Bile Pigment Structures, III. Crystal and Molecular Structure of Diethoxybilirubin Diethyl Ester

Diethoxybilirubin diethyl ester crystallises triclinic P1 with a = 13.903(5), b = 17.211(7), c = 9.831(5) Å, α= 110.07(3), β = 111.22(3), γ = 69.04(3)°, Z = 2, Dx- 1.15 gcm-3. The two pyrromethene systems of the tetrapyrrole are orientated almost perpendicular to one another (interplanar angle = 91.5°). Considerable bond delocalisation is observed within the individual pyrromethene units, which contain intramolecular N-H···N hydrogen bonds of length 2.73 and 2.80 Å. Parallel stacking of the chromophores is not observed in the crystal lattice.