New Routes to Polymetallic Clusters: Fluoride-Based Tri-, Deca-, and Hexaicosametallic MnIII Clusters and their Magnetic Properties
✍ Scribed by Leigh F. Jones; Gopalan Rajaraman; Jonathon Brockman; Muralee Murugesu; E. Carolina San̂udo; Jim Raftery; Simon J. Teat; Wolfgang Wernsdorfer; George Christou; Euan K. Brechin; David Collison
- Book ID
- 102792978
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 623 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The syntheses, structures and magnetic properties of three new Mn^III^ clusters, [Mn~26~O~17~(OH)~8~(OMe)~4~F~10~(bta)~22~(MeOH)~14~(H~2~O)~2~] (1), [Mn~10~O~6~(OH)~2~(bta)~8~(py)~8~F~8~] (2) and [NHEt~3~]~2~[Mn~3~O(bta)~6~F~3~] (3), are reported (bta=anion of benzotriazole), thereby demonstrating the utility of MnF~3~ as a new synthon in Mn cluster chemistry. The “melt” reaction (100 °C) between MnF~3~ and benzotriazole (btaH, C~6~H~5~N~3~) under an inert atmosphere, followed by dissolution in MeOH produces the cluster [Mn~26~O~17~(OH)~8~(OMe)~4~F~10~(bta)~22~(MeOH)~14~(H~2~O)~2~] (1) after two weeks. Complex 1 crystallizes in the triclinic space group P$\bar 1$, and consists of a complicated array of metal tetrahedra linked by μ~3~‐O^2−^ ions, μ~3~‐ and μ~2~‐OH^−^ ions, μ~2~‐MeO^−^ ions and μ~2~‐bta^−^ ligands. The “simpler” reaction between MnF~3~ and btaH in boiling MeOH (50 °C) also produces complex 1. If this reaction is repeated in the presence of pyridine, the decametallic complex [Mn~10~O~6~(OH)~2~(bta)~8~(py)~8~F~8~] (2) is produced. Complex 2 crystallizes in the triclinic space group P$\bar 1$ and consists of a “supertetrahedral” [Mn^III^~10~] core bridged by six μ~3~‐O^2−^ ions, two μ~3~‐OH^−^ ions, four μ~2~‐F^−^ ions and eight μ~2~‐bta^−^ ions. The replacement of pyridine by triethylamine in the same reaction scheme produces the trimetallic species [NHEt~3~]~2~[Mn~3~O(bta)~6~F~3~] (3). Complex 3 crystallises in the monoclinic space group __P__2~1~/c and has a structure analogous to that of the basic metal carboxylates of general formula [M~3~O(RCO~2~)~6~L~3~]^0/+^, which consists of an oxo‐centred metal triangle with μ~2~‐bta^−^ ligands bridging each edge of the triangle and the fluoride ions acting as the terminal ligands. DC magnetic susceptibility measurements in the 300–1.8 K and 0.1–7 T ranges were investigated for all three complexes. For each, the value of χ~M~T decreases with decreasing temperatures; this indicates the presence of dominant antiferromagnetic exchange interactions in 1–3. For complex 1, the low‐temperature value of χ~M~T is 10 cm^3^ K mol^−1^ and fitting of the magnetisation data gives S=4, g=2.0 and D=−0.90 cm^−1^. For complex 2, the value of χ~M~T falls to a value of approximately 5.0 cm^3^ K mol^−1^ at 1.8 K, which is consistent with a small spin ground state. For the triangular complex 3, the best fit to the experimental χ~M~T versus T data was obtained for the following parameters: J~a~=−5.01 cm^−1^, J~b~=+9.16 cm^−1^ and g=2.00, resulting in an S=2 spin ground state. DFT calculations on 3, however, suggest an S=1 or S=0 ground state with J~a~=−2.95 cm^−1^ and J~b~=−2.12 cm^−1^. AC susceptibility measurements performed on 1 in the 1.8–4.00 K range show the presence of out‐of‐phase AC susceptibility signals, but no peaks. Low‐temperature single‐crystal studies performed on 1 on an array of micro‐SQUIDS show the time‐ and temperature‐dependent hysteresis loops indicative of single‐molecule magnetism behaviour.