Crystal structures of (E)-1-{3-[(5-fluoro-2-hy­droxy­benzyl­idene)amino]­phen­yl}ethanone and of a fourth polymorph of (E)-1-{3-[(2-hy­droxy-3-meth­oxy­benzyl­idene)amino]­phen­yl}ethanone

In the mol­ecules of both (E)-1-{3-[(5-fluoro-2-hy­droxy­benzyl­idene)amino]­phen­yl}ethanone, C(15)H(12)FNO(2), (I), and (E)-1-{3-[(2-hy­droxy-3-meth­oxy­benzyl­idene)amino]­phen­yl}ethanone, C(16)H(15)NO(3), (II), which crystallizes with Z′ = 2 in space group Pca2(1), there are intra­molecular O—H⋯N hydrogen bonds, and the non-H atoms in each mol­ecule are essentially coplanar. In the crystal of (I), mol­ecules are linked by a single C—H⋯O hydrogen bond to form a C(8) chain, whereas in the crystal of (II), mol­ecules are linked by three C—H⋯O hydrogen bonds to form sheets within which orthogonal C (2) (2)(16) and C (2) (2)(17) chains can be identified. Comparisons are made with some related structures.