CONFORMATIONAL EFFECTS ON HIGH-SPIN ORGANIC-MOLECULES

The ability of m-phenylene to ferromagnetically couple spin-containing substituents that are substantially twisted out of conjugation is investigated. The ''bis(TMM)'' strategy is employed, in which two triplet TMM biradicals am linked through m-phenylene to produce relatively stable, organic tetraradicals that are characterized by EPR spectroscopy. Under conditions of moderate twisting (4), ferromagnetic coupling is seen, and the tetraradical has a quintet ground state. Severely twisting both TMMs as in 13 disrupts spin communication, and two noninteracting triplets are produced. This is in contrast to other highly twisted m-phenylene derivatives, in which antiferromagnetic coupling has been observed. Surprisingly, severely twisting only one TMM (14) still produces ferromagnetic coupling and a quintet ground state through a spin polarization mechanism analogous to that proposed for 90-degrees twisted ethylene. Several ring-constrained TMMs (17-19) are investigated as models for mom nearly planar systems.