Copper(II) Interaction with Mono-, Bis- and Tris-Ring N3O2 Macrocycles: Synthetic, X-ray, Competitive Membrane Transport, and Hypochromic Shift Studies

Abstract

New N-phenyl (L(1)), azo-coupled (L(2)), and tri-linked (L(3)) substituted derivatives of a parent dibenzo-N(3)O(2) macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane (L(4)), have been synthesized. Competitive seven-metal transport studies across a bulk chloroform membrane employing an aqueous source phase containing equal molar concentrations of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ag(I), and Pb(II) as their nitrate salts have been performed using both L(1) and L(3) as the ionophore, with the results discussed in terms of those obtained previously for related mono-ring (L(5)) and di-linked (L(6)) macrocyclic systems. Sole transport selectivity for Cu(II) was observed in each case. On a per macrocyclic cavity basis the tri-linked analogue L(3) gave less efficient Cu(II) transport than its monomeric or di-linked analogues. At least in part, this may reflect the tendency of tri-linked derivative L(3) to form a 2:1 complex (metal/ligand) with Cu(II) under the conditions employed; such a stoichiometry was demonstrated to occur in acetonitrile using both spectrophotometric titration and Job plot procedures. The azo-coupled derivative (L(2)) yields a red solution (lambda(max) = 495 nm, epsilon(max) = 23000 M(-1) cm(-1)) and undergoes significant hypochromic metal-induced shifts (Delta lambda(max) = 54-174 nm) on metal addition. Cu(II) induces the largest shift (Delta lambda(max) = 174 nm), corresponding to a color change from red to pale-yellow. The X-ray structures of red L(2) x HNO(3) together with its Cu(II) complexes, [Cu(L(2))NO(3)]NO(3) x CH(2)Cl(2) (6) (pale-yellow) and [{Cu(L(2))}(2)(mu-OH)(2)](ClO(4))(2) x 2 CH(2)Cl(2) x 2 H(2)O (7) (dark-red), are reported. The structural determinations have allowed insight into the structure-function relationships governing the observed color variation between these species.