Abstract
In the crystal structure of the title magnesium salt of the phen-oxy herbicide (2,4-di-chloro-phen-oxy)acetic acid (2,4-D), [Mg(C8H5Cl2O3)(H2O)5](C8H5Cl2O3)·0.5H2O, the discrete cationic MgO6 complex unit comprises a carboxyl-ate O-donor from a monodentate 2,4-D anionic ligand and five water mol-ecules, resulting in a slightly distorted octa-hedral coordination sphere. The free 2,4-D anions are linked to the complex units through duplex water-carboxyl-ate O-H⋯O hydrogen bonds through the coordinating water mol-ecules. In the crystal, inter-unit O-H⋯O hydrogen-bonding inter-actions involving coordinating water mol-ecules as well as the solvent water mol-ecule (occupancy 0.5) with carboxyl-ate O-atom acceptors, give a layered structure lying parallel to (001), in which π-π ligand-cation inter-actions [minimum ring centroid separation = 3.6405 (17) Å] and a short O-H⋯Cl inter-action are also found.
Highlights
In the crystal structure of the title magnesium salt of the phenoxy herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D), [Mg(C8H5Cl2O3)(H2O)5](C8H5Cl2O3)Á0.5H2O, the discrete cationic MgO6 complex unit comprises a carboxylate O-donor from a monodentate 2,4-D anionic ligand and five water molecules, resulting in a slightly distorted octahedral coordination sphere
The free 2,4-D anions are linked to the complex units through duplex water–carboxylate O— HÁ Á ÁO hydrogen bonds through the coordinating water molecules
The free 2,4-DÀ counteranion is linked to the complex unit through an unusual duplex water–carboxylate O—HÁ Á ÁO hydrogen-bonding association involving the coordinating water molecules O1W and O2W (Table 1), giving a cyclic ring motif incorporating the Mg2+ cation [graph set R22(8)]
Summary
The phenoxyacetic acids comprise an important group of chemicals which has among its members those ring-substituted representatives having selective herbicidal activity, e.g. the commercial but in some cases, prohibited (2,4-dichlorophenoxy)acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) and (4-chloro-2-methylphenoxy)acetic acid (MCPA) (O’Neil, 2002; Zumdahl, 2010; Cobb & Reade, 2011). Of interest have been the structures of the metal complexes with these acids, including those with magnesium in which the monoanionic phenoxyacetate ligands (L) display a variety of coordination modes, all based on an octahedral MgO6 metal stereochemistry. These include discrete monomeric {[MgL2(H2O)4] [L = 2-(2-fluorophenoxy)acetate (Kennard et al, 1986) and L = MCPAÀ (Smith et al, 1981)] and [MgL(H2O)5]ÁL [L = 2,4,5-TÀ (Smith et al, 1982)]} or polymeric {[MgL2(H2O)2]}n [L = phenoxyacetate, (4-chlorophenoxy)acetate or (4-fluorophenoxy)acetate] (Smith et al, 1980; Smith, 2012)}. 2. Structural commentary In the title complex (Fig. 1), the discrete MgO6 complex units have, as expected, essentially octahedral stereochemistry [Mg—O bond length range = 2.031 (2)–2.094 (2) A ], comprising a carboxylate O-donor from a monodentate 2,4DÀ ligand and five water molecules. Symmetry codes: (i) Àx þ 1; Ày þ 1; Àz þ 1; (ii) Àx þ 2; Ày; Àz þ 1; (iii) x; y À 1; z; (iv) Àx þ 1; Ày; Àz þ 1; (v) x þ 1; y; z; (vi) Àx þ 2; Ày þ 1; Àz þ 1
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