Ionic association with anions of alizarin red S in aqueous solutions with surfactants

The formation of associates of single (H₂An⁻) or doubly charged anions (HAn²⁻) of alizarin red S with cations (Ct⁺) of cyanine dye pinacyanol in aqueous solution is considered. Thermodynamic values of equilibrium association constants were determined according to spectrophotometric data. Values of enthalpy of formation for the associates of the composition Ct⁺ · H₂An⁻ and (Ct⁺)₂ · HAn²⁻ were calculated with the help of semi-empirical methods. It was determined that the addition of cationic or anionic surfactant results in the destruction of associates.     

Association of anions of phenolsulfonephthalein and its alkyl-substituted derivatives with single-charged cations of polymethines

The interaction of single- and double-charged anions (HAn⁻, An²⁻) of sulfonephthaleins (phenolsulfonephthaleins and its alkyl-substituted derivatives, viz., o-cresolsulfonephthalein and thymolsulfonephthalein) with single-charged cations (Ct⁺) of polymethines (pinacyanol, quinaldine red) was studied. The interaction in an aqueous solution affords heteroassociates of stoichiometric composition (Ct⁺)·HAn⁻ and (Ct⁺)₂·An²⁻. The association constants were estimated from the spectrophotometric data. The enthalpies of formation of dye and heteroassociate ions were calculated and the most probable structure of the heteroassociates was deter- mined using the semiempirical methods.     

(Dicarbonyl)(π-cyclohexadienyl)iron iodide,trichlorostannate, and tris(cymantrenecarboxylato)stannate: Synthesis and molecular structures

A reaction of [(η⁵-C₆H₇)Fe(CO)₃]BF₄ with KI in acetone gave brown crystals of the complex [(η⁵-C₆H₇)Fe(CO)₂]I (I), which was treated with SnCl₂ in THF to form orange crystals of the complex [(η⁵-C₆H₇)Fe(CO)₂]SnCl₃ (II). A reaction of complex II with potassium cymantrenecarboxylate ((CO)₃MnC₅H₄COOK, or CymCOOK) in THF yielded yellow crystals of the complex [(η⁵-C₆H₇)Fe(CO)₂]Sn(CymCOO)₃ (III). Structures I–III were identified using X-ray diffraction. The fragment (η⁵-C₆H₇)Fe(CO)₂ in complexes I–III remains virtually unchanged. The Fe-I bonds in complex I (2.6407(3) Å) and the Fe-Sn bonds in complexes II and III (2.4854(3) and 2.4787(4) Å, respectively) are appreciably shorter than the sum of the covalent radii of the corresponding elements, probably because of an additional dative interaction of the d electrons of iron with the vacant d orbitals of iodine or tin.     

Neutral and monocationic dinuclear (carbonyl)(cyclopentadienyl)(phenylchalcogenate) iron complexes of the general formulas [(RC5H4)Fe(CO)EPh]2 and [(RC5H4)Fe(CO)EPh]2PF6 (E = S or Te; R = H or Me): Synthesis, molecular structures, and EPR spectra

Heating of the compounds (RC₅H₄)Fe(CO)₂TePh (R = H (I) and Me (II)) in heptane afforded the dinuclear complexes [(RC₅H₄)Fe(CO)TePh]₂ (III and IV, respectively). By oxidation with Fc⁺PF ₆ ^? , these complexes were transformed into the paramagnetic cationic complexes [(RC₅H₄)Fe(CO)TePh]₂PF₆ (V and VI, respectively). Structures III–V and [(C₅H₅)Fe(CO)SPh]₂PF₆ (VII) were characterized by X-ray diffraction.     

Synthesis and molecular structures of cymantrenecarboxylate derivatives of titanium(IV) and vanadium(III) cyclopentadienyl complexes and of copper(II) and manganese(II) lutidine complexes

The reactions of dimethyltitanocene borohydride and vanadocene with cymantrenecarboxylic acid CymCOOH gave the monomer (C₅H₄Me)₂Ti(OOCCym)₂ (I) and dimer (C₅H₅)V(OOCCym)₄V(C₅H₅) (II), respectively. Treatment of Cu(II) cymantrenylcarboxylate with excess lutidine gives the monomer (C₇H₉N)₂Cu(COOCym)₂ (III). The reaction of lutidine with a mixture of Cu(II) and Mn(II) bis-cymantrenecarboxylates affords the heterometallic trinuclear complex (C₇H₉N)Cu(OOCCym)₃Mn(OOCCym)₃Cu(C₇H₉N) (IV). The structures of I–IV were established by X-ray diffraction. In I and III, the cymantrenecarboxylate groups are terminal and in II and IV, they are bridging, which is also manifested as characteristic OCO stretching bands in the IR spectra.     

Breakdown of the Gouy-Chapman model for highly charged Langmuir monolayers: counterion size effect

Deviations from the classic Gouy-Chapman (GC) model due to the finite size of hydrated counterions were tested for negatively charged Langmuir monolayers with different surface charge densities. Monolayers with the largest charge density (>0.6 C.m(-2)) show an increase of the surface potential for a series of alkali metal cations from Li(+) to Cs(+) by 200-250 mV. The increase is similar for different monolayers and suggests that this effect is independent of the particular type of headgroup. The magnitude of variation is comparable with model estimations of the electrical double layer (EDL) potential implying that the deviation from the GC model is drastic. Deviations from the GC model rapidly vanish with decreasing monolayer charge density and become hardly observable below 0.3 C.m(-2). For monolayers with a high charge density on subphases containing different sized counterions, preferential participation of the smallest ions in the EDL should be favorable in terms of electrostatic free energy because of packing density limitations. This effect was demonstrated for behenyl sulfate (BS) monolayers (0.64 C.m(-2)) with the X-ray reflectivity technique. For the Cs(+)-Li(+) system, the fraction of Cs(+) in the EDL is 50-60% compared with only 10% of Cs(+) in the subphase. Providing high surface charge density, a small univalent Cs(+) is capable to compete even with a bulky divalent Mg(2+). For equal concentrations of Cs(+) and Mg(2+) in the subphase, the Cs(+)/Mg(2+) ratio in EDL of BS monolayer is 1.3 to 2.0 (in contrast to 0.04, predicted by the GC model). All experimental results of this study are described in terms of packing density limitations for hydrated counterions in the EDL.     

Effect of surface traps on relaxation of injected charge in dielectric films

The problem of relaxation of the charge injected into a dielectric film has been analytically solved taking into account its conductivity and carrier trapping by both bulk and surface deep traps with fast (almost instantaneous) charging and finite discharge rates. The charge behavior in one-zone and two-zone relaxation modes has been analyzed. In particular cases, general analytical expressions give previously published results. Numerical calculations and an analysis of experimental data for titanium dioxide films deposited on metal substrates confirm the applicability of the developed model.