Single-Molecule Magnets: Novel Mn8 and Mn9 Carboxylate Clusters Containing an Unusual Pentadentate Ligand Derived from Pyridine-2,6-dimethanol (original) (raw)
2002, Inorganic Chemistry
The reactions of the Mn III 3 and Mn II Mn III 2 complexes [Mn 3 O(O 2 CEt) 6 (py) 3 ][ClO 4 ] and [Mn 3 O(O 2 CEt) 6 (py) 3 ] with pyridine-2,6-dimethanol (pdmH 2) afford the mixed-valence Mn II 6 Mn III 2 octanuclear complex [Mn 8 O 2 (py) 4 (O 2 CEt) 8 (L) 2 ][ClO 4 ] 2 (1) and the Mn II 7 Mn III 2 enneanuclear complex [Mn 9 (O 2 CEt) 12 (pdm)(pdmH) 2 (L) 2 ] (2), respectively. Both compounds contain a novel pentadentate ligand, the dianion of (6-hydroxymethylpyridin-2-yl)-(6-hydroxymethylpyridin-2-ylmethoxy)methanol (LH 2), which is the hemiacetal formed in situ from the Mn-assisted oxidation of pdmH 2. Complex 1 crystallizes in the monoclinic space group P2 1 /n with the following cell parameters at −160°C: a) 16.6942(5) Å, b) 13.8473(4) Å, c) 20.0766(6) Å,) 99.880(1)°, V) 4572.27 Å 3 , and Z) 2, R (R w)) 4.78 (5.25). Complex 2‚0.2MeCN crystallizes in the triclinic space group P1 h with the following cell parameters at −157°C: a) 12.1312(4) Å, b) 18.8481(6) Å, c) 23.2600(7) Å, R) 78.6887(8)°,) 77.9596(8)°, γ) 82.3176(8)°, V) 5076.45 Å 3 , and Z) 2, R (R w)) 4.12 (4.03). Both complexes are new structural types comprising distorted-cubane units linked together, albeit in two very different ways. In addition, complex 2 features three distinct binding modes for the chelating ligands derived from deprotonated pdmH 2. Complexes 1 and 2 were characterized by variabletemperature ac and dc magnetic susceptibility measurements and found to possess spin ground states of 0 and 11/2, respectively. Least-squares fitting of the reduced magnetization data gave S) 11/2, g) 2.0, and D) −0.11 cm-1 for complex 2, where D is the axial zero-field splitting parameter. Direct current magnetization versus field studies on 2 at <1 K show hysteresis behavior at <0.3 K, establishing 2 as a new single-molecule magnet. Magnetization decay measurements gave an effective barrier to magnetization relaxation of U eff) 3.1 cm-1) 4.5 K.