Inorg. Chem. 2009, 48, 9831–9845 9831 DOI: 10.1021/ic901393m
Spin Maximization from S = 11 to S = 16 in Mn7 Disk-Like Clusters: Spin Frustration Effects and Their Computational Rationalization )
Theocharis C. Stamatatos,† Dolos Foguet-Albiol,† Katye M. Poole,‡ Wolfgang Wernsdorfer,§ Khalil A. Abboud,† Ted A. O’Brien,‡, and George Christou*,† Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, ‡Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana 46202-3274, and §Institut Neel, CNRS and Universite J. Fournier, BP 166, 38042 Grenoble Cedex 9, France. Deceased, March 2008.
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†
Received July 17, 2009
The use has been explored in Mn cluster chemistry of N3- or Cl- in combination with N-methyldiethanolamine (mdaH2) or triethanolamine (teaH3). The reactions of Mn(ClO4)2 3 6H2O, NEt3, NaN3, and either mdaH2 or teaH3 (1:2:1:2) in DMF/MeOH afford {[Na(MeOH)3][Mn7(N3)6(mda)6]}n (1) and {Na[Mn7(N3)6(teaH)6]}n (2), respectively, whereas the 2:1:1 reaction of MnCl2 3 4H2O, mdaH2, and NEt3 in MeCN gives (NHEt3)[Mn7Cl6(mda)6] (3). Similar reactions using NBun4N3 in place of NaN3 gave (NHEt3)[Mn7(N3)6(mda)6] (4) and (NHEt3)[Mn7(N3)6(teaH)6] (5). The Mn7 anions consist of a Mn6 hexagon of alternating MnII and MnIII ions surrounding a central MnII ion. The remaining ligation is by six bridging and chelating mda2- or teaH2- groups, and either six terminal N3- (1, 2, 4, 5) or Cl- (3) ions. Each bridging mda2- or teaH2- ligand contains both μ- and μ3-O atoms, resulting in a similar, nearplanar [Mn7( μ3-OR)6( μ-OR)6]5+ core for all three complexes. The Mn7 anions of 1 and 2 are connected via Na+ cations to yield one-dimensional zigzag chains and three-dimensional windmill-like “hexagons-of-hexagons”, respectively. In contrast, the Mn7 anion of 3 forms a strong hydrogen-bond between the NHEt3+ cation and a terminal Cl- ion giving a discrete ion-pair. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out in the 5.0-300 K range. Fits of dc magnetization versus field (H ) and temperature (T) data by matrix diagonalization gave S = 11, g = 1.95, D = -0.15 cm-1 for 1, S = 16, g = 1.95, D = -0.02 cm-1 for 2, and S = 11, g = 1.92, D = -0.13 cm-1 for 3 (D is the axial zero-field splitting parameter). Complexes 4 and 5 were also found to possess S = 11 and S = 16 ground states, respectively. The different ground states of 1 and 2 were rationalized on the basis of the sign and magnitude of the various Mn2 exchange parameters obtained from density functional theory (DFT) calculations. This analysis confirmed the presence of spin frustration effects, with the ground states being determined by the relative magnitude of the two weakest interactions. The combined results demonstrate the usefulness of N-based dipodal and tripodal alkoxide-based chelates as a route to structurally and magnetically interesting Mn clusters.
Introduction There continues to be great interest in the study of polynuclear manganese complexes at intermediate oxidation states. The reasons for this continued interest include the architectural beauty such molecules often possess, their relevance to Mn biomolecules such as the photosynthetic oxygen-evolving center, and the intriguing property of MnIII-containing clusters to often possess large, and sometimes abnormally large, ground-state spin (S) values. When *To whom correspondence should be addressed. E-mail: christou@chem. ufl.edu. (1) For some representative references, see: (a) Christou, G.; Gatteschi, D.; Hendrickson, D. N.; Sessoli, R. MRS Bull. 2000, 25, 66. (b) 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.
