X-Ray Crystal Structure, Acid–Base Properties and Complexation Characteristics of a Methylenephosphonate Derivative of 1,4,7,10-Tetraazacyclododecane

Ute Kreher; Milton T. W. Hearn; Leone Spiccia

doi:10.1071/CH09337

RESEARCH ARTICLE

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X-Ray Crystal Structure, Acid–Base Properties and Complexation Characteristics of a Methylenephosphonate Derivative of 1,4,7,10-Tetraazacyclododecane

Ute Kreher ^A ^B , Milton T. W. Hearn ^B and Leone Spiccia ^A ^C

+ Author Affiliations

- Author Affiliations

^A School of Chemistry, Monash University, Clayton, Vic. 3800, Australia.

^B Australian Research Council Special Research Centre for Green Chemistry, Monash University, PO Box 75, Clayton, Vic. 3800, Australia.

^C Corresponding author. Email: leone.spiccia@sci.monash.edu.au

Australian Journal of Chemistry 62(12) 1583-1592 https://doi.org/10.1071/CH09337
Submitted: 16 June 2009 Accepted: 14 July 2009 Published: 10 December 2009

Abstract

The X-ray crystal structures of 1,4,7-tris(methylenephosphonate)-1,4,7,10-tetraazacyclododecane (DO3P·3.5H₂O) and 1,7-bis(methylenephosphonate)-1,4,7,10-tetraazacyclododecane dihydrochloride trihydrate (DO2P·2HCl·3H₂O) reveal that two nitrogen atoms in the trans-annular positions are protonated. The macrocyclic ring adopts a (3,3,3,3)-B conformation stabilized by intramolecular hydrogen bonding involving oxygen atoms from the phosphonate groups and the protonated amines. The acid–base dissociation constants of DO3P and metal complex formation constants (for Ca²⁺, Mg²⁺, Zn²⁺, Fe³⁺) were determined using potentiometric measurements. The first two protonations of DO3P occur at quite high pH and, consequently, were determined by NMR measurements. The stability constants indicate that DO3P forms more stable complexes with the transition metal ions Zn²⁺ and Fe³⁺ (log K _[ML] = 21.23(4) and 22.74(5) respectively) than with the alkaline earth metal ions Ca²⁺ and Mg²⁺ (log K _[ML] = 10.96(6) and 8.72(6) respectively). For Fe³⁺, Ca²⁺ and Mg²⁺, the data support the formation of dinuclear species, presumably through the coordination of an additional metal ion to the phosphonate groups.

Acknowledgements

L.S. and M.T.W.H. acknowledge financial support from the Australian Research Council. U.K. was the recipient of a Postgraduate Research Scholarship from the Centre for Green Chemistry.

References

X-Ray Crystal Structure, Acid–Base Properties and Complexation Characteristics of a Methylenephosphonate Derivative of 1,4,7,10-Tetraazacyclododecane

Abstract

Acknowledgements

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