Sepulchrates structure

Thus, for theoretical calculations of the sarcophaginate and sepulchrate structures, one should take into account inter- and intramolecular nonbonded interactions and electronic effects. The calculations based on geometric and/or repulsion models are obviously justified only for complexes with insufficient or no preference for TAP or TP structure (ALFSE = 0). In this case, the ligand determines the complex geometry. In all other cases, the contribution of the metal ion electronic configuration cannot be neglected [178],... 

X-ray diffraction studies of the Co(n) and Co(m) sepulchrate complexes indicate that they have similar structures although, as expected, the M-N bond lengths are shorter (1.99 A) in the Co(m) complex than in the Co(ii) species (2.16 A). The Co(n) complex was obtained by direct reduction of the Co(m) analogue using zinc dust. A striking feature of the syntheses of these species is that the reactions proceed with retention of the configuration of the [Co(l,2-diaminoethane)3]3+ starting complex. 

A.-M. Sepulchre, G. Lukacs, G. Vass, and S. D. Gero, Synthese d hydrates de carbone a chaine ramifiee ou allongee, par acylation nucleophile. Determination de structure par resonance magnetique nucleaire H et 13C, Bull. Soc. Chim. France, (1972) 4000-4007. 

Naden continued in verse to describe the presentation, then reported how a member of the audience in sad sepulchral tone 95 had disputed the speaker s view of molecules, particularly, it can be inferred, the cyclic structure of benzene first proposed by Kekule only 20 years earlier. Her Demonstrator, Thomas Turner, obviously contested the ring structure of benzene, as he replied in verse ... 

Since sarcophaginates and sepulchrates are relatively easy to crystallize, a great number of these compounds are studied by X-ray crystallography, which together with molecular geometry calculations makes it possible to establish their three-dimensional structures both in crystal and in solution. The optical activity of such clathrochelates enables one routinely to utilize circular dichroism measurements to investigate their structure. The spatial and electronic structures of sarcophaginates and sepulchrates are much more seldomly determined by alternative spectral techniques compared with clathrochelates of other types. 

As mentioned above, the three-dimensional structure of a considerable number of these compounds has been established mainly by X-ray crystallography. The main structural characteristics for sepulchrate and sarcophaginate complexes as well as for free ligands are listed in Tables 2 and 3. 

Owing to the relative flexibility of these structures and the presence of numerous chiral centres in sepulchrate and... 

The main structural parameters for d-metal sepulchrates and sarcophaginates. 

The essential information on the spatial and electronic structure of diamagnetic sarcophaginates and sepulchrates in solution has been obtained from their and NMR spectra, NMR is a more precise and more reliable instrument for investigations of such complexes due to a wide chemical shift range. The carbon atoms of the macrobicyclic framework are numbered as shown in Scheme 101. 

In the case of sarcophaginates and sepulchrates, the M-N distances exceed the sum of the nitrogen radius and the corresponding metal ionic radius in the appropriate oxidation state. Thus, a redox process is not limited by the cavity size, which in bonding can either decrease or increase with the change in the radius of the central ion owing to structural rearrangement. The increase in the cavity size in a reduction process occurs on translational rotation... 

Most of the investigations in this field have focused on the use of cobalt sepulchrate and sarcophaginates as electron-transfer sensitizers in photocatalytic cyclic solar energy conversion processes [340, 375-378]. This is mainly due to their specific redox behaviour stipulated by peculiarities of the cobalt ion electronic structure and screening of this ion by an encapsulating ligand. 

When immobilized on polymer surfaces, cage complexes may be utilized for modifications of electrodes. The increase in the electron-transfer rate on such surfaces is governed by two factors a high rate of electron transfer in cobalt clathrochelates and the regular disposition of these complexes on the surface. The properties of immobilized macrobicyclic complexes have been considered in Refs. 94, 410, and 411. Cyclic voltammetry has been used to characterize the incorporation of a range of structurally different d-metal sarcophaginates and sepulchrates into Nafion polymer [412]. 

The inner-sphere reductions of [Co(NH3)5(SCONHR)] and [Co(NH3)5 (OCSNHR)] by Gr involve attack at the remote oxygen and sulfur atoms, respectively, with a subsequent isomerization of the 0-bonded ehromium(III) product in the former reaction. The unusually rapid reactions of the S-bonded cobalt(III) complexes are attributed to a structural tran -effect on the Co—N bond length, reducing the reorganization energy needed to form the transition state. A kinetic study of the Cr reduction of [Co(NH3)5(pyruvate)] reveals that the rate of reduction is dependent on the nature of pyruvate ligand, with the keto form about 400 times as reactive as the hydrated form. An inner-sphere mechanism has be postulated for the Cr reduction of [Co(NH3)5(pyridine N-oxide)] on the basis of the rate and activation parameters. The outer-sphere Cr reduction of [Co(sepulchrate)] is catalyzed by halide ions, with the ion-pair formation constants for [Co(sep), estimated to be 5.5, 2.3, and 1.7 M" for Cl", Br", and I", respectively. ... 

Olewnik, E., Czerwinski, W., Nowaczyk, X, Sepulchre, M.O.,Tessier, M., SaM, S., Fradet, A. (2007) Synthesis and structural study of copolymers of L-lactic acid and bis (2-hydrosyethyl terephthalate). Europ. Polym. Journ., 43, 1009-1019. 

Figure 15 X-ray structure of the [Co(sepulchrate)] + ion showing the octahedral coordination of the central Co(III) (blue, nitrogen gray, carbon). ...

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