Evidence for Single-Chain Magnet Behavior in a MnIII-NiII Chain Designed with High Spin Magnetic Units: A Route to High Temperature Metastable Magnets
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- 作者：Rodolphe Clé ; rac ; Hitoshi Miyasaka ; Masahiro Yamashita ; and Claude Coulon
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：October 30, 2002
- 年：2002
- 卷：124
- 期：43
- 页码：12837 - 12844
- 全文大小：222K
- 年卷期：v.124,no.43(October 30, 2002)
- ISSN：1520-5126
文摘
We herein present the synthesis, crystal structure, and magnetic properties of a new heterometallicchain of MnIII and NiII ions, [Mn2(saltmen)2Ni(pao)2(py)2](ClO4)2 (1) (saltmen2- = N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate) and pao- = pyridine-2-aldoximate). The crystal structure of 1 wasinvestigated by X-ray crystallographic analysis: compound 1 crystallized in monoclinic, space group C2/c(No. 15) with a = 21.140(3) Å, b = 15.975(1) Å, c = 18.6212(4) Å, 
= 98.0586(4)
, V = 6226.5(7) Å3, andZ = 4. This compound consists of two fragments, the out-of-plane dimer [Mn2(saltmen)2]2+ as a coordinationacceptor building block and the neutral mononuclear unit [Ni(pao)2(py)2] as a coordination donor buildingblock, forming an alternating chain having the repeating unit [-Mn-(O)2-Mn-ON-Ni-NO-]n. In the crystalstructure, each chain is well separated with a minimum intermetallic distance between Mn and Ni ions of10.39 Å and with the absence of interchain 
overlaps between organic ligands. These features ensure agood magnetic isolation of the chains. The dc and ac magnetic measurements were performed on boththe polycrystalline sample and the aligned single crystals of 1. Above 30 K, the magnetic susceptibility ofthis one-dimensional compound was successfully described in a mean field approximation as an assemblyof trimers (Mn···Ni···Mn) with a NiII···MnIII antiferromagnetic interaction (J = -21 K) connected through aferromagnetic MnIII···MnIII interaction (J'). However, the mean field theory fails to describe the magneticbehavior below 30 K emphasizing the one-dimensional magnetic character of the title compound. Between5 and 15 K, the susceptibility in the chain direction was fitted to a one-dimensional Ising model leading tothe same value of J'. Hysteresis loops are observed below 3.5 K, indicating a magnet-type behavior. In thesame range of temperature, combined ac and dc measurements show a slow relaxation of the magnetization.This result indicates the presence of a metastable state without magnetic long-range order. This materialis the first experimental design of a heterometallic chain with ST = 3 magnetic units showing a "single-chain magnet" behavior predicted in 1963 by R. J. Glauber for an Ising one-dimensional system. This workopens new perspectives for one-dimensional systems to obtain high temperature metastable magnets bycombining high spin magnetic units, strong interunit interactions, and uniaxial anisotropy.
= 98.0586(4), V = 6226.5(7) Å3, andZ = 4. This compound consists of two fragments, the out-of-plane dimer [Mn2(saltmen)2]2+ as a coordinationacceptor building block and the neutral mononuclear unit [Ni(pao)2(py)2] as a coordination donor buildingblock, forming an alternating chain having the repeating unit [-Mn-(O)2-Mn-ON-Ni-NO-]n. In the crystalstructure, each chain is well separated with a minimum intermetallic distance between Mn and Ni ions of10.39 Å and with the absence of interchain overlaps between organic ligands. These features ensure agood magnetic isolation of the chains. The dc and ac magnetic measurements were performed on boththe polycrystalline sample and the aligned single crystals of 1. Above 30 K, the magnetic susceptibility ofthis one-dimensional compound was successfully described in a mean field approximation as an assemblyof trimers (Mn···Ni···Mn) with a NiII···MnIII antiferromagnetic interaction (J = -21 K) connected through aferromagnetic MnIII···MnIII interaction (J'). However, the mean field theory fails to describe the magneticbehavior below 30 K emphasizing the one-dimensional magnetic character of the title compound. Between5 and 15 K, the susceptibility in the chain direction was fitted to a one-dimensional Ising model leading tothe same value of J'. Hysteresis loops are observed below 3.5 K, indicating a magnet-type behavior. In thesame range of temperature, combined ac and dc measurements show a slow relaxation of the magnetization.This result indicates the presence of a metastable state without magnetic long-range order. This materialis the first experimental design of a heterometallic chain with ST = 3 magnetic units showing a "single-chain magnet" behavior predicted in 1963 by R. J. Glauber for an Ising one-dimensional system. This workopens new perspectives for one-dimensional systems to obtain high temperature metastable magnets bycombining high spin magnetic units, strong interunit interactions, and uniaxial anisotropy.