Effective double-ended chelating agents: crystal structures of N,N,N′,N′-tetraacetyl diamino derivatives and their chelates

Abstract

Crystal structure determinations of six N,N,N′,N′-tetraacetyl diamino derivatives, N,N,N′,N′-tetraacetyl m-xylylenediamine 1, N,N,N′,N′-tetraacetyl p-xylylenediamine 2, N,N,N′,N′-tetraacetyl 1,5-diaminonaphthalene 3, N,N,N′,N′-tetraacetyl 1,4-diaminocyclohexane 4, N,N,N′,N′-tetraacetyl 1,4-diaminobutane 5 and N,N,N′,N′-tetraacetyl 1,8-diaminooctane 6 have been carried out. In all these compounds the anti–syn configuration, in each DAA group, is preferred and the two DAA groups, at each end of the extended ligand, are coplanar with respect to one another. Further, the syntheses and crystal structures of two metal complexes [Cu(N,N,N′,N′-tetraacetyl 1,4-diaminobutane)₂(H₂O)₂](ClO₄)₂5a and [Zn(N,N,N′,N′-tetraacetyl 1,6-diaminohexane)₂(H₂O)₂](ClO₄)₂7 are also reported. Single crystal analysis confirmed that the N,N,N′,N′-tetraacetyl diamino derivatives act as bis-chelating, double-ended ligands. In an unbound state all the tetraacetyl derivatives adopt the expected anti–syn configuration but on complex formation this configuration of the ligand changes to anti–anti resulting in the formation of chelate complexes.