Paramagnetism in Metal-Metal Bonded Paddlewheel Complexes

The pairing of metal-based electrons to form metal-metal bonds in paddlewheel complexes would suggest that this chemistry is limited to diamagnetic complexes. However, a wide variety of paramagnetic complexes exist in this geometry. Whether obtained by oxidation or reduction of the divalent dinuclear species, as a result of degeneracy or neardegeneracy of their metal-based molecular frontier orbitals, or due to unpaired electrons in extended metal atom chains, paramagnetic paddlewheel complexes can be found in each group of the transition series. This review will present some of these molecules, their polynuclear analogues, and their use in supramolecular and extended architectures, with an emphasis on electronic structure.