r 2009 American Chemical Society
the latter is combined with a significant and negative magnetoanisotropy (negative zero-field splitting parameter, D), singlemolecule magnets (SMMs) result.1 SMMs are molecular species that can function as nanoscale magnetic particles at sufficiently low temperatures because of a significant energy barrier to magnetization relaxation.2 In addition, they display quantum effects such as quantum tunneling of the magnetization3 and :: (2) (a) Bircher, R.; Chaboussant, G.; Dobe, D.; Gudel, H. U.; Oshsenbein, S. T.; Sieber, A.; Waldmann, O. Adv. Funct. Mater. 2006, 16, 209. (b) Gatteschi, D.; Sessoli, R. Angew. Chem., Int. Ed. 2003, 42, 268. (c) Aubin, S. M. J.; Gilley, N. R.; Pardi, L.; Krzystek, J.; Wemple, M. W.; Brunel, L.-C.; Maple, M. B.; Christou, G.; Hendrickson, D. N. J. Am. Chem. Soc. 1998, 120, 4991. (d) Oshio, H.; Nakano, M. Chem.;Eur. J. 2005, 11, 5178. (3) (a) Friedman, J. R.; Sarachik, M. P. Phys. Rev. Lett. 1996, 76, 3830. (b) Thomas, L.; Lionti, L.; Ballou, R.; Gatteschi, D.; Sessoli, R.; Barbara, B. Nature 1996, 383, 145.
Published on Web 09/18/2009
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9832 Inorganic Chemistry, Vol. 48, No. 20, 2009 quantum phase interference.4 As a result, SMMs represent potential molecular memory elements for specialized, molecule-based information storage devices and molecular spintronics,5 as well as potential quantum bits for quantum information processing.6 The ability of clusters to possess large numbers of unpaired electrons is the primary focus of the present paper. Molecules with a large S are a fascinating area of importance to fields spanning chemistry, physics, materials science, and medicine. At one extreme is the fundamental desire to understand exactly how the sign and relative magnitudes of the constituent exchange interactions yield the high S value, whereas at the other are, for example, applications such as in MRI imaging and the SMM behavior mentioned above. For such reasons, we have a general interest in high-spin species and are seeking (i) new synthetic procedures to obtain such molecules using simple reagents;7 (ii) to understand exactly how the large ground state S arises; and (iii) to attain some rudimentary level of control of S in such often high-nuclearity molecules.8 If an obtained molecule also has a large D value, then its potential SMM properties are also of interest, but in fact complexes with the largest S values usually possess small D values,9 as seen for Mn28Cu17, Mn25, Mn19, Mn17, and Mn10 complexes with S = 51/2,10 51/211 or 61/2,8a 83/2,12 3713a or 28 ( 113b and 2214 ground states, respectively. Large S values can result from (a) ferro- or ferrimagnetic spin alignments and/or (b) competing interactions (spin frustration) in certain Mx topologies that prevent (4) (a) Wernsdorfer, W.; Sessoli, R. Science 2000, 2417. (b) Wernsdorfer, W.; Soler, M.; Christou, G.; Hendrickson, D. N. J. Appl. Phys. 2002, 91, 7164. (c) Wernsdorfer, W.; Chakov, N. E.; Christou, G. Phys. Rev. Lett. 2005, 95, 037203 (1-4). (5) Bogani, L.; Wernsdorfer, W. Nature Mater. 