Determination of molecular hydration in solution changes in magnetic anisotropy.

The hydration behaviour of coordination complexes is important for understanding their roles as bio-imaging agents. Determination of hydration is difficult, and various optical and NMR-based techniques have been used. Here we use EPR spectroscopy to unambiguously demonstrate that a -butyl-pyridyl-functionalised Er DOTA derivative coordinates water, while its methylphosphinate analogue does not.