Cacodyl

Alkarsin; a colorless, poisonous, arsenical liquid, As2(CH3)4, spontaneously inflammable and possessing an intensely disagreeable odor. It is the type of a series of compounds analogous to the nitrogen compounds called hydrazines.

the univalent group derived from arsine

a poisonous oily liquid with a garlicky odor composed of 2 cacodyl groups; undergoes spontaneous combustion in dry air