Cyanide‐Bridged Iron(III)–Cobalt(II) Double Zigzag Ferromagnetic Chains: Two New Molecular Magnetic Nanowires

Abstract

The occurrence of a slow relaxation of the magnetization in a one-dimensional (1D) system was recently reported by one of us.[1] The system was claimed to illustrate, for the first time, a theoretical model designed by Glauber in 1963 for anisotropic Ising systems [2] and opened the perspective of a potential use of 1D magnetic molecular nanowires for information storage. Even though 1D magnetism is a very active area of research, such dynamic behavior was never detected before since it is not clear how to fulfill experimentally the requirements of a perfect 1D Ising-type chain. This finding prompted us to look carefully at 1D systems containing anisotropic elements, such as cobalt(ii) and low-spin iron(iii) centers that we synthesized recently, [3] to investigate their anisotropic magnetic properties and to study the dynamics of their magnetization.The stable low-spin cyanide-containing iron(iii) precur-À (L = bidentate nitrogen donor) react with hydrated metal ions in aqueous solution [4,5] and afford single crystals of the bimetallic double zigzag chains [{Fe(1 with L = 2,2'-bipyridine (bpy) and 2 with L = 1,10-phenanthroline (phen)). We found that 1 and 2 show intrachain ferromagnetic coupling, 1D Ising-type behavior, slow relaxation of the magnetization, and hysteresis effects and thus are the second examples of anisotropic molecular magnetic nanowires and the first with an intrachain ferromagnetic coupling. Their preparation, Xray crystal structure, [6] and preliminary static and dynamic magnetism are reported herein.Compounds 1 and 2 are isostructural (monoclinic system, space group P2 1 /n). They are made up of neutral cyanidebridged Co II

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.…”

“…The two crystallographically independent iron atoms (Fe(1) and Fe(2)) exhibit the same distorted octahedral surrounding FeN 2 C 4 as in previous reports. 6,8 The difference between [Fe(1)(bipy)(CN) 4 ] 2 and [Fe(2)(bipy)(CN) 4 ] 2 is that the former acts as a trismonodentate ligand toward the M atoms through three cyanides in fac position whereas the latter adopts a bismonodentate coordination mode (two cyanides in cis position). The M atom is six-co-ordinated with five cyanide-nitrogen atoms and a water molecule forming a distorted MN 5 O octahedron.…”

Finite-sized Heisenberg chains and magnetism of one-dimensional metal systems

“…In the past, quasi-1D inorganic crystals have been traditionally investigated as 1D Heisenberg model systems [4,5]; typical examples include tetramethylammonium copper and manganese chloride compounds, where Cu 2+ and Mn 2+ ions couple ferromagnetically or antiferromagnetically, respectively, along weakly interacting linear chains separated by intervening non-magnetic complexes [6][7][8]. More recently, the synthesis of molecular ferriand ferromagnetic chain-like compounds containing magnetically anisotropic ions has allowed to realize 1D Ising model systems where the known absence of permanent magnetic order is accompanied by a slow relaxation of the magnetization [9][10][11][12], as predicted by Glauber more than 40 years ago [13].…”

Local spin dynamics at low temperature in the slowly relaxing molecular chain [Dy(hfac)3{NIT(C6H4OPh)}]: A μ+ spin relaxation study

“…1,9,11 The magnetic properties of such 1D systems were theoretically predicted by Glauber in the 1960s: 12 At low temperature, the magnetization relaxes slowly with a relaxation time that follows an Arrhenius law s ¼ s 0 Áexp(D/k B T), and no phase transition to threedimensional (3D) magnetic long-range order occurs before the magnetization blockage. 10,13 Subsequently, several other compounds were shown to exhibit SCM behavior, 11,[14][15][16][17][18][19][20][21] with quantum effects influencing the magnetization dynamics at low temperatures. 22 In particular, several works [23][24][25] showed that the requirements necessary to observe Glauber dynamics-a strong Ising-like anisotropy and a very low ratio of interchain/intrachain magnetic exchange interactions-are fulfilled in [Dy(hfac) 3 {NIT(C 6 H 4 OPh)}] (in short DyPhOPh).…”