Abstract
Abstract Alkali, alkaline earth, Group IB, IIB, IIIA, IVA, VIIB, VIII, lanthanide and ammonium 2,4,6-trinitro-3,5-dichlorophenoxides (dichloropicrates, PiCl2) although quite soluble in water, can precipitate in the presence of the ligands 12-crown-4, 15-crown-5, 18-crown-6, dicyclohexano-18-crown-6 (cis-syn-cis isomer) and 21-crown-7. Open chain polyether analogues of the above are much less effective precipitants. Solubility products, Ksp, of 18-crown-6 M(PiCl2)n(Mn+ = NH+ 4, Na+, K+, Cs+, Ag+, Tl+, Ca2+, Sr2+, Ba2+ and Pb2+) were estimated in water; log Ksp values of the complexed univalent metal dichloropicrates are a linear function of the free energy of hydration of M+. The difference in lattice energies of 18-crown-6 MPiCl2 and 18-crown-6 AgPiCl2 (as reference) amounts to only ∼4kcal mol−1 less than that between MPiCl2 and AgPiCl2. Apparantly, the crown metal ion binding has little effect on the strong electrostatic M+ PiCl2 − interaction. Comparison of lattice energies of 18-crown-6 MPiCl2 and MPiCl2 reveals that the crown-metal ion binding further stabilizes 18-crown-6 MPiCl2 in the solid state.
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