Crystal and molecular structure of Bis(4-amino-3,5,6-trichloropicolinato)-manganese(II) dihydrate

Abstract

The manganese(II) complex [Mn(picl)₂,2H₂O]_n of the herbicide picloram has been prepared and the crystal and molecular structure determined from three-dimensional X-ray data collected by counter methods. The crystals of the complex are monoclinic, space group 12/a with two complex units in a cell of dimensions a 23·052(5), b 13·840(2), c 6·441(1) Å, β 98·20(1)º. The structure was solved by direct methods and refined by full matrix least squares to unweighted and weighted Rfactors of 0·035 and 0·038 respectively for 887 'observed' reflections. The polymer is best described as having a centrosymmetric two-molecule unit [Mn-O, 2·162(3), 2·246(3) Å] with two oxo bridges between manganese centres through two single carboxylate oxygens of the four substituted picolinate ligands. The two molecules are related by a twofold axis. The units form infinite one-dimensional polymer chains in the c direction through oxo bridges involving one oxygen from the other two picolinate ligands [Mn-Mn 3·636(1)Å]. The bis(bidentate)picolinate bites are completed by the pyridlne nitrogens [Mn-N, 2·313(4) Å] giving a very distorted octahedral MnO₄N₂ coordination sphere about each manganese [N-Mn-N', 97.0(3)º; O-Mn-O range, 68·9-168.2(3)º; O-Mn-Nrange, 69·9-138·5(3)º]. The lattice waters are involved in hydrogen-bonding interactions which link the polymer in the a crystallographic direction with the uncoordinated carboxylate oxygen ( O···O,2·824, 2·936 Å) and the 4-amino groups from the adjacent picolinate ligand (N· ··0, 2·852, 3·030Å).