氰根桥连4f-nd单分子磁体的合成及磁构关系研究

Single-molecule and single-chain magnets(SMMs and SCMs)have been observed to exhibit magnetic bistability at a single-molecule level, thermal-activiated slow magnetic relaxation and quantum tunneling effect at low temperature, which makes them become the model systems for the investigation of quantum information high-density storage and the promising candidates for the study of the coexistence of classical and quantum mechanical phenomenon. Beginning with such special properties found in Mn12 complex, SMMs and SCMs containing transition metal ions have gone through a rapid growth in the past two decades. Due to the high ground-state spin and large single-ion anisotropy, for the latest several years, lanthanide ions have attracted considerable attention to construct SMMs and SCMs, including pure 4f isolated systems, 4f-3d and 4f-2p magnetically interacting systems. The systems with magnetic interactions have almost been assembled through single-atom-oxygen bridge between the metal ions.The objectives of this proposal are to synthesize the rarely-investigated novel two-atom cyano-bridged 4f-nd (n = 3, 4, 5) low-dimensional structures and to obtain SMMs and SCMs with abundant structural types. The subsequent theme is to explore the effect of the parameters such as the ground-state spin of the metal ions, the single-ion anisotropy, the symmetry of the ligand field and the types of the magnetic interactions on the low-dimensional magnetic properties. In this direction the proposed research would achieve to finely tune the low-dimensional magnetism among the cyano-bridged 4f-nd complexes and lead towards the SMMs and SCMs with high anisotropy energy barrier and long magnetic relaxation time.

低温下单分子单链磁体在单个分子水平上表现出磁双稳态性质，以及热激发慢的磁弛豫和量子隧穿效应，为量子信息高密存储的研究提供了模型体系，并对经典和量子力学现象共存问题的研究具有重要的科学意义。二十多年来，由Mn12开始，含过渡金属的SMMs和SCMs获得了充分发展。而由于稀土离子具有大基态自旋和强单离子各向异性，近几年成为研究的焦点，包括纯4f孤立体系、4f-3d或4f-2p相互作用体系，相互作用体系主要采用单原子O桥传递磁作用，本项目旨在利用氰基过渡金属前驱体与4f离子组装合成目前研究较少的，具有新颖结构的双原子CN桥连4f-nd (n=3,4,5)低维结构，获得具有丰富结构类型的SMMs和SCMs，并探索金属离子的基态自旋、单离子各向异性、晶体场对称性、磁相互作用等因素对低维磁性的影响，实现对氰根桥连4f-nd低维磁性质的精确调控，获得具有较大磁各向异性能垒和慢磁弛豫时间的单分子单链磁体。

本项目的主要研究内容为合成氰根桥连的4f-3d低维单分子单离子磁体，研究4f和3d离子通过氰根桥连的磁相互作用本质，探索所形成低维磁体的磁弛豫来源和机理。采用的研究策略为：在研究氰根桥连的4f-3d低维单分子单链磁体磁行为的同时，合成出以单原子O桥和三原子羧酸等与氰根相似的短桥连配体形成的纯4f或4f-3d低维单分子单链磁体进行对比研究。在本项目的研究工作中，主要开展了三方面的研究。一是以含羰基或配位O原子的配体作为辅助配体，采用[M(CN)6]3–作为桥连配体，合成了多类氰根桥连的4f–3d类型的SMMs，通过定点替代3d或4f金属离子的策略，调控所形成3d–4f配合物中磁弛豫的起源和机理，为进一步研究氰根桥连3d–4f单分子或单离子磁体提供了一种很好的合成策略，有利于深入研究此类配合物中晶体场、磁相互作用、金属空间格子排列等因素对其动态弛豫性质的影响，为探寻具有较大各向异性能垒和较高冻结温度的单分子磁体提供可行途径；二是采用具有较大位阻的有机羧酸配体作为螯合或桥连配体，合成了羧酸螯合形成的相对孤立单核结构的纯4f离子SIMs，以及羧酸桥连形成的纯4f离子SMMs；三是以吡啶衍生物作辅助配体，采用有机羧酸配体作为桥连配体，合成了几类羧酸桥连的纯4f离子SMMs和SCMs，研究了配体上取代基位置对其动态磁弛豫性质的影响，配体的改变及其取代基的修饰所产生的电子效应对含稀土离子SMMs动态磁弛豫行为的影响正成为当前的一个研究热点。