Diacetyl Ferrocene Research Articles

Amphoteric reactivity of a putative Cu(II)-mCPBA intermediate.

In copper-based enzymes, Cu-hydroperoxo/alkylperoxo species are proposed as key intermediates for their biological activity. A vast amount of literature is available on the functional and structural mimics of enzymatic systems with heme and non-heme ligand frameworks to stabilize high valent metal intermediates, mostly at low temperatures. Herein, we report a reaction between [CuI(NCCH3)4]+ and meta-chloroperoxybenzoic acid (mCPBA) in CH3CN that produces a putative CuII(mCPBA) species (1). 1 was characterized by UV/Vis, resonance Raman, and EPR spectroscopies. 1 can catalyze both electrophilic and nucleophilic reactions, demonstrating its amphoteric behavior. Additionally, 1 can also conduct electron transfer reactions with a weak reducing agent such as diacetyl ferrocene, making it one of the reactive copper-based intermediates. One of the most important aspects of the current work is the easy synthesis of a CuII(mCPBA) adduct with no complicated ligands for stabilization. Over time, 1 decays to form a CuII paddle wheel complex (2) and is found to be unreactive towards substrate oxidation.

Bio functional molecular complexes, ferrocenyl hydrazone based binuclear Cu (II) derivatives: Synthesis, spectral, DNA/BSA binding &in-silico analyses

As a first stage intermediate, designing mononuclear complexes of amine-based phenolic derivatives employing Cu (II) acetate as a central metal ion in a 1:2:1 ratio. In a methanolic solution treated with 1,1′-diacetyl ferrocene dihydrazone and Cu (II) perchlorate hexahydrate to generate a new group of ferrocene based macrocyclic binuclear Cu (II) complexes. To characterize the macrocyclic complexes, physico-chemical studies such as FT-IR, UV–vis, and photoluminescence were used. The binuclear Cu(II) complex [Cu2L1] exhibits two quasi-reversible reduction waves in the potential range The binuclear complex [Cu2L1]hastwowaves of virtually reversible reductionin the potential range of E1pc = −1.01 V and E2pc = −1.37 V in the electrochemical investigation. They show a reduction process that involves two one-electron reductions in steps. The ferrocenyl group of the complexes shows one-electron ferrocene/ferrocenium redox activity, although with differing peak potentials. CT-DNA was used to study DNA binding utilizing spectroscopic techniques such as Circular Dichroism, UV–vis, and Fluorescence. The binding constant (Kb) values for the series of complexes range from 1.3x105 to 5.8 × 105 M−1. The metal complexes all interacted with CT-DNA by an intercalative form of binding, according to fluorescence spectrum analyses. BSA protein binding, on the other hand, indicates a quenching manner of interaction with the binuclear complex system, with binding constants of 1.77 × 106, 1.65 × 106, 2 × 106, 4.8 × 106 and 5.12 × 106 M−1. Molecular docking analysis was used to support and augment the experimental biological studies. Intercalation was seen during the docking of 1BNA with a metal complex due to multiple hydrogen bonding interactions. The ferrocene heterocyclic ring and the naphthyl group of complexes interacted with the BSA protein's ARG and TYR systems.

Spontaneous Formation of an Fe/Mn Diamond Core: Models for the Fe/Mn Sites in Class 1c Ribonucleotide Reductases.

A handful of oxygen-activating enzymes has recently been found to contain Fe/Mn active sites, like Class 1c ribonucleotide reductases and R2-like ligand-binding oxidase, which are closely related to their better characterized diiron cousins. These enzymes are proposed to form high-valent intermediates with Fe-O-Mn cores. Herein, we report the first examples of synthetic Fe/Mn complexes that mimic doubly bridged intermediates proposed for enzymatic oxygen activation. Fe K-edge extended X-ray absorption fine structure (EXAFS) analysis has been used to characterize the structures of each of these compounds. Linear compounds accurately model the Fe···Mn distances found in Fe/Mn proteins in their resting states, and doubly bridged diamond core compounds accurately model the distances found in high-valent biological intermediates. Unlike their diiron analogues, the paramagnetic nature of Fe/Mn compounds can be analyzed by EPR, revealing S = 1/2 signals that reflect antiferromagnetic coupling between the high-spin Fe(III) and Mn(III) units of heterobimetallic centers. These compounds undergo electron transfer with various ferrocenes, linear compounds being capable of oxidizing diacetyl ferrocene, a weak reductant, and diamond core compounds being capable of oxidizing acetyl ferrocene. Diamond core compounds can also perform HAT reactions from substrates with X-H bonds with bond dissociation free energies (BDFEs) up to 75 kcal/mol and are capable of oxidizing TEMPO-H at rates of 0.32-0.37 M-1 s-1, which are comparable to those reported for some mononuclear FeIII-OH and MnIII-OH compounds. However, such reactivity is not observed for the corresponding diiron compounds, a difference that Nature may have taken advantage of in evolving enzymes with heterobimetallic active sites.

