Effect of Metal Alkoxide Complexes on Condensation Reactions of Hydrolyzed Phenyltriethoxysilane

Metal alkoxide complexes, in which alkoxy groups were substituted with ethyl acetoacetate (EAcAc), were found to accelerate condensation reactions of hydrolyzed phenyltriethoxysilane (PTES) and affect the structure of phenylsiloxane networks. The ²⁹Si NMR study revealed that the acceleration effect increased in the order Al(O-sec-C₄H₉)_3–x (EAcAc) _x < Ta(OC₂H₅)_5–x (EAcAc)_x < Ti(OC₂H₅)_4–x (EAcAc) _x . However, the GPC study revealed that the solution contained the high molecular weight species in the order Al(O-sec-C₄H₉)_3–x (EAcAc) _x < Ti(OC₂H₅)_4–x (EAcAc) _x < Ta(OC₂H₅)_5–x (EAcAc) _x . In the case of Ti(OC₂H₅)_4–x (EAcAc) _x , the smaller size of phenylsiloxane networks with a low content of silanol groups was formed in the solution. In the case of Ta(OC₂H₅)_5–x (EAcAc) _x , the larger size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. In the case of Al(O-sec-C₄H₉)_3–x (EAcAc) _x , the small size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. During gelation, the catalytic effect of the metal alkoxide complexes on the development of phenylsiloxane networks was also found. However, the average molecular weight of the gels increased in the order Ta(OC₂H₅)_5–x (EAcAc) _x < Ti(OC₂H₅)_4–x (EAcAc) _x Al(O-sec-C₄H₉)_3–x (EAcAc) _x . The metal alkoxide complexes were hydrolyzed and finally incorporated into the phenylsiloxane networks of gels to form M—O—Si bonds, which were indicated by the results of FT-IR analysis.     

29Si and 17O NMR investigations on Si−O−Ti bonds in solutions of diphenylsilanediol and titanium-tetra-isopropoxide

The structural units in diphenylsilanediol/titanium-isopropoxide solutions with molar ratio Si:Ti between 1:0.1 and 1:5 were examined by means of ²⁹Si and ¹⁷O NMR. The main component in solutions with molar ratio Si/Ti=1:0.1 is the chain-like octaphenyltetrasiloxanediol. With increasing Ti-isopropoxide content (1:0.25–1:05) Si–O–Ti units of the spirocyclic titanosiloxane Ti[O₅Si₄(C₆H₅)₈]₂ prevail in the solutions accompanied by the chain-like tetrasiloxanediol. The ²⁹Si NMR spectra of 1:1 solutions indicate a lot of different Si containing building units with chemical shifts mainly between-40 and-46 ppm. The signals with a chemical shift between-40 and-46 ppm are probably caused by Si atoms which are connected via oxygen bridges directly (Si–O–Ti) or indirectly (Si–O–Si–O–Ti) with titanium. Contrary to the 1:1 solutions only one or two different species with Si–O–Ti units are present in high Ti-alkoxide containing solutions (1:5). ²⁹Si and ¹⁷O NMR results reveal a quick hydrolysis of the Ti–O–Si bonds to titanium-oxo-hydroxo-polymers and phenylsiloxanediols or their isopropyl esters after the addition of water to the solutions. This separation into species only containing either Ti–O–Ti or Si–O–Si bonds can entail a decreased homogeneity of the reaction products on a molecular level.     

Effect of Inorganic Components on Thermal Stability of Methylsiloxane-Based Inorganic/Orgnaic Hybrids

The thermal decomposition behavior of methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides such as Si(OCH₃)₄, Al(O^sC₄H₉)₃, Ti(OⁱC₃H₇)₄ and Nb(OC₂H₅)₅ was investigated by means of thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The decomposition temperature of methyl groups in methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides was higher than that in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. In particular, when incorporating Nb and Ti inorganic components, methyl groups in methylsiloxane-based inorganic/organic hybrids decomposed at about 100 and 200^∘C higher temperatures, respectively, than those in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. The incorporation of an inorganic component other than siloxane into methylsiloxane-based inorganic/organic hybrids was found to thermally stabilize the methyl groups of methylsiloxane networks.     

