New Routes to Polymetallic Clusters: Fluoride-Based Tri-, Deca-, and Hexaicosametallic Mn III Clusters and their Magnetic Properties Leigh F. Jones, [a] Gopalan Rajaraman, [a] Jonathon Brockman, [b] Muralee Murugesu, [b] E. Carolina San ˆudo, [b] Jim Raftery, [a] Simon J. Teat, [d] Wolfgang Wernsdorfer, [c] George Christou, [b] Euan K. Brechin,* [a] and David Collison* [a] Introduction Many Mn-based clusters have been reported over the last 20 years for two main reasons: the first is biological in origin, because Mn is prominent in the active sites of many metallo-biomolecules. [1] The most commonly studied is the water-oxidising complex (WOC) of photosystem II (PS II), the species in plants (and cyanobacteria) that brings about the oxidation of water into dioxygen. The WOC is a tetranu- clear Mn cluster of yet unknown structure. [2] Thus, numerous Mn 4 complexes have been synthesised as models to probe the structural changes and mechanistic processes occurring in PS II. [3] The second reason is the paramagnetic nature of Mn clusters, many of which exhibit large ground spin states [a] L.F. Jones, G. Rajaraman, Dr. J. Raftery, Dr. E.K. Brechin, Dr. D. Collison Department of Chemistry, The University of Manchester Oxford Road, Manchester, M13 9PL (UK) Fax:(+ 44)161-275-4616 E-mail: euan.k.brechin@man.ac.uk david.collison@man.ac.uk [b] J. Brockman, Dr. M. Murugesu, E. C. San ˆudo, Prof. G. Christou Department of Chemistry, University of Florida Gainesville, Florida 32611-7200 (USA) [c] Dr.W. Wernsdorfer Laboratoire Louis NØel-CNRS 38042 Grenoble, Cedex 9 (France) [d] Dr. S.J. Teat CCLRC Daresbury Laboratory Daresbury, Warrington, Cheshire,WA4 4AD (UK) Supporting information for this article is available on the WWW under http://www.chemeurj.org/ or from the author. 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 dem- onstrating the utility of MnF 3 as a new synthon in Mn cluster chemistry. The “melt” reaction (100 8C) 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 tri- clinic space group P1 ¯ , and consists of a complicated array of metal tetrahedra linked by m 3 -O 2 ions, m 3 - and m 2 -OH  ions, m 2 -MeO  ions and m 2 -bta  ligands. The “simpler” reaction between MnF 3 and btaH in boiling MeOH (50 8C) also produces complex 1. If this reac- tion is repeated in the presence of pyridine, the decametallic complex [Mn 10 O 6 (OH) 2 (bta) 8 (py) 8 F 8 ](2) is pro- duced. Complex 2 crystallizes in the tri- clinic space group P1 ¯ and consists of a “supertetrahedral” [Mn III 10 ] core bridg- ed by six m 3 -O 2 ions, two m 3 -OH  ions, four m 2 -F  ions and eight m 2 -bta  ions. The replacement of pyridine by tri- ethylamine 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 P2 1 /c and has a structure analo- gous to that of the basic metal car- boxylates of general formula [M 3 O(RCO 2 ) 6 L 3 ] 0/ + , which consists of an oxo-centred metal triangle with m 2 - bta  ligands bridging each edge of the triangle and the fluoride ions acting as the terminal ligands. DC magnetic sus- ceptibility measurements in the 300– 1.8 K and 0.1–7 T ranges were investi- gated for all three complexes. For each, the value of c M T decreases with de- creasing temperatures; this indicates the presence of dominant antiferro- magnetic exchange interactions in 1–3. For complex 1, the low-temperature value of c M T is 10 cm 3 Kmol 1 and fit- ting of the magnetisation data gives S = 4, g = 2.0 and D = 0.90cm 1 . For complex 2, the value of c M T falls to a value of approximately 5.0 cm 3 Kmol 1 at 1.8 K, which is consistent with a small spin ground state. For the trian- gular complex 3, the best fit to the ex- perimental c M T versus T data was ob- tained 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 = 2.95cm 1 and J b = 2.12cm 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 hys- teresis loops indicative of single-mole- cule magnetism behaviour. Keywords: cluster compounds · density functional calculations · fluorides · magnetic properties · manganese · N ligands # 2004 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim DOI: 10.1002/chem.200400301 Chem.Eur.J. 2004, 10,5180–5194 5180 FULL PAPER