2008, 7, 179. (6) Leuenberger, M. N.; Loss, D. Nature 2001, 410, 789. (7) For a comprehensive review, see: Stamatatos, Th. C.; Christou, G. Inorg. Chem. 2009, 48, 3308, and references therein. (8) (a) Stamatatos, Th. C.; Abboud, K. A.; Wernsdorfer, W.; Christou, G. Angew. Chem., Int. Ed. 2007, 46, 884. (b) Stamatatos, T. C.; Abboud, K. A.; Wernsdorfer, W.; Christou, G. Polyhedron 2007, 26, 2095. (c) Milios, C. J.; Inglis, R.; Vinslava, A.; Bagai, R.; Wernsdorfer, W.; Parsons, S.; Perlepes, S. P.; Christou, G.; Brechin, E. K. J. Am. Chem. Soc. 2007, 129, 12505. (d) For an excellent review, see: Milios, C. J.; Piligkos, S.; Brechin, E. K. Dalton Trans. 2008, 1809. (9) (a) Waldmann, O. Inorg. Chem. 2007, 46, 10035. (b) Ruiz, E.; Cirera, J.; Cano, J.; Alvarez, S.; Loose, C.; Kortus, J. Chem. Commun. 2008, 52. (10) Wang, W.- G.; Zhou, A.- J.; Zhang, W.- X.; Tong, M.- L.; Chen, X.- M; Nakano, M.; Beedle, C. C.; Hendrickson, D. N. J. Am. Chem. Soc. 2007, 129, 1014. (11) (a) Murugesu, M.; Habrych, M.; Wernsdorfer, W.; Abboud, K. A.; Christou, G. J. Am. Chem. Soc. 2004, 126, 4766. (b) Murugesu, M.; Takahashi, S.; Wilson, A.; Abboud, K. A.; Wernsdorfer, W.; Hill, S.; Christou, G. Inorg. Chem. 2008, 47, 9459. (12) (a) Ako, A. M.; Hewitt, I. J.; Mereacre, V.; Clerac, R.; Wernsdorfer, W.; Anson, C. E.; Powell, A. K. Angew. Chem., Int. Ed. 2006, 45, 4926. :: (b) Waldmann, O.; Ako, A. M.; Gudel, H. U.; Powell, A. K. Inorg. Chem. 2008, 47, 3486. (13) (a) Moushi, E. E.; Stamatatos, Th. C.; Wernsdorfer, W.; Nastopoulos, V.; Christou, G.; Tasiopoulos, A. J. Inorg. Chem. 2009, 48, 5049. (b) Nayak, S.; Beltran, L. M. C.; Lan, Y.; Clerac, R.; Hearns, N. G. R.; Wernsdorfer, W.; Anson, C. E.; Powell, A. K. Dalton Trans. 2009, 1901. (14) (a) Stamatatos, Th. C.; Abboud, K. A.; Wernsdorfer, W.; Christou, G. Angew. Chem., Int. Ed. 2006, 45, 4134. (b) Stamatatos, Th. C.; Abboud, K. A.; Wernsdorfer, W.; Christou, G. Polyhedron 2007, 26, 2042. (c) Stamatatos, Th. C.; Poole, K. M.; Abboud, K. A.; Wernsdorfer, W.; O'Brien, T. A.; Christou, G. Inorg. Chem. 2008, 47, 5006. (d) Manoli, M.; Johnstone, R. D. L.; Parsons, S.; Murrie, M.; Affronte, M.; Evangelisti, M.; Brechin, E. K. Angew. Chem., Int. Ed. 2007, 46, 4456. (15) (a) Kahn, O. Molecular Magnetism; VCH Publishers: New York, 1993. (b) Stamatatos, Th. C.; Christou, G. Philos. Trans. R. Soc. A 2008, 366, 113, and references cited therein.
