The hexadentate ligand 1,4,7-tris(o-aminobenzyl)-1,4,7-triazacyclononane and its complexes with zinc(II), cadmium(II), and mercury(II) in solution and in the solid state

The new hexadentate ligand 1,4,7-tris(o-aminobenzyl)-1,4,7-triazacyclononane (L) has been prepared from the reaction of 1,4,7-triazacyclononane and a-nitrobenzyl bromide (1:3) in toluene and subsequent reduction of 1,4,7-tris(o-nitrobenzyl)-1,4,7-triazacyclononane with hydrazine hydrate and a graphite catalyst. The ligand forms stable complexes with the salts M(ClO4)(2) . 6H(2)O in methanol (M = Zn2+, Cd2+, Hg2+). The complexes [LZn](ClO4)(2), 1, [LCd](ClO4)(2) . 0.5H(2)O, 2, and [LHg](ClO4)(2) . 0.5H(2)O, 3, have been isolated, and their solid state structures have been determined by X-ray single-crystal crystallography. Complex 1, [Zn(C27H36N6)](ClO4)(2), crystallizes in the monoclinic space group P2(1)/n with Z = 4, a = 9.222(5) Angstrom, b = 17.01(1) Angstrom, c = 19.41(1) Angstrom, and beta = 97.03(5)degrees; 2 and 3 (data in parentheses), [Cd(C27H36N6)](ClO4)(2) . 0.5H(2)O and [Hg(C27H36N6)](ClO4)(2) . 0.5H(2)O, crystallize in the orthorhombic space group Pc2(1)n, which is a nonstandard setting of Pna2(1) (No. 33), with Z = 4, a = 10.882(2) Angstrom (10.880(3) Angstrom), b = 14.666(2) Angstrom, (14.733(6) Angstrom, and c = 21.516(2) Angstrom (21.278(7) Angstrom). The metal ions are six-coordinate and the dications are asymmetric (C-1) in the solid state. The MN(6) polyhedra are distorted trigonal prisms. The three five-membered chelate rings M-N-C-C-N of the 1,4,7-triazacyclononane backbone adopt a (lambda lambda lambda)(5) (or (delta delta delta)(5)) conformation whereas two of the six-membered chelate rings of the aniline pendant arms adopt a boat (lambda' or delta') and the third adopts a twist-boat conformation (lambda '' or delta ''). Thus in the solid state the conformation of all three dications is described as Lambda(delta delta delta)(5)(lambda ''lambda'lambda')(6) and its enantiomeric form as Delta delta delta delta)(5)(delta ''delta'delta')(6). In solution, complexes 1-3 are fluxional, as shown by a detailed NMR study.