An x-ray diffraction structural investigation of organic complexone ligands. XVI. Crystal and molecular structure of the dihydro-chloride salts of ethylene-diamine-N,N?-Di-3-propionic and ethylenediamine-N,N,N?,N?-tetra-3-propionic acids and the monohydrobromide salt of ethylenediamine-N,N,N?,N?-tetraacetic acid monohydrate

Abstract

An x-ray diffraction structural analysis was carried out on the cationic forms of three complexones: the dihydrochloride salts C8H18N2O4Cl2 (I) and C14H26N2O8Cl2 (II) and monohydrobromide salt C10H19N2O9Br (III). The data were collected on a diffractometer using λMo radiation. The structure was solved by the direct method and refined anisotropically for the nonhydrogen atoms and isotropically for the hydrogen atoms by the method of least squares, R=0.026 (I), 0.040 (II), and 0.044 (III). The crystals of I and II are monoclinic, while the crystals of III are triclinic. I: a=8.047(2), b=10.542(2), c=7.377 A, β=95.10(2)°, Z=2, space group P21/c. II: a=6.894(2), b=19.901(5), c=7.738(3) A, β=111.32(2)°, Z=2, space group P21/c. III: a=5.458(2), b=6.889(1), c=10.631(2) A, α=107.72(1), β=107.02(3), γ=77.93(2)°, Z=1, space group P1. Differences were found in the structures of the cationic forms and neutral molecules of these complexones in the crystalline state. Bis-zwitter-ionic structure is lacking in centrosymmetric doubly-charged cations I and II. A strong intermolecular hydrogen bond O(1)−O(1′) (2.455(5) A) was found in noncentrosymmetric singly-charged cation III with participation of the proton of dissociated HBr. The cations in the structures of I and II participate only in intermolecular hydrogen bonds, while intramolecular hydrogen bonding is also found in III with the formation of five-membered rings. The structure of these cations depends on the acid properties of the corresponding complexone and composition of the crystals.