Stamatatos et al. (frustrate) the preferred spin alignments.15 In case (a), ferromagnetic interactions can result from ligands or structural characteristics known to give ferromagnetic coupling between metal centers. One of the best ferromagnetic couplers is the azide (N3-) group when it bridges metals in the 1,1-(end-on) fashion.7,11-14,16 Others include pyridine-based alkoxide ligands,8a,11,14a-14c,17 or diolate-18 and triolatebased10,12,14d,19 groups such as, N-methyldiethanolamine (mdaH2) and triethanolamine (teaH3), which are versatile chelating/bridging ligands whose bridging alkoxide arms often support ferromagnetic coupling. The rationalization of the observed ground state spins in purely ferromagnetic compounds is trivial, being the sum of the parallel-aligned individual spins. Similarly, purely ferrimagnetic complexes can be readily understood, being arrays of antiferromagnetically coupled metals with unequal single-ion spin values that lead to a significant net molecular spin S. In case (b), which includes the majority of polynuclear valence-trapped Mn clusters exhibiting a non-zero ground state, the molecular S value is a consequence of the many competing (predominantly) antiferromagnetic interactions that prevent (frustrate) perfectly antiparallel spin alignments. This is particularly true for antiferromagnetically coupled triangular M3 subunits, since the spins cannot all be aligned antiparallel to both their neighbors. The ground state then becomes extremely difficult to predict from structural and simple spin-up/spin-down considerations. In fact, the net molecular S is dependent on the precise topology of the Mnx framework and very sensitive to the relative strengths of the competing interactions. Crucial to the latter in mixed-valence Mn chemistry is the fact that MnII-O-MnIII and MnIII-O-MnIII interactions are often of similar magnitude, either weakly antiferromagnetic or, occasionally, weakly ferromagnetic.15 Thus, one of the major challenges in Mn (16) (a) Escuer, A.; Aromi, G. Eur. J. Inorg. Chem. 2006, 4721, and references cited therein. (b) Ruiz, E.; Cano, J.; Alvarez, S.; Alemany, P. J. Am. Chem. Soc. 1998, 120, 11122. (17) (a) Brechin, E. K.; Sanudo, E. C.; Wernsdorfer, W.; Boskovic, C.; Yoo, J.; Hendrickson, D. N.; Yamaguchi, A.; Ishimoto, H.; Concolino, T. E.; Rheingold, A. L.; Christou, G. Inorg. Chem. 2005, 44, 502. (b) Boudalis, A. K.; Donnadieu, B.; Nastopoulos, V.; Clemente-Juan, J. M.; Mari, A.; Sanakis, Y.; Tuchagues, J.- P.; Perlepes, S. P. Angew. Chem., Int. Ed. 2004, 43, 2266. (c) Papaefstathiou, G. S.; Perlepes, S. P.; Escuer, A.; Vicente, R.; Font-Bardia, M.; Solans, X. Angew. Chem., Int. Ed. 2001, 40, 884. (d) Papaefstathiou, G. S.; Escuer, A.; Vicente, R.; Font-Bardia, M.; Solans, X.; Perlepes, S. P. Chem. Commun. 2001, 2414. (e) Stamatatos, Th. C.; Foguet-Albiol, D.; Stoumpos, C. C.; Raptopoulou, C. P.; Terzis, A.; Wernsdorfer, W.; Perlepes, S. P.; Christou, G. J. Am. Chem. Soc. 2005, 127, 15380. (f ) Stamatatos, Th. C.; Foguet-Albiol, D.; Lee, S.- C.; Stoumpos, C. C.; Raptopoulou, C. P.; Terzis, A.; Wernsdorfer, W.; Hill, S.; Perlepes, S. P.; Christou, G. J. Am. Chem. Soc. 2007, 129, 9484. (g) Stamatatos, Th. C.; Abboud, K. A.; Wernsdorfer, W.; Christou, G. Angew. Chem., Int. Ed. 2008, 47, 6694. (h) Stamatatos, Th. C.; Efthymiou, C. G.; Stoumpos, C. C.; Perlepes, S. P. Eur. J. Inorg. Chem. 2009, 3361. (18) (a) Moushi, E. E.; Stamatatos, Th. C.; Wernsdorfer, W.; Nastopoulos, V.Christou, G.; Tasiopoulos, A. J. Angew. Chem., Int. Ed. 2006, 45, 7722. (b) Moushi, E. E.; Lampropoulos, C.; Wernsdorfer, W.; Nastopoulos, V.; Christou, G.; Tasiopoulos, A. J. Inorg. Chem. 2007, 46, 3795. (c) Foguet-Albiol, D.; O'Brien, T. A.; Wernsdorfer, W.; Moulton, B.; Zaworotko, M. J.; Abboud, K. A.; Christou, G. Angew. Chem., Int. Ed. 2005, 44, 897. (d) Shah, S. J.; Ramsey, C. M.; Heroux, K. J.; DiPasquale, A. G.; Dalal, N. S.; Rheingold, A. L.; del Barco, E.; Hendrickson, D. N. Inorg. Chem. 2008, 47, 9569. (e) Tasiopoulos, A. J.; Perlepes, S. P. Dalton Trans. 2008, 5537, and references therein (Tutorial Review). (19) (a) For a representative review, see: Brechin, E. K. Chem. Commun. 2005, 5141, and references therein. (b) Scott, R. T. W.; Milios, C. J.; Vinslava, A.; Lifford, D.; Parsons, S.; Wernsdorfer, W.; Christou, G.; Brechin, E. K. Dalton Trans. 2006, 3161. (c) Scott, R. T. W.; Parsons, S.; Murugesu, M.; Wernsdorfer, W.; Christou, G.; Brechin, E. K. Angew. Chem., Int. Ed. 2005, 44, 6540.
