Controlling the singlet-triplet splitting in bisverdazyl diradicals: Steps toward magnetic polymers

Density functional calculations were performed on 1,1',5,5'-tetramethyl-6,6'-dioxo-3,3'-biverdazyl diradical (BVD) and BVD[CuI(PL3)](2) complexes (L = H, Me, OH, OMe, F) in order to investigate how Cu chelation affects the singlet-triplet splitting of the verdazyl system. It was found that donating ligands on Cu destabilize the singlet ground state. Size was also found to play a role, as smaller ligands allow for closer Cu-verdazyl contacts. Although a triplet ground state was not obtained for any of the molecules examined, a very small splitting of 40 cm(-1) was calculated for the phosphine complex.