Two novel homodinuclear Ni(II) and Cu(II) complexes with a 24-membered octadentate hexaazamacrocyclic ligand: stability and X-ray crystal structures

A dinucleating 24-membered hexaazadiphenol macrocyclic ligand, 3,6,9,17,20, 23-hexaaza-29,30-dihydroxy-13,27-dimethyl-tricyclo[23,3,1,1(11,15)]triacont a-1(28),11,13,15(30),25,26-hexaene (H2L or [24]BDBPH), is prepared by the N aBH4 reduction of the Schiff base obtained from [2 + 2] template condensati on of 2,6-diformyl-p-cresol with diethylenetriamine. The ligand maintains d inuclear integrity for copper(II) and nickel(II) complexes, while facilitat ing the formation of non-bridged dicopper and bridged phenolic dinickel cor es. Potentiometric equilibrium studies indicate that a variety of protonate d, mononuclear and dinuclear complexes are formed with nickel(II) from p[H] 2 through 11 in aqueous solution. The stability constants and species dist ribution as a function of p[H] of the 1:1 and 1:2 [ligand:Ni(II)] complexes were determined in KCI supporting electrolyte ( mu = 0.100 M) at 25 degree sC. The pH potentiometric studies show that the dinuclear complexes are for med via mononulear chelates in which two kinds of coordination patterns are proposed. Copper is complexed by half of the coordination sites of the din ucleating macrocycle (N3O-), and the nickel occupies salen-like sites of th e macrocycle (N2O2-), which form dibridged dinuclear complexes. The neutral homodinuclear complex [Cu2L](Cl)(Br) forms monoclinic crystals, of space g roup P2(1)/c, with a = 9.9125(17), b = 13.559(2), c = 22.713(4) Angstrom, b eta = 98.145(4)degrees, and Z = 4. A dinulear Ni(II) complex forms with the formula [Ni2L(H2O)(2)](Br-2). 2H(2)O. Dibridged phenolic oxygen atoms were observed. The complex crystallizes in monoclinic form, space group P2(1)/c , with a=18.262(2), b=11.7520(15), c = 15.755(2) Angstrom, beta = 107.817(2 )degrees, and Z = 4. (C) 2001 Elsevier Science B.V. All rights reserved.