Article
cluster chemistry is to rationalize exactly how the large ground state S of such often complicated complexes arises on the basis of the constituent spin frustration effects and the individual metal spin alignments that result. Here we report a study of some MnII4MnIII3 complexes, and we shall show that we can rationalize both the origin of the S = 11 ground state normally observed, and the use of this knowledge to target and successfully attain an S = 16 variant with the maximum possible ground state spin. In addition, we also describe the fascinating supramolecular architectures that these clusters display. Portions of this work have been previously communicated.20
Experimental Section Syntheses. All manipulations were performed under aerobic conditions using materials as received. Caution! Although no such behavior was observed during the present work, perchlorate and azide salts are potentially explosive; such compounds should be synthesized and used in small quantities, and treated with utmost care at all times. [Na(MeOH)3][Mn7(N3)6(mda)6] (1). To a stirred solution of mdaH2 (0.24 g, 2.0 mmol) and NEt3 (0.28 mL, 2.0 mmol) in DMF/MeOH (25/5 mL) was added solid NaN3 (0.07 g, 1.0 mmol). The mixture was stirred for a further 10 min and then solid Mn(ClO4)2 3 6H2O (0.36 g, 1.0 mmol) was added, which caused a rapid color change from pale yellow to dark red. The solution was stirred for a further 1 h, filtered, and the filtrate layered with Et2O (60 mL). After 4 days, X-ray quality dark-red crystals of 1 3 MeOH were collected by filtration, washed with cold MeOH (2 3 mL) and Et2O (2 5 mL), and dried in air; the yield was 55%. Anal. Calcd for 1 (solvent-free): C, 27.17; H, 5.39; N, 23.05%. Found: C, 27.12; H, 5.52; N, 23.14%. Selected IR data (cm-1): 3431 (mb), 2956 (w), 2856 (m), 2056 (vs), 1594 (m), 1518 (m), 1456 (m), 1401 (m), 1336 (m), 1261 (m), 1202 (w), 1066 (m), 1032 (m), 999 (m), 912 (w), 888 (m), 760 (m), 735 (w), 670 (w), 644 (w), 580 (m), 442 (w). Na[Mn7(N3)6(teaH)6] (2). This complex was prepared in the same manner as complex 1 but using teaH3 (0.30 g, 2.0 mmol) in place of mdaH2. After 6 days, dark-red crystals of 2 3 DMF 3 Et2O were isolated, collected by filtration, washed with cold MeOH (2 3 mL) and Et2O (2 5 mL), and dried under vacuum; the yield was 63%. Anal. Calcd for 2 3 DMF: C, 28.99; H, 5.30; N, 21.67%. Found: C, 28.82; H, 5.19; N, 21.67%. Selected IR data (cm-1): 3408 (mb), 2849 (m), 2071 (vs), 1672 (m), 1418 (w), 1383 (w), 1347 (w), 1268 (w), 1223 (w), 1063 (m), 1031 (m), 1000 (m), 892 (m), 777 (w), 588 (m), 525 (m). (NHEt3)[Mn7Cl6(mda)6] (3). To a stirred solution of mdaH2 (0.06 g, 0.5 mmol) and NEt3 (0.07 mL, 0.5 mmol) in MeCN (25 mL) was added solid MnCl2 3 4H2O (0.20 g, 1.0 mmol). The resulting brown slurry was stirred for 10 min and then refluxed for a further 2 h, during which time all solids dissolved. The dark brown solution was cooled down to room temperature, filtered, (20) Stamatatos, Th. C.; Poole, K. M.; Foguet-Albiol, D.; Abboud, K. A.; O’Brien, T. A.; Christou, G. Inorg. Chem. 2008, 47, 6593.