A ferrocene-linked metal-covalent organic polymer as a peroxidase-enzyme mimic for dual channel detection of hydrogen peroxide.

A novel ferrocene-linked metal-covalent organic polymer (MCOP-NFC) was synthesized through the Claisen-Schmidt condensation reaction of 1,1'-diacetyl ferrocene and tris(4-formylphenyl)amine. MCOP-NFC acts as a highly efficient artificial enzyme for mimicking peroxidase, and shows good stability in harsh chemical environments including strong bases and acids, and boiling water. Based on the peroxidase-like activity of MCOP-NFC, a highly sensitive dual channel detection method for hydrogen peroxide was developed. For the colorimetric detection strategy, the limit of detection (LOD) reached 2.1 μM, while the limit of detection was found to be as low as 0.08 μM based on the electrochemical detection channel. This study offers a new strategy for the development of an enzyme mimetic on the basis of the covalent assembly of nanostructures, and the proposed electrochemical-colorimetric sensor for H2O2 detection has great potential for applications in biology and biomedicine.

Slow Magnetic Relaxation in Dinuclear CoIIYIII Complexes.

Four new dinuclear complexes, [Co(μ-L)(μ-CCl3COO)Y(NO3)2]·2CHCl3·CH3CN·2H2O (1), [Co(μ-L)(μ-CH3COO)Y(NO3)2]·CH3CN (2), [Co(μ-L)(μ-PhCOO)Y(NO3)2]·3CH3CN·2H2O (3), and [Co(μ-L)(μ-tBuCOO)Y(NO3)2]·CHCl3·2H2O (4), having a CoIIYIII core, have been synthesized by employing a ferrocene based compartmental ligand which was synthesized by the reaction of diacetyl ferrocene with hydrazine hydrate followed by a condensation reaction with o-vanillin. A general synthetic protocol was employed to synthesize complexes 1-4, where the metallic core was kept the same with changing the bridging carboxylate groups. In all the complexes, the main structural motif is kept similar by only slightly varying the substitution on the bridging acetate groups. This variation has resulted in a small but subtle influence on the magnetic relaxation of all these four compounds. Ab initio CASSCF/NEVPT2 calculations were carried out to assess the effect of the different substitutions of the bridging ligands on the magnetic anisotropy parameters and on orbital arrangements. Ab initio calculations yield a very large positive D value, which is consistent with the geometry around the CoII ion and easy plane anisotropy (gxx, gyy > gzz), with the order of the calculated D in the range of 72.4 to 91.7 cm-1 being estimated in this set of complexes. To ascertain the sign of zero-field splitting in these complexes, EPR spectra were recorded, which support the sign of D values estimated from ab initio calculations.

Using hydrazine to link ferrocene with Re(CO)3: A modular approach

Acetyl ferrocene and diacetyl ferrocene both readily react with an excess of hydrazine to afford the corresponding hydrazone compounds. These compounds can then be linked to Re(CO)3 via a metal-mediated Schiff base reaction, resulting in a series of ferrocene-Re(CO)3 conjugates with different stoichiometries. Conjugates with 1:1, 1:2, and 2:1 ferrocene: Re(CO)3 ratios can be produced via this “modular” type synthesis approach. Several examples of these conjugates were structurally characterized, and their spectroscopic, electrochemical, and spectroelectrochemical behaviors were investigated. The electronic structures of these compounds were also probed using DFT and TDDFT calculations.

