Sodium Copper Oxalate Dihydrate: Na2Cu (C2O4)2. 2H2O Synthesis, Characterization, Morphology and Optical Properties

Abstract

AbstractCrystals of sodium copper oxalate dihydrate [Na2Cu (C2O4)2.2H2,O] were obtained by the gel method, from solutions of oxalic acid and copper chloride. The crystals form blue needles with idiomorphic faces of brilliant luster, permitting goniometric measurements and the determination of the morphology with the aid of crystallographic parameters. Optically the crystals are biaxial negative, 2V = 38°, with a weak dispersion r<v. The orientation of the indicatrix was determined using a universal stage.Crystals of sodium copper oxalate dihydrate, Na2Cu (C2O4)2.2H2O, were apparently first obtained in 1929 by Riley. Gleizes et al. (1980) undertook a preliminary crystallographic study of crystals obtained by a different technique from Riley's. In the first case, a solution of 33.5 g/L of sodium oxalate was heated and then poured gradually into a nearly saturated solution of copper sulfate until slight turbidity appeared. The turbidity was eliminated and the solution clarified by the addition of a little more sodium oxalate solution. In this way Riley obtained a dark blue solution which after filtration yielded extremely fine sky-blue needle-like crystals, rarely more than 8mm long. In the method of Gleizes et al. (1980), copper oxalate was dissolved in an aqueous solution of sodium oxalate; those authors observed complete dissolution when the molar ratio of sodium oxalate to copper oxalate was near 2. By evaporating the solution, they obtained long, prismatic crystals whose crystallographic constants they determined.In order to obtain crystals large enough for further crystallographic study, we set out to produce crystals of sodium copper oxalate by the gel method (Triché, 1984). We found that slow crystallization did encourage the formation of large crystals.