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and the filtrate layered with Et2O (50 mL). After 2 days, X-ray quality dark-red crystals of 3 3 MeCN 3 Et2O were collected by filtration, washed with cold MeCN (2 2 mL) and Et2O (2 5 mL), and dried in air; the yield was 25%. Anal. Calcd for 3 (solvent-free): C, 30.83; H, 5.89; N, 6.99%. Found: C, 30.44; H, 6.10; N, 6.58%. Selected IR data (cm-1): 3431 (mb), 2850 (m), 1652 (w), 1558 (w), 1456 (m), 1070 (s), 1039 (m), 1002 (w), 913 (w), 890 (m), 667 (w), 647 (w), 596 (w), 526 (w). (NHEt3)[Mn7(N3)6(mda)6] (4). To a stirred solution of mdaH2 (0.24 g, 2.0 mmol) and NEt3 (0.28 mL, 2.0 mmol) in DMF/ MeOH (25/5 mL) was added solid NBun4N3 (0.24 g, 1.0 mmol). The mixture was stirred for a further 20 min and then solid Mn(ClO4)2 3 6H2O (0.36 g, 1.0 mmol) was added under vigorous stirring, which caused a rapid color change from pale yellow to dark red. The solution was stirred for a further 30 min, filtered, and the filtrate layered with Et2O (60 mL). After 3 days, darkred crystals were collected by filtration, washed with cold MeOH (2 3 mL) and Et2O (2 5 mL), and dried under vacuum; the yield was 50%. Anal. Calcd for 4: C, 29.99; H, 5.73; N, 24.29%. Found: C, 29.82; H, 5.59; N, 24.45%. Selected IR data (cm-1): 3439 (mb), 2946 (m), 2876 (m), 2058 (vs), 1630 (m), 1616 (m), 1575 (m), 1540 (m), 1456 (m), 1419 (m), 1395 (m), 1296 (w), 1261 (w), 1205 (w), 1160 (w), 1066 (m), 1033 (m), 1002 (m), 890 (m), 802 (w), 746 (w), 667 (m), 647 (m), 596 (m), 526 (m), 442 (w). (NHEt3)[Mn7(N3)6(teaH)6] (5). This complex was prepared in the same manner as complex 4 but using teaH3 (0.30 g, 2.0 mmol) in place of mdaH2. After 5 days, dark-red crystals were collected by filtration, washed with cold MeOH (2 3 mL) and Et2O (2 5 mL), and dried under vacuum; the yield was 55%. Anal. Calcd for 5: C, 31.10; H, 5.84; N, 21.59%. Found: C, 30.95; H, 5.67; N, 21.74%. Selected IR data (cm-1): 3438 (mb), 2949 (m), 2866 (m), 2061 (vs), 1681 (m), 1423 (w), 1390 (w), 1356 (w), 1269 (w), 1227 (w), 1160 (w), 1061 (m), 1037 (m), 997 (m), 895 (m), 772 (w), 592 (m), 525 (m), 458 (w). X-ray Crystallography. Data were collected on a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing Mo KR radiation (λ = 0.71073 A˚). Suitable crystals of 1 3 MeOH, 2 3 DMF 3 Et2O, and 3 3 MeCN 3 Et2O were attached to glass fibers using silicone grease and transferred to a goniostat where they were cooled to 173 K for data collection. An initial search for reciprocal space revealed a monoclinic cell for 1 3 MeOH and 3 3 MeCN 3 Et2O, and a rhombohedral cell for 2 3 DMF 3 Et2O; space groups Cc (1 3 MeOH), R3 (2 3 DMF 3 Et2O) and P21/c (3 3 MeCN 3 Et2O) were confirmed by the subsequent solution and refinement of the structures. Cell parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the ω-scan method (0.3 frame width). The first 50 frames were remeasured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was 2σ(I) to yield R1 and wR2 of 4.29 and 9.90%, respectively. (21) SHELXTL6; Bruker-AXS: Madison, WI, 2000.
