Beyond cyanide: Future synthons based on the cyaphide and cyarside ions for the synthesis of designer magnetic coordination polymers

1706年迪斯巴赫偶然发现了普鲁士蓝，这一发现立即对艺术界产生了革命性的影响，并将在艺术和科学的许多其他领域产生持久的影响。这种廉价、无毒的深蓝色颜料使蓝色变得大众化，并出现在北井和梵高等艺术家的版画和绘画中。有趣的是，这种化合物的多功能性超出了艺术的范畴，与大多数其他颜料相比，普鲁士蓝也发现了重要的医疗应用。普鲁士蓝具有将单阳离子结合到晶格中的能力，使其成为有毒重金属的有效隔离剂；药用级普鲁士蓝被用于治疗摄入有毒铊或放射性钙的个人。普鲁士蓝具有一种看似简单的骨架状结构，由铁金属中心(在+2和+3氧化态)组成，这些中心由氰离子沿着所有三个笛卡尔轴连接，产生扩展的面心立方(FCC)晶格。这种结构的模块化性质允许金属离子及其电荷的变化，从而允许每个金属位置的未配对电子的数量的变化。通过改变这些变量，有可能获得具有丰富磁性的新材料，所有这些都是通过氰离子的强烈金属间耦合而促进的。这些与结构相关的配位聚合物通常被称为普鲁士蓝类似物(PBAs)，它们被用作设计的磁性材料，最近被用于气体吸附、烃类分离、水氧化催化和电池组件等领域。虽然PBAs可以通过改变金属中心的性质很容易地改变，但氰离子是所有这些材料的共同构建块。人们曾尝试开发其他类型的高共轭含氰桥联单元来合成固体，但从经验上看，基于氰离子的体系似乎最明显的是金属间电子通信。这在一定程度上是由于这类化合物中的金属-金属距离较短，但也无疑与可以用短的线性桥实现的更密集和有序的面心立方晶格有关。这限制了该领域的进一步发展，并对合成更复杂的PBAs造成了显著的设计限制。该项目的目标是通过利用与氰化物相关的价态等电子配体，如氰化物和氰苷离子(其中氰化物的氮原子分别被磷原子或砷原子取代)来获得与PBAS相关的新型材料。与其较轻的同源氰化物一样，赛普赛德和赛普赛德离子是两齿配体，能够产生与普鲁士蓝相关的紧密堆积结构。到目前为止，还没有已知的合成方法来分离这些离子。这就是我们提出要应对的挑战。将利用磷和砷与重金属结合的偏好，以确定含有整个元素周期表中元素的混合金属系统为目标。我们还将扩大这些研究，以获得含磷和砷的氰基连接物的异感类似物，如二氰胺和三氰甲胺。这项建议旨在设计、合成和研究与普鲁士蓝相关的全新类型的扩展固体，目的是获得具有潜在变化的物理和化学性质的新材料。

The serendipitous discovery of Prussian blue by Diesbach in 1706 had an immediate revolutionary effect on the art world, and would go on to have long-lasting repercussions in many other areas of the arts and sciences. This inexpensive, non-toxic, dark blue pigment democratized the colour blue, and features in prints and paintings from artists such as Hokusai and van Gogh. Interestingly, the versatility of this compound transcends the arts, and in contrast to most other pigments, Prussian blue has also found important medical applications. Its ability to incorporate monocationic ions into its lattice makes it a powerful sequestering agent for toxic heavy metals; pharmaceutical-grade Prussian blue is used to treat individuals who have ingested poisonous thallium or radioactive caesium.Prussian Blue has a deceptively simple framework-like structure, consisting of iron metal centres (in the +2 and +3 oxidation states) that are bridged by cyanide anions along all three Cartesian axes, giving rise to an extended face-centred cubic (FCC) lattice. The modular nature of this structure allows for the variation of the metal ions, their charges, and consequently the number of unpaired electrons per metal site. By altering these variables, it is possible to access novel materials with a wealth of magnetic behaviours, all of them facilitated by strong intermetallic coupling through the cyanide ions. These structurally-related coordination polymers are commonly referred to as Prussian blue analogues (PBAs), and have found use as designer magnetic materials and, more recently, in the fields of gas sorption, hydrocarbon separation, water oxidation catalysis, and as battery components.While PBAs can be readily altered by changing the nature of the metal centres, the cyanide ion is a common building block to all of them. Attempts have been made to exploit other types of highly-conjugated cyanide-containing bridging units for the synthesis of solids, however empirically it appears that intermetallic electronic communication is most pronounced for systems based on the cyanide ion. This is in part due to the short metal-metal distances available in such compounds, but also undoubtedly related to the more densely packed and ordered FCC lattice that can be achieved with a short linear bridge. This limits further developments in the field, and places a significant design constraint on the synthesis of more complex PBAs.The goal of this project is to access novel materials related to PBAs by making use of valence isoelectronic ligands related to cyanide, such as the cyaphide and cyarside ions (where the nitrogen atom of cyanide is replaced by a phosphorus or arsenic atom, respectively). Like their lighter congener cyanide, the cyaphide and cyarside ions are ambidentate ligands capable of giving rise to close-packed structures related to Prussian blue. To date, there is no known synthetic methodology that allows for the isolation of such ions. This is the challenge we propose to address. The preference of phosphorus and arsenic for binding to heavy metals will be exploited in order to target mixed metal systems containing elements from the entirety of the periodic table. We will also extend these studies to access heteroleptic phosphorus- and arsenic-containing analogues of cyanide-based linkers such as dicyanamide and tricyanomethanide.This proposal aims to design, synthesise and study and entirely new class of extended solids related to Prussian blue with the objective of accessing new materials with potentially transformative physical and chemical properties.