Hydrogen bonding and sodium coordination in the crystal structure of tetrasodium (3-((2,4-dinitrophenyl)amino)-1-hydroxypropane-1,1-diyl)-bis-phosphonate pentahydrate – a N-substituted Pamidronate

Abstract

The reaction of 1-fluoro-2,4-dinitrobenzene with (3-amino-1-hydroxypropane-1,1-diyl)bis(phosphonic acid) (pamidronic acid) 1a in combination with NAOH leads to disodium (3-((2,4-dinitrophenyl)amino)-1-hydroxy-propane-1,1-diyl)bis(phosphonate) heptahydrate 2 and further to tetrasodium (3-((2,4-dinitrophenyl)amino)-1-hydroxy-propane-1,1-diyl)bis(phosphonate) pentahydrate 3. The crystal structure of 3 is composed of the organic anion, which is coordinated to the sodium counter cations and furthermore is involved in hydrogen bonds. The 2,4-dinitrophenyl moiety gives rise to π–π connected hydrophobic layers. The hydrophilic moiety of the anions, sodium cations and water molecules form a hydrophilic layer. The individual conformation of this N-substituted pamidronate anion is a compromise between its geometric limitations and the intermolecular interactions with sodium and the water molecules.