Fluorene-1-carboxylic acid.

@article{Blackburn1996Fluorene1carboxylicA,
  title={Fluorene-1-carboxylic acid.},
  author={Anthony C. Blackburn and Allison J. Dobson and R. E. Gerkin},
  journal={Acta crystallographica. Section C, Crystal structure communications},
  year={1996},
  volume={52 ( Pt 4)},
  pages={
          907-10
        }
}
In fluorene-1-carboxylic acid, C14H10O2, the sole hydrogen bond is of the cyclic dimer type about a center of symmetry. The carboxyl H atom is ordered. Distances in the fluorene core are very similar to those in fluorene itself; the fluorene core dihedral angle is, however, larger than in fluorene. 
2 Citations
X-ray diffraction study of fluorene, 9-fluorenone, and 9-dicyanomethylenefluorene derivatives
The results of a single-crystal X-ray diffraction analysis of fluorene, 9-fluorenone, and 9-dicyanomethylenefluorene derivatives as individual compounds, as well as their crystal solvates, molecular