Structural characterization, magnetic properties, and electrospray mass spectrometry of two Jahn−Teller isomers of the single-molecule magnet [Mn<SUB>12</SUB>O<SUB>12</SUB>(CF<SUB>3</SUB>COO)<SUB>16</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>]

The syntheses and characterization of two new, highly soluble, single-molecule magnets [Mn<SUB>12</SUB>O<SUB>12</SUB>(CF<SUB>3</SUB>COO)<SUB>16</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>]·2CF<SUB>3</SUB>COOH·4H<SUB>2</SUB>O (1) and [Mn<SUB>12</SUB>O<SUB>12</SUB>(CF<SUB>3</SUB>COO)<SUB>16</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>]·CF<SUB>3</SUB>COOH·7H<SUB>2</SUB>O (2) are reported. Compound 1 was isolated from the reaction of [Mn<SUB>12</SUB>O<SUB>12</SUB>(CF<SUB>3</SUB>COO)<SUB>16</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>] with trifluoroacetic acid in CH<SUB>2</SUB>Cl<SUB>2</SUB>. Compound 1 crystallizes in the tetragonal space group I4<SUP>-</SUP> (No. 82) with unit cell parameters a = b = 18.128(3) Å, c = 13.048(3) Å, V = 4287.9(19) Å<SUP>3</SUP>, Z = 2 and is isostructural to [Mn<SUB>12</SUB>O<SUB>12</SUB>(CF<SUB>3</SUB>COO)<SUB>16</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>]. Compound 2 was prepared from the reaction of [Mn<SUB>12</SUB>O<SUB>12</SUB>(CF<SUB>3</SUB>COO)<SUB>16</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>] with neat trifluoroacetic acid, and crystallizes in the monoclinic space group P2<SUB>1</SUB>/n (No. 14) with unit cell parameters a = 15.221(8) Å, b = 21.870(12) Å, c = 27.217(15) Å, β = 90.53(1)°, V = 9060(9) Å<SUP>3</SUP>, and Z = 4. The dc magnetic susceptibility measurements in the 2−300 K temperature range support a high-spin ground state. The magnetization data collected in the 1−7 T field range from 1.8 to 4.0 K were best fit to the parameters S = 10, g = 2.15, D = −0.65 cm<SUP>-1</SUP>, and E = 0 cm<SUP>-1</SUP> for 1 and S = 10, g = 1.87, D = −0.34 cm<SUP>-1</SUP>, and E = −0.10 cm<SUP>-1</SUP> for 2. The ac susceptibility data for compound 1 reveal out-of-phase (χ<SUB>m</SUB>") signals in the 4−7 K temperature range, whereas the χ<SUB>m</SUB>" signals for compound 2 appear below temperatures of 4 K. This variation in blocking temperatures is a consequence of the two different crystallographic forms of compounds 1 and 2. Compound 1 exhibits the same structural geometry and distortions found in [Mn<SUB>12</SUB>O<SUB>12</SUB>(CF<SUB>3</SUB>COO)<SUB>16</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>], while compound 2 is of lower molecular symmetry with two Jahn−Teller axes of distortion being oriented along oxide ligands. This different structural arrangement facilitates a different tunneling pathway that leads to a lower effective barrier for magnetization reorientation for compound 2. The substitution of the acetate ligands by trifluoroacetic acid was monitored by mass spectrometry, which is a convenient tool for judging completion of the substitution process