Diffraction methods displaying

Infrared spectral identification of adduct formation involving carbon dioxide and a transition metal complex has often been in error because of subsequent reactions of C02 with concomitant production of carbonato-, hydrogen-carbonato-, or carboxylato-metal complexes. Indeed Mason and Ibers (9) have suggested that the only acceptable structural characterization forjudging the authenticity of a class of transition metal-C02 complexes should be diffraction methods. X-ray structural studies have verified at least six C02 adducts which display all three types of bonding modes of... 

Molecular and crystal structures of the parent 1,3-ditellurole were studied by use of an X-ray diffraction method (85JA6298). Figure 6 displays the molecular geometry of 1,3-ditellurole. 

The crystal structures of the AuI/Fe11 complexes have been determined by X-ray diffraction methods showing a typical linear environment for the gold(I) center and none of them display intramolecular Au- Fe interactions (see Fig. 8). The phosphino derivative does not display intermolecular Au- -Au interactions either (the shortest gold-gold distance is 5.560 A), but the lattice shows F- -F (2.858 A) and F- -H (2.55 and 2.60 A) contacts. In contrast, ferrocenylpyridine complex molecules are associated into pairs across inversion centers via a weak intermolecular Au- -Au interaction of 3.301(2) A, similar to that observed in the case of the (thiophenylmethyl)diphenylpho-sphine derivative [ (C6F5)Au 2 p.-PPh2C(=S)N(H)Me described above (Au- -Au 3.2712(5) A).34... 

With the advent of relatively accurate experimental electron density maps based on high-precision X-ray diffraction methods, it became possible to see more realistically how electron density actually varies along the line between adjacent nuclei in an ionic crystal. An example is provided by LiF, as shown in Fig. A4-1. It can be seen that neither the Goldschmidt (G) nor, a fortiori, the Pauling (P) radii for Li+ are at the minimum (M) of electron density. Thus these radii could be said to be wrong in an absolute sense, even though the complete sets to which they belong display internal consistency. 

Surfiice order and cleanliness. The most common use of LEED is in association with other surface analysis or surfiice research methods, to check surfiice structural order and cleanliness. A visual display of the diffraction pattern is used. An expected pattern, with sharp diffracted beams, is an indication that the surfiice is clean and well ordered. 

How then can an exact match be made In this case there must be some outside knowledge supplied and an examination of the X-ray fluorescence spectra would indicate the presence of only Co and O in the unknown powder. When this information is used, the unknown is identified as Co304, card 9-418. However, when the card is examined the weak line 2.13 A remains unidentified in the unknown pattern. X-ray intensity is proportional to the amount of the diffracting material present, so it is natural to suspect that a contaminant phase will only display its most intense lines. The problem in this case is that there is only one line remaining so that the Hanawalt manual is useless to help in the identification. The intuitive method must be used. The key question to be answered is, what contaminants might be found in a sample containing only Co and O The two possibilities that come to mind are elemental Co or another oxide of Co. When these two possibilities are checked, it is quickly found that the most intense line of CoO, card 9-402, is indeed 2.13 A, and the identification is complete. 

---