Six molecular complexes containing the herbicidally active
(2,4-dichlorophenoxy)acetic acid (2,4-d) and (2,4,5-trichlorophenoxy)acetic
acid (2,4,5-t) have been prepared and studied by using single-crystal X-ray
diffraction techniques. These adduct structures are 2,4-d with
4,4′-dipyridine (2 : 1 complex), and 2,4,5-t with respectively
5-nitroquinoline (1 : 1), 4,4′-dipyridine (2 : 1), 2-amino-2-thiazoline
(1 : 1), 2-aminobenzothiazole (1 : 1) and 2-amino-5-ethyl-1,3,4-thiadiazole (1
: 1). The conformations of the phenoxyacetic acid molecules were found to be
either synclinal (in three cases) or antiperiplanar (in the other three
cases). A general review is also made about the conformational aspects of
previously reported adducts of phenoxyacetic acid derivatives and how they
compare to their free acid structures.