Abstract
Recently, we reported the first monoclinic [Kuai & Cheng (2011). Acta Cryst., E67, o2787] and the ortho-rhom-bic polymorph [Kuai & Cheng (2011). Acta Cryst., E67, o3014] of the title compound, C(15)H(12)N(2)O(2). Another monoclinic polymorph was obtained accidentally by the hydro-thermal reaction of the title compound with manganese chloride in the presence of potassium hydroxide at 413 K. The asymmetric unit consists of four independent mol-ecules. In the crystal, O-H⋯N hydrogen bonds link the independent mol-ecules into four separate chains parallel to the b axis.