Design, Synthesis, and X-ray Structural Characterization of New Dinucleating Macrocyclic Ligands and a Novel Phenolate-Bridged Dilanthanum(III) Complex

The [2+2] template condensation of 6,6‘-bis(aminomethyl)-2,2‘-bipyridyl with 2,6-diformyl- p -cresol in the presence of lanthanum acetate yields a homodinuclear complex of a Schiff base macrocycle (babp) 2 (dfc) 2, 1 . The crystal of [La 2 1 (OAc) 4 ]·4CH 3 CN·3H 2 O is triclinic, space group P 1̄, with cell constants a = 10.986(6) Å, b = 12.231(8) Å, c = 23.818(12) Å, α = 86.63(5)°, β = 85.99(5)°, γ = 79.45(4)°, V = 3135(3) Å 3, and Z = 2. The decacoordination geometry around each identical La 3+ ion is a bicapped dodecahedron made up of two bidentate acetate anions, two phenolate oxygens, and four imine nitrogens. The 1 H, 13 C, and 2D-COSY NMR and UV−visible spectra of the complex are consistent with the solid state structural information obtained by IR and X-ray diffraction studies. Treatment of a solution of La 2 1 (OAc) 4 in methanol with sodium cyanotrihydroborate yields the hydrogenated octaaza macrocycle R(babp) 2 (dfc) 2, 2 . The [2+2] metal-free condensation of 2,6-bis(aminomethyl)- p -cresol with 2,6-diformylpyridine yields a Schiff base macrocycle (bac) 2 (dfp) 2, 3 . Reduction of 3 with sodium borohydride yields the hydrogenated hexaaza macrocycle R(bac) 2 (dfp) 2, 4 . Under strongly acidic conditions (48% HBr), the free ligand 4 crystallizes as a hydrobromide salt 4 ·H 2 O·7HBr in the monoclinic system, space group C 2/ m, with cell constants a = 26.737(11) Å, b = 16.885(7) Å, c = 10.325(4) Å, β = 101.94(3)°, V = 4560(3) Å 3, and Z = 4. The [2+2] nature of the macrocycles 3 and 4 is identified by 1 H and 13 C NMR, FAB mass spectra and by X-ray crystallography.