Synthesis and magnetic properties of mixed crystals of paramagnetic transition metal thiocyanato coordination polymers.

近年来，开发更合理地合成具有明确磁性能的新配位化合物的策略已成为人们日益关注的问题。大多数化合物仅由一种金属阳离子组成，但双金属化合物的制备也日益引起人们的兴趣。这可以通过阴离子金属配合物与不同金属阳离子的反应来实现。相比之下，以更详细地修饰配位化合物的磁性为主要目标的固溶体的定向合成很少使用，这正是本项目的内容。[M1xM21-x(NCS)2(L1)2]n和[M1xM21-x(NCS)2(L2)]n (M1, M2 = Mn(II), Fe(II), Co（II）和Ni（II）的混合晶体；L1 =单齿n供体配体；应制备L2 =桥接n给体)，并对其组成、均匀性和磁性进行研究。初步研究表明，从溶液中不能得到所需化合物的均相样品。因此，采用了一种以前从未用于合成配位化合物混合晶体的替代合成路线。该策略的基础是合成化合物[M1M21-x(NCS)2(L1)4]n和[M1xM21-x(NCS)2(L2)2]n的前体，最后通过热分解转化为所需的化合物。初步结果表明，用这种方法可以制备出由Co和Ni组成的均匀混合晶体，其组成与合成中使用的成分完全对应。加热时，它们定量地转化为所需的化合物。磁性测量表明，在热分解时没有发生相分离，因为这些样品显示出磁性行为，这与同金属化合物完全不同。在这种情况下，我们注意到[Co(NCS)2（吡啶）2]n表现出铁磁基态并表现出磁化的缓慢弛豫，而[Ni(NCS)2（吡啶）2]n表现出反铁磁基态并表现出超磁跃迁。相反，[Co0.5Ni0.5(NCS)2(Pyridin)2]n的混合晶体表现为纯Ni化合物的典型的超磁转变，而在反铁磁相中观察到纯Co化合物的典型的慢弛豫。在这个项目的过程中，应该研究这个合成工具是否可以普遍用于合成这类化合物的混合晶体，以及混合晶体形成时磁性能发生了哪些变化。

Recently, the development of strategies for a more rational synthesis of new coordination compounds with defined magnetic properties has become of increasing interest. Most compounds consists of only one kind of metal cation but there is also increasing interest for the preparation of bimetallic compounds. This can be achieved, e.g., by the reaction of anionic metal complexes with different metal cations. In contrast, the targeted synthesis of solid solutions with the major goal to modify the magnetic properties of coordination compounds in more detail was rarely used and this is exactly the content of the present project. Mixed crystals of compositions [M1xM21-x(NCS)2(L1)2]n and [M1xM21-x(NCS)2(L2)]n (M1, M2 = Mn(II), Fe(II), Co(II) and Ni(II); L1 = monodentate N-donor ligand; L2 = bridging N-donor) should be prepared and investigated for their composition, their homogeneity and their magnetic properties. Preliminary investigations have shown, that from solution no homogenous samples of the desired compounds can be obtained. Therefore, an alternative synthetic route was used, which was never used before for the synthesis of mixed crystals of coordination compounds. This strategy is based on the synthesis of precursors of composition [M1M21-x(NCS)2(L1)4]n and [M1xM21-x(NCS)2(L2)2]n, which finally are transformed into the desired compound by thermal decomposition. First results shows, that with this method homogenous mixed crystals consisting of Co and Ni can be prepared, that exhibits a composition, which exactly corresponds to that, used in the synthesis. On heating they transform quantitatively into the desired compounds. As shown by magnetic measurements, on thermal decomposition no phase separation take place, because these samples shows a magnetic behavior, which is completely different from that of the homometallic compounds. In this context it is noted that [Co(NCS)2(pyridine)2]n exhibits a ferromagnetic ground state and shows a slow relaxation of the magnetization, whereas [Ni(NCS)2(pyridine)2]n exhibits an antiferromagnetic ground state and shows a metamagnetic transition. In contrast, mixed crystals of composition [Co0.5Ni0.5(NCS)2(Pyridin)2]n shows a metamagnetic transition, which is typical for the pure Ni compound but in the antiferromagnetic phase slow relaxations are observed, which are typical for the pure Co compound. In the course of this project, it should be investigated if this synthetic tool can be used in general for the synthesis of mixed crystals of this class of compounds and which changes in the magnetic properties occur on mixed crystal formation.