Perovskite-type layer structures

Later, Tieke reported the UV- and y-irradiation polymerization of butadiene derivatives crystallized in perovskite-type layer structures [21,22]. He reported the solid-state polymerization of butadienes containing aminomethyl groups as pendant substituents that form layered perovskite halide salts to yield erythro-diisotactic 1,4-trans polymers. Interestingly, Tieke and his coworker determined the crystal structure of the polymerized compounds of some derivatives by X-ray diffraction [23,24]. From comparative X-ray studies of monomeric and polymeric crystals, a contraction of the lattice constant parallel to the polymer chain direction by approximately 8% is evident. Both the carboxylic acid and aminomethyl substituent groups are in an isotactic arrangement, resulting in diisotactic polymer chains. He also referred to the y-radiation polymerization of molecular crystals of the sorbic acid derivatives with a long alkyl chain as the N-substituent [25]. More recently, Schlitter and Beck reported the solid-state polymerization of lithium sorbate [26]. However, the details of topochemical polymerization of 1,3-diene monomers were not revealed until very recently. 

This article describes the solid state polymerization of 1,i-disubstituted butadiene derivatives in perovskite-type layer structures, in layered structures of organic ammonium halide salts, and in lipid layer structures. Recent investigations by spectroscopic methods and x-ray structure analyses are described. The studies clearly indicate that the photolysis in the crystalline state leads to the formation of 1,i-trans-polymers exclusively. Crystal structure analyses of monomeric and polymeric layer perovskites demonstrate that upon y-irradiation a stereoregular polymer is obtained in a lattice controlled polymerization. 

Primary amines R-NH with R representing an unbranched alkyl chain are able to form complex salts with divalent transition metal halides MtX. The complex salts of the general formula (R-NH ) MtX are often called layer perovskites or perovskite-type layer structures and exhibit a structure as schematically shown in Figure 1 (1 ). As indicated by the Figure, a corresponding complex is also formed by a, is-substituted diamines. 

Perovskite type layered structures and especially layered oxides are intensively studied because they exhibit a wealth of "modem" physical phenomena, such as high-Tc superconductivity, colossal magnetoresistance, ferroelectricity and quantum critical behavior. Due to this layered oxides create the basis for many technological applications including information storage and transmission, micro-electronics and micro-manipulation. 

In perovskite type layered structure the consequence of perovskite layers and other blocks is not usual geometrical one, it is really the intergrowth of different structures. Stability of intergrowth depends on the extent of geometrical constrains between different types of structme, and thermodynamic equilibrium between different layers. 

Perovskite structures, 5 598 Perovskite-type layered superconductors, 23 852... 

Simple perovskite-type layers were first evidenced by Brosset in KAIF4 in 1938 (Figure 12.30a) the symmetry is tetragonal and the Al-F-Al angle is ideal, 180°. Numerous other layered fluorides were found further however, most of the structures are distorted, due to a concerted rotation and/or a tilting of the octahedra. For example,... 

Another important family of materials based on Bi203 are those that adopt the Aurivillius type structure (perovskite-related layered structure) with the chemical formula Bi4V20n, first reported by Abraham et The low temperature phase is a-Bi4V20n, and it presents two... 

Perovskite-type layered compounds are the intergrowth of perovskite l ers (P) ABO3 and slabs of the differ type of structure (rock salt, calcium fluorite type, cations of metals). Depending on the nature of slabs between perovskite blocks, layered compounds belong to three big groups Ruddlesden-Popper phases, Aurivillius phases, Dion-Jacobson phases. 

Among the high-temperature superconductors one finds various cuprates (i.e., ternary oxides of copper and barium) having a layered structure of the perovskite type, as well as more complicated oxides on the basis of copper oxide which also include oxides of yttrium, calcium, strontium, bismuth, thallium, and/or other metals. Today, all these oxide systems are studied closely by a variety of specialists, including physicists, chemists, physical chemists, and theoreticians attempting to elucidate the essence of this phenomenon. Studies of electrochemical aspects contribute markedly to progress in HTSCs. 

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