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

Reduction of 1,4-dimethylenecyclohexane-2,3,5,6-tetron forms the title dian ion 1(2-), which may also be formulated as the 1,4-dimethide of deprotonate d rhodizonic acid, Substituted versions of this species, designed as a char ged electronic analogue of dimethylenecyclobutadiene, are proposed as build ing blocks for assembly of molecule-based magnets. A possible mode of self- organization of their metal salts into 2-D structures with intermolecular f erromagnetic 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 (si nglet vs tripler) of 1(2-) as a function of substituent variations. This st udy has found that a triplet ground state preference as high as 4.5 kcal/mo l may be achieved for the symmetrically coordinated dianion.