Preparation of Silicates Using HSi(OC2H5)3 and Their NO x -Adsorption Behavior

The preparation and NO-adsorption/desorption behavior of Li, Ca and Ba silicates were investigated aiming at the application to a NO_x-absorbent. Li silicate was prepared by reaction of HSi(OC₂H₅)₃ with aqueous lithium silicate solution (LSS). Ca and Ba silicates were prepared from gels obtained using CH₃Si(OC₂H₅)₃, Si(OC₂H₅)₄, HSi(OC₂H₅)₃ and alkaline-earth alkoxides. The surface of these silicates indicated the solid basicity of H₀ = 9 and adsorbed the acidic gas of NO. FT-IR spectra of the silicates adsorbing NO showed the absorption peaks in the range of 1300–1600 cm^{– 1} corresponding to ionic and covalent nitrate NO₃^–. The complete desorption of adsorbed NO species occurred above 500°C in the Li silicate, above 500°C in the Ca and Ba silicates prepared using CH₃Si(OC₂H₅)₃, and above 700°C in the Ba and Ca silicates prepared using Si(OC₂H₅)₄. Regarding the Ca and Ba silicates, the difference in siloxane structure is thought to cause the difference in adsorption state and desorption behavior of NO.     

Alkyloxy- and aryloxy-titanocenes: Synthesis, solid-state structure and cyclic voltammetric studies

Alkyloxy- and aryloxy-functionalized titanocenes of type [Ti](Cl)(OR) (R = Me (2), CH₂PPh₂ (3), CH₂Fc (4), C₆H₅ (5), C₆H₄-4-CN (6), C₆H₄-4-NO₂ (7), C₆H₄-4-Me (8), C₆H₄-4-OMe (9), C₆H₄-4-C(O)Me (10), C₆H₄-4-CO₂Me (11), C₆H₄-3-NO₂ (12); [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; Fc = (η⁵-C₅H₄)(η⁵-C₅H₅)Fe) were synthesized by the reaction of [Ti]Cl₂ (1) with ROH in a 1:1 molar ratio and in presence of Et₂NH. Diaryloxy-titanocenes (e.g., [Ti](OC₆H₄-4-NO₂)₂ (13)) are accessible, when the ratio of 1 and ROH is changed to 1:2. This synthesis methodology also allowed the preparation of dinuclear complexes of composition ([Ti](Cl))₂(μ-OC₆H₄O) (14) and ([Ti](Cl)(μ-OC₆H₄-4))₂ (15) by the reaction of 1 with hydroquinone or 1,1′-dihydroxybiphenyl in a 2:1 stoichiometry.Cyclic voltammetric studies show the characteristic [Ti(IV)/Ti(III)] reductions. It was found that the potentials of the alkyloxy titanocenes 2–4 do not differ, while for the aryloxy-titanocenes 5–15 the reduction potentials correlate linearly with the σ_p/m Hammett substituent constants showing a strong influence of the substituents on the electron density at titanium.The structures of titanocenes 4, 5, 9, and 11–13 in the solid state are reported. Typical for these organometallic sandwich compounds is a distorted tetrahedral coordination geometry around titanium with D1–Ti–D2 angles (D1, D2 = centroids of the cyclopentadienyl ligands) of ca. 130 °. In comparison to FcCH₂O-functionalized 4, for the aryloxy-titanocenes 5, 9, and 11–13 a significant larger Ti–O–C angle was found confirming electronic interactions between the titanium atom and the appropriate aryl group.     

Activation of the Ti(OC4H9)4-Al(C2H5)3 catalytic system in the selective dimerization of ethylene to 1-butene by the grignard reagent

The effect of an organomagnesium compound on the dimerization of ethylene to 1-butene was studied. The organomagnesium compound increases the catalytic activity of the Ti(OC₄H₉)₄-Al(C₂H₅)₃ system by 5–10 times. A high degree of selectivity (up to 99%) with respect to 1-butene was obtained. This makes it possible to eliminate a series of technological difficulties involved in the industrial production of 1-butene. The kinetics of the reduction of Ti(OC₄H₉)₄ by butylmagnesium chloride were studied by ESR and polarography.Chernogolovka Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2277–2283, October, 1992.     

Low-Temperature Preparation of (Ba,Sr)TiO3 Perovskite Phase by Sol-Gel Method

We have investigated on the synthesis of Ba_{1 – x}Sr_xTiO₃ (BST, x = 0.0–1.0) solid solution at low temperature by a sol-gel method using precursor solutions of Ba(OC₂H₅)₂, Sr(OC₂H₅)₂, and Ti(OCH(CH₃)₂)₄ dissolved in 2-methoxyethanol. Crystalline BST solid solution monolithic gels were obtained as dried at 90°C. Crystalline fraction of BST gels increased with increasing concentration of the precursor solution and increasing amount of the hydrolysis water used. Ba_0.4Sr_0.6TiO₃ (x = 0.6) gels from a precursor solution of 0.5 mol/l with hydrolysis water of H₂O/Ti = 50 crystallized during aging at 30°C.     

