The macrocycle 1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (THP) prepared from racemic propylene oxide and cyclen (1,4,7,10-tetraazacyclododecane) consists of a mixture of stereoisomers that arise from the chiral alpha-carbons of the hydroxypropyl groups. C-13 NMR studies suggest that five different diastereomers are formed. Lanthanum(III), europium(III), and lutetium(III) THP complexes are synthesized from the mixture of THP stereoisomers. Europium(III) THP complexes containing R,R,R,S and S,S,S,R configurations at the alpha-carbons of the hydroxypropyl groups cocrystallize from solution. The complex [Eu(THP)(H2O)]2(CF3SO3)6.2EtOH.H2O crystallizes in the centrosymetric monoclinic space group P2(1)/c (No. 14) with a = 22.5019(60) angstrom, b = 20.1684(33) angstrom, c = 19.8962(39) angstrom, beta = 105.923(17)degrees, V = 8683(3) angstrom3, and Z = 4. Four stereoisomers (two enantiomeric pairs) of the complex appear in the crystal. Each asymmetric unit consists of two different diastereomers of the europium(III) cation, six triflate anions, two ethanol molecules, and one water molecule of solvation. The structure was solved and refined to R = 5.54% and R(w) = 5.72% for those 3351 reflections with F(o) > 6sigmaF(o). The nine-coordinate Eu3+ ion of each cation is partially encapsulated by an octadentate macrocyclic ligand (the four donor N atoms form a plane and are staggered by only about 19.0-24.2-degrees from the orientations of the four donor O atoms) and has a water molecule capping the metal atom above the O4 plane of the coordination sphere. The coordination sphere is thus a 4:4:1 arrangement, midway between a capped cube and a capped square antiprism. In addition, synthesis of the THP stereoisomer with all hydroxypropyl groups containing the S-configuration (S-THP) is accomplished by use of S-propylene oxide. The synthesis of lanthanum(III), europium(III), and lutetium(III) complexes of S-THP is reported; H-1 and C-13 NMR spectra of the lanthanum and lutetium complexes indicate that only one diastereomer is present in solution. Complexes of lanthanum(III), europium(III), and lutetium(III) are remarkably robust in water with half-lives of 73, 100, and 53 days, respectively, at 37-degrees-C and pH 6.0.