Tuning of structural and magnetic properties of nitronyl nitroxides by theenvironment. A combined experimental and computational study

The geometry, conformational behavior, and magnetic properties of 2-(2-imid azolyl-)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, an important spin c arrier in molecular magnetic materials, have been studied by a combined exp erimental and theoretical approach. From the experimental point of view, th e available structural data have been completed by new electronic spin reso nance spectra in different solvents. From the computational point of view, we have used a hybrid Hartree-Fock/density functional method which provides very reliable structural data. Next, the properties computed at this level have been corrected with reference to refined post Hartree-Fock computatio ns for a smaller model system. Solvent effects have been taken into account by the polarizable continuum model, and crystal field effects have been mi micked by a suitable model cluster. Our computations show that the molecule has a planar structure in the gas phase and in solution, even if the rotat ional barrier significantly decreases with the polarity of the solvent. In contrast, strong intermolecular hydrogen bonds favor a nonplanar structure in the solid state. As a consequence, a significant modification of the mol ecular properties is observed going from vacuo to different condensed phase s. All of these results are in good agreement with experiments and point ou t the interpretative power of our integrated computational tool.