CoII Chemistry of 2,6‐Bis(2‐pyridylcarbonyl)pyridine: An Icosanuclear Co Cluster Exhibiting Superparamagnetic Relaxation

High-nuclearity transition-metal complexes (clusters) are of special interest in chemistry and physics because, both in terms of size and physical properties, they bridge the gap between the microscopic and macroscopic world, and between quantum and classical systems. In terms of size, the smallest classical nanoparticles fabricated today are the same size as the largest metal clusters that are synthesized by bottom-up methods. In terms of physical properties, certain transition-metal clusters exhibit single-molecule magnetism at low temperatures, that is, they retain their magnetization in zero field in a manner analogous to that of classical macroscopic magnets, but at the same time they exhibit quantum tunneling of magnetization (QTM), clearly a quantum property. For these reasons transition-metal clusters are of great interest from the viewpoint of fundamental research, and applications have been proposed relating to memory devices and quantum computing. From the structural viewpoint, while the number of polynuclear 3d-metal complexes continues to grow rapidly, some nuclearities remain rare. Icosanuclear complexes are particularly uncommon. A key factor in synthesizing such compounds is the proper use of ligands that can bind together a large number of metal ions. Di-2-pyridyl ketone ((py)2CO or dpk, Scheme 1) has