Synthesis and crystal structures of 5,5′-(propane-2,2-di­yl)bis­(2-hy­droxy­benzaldehyde) and 5,5′-(propane-2,2-di­yl)bis­(2-hy­droxy­isophthalaldehyde)

The title compounds 5,5′-(propane-2,2-di­yl)bis­(2-hy­droxy­benzaldehyde), C(17)H(16)O(4), (1), and 5,5′-(propane-2,2-di­yl)bis­(2-hy­droxy­isophthalaldehyde), C(19)H(16)O(6), (2), crystallize with one mol­ecule in the asymmetric unit. In mol­ecule (1), a >C(CH(3))(2) group bridges two nearly planar salicyl­aldehyde groups [r.m.s deviations = 0.010 (1) and 0.025 (2) Å], each comprising a planar phenyl ring bonded with a hydroxyl and an aldehyde group. Similarly, compound (2) has the same bridging group, but it connects two nearly planar appendants [r.m.s deviations = 0.034 (1) and 0.035 (1) Å], each comprising a phenyl ring bonded with a hydroxyl and two aldehyde groups. Mol­ecule (1) exhibits a bridge angle of 109.5 (2)° with the salicyl­aldehyde planes subtending a dihedral angle of 88.4 (1)°. In contrast, mol­ecule (2) presents a bridge angle of 108.9 (2)° with its appendants subtending a dihedral angle of 79.6 (3)°. Both mol­ecules exhibit two intra­molecular O—H⋯O hydrogen bonds involving the phenolic H atoms and carboxyl O-atom acceptors. In the crystal of (2), O—H⋯O hydrogen bonds between one of the hydroxyl H atoms and a carboxyl O atom from a symmetry-related mol­ecule form a chain along [10[Image: see text]]. In addition, (2) exhibits a strong visible luminescence when excited with ultraviolet radiation.