Coordination Complexes of Groups 1 and 2. Potassium O,O′-Catecholdiacetate

Potassium chloride and catecholdiacetate form a 1:2 potassium, catecholdiacetate complex. The crystals are monoclinic with a = 23.650 (5) Å, b = 11.889 (2) Å, c = 7.857 (2) Å, β = 106.61 (3)°, Z = 8, and space group C2/c. The crystal structure has been determined by tangent and cosine direct phasing methods and refined by block diagonal least squares to a final R of 0.029 on 1635 observed diffractometer data. The complex cation has crystallographic symmetry 2 with the potassium lying between a pair of twofold related ligand molecules. The coordinating atoms are the ether and carboxyl oxygens ffcm one crystallographic asymmetric unit and a carboxyl oxygen from a symmetry related unit. This pentagonal group is then transformed by a crystallographic rotation axis, containing the potassium atom, to give a ten-coordinated unit. The geometry of the coordination can be described as an irregular pentagonal antiprism. The K-O distances range between 2.75 and 2.92 Å. The potassium cation lies 1.55 Å from the least-squares plane of a pentagonal group of oxygens. A hydrogen atom located on a crystallographic inversion center is shared between two catecholdiacetate ligands.