High-Spin Molecules: Hexanuclear [Mn 6 O 4 Cl 4 (Me 2 dbm) 6 ] (Me 2 dbmH ) 4,4′-Dimethyldibenzoylmethane) with a Near Tetrahedral [Mn 6 O 4 Cl 4 ] 6+ Core and a S ) 12 Ground State Guillem Aromı ´, 1a Juan-Pablo Claude, 1a,c Michael J. Knapp, 1b John C. Huffman, 1a David N. Hendrickson,* ,1b and George Christou* ,1a Department of Chemistry and Molecular Structure Center, Indiana UniVersity Bloomington, Indiana 47405-4001 Department of Chemistry-0358 UniVersity of California at San Diego La Jolla, California 92093-0358 ReceiVed NoVember 24, 1997 An interesting sub-area of transition-metal cluster chemistry is the small but growing family of molecules that, in their ground states, have unusually large numbers of unpaired electrons. Molecular clusters with spin (S) values as high as double figures have been discovered, with the highest value to date being S ≈ 16 1 / 2 for one of the clusters in a sample of cocrystallized Fe 17 and Fe 19 species, 2 but examples with S g 8 are nevertheless very rare. 3,4 The study of such molecules has shown that the high spin value is a result of the presence of (at least some) ferromagnetic exchange interactions between the metal ions and/ or spin frustration effects arising from the presence in certain M x topologies of competing exchange interactions which prevent (frustrate) the preferred spin alignments that would otherwise normally yield low-spin species. The study of high-spin molecules has taken on additional importance in recent years as it has been realized that a fairly large S value is a necessary (but not sufficient) property for molecules to exhibit the new magnetic phenomenon of single- molecule magnetism, i.e., the ability of material composed of discrete, (magnetically) noninteracting molecules to be magnetized by an external magnetic field below a critical blocking temperature (T B ). 3a,5,6 The importance of a high S value in such nanoscale magnets has stimulated a search for new examples of species with this property. We herein report the preparation of a new hexanuclear Mn III cluster with an aesthetically pleasing [Mn 6 O 4 - Cl 4 ] 6+ core and show that it possesses a S ) 12 ground state, one of the highest yet identified. Treatment of [Mn 4 O 2 (O 2 CMe) 6 (py) 2 (Me 2 dbm) 2 ](1) (Me 2 dbmH ) 4,4′-dimethyldibenzoylmethane), prepared as for the dbm analogue, 7 in CH 2 Cl 2 with 6 equiv of Me 3 SiCl and 2 equiv of Me 2 dbmH gave a brown solution from which was isolated crude [MnCl(Me 2 dbm) 2 ](2) on addition of Et 2 O. Redissolution in MeCN:CH 2 Cl 2 (1:1) followed by standing and slight concentration at room temperature over ∼3 weeks gave black crystals of [Mn 6 O 4 Cl 4 (Me 2 dbm) 6 ]‚3CH 2 Cl 2 (3‚3CH 2 Cl 2 ), together with some white powder. The latter was removed by filtration and washing of the black crystals with EtOH. Complex 3 can also be obtained by dissolving purified 2 in MeCN:CH 2 Cl 2 (1:1), and subsequent treatment as above, suggesting the formation of 3 to involve a slow hydrolysis of the mononuclear species. 8 Nonoptimized yields up to 14% have been obtained to date. 8 The structure 9 of 3 (Figure 1) consists of a (Mn III ) 6 octahedron with four nonadjacent faces bridged by the µ 3 -O 2- ions and the other four faces by µ 3 -Cl - ions. Six-coordinate, approximately octahedral geometry at each metal is completed by a chelating Me 2 dbm group. The cluster has virtual T d symmetry. As expected for high-spin, octahedral Mn III , there is a Jahn-Teller (JT) distortion, taking the form of an axial elongation of the two trans Mn-Cl bonds, making them unusually long (2.618(3)- 2.692(3) Å). In contrast, the Mn-O 2- (1.876(4)-1.899(5) Å) and Mn-O(Me 2 dbm) (1.903(5)-1.925(5) Å) bond lengths are as expected. As a result of (i) the long Mn-Cl - versus short Mn-O 2- bonds and (ii) the near trigonal planar geometry at the latter (sum-of-angles (soa) ≈ 349°) compared with marked trigonal pyramidal geometry at the former (soa ≈ 223°), the [Mn 6 O 4 Cl 4 ] 6+ core is a near tetrahedron with a Cl - at each vertex, a Mn at the midpoint of each edge, and a O 2- bridging each face. Although many [M 6 (µ 3 -X) 8 ] face-capped metal octahedra are known, 10 only a relative few contain two types of X group, e.g., the [Ti 6 O 6 Cl 2 ], 11 [Ti 6 Te 6 O 2 ], 12 and [Re 6 Y x Z 8-x ](x ) 5, Y ) S or Se, Z ) Cl; x ) 6, Y ) S, Z ) Cl) 13 cores. Only the [Ti 6 (µ 3 - O) 4 (µ 3 -Cl) 4 ] core of [(C 5 H 5 Me) 6 Ti 6 O 4 Cl 4 ] 11 contains, like 3, four O 2- and 4 Cl - bridges, but the structure does not approximate to a tetrahedron. [Mn III 6 X 8 ] species have been unknown to date, although a [Mn 6 (µ 3 -O) 4 (µ 3 -Cl) 4 ] 4+ unit as found in 3 but at the 2Mn II , 4Mn III level is also a recognizable fragment within the higher nuclearity cluster [Mn 10 O 4 Cl 12 (biphen) 4 ] 4- (biphen ) 2,2′- biphenoxide). 