Abstract
In the title compound, C18H15OP.C11H8O2, co-crystallization of triphenylphosphine oxide with 1-naphthoic acid yields a supramolecular structure held together by one O-H...O and three C-H...O hydrogen bonds. The O-H...O hydrogen bond [O...O = 2.592 (2) A] has little effect on the O=P bond distance.