L-HYDROXY-2,1-LAMBDA(5)-BENZOXARSOL-3-ONE MONOHYDRATE

The stereochemistry around arsenic in the title compound, 1-hydroxyben z[c][1,2]oxarsol-3-one monohydrate, C7H5AsO3.H2O, is distorted trigona l bipyramidal, with the carboxylate O atom and the water molecule occu pying apical positions, and the phenyl C atom, the hydroxyl group and the lone pair occupying equatorial positions. The formation of a bond between the As and carboxylate O atoms leads to the formation of a fiv e-membered ring fused with the phenyl ring. The water molecule forms a coordinate bond with arsenic(III). The earlier assignment of the titl e compound as o-carboxyphenylarsonous acid is thus incorrect.