GROUP-15 COMPLEXES WITH CARBOXYLIC-ACIDS .6. PREPARATION AND CRYSTAL-STRUCTURES OF POTASSIUM ANTIMONY(III) CITRATE, ([K2SB4(CITRATE)8(H2O)2]) AND LITHIUM ANTIMONY(III) CITRATE, ([LISB(CITRATE)2(H2O)] .2H2O)

Potassium antimony(III)citrate, {[K2Sb4(citrate)8(H2O)2]} (1), and lit hium antimony(III) citrate, {[LiSb(citrate)2(H2O)] . 2H2O} (2), have b een prepared and their structures determined by X-ray diffraction. Wit h 1 each of the two independent centrosymmetric tetramers in the repea ting unit of the complex comprises four independent antimony ions and eight citrate residues interlinked by two potassium centres [K-O range 2.62-3.06(1) angstrom]. The difference between the two tetramers is t hat potassium is seven-coordinate in one and eight-coordinate in the o ther. The water molecules are coordinated to the potassium ions. Each antimony forms the usual distorted pseudo-trigonal bipyramidal four-co ordinate complex through the alpha-hydroxy carboxylate oxygens of two citrate residues. A feature of the structure is the presence of three differently charged citrate species (1-, 2-, 3-), giving the formula { K2[Sb(C6H6O7)2]2[Sb(C6H7O7)(C6H5O7)]2(H2O)2}. The coordination about a ntimony in 2 is similar, but the lithium links the two citrate residue s together via a carboxyl and a hydroxyl oxygen from one ligand and a carboxyl oxygen from the second. A water completes the tetrahedral coo rdination sphere [mean Li-O, 1.942(5) angstrom]. Except for the four-c oordination about lithium, the complex is similar to the analogous sod ium complex {[NaSb(citrate)2(H2O)2].H2O}.