Colloquium: Switchable Magnetic Materials Derived from Octacyanometallates

Molecule-based magnets represent a diverse and rapidly developing category of bistable materials which have received much interest for their exciting physical properties and potential applications. These materials exhibit unique characteristics such as energy-efficient synthesis, solubility in conventional organic solvents, ability to fabricate into devices, tunable photo and thermochromic properties etc.¹ Furthermore, molecular magnetism offers the opportunity to design a broad range of materials having different dimensionalities, extending from zero-dimensional (0D) to three-dimensional (3D) networks. These materials hold promise for several modern day applications, such as information storage devices,² molecular qubits,³ spintronics,⁴ quantum computing,⁵ nanotechnology,⁶ and many more. My thesis is focused mainly on the design and synthesis of multifunctional molecule-based magnetic materials exhibiting novel feature such as spin-state switching, metal-to-metal electron transfer (MMET), and single-molecule magnets (SMMs)properties.^{7, 8} The efforts were put to design materials with different dimensionalities (0D, 1D, 2D and 3D) incorporating the magnetic interactions between the 3d and 4d/5d transition metal ions via cyanide bridge. Therefore, I have used highly anisotropic 4d/5d octacyanometallate building blocks, as the cyanide group is well-known for facilitating strong magnetic exchange interactions between metal centers.⁹ Additionally, the cyanide ligand possesses distinct coordination environments, making it an ideal choice for designing heterometallic magnetic systems. On the other hand, I have selectively employed 3d transition metal ions and suitable blocking or capping ligands in order to tune the ligand field and control the dimensionality of the final complex and achieve the desired bistable properties. Using this strategy, I have rationally designed a series of new multifunctional hetero-bimetallic W-Fe (square), Mo-Fe (3D-framework) , W-Mn (1D chain), W-Co (2D framewrok), Mo-Co (square), Mo-Cu (molecular and 3D systems), complexes.^{10, 11,12,13} To gain a deeper understanding of the Spin Crossover (SCO) and MMET properties, including solvent effect, cooperativity, ligand field effect, etc. a detailed studies have been carried out that involves various physical techniques such as magnetic, optical, spectroscopic, electrochemical, X-ray fine structure characterizations. Notably, these complexes exhibit various exciting properties, such as thermo- and photo-switching behavior, photo and thermochromic properties, single-crystal to single-crystal transformation, magnetic ordering, and several interesting bistable properties. Finally, this work is summarized with a comprehensive conclusion that offers valuable insights for future advancements in the field of multifunctional materials, thereby contributing to the enrichment of this area of research.