Synthesis and Crystal Structure of 1,4,7-Tris(2-mercaptoethyl)-1,4,7-triazacyclononane

Abstract

There has been considerable interest in the coordination chemistry of tacn-based macrocyclic ligands (tacn = 1,4,7-triazacyclononane).1 Recently, we reported on an octahedral nickel(II) complex with a hexadenetate ligand based on tacn, 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane, where three 2-aminoethyl-pendant groups bind a nickel(II) ion in an octahedral geometry with the basal three tacn-nitrogen atoms.2 Concerning this study, 1,4,7-tris(2-mercaptoethyl)1,4,7-triazacyclononane (H3tmtacn) is an interesting hexadentate ligand, having three thiolic-sulfur and three amino-nitrogen donor atoms to give an octahedral mononuclear gallium(III),3 indium(III)4,5 and iron(III)6 complexes with three bidentate S,Nchelates. However, there is no report on the crystal structure of the ligand, itself. In this study, we successfully prepared singlecrystals of the hexadentate ligand as dihydrochloric acid salt (Fig. 1), and determined the crystal structure in order to elucidate the molecular structure of the hexadentate ligand. The ligand was synthesized by a method described by Moore et al.3 1,4,7-Triazacyclononane (0.4802 g, 3.7 mmol) was dissolved in benzene (25 cm3) under argon. To this solution was added ethylene sulfide (2.280 g, 37 mmol); the mixture was heated under reflux for 5 h. The solution was concentrated to dryness by using a rotary evaporator. A mixed solution of 60% hydrochloric acid (6 cm3) and ethanol (40 cm3) was added, and the mixture was left at 4 C to precipitate. The resulting white precipitate was filtered off, washed by ethanol, and dried under a vacuum. Yield, 1.285 g (81%). Anal. Found: C, 35.81; H, 7.97; N, 10.14%. Calcd for C12H31Cl2N3OS3 (H3tmtacn·2HCl·H2O): C, 35.99; H, 7.80; N, 10.49%. IR (KBr, Synthesis and Crystal Structure of 1,4,7-Tris(2-mercaptoethyl)-1,4,7triazacyclononane