Single-chain magnet behavior in an alternated one-dimensional assembly of a Mn(III) Schiff-base complex and a TCNQ radical.
Single-chain magnet behavior in an alternated one-dimensional assembly of a Mn(III) Schiff-base complex and a TCNQ radical.
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DOI：
10.1002/chem.200600289
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发表时间：
2006-09
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通讯作者：
H. Miyasaka;Tomokura Madanbashi;K. Sugimoto;Y. Nakazawa;W. Wernsdorfer;K. Sugiura;M. Yamashita;C. Coulon;R. Clérac
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作者：
H. Miyasaka;Tomokura Madanbashi;K. Sugimoto;Y. Nakazawa;W. Wernsdorfer;K. Sugiura;M. Yamashita;C. Coulon;R. Clérac
合成了一种锰（III）沙仑衍生物与四氰基对苯醌单自由基的交替1:1链状化合物：[Mn(5 - TMAMsaltmen)(TCNQ)](ClO₄)₂ (1)（TCNQ = 四氰基 - 对 - 苯醌二甲烷；5 - TMAMsaltmen = N,N' - (1,1,2,2 - 四甲基乙烯)双(5 - 三甲基氨甲基水杨醛亚胺基)）。化合物1具有锯齿链结构，相邻链堆积，链间锰 - 锰距离超过8埃。由于化合物1不含有结晶溶剂，链间的空隙仅被ClO₄⁻ 反离子占据。化合物1的结构让人联想到米勒及其同事先前报道的锰（III）（卟啉） - TCNE或 - TCNQ化合物家族中所观察到的结构，并且我们在此证明了它在这类化合物中独特的单链磁体行为。直流（dc）磁性测量确定了化合物1的一维性质，锰（III）离子与TCNQ自由基之间存在反铁磁交换耦合，J/kB约为 - 96 K，并且在低温（50 - 15 K）下具有激活相关长度（Δ(ξ) = 26.5 K）。在化合物1中，通过在3.5 K以下观察到的磁化场滞回现象（在1.8 K时矫顽场高达14 kOe）显示出磁化的缓慢弛豫。单晶磁化测量证明了该化合物的单轴对称性，并允许估算各向异性场，Ha约为97 kOe。通过热容测量确定不存在磁有序相或自旋玻璃行为，在0.5 K和10 K之间热容Cp没有异常。通过交流（ac）和直流技术相结合对磁化弛豫的研究表明，化合物1具有单一弛豫时间（τ）。由于链的有限尺寸，τ的温度依赖性在4.5 K上下呈现两种激活机制，分别为τ₀₁ = 2.1×10⁻¹⁰ s，Δ(τ₁) = 94.1 K以及τ₀₂ = 6.8×10⁻⁸ s和Δ(τ₂) = 67.7 K。对这些动力学性质以及相关长度的详细分析，明确证明了1中的单链磁体行为。
An alternated 1:1 chain compound of a Mn(III) salen derivative and the TCNQ monoradical was synthesized: [Mn(5-TMAMsaltmen)(TCNQ)](ClO(4))(2) (1) (TCNQ=tetracyano-p-quinodimethane; 5-TMAMsaltmen=N,N'-(1,1,2,2-tetramethylethylene) bis(5-trimethylammoniomethylsalicylideneiminato)). Compound 1 has a zigzag chain structure packed with adjacent chains with an interchain MnMn distance of over 8 Angatrom. As compound 1 contains no crystallization solvent, the void spaces between chains are occupied only by ClO(4) (-) counter ions. Compound 1 has a structure reminiscent of what has been observed in the family of Mn(III)(porphyrin)-TCNE or -TCNQ compounds reported previously by Miller and co-workers and we demonstrate herein its unique single-chain magnet behavior among this family of compounds. The direct current (dc) magnetic measurements established the one-dimensional nature of compound 1 with an antiferromagnetic exchange coupling, J/k(B) approximately -96 K, between the Mn(III) ion and TCNQ radical and with an activated correlation length (Delta(xi)=26.5 K) at low temperatures (50-15 K). The slow relaxation of the magnetization was shown in compound 1 by the field hysteresis of the magnetization observed below 3.5 K (with a coercive field up to 14 kOe at 1.8 K). Single-crystal magnetization measurements demonstrated the uniaxial symmetry of this compound and allowed an estimation of the anisotropy field, H(a) approximately 97 kOe. The absence of magnetic ordered phase or spin-glass behavior was established by heat-capacity calorimetry measurements that exhibit no abnormality of C(p) between 0.5 K and 10 K. The study of the magnetization relaxation by combined ac (alternating current) and dc techniques showed that compound 1 possesses a single relaxation time (tau). As the consequence of the finite size of the chain, the temperature dependence of tau presents two activated regimes above and below 4.5 K with tau(01)=2.1 x 10(-10) s, Delta(tau1)=94.1 K and tau(02)=6.8 x 10(-8) s and Delta(tau2)=67.7 K, respectively. The detailed analysis of these dynamics properties together with the correlation length, allows an unambiguous demonstration of the single-chain magnet behavior in 1.