Variable temperature complexation studies of Cd(II)-dipicolinic acid revealing an endothermically formed species at T = 313 K

• Studied the Cd(II)-dipicolinic acid system at T = (298, 305 and 313) K and from pH 1.
• Two unreported solution species for this system were revealed, namely ML3 and MLH.
• ML3 only occurred to a significant extent from T = 313 K under the solution conditions used.
• MLH was the dominant species below pH 2.

The Cd(II)-dipicolinic acid (pyridine-2,6-dicarboxylic acid) system was studied by polarography in the temperature range (298 to 313) K and ionic strength of (0.25 to 0.5) mol · dm−3 (H,K)NO3. Apart from detecting the already reported ML and ML2 complexes and reporting the log β values at T = (298, 305 and 313) K, an ML3 complex was also found to form at 40 °C giving a log β value of 13.5 ± 0.1. ML3 was not present to a significant extent at lower temperatures indicating an endothermic formation process. This finding is supported by the ML3 structure being reported for crystals grown at T = 313 K. The system was also studied from pH 1 using protocols developed employing Tl(I) as an internal reference. The MLH species was found in the low pH range with log β values of 8.4 ± 0.2, 8.2 ± 0.2 and 8.0 ± 0.1 found at T = (298, 305 and 313) K, respectively.

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