Miyasaka Hitoshi, Madanbashi Tomokura, Sugimoto Kunihisa, Nakazawa Yasuhiro, Wernsdorfer Wolfgang, Sugiura Ken-Ichi, Yamashita Masahiro, Coulon Claude, Clérac Rodolphe
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami-ohsawa Hachioji, Tokyo 192-0397, Japan.
Chemistry. 2006 Sep 18;12(27):7028-40. doi: 10.1002/chem.200600289.
An alternated 1:1 chain compound of a Mn(III) salen derivative and the TCNQ monoradical was synthesized: Mn(5-TMAMsaltmen)(TCNQ)(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.
合成了一种锰（III）双水杨醛缩邻苯二胺衍生物与TCNQ单自由基的交替1:1链状化合物：Mn(5-TMAMsaltmen)(TCNQ)(2) (1)（TCNQ = 四氰基对苯二醌二甲烷；5-TMAMsaltmen = N,N'-(1,1,2,2-四甲基乙烯)双(5-三甲基铵甲基水杨醛亚氨基)）。化合物1具有锯齿形链结构，相邻链堆积，链间Mn-Mn距离超过8埃。由于化合物1不含结晶溶剂，链间的空隙仅被ClO(4) (-)抗衡离子占据。化合物1的结构让人联想到Miller及其同事之前报道的Mn(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其在该化合物家族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，在锰（III）离子与TCNQ自由基之间存在反铁磁交换耦合，J/k(B)约为 -96 K，并且在低温（50 - 15 K）下具有激活的关联长度（Δξ = 26.5 K）。在低于3.5 K时通过观察到的磁化场滞后现象表明化合物1中存在磁化的缓慢弛豫（在1.8 K时矫顽场高达14 kOe）。单晶磁化测量证明了该化合物的单轴对称性，并允许估计各向异性场，H(a)约为97 kOe。通过热容量量热法测量确定不存在磁有序相或自旋玻璃行为，在0.5 K至10 K之间C(p)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以上和以下呈现两个激活区域，τ(01)=2.1×10(-10) s，Δτ1 = 94.1 K，τ(02)=6.8×10(-8) s，Δτ2 = 67.7 K。对这些动力学性质以及关联长度的详细分析，明确证明了1中的单链磁体行为。