Ferrocene-based compartmental ligand for the assembly of neutral ZnII/LnIII heterometallic complexes

A ferrocene-based compartmental ligand, H2L, was synthesized by the reaction of diacetyl ferrocene with hydrazine hydrate followed by a condensation reaction with o-vanillin. [L](2-) possesses a dual coordination pocket, an inner pocket of 2 imino nitrogens and two phenolate oxygens and an outer pocket of two phenolate and two methoxy oxygen atoms. Utilizing this ligand, several Zn(II)/Ln(III) heterobimetallic complexes were assembled: [LZn(μ-OAc)Dy(NO3)2] (2), [LZn(μ-OAc)Tb(NO3)2] (3), [LZn(μ-OAc)Gd(NO3)2·2CHCl3] (4), [LZn(μ-OAc)Er(NO3)2] (5), [LZn(μ-OAc)Ho(NO3)2] (6), [LZn(μ-OAc)Eu(NO3)2] (7). All of these metal complexes are neutral and isostructural: the Zn(II) ion occupies the inner coordination pocket while the Ln(III) ion occupies the outer coordination pocket of the doubly deprotonated ligand [L](2-). Zn(II) has a coordination number of 5 (2N, 3O) in a square pyramidal coordination geometry while Ln(III) has a coordination number of 9 (9O) in a distorted tricapped trigonal prismatic geometry. Zn(II) and the 4f metal ion are bridged to each other by two phenolate oxygen atoms and an acetate ligand. ESI-MS reveals that 2-7 retain their structural integrity in solution. Cyclic voltammetry of 1-7 revealed a quasi-reversible oxidation (involving the ferrocene motif) and an irreversible reduction of the hydrazone unit. Magnetic studies of 2, 3 and 6 were carried out. Ac susceptibility studies did not reveal slow relaxation of magnetization.

Experimental Charge Density Analysis of Symmetrically Substituted Ferrocene Derivatives

Experimental charge density analysis of three symmetrically substituted ferrocene derivatives: 1,1'- dimethyl ferrocene (1), decamethyl ferrocene (2), and 1,1'-diacetyl ferrocene (3) was conducted. The electron donating or accepting propensities of the ferrocene substituents were evaluated. The metal ligand interactions in all analyzed compounds were found to be similar in terms of charge density concentrations at Bond Critical Points (BCPs), laplacian values, and deformation density features. The monopole population of iron in all cases tend to be slightly negative, suggesting charge donation from Cp ligands. d orbital populations in all cases adopt values in agreement with theoretical calculations and ligand field theory. The charge distribution over analyzed molecules does not correlate with the formal oxidation potential in the analyzed compounds, as compound 2 in the currently studied structure takes the place suitable for an unsubstituted ferrocene. The non-intuitive low energy of the eclipsed conformation of 1 compound finds some explanation in the existence of a bond critical point between atoms of the two methyl groups in the structure. An asymmetry of the atomic surroundings of the two oxygen atoms in the 3 structure, reflected by the differences in charge rho(r(BCP)) and nabla(2)rho(r(BCP)) values and the shape of deformation density in the regions of oxygen lone electron pairs, is described.

Synthesis and electrochemical properties of a series of ferrocene-containing alcohols

A series of primary ferrocenylalcohols, Fc–(CH 2) m –OH with m = 1–4 and Fc = ferrocenyl, was synthesised by reduction of the appropriate ferrocenylcarboxylic acids, Fc–(CH 2) n –COOH ( n = 0–3) and the ester methyl 4-ferrocenylbutanoate with LiAlH 4, the reduction of the γ-ketoacid ferrocylpropanoic acid, Fc–CO–(CH 2) 2–COOH, with AlCl 3/LiAlH 4, and the reduction of ferrocenylcarboxaldehyde, FcCHO, with NaBH 4. The secondary ferrocenyl alcohols CpFe(C 5H 4–CH(OH)–CH 3) and Fe(C 5H 4–CH(OH)–CH 3) 2 were obtained by NaBH 4 reduction of acetyl and diacetyl ferrocene. The different reduction methods are compared. The electrochemistry of the alcohols was studied by cyclic voltammetry in CH 3CN/0.1 M N( n Bu) 4PF 6 utilising a platinum working electrode. The ferrocenyl group showed reversible electrochemistry with the formal reduction potential ( E o′ versus Fc/Fc +) of the ferrocenyl group inversely proportional to side chain length. The influence of the side chain length on E o′ was more pronounced for the acids because the electron-withdrawing properties of the carbonyl group is stronger than that of the alcohol group. Ion pairing was found to play a major role in the electrochemical behaviour of ferrocenylmethanol, Fc–CH 2–OH.

Reductive Quenching of Photoexcited Cu(dipp)(2)(+) and Cu(tptap)(2)(+) by Ferrocenes (dipp = 2,9-Diisopropyl-1,10-phenanthroline and tptap = 2,3,6,7-Tetraphenyl-1,4,5,8-tetraazaphenanthrene).

