Crystallography protonic

There is no firm evidence for the structure of the initial protonated species, but, bearing in mind that the HOMO of a /<-peroxo complex is essentially a jTg orbital of dioxygen (Sect. D), and on the basis of other structural evidence, it seems probable that the proton is bound to one oxygen only. The structure of the final isomerised product has been determined by X-ray crystallography Protonation of a /<-peroxo complex of cobalt with tertiary arsine ligands has also been reported ... 

It is interesting to note that the acyclic analog, nitroguanidine, exists in the symmetrical form 288 rather than as 289. Structure 288 has been established by ultraviolet and proton nuclear magnetic resonance spectroscopy. X-ray crystallography, dipole moments, and ipK measurements (see reference 367 and references therein). 

The results for [16] annulene are similar. The compound was synthesized in two different ways, both of which gave 103, which in solution is in equilibrium with 104. Above -50°C there is conformational mobility, resulting in the magnetic equivalence of all protons, but at — 130°C the compound is clearly paratropic there are 4 protons at 10.565 and 12 at 5.35 5. In the solid state, where the compound exists entirely as 103, X-ray crystallography shows that the molecules are nonplanar with almost complete bond alternation The single bonds are 1.44-1.47 A and the double bonds are 1.31-1.35 A. A number of dehydro and bridged... 

Both dialkynylated cymantrenes 16 and 17 have the same symmetry and similar NMR spectra, so that the ultimate structure elucidation had to rest upon X-ray crystallography. It was reasoned that the dialkynylcymantrene with the smaller /(H,H) coupling of the cyclopentadienyl protons should be 17, an interpretation reinforced [23 a] by the result of the single-crystal structure. 

In the case of the smaller macrocycle [13]aneN4, six configurational isomers exist for [Ni([13]aneN4)]2+ due to the orientation of the N—H protons above or below the plane of the macrocycle. X-ray crystallography and NMR spectroscopy, respectively, revealed that the R,iS,7 ,iS -[Ni([13]aneN4)]2+ form (trans- ) is the preferred one both in aqueous solution and in the solid state.1 43... 

Protein-crystallography has revealed many of these groups as binding centers of heavy metals such as Pt(II), Hg(II), Au(III). It is important to note that the solution conditions in which the reagent has been applied to these crystals differ widely. If an acid pH has been used then groups with a high affinity for protons. 

Protonation of 12 yields a compound best described as a face-protonated methylidyne complex, the tungsten-carbon bond length lying in the range observed for a triple bond (28). Protonation of the osmium compound 13 yields a true carbene complex, which for R = Ph has been characterized by X-ray crystallography (see Sections IV and VI). 

Siderophore-ionophore supramolecular assembly formation via host-guest complexation of the pendant protonated amine arm of ferrioxamine B has been confirmed by X-ray crystallography (Fig. 28) (203). The stability and selectivity of this interaction as a function of ionophore structure, metal ion identity, and counter anion identity were determined by liquid-liquid extraction, isothermal calorimetry, and MS (204 -211). Second-sphere host-guest complexation constants fall in the range 103— 106M-1 in CHC13 and methanol depending on ionophore structure. 

The coordination properties of pyrimidine bases seem to be less versatile than those of purine derivatives. Various Pt(II) and Pt(IV) compounds, including cis- and rrans-DDP, preferentially bind to the N3 site in N1-substituted cytosine derivatives (Figure 7), as verified by a variety of methods [7]. Simultaneous binding to N3 and to the exocyclic amino group C(4)-NH2 upon loss of a proton has been observed in a bridged Pt(II) system and in a chelated Pt(IV) system [7]. With 1,3-di-methyluracil, Pt(II) coordination to the C5 atom has been ascertained by X-ray crystallography [22]. 

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