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Linear NiII−MnIII2−NiII Tetramers:  An Oligomeric Component of the MnIII2NiII Single-Chain Magnets

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posted on 06.09.2004, 00:00 by Hitoshi Miyasaka, Tomohiro Nezu, Kunihisa Sugimoto, Ken-ichi Sugiura, Masahiro Yamashita, Rodolphe Clérac
Heterometallic linear tetramers [Mn(5-R-saltmen)Ni(pao)(bpy)2]2(ClO4)4 (5-R-saltmen2- = N,N-1,1,2,2-tetramethylethylene bis(5-R-salicylideneiminate); pao- = pyridine-2-aldoximate; bpy = 2,2‘-bipyridine, R = H, 1; Cl, 2; Br, 3; MeO, 4) have been synthesized and structurally characterized. These compounds exhibit a [NiII−NO−MnIII−(O)2−MnIII−ON−NiII] skeleton where −ON− is an oximate bridge between MnIII and NiII ions and −(O)2− is a bi-phenolate bridge between MnIII ions. These tetramers can be seen as oligomeric units of the heterometallic MnIII2−NiII chain observed in a family of single-chain magnets (Clérac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837. Miyasaka, H.; Clérac, R.; Mizushima, K.; Sugiura, K.; Yamashita, M.; Wernsdorfer, W.; Coulon, C. Inorg. Chem. 2003, 42, 8203.). Magnetic measurements on these tetramers confirm the nature of the magnetic interactions reported for the MnIII2−NiII chains:  a strong antiferromagnetic MnIII/NiII coupling via the oximate bridge (JNi-Mn ranges from −23.7 to −26.1 K) and a weak ferromagnetic MnIII/MnIII coupling through the bi-phenolate bridge (JMn-Mn ranges from +0.4 to +0.9 K). These magnetic interactions lead to tetramers with an S = 2 ground state.