Neutral solutions Neutrons

Niunerous scattering methods, along with diffiision, viscosity, birefringence, spectroscopy, and microscopy methods, have been employed to measure the structure of polyelectrolsAe chains in dilute solution. A discussion of these methods is not attempted here. Most methods are employed in the same way as for neutral polymers. Neutron scattering makes accessible measurements of polyelectrolyte chain structure in nondilute solutions (87). 

The observation of a bent Cr-H-Cr bond in the tetraethylammonium salt without an accompanying substantial deformation of the linear architecture of the nonhydrogen atoms in the [Cr2(CO)io(M2-H)] monoanion reflects the inherent flexibility of the bond. The deformability of the[M2(CO)io(M2-H)] monoanion species to adopt an appreciably bent, staggered carbonyl structure was first reported by Bau and co-workers (23) from neutron diffraction studies of two crystalline modifications of the electronically equivalent, neutral W2(CO)9(NO)(m2-H) molecule. Subsequent x-ray diffraction studies (15) of the analogous [W2(CO)io(m2-H)] monoanion found that the nonhydrogen backbone can have either an appreciably bent structure for the bis(triphenylphosphine)-iminium salt or a linear structure for the tetraethylammonium salt, with the W-W separation 0.11 A less in the bent form. Crystal packing forces probably were responsible (15) for the different molecular configurations of the monoanion in the two lattices. In solution, however, all known salts of the [W2(CO)io(m2-H)] monoanion exhibit the same three-band carbonyl ir absorption spectrum char-... 

The molecule with X = S is simply and quantitatively made by passing H2S though a refluxing octane solution of Os3(CO)12 (46). The X-ray and neutron diffraction structures of Os3H2(S)(CO)9 (206) and the X-ray structure of the anion [Os3H(S)(CO)9] (207) are known. In the neutral compound the hydride ligands occupy octahedral sites at osmium so that Os—H—Os... 

The structure found in salts like Na2[Gd(dtpa)(H20)] is thought to represent the species found in solution - data from a number of measurements on solutions containing [Ln(dtpa)(H20) ] species, such as luminescence spectra of the Eu and Tb analogues, indicate that one water molecule is coordinated. A wide variety of complexes of amide derivatives of DTPA have also been synthesised, in order to create neutral species. Using [Gd(DTPA)(H20)] it has been shown that these complexes get absorbed by the DNA of the cell they have been used to locate and that they could act as an agent for neutron capture cancer therapy. 

It should be remarked that samples highly neutralized by use of aqueous FeCl3 salts which have been analysed chemically and by neutron activation, sometimes contain an excess of iron beyond what is needed for complete neutralization of the sulfonate groups. This may be due to the presence of Cl ions in the membranes. However, the spectra of figure 6a)-d), which have the same basic structure regardless of the salt used, indicate that anions from the aqueous salt solution are not directly involved in the coordination sphere of the ferric cations. 

Although a discussion of solution properties is outside the scope of this review, it is worth mentioning that Frangis et al. [167,168] have studied diblock copolymers of PPP-polystyrene and PPP-PMMA in solution by means of neutron small-angle scattering, in both neutral and K-doped states. 

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