Chromium(III)-pyrazole complexes. X-Ray crystal structures, 1H NMR investigation of ligand fluxional behavior and EPR studies

Mononuclear chromium(III) complexes of formula mer-[(CrCl3)-Cl-III(pz*H)(3)] (pz*H = pyrazole (pzH), and substituted pyrazoles: 3-Me-pzH, 4-Me-pzH, 4-Cl-pzH, 4-BrpzH, 4-I-pzH) and trans-[(CrCl2)-Cl-III(pzH)(4)]Cl were synthesized from reactions of CrCl3 hydrate and pyrazole ligands and crystallographically characterized. The fluxional behavior of the complexes, attributed to pyrazole tautomerization, was probed by variable temperature H-1 NMR spectra in the - 50 degrees C to + 23 degrees C range and activation parameters were derived. Q-band EPR were recorded and analyzed for mer-[(CrCl3)-Cl-III(pz*H)(3)] (R = H, Me, Cl) showing satellite features corresponding to weak zero-field splitting (zfs).