X-ray diffraction, studies of complexes

X-Ray diffraction studies of complexes of 2,9-dimethyl-1,10-phenanthroline (cf. e.g. Preston and Kennard33 and Power34) and 2,4,7,9-tetramethyl-l,10-phenanthroline (e.g., Canty and Gatehouse35) and the overcrowded molecule, l,10-dichloro-3,8-dimethyl-4,7-phenanthroline,36 have also been determined. 

Detailed structures for the active sites of enzymes are difficult to obtain and have been worked out only for a few enzymes that have been studied extensively by both chemical and x-ray methods. Very revealing information has been obtained by x-ray diffraction studies of complexes between the enzyme and nonsubstrates, which are molecules similar to actual substrates and complex with the enzyme at the active site, but do not react further. These substances often inhibit reaction of the normal substrate by associating strongly with the enzyme at the active site and not moving onward to products. The x-ray studies of enzymes complexed with nonsubstrates show that the active site generally is a cleft or cavity in the folded structure of the enzyme that is largely hydrophobic in character. The enzyme-substrate complex can... 

It is interesting that x-ray diffraction studies of complex 7c revealed a significant degree of ring strain imposed by the formation of the five-membered metallacycle (Figure 12.3) [8c, 8d] as shown by the nonplanarity of the sp2 carbon C(l) (see Figure 12.3). 

An X-ray diffraction study of complex 52 showed that this mixed oligomer is not planar. The thiophene-thiophene, thiophene-phosphole and phosphole-phosp-hole twist angles are 6.35, 24.24 and 66.26°, respectively [43a]. Compound 51 un-... 

Proton NMR spectral analysis of the protonated complexes 5.89-5.91 revealed highly unsymmetrical structures, each of which appeared (on the basis of integration studies) to contain three internal NH protons. For these reasons, a sitting-a-top structure was proposed for these complexes. Subsequently, the out-of-plane metal ligation that these structures required was confirmed via a single crystal X-ray diffraction study of complex 5.90. The resulting structure is shown in Figure 5.5.3. ... 

Interestingly, the X-ray diffraction study of complex 7h (Scheme 11.6) and 8h,i (Scheme 11.7) revealed that the twist angle between the phosphole ring and the azahelicene (<50°) allows an electronic interaction between these two 7r-units to take place. [46, 45] The helical shape of the aza[4]helicene part is not perturbed upon complexation since the twist angle between the two terminal aromatic rings of the aza[4]helicene (33.1°) is comparable to that of the free ligand (30.1°) [45,46]. This result shows that mixed phosphole-azahelicene derivatives can act as... 

The square-planar complex (383) shows a monotropic smectic A-phase, and the X-ray diffraction study of the yellow form shows that the whole molecule adopts an extended rod-like shape with an all-trans conformation of the decycloxy chain.616... 

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. 

Fullerene The reaction of 1 with an equimolar amount of fullerene- 60 in toluene at room temperature gives the first fullerene complex of titanium Cp2Ti(q2-C60) 121 [60]. An X-ray diffraction study of this complex has shown that it has the structure of a titanacyclopro-pane derivative, which should have a high potential for further derivatization of the fullerene. 

Interestingly, on warming a solution of 94 the phosphine ligand dissociates to afford the new complex 95. An X-ray diffraction study of the latter complex indicates that the phosphinocarbene behaves as a 4-electron ligand (coordination mode B).86... 

A -chlorosuccinimide yields dichloro-substituted [N(PPh3)2][7,l l-Cl2-2,2,2-(CO)3-c/o50-2,l-FeCBioH9] (42). In each of these products, hydride replacement again occurs at boron atoms that are p with respect to the carbon atom in the iron-bound CBBBB face, a feature confirmed by an X-ray diffraction study upon complex 42. This site of substitution was also verified by treatment of 41 with Ag[Bp4] in the presence of THF, which afforded compound 30 via Agl elimination. 

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