Electrocrystallisation

Charge-Transfer (CT) compounds containing 1,2-dichalcogenolene complexes and NIOS salts were generally prepared using electrocrystallisation techniques.170... 

One approach to chiral conductors using the counterions as the source of asymmetry is that employed in the preparation of a conductor based on bis(ethylenedithio)-tetrathiafulvalene (BEDT, Fig. 3) [39]. When this organic donor is electrocrystallised in the presence of the L-tartrate salt K2[Sb2 (L-tart)2] the compound that is formed is BEDT3Sb2(L-tart)2 MeCN. Thus, the BEDT is in a mixed valence state, with two third charge per molecule on average. The salt, which pertains to the P2i2i2i space group, has layers of donor molecules and ions derived from BEDT which alternate with layers of the chiral counter-ions. 

Simmons, W., Gonnissen, D., and Hubin, A. 1997. Study of the initial stages of silver electrocrystallisation from silver thiosulphate complexes Part I. Modelling of the silver nuclei formation during the induction period. Journal of Electroanalytical Chemistry 433, 141-151. 

Electrocrystallisation is the usual method appHed to grow single crystals of molecule-based conductive materials. Confined electrocrystallisa-... 

P. Cassoux, L. Valade and P.-L. Fabre, Electrochemical methods, electrocrystallisation, in Comprehensive Coordination Chemistry II From Biology to Nanotechnology, Fundamentals ligands. Complexes, Synthesis, Purification and Structure, Vol. 1 (ed. A.B.P. Lever), Elsevier, Amsterdam, 2003, pp. 761-773. 

Dihydroxynaphthalene and 9,10-diacetoxyphenanthrene react with 1,2-diols and 1,2-dithiols in a one-pot synthesis of annulated 2,3-dihydro-1,4-dioxins and -1,4-dithiins (Scheme 26) <04TL1343>. The reaction of 2,3-dihydroxynaphthalene with 1,2-dihalogenated aromatic compounds leads to linearly annulated dioxins of particular interest are tri- and tetra-dioxins and various hetero-fused dioxins e.g. 62 (34%). Several examples yield cation radical salts on electrocrystallisation <04T8899>. Linear arrays of fused pyran-dioxin-cyclohexane rings as found in natural products derived from the milkweed family have been described e.g. 63 <04EJO4911>. 

Some purification methods are connected with the growth of single crystals. On the whole, the growth of organic crystals is an independent process which must be carried out with great care. There are growth methods starting from the gas phase, from the melt and from liquid solutions, as well as electrocrystallisation. 

Fig. 3.12 An apparatus for electrocrystallisation. Depending upon the polarity, the crystals grow from a suitable solution when a voltage is applied to one of the two electrodes. A sintered-glass filter in the lower part of the apparatus prevents contamination from the reference electrode during the slow crystal-growth process.

Bechgaard salts. These salts are therefore nearly one-dimensional conductors with a temperature dependence of their conductivity that is characteristic of these (compare Figs. 10.3 and 10.4). By electrocrystallisation, one can obtain them in the form of long, thin needles with the a axis in the long axis of the needles. Here, the oxida-... 

Bockris, J. O M. and Razumney, G. (1967) Fundamental Aspects of Electrocrystallisation, Plenum Press, New York. 

Vetter. K. J.. Electrochemical Kinetics, English edn.. Academic Press. New York (1967) Bockris. J. O M. and Razurnney. G. A.. Fundamental Aspects oj Electrocrystallisation, Plenum Press (1967)... 

Aravinda CL, Freyland W (2006) Nanoscale electrocrystallisation of Sb and the ctunpound semiconductor AlSb from an ionic liquid. Chem Commun 16 1703-1705. doi 10.1039/ b517243h... 

Vasilakopoulos D, Bouroushian M, Spyrellis N (2009) Electrocrystallisation of zinc from acidic sulphate baths A nucleation and crystal growth process. Electrochim Acta 54 2509-2514. doi 10.1016/j.electacta.2008.11.059... 

A literature survey shows that the corresponding data are rather contradictory, as far as the solubilities of CrCk and CrCls are concerned, and as far as the Cr(II) / Cr deposition step is concerned. In fact, the kinetics of this step has been reported to be fast, or slow, and there is some agreement to think that this step is complicated by adsorption or electrocrystallisation phenomena. In this talk, we will tackle the questions of the chromium chlorides solubility, of the Cr(III) or Cr(II) adsorption on various substrates and the kinetics of the final electron exchange. 

We see that the characteristics cited above are correlated with each other thus a preliminary investigation on the electrocrystallisation of refractory metals is necessary to optimize all the parameters intervening in the growth of the coating. 

As Girginov et al have pointed out [15], very little attention has been paid to the electrocrystallisation kinetics of refractory metals and factors influencing the process, which are fundamental for the monitoring of the process. Nevertheless, we have recently reported chronoamperometric investigations on niobium electrocrystallisation [20] and concluded that the nucleation is instantaneous and further growth of the nuclei is controlled by diffusion. This situation favours an unequal current distibution when high current densities are applied to the cathode and so it is conducive to the inequality of the thickness of the plate. 

The above discussion was included largely to enable the identification of the cyclic voltammetric behaviour of a deposition process. However, cyclic voltammetry is generally not a good choice of technique for investigations of this type. Electrocrystallisation is discussed in detail in Chapter 9. 

The subject of the study of passivation processes by impedance analysis has been extensively reviewed by Epelboin et al [19]. Other areas where the impedance method has been developed include solid electrolytes and superionic conductors [20], electrocrystallisation [21] and state-of-charge testing of primary batteries [22]. Numerous other examples of the use of a.c. techniques have been collected together by Gabrielli [23],... 

Many important electrode reactions involve the formation of a solid phase, either as the result of the reduction of ions in solution, as in the case of metal deposition, or by oxidation of the electrode and subsequent reaction with anions to form an anodic film. The term electrocrystallisation is used to describe electrode processes of this kind. 

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