Monitoring dynamic pre-crystallization aggregation processes in solution by VT-DOSY-NMR spectroscopy.

Equimolar mixtures of pyridine (Py) with -halotetrafluoropyridine (BrTFP and ITFP) were investigated by VT-diffusion NMR experiments. The formation of a halogen-bond-stabilized ITFPPy complex was detected upon cooling a solution in methylcyclohexane- to 260 K; this allows monitoring a halogen-bond-driven aggregation process preceding crystallization in solution.