Single-Chain Magnet (NEt₄)[Mn₂(5-MeOsalen)₂Fe(CN)₆] Made of Mn^III−Fe^III−Mn^III Trinuclear Single-Molecule Magnet with an S_T = ⁹/₂ Spin Ground State

Abstract

The cyano-bridged trinuclear compound, (NEt(4))[Mn(2)(salmen)(2)(MeOH)(2)Fe(CN)(6)] (1) (salmen(2)(-) = rac-N,N'-(1-methylethylene)bis(salicylideneiminate)), reported previously by Miyasaka et al. (ref 19d) has been reinvestigated using combined ac and dc susceptibility measurements. The strong frequency dependence of the ac susceptibility and the slow relaxation of the magnetization show that 1 behaves as a single-molecule magnet with an S(T) = (9)/(2) spin ground state. Its relaxation time (tau) follows an Arrhenius law with tau(0) = 2.5 x 10(-)(7) s and Delta(eff)/k(B) = 14 K. Moreover, below 0.3 K, tau saturates around 470 s, indicating that quantum tunneling of the magnetization becomes the dominant process of relaxation. (NEt(4))[Mn(2) (5-MeOsalen)(2)Fe(CN)(6)] (2) (5-MeOsalen(2)(-) = N,N'-ethylenebis(5-methoxysalicylideneiminate)) is a heterometallic one-dimensional assembly made of the trinuclear [Mn(III)(SB)-NC-Fe(III)-CN-Mn(III)(SB)] (SB is a salen-type Schiff-base ligand) motif similar to 1. Compound 2 has two types of bridges, a cyano bridge (-NC-) and a biphenolate bridge (-(O)(2)-), connecting Mn(III) and Fe(III) ions and the two Mn(III) ions, respectively. Both bridges mediate ferromagnetic interactions, as shown by modeling the magnetic susceptibility above 10 K with g(av) = 2.03, J(Mn)(-)(Fe)/k(B) = +6.5 K, and J'/k(B) = +0.07 K, where J' is the exchange coupling between the trimer units. The dc magnetic measurements of a single crystal using micro-SQUID and Hall-probe magnetometers revealed a uniaxial anisotropy (D(T)/k(B) = -0.94 K) with an easy axis lying along the chain direction. Frequency dependence of the ac susceptibility and time dependence of the dc magnetization have been performed to study the slow relaxation of the magnetization. A mean relaxation time has been found, and its temperature dependence has been studied. Above 1.4 K, both magnetic susceptibility and relaxation time are in agreement with the dynamics described in the 1960s by R. J. Glauber for one-dimensional systems with ferromagnetically coupled Ising spins (tau(0) = 3.7 x 10(-)(10) s and Delta(1)/k(B) = 31 K). As expected, at lower temperatures below 1.4 K, the relaxation process is dominated by the finite-size chain effects (tau'(0) = 3 x 10(-)(8) s and Delta(2)/k(B) = 25 K). The detailed analysis of this single-chain magnet behavior and its two regimes is consistent with magnetic parameters independently estimated (J'and D(T)) and allows the determination of the average chain length of 60 nm (or 44 trimer units). This work illustrates nicely a new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension.

Neutral Low-Dimensional Assemblies of a Mn(III) Schiff Base Complex and Octacyanotungstate(V): Synthesis, Characterization and Magnetic Properties

“…In addition, unlike the reported in ref. 48 assembly by means of a mutual bridging of the {Mn(5TMAMsalen)} units by phenolate oxygen atoms similar to in ref [47] and forming the 7(CN)-W-CN-Mn(-O-)2-Mn-NC-W(CN)7 core. However, in such a case the valence stretches of CN would not experience some significant shifting in higher frequencies as it take place for 2.…”

“…Cyano-bridged metal assemblies have provided a large number of compounds with SMM [31][32][33][34][35][36][37][38] and SCM behavior [39][40][41][42][43][44][45][46][47][48]. The greater part of these materials comprises 3d metal ions as the core magnetic units.…”

Frustrated lattices of Ising chains

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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).…”