X-rays crystallography tables

Acyl-, 4-alkoxycarbonyl- and 4-phenylazo-pyrazolin-5-ones present the possibility of a fourth tautomer with an exocyclic double bond and a chelated structure. The molecular structure of (138) has been determined by X-ray crystallography (Table 5). It was shown that the hydroxy group participates in an intramolecular hydrogen bond with the carbonyl oxygen atom of the ethoxycarbonyl group at position 4 (8OCSCII21). On the other hand, the fourth isomer is the most stable in 4-phenylazopyrazolones (139), a chelated phenyl-hydrazone structure. 

Structures of some of the phosphaquinoid and phosphathienoquinoid compounds were further studied by X-ray crystallography (Table 2, Fig. 1) [9, 11, 12],... 

Indeed, Orpen and Connelly, in their analysis of bond length data derived from X-ray crystallography (Table 7), support the a theory but in modified form, reintroducing a 3d orbital contribution from phosphorus. This revisionist view, maintaining a role for the phosphorus 3d orbitals, albeit diminished, has received support from quantum mechanics... 

The presence of a 8-agostic interaction in 10a was later confirmed by DFT calculations (BPW91) on the model complex EtTi(Cl)3(H2PCH2 CH2PH2) (10c) [43]. The calculated geometrical parameters were in excellent agreement with the experimental structure determined by X-ray crystallography (Table 1) [41]. 

The complexes [(C5H4-f-Bu)3UL] (L = pyridine, picoline) and [(C5H4SiMe3)3UL] (L = pyridine, lutidine, pyrimidine, and dimethylpyrazine) have been characterized by single crystal X-ray crystallography (Table 4). All the mononuclear complexes were found in the familiar pseudotetrahedral arrangement of the three ri -cyclopentadienyl ligands and the coordinated Lewis base. 

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