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STEFÃNESCU et al.: HOMOPOLYNUCLEAR GLYOXYLATE COMPLEX
The method of obtaining homopolynuclear complex combinations containing as
ligand the glyoxylate dianion is based on the hot oxidation reaction in aqueous solu-
tion of 1,2-ethanediol simultaneously with the formation in the solid state reaction
system of their glyoxylates. The oxidative medium is provided by introducing the
cations as nitrates [9, 10].
For this process the synthesis yield is practically 100%.
C2H4(OH)2+(2NO– +[M(H2O)x]2+)→MC2H2O4 yH2O+2NO+(x–y+2)H2O
3
2NO(g)+O2(g)→2NO2(g)
The thermal decomposition of glyoxylates in order to obtain oxides of remark-
able properties presents a series of advantages over other complex combinations or
conventional methods.
Thus, the combinations with carboxylic acid anions as ligands decompose at rela-
tively low temperatures and generate highly volatile decomposition products [11, 12].
In this paper the thermal behaviour of glyoxylate homopolynuclear complex
combinations formed by Cu(II), respectively Cr(III) is studied.
There are the decomposition mechanisms established using thermal analysis in air
and nitrogen, IR spectrometry, gas–liquid chromatography and diffractometric X-ray
analysis.
Experimental
The complex homopolynuclear combinations of Cu(II) and Cr(III) have been synthe-
sised according to the previous patent [9] and papers [10] using as reagents
1,2-ethanediol (Fluka), Cu(NO3)2 3H2O (Merck), and Cr2(NO3)3 9H2O (Merck).
After synthesis the Cu(II) and Cr(III) glyoxylates were purified by refluxing in a
water–acetone mixture and characterized by elemental analysis [Cu(II), Cr(III), C,
H], electronic diffuse reflectance, thermal analysis, IR spectroscopy, assigning the
composition formulae Cu(C2H2O4) 0.5H2O and [Cr2(OH)2(C2H2O4)2(OH2)4] 2H2O,
respectively [10, 13].
The thermal analysis of the obtained compounds has been carried out with a
model 1500D derivatograph (MOM, Hungary), in plate-type crucibles, at a heating
rate of 5°C min–1 in static air atmosphere and flowing nitrogen atmosphere of
100 mL min–1. The mass of the samples taken from each compound was 100.00 mg.
There have been studies for the thermal behaviour of both the initial complexes
and the intermediate compounds obtained by heating the glyoxylates at certain tem-
peratures for certain periods of time. The intermediate compounds were stabilized by
cooling in nitrogen in a Ugine–Eyraud balance.
The IR spectra of the synthesised complex combinations, intermediate com-
pounds or end-products have been recorded with a Specord M 80 spectrophotometer
(Carl Zeiss, Jena) in the range 4000–400 cm–1 at room temperature using the KBr pel-
let technique.
J. Therm. Anal. Cal., 72, 2003