Structural Characterization by X-Ray Diffraction

X-ray diffraction is without question the most important initial method for characterizing materials in the solid state because the results are derived rather directly from the atomic or molecular arrangement of the substance, and the methods are relatively routine and simple. X-ray methods are used in research, development, and quality control in metallurgy, ceramics, and the mineral, chemical, and pharmaceutical industries, and practically anywhere chemical and physical properties must be related to crystal structure. A modern materials program thus requires extensive use of X-ray diffraction analysis. This section outlines the use of the method for the study of materials in the form of powders and single crystals. 

Polycrystalline specimens are used for identification of the phase and for lattice parameter determination. Well-crystallized single crystals are used in structure determination and X-ray topographic study of perfection. The capability at room temperature and pressure will be treated first, followed by sections dealing with high- and low-temperature studies and high-pressure work. 

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Complexation via amidinate units was found in ruthenium complexes containing tri- and pentacyclic trifluoromethylaryl-substituted quinoxalines. The complex fragment [(tbbpy)2Ru] (tbbpy = bis(4,4 -di-ferf-butyl-2,2 -bipyridine) has been employed in these compounds which have all been structurally characterized by X-ray diffraction. ... 

For some other examples of bicarbonate complexes that have not been structurally characterized by x-ray diffraction see ... 

The monomeric terminal imido complexes cp IrNR (R = tBu, SiMe2 Bu, 2,6-Me2C6H3, 2,6-1Pr2C6H3) were prepared from [cp IrCl2]2 and four equivalents of LiNHR in THF.104 All four product species were structurally characterized by X-ray diffraction and exhibit short Ir—N distances (1.712(7)—1.759(3) A) and nearly linear Ir—N C (Si) angles. Some reactions of cp IrN Bu are highlighted in Reaction Scheme 9. Complexes (77) and (78) have been studied by single-crystal X-ray diffraction. 

With the rapid development of modem analysis techniques, especially the popularization of single-crystal X-ray diffraction equipment, the origin of various physical and chemical properties, and the clear elucidation of correlations between the structure and properties of Pcs have become possibilities. Together with the maturity and diversification of their modifications, many Pcs have been synthesized and their molecular structures characterized by X-ray diffraction analysis in the past 5 years [15-77]. 

This extremely air-sensitive compound, which is valence isoelectronic to an olefin, has been structurally characterized by X-ray diffraction. It has a short carbon-phosphorus double bond (1.62 A) the phosphorus and carbon atoms adopt a trigonal planar geometry with a dihedral angle of 60° (Fig. 3). This value is significantly larger than that reported for the most crowded olefin.61 Formally, this compound can be viewed as the product of a car-bene-carbenoid coupling between bis(trimethylsilyl)carbene and bis(diiso-propylamino)phosphenium triflate. Note that another route to methylene-phosphonium salt has been reported by Griitzmacher et al.62... 

The use of KN(SiMe3)2 as metalating reagent enabled us to prepare the dimeric potassium derivative [(Cy7Si70i2)2Kg(DME)4] (18) as a crystalline solid, which was structurally characterized by X-ray diffraction (Scheme 7). Here again a box-shaped KgOg polyhedron forms the central structural unit. Four potassium ions are coordinated by DME (1,2-dimethoxyethane) ligands. ... 

Subsequent reaction of 91 with the homoleptic samarium aryloxide Sm(OC6H3tBu2-2,6)3 according to Scheme 29 gave the novel heterobimetallic Li/Sm silsesquioxane complex 92, which was structurally characterized by X-ray diffraction. 

The first iron-containing silsesquioxanes which appeared in the literature were compounds containing ferrocenyl units as side-groups.However, these are not within the scope of this review as iron is not part of the metallasilsesquioxane skeleton. Meanwhile, several ferrasilsesquioxane complexes have been synthesized. The first iron(III) compound of this type was prepared in our laboratory according to Scheme 56. ° In 161, the coordination sphere of iron is completed by TMEDA (N,N,N, N -tetramethylethylenediamine) as a chelating amine ligand. Pale yellow, crystalline 161 was isolated in 80% yield and structurally characterized by X-ray diffraction. This compound was later used by Maxim et to prepare iron... 

The benzyl derivative Cp Ta( j -02)Bn was structurally characterized by X-ray diffraction the 02-ligand is side-on coordinated and lies in the equatorial plane of the bent metallocene fragment. The 0-0 distance of 1.477(8) A and the 0-0 stretching frequency (vo-o = 863cm ) are consistent with a peroxo hgand (02 ) coordinated to tantalum in its highest possible formal oxidation state (+V). Notably, base appears to stabihze these complexes i.e., in the presence of triethylamine Cp Ta( 7 -02)Me did not decompose even when heated to 80 °C. 

While most superoxo complexes—in contrast to peroxo compounds— have been assigned a bent, end-on coordination mode [9], the superoxide ligand of Tp Cr(02)Ph was suggested to exhibit the more unusual side-on (r] ) coordination [10]. The reactivity of the complex did not allow for the determination of its molecular structure however, close analogs could be isolated, crystallized and structurally characterized by X-ray diffraction. For example, the reaction of [Tp Cr(pz H)]BARF (pz H = 3-tert-butyl-5-methylpyrazole, BARF = tetrakis(3,5-bis(trifiuoromethyl)phenyl)borate) with O2 produced the stable dioxygen complex [Tp Cr(pz H)( ] -02)]BARF (Scheme 3, bottom), which featured a side-on bound superoxide ligand (do-o = 1.327(5) A, vo-o = 1072 cm ) [11]. Other structurally characterized... 

In this context, it is worth mentioning that there is only one other, clear-cut example for the simultaneous occurrence of the acyl(silyl)carbene-to-acylsilene and the acylcarbene-to-silylketene rearrangement of an acylcarbene bearing a Si—Si substituent. Carbene 57, generated by photolysis of diazoketone 56 in benzene, isomerized to both 58 and 59 in about equal amounts44. While the acylsilene cyclized to 1,2-silaoxetene 60, the ketene was isolated and structurally characterized by X-ray diffraction analysis of the derived... 

The tetrachlorobenzodithiadiazepine 4 (Figure 9) was structurally characterized by X-ray diffraction. The puckered seven-membered ring displays localized single and double bonds. The structural data indicated that there is no steric strain on the amidine moiety <1997IC4772>. This compound is also a precursor to obtain the radical (Section 13.17.7.4). 

These three phenyl gold(I) derivatives have been structurally characterized by X-ray diffraction methods, showing discrete linear molecules with similar Au-C and Au-P... 

Although none of them have been structurally characterized by X-ray diffraction, no intramolecular Au- -Au interaction is expected in these species because of the presence of a large number of pentafluorophenyl rings in each anion. Thus, in the crystal structure of the trinuclear starting methanide, which is less hindered, the shortest intramolecular Au- -Au separation is 6.10 A.90... 

The blue-green neodymium complex 58f was structurally characterized by X-ray diffraction (Fig. 18). Despite the presence of both the large, flat C8Hl ligand and the very bulky diphenyl-bis(JV-trimethylsilylimino)phosphinate anion, the coordination sphere of neodymium leaves enough room to accomodate an additional THF ligand. The central four-membered ring formed by the neodymium atom and the NPN chelate system is nearly planar. 

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