Structurally diverse copper(II) herbicide complexes: Mono- and bi-nuclear neutral or cationic complexes

Copper complexes with the commercial auxin herbicides 2,3-dichlorophenoxyacetic acid and 2-(2,4-dichlorophenoxy)propanoic acid and 2,2'-bipyridine (bipy) were prepared and characterized: [Cu-2(Cl2C6H3OCH2CO2)(4)(MeOH)(2)] 1, [Cu{Cl2C6H3OCH(Me)CO2}(2)(bipy)(H2O)] 2 and [Cu{Cl2C6H3OCH(Me)CO2)(bipy)(2)]Cl 3. The available evidence supports a dimeric structure for complex 1 while the presence of bipy leads to monomeric forms. In dimethylformamide solution the binuclear complex is converted into a monomeric complex upon addition of a > 1:2 ratio of bipy. The ESR powder spectrum of compound 2 exhibits features characteristic of the presence of a S = 1 triplet state which may be assigned to a hydrogen-bond network. The crystal structures of the three complexes have been determined.