Abstract
By introducing large counter cations as the spacer, two isolated 3, 3-ladder compounds, (Ph4P)[CoII(3-Mepy)2.7(H2O)0.3WV(CN)8]·0.6H2O (1) and (Ph4As)[CoII(3-Mepy)3WV(CN)8] (2, 3-Mepy = 3-methylpyridine), were synthesized and characterized. Static and dynamic magnetic characterizations reveal that compounds 1 and 2 both behave as the single-chain magnets (SCMs) with very high energy barriers: 252(9) K for 1 and 224(7) K for 2, respectively. These two compounds display the highest relaxation barriers for cyano-bridged SCMs and are preceded only by two cobalt(II)-radical compounds among all SCMs. Meanwhile, a large coercive field of 26.2 kOe (1) and 22.6 kOe (2) were observed at 1.8 K.
Highlights
Octacyanometallates [MIV/V(CN)8]4−/3− (M = Nb, Mo, W) are of great importance in the molecule-based magnets[26,27,28,29,30]
In the famous [Mn2Ni] single-chain magnets (SCMs) family reported by Clérac and Miyasaka et al, the 1D [Mn2Ni] chains were isolated by various anions such as ClO4−, PF6−, BF4−, ReO4−, and BPh4−, leading to the modification of their magnetic properties[3,34,36,37]
In 2005, we reported the first SMMs based on the 4d/5d metal centers, namely CoII[CoII(CH3OH)3]8[MV(CN)8]6· Solv (M = Mo, W)[38]
Summary
From the Arrhenius plots of relaxation times τ obtained from the frequency-dependent χM′ ′ peaks, two thermally activated regions were obviously observed above and below the crossover temperatures of T* = 10.4 and 10.8 K for 1 and 2, respectively These two regions are corresponding to the infinite-size and finite-size regimes of relaxation, commonly encountered for SCMs. The energy barriers for both of these thermally activated processes were estimated using the Arrhenius law τ = τ0 exp (Δτ/kBT), giving the Δτ1 (τ01) and Δτ2 (τ01) as 252(9) K (1.5(2) × 10−13 s) and 169(2) K (4.6(1) × 10−10 s) for 1 and 224(7) K (6.3(2) × 10−13 s) and 154(1) K (4.0(1) × 10−10 s) for 2, respectively (Fig. 4). Because of the intrachain ferromagnetic interaction, strong magnetic anisotropy, as well as the well isolation of individual chains, these 1D compounds behave as single-chain magnets with record high spin reversal barriers (252(9) and 224(7) K) for the cyano-bridged SCMs. hysteresis loops can be observed for both compounds below 5 K with large coercivities of 26.2 and 22.6 kOe at 1.8 K. Efforts to extend this synthetic strategy towards other SCMs using the 4d/5d cyanometallates and other anisotropic metal centers with higher energy barriers and blocking temperatures are underway
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