Single crystal X-ray diffraction analysis was performed to determine the molecular geometry of four dipyrrins (Fig. ) and the majority of homoleptic tris(dipyrrinato)aluminum(III) complexes. Crystal structures of such aluminum complexes have not been reported yet. The dipyrrin core mainly adopted a planar conformation with the contribution of the intramolecular hydrogen bonds (N•••H) and an average distance ~2.06 Å. Compound 12h crystallized with two independent molecules in the asymmetric unit. One molecule presented an intramolecular hydrogen bond keeping it in a planar conformation whereas the other had a more twisted conformation and no intramolecular hydrogen bond (Fig. ). The dihedral angle between the dipyrrin plane and the 5substituent is locked between 55 -90 degrees in the order: 12f with 52.57(3)° < 12a with 67.52(4)° < 12g with 83.45(2)° < 12h with 93.20( )° (Fig. ). The trimeric octahedral configuration of tris(dipyrrinato)aluminum(III) complexes was confirmed by singlecrystal X-ray crystallography. The crystal structure obtained of the phenyl tris(dipyrrinato) derivative 13a (Fig. ) is isostructural to the iron(III) analogue. The dihedral angle between the dipyrrin and the substituent for the two moieties is between 65-76° and the structure is tightly packed without any solvent (Fig. ). Compound 13b (Fig. ) exhibited disorder of the mesityl group and showed a crystal lattice tightly packed with encapsulated solvent and a dihedral angle of 83.44° between the dipyrrin plane and the mesityl group (Fig. ). Indium and gallium analogues have been reported by Thoi et al. with equal asymmetric units, similar metal-nitrogen distances and degrees of dihedral angles of mesityl group and dipyrrin moieties. Complex 13c (Fig. ) crystallized with one AL(DIPY)3 and a partially occupied hexane in the asymmetric unit. The solvate molecules are located in a channel parallel to the a-axis (Fig. ). The bromophenyl vs. dipyrrin twist angle was 120.2°. A similar structure of 13d (Fig. ) contained half of the molecule in the asymmetric unit and a partially occupied hexane. The dihedral angle between the dipyrrins and C6F5 groups was 74-84°. The solvate molecules are incorporated in channels running parallel to the c-axis (Fig. ). Analogous structures of gallium and indium were previously reported by us. Figure . View of the molecular structure in the crystal of 13a, 13b, 13c,13d (disordered hexanes omitted), and 13f. Thermal ellipsoids show atomic displacement at 50% probability.