Spin alignment in high-spin carbenes of heteroatomic π-conjugation

2,6-, 2,4-, And 3,5-pyridine-bis (phenylmethylene) (3,5-PY), in which heterocycle plays a ferromagnetic or antiferromagnetic linker between carbenic units, have been studied by random orientation ESR spectroscopy. The electronic structures of isomers are important for the understanding of spin alignment vs. topology of the heteroatomic π-electron networks. In 2,6-PY and 2,4-PY, the perturbing nitrogen atoms are in active positions, giving rise to a larger influence on their spin structure than in 3,5-PY. A simple application of molecular Hundʹs rule is invalidated