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- Title
X-ray evidence for the relationship between pyridyl side chain basicity and the Z/E preferences of 5-halogen substituted (pyridin-2-yl)aminomethane-1,1-diphosphonic acids; implications for metal ions coordination in solution.
- Authors
Matczak-Jon, Ewa; Ślepokura, Katarzyna; Kurzak, Barbara
- Abstract
The crystal structures of three salts (1-a-3-a), products of the reactions between 5-chloro (1), 5- bromo (2) and 5-iodo (3) substituted (pyridin-2-yl)aminomethane-1,1-diphosphonic acids and 4- aminopyridine were determined by single crystal X-ray diffraction and discussed with respect to molecular geometry and solid state organization. In all 1-a-3-a, bisphosphonate dianion adopts the opposite (E) conformation with respect to the C2-N1 bond, compared with the parent zwitterion. This provides further evidence that intermolecular N-H···O hydrogen bonds involving both exocyclic and pyridinium N atoms as proton donors and an O atom of the phosphonic/phosphonate group as acceptor play a significant role in stabilizing the Z conformation of this particular subclass of acids. The solution behavior and complex-formation abilities of [(5-iodopyridin-2-yl)amino]methane-1,1-diphosphonic acid (3) were also studied. Compound 3 exists in solution as the Z/E mixture. However, the barrier to rotation around the C2-N1 bond in 3 is lower, compared with 1 and 2. This is important for the complex-formation processes in the Zn(II), Mg(II) and Ca(II) solutions with 3.
- Subjects
PYRIDYL compounds; HALOGEN acids; SUBSTITUTION reactions; PHOSPHONIC acids; COORDINATE covalent bond; SOLUTION (Chemistry); METAL ions; X-ray diffraction
- Publication
ARKIVOC: Online Journal of Organic Chemistry, 2012, p167
- ISSN
1551-7004
- Publication type
Article