Triplet bismuthinidenes featuring unprecedented giant and positive zero field splittings

Abstract

Isolation of triplet pnictinidenes, which bear two unpaired electrons at the pnictogen centers, has long been a great challenge due to their intrinsic high reactivity. Herein, we report the syntheses and characterizations of two bismuthinidenes M^sFluind<i>^t</i>^Bu-Bi (<b>3</b>) and M^sFluind*-Bi (<b>4</b>) stabilized by sterically encumbered hydrindacene ligands. They were facilely prepared through reductions of the corresponding dichloride precursors with 2 molar equivalents of potassium graphite. The structural analyses revealed that <b>3</b> and <b>4</b> contain a one-coordinate bismuth atom supported by a Bi-C single σ bond. As a consequence, the remaining two Bi 6p orbitals are nearly degenerate, and <b>3</b> and <b>4</b> possess triplet ground states. Experimental characterizations with multinuclear magnetic resonance, magnetometry and near infrared spectroscopy coupled to wavefunction based <i>ab initio</i> calculations concurred to evidence that there exist giant and positive zero field splittings (>4300 cm^-1) in their <i>S</i> = 1 ground states. Hence even at room temperature the systems almost exclusively populate the lowest-energy nonmagnetic <i>Ms</i> = 0 level, which renders them seemingly diamagnetic.