Oligomerization of ethylene catalyzed by Ti(OR)4-alkylaluminium catalysts

Ti(OC₆H₄CH₃)₄ in combination with Et₃Al₂Cl₃ and Et₃Al forms an active catalytic system for oligomerizing ethylene to low molecular weight -olefins. At room temperature with Ti(OC₆H₄CH₃)₄–Et₃Al C₄–C₁₀ -olefins are formed. At elevated temperature and under the influence of various phosphorus additives Ti(OC₆H₄CH₃)₄–Et₃Al₂Cl₃ yields linear olefins in the C₄–C₂₀ range. Selectivities greater than 97% could be achieved in most cases with the Ti(OR)₄–Et₃Al₂Cl₃-additive system.     

Fourier Transform and Multi Dimensional EPR Spectroscopy for the Characterization of Hydroxyapatite Gels

Calcium hydroxyapatite powder was prepared by the sol-gel method, using calcium acetate and PO(OC₂H₅)₃ as initialcompounds, and alcohol(methyl, ethyl, and propyl-alcohol) as solvent. Homogenous solutions andgels were prepared, using a molar ratio of Ca / P = 1.67. Theevolution of the structure was followed by XRD (X-ray diffraction), IR(Infrared), and FT-n(= 1, 2, 3)D-EPR (Fourier transform Electron Paramagnetic Resonance) spectroscopy. The dried gel exhibits a signalcharacterized by a central line and two satellites. The 2D spectrum(Electron Spin Echo Envelop Modulation ESEEM vs. field sweep) showed thesame modulation for the central line. The FT-EPR spectrum vs. field sweep2D-spectrum indicated that the satellites are due to an hfs splitting withwater. The central region of this 2D spectrum is influenced by P and H in a concentration ratio of[H] / [P] = 2.5. TheESEEM spectrum was simulated, assuming the equation for two spin systems S = 1/2 andI = 1/2. This simulation gave, for m and n, the values of 2 and5, respectively. This finding suggests a–P–O–P–O–P– linear evolution of thestructure. It appears that one ethyl group does not hydrolyze in thegelation process. This result was confirmed by IRspectroscopy.     

Synthesis, network structure and morphology of s-triazine-organosilane glassy hybrid materials

A series of five hybrid materials are synthesized by the reaction of cyanuric chloride (C₃N₃Cl₃) with different alkoxysilanes (R_xSi(OC₂H₅)_4−x, R=CH₃, C₆H₅ and x=0, 1, 2) in ethanol using sol–gel technique. The resulting s-triazine-organosilane products were examined using spectroscopic (UV–visible, FT-IR), thermal (thermogravimetric analysis, TGA), powder X-ray diffraction (P-XRD), BET analysis and microscopic (scanning electron microscopy, SEM) techniques. These hybrid materials exhibit globular and two-dimensional morphological textures with varying degrees of crystalline microstructures. Depending on the functionality of the organosilane building blocks the obtained hybrid materials exhibit different material characteristics including their solid state, Vicat softening point (Vicat hardness), density and porosity. BET surface area measurements indicate that these materials possess small specific surface areas of 0.36–2.3 m²/g with external surface area of ~0.02 m²/g. The phenyl-containing hybrids exhibit pronounced hydrolytic stability compared to the methyl- and silica-based analogs. The DMSO and sulfolane solutions of the prepared hybrids are transparent to visible light whereas their cold-compressed discs are optically opaque.     

Reaction of perchloric anhydride with ethyl carbamate

Conclusions The reaction of Cl₂O₇ with H₂NC(O)OC₂H₅ in CCl₄ leads to the formation of the ionic perchlorate of ethyl carbamate, the covalent perchlorate — the ethyl ester of perchloric acid, and the ethyl ester of allophanic acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1650–1652, July, 1979.     

