulliken analysis of the N_A atomic orbitals: N_A (p_x) involved in the Fe−N σ-bond vs. the perpendicular N_A (p_z) employed in the ligand aromatic π-system. As X changes EDG → EWG , the electron population on N_A (p_z) decreases, making it a better π-acceptor, whilst that in N_A (p_x) increases, making it a better σ-bond donor; both increase ligand field, and T_1/2 as observed. In 2016, Halcrow, Deeth and co-workers proposed an intuitively reasonable explanation of the effect of the para- X substituents on the T_1/2 values in this family of complexes, consistent with the calculated MO energy levels, that M→L π-backdonation dominates in these M−L bonds. Here the quantitative EDA-NOCV analysis of the M−L bond contributions provides a more complete, coherent and detailed picture of the relative impact of M−L σ-versus π-bonding in determining the observed T_1/2, refining the earlier interpretation and revealing the importance of the σ-bonding. Furthermore, our results are in perfect agreement with the ΔE(HS-LS) vs. σ_p⁺(X) correlation reported in their work.     

Complexes of the Triolide from (R)-3-Hydroxybutanoic Acid with Sodium,Potassium, and Barium Salts: Crystal Structures,Ester Chelates and Ester Crowns,Crystal Packing,Bonding, and Electron-Localization Functions

The triolide of (R)-3-hydroxybutanoic acid ((R,R,R,))-3,7,11-trimethyl-2,6,10-trioxadodecane-1,5,9-trione; ( 1 ), readily available from the corresponding biopolymer P(3-HB) in one step, forms crystalline complexes with alkali and alkaline earth salts. The X-ray crystal structures of three such complexes, (3 NaSCN)·4 1 ( 2 ), (2 KSCN)·2 1 · H₂O ( 3 ), and (2) Ba(SCN)₂ · 2 1 · 2 H₂O · THF ( 4 ), have been determined and are compared. The triolide is found in these structures (i) as a free molecule, making no contacts with a cation (clathrate-type inclusion), (ii) as a monodentate ligand coordinated to a single ion with one carbonyl O-atom only, (iii) as a chelator, forming an eight-membered ring, with two carbonyl O-atoms attached to the same ion, (iv) as a linker, using two carbonyl O-atoms to bind to the two metals of an ion-X-ion unit (ten-membered ring), and (v), in a crown-ester complex, in which an ion is sitting on the three unidirectional C?O groups of a triolide molecule (Figs. 1–3). The crystal packing is such that there are columns along certain axes in the centers of which the cations are surrounded by counterions and triolide molecules, with the non-polar parts of 1 on the outside (Fig. 4). In the complexes 2–4 , the triolide assumes conformations which are slightly distorted, with the carbonyl O-atoms moved closer together, as compared to the ‘free’ triolide 1 (Fig. 5). These observed features are compatible with the view that oligo (3-HB) may be involved in the formation of Ca polyphosphate ion channels through cell membranes. A comparison is also made between the triolide structure in 1–4 and in enterobactin, a super Fe chelator (Fig. 5). To better understand the binding between the Na ion and the triolide carbonyl O-atoms in the crown-ester complex, we have applied electron-localization function (ELF) calculations with the data set of structure 2 , and we have produced ELF representations of ethane, ethene, and methyl acetate (Figs. 6–9). It turns out that this theoretical method leads to electron-localization patterns which are in astounding agreement with qualitative bonding models of organic chemists, such as the ‘double bond character of the CO? OR single bond’ or the ‘hyperconjugative n → σ* interactions between lone pairs on the O-atoms and neighbouring σ-bonds’ in ester groups (Fig. 8). The noncovalent, dipole/pole-type character of bonding between Na⁺ and the triolide carbonyl O-atoms in the crown-ester complex (the Na? O?C plane is roughly perpendicular to the O? C?O plane) is confirmed by the ELF calculation; other bonding features such as the C?N bond in the NaSCN complex 2 are also included in the discussion (Fig. 9).     

Valence-bond calculations on N2 and isoelectronic species

Valence-bond calculations are reported for the isoelectronic series of molecules and ions: N₂, CO, BF, NO⁺ and CN^?. The most important structures are N?N, C?O, B_π? F, N⁺?O and C?N. Hybridization of the 2s and 2p orbitals is important. Only two or three structures are required to obtain an energy lower than that obtained with the molecular orbital approximation. Structures in which the electronegative element loses a σ-orbital or gains a π-orbital are favored. π-bonds tend to be favored over σ-bonds. The bond in NO⁺ resembles that in CO, whereas that in CN^? resembles the bonding in N₂.     

Effect of the lithium cation on the sorption and electrical properties of amphiphilic block copolymers and their composites

The use of lithium cation in composites of block copolymers [polyethylene‐b‐polyethylene oxide (PE‐b‐50%PEO and PE‐b‐80%PEO)] and their derivatives was tested as a modifier of the vapor sorption and impedance of these complexes. The block copolymer PE‐b‐80%PEO was modified by oxidation of its hydroxyl end group to both a carboxylic acid group (PE‐b‐80%PEO)CH₂COOH and its sodium salt (PE‐b‐80%PEO)CH₂COO^? Na⁺ for the purpose of improving its compatibility and performance as a matrix for composites. These modified copolymers were characterized by FTIR, DSC, and mass spectrometry. The sorption of water of these copolymers and their composites with lithium nitrate was also compared, as well as the electrical properties of their composites were measured by electrical impedance spectroscopy. For the composites obtained with PE‐b‐80%PEO and lithium nitrate, it was found that lithium cation plays an important role increasing the sorption rate, which is maximized for the PE‐b‐80%PEO + (21% lithium nitrate) composite. For the copolymers (PE‐b‐80%PEO)CH₂COOH and (PE‐b‐80%PEO)CH₂COO^? Na⁺ and their composites, the highest sorption rate was observed for salt in the following order: COO^? Na⁺ > COOH > OH. The PE‐b‐80%PEO + (21% lithium nitrate) composite behaves as a solid polymeric ionic conductor fitting the Williams–Landel–Ferry equation. However, both (PE‐b‐80% PEO)CH₂COOH and (PE‐b‐80%PEO)CH₂COO^? Na⁺ + (21% lithium nitrate) composites fitted the Variable Range Hopping equation, indicating a conductance trend with temperature governed by a thermally activated with energy of 0.482 and 0.524 eV and not by a relaxation process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1809–1817, 2010