Metal complexes of Imazapyr, a herbicide provided with efficient metal-chelating ability: crystal structure of the cobalt(III) and manganese(II) complexes

The complexes formed by the imidazolinone herbicide Imazapyr, (+/-)-2-(4-isopropyl-4-methyl-5-oxo-4,5-dihydro-1H-2-imidazol-2-yl)nicotinic acid (Imz) with Co(III), Mn(II), Co(II) and Ni(II) ions are described. The compounds [Co(Imz)(3)]. 3H(2)O and [Mn(Imz)(2)]. 2H(2)O were characterized by single-crystal X-ray analysis. [Co(Imz)(3)]. 3H(2)O crystallizes in the trigonal space group R-3 with a = b = 17.485(2), and c = 26.257(7) Angstrom, alpha = beta = 90 and gamma = 120 degrees, Z = 6. The cobalt ion is hexa-coordinated, being surrounded by three bipy-like chelating ligands. Noticeably, although Imazapyr acts as a mononegative anionic ligand, the imidazolinone moiety binds the metal through the lactam nitrogen. The finding supports an isomeric form for the Imazapyr(-1) anion where the lactam site is deprotonated. This feature is most probably imposed by the strong intramolecular bond between the imidazole and the carboxylate sites sharing a proton. [Mn(Imz)(2)]. 2H(2)O crystallizes in the monoclinic space group P2(1)/c with a = 10.584(5), b = 11.633(2), and c = 13.072(6) Angstrom, alpha = 90, beta = 108.63(2) and gamma = 120 degrees, Z = 2. The structure consists of a polymeric three-dimensional network in which each metal ion is surrounded by two couples of nitrogen atoms belonging to two mutually trans ligands and two monodentate carboxylate groups from two further ligands. Each Imazapyr(-1) anion acts as a bridging ligand in as much as it binds a metal ion through the bipy-like couple of pyridine and lactam nitrogens and another through the carboxylate group. Based on the spectral properties, the Co(II) and Ni(II) derivatives adopt the same structure as [Mn(Imz)(2)]. 2H(2)O. (C) 1998 Elsevier Science S.A. All rights reserved.