Abstract
The materials studied in this investigation were aqueous solutions (0.02-25.0 mM) of the salts of alkali metal ion (Me(+)) and 2-nitrophenol (2-NP). In the investigation, small-angle X-ray scattering, wide-angle X-ray scattering, and membrane-pressure osmometry were used to study the 2-NP-Me(+) molecular salt structures and the onset of crystallization as a function of concentration and temperature. The experimental methods used to examine the 2-NP-Me(+) molecular salt complexes provided corroborative evidence for the existence of spherical clusters with hydrodynamic diameters between ∼12 Å (Li) and 14 Å (Cs). Guinier plots of the zero-angle scattering peak were characteristic of the scattering from lamellae-like shapes with thicknesses of ∼290 Å. Tetramer and pentamer 2-NP-Me(+) molecular clusters for Me(+) = Li, Na, K, and Rb were assembled from four or five 2-NP molecules bound to a central alkali metal ion. The coordination symmetry around the six coordinated Li(+), Na(+), and K(+) ions was that of a trigonal prism (D3h), with an octahedral arrangement (D2h). The Rb(+) also revealed six-coordinate geometry and the central Rb(+) ion adopted an octahedral arrangement (D2h). The eight-coordinated Cs(+) ions with six 2-NP ligands were characteristic of a square antiprism (D4d). The square antiprism was the outcome of leaving two o-nitro groups and two phenolic oxygens being left intermolecularly uncoordinated to the Cs(+) ion. The 2-NP residues were strictly planar and contained short non-bonded intramolecular distances. van der Waals forces were present between the adjacently stacked phenyl rings. No water molecules were involved as ligands for any of the 2-nitrophenol-Me(+) complexes.
Highlights
Nitrophenols are important raw materials used in pharmaceuticals, dyes, herbicides, and in the chemical industry, in general
Tetramer and pentamer 2-NP-Me+ molecular clusters for Me+ = Li, Na, K, and Rb were assembled from four or five 2-NP molecules bound to a central alkali metal ion
We present a comprehensive study of the 2NP-Me+ alkali salts in aqueous solutions (Fig. 1(b)), their sizes, and structure of their crystalline clusters
Summary
Nitrophenols are important raw materials used in pharmaceuticals, dyes, herbicides, and in the chemical industry, in general. The bonding was, related to a reduction in both the melting point and the boiling point These reductions can be demonstrated by adding the appropriate alkali metal solution to the aqueous 2-NP or p-. We present a comprehensive study of the 2NP-Me+ alkali salts in aqueous solutions (Fig. 1(b)), their sizes, and structure of their crystalline clusters. In 2NP-Me+ systems, the clusters were small compared with those of colloidal particle systems Such small-cluster systems represent an important transition between solution conditions and crystalline structures dispersed in an aqueous system. This contribution is organized as follows: In Sec. II, the preparation of the aqueous 2-NP-Me+ salt solutions and the crystallization of the different 2-NP-Me+ (Me+ = Li, Na, K, Rb, and Cs) are disclosed.
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