Preparation of Lead Zirconate Titanate Ceramic Fibers by Sol-Gel Method

PZT fibers with the nominal composition of Pb(Zr_0.53Ti_0.47)O _x have been successfully drawn by the sol-gel techniques. Ti(O·i–C₃H₇)₄, Zr(O·n–C₄H₉)₄, and Pb(O₂C₈H₁₅)₂ were used as the starting materials. The rheological conditions for continuous gel fiber drawing were determined. Thermal and microstructural evolutions of gel fibers were investigated by X-ray diffraction and Fourier-transform infrared spectroscopy. Perovskite crystalline fibers without breakage were obtained by a two-stage heat treatment on the gel fibers up to 600°C in air. Bending strength of the fibers decreases with the increase of the fiber diameter and is ranged from 10 to 30 MPa.     

Excess Volumetric and Spectroscopic Properties of Mixtures of Some <Emphasis Type="Italic">n</Emphasis>-Alkoxyethanols and of Some Polyethers with 2-Pyrrolidinone and <Emphasis Type="Italic">N</Emphasis>-Methyl-2-Pyrrolidinone at 298.15 K

Excess molar volumes V_m^E for binary liquid mixtures of n-alkoxyethanols or polyethers + 2-pyrrolidinone or N-methyl-2-pyrrolidinone have been measured with a continuous dilution dilatometer at 298.15 K and atmospheric pressure as a function of composition. The alkoxyethanols are diethylene glycol monomethylether, 2-(2-methoxyethoxy) ethanol, CH₃(OC₂H₄)₂OH; diethylene glycol monoethylether, 2-(2-ethoxyethoxy) ethanol, C₂H₅(OC₂H₄)₂OH; and diethylene glycol monobutylether, 2-(2-butoxyethoxy) ethanol, C₄H₉(OC₂H₄)₂OH; whereas the polyethers are diethylene glycol dimethylether, bis(2-methoxyethyl)ether, CH₃(OC₂H₄)₂OCH₃; diethylene glycol diethylether, bis(2-ethoxyethyl)ether, C₂H₅(OC₂H₄)₂OC₂H₅; and diethylene glycol dibutylether, bis(2-butoxyethyl)ether, C₄H₉(OC₂H₄)₂OC₄H₉. In all mixtures the excess molar volumes are negative and symmetric across the entire composition range. The excess volumes are fitted to the Redlich–Kister polynomial equation to obtain the binary coefficients and the standard errors. The experimental results have also been discussed on the basis of IR measurements.     

Some data on the character of the titanium -cyclopentadienyl ring bond in C5H5Ti(OC2H5)3 and (C5H5)2 Ti(OCOCH3)2

Summary On the basis of the formation of ferrocene during the reaction of C₅H₅Ti(OC₂H₅)₃ and (C₅H₅)₂Ti(OCOCH₃)₂ with FeCl₂ and the ease with which the bond of the cyclopentadienyl ring with the metal in these compounds may be hydrolyzed the hypothesis has been stated that the bond of the titanium atom with the cyclopentadienyl rings in (C₅H₅)₂Ti(OCOCH_{5 2} and C₅H₅Ti(OC₂H₅)₃ has an ionic character to a considerable degree.     

Synthesis and spectroscopic characterization of aryloxide derivatives of titanium(IV) and zirconium(IV)

Homo- and heteroleptic aryloxides of the type MX_4–x(OAr)_x [M = Ti^IV, Zr^IV; X = OPrⁱ, Cl; x = 1,2,3,4; OAr = OC₆H₄Prⁱ-4(OAr¹), OC₆H₃Me-2-Prⁱ-5(OAr²), OC₆H₃Me-5-Prⁱ-2(OAr³), OC₆H₂Me₃-2,4,6(OAr⁴), OC₆H₃Bu^t₂-2,4(OAr⁵), OC₆H₃Bu^t₂-2,6(OAr⁶)] have been prepared either by alkoxo–aryloxo or chloro-aryloxo exchange reactions in benzene or tetrahydrofuran. All these new derivatives have been characterized by elemental analyses, spectroscopic (i.r., ¹H-, ¹³C-n.m.r.) studies and molecular weight measurements. The FAB mass spectral studies of four representative derivatives Support a dimeric nature for [Ti(OC₆H₃Me-5-Prⁱ-2)₄], [TiCl₂(OC₆H₃Me-5-Prⁱ-2)₂], and [Zr(OC₆H₃Bu^t₂-2,4)₄(thf)], whereas the derivative [ZrCl(OC₆H₃Bu^t₂-2,4)₃(thf)] is monomeric.     

