CRYSTAL-CHEMICAL ANALYSIS OF THE STRUCTURES OF OXALIC-ACID AND ITS SALTS M(X)(C2O4)(Y)CENTER-DOT-NH(2)O (N=0-3)

Crystal-chemical analysis of the structures of oxalic acid and its sal ts M(x)(C2O4)(y) . nH(2)O (n = 0-3) is carried out. It is shown that t he dimensions of oxalate ions play a critical role for closest packing in the structures of the acid and anhydrous and aqueous metal salts. In most compounds, the centers of masses: of oxalate ions lie in the p lanes and form trigonal loops with average bond lengths and angles of 5-6 Angstrom and 60 degrees, respectively. The dimensions and distorti ons of the nets depend on the proximity of the cations and/or water mo lecules to the planes. For the structures of one cation, the influence of the quantity of water on the arrangement of oxalate ions is shown. The relationship between the polymorphism and variations of orientati ons and packings of oxalate ions is discussed. The analysis gives grou nds for predicting the structural arrangement of ionic or molecular co mpounds provided that the structure-forming units have a pseudospheric al form.