Evidence for Single-Chain Magnet Behavior in a Mn^III−Ni^II Chain Designed with High Spin Magnetic Units:  A Route to High Temperature Metastable Magnets

Abstract

We herein present the synthesis, crystal structure, and magnetic properties of a new heterometallic chain 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 was investigated by X-ray crystallographic analysis: compound 1 crystallized in monoclinic, space group C2/c (No. 15) with a = 21.140(3) A, b = 15.975(1) A, c = 18.6212(4) A, beta = 98.0586(4) degrees , V = 6226.5(7) A3, and Z = 4. This compound consists of two fragments, the out-of-plane dimer [Mn2(saltmen)2]2+ as a coordination acceptor building block and the neutral mononuclear unit [Ni(pao)2(py)2] as a coordination donor building block, forming an alternating chain having the repeating unit [-Mn-(O)2-Mn-ON-Ni-NO-]n. In the crystal structure, each chain is well separated with a minimum intermetallic distance between Mn and Ni ions of 10.39 A and with the absence of interchain pi overlaps between organic ligands. These features ensure a good magnetic isolation of the chains. The dc and ac magnetic measurements were performed on both the polycrystalline sample and the aligned single crystals of 1. Above 30 K, the magnetic susceptibility of this one-dimensional compound was successfully described in a mean field approximation as an assembly of trimers (Mn...Ni...Mn) with a NiII...MnIII antiferromagnetic interaction (J = -21 K) connected through a ferromagnetic MnIII...MnIII interaction (J'). However, the mean field theory fails to describe the magnetic behavior below 30 K emphasizing the one-dimensional magnetic character of the title compound. Between 5 and 15 K, the susceptibility in the chain direction was fitted to a one-dimensional Ising model leading to the same value of J'. Hysteresis loops are observed below 3.5 K, indicating a magnet-type behavior. In the same 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 material is 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 work opens new perspectives for one-dimensional systems to obtain high temperature metastable magnets by combining high spin magnetic units, strong interunit interactions, and uniaxial anisotropy.

Cyanide-bridged Fe(iii)–Co(ii) bis double zigzag chains with a slow relaxation of the magnetisation

“…Between 2 and 7 K, the relaxation times follow an Arrhenius law [t = t 0 exp(E a /k B T)] with E a /k B = 152 K and t 0 = 1.5 3 10 217 s. The energy barrier E a /k B is close to those found in the previous nanowires. [5][6][7] Instead, the t 0 prefactor is much smaller: obtained under an applied magnetic field, it deserves more study.…”

Synthesis, structures, and spectroscopic properties of Hg(II) complexes of bidentate NN and tridentate NNO Schiff-base ligands

“…Care must be taken when handling samples, and appropriate disposal procedures are necessary. All chemicals were used as purchased without purification: HgCl 2 , NaN 3 , pyridine-2-carboxaldehyde (Merck), Hg(NO 3 ) 2 (Sarabhai Chemicals), Hg(OAc) 2 , o-anisidine, p-anisidine (Sd fine). (E)-2-methoxy-N-(pyridin-2-ylmethylene)aniline (L 1 ) and (E)-4-methoxy-N-(pyridin-2-ylmethylene)aniline (L 2 ) were generated in situ from pyridine-2-carboxaldehyde and the corresponding anisidine.…”

“…Schiff-base ligands and their metal complexes have received attention owing to their distinctive coordination and structural properties [1][2][3][4][5]. In addition, Schiff-base compounds of transition metals have become important components for the generation of supramolecular aggregates through the formation of coordination bonds, hydrogen bonding and other intermolecular interactions, thereby creating a large variety of supramolecular architectures including highdimensional frameworks [6][7][8][9].…”

Magnetic tetrastability in a spin chain

“…Using numerical and analytical calculations, we show that the so-called π/4 canted spin chain presents four stable magnetic domains with orthogonal magnetizations. Finally we show that domain walls, which are responsible for the relaxation of the magnetization (loss of information), have a finite energy which should avoid their nucleation at low temperature and therefore preserve the encoded information.Among the variety of low dimensionnal magnets, single chain magnets (SCMs) [7,8], have been extensively studied as they present a slow relaxation of magnetization, promising for information storage [7][8][9][10]. SCMs are generally made by assembling together single-molecule magnets that owns a strong uni-axial anisotropy [11].…”

“…Among the variety of low dimensionnal magnets, single chain magnets (SCMs) [7,8], have been extensively studied as they present a slow relaxation of magnetization, promising for information storage [7][8][9][10]. SCMs are generally made by assembling together single-molecule magnets that owns a strong uni-axial anisotropy [11].…”