Building Blocks for Molecule-Based Magnets:  A Theoretical Study of Triplet−Singlet Gaps in the Dianion of Rhodizonic Acid 1,4-Dimethide and Its Derivatives

Abstract

Reduction of 1,4-dimethylenecyclohexane-2,3,5,6-tetrone forms the title dianion 1(2-), which may also be formulated as the 1,4-dimethide of deprotonated rhodizonic acid. Substituted versions of this species, designed as a charged electronic analogue of dimethylenecyclobutadiene, are proposed as building blocks for assembly of molecule-based magnets. A possible mode of self-organization of their metal salts into 2-D structures with intermolecular ferromagnetic coupling is outlined. Full pi space CAS(14,12)/6-31+G//CAS(14,12)/ 6-31G calculations were performed to probe the ground spin state (singlet vs triplet) of 1(2-) as a function of substituent variations. This study has found that a triplet ground state preference as high as 4.5 kcal/mol may be achieved for the symmetrically coordinated dianion.

High-Spin Metal Complexes Containing a Ferromagnetically Coupled Tris(semiquinone) Ligand

“…At this step there is therefore the problem concerning the utility of these metal−polyoxolene complexes as building blocks for a network coordination polymer. It has been suggested that to achieve this goal the chemist should predetermine the structure of the network, and in this sense simpler units to be assembled than those we propose should be required …”

Bonding Coordination Requirements Induce Antiferromagnetic Coupling between m-Phenylene Bridged o-Iminosemiquinonato Diradicals

“…Paramagnetic radical ligands are of considerable interest for the design of molecule-based magnetic materials, − in particular those that can bridge pairs of metal ions, thus opening the way to extended magnetic structures. − A class of ligands that have been used for this purpose are the trimethylene-type and m -phenylene-type bis-semiquinonates, in which the two paramagnetic moieties are ferromagnetically coupled to give a triplet ground state. − The ferromagnetic coupling originates from the nondisjoint nature of the nonbonding molecular orbitals of the biradicals . Following this paradigm, some of us have recently shown how this approach can be extended to trinuclear metal complexes using a properly designed tris-dioxolene ligand …”

Current Chemistry: Transition Metal Coordination Complexes of Verdazyl Radicals: New Building Blocks for Molecule-Based Magnets

“…A compelling case was made for new 'building blocks' for molecular magnetic materials in a review several years ago: [32] 'The discovery of new molecule-based magnets is currently limited by the rational design of radicals and their solid-state structures. The latter remains an art… …New radicals and new structure types are essential for further developments' The essence of the italicized portion of the quote (emphasis mine) has been reiterated recently [33] and provides the point of departure for my group's efforts to examine new metal-radical assemblies. We viewed a family of radicals known as verdazyls [34,35] (whose general structure is shown in Fig.…”