The metal-to-ligand charge-transfer excited states of Cu(NN)(2)(+) systems tend to be good reducing agents but poor oxidants for kinetic and thermodynamic reasons. However, this report demonstrates that reductive electron-transfer quenching is an important pathway for ferrocenes that react with the photoexcited states of Cu(dipp)(2)(+) and Cu(tptap)(2)(+) in methylene chloride (dipp = 2,9-diisopropyl-1,10-phenanthroline and tptap = 2,3,6,7-tetraphenyl-1,4,5,8-tetraazaphenanthrene). In the case of the dipp complex the bulky isopropyl substituents inhibit structural relaxation within the excited state, and the self-exchange rate for reductive quenching is quite favorable, k() approximately 2 x 10(8) M(-)(1) s(-)(1). Even in the absence of a significant kinetic barrier to reaction, however, for energetic reasons only extensively methylated ferrocene derivatives with relatively negative reduction potentials are capable of transferring an electron to the excited state. In contrast, every ferrocene derivative investigated, except diacetyl ferrocene, reacts with the charge-transfer excited state of the tptap complex by an electron-transfer mechanism. This is mainly due to a difference in driving force which is about 0.5 V greater for the tptap complex. This system also has a favorable self-exchange rate, k() approximately 5 x 10(7) M(-)(1) s(-)(1), evidently because the juxtapositioned phenyl substituents inhibit low-symmetry distortions within the ground state as well as the excited state. Although energy transfer to ferrocene is also possible, this is a less competitive process with the tptap complex because the zero-zero energy of the reactive excited state is rather low ((3)E(00) approximately 1.7 V).

A Mössbauer Temperature Study of 1,1′-diacetylferrocene in the Liquid Crystal, N-(P-hexyloxybenzylidene)-P-toluidine

The Fe-57 Mössbauer Effect was used to study a solution (0.2% by Weight) of 1,1′-diacetylferrocene (DAF) in the liquid crystalline material p-n-hexyloxy-benzylidene-p-toluidine (HBT). The DAF contained enriched Fe-57. The Mössbauer Effect parameters were determined for the temperature range 100–300K in the crystalline solid phase and 100–200K in the cold smectic ß phase of HBT. Here “cold” means the smectic glass and the supercoded smectic phase. The Ln recoil-free intensity (f) vs T data exhibited linear Debye behavior for the solid phase over the entire temperature range. The low temperature (T < 190) portion of the cold smectic Inf vs T data also exhibited Debye behavior, and the smectic glass gave a Mössbauer-Debye temperature (θ lc ) about 30 K. lower than the crystalline phase. The smectic glass-super cooled smectic transition was determined to be Tg = 190 K from the deviation of the Inf vs T data from linear behavior. Above Tg , the deviation from linear Debye behavior followed a (T-Tg)2 dependence. The smectic B glass yielded an order parameter of S = 0.06 for DAF molecules at 100 K. Rotational and transitional diffusion were not observed for the cold smectic B phase.

Mössbauer-effect-temperature study of 1,1'-diacetylferrocene in a cold smectic-B liquid crystal.

The $^{57}\mathrm{Fe}$ M\ossbauer-effect (ME) measurements were obtained from a 0.8-wt. % solution of 1,1'-diacetylferrocene (DAF) in the liquid-crystalline material 4-n-octyloxybenzylidene-4'-ethylaniline. The ME parameters were determined for the temperature range of 100--290 K in the crystalline solid phase and 100--150 K in the cold smectic-B phase. The ln f-versus-T data, where f is the recoil-free intensity, exhibited linear Debye behavior for the solid phase over the entire temperature range. The cold smectic ln f-versus-T data also exhibited Debye behavior, and the smectic glass gave a M\ossbauer-Debye temperature (${\ensuremath{\theta}}_{\mathrm{LC}}$) about 12 K lower than the crystalline phase. The smectic-B glass yielded an order of S=0.09 at 100 K. Also, the intermolecular contribution to the vibrational ellipsoid (${\ensuremath{\epsilon}}_{L}$) declined linearly with increasing temperature and a comparison of this sample with two other liquid-crystal samples (40.8 and 8\ifmmode\bar\else\textasciimacron\fi{}09) provides information on the mechanism of dissolution of the DAF.

