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The effect of solutes on the structure of water has been debated intensively over the past years. Typical scenarios label different ions as water structure "makers" or "breakers": this is a quite elusive definition, which has been first introduced in the description of the effect of solutes on the viscosity of water and, although criticized, is still used in the current literature. Here, using a combination of neutron diffraction and computer modeling, we present a possible relation between the viscosity B coefficient and a local structural property of the solution. In particular, B appears in the Jones-Dole relation and its sign is traditionally used to characterize a solute as "structure maker" or "breaker". We find that B is linearly correlated to the difference between the average solute-water distance and the water-water distance in the pure liquid, in the case of monovalent electrolyte solutions.

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The concept of ions being either water "structure makers" or water "breakers" seems to be inconsistent with the existence of a critical number of water molecules per ion dictating the properties of an aqueous solution, independent of the ion identity. To investigate this issue, Raman spectra of hydroxide aqueous solutions in the region of the OH stretching mode have been obtained under ambient conditions and at concentrations ranging from extreme dilution to the solubility limit. Spectra have been analyzed with a relatively model-free approach, in terms of a superposition of contributions due to the vibrations of the OH ions, with two contributions due to the solvent. One of these latter contributions falls at wavenumbers very close to that of the OH stretching band, sharing with it its concentration dependence of the full width at half maximum (FWHM). The other contribution due to the solvent is very broad, with increasing FWHM with increasing ion concentration. In the light of these observations, an interpretation of the Raman spectra, based on the possibility of distinguishing the self and distinct contributions, is proposed. The present analysis is supported by structural data on the same solutions and puts into evidence relevant structural and dynamical changes occurring when the number of water molecules available per solute is below ∼20, irrespective of the ion identity.

The crystal and magnetic structures of ͑La 0.70 Ca 0.30 ͒͑Cr y Mn 1−y ͒O 3 for y = 0.70, 0.50, and 0.15 have been investigated using neutron powder diffraction. The three samples crystallize in the Pnma space group at both 290 and 5 K and exhibit different magnetic structures at low temperature. In ͑La 0.70 Ca 0.30 ͒͑Cr 0.70 Mn 0.30 ͒O 3 , antiferromagnetic order with a propagation vector k = 0 sets in. The magnetic structure is G x , i.e., of G type with spins parallel to the a axis. On the basis of our Rietveld refinement and the available magnetization data, we speculate that only Cr 3+ spins order, whereas Mn 4+ act as random magnetic impurities. In ͑La 0.70 Ca 0.30 ͒͑Cr 0.50 Mn 0.50 ͒O 3 the spin order is still of the type G x , although the net magnetic moment is smaller. No evidence for magnetic order of the Mn ions is observed. Finally, in ͑La 0.70 Ca 0.30 ͒͑Cr 0.15 Mn 0.85 ͒O 3 a ferromagnetic ordering of the Mn spins takes place, whereas the Cr 3+ ions act as random magnetic impurities with randomly oriented spins.