Structures and thermal properties of strontium and barium 1,3-propanediaminetetraacetates

Abstract

In neutral and acidic solution, homonuclear s-block metal complexes [Sr₂(1,3-pdta)(H₂O)_3.5] _n (1), {[Ba₂(1,3-pdta)(H₂O)₆]·H₂O} _n (2), {[Sr(1,3-H₂pdta)]·(H₂O)} _n (3), and [Ba(1,3-H₂pdta)(H₂O)₃] _n (4) {1,3-H₄pdta=1,3-propanediamine-N,N,N′,N′-tetraacetic acid, CH₂[CH₂N(CH₂CO₂H)₂]₂} were isolated. In 1 and 2, hexadentate 1,3-pdta joins two metal ions via the diamine chain. In 3 and 4, the nitrogens of 1,3-H₂pdta were protonated and show no coordination. There is no coordinated water in 3, unusual coordination for strontium. In 4, the coordination number is nine and there are three coordinated waters for each barium. One carboxy group of pdta is free without coordination. Thermal decomposition shows that temperatures of ligand elimination start at 408, 423, 298, and 250 °C for 1–4, respectively. Acidic condition is favorable for preparation of metal oxide at low temperature.

Keywords :

• 1,3-Propanediaminetetraacetic acid
• Barium
• Strontium
• Thermal decomposition
• Coordination mode

Acknowledgements

Financial contributions from the National Science Foundation of China (21073150) and the National Basic Research Program of China (2010CB732303) are gratefully acknowledged.