14 (1) (a) Indiana University. (b) University of California at San Diego. (c) Present address: Department of Chemistry, University of Alabama at Birmingham. (2) Powell, A. K.; Heath, S. L.; Gatteschi, D.; Pardi, L.; Sessoli, R.; Spina, G.; Del Giallo, F.; Pieralli, F. J. Am. Chem. Soc. 1995, 117, 2491. (3) (a) Eppley, H. J.; Tsai, H.-L.; de Vries, N.; Folting, K.; Christou, G.; Hendrickson, D. N. J. Am. Chem. Soc. 1995, 117, 301. (b) Tsai, H.-L.; Wang, S.; Folting, K.; Streib, W. E.; Hendrickson, D. N.; Christou, G. J. Am. Chem. Soc. 1995, 117, 2503. (c) Eppley, H. J.; Wang, S.; Tsai, H.-L.; Aubin, S. M.; Folting, K.; Streib, W. E.; Hendrickson, D. N.; Christou, G. Mol. Cryst. Liq. Cryst. 1995, 274, 159. (4) (a) Scuiller, A.; Mallah, T.; Verdaguer, M.; Nivorozkhin, A.; Tholence, J.-L.; Veillet, P. New J. Chem. 1996, 20, 1. (b) Delfs, C. D.; Gatteschi, D.; Pardi, L.; Sessoli, R.; Wieghardt, K.; Hanke, D. Inorg. Chem. 1993, 32, 3099. (c) Caneschi, A.; Gatteschi, D.; Laugier, J.; Rey, P.; Sessoli, R.; Zanchini, C. J. Am. Chem. Soc. 1988, 110, 2795. (d) Goldberg, D. P.; Caneschi, A.; Delfs, C. D.; Sessoli, R.; Lippard, S. J. J. Am. Chem. Soc. 1995, 117, 5789. (e) Blake, A. J.; Grant, C. M.; Parsons, S.; Rawson, J. M.; Winpenny, R. E. P. J. Chem. Soc., Chem. Commun. 1994, 2363. (f) Bolcar, M. A.; Aubin, S. M. J.; Folting, K.; Hendrickson, D. N.; Christou, G. J. Chem. Soc., Chem. Commun. 1997, 1485. (g) Benelli, C.; Parsons, S.; Solan, G. A.; Winpenny, R. E. P. Angew. Chem., Int. Ed. Engl. 1996, 35, 1825 (5) (a) Sessoli, R.; Tsai, H.-L.; Schake, A. R.; Wang, S.; Vincent, J. B.; Folting, K.; Gatteschi, D.; Christou, G.; Hendrickson, D. N. J. Am. Chem. Soc. 1993, 115, 1804. (b) Sessoli, R.; Gatteschi, D.; Caneschi, A.; Novak, M. A. Nature 1993, 365, 141. (6) Aubin, S. M. J.; Wemple, M. W.; Adams, D. M.; Tsai, H.-L.; Christou, G.; Hendrickson, D. N. J. Am. Chem. Soc. 1996, 118, 7746. (7) Wang, S.; Folting, K.; Streib, W. E.; Schmitt, E. A.; McCusker, J. K.; Hendrickson, D. N.; Christou, G. Angew. Chem., Int. Ed. Engl. 1991, 30, 305. (8) The reaction is more complicated than this statement suggests, with [Mn(Me2dbm)3] identified in the filtrate; the isolation of pure 3 is undoubtedly due to its low solubility in this solvent mixture. Isolated solid is soluble in CH2Cl2 and CHCl3. 1 H NMR spectra in these solvents suggest the structure is retained on dissolution. (9) Dried solid analyzed as 3‚0.4CH2Cl2. Anal. Calcd (found) for C102.4- H90.8O16Cl4.8Mn6: C, 59.21 (59.28); H, 4.49 (4.41). Crystal data for 3‚3CH2- Cl2: monoclinic; P21/c; a ) 17.172(2) Å, b ) 18.302(2) Å, c ) 34.534(4) Å;  ) 100.36(1)°; Z ) 4; V ) 10677 Å 3 ; dcalcd ) 1.430 g cm -3 ; T )-171 °C. The structure was solved using MULTAN and refined on F to R(Rw) ) 5.80 (5.73) using 9989 unique reflections with F > 2.33σ(F). All non-hydrogen atoms were refined anisotropically, and all hydrogen atoms were included as fixed-atom contributors at calculated positions, except for the disordered CH2- Cl2 molecules. Electronic spectrum in CH2Cl2, λmax/nm (ǫm/L mol -1 cm -1 ): 456 (6380), 486 (5000), 540 (2720), 584 1930. (10) Lee, S. L.; Holm, R. H. Angew. Chem., Int. Ed. Engl. 1990, 29, 840 and references therein. (11) (a) Roth, A.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J. Am. Chem. Soc. 1986, 108, 6823. (b) Carofiglio, T.; Floriani, C.; Roth, A.; Sgamellotti, A.; Rosi, M.; Chiesi-Villa, A.; Rizzoli, C. J. Organomet. Chem. 1995, 488, 141. (12) Gindelberger, D. E. Acta Crystallogr. Sect. C. 1996, 52, 2493. (13) Dolbecq, A.; Boubekeur, K.; Batail, P.; Canadell, E.; Auban-Senzier, P.; Coulon, C.; Lerstrup, K.; Bechgaard, K. J. Mater. Chem. 1995, 5, 1707. (14) Goldberg, D. P.; Caneschi, A.; Lippard, S. J. J. Am. Chem. Soc. 1993, 115, 9299. 2977 J. Am. Chem. Soc. 1998, 120, 2977-2978 S0002-7863(97)03996-6 CCC: $15.00 © 1998 American Chemical Society Published on Web 03/12/1998