Mechanism of the Effect of Thermal Treatment on the Formation of Strong Acid Sites in the Surface Layers of Sulfated Metal Oxides

Strong acid catalysts were synthesized by the impregnation of hydrated ZrO₂ and TiO₂ with sulfuric acid followed by thermal treatment at different temperatures. The surface acidity and crystallochemical characteristics of the catalysts were studied by potentiometry and X-ray diffraction analysis, respectively. It was found that the surface acidity gradually increased as the temperature of thermal treatment was increased from 350 to 600°C for SO^2– ₄/ZrO₂ or to 200°C for SO^2– ₄/TiO₂; this increase correlated with the degrees of crystallinity of the samples. A hypothesis was proposed to explain the gradual accumulation of acid sites in the surface layer in the course of thermal treatment. It was assumed that, because of crystallographic changes that caused the weakening or even rupture of Zr–O–S and Ti–O–S bonds in modified surface layers, these layers exhibited an enhanced reactivity in contact with water vapor. Subsequently, this resulted in the formation of strongly acidic grafted M–O–SO₃–H⁺ groups.     

Synthesis and structure of diamine bis(phenolate) complexes containing the Ti(OEt)–O–Ti(OEt) function

Reaction of diamine-bis(phenol) ligands containing a mixture of N-methyl and N,N′-dimethyl-N,N-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine, H₂L¹ and H₂L³, with [Ti(OCHMe₂)₄ in absolute ethanol under reflux without exclusion of air and moisture gives [(L¹)Ti (OEt–O–Ti(OEt)(L¹)] (1). [(L³)Ti(OEt)–O–Ti(OEt)(L³)] (2) forms when the remaining solution containing [(L³)Ti(OEt)₂] (3) (characterised by X-ray crystallography) is hydrolysed with H₂O. For the N-methyl and N,N′-dimethyl ligand mixture H₂L² and H₂L⁴, which contain tert-butyl groups on the ortho-positions of the aryl rings, [(L²)Ti(OEt)–O–Ti(OEt)(L²)] (4) forms much more slowly and [(L⁴)Ti(OEt)₂] (5) does not hydrolyse when H₂O is added. When the N-protonated ligand N,N-bis(2-hydroxy-3-methyl-5-tert-butylbenzyl)ethylenediamine, H₂L⁵, is used, rapid hydrolysis to two isomers of [(L⁵)Ti(OEt–O–Ti(OEt)(L⁵)] (6) occurs without addition of water. For N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine, H₂L⁶, hydrolysis to [(L⁶)Ti(OEt)–O–Ti(OEt)(L⁶)] (7) occurs slowly when H₂O is added. For pendant NMe₂ ligand N,N-dimethyl-N′,N′-bis(2-hydroxy-3-methyl-5-tert-butylbenzyl)ethylenediamine, H₂L⁷, the hydrolysis reaction readily gives [(L⁷)Ti(OEt)–O–Ti(OEt)(L⁷)] (8) for which an X-ray crystal structure was obtained. The ortho-tert-butyl ligand derivative H₂L⁸ formed a complex analysing as [(L⁸)Ti(OEt)–O–Ti(OEt)(L⁸)] (9) which could not be studied further due to insolubility. Pendant pyridine ligand N-(2-pyridylmethyl)-N,N-bis(2′-hydroxy-3′-methyl-5′-tert-butylbenzyl)amine, H₂L⁹, apparently forms isomers of [(L⁹)Ti(OEt)–O–Ti(OEt)(L⁹)] and possibly [{(L⁹)Ti(O)}₂] from [(L⁹)Ti(OEt)₂] (10). The ortho-tert-butyl ligand derivative H₂L¹⁰ formed [(L¹⁰)Ti(OEt)–O–Ti(OEt)(L¹⁰)] (11) for which an X-ray crystal structure was obtained.     

Application of organolithium and related reagents in synthesis,Part X. Metallation-electrophilic substitution sequence of secondary chlorobenzamides

Summary The lithiation (Bu ⁿLi/THF) of 2-chloro- (1), 3-chloro- (2) and 4-chlorobenzanilides (3) and the subsequent reactions of the corresponding bis-lithiated anilides4–6 with electrophiles (MeI, CH₂=CH-CH₂Br,Me ₃SiCl,MeCHO,o-MeOC₆H₄CHO,p-MeOC₆H₄CHO,Me ₂NCHO andp-MeOC₆H₄CONMe ₂) towards the synthesis of theortho substituted chlorobenzoesic acids derivatives12–14 have been described. The effect of the chlorine substituent upon the generation and stability of the bis-lithiated chloro-anilides4–6 has been studied. It has been found that the bis-lithiated chloro-anilide5 derived fromm-chloro-benzanilide (2) at a temperature above –30°C converts into the corresponding benzyne9. The anilide moiety (masking group) of the formedortho-substituted chlorobenzanilides appeared to be effectively removable on acid-driven hydrolysis.

