ZINC(II) BIS(PHOSPHOGLYCOLATE) DIHYDRATE AND CALCIUM BIS(PHOSPHOGLYCOLATE) DIHYDRATE

Crystals of zinc(II) bis(phosphoglycolate) dihydrate, Zn2+.2C2H4O6P-.2 H2O, are almost isomorphous with crystals of zinc(II) bis(phosphoenolp yruvate) dihydrate. The Zn atoms occupy centres of symmetry and are si x-coordinate (through two water molecules and four phosphate O atoms). Two terminal O atoms of each phosphate group bridge pairs of Zn atoms , thereby forming linear chains along the b axis. In crystals of calci um bis(phosphoglycolate) dihydrate, Ca2+.2C2H4O6P-.-2H2O, the Ca atoms are coordinated by two trans water molecules and four phosphate O ato ms. One of the terminal atoms of each phosphate group bridges pairs of Ca atoms, thereby forming linear chains along the a axis. The orienta tion of the phosphate group relative to the glycolate moiety is differ ent in the two salts. All O-atom-bonded H atoms (in both crystals) par ticipate in hydrogen bonding.