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Table 1. Crystallographic Data for 1 3 MeOH, 2 3 DMF 3 Et2O, and 3 3 MeCN 3 Et2O parameter
1
formulaa fw, g mol-1a crystal system space group a, A˚ b, A˚ c, A˚ β, deg V, A˚3 Z T, K radiation, A˚b Fcalc, g cm-3 μ, mm-1 R1c,d wR2e
C34H82N24O16Mn7Na 1490.81 monoclinic Cc 17.2034(8) 15.4286(7) 22.9340(11) 98.398(1) 6022.0(5) 4 173(2) 0.71073 1.644 1.507 0.0429 0.0990
2
3
C41H95N25O20Mn7Na C42H95N8O13Cl6Mn7 1665.99 1517.54 rhombohedral monoclinic R3 P21/c 15.8536(6) 11.1009(7) 15.8536(6) 19.0949(12) 22.7938(12) 29.2126(19) 90 97.502(2) 4961.4(4) 6139.2(7) 3 4 173(2) 173(2) 0.71073 0.71073 1.673 1.642 1.386 1.716 0.0348 0.0655 0.0906 0.1678 P P P P a Including solvate molecules. b Graphite monochromator. c I > 2σ(I). d R1 = ||Fo| - |Fc||/ |Fo||. e wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2, w = 2 2 2 2 2 1/[σ (Fo ) + [(ap) + bp], where p = [max(Fo , 0) + 2Fc ]/3.
For 2 3 DMF 3 Et2O, the asymmetric unit consists of a 1/3 Mn7 cluster, a sodium cation, and 1/3 DMF and 1/3 Et2O molecules of crystallization, all lying on 3-fold rotation axes. The two solvent molecules are disordered and could not be modeled properly; thus, program SQUEEZE,22 a part of the PLATON package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. The protons on O5 and O6 were located in a difference Fourier map and refined riding on their parent O atoms. A total of 259 parameters were included in the structure refinement on F2 using 4422 reflections with I > 2σ(I ) to yield R1 and wR2 of 3.48 and 9.06%, respectively. For 3 3 MeCN 3 Et2O, the asymmetric unit consists of the complete Mn7 cluster, a triethylammonium cation, and MeCN and Et2O molecules of crystallization. The latter two could not be modeled properly, thus the program SQUEEZE was again used to calculate the solvent disorder area and remove its contribution to the overall intensity data. A total of 627 parameters were included in the final cycle of refinement on F2 using 39381 reflections with I > 2σ(I ) to yield R1 and wR2 of 6.55 and 16.78%, respectively. Unit cell data and details of the structure refinements for the three complexes are collected in Table 1. Physical Measurements. Infrared spectra were recorded in the solid state (KBr pellets) on a Nicolet Nexus 670 FTIR spectrometer in the 4000-450 cm-1 range. Elemental analyses (C, H, and N) were performed on a Perkin-Elmer 2400 Series II Analyzer. Variable-temperature direct current (dc) and alternating current (ac) magnetic susceptibility data were collected at the University of Florida using a Quantum Design MPMS-XL SQUID susceptometer equipped with a 7 T magnet and operating in the 1.8-300 K range. Samples were embedded in solid eicosane to prevent torquing. The ac magnetic susceptibility measurements were performed in an oscillating ac field of 3.5 Oe and a zero dc field. The oscillation frequencies were in the 5-1488 Hz range. Magnetization versus field and temperature data were fit using the program MAGNET.23 Pascal’s constants were used to estimate the diamagnetic corrections, which were subtracted from the experimental susceptibilities to give the molar paramagnetic susceptibilities (χΜ). Low-temperature (
