Formation of Two Types of Crystals of Protonated Erbium Bis(1-hydroxyethylidene)diphosphonate Tetrahydrate in the Reaction of Erbium Carbonate with (1-Hydroxyethylidene)diphosphonic Acid. Selection of Lamellar Crystals

摘要

Poorly soluble protonated erbium bis(1-hydroxyethylidene)diphosphonate tetrahydrate (HEr(H2L)(2) center dot 4H(2)O), formed as a result of the reaction of erbium carbonate (Er-2(CO3)(3) center dot 4H(2)O) with an excess of (1-hydroxyethylidene)diphosphonic acid (CH3(OH)C[P(O)(OH)(2)](2), H4L), consists of two types of crystals (needle-like and lamellar ones). This compound slowly dissolves in an aqueous medium when adding the following organic amines: 2-aminoethanol, 2-amino-2-(hydroxymethyl)propane-1,3-diol, and 2,2'-(ethylidenedioxy)bis(ethylamine). The latter are attached to the complex-molecule periphery (i.e., free -P(O)OH groups) to form fragments of amine salt (-P(O)O-+NH3-CH2-). The first coordination sphere of the complex does not change; therefore, the energies of the f-f transitions of the Er3+ cation in the electronic absorption spectra remain invariable after the attachment of various amines, which act as solubility promoters. The interaction of suspension of protonated erbium bis(1-hydroxyethylidene)diphosphonate tetrahydrate with equimolar amounts of amines leads to selective dissolution of fine-grained needles and makes it possible to select the fraction of lamellar crystals in the pure form.