Dielectric relaxation of para-azoxy anisole and 1,1'diacetyl ferrocene in dioxane solution

The dielectric study of p-azoxy anisole and 1,1'diacetyl ferrocene liquid crystalline substances in dioxane solution at different concentration and at room temperature is reported. The dipole moment and the relaxation time are evaluated, and a comparison of the dipole moment value with those calculated by using static methods is made. The average value of the dipole moment for p-azoxy anisole is 9.6*10/sup -30/ Cm unit and that for 1,1'diacetyl ferrocene 20.9*10/sup -30/ Cm. The contributions of electronic polarizability, London dispersion attraction, exchange repulsion and dipole-dipole forces to the molar volume are determined using the free volume calculated from the measured ultrasonic data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Mössbauer Temperature Study of 1, 1′-Diacetylferrocene in A Cold Smectic C Liquid Crystal

Abstract The Fe-57 Mosshauer effect (ME) was used to study a solution (0.2% by weight) of 1,1′-diacetylferrocene (DAF) in the liquid crystalline material 4-n-pentylphenyl-4′-n-heptyloxythiobenzoate (7S5). The ME parameters were determined for the temperature range 110–300K in the crystalline solid phase and 110–240K in the cold smectic C phase of 7S5. Here “cold” means the smectic glass and the supercooled smectic phase. The In recoil-free intensity (f) vs T data exhibited linear Debye behavior for the solid phase over the entire temperature range. The low temperature (T<215) portion of the cold smectic In f vs, T data also exhibited Debye behavior, and the smectic glass gave a Mossbauer-Debye temperature (θLC) about 10K lower than the crystalline phase. The smectic glass-supercooled smectic transition was determined to be Tg = 215K from the deviation of the In f vs, T data from linear behavior. Above Tg, the deviation from linear Debye behavior followed a (T-Tg)2 dependence. The intermolecular contributi...

Mössbauer studies on ferrocene complexes VIII. Diacetylferrocene-metal halide complexes

Mössbauer parameters are reported for a series of diacetylferrocene (DAF) complexes with Lewis acids (AlCl 3, SnCl 4, FeCl 3, TiCl 4). All the complexes show a lowering of quadrupole splitting ( QS) relative to uncomplexed DAF. The decreases in QS are discussed in terms of their stereochemistry and related to previous findings in the ferrocenyl ketone series. 119Sn Mössbauer data are presented for SnCl 4 · DAF.

A mössbauer study of anisotropic molecular diffusion in the supercooled nematic liquid crystalline phase

The effect of the anisotropic diffusion of the Mössbauer probe 1,1'-diacetyl ferrocene (DAF) dissolved in the cold liquid crystals p-methoxybenzylidence- p-butylaniline and an eutectic mixture of cyano biphenyls and terphenyls, commercially known as E8, on the Mössbauer line broadening has been studied using 57Fe Mössbauer spectroscopy in the temperature range 80–300 K. The Mössbauer spectral lines begin to broaden as one approaches the glass transition temperature (∼199 K for MBBA and ∼ 175 K for E8). The anisotropy in the line broadening is due to the easier transport of the DAF molecules in the direction parallel to the liquid crystal molecular direction than in the perpendicular direction. The diffusion coefficients in the directions parallel ( D ⌈) and perpendicular ( D ⊥) to the liquid crystal molecular direction have been calculated assuming a continuous diffusion model. It has been found that D ⌈> D ⊥. The disappearance and subsequent reappearance of the Mössbauer effect above the glass transition temperature is shown to be due to the nematic liquid crystal glass converting itself into supercooled liquid and then the recrystallization of the supercooled liquid crystal. The anisotropic diffusive line broadening in the supercooled liquid crystalline phase is associated with the anisotropy of the Lamb-Mössbauer factor.

Vapor pressure measurements of ferrocene, mono- and 1,1′-di-acetyl ferrocene

By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 − (3805 ± 46)/ T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 − (5916 ± 48)/ T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 − (4289 ± 44)/ T By second- and third-law treatment of the vapor data the Δ H 0 sub,298 = 74.0 ± 2.0 kJ mole −1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values Δ H 0 sub,298 = 115.6 ± 2.5 kJ mole −1 and Δ H 0 sub,298 = 91.9 ± 2.5 kJ mole −1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.

