Single-molecule magnets: Jahn–Teller isomerism and the origin of two magnetization relaxation processes in Mn12 complexes

Abstract Different crystallographic forms of the single molecule magnet [Mn 12 O 12 (O 2 CR) 16 (H 2 O) 4 ] with a given R substituent have been isolated. X-ray structures are reported for two isomeric forms of the p -methylbenzoate complex, [Mn 12 O 12 (O 2 CC 6 H 4 - p -Me) 16 (H 2 O) 4 ]·(HO 2 CC 6 H 4 - p -Me) ( 2 ) and [Mn 12 O 12 (O 2 CC 6 H 4 - p -Me) 16 (H 2 O) 4 ]·3H 2 O ( 3 ). The Mn 12 molecules in complexes 2 and 3 are geometrical isomers differing in the positions of the H 2 O and carboxylate ligands. In complex 2 , one Mn III ion has an abnormal Jahn–Teller distortion axis oriented at an oxide ion, and thus 2 and 3 are also Jahn–Teller isomers. This reduces the symmetry of the core of complex 2 compared with that of complex 3 . Complex 2 likely has a larger tunneling matrix element and this explains why this complex shows an out-of-phase ac peak ( χ M ″) in the signal in the 2–3 K region, whereas complex 3 has its χ M ″ peak in the 4–7 K range, i.e. the rate of tunneling of magnetization is greater in complex 2 than complex 3 .