Zinc(II) and cadmium(II) complexes of the potentially tridentate ligands 2-[[2-pyridinylmethyl)amino]methyl]phenol (HSALAMP) and 2-[[[2-(2-pyridinyl)ethyl]amino]methyl]phenol (HSALAEP). X-ray crystal structures of the [Zn(SALAMP)(NO 3)] 2 and the [Cd(SALAEP)(NO 3)] 2 dimers

Abstract

Zinc(II) and cadmium(II) complexes with two potentially tridentate (NNO) ligands 2-[[(2-pyridinylmethyl)amino]methyl]phenol (HSALAMP) and 2-[[[2-(2-pyridinyl)ethyl]amino]methyl]phenol (HSALAEP) have been isolated and structurally characterized through 1H, 13C and 2-D NMR spectroscopy and in two cases by X-ray crystallography. HSALAMP behaves as a tridentate (NNO) or a bidentate (NN) ligand, depending upon the nature of the anion and the reaction conditions and on reaction with zinc( II) salts gives three types of complex: (a) [Zn(SALAMP)X] 2· yC 2H 5OH (X = Cl, y = 0 ( I); X = I, y = 0 ( II); X = NO 3 y = 1 ( III); (b) [Zn(HSALAMP)X 2]· yH 2O (X = Cl, y = 1 ( IV); X = I, y = 0 ( V); (c) [Zn(HSALAMP) 2](CIO 4) 2·C 2H 5OH·H 2O ( VI). However HSALAEP, a similar compound with one additional carbon atom in the chain, acts as a tridentate ligand irrespective of the nature of the anion and the reaction conditions, forming compounds with zinc( II) and Cd(II) salts, [M(SALAEP)X] 2· yC 2H 5OH (M = Zn, X = CI, y = 0 ( VII); M = Zn, X = I, y = 0 ( VIII); M = Zn, X = NO 3, y = 0 ( IX) and M = Cd, X = NO 3, y = l ( X). The single crystal X-ray structures of the [Zn(SALAMP)(NO 3)] 2 ( III) and the [Cd(SALAEP)(NO 3)] 2 (X) dimers have been determined. III crystallized in the monoclinic system, space group P2 1/ c, with a = 10.156(4), b = 17.424(4), c = 8.090(4) Å, β = 107.56(2)°, V = 1365(2) Å 3 and Z = 4. X crystallized in the monoclinic system, space group P2 1/ n, with a=9.728(2), b=15.132(4), c=10.223(4) Å, β = 92.910(10)° V= 1502.9(8) Å 3 and Z = 2. The structures of III and X are similar and consist of centrosymmetric dimers in which deprotonated phenolates bridge the two metal atoms and link the two halves of the dimer. In III and X the zinc(II) and cadmium(II) ions have a highly distorted six-coordinate structure, bonded to two oxygen atoms from a bidentate nitrate group, the pyridine nitrogen, an amine nitrogen and a phenolate oxygen. The metal-metal separations are quite short (3.063(1) Å ( III), 3.429(1) Å ( X) with M-O-M angles of 98.33(9) ( III) and 99.2(1° ( X). Compounds I and II and VII–IX have been proposed to have dimeric structures similar to those of III and X, with SALAMP or SALAEP acting as tridentate (NNO) ligands with the two zinc(II) ions bridged similarly by phenolate oxygens. Compounds IV, V and VI appear to have four-coordinate, monomeric structures with (HSALAMP) acting as a bidentate ligand (NN).