Properties of a mixed-valence (Fe(II))2(Fe(III))2 square cell for utilization in the quantum cellular automata paradigm for molecular electronics

The di-mixed-valence complex [{(eta(5)-C5H5)Fe(eta(5)-C5H4)}4(eta(4)-C4)Co(eta(5)-C5H5)]2+, 1(2+), has been evaluated as a molecular four-dot cell for the quantum cellular automata paradigm for electronic devices. The cations 1(1+) and 1(2+) are prepared in good yield by selective chemical oxidation of 1(0) and are isolated as pure crystalline materials. The solid-state structures of 1(0) and 1(1+) and the midrange- and near-IR spectra of 1(0), 1(1+), 1(2+), and 1(3+) have been determined. Further, the variable-temperature EPR spectra of 1(1+) and 1(2+), magnetic susceptibility of 1(1+) and 1(2+), M?ssbauer spectra of 1(0), 1(1+), and 1(2+), NMR spectra of 1(0), and paramagnetic NMR spectra of 1(1+) and 1(2+) have been measured. The X-ray structure determination reveals four ferrocene "dots" arranged in a square by C-C bonds to the corners of a cyclobutadiene linker. The four ferrocene units project from alternating sides of the cyclobutadiene ring and are twisted to minimize steric interactions both with the Co(eta(5)-C5H5) fragment and with each other. In the solid state 1(2+) is a valence-trapped Robin and Day class II compound on the 10(-12) s infrared time scale, the fastest technique used herein, and unambiguous evidence for two Fe(II) and two Fe(III) sites is observed in both the infrared and M?ssbauer spectra. Both EPR and magnetic susceptibility measurements show no measurable spin-spin interaction in the solid state. In solution, the NMR spectra show that free rotation around the C-C bonds connecting the ferrocene units to the cyclobutadiene ring becomes increasingly hindered with decreasing temperature, leading to spectra at the lowest temperature that are consistent with the solid-state structure. Localization of the charges in the cations, which is observed in the paramagnetic NMR spectra as a function of temperature, correlates with the fluxional behavior. Hence, the alignment between the pi systems of the central linker and the ferrocene moieties most likely controls the rate of electron exchange between the dots.     

Kinetic parameters of surfactant remotion occluded in the pores of the AlMCM-41 nanostructured materials

A series of AlMCM-41 molecular sieves was synthesized starting from a hydrogel with the following molar composition: 1CTMABr:4.58SiO₂:(0.437 + X)Na₂O:XAl₂O₃:200H₂O. Tetramethylammonium silicate (TMAS) was used as silicon source and cethyltrimethylammonium bromide (CTMABr) was used as structure template. The obtained materials were characterized by nitrogen adsorption, XRD, FT-IR and TG/DTG. Model-free kinetic algorithms were applied in order to determinate conversion, isoconversion and apparent activation energy to decomposition of CTMA+ species from the AlMCM-41 materials with different silicon/aluminium (Si/Al) ratios of 20, 40, 60 and 80.     

Deciphering Siloxane Bond Exchanges: From a Molecular Study to Vitrimerization and Recycling of Silicone Elastomers

The activity of various additives promoting siloxane equilibration reactions is examined and quantified on model compounds. We found in particular that the “superbase” phosphazene derivative P₄-^tBu can promote very fast exchanges (a few seconds at 90 °C) even at low concentration (<0.1 wt %). We demonstrate that permanent silicone networks can be transformed into reprocessable and recyclable dynamic networks by mere introduction of such additives. Annealing at high temperature degrades the additives and deactivates the dynamic features of the silicone networks, reverting them back into permanent networks. A simple rheological experiment and the corresponding model allow to extract the critical kinetic parameters to predict and control such deactivations.     

Syntheses, structure, and a Mössbauer and magnetic study of Ba(4)Fe(2)I(5)S(4)

The compound Ba4Fe2I5S4 has been prepared at 1223-1123 K by the "U-assisted" reaction of FeS, BaS, S, and U with BaI2 as a flux. A more rational synthesis was also found; however, the presence of U appears to be essential for the formation of single crystals suitable for X-ray diffraction studies. Ba4Fe2I5S4 crystallizes in a new structure type with two formula units in space group I4/m of the tetragonal system. The structure consists of a Ba-I network penetrated by (1)infinity[Fe2S4] chains. Each Fe atom, which is located on a site with 4 symmetry, is tetrahedrally coordinated to four S atoms. The FeS4 tetrahedra edge-share to form linear (1)infinity[Fe2S4] chains in the [001] direction. The Fe-Fe interatomic distance in these chains is 2.5630(4) A, only about 3% longer than the shortest Fe-Fe distance in -Fe metal. Charge balance dictates that the average formal oxidation state of Fe in these chains is +2.5. The M?ssbauer spectra obtained at 85 and 270 K comprise a single quadrupole doublet that has hyperfine parameters consistent with an average Fe oxidation state of +2.5. The M?ssbauer spectrum obtained at 4.2 K consists of a single magnetic sextet with a small hyperfine field of -15.5 T. This spectrum is also consistent with rapid electron delocalization and an average Fe oxidation state of +2.5. The molar magnetic susceptibility of Ba4Fe2I5S4, obtained between 3.4 and 300 K, qualitatively indicates the presence of weak pseudo-one-dimensional ferromagnetic exchange within a linear chain above 100 K and weak three-dimensional ordering between the chains at lower temperatures.     