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Anwendungen von Organolithium und verwandten Reagenzien in organischen Synthesen, 10. Mitt. Metallierung und nachfolgende elektrophile Substitution sekundärer Chlorbenzamide

Zusammenfassung Die Lithiierung (Bu ⁿLi/THF) der 2-Chlor-(1), 3-Chlor- (2) and 4-Chlorbenzanilide (3) und nachfolgende Reaktion der entsprechenden doppellithiierten Anilide4–6 mit elektrophilen Reagenzien (MeI, CH₂=CH-CH₂Br,Me ₃SiCl,MeCHO,o-MeOC₆H₄CHO,p-MeOC₆H₄CHO,Me ₂NCHO undp-MeOC₆H₄CONMe ₂) zur Synthese vonortho-substituierten Benzoesäurederivaten12–14 wird beschrieben. Der Einfluß des Chlorsubstituierten auf die Bildung und Stabilität der doppellithiierten Chloranilide4–6 wurde untersucht. Es wurde festgestellt, daß das doppellithiierte, vomm-Chlorbenzanilid erhaltene Chloranilid5 bei Temperaturen über –30°C das entsprechende Arin9 bildet. Der Anilidrest (eine maskierende Gruppe) der gebildetenortho-substituierten Chloranilide kann durch saure Hydrolyse abgespalten werden.

     

Dimerization and Coordination Properties of Zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine in Relation to DABCO in <Emphasis Type="Italic">o</Emphasis>-Xylene and Chloroform

For the first time the interactions between zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc) and 1,4-diazabicyclo[2.2.2]octane (DABCO) in o-xylene and chloroform have been studied by calorimetric titration and NMR and electron absorption spectroscopic methods. It has been found that in o-xylene at concentrations of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc higher than 6×10⁻⁴ mol⋅L⁻¹ π–π dimers species are formed (λ _max= 685 nm). Additions of DABCO to the solution up to mole ratio 1 : 8 (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc : DABCO) lead to a shift of the aggregation equilibrium towards monomer species due to formation of monoligand axial complexes. Further increasing the DABCO concentration results in formation of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc—DABCO—Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc sandwich dimers (λ _max= 675 nm).     

Monte Carlo Studies of the Structural and Thermodynamic Properties of Some Smectic and Ferroelectric Liquid Crystals

Monte Carlo simulation based on the Gaussian overlap model was used to study the thermodynamic properties of smectic C: C₅H₁₁O–(OH)C₆H₃–CH=N–C₆H₄–C₅H₁₁ (A), C₁₀H₂₁O–C₆H₄–CH=CH–C₆H₄–OC₁₀H₂₁ (B), ferroelectric smectic C* liquid crystals (LC): C₇H₁₅O–C₆H₄–C₆H₄–COO–CH₂C*H(CH₃)C₂H₅ (C), C₈H₁₇O–C₆H₄–C₆H₄–C₂H₄C*H(CH₃)C₂H₅ (D), and an equimolar mixture of {A+C} and {A+D}. A system of N = 125 pairwise interacting ellipsoids of revolution placed in a volume V at a temperature T (that is, a system described by a canonical NVT-ensemble) is considered. These interactions were calculated using a specially devised Lennard-Jones potential, allowing for both mild anisotropic repulsion of particles (ellipsoids) and their dispersion attraction. Dipole–dipole interactions were also taken into account, since the molecules have highly polar groups: –O–, OH, CH=N, and COO and hence a high dipole moment (4.2-5.3 D). Calculations were carried out for a rectangular parallelepiped with periodic boundary conditions imposed on its faces. An elementary object of the NVT-ensemble was a two-molecule microcluster (dimer) but not a single molecule from the group under study. Smectic A ordering in the system has been unambiguously proven for different temperatures and fixed densities (0.32 0.44, where is the close packing coefficient). The ordering is attributed to the large (transverse) dipole moment inherent in molecules {A}-{D}. Temperature dependences of free energy, configuration energy, heat capacity C_v, and orientational order parameter were obtained. The curves agree well with the experimental data on variation of the properties of smectic LC.