Guest-dependent single-ion magnet behaviour in a cobalt() metal-organic framework

Single-ion magnets (SIMs) are the smallest possible magnetic devices for potential applications in quantum computing and high-density information storage. Both, their addressing in surfaces and their organization in metal-organic frameworks (MOFs) are thus current challenges in molecular chemistry. Here we report a two-dimensional 2D MOF with a square grid topology built from cobalt( ii ) SIMs as nodes and long rod-like aromatic bipyridine ligands as linkers, and exhibiting large square channels capable to host a large number of different guest molecules. The organization of the cobalt( ii ) nodes in the square layers improves the magnetic properties by minimizing the intermolecular interactions between the cobalt( ii ) centres. Moreover, the SIM behaviour was found to be dependent on the nature of the aromatic guest molecules. The whole process could be followed by single-crystal X-ray diffraction, providing comprehensive evidence of the putative role of the solvent guest molecules that leave a "fingerprint" on the 2D structures and thus, on the cobalt environment. Such exciting properties as porosity and single-ion magnetic behavior are merged into a single unique material which affords the first in-depth study of guest-dependent SIM behavior in a MOF.