3-Hydroxyphthalide and its adduct with dibutyltin oxide

3-Hydroxyphthalide, C8H6O3, reacts with dibutyltin oxide to give bis{mu(3)- oxo-(mu-2-formylbenzoato-O:O')(2-formylbenzoato-O)bis[dibutyltin(IV)]}, [Sn -4(C4H9)(8)(C8H5O3)(4)(mu-O)(2)], in which the four Sn atoms are all five-c oordinated to three O and two C atoms arranged at the corners of a distorte d trigonal bipyramid. The equatorial Sn-mu(3)-O distances are in the range 2.039 (2)-2.048 (2) Angstrom and are significantly shorter than the axial S n-mu(3)-O distances of 2.170 (3) and 2.182 (2) Angstrom. The Sn-O-carboxyla te bonds are all axial and have distances in the range 2.204 (3)-2.271 (3) Angstrom, which are inversely correlated with the respective C-O bond dista nces. The mean Sn-C distance is 2.136 (6) Angstrom. 3-Hydroxy phthalide und ergoes ring opening to give the anion of 2-formylbenzoic acid which bonds t o the Sn atoms. The structure of 3-hydroxyphthalide is stabilized by O-H .. . O hydrogen bonds [O ... O = 2.766 (1) Angstrom] which link the molecules in a zigzag chain parallel to b.