Metal complexes of dicamba: the crystal and molecular structures of dicamba(3,6-Dichloro-2-methoxybenzoic acid) and catena-μ-Aqua-diaquabis(3,6-dichloro-2-methoxybenzoato)zinc(II) dihydrate

Abstract

The crystal structures of the herbicide, dicamba (3,6-dichloro-2-methoxybenzoic acid) and the zinc(II) complex of this acid, {[Zn(dicamba)₂(H₂O)₃].2H₂O}}_n (1), have been determined from X-ray diffraction data and refined by least squares to final residuals of 0.034 and 0.043 respectively. Dicamba is triclinic, space group P1, Z 2 with a cell a 7.232(1), b 7.971(1), c 9.050(3) Å, α 102.76(3), β 91.33(3), γ 110.38(1)º, while (1) is monoclinic, space group P2₁/n, Z 4 with a cell a 10.467(1), b 8.135(3), c 28.079(2) Å, β 96.497(7)º. Dicamba forms hydrogen-bonded cyclic dimers [O---O, 2.655(7) Å] with the carboxyl and the methoxy groups synclinal to the benzene ring. The dicamba ligands retain their conformation in the Zn^II complex and are cis-related and unidentate [Zn-0,2.083,2.095(4) Å]. Three of the waters are coordinated [Zn-0, 2.036, 2.055, 2.099(4) Å] with one of these also acting as a bridging ligand between the octahedral zinc centres [Zn-0, 2.326(4) Å], giving a 'linear' polymer structure [Zn-0-Zn bridge angle, 133.6(3)º]. The Mn^II and Co^II complexes of dicamba [(2) and (3)] have been confirmed as isomorphous and isostructural with the Zn^II analogue.