CU-II-HERBICIDE COMPLEXES - STRUCTURE AND BIOACTIVITY

Copper complexes with the commercial auxin herbicides 2,4-dichloropben oxy-acetic acid (2,4-D), 3,4-dichlorophenoxy-acetic acid (3,4-D), 2,4, 5-trichlorophenoxy-acetic acid (2,4,5-T), 2-methyl-4-chloro-phenoxy-ac etic acid (MCPA), 2,3-dichlorophenoxy-acetic acid (2,3-D) and 2-(2,4-d ichlorophenoxy)-propanoic acid (2,4-DP) in the presence or not of 2,2' -bipyridine (bipy), an antimicrobial agent, were prepared and characte rized. The available evidence supports a dimeric structure for the 2,3 -D complex, while the presence of bipy leads to monomeric forms. The s olution behaviour of dinuclear complexes in dimethylformamide (DMF) ha s shown that the complexes are converted to monomeric compounds by the addition of more than 1:2 of bipy. The cyclic voltammograms of dimers in DMF suggest that the complexes retain the dimeric structure in sol ution. The electron spin resonance spectra of the compound (aqua) 2'-b ipyridine)bis(2-methyl-4-chlorophenoxyacetato) copper(II) (1) show fea tures characteristic of the presence of an S = 1 triplet state. The cr ystal structure of 1 was determined and refined by least-squares metho ds using three-dimensional Mo Ka data. 1 crystallizes in the space gro up C2/c, in a cell of dimensions a = 40.49(1), b = 7.286(3), c = 19.61 7(6) Angstrom, beta = 103.23(1)degrees, V = 5634(3) Angstrom(3), Z = 8 . Study of the antimicrobial activity showed that the presence of bipy increases the efficiency 4-8 times. (C) 1998 Elsevier Science S.A. Al l rights reserved.