Chlorine dioxide: An exception that proves the rules of localized chemical bonding

We employ natural bond orbital and natural resonance theory tools to analyze the enigmatic properties of the C_2v-symmetric isomer of chlorine dioxide radical (ClO₂), whose many challenges to Pauling-type localized bonding concepts were recognized by Linus Pauling himself. Although spin-contamination is minimal in this species, ClO₂ exhibits an unusually strong form of "different Lewis structures for different spins" bonding pattern, intrinsically outside the framework of "maximal pairing" concepts. We show how the novel spin-unpaired donor-acceptor interactions lead to weakened bonding in the supramolecular domain of polyradical (ClO₂)_n homoclusters and aqueous ClO₂(H₂O)_n heteroclusters. Despite feeble binding energies and large inter-radical separations, the polyradical clusters are found to maintain coherent spin patterns in each cluster component, attesting to the quantal donor-acceptor nature of their interactions and the cooperative and anticooperative couplings that govern intra- and intermolecular spin distributions in such spin-clusters.