Structure determination 270 INDEX

Several structural determinations indicate that the interaction... 

Electronic and NMR spectra of these complexes, together with X-ray structural determinations, indicate that the valence is completely averaged over at least six Mo atoms (251, 253, 254). 

The only pentosans which have been studied to any great extent are the xylans. These can be obtained from all lignified cell membranes by extraction with 5% sodium hydroxide solution after lipids, pectic materials etc. have been removed. The conditions necessary to avoid degradation during isolation have been outlined.2 Early structural determinations indicated that arabinose was present as a non-reducing end-group in a branched molecule which had a chain-length of 18-20 D-xylo-furanose residues.27 It has been shown recently, however, that the xylan from esparto holocellulose can be purified free of arabinose after several re-precipitations of the copper-complex.28... 

An X-ray structure determination indicated that in the solid state, compound 11 exists as the tetrameric structure shown in Figure 5. 

The high-oxidation state Mo complexes do not follow the 18 VE rule. However, they contain n-donor ligands such as O2- or Cl. Metal donor distances obtained from X-ray structure determinations indicate that in these complexes n-donor bonds reduce the electron deficiency of the metal centers. Another example is [Mo(NMe2)(NO)(S4)] obtained according to Eq. 14. 

The reaction of Cp2Ti(CF3 803)2 with bipy or phen forms [Cp2Ti(bipy)](CF3 803)2 and [Cp2Ti(phen)](CF3 803)2, respectively. An X-ray structure determination indicates that the Ti atoms are to a first approximation tetrahedrally coordinated, and the atoms of the bipy or phen chelate ligands are nearly coplanar. ... 

The position of [Ag(bpy)2] salts is slightly clearer. Although crystal structural determinations indicate weak interactions between [Ag(bpy)2l cations and anions or solvent molecules, the cations can be regarded as homoleptic [Ag(bpy)2] complexes (1, 617, 728). Reddish-brown salts of [Ag(bpy)2l are readily obtained by electrochemical, persulphate, or ozone oxidation of either [Ag(bpy)2l or silver(I) salts in the presence of excess bpy (543, 621, 629, 641, 926, 967). The salt [Ag(bpy)2]fS03Fl2 is prepared by the reaction of bpy with Ag(S03F)2, obtained from the direct reaction of silver with S2O6F2 (541, 542). 

Novel lanthanide fi-diketonate complexes have been synthesized, Their properties include thermal, hydrolytic and oxidative stabilities, volatility, Lewis acidity, and unusually high solubility in nonpolar organic solvents. Various combinations of these properties make lanthanide complexes useful as NMR shift reagents and fuel antiknock additives and in other applications. NMR spectral studies revealed that the Pr(III), Yb(III), and Eu(III) complexes of 1,1,1,2,2,3,3,7,7,7- decafluoro-4,6-heptanedione have sufficient Lewis acidity to induce appreciable shifts in the proton resonances of weak Lewis bases such as anisole, acetonitrile, nitromethane, and p-nitrotoluene. Data from single-crystal structure determinations indicate that the NMR shift reagent-substrate complexes are not stereochemically rigid and that effective axial symmetry may exist by virtue of rapid intramolecular rearrangements. 

The air- and moisture-sensitive compound can be stored for several weeks in a carefully sealed flask under an atmosphere of dry nitrogen, mp 289° IR vco at 1980, 1940, 1690 cm" (Nujol mull) H NMR (CHjClj, 60 MHz) 8nch, 3.0, P NMR (85% H3PO4, CH2CI2, 36.43 MHz) 8 69.5. The X-ray structure determination indicates that two (CO)3Mo fragments are bridged by three diphosphane... 

The experimental barrier for the N-(l-naphthyl) analogue (121.0 kJ mol ) was quoted in a contribution dealing with molecular-mechanics calculations (91MI207). An X-ray structure determination indicated that the inter-ring angle is 85.5° (89AX(C)126). Molecular-mechanics calculations reproduce the experimental barriers (91MI207). 

Crystal structure determinations indicate covalent structures for (trialkylsilyl) phosphanides Mg[P(SiMe3)2]2 DME and M[P(SiR3)2]2, where M = Zn, Cd, Hg, Sn. These may be monomeric (9.212a) or dimeric (9.212b) depending upon R and whether in solid state or in solution [21,22]. 

Reaction of hexa-2,4-diyne with Fe(CO)6 yields the cyclopentadienone complex (108), characterized crystallographically. Reaction of Fe(CNBu )6 with PhC=CPh yields (109), characterized crystallographically. The ion HFe(CO)4 reacts with acetylenes HC=CCOR to yield products of structure (110), although a crystal structure determination indicates some contribution from a -olefin- -acyl structure. Protonation of (110) yields Fe[t -HRC=C(H)(COR)](CO)4 via an intramolecular decarbonylation. - Photochemical reaction between... 

The complex Cp2Ti(CO)(PhC=CPh) has been prepared a structural determination indicates that the complex is best regarded as metallocyclopropene. ... 

Another illustration is provided by the common substance sulfuric acid, (H0)2S02. The absorption spectrum of discrete sulfuric acid molecules has been recently studied by microwave spectroscopy. A detailed molecular structure determination indicates the free acid does not have the expected C2v symmetry, but rather the symmetry is only C2. The stable conformation is depicted in Fig. 13b. The interesting features found, which show the power of the method, are that the OH groups are rotated ca. 90° from the compact C2v form and the heavy-atom framework is slightly twisted and its symmetry is also not precisely C2v... 

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