New routes to polymetallic clusters:: Fluoride-based tri-, deca-, and hexaicosametallic MnIII clusters and their magnetic properties

The syntheses, structures and magnetic properties of three new Mn-III clusters, [Mn26O17(OH)(8)(OMe)(4)F-10(bta)(22)(MeOH)(14)(H2O)(2)] (1), [Mn10O6(OH)(2)(bta)(8)(py)(8)F-8] (2) and [NHEt3](2)[Mn3O(bta)(6)F-3] (3), are reported (bta anion of benzotriazole), thereby demonstrating the utility of MnF3 as a new synthon in Mn cluster chemistry. The "melt" reaction (100 degreesC) between MnF3 and benzotriazole (btaH, C6H5N3) under an inert atmosphere, followed by dissolution in MeOH produces the cluster [Mn26O17(OH)(8)(OMe)(4)F-10(bta)(22)(MeOH)(14)(H2O)(2)] (1) after two weeks. Complex 1 crystallizes in the triclinic space group P!, and consists of a complicated array of metal tetrahedra linked by mu(3)-O2- ions, mu(3)- and mu(2)-OH- ions, mu(2)-MeO- ions and mu(2)-bta(-) ligands. The "simpler" reaction between MnF3 and btaH in boiling MeOH (50 degreesC) also produces complex 1. If this reaction is repeated in the presence of pyridine, the decametallic complex [Mn10O6(OH)(2)(bta)(8)(py)(8)F-8] (2) is produced. Complex 2 crystallizes in the triclinic space group Pi and consists of a "supertetrahedral" [Mn-10(III)] core bridged by six mu(3)-O2- ions, two mu(3)-OH- ions, four mu(2)-F- ions and eight mu(2)-bta(-) ions. The replacement of pyridine by triethylamine in the same reaction scheme produces the trimetallic species [NHEt3](2)[Mn3O(bta)(6)F-3] (3). Complex 3 crystallises in the monoclinic space group P2(1)/c and has a structure analogous to that of the basic metal carboxylates of general formula [M3O(RCO2)(6)L-3](0/+), which consists of an oxo-centred metal triangle with mu(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 chi(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 chi(M)T is 10 cm(3) Kmol(-1) and fitting of the magnetisation data gives S=4, g=2.0 and D=-0.90cm(-1). For complex 2, the value of chi(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 chi(M)T versus T data was obtained for the following parameters: J(a)=-5.01cm(-1), J(b)=+9.16cm(-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.