Examples of structure derivations

Two straightforward structure derivations can be used to illustrate the analysis of a diffraction curve and the structural information that can be extracted when conditions are favorable. 

One example is the square-planar tetrachloro- and tetrabromo-complexes formed by gold(III) in aqueous solution, which can be uniquely and precisely structure determined from a single diffraction curve (18). The heavy atoms in the complexes and the highly concentrated solutions, that can be prepared, result in dominant contributions from the complexes to the scattering curve. 

The other example is the chloro complexes of platinum(II) and palla-dium(II), which also have square-planar structures (13). The PtCl42-and the PdCl42 complexes have identical structures, with the same bond lengths, and form isostructural solutions. By using the difference between their normalized diffraction curves contributions from interactions not involving the metal atoms can be eliminated and precise structures can be derived, not only for the complex but also for the structure beyond the first coordination sphere of the metal ion. 

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Scheme 6.11. Examples of structures derived from polymer-bound 5-(2-bromoacetyl)-pyrroles.

Two structures are homeotypic if they are similar, but fail to fulfill the aforementioned conditions for isotypism because of different symmetry, because corresponding atomic positions are occupied by several different kinds of atoms (substitution derivatives) or because the geometric conditions differ (different axes ratios, angles, or atomic coordinates). An example of substitution derivatives is C (diamond)-ZnS (zinc blende)-Cu3SbS4 (famatinite). The most appropriate method to work out the relations between homeotypic structures takes advantage of their symmetry relations (cf. Chapter 18). 

A number of compounds derived from the basic peptidomimetic 429 have been prepared for different purposes in medicinal chemistry. In most cases, the source of the sulfur atom is cysteine. Some examples of structures and targeted applications are reported in Table 17. 

Apart from this type of superstructure, which could then be described as superstructure of the first kind, another type of structure derivation can be considered an example could be given by the relation between the CaCu5 and the CeCo3B2 structures. 

FDA) for use in humans to treat malaria because this drug is considered a safe drug with few side effects.These features prompted various scientists around the world to evaluate the potential of artemisinin (1) and derivatives to control cancer cells proliferation. This chapter reviews the recent advances on analytical methods for extraction and quantification of artemisinin (1) from A. annua. Examples of artemisinin-derivatives with antiproliferative activities are listed, describing the structure-activity relationships of 96 compounds. This knowledge is essential for future development and use of artemisinin derivatives in cancer therapy. The mechanism of action of artemisinin and derivatives on cancer cells have been well reviewed in literature and therefore is not discussed in this chapter. 

In this group of derivatives, we have included all compounds in which attachment of the substituent results in the formation of a cyclopropane ring on the surface of Cgo- The bridging atom may be carbon, nitrogen, a transition metal, or oxygen (epoxyfullerene). Basic structures for these compounds are shown in Fig. 16. The electrochemistry of representative examples of all of these derivatives has been reviewed previously [83], and only general observations are presented below, along with some specific examples of new derivatives with novel electrochemical behavior. 

Another example of structural changes induced in the complex involving porphyrin derivative are shown in Figure 1.6. 

The case study of the tetranuclear manganese complex presented above and the specific examples of structure/spectroscopy correlations have established the validity of the proposed methods and set the stage for more ambitious applications. The first such application has been the recent evaluation of several structural models of the OEC in the S2 state ( 1 3) of the Kok cycle (107). Twelve structural models were considered, 10 of which were based on Mn405Ca core topologies derived by polarized EXAFS spectra. Figure 19 shows one of the models included in the set. 

An important recent development in the area of the monodentate amido metal chemistry has come from the group of Cummins who introduced ligands of the type —N(R)Ar (for example, R = Bu , 1-adamantyl (I-Ad), 2-adamantyl (2-Ad), —C(CD3)2(CH3) Ar = Ph, C6H3Me2-3,5, C6H4F-4).These allowed the isolation of an Mo N(R)Ar 3 species having three-coordinate molybdenum as well as three-coordinate derivatives of several other metals. Apart from [M N(SiMe3)2 3] (M = Y," La), the molybdenum compounds are the only examples of structurally characterized open shell, three-coordinate homoleptic amides... 

Part II deals, in six chapters, with the principles underlying the progressive stages in the elucidation of internal structure. Chapters VI and VII deal with the principles of structure determination by trial Chapter VIII with the use of physical properties (such as habit, cleavage, and optical, magnetic, pyro- and piezo-electric properties) as auxiliary evidence in structure determination. In Chapter IX are to be found several examples of the derivation of complete structures. Chapter X gives an introductory account of the use of direct and semi-direct methods based on the calculation of electron density distributions and vector distributions from X-ray diffraction data. 

Examples of radicals derived from the largest parent compounds of the four types of bicyclics and the recommended names are given below The recommended fixed numberings for these structures are shown on 3-thujyl, 2-caryl, 3-pinanyl, and 2-bomyl. Names in parentheses under some of the recommended radical names are the common terpene radical names ... 

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