An arene-stabilized cobalt(I) aryl: reactions with CO and NO

The half-sandwich cobalt(I) complex (eta (6)-C 7H 8)CoAr*-3,5- ( i )Pr 2 (Ar*-3,5- ( i )Pr 2 = -C 6H-2,6-(C 6H 2-2,4,6- ( i )Pr 3) 2-3,5- ( i )Pr 2) was synthesized by reduction of [3,5- ( i )Pr 2Ar*Co(mu-Cl)] 2 in toluene. It reacts with CO or NO to afford the unusual complexes [3,5- ( i )Pr 2Ar*C(O)Co(CO)] or [3,5- ( i )Pr 2Ar*N(NO)OCo(NO) 2].     

Well‐defined polyolefin/poly(ε‐caprolactone) diblock copolymers: New synthetic strategy and application

A new synthetic strategy, the combination of living polymerization of ylides and ring‐opening polymerization (ROP), was successfully used to obtain well‐defined polymethylene‐b‐poly(ε‐caprolactone) (PM‐b‐PCL) diblock copolymers. Two hydroxyl‐terminated polymethylenes (PM‐OH, M_n= 1800 g mol^?1 (PDI = 1.18) and M_n = 6400 g mol^?1 (PDI = 1.14)) were prepared using living polymerization of dimethylsulfoxonium methylides. Then, such polymers were successfully transformed to PM‐b‐PCL diblock copolymers by using stannous octoate as a catalyst for ROP of ε‐caprolactone. The GPC traces and ¹H NMR of PM‐b‐PCL diblock copolymers indicated the successful extension of PCL segment (M_n of PM‐b‐PCL = 5200–10,300 g mol^?1; PDI = 1.06–1.13). The thermal properties of the double crystalline diblock copolymers were investigated by differential scanning calorimetry (DSC). The results indicated that the incorporation of crystalline segments of PCL chain effectively influence the crystalline process of PM segments. The low‐density polyethylene (LDPE)/PCL and LDPE/polycarbonate (PC) blends were prepared using PM‐b‐PCL as compatibilizer, respectively. The scanning electron microscopy (SEM) observation on the cryofractured surface of such blend polymers indicates that the PM‐b‐PCL diblock copolymers are effective compatibilizers for LDPE/PCL and LDPE/PC blends. Porous films were fabricated via the breath‐figure method using different concentration of PM‐b‐PCL diblock copolymers in CH₂Cl₂ under a static humid condition. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Efficient carbonyl hydrosilylation reaction: Toward EVA copolymer crosslinking

In this article, the hydrosilylation reaction of carbonyl groups of acetate derivatives and SiH groups of hydride‐terminated polydimethylsiloxane at high temperature (100–130 °C) are described. Triruthenium dodecacarbonyl, Ru₃(CO)₁₂, was used as effective catalyst for hydrosilylation reaction. The hydrosilylation reactions with octyl acetate and 4‐heptyl acetate were investigated by multinuclear NMR spectroscopy (¹H, ¹³C, and ²⁹Si). This work provides evidence of the addition reaction of SiH groups onto carbonyl groups. The influence of the nature of the acetate structure on the reaction kinetics was shown and the slight contribution of side reactions at high temperature highlighted. Hydrosilylation reaction was extent to the crosslinking of ethylene‐vinyl acetate (EVA) copolymer in the same range of temperature. The formation of EVA chemical network was demonstrated by HR‐MAS NMR spectroscopy and by measuring the gel fraction of EVA chains in hot toluene. From Flory theory, the crosslinking density of elastic strand was calculated to be 80 mol m^?3 in agreement with the measurements from swelling ratio (VA/SiH molar ratio: 11.8). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Block copolymers via macromercaptan initiated ring opening polymerization

Poly(styrene) macromercaptanes (M_n = 1900, 3600, and 6100 g mol^?1, PDI ≈ 1.2) derived from thiocarbonyl thio capped polymers prepared via reversible addition fragmentation chain transfer polymerization were employed to initiate the ring opening polymerization (ROP) of D ,L ‐lactide under conditions of organo‐catalyis employing 4,4‐dimethylaminopyridine. Poly(styrene)‐block‐poly(lactide) polymers of number average molecular weights up to 25,000 g mol^?1 (PDI ≈ 1.2 to 1.6) were obtained and characterized via multiple detection size exclusion chromatography (SEC) using refractive index as well as UV detection. In addition, diffusion ordered nuclear magnetic resonance and liquid chromatography at critical conditions (of both polystyrene as well as poly(lactide) were employed to assess the copolymers' structure. Furthermore, it was demonstrated that polyethylenes capped with a thiol moiety can also be readily chain extended in a ROP employing D ,L ‐lactide, evidenced via NMR and high temperature SEC. This study indicates that the direct use of macromercaptantes is indeed a methodology to switch from a radical to a ROP process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011