Monoprotic Tetradentate N₃O-Donor Ligands and Their Cu(II) and Ni(II) Complexes

A convenient four-step procedure was developed to prepare the novel monoprotic tetradentate ligands N-(2-hydroxy)benzyl-N-methyl-N‘-(2-pyridyl)methyl-1,3-propanediamine (Hpamap) and N-(2-hydroxy)benzyl-N‘-methyl-N‘-(2-pyridyl)methyl-1,3-propanediamine (Hpmaap), which provide an N3O metal coordination sphere. A mononuclear copper(II) complex, [Cu(pamap)Cl] (A), was obtained by reaction of Hpamap with CuCl2·2H2O. The binuclear copper(II) complexes [Cu(pamap)]2(BF4)2 (B) and [Cu(pmaap)]2(BF4)2 (C) were obtained when these ligands were reacted with Cu(II) in the presence of the noncoordinating BF4- anion. Reaction of nickel(II) with the Hpamap ligand generated the binuclear Ni(II) complex [Ni2(pamap)2(NO3)]NO3 (D). The crystal of A (C17H22ClCuN3O) is orthorhombic Pbca (No. 61), a = 11.837(4) Å, b = 15.648(5) Å, c = 11.002(11) Å, Z = 8; that of B (C34H44B2Cu2F8N6O2) is triclinic P1̄ (No. 2), a = 9.147(0) Å, b = 10.375(0) Å, c = 10.535(1) Å, α = 107.20(0)°, β = 91.19(0)°, γ = 105.05(0)°, Z = 1; that of C (C34H44B2Cu2F8N6O2) is monoclinic P21/c (No. 14), a = 9.158(2) Å, b = 10.714(2) Å, c = 19.085(4) Å, β = 90.58(2)°, Z = 4; and that of D (C34H44N8NiO8) is monoclinic C2/c (No. 15), a = 13.849(0) Å, b = 13.609(0) Å, c = 19.558(1) Å, β = 92.34 (0)°, Z = 4. The copper atoms of all three complexes are five-coordinate in the solid state, assuming the geometry of a distorted square pyramid with the deprotonated tetradentate ligand in the basal plane. The mononuclear complex A has a chloride ligand in the axial position, while each copper center in the binuclear complexes B and C has, in the axial position, a bridging phenolate O donor from the other unit of the dimer. Each nickel center in the binuclear complex D is six-coordinate, with the pseudo-octahedron formed by a deprotonated tetradentate ligand, a bridging nitrato oxygen atom, and a bridging phenoxy donor from the tetradentate ligand bound to the second nickel center.