Synthesis, Crystal Structure, and Potentiometry of Pyridine-Containing Tetraaza Macrocyclic Ligands with Acetate Pendant Arms

Abstract

Tetraazamacrocycles containing the pyridine moiety as part of the cyclic backbone and acetate pendant arms were prepared. The resulting products were characterized by high resolution NMR (‘H and I3C) spectroscopy and single-crystal X-ray diffraction. Single-crystal X-ray diffraction data were obtained for the following compounds: py[l2]aneN4*HC1, C I I H I ~ N ~ C ~ , orthorhombic Pnma (No. 62), a = 10.304(6) A, b = 9.160(2) A, c = 13.552(2) A, Z = 4, Mo Ka, ;1 = 0.710 69, R = 0.037, R, = 0.036; and BP2A.2HC1-3H20, C18H22N404c ~ ~ . ~ H ~ o , triclinic pi (NO. 21, u = 10.201(0) A, b = i3.267(3) A, c = 8.612(6) A, a = 97.676(2)”, p = 105.821(0)”, I. = 86.363(7)”, Z = 2, Mo Ka, = 0.710 69, R = 0.039, R , = 0.038. In addition, protonation constants (log KH~L) and metal ion stability constants (log KML) for BP2A (log KH,-L = 9.57, 5.99, 2.59, 2.22; log KMgL = 8.9; log K c ~ L = 10.0; log KGdL = 14.5) and PC2A (log KH,-~L = 12.5, 5.75, 3,28, 2.38, -1; log KMgL = 8.4, log Kc& = 10.0, log KGdL = 16.6) were determined using potentiometric and NMR pH titrations. These values agree well with previously reported literature values for analogous ligand systems.