Conformational Effects on High-Spin Organic Molecules

Article abstract of DOI:10.1021/j100152a035

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 are 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 TMM 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 deg C twisted ethylene.Several ring-constrained TMMs (17-19) are investigated as models for more nearly planar systems.