基于四嗪自由基配体的过渡金属簇合物的超分子组装和磁性研究

自旋载体之间强磁耦合的构建及特定结构的分子定向组装是当前构筑高性能分子基磁性材料的一个重要研究课题。相对于闭壳型抗磁性配体，开壳型顺磁性桥连配体（自由基）不仅具有更强的传递磁耦合的能力（磁耦合常数可达到几十甚至几百个波数），同时其电子的离域特性赋予其在构筑大孔径磁性分子及导电磁体方面的独特能力。另外，研究发现强磁耦合作用可有效抑制量子隧穿，提高单分子磁体的有效能垒。四嗪类配体可被还原成空气稳定的自由基，而且在合成上具有丰富的选择性和可控组装优势。本论文基于国内外的四嗪基配合物的研究现状，设计合成了一系列3，6-取代的四嗪类双螯合配体（bpz*tz，bpz^3Phtz，pz^3Ph(Cl)tz，bpz^Itz），并基于超分子自组装策略构筑了一系列过渡金属环状化合物，研究了它们的结构和磁性及构效关系，结果如下：

构筑了四例金属环状配合物：[M₄(bpz*tz^·-)₄(N₃)₄] (M = Ni, 1; Mn, 2)，[Ni₃(bpz^3Phtz^·-)₃(pz^3Ph(Cl)tz^·-)₃]·sol (3)和 [Ni₄(pydz)₄(N₃)₄] [BPh₄]₄·2CH₃CN (4)。其中配合物1和2为四嗪自由基和EO-叠氮桥混桥构筑的平面四方分子，其变温直流磁化率显示金属与自由基之间为强铁磁耦合，1中磁耦合常数达到90.8 cm^-1；配合物3是由两种不同四嗪自由基构筑而成的平面三角形分子，磁性研究表明，Ni(II)离子与端基四嗪自由基为反铁磁耦合，而与桥连四嗪自由基之间为强的铁磁耦合。

构筑了两例四嗪自由基和EO-叠氮离子桥连的钴基平面四方分子配合物：[Co₄(L)₄(N₃)₄]·sol (L = bpz^3phtz^·-, 5; L = bpz^Itz^·-, 6)。磁性研究表明，这两例配合物均为单分子磁体。其中5在零场下量子隧穿严重，而在外加500 Oe磁场下，表现出缓慢的磁弛豫行为，有效能垒(U_eff/K_B)为29.4 K，弛豫时间(τ₀)为9.2 × 10^-9 s。配合物6在零场下表现出慢磁弛豫行为，其有效能垒为25.1 K；在优化场下，其有效能垒达到52.5 K，磁弛豫时间为1.27 × 10^-10 s。

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