Synthesis and Structural Characterization of Praseodymium(III) and Neodymium(III) Complexes of Tripodal Tris[2-(salicylideneamino)ethyl]amine

The preparation and characterization of praseodymium(III) and neodymium(III) complexes of heptadentate (N4O3) ligand trensal, tris[2-(salicylideneamino)ethyl]amine (H3L1), have been studied. These complexes (PrL1 and NdL1) were prepared by the reaction of the praseodymium(III) or neodymium(III) complex of 1,9-bis(2-aminoethyl)-1,4,6,9,12,14-hexaazacyclohexadecane with salicylaldehyde in acetonitrile. Alternatively, the reaction of tris(2-aminoethyl)amine and salicylaldehyde in the presence of praseodymium(III) or neodymium(III) salt in acetonitrile also gave praseodymium(III) and neodymium(III) complexes of trensal. The molecular structures of PrL1 and NdL1 were determined by X-ray structural analysis; these are rare examples of lanthanide heptadentate complexes in which the metal ions are coordinated by the four nitrogen atoms and the three oxygen atoms. The crystals of Pr(C27H27N4O3)·0.5CH3CN and Nd(C27H27N4O3)·0.5CH3CN are both trigonal, space group , a = 13.713(2), c = 8.093(3) Å, U = 1318.0(7) Å3, Z = 2 for [PrL1]·0.5CH3CN, and a = 13.724(3), c = 8.067(3) Å, U = 1315.8(7) Å3, Z = 2 for [NdL1]·0.5CH3CN. The structures were solved by heavy-atom Patterson methods and expanded using Fourier techniques; they were then refined by full-matrix least-squares procedures to R = 0.033 and Rw = 0.043 for 1547 observed reflections with I ≥ 3σ(I), R = 0.028 and Rw = 0.039 for 1923 observed reflections with I ≥ 3σ(I) for [PrL1]·0.5CH3CN and [NdL1]·0.5CH3CN, respectively. The individual metal ions and the apical nitrogen atoms lie on a 3-fold axis in each crystal; the molecules possess a C3 molecular symmetry.