Investigation of the Structure of Crystal-Forming Solutions of Potassium Dihydrogen Phosphate K(H2PO4) (KDP type) on the Basis of Modeling Precursor Clusters and According to Small-Angle X-Ray Scattering Data

The potassium dihydrogen phosphate K(H2PO4) (KDP) cluster structures formed in aqueous solutions have been theoretically and experimentally investigated. Cluster modeling of the self-assembly of supramolecular KDP structures is performed, and oligomer clusters (dimers, tetramers, and octamers) are determined. Oligomer clusters are found for the first time in saturated KDP aqueous solutions in the temperature range of 5-80 degrees C by small-angle X-ray scattering; their oligomeric composition is quantitatively estimated. It is shown that potassium dihydrogen phosphate exists in the form of dimers in a supersaturated solution in a wide temperature range, and only sharp cooling leads to the occurrence of other clusters: first tetramers and then octamers; the latter are presumably primary chains of the KDP crystal structure. The distance between tetramer centers corresponds to the translation period c = 6.906 angstrom.