A Mössbauer temperature study of two cold smectic (B and H) liquid crystals

We have used the Fe-57 Mössbauer effect (ME) to study solutions (0.2% by weight) of 1,1′-diacetylferrocene (DAF) in two liquid crystalline materials, 4-n-butoxybenzylidene-4′-n-′octylaniline (BBOA or 40,8) and 4-n-hexoxybenzylidene-4′-n-′ propylaniline (HBPA or 60,3). The ME parameters were determined for the temperature range 100–300 K in the crystalline solid phase of both systems and in the cold smectic B phase of BBOA and the cold smectic H phase of HBPA. Here ’’cold’’ means the smectic glass and the supercooled smectic phase. The lnf (recoil-free intensity) versus T plots exhibited linear Debye behavior for the solid phases of each system over the entire temperature range. The low temperature portion of the cold smectic lnf versus T data also exhibited Debye behavior for both systems. In both instances the smectic glass gave lower Mössbauer–Debye temperatures (ϑL) than the corresponding crystalline phase. For the smectic H glass of HBPA, ϑL=46 K and is independent of molecular orientation. For the smectic B glass of BBOA, ϑL=64 K for preferred molecular alignment parallel to the ME gamma direction and ϑL=49 K for perpendicular alignment. The smectic glass–supercooled smectic transition was determined to be Tg=175 K for BBOA and Tg=190 K for HBPA from the deviation of the lnf versus T data from linear behavior. Above Tg, the deviation from linear Debye behavior followed a (T−Tg)2 dependence. For DAF in HBPA, the intermolecular contribution to the Fe-57 vibrational ellipsoid (εL) was isotropic. For DAF in BBOA, εL declined linearly with increasing temperature below Tg. For 220–245 K line broadening and quadrupole relaxation were observed for the supercooled smectic H solution of HBPA. These results are accounted for using a model for rotational diffusion of the DAF molecule. The rotational diffusion apparently occurs without simultaneous translational diffusion.

A Mössbauer temperature study of a cold nematic liquid crystal: Nematic glass–supercooled nematic

A 0.2% (by weight) solution of 1,1′-diacetylferrocene (DAF) in n- (p-methoxybenzylidene) -p-butylaniline (MBBA) was prepared and studied with the Fe-57 Mössbauer effect. The Mössbauer parameters were observed for the temperature range 110–300 K. The recoil-free fraction (f) data showed that the MBBA crystal phase exhibited Debye behavior for the entire temperature range with a Mössbauer–Debye temperature (ϑL) of 70 K. The lower temperature data for the cold nematic also gave a linear lnf vs T plot with ϑL=47 K for the MBBA glass. The ϑL for the nematic glass was indepentent of molecular orientation. The nematic glass–supercooled nematic transition was determined to be Tg=181 K from the deviation of the lnf vs T curve from linear behavior. The nematic glass provided a nonvanishing temperature independent contribution to the Fe-57 vibrational ellipsoil (εL). Above 180 K εL became temperature dependent. Line broadening and a reduction of the quadrupole splitting were observed for the supercooled nematic with increasing temperature in the range 220–240 K. We interpret these results in terms of a model for rotational diffusion of the DAF molecule in the MBBA supercooled nematic. The rotational diffusion appears to occur without simultaneous translational diffusion.

Some new polymeric semiconductors

AbstractThis paper deals with some new methods for synthesis of the polymeric semiconductors by conjugated reactions and also with electrophysical properties of the polymers. Elimination of hydrogen halides from α,β‐dihalo derivatives by bases (calcium oxide or tertiary amines) yields polymers with conjugated bonds. The reaction proceeds at 200–300°C. under atmospheric or elevated pressures, acetylenes being the intermediates. α,β‐Dihalo compounds with calcium carbide above 150°C. produce polyacetylenic copolymers by elimination of two moles of hydrogen halide, also by generating acetylene from calcium carbide. The identical reaction (elimination of water) was observed between carbonyl compounds and calcium carbide. Elimination of water from monoand bifunctional phenols in the presence of zinc chloride under pressure above 200°C. yields polyphenylenes and polyhydroxyphenylenes, dehydrobenzene (benzyne) and hydroxybenzyne being intermediates. The polyhydroxyphenylenes prepared have a degree of polymerization from 4–5 to several thousand and are of interest as intermediates for thermostable resins, inhibitors etc. Linear polycyanamide and polycyanic acid were first prepared by polycondensation of urea with ammonium bicarbonate in the presence of zinc chloride. Analogous polymers were obtained from the ring‐opening polymerization of melamine and cyanuric acid. The polymers show good semiconductor and ion‐exchange properties. Polycondensation of ketones with ammonium bicarbonate also gave conjugated polymers. Thus, organometallic polymers were prepared from acetyl‐ and diacetyl ferrocene. We have also studied electrophysical, magnetic, and catalytic properties of the conjugated polymers prepared by the new methods. The electrical conductivity of the best specimens ranged from 10−3 to 10−6 ohm−1 cm.−1; the number of electrons unpaired was 1018–1019 spins/g.