- Email: [email protected]
Lanthanide chelates of decan-2,4-dione
J.inorg.nucI.Chem.,1971,Vol. 33,pp. 817to822. PergamonPress. Printedin GreatBritain
LANTHANIDE
CHELATES
OF
DECAN-2,4-DIONE
M. A. G O U V E I A , M. De J E S U S T A V A R E S and R. G. De C A R V A L H O Laborat6rio de Fisica e Engenharia Nucleates, Sacav6m, Portugal (Received 8 April 1970) Abstract--Chelates of eight rare earths with decan-2,4-dione have been prepared. The compounds were characterized by chemical and thermogravimetric analysis. INTRODUCTION
SINCE Urbain's work [ 1] on rare earth acetylacetonates, in 1896, a rather extensive literature has appeared on the/3-diketone chelate complexes of rare earths. Much of it concerns the preparation of the chelates, study of physical and chemical properties, structure, solvates, stability constants of complexes, etc. From a practical point of view, and ignoring some not very successful trials of separations based on/3-diketonate complexes [2, 3], it seems that nowadays three main subjects interest the research workers in this field: laser action of some/3-diketone chelates (namely of Eu and Tb) when dissolved in organic solvents [4], volatility of some diketonates and their fluorine derivatives with the possibility of separations based on gas chromatography [5] and fractional sublimation [6] and solvent extraction separations either with ~-diketones as chelating agent[7] or as nonaqueous solvent [8]. Concerning volatility the more promising lanthanide chelates are the tris compounds. However it has been shown[9] that the lanthanide atoms easily accommodate extra donor groups forming complexes with coordination numbers larger than six. Cunningham et al.[10] concluded from an X-ray crystallographic study of a tris yttrium acetylacetonate that the yttrium ion is 8-coordinated, by bonding to three acetylacetonate tings and two water molecules, with a third water molecule not bonded to the metal: [Y(acac)3(H~O)2] • H20. The presence of these water molecules seems to be the reason for the absence of volatility in some lanthanide chelates, there is evidence of hydrolysis occurring at high temperatures or even at room temperature when the compounds are stored in v a c u o [ 11 ]. As noted by Sievers et al.[5] and experimentally confirmed by theirs and Berg's 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 1 I.
O. Urbain, Bull. Soc. Chim. Fr. [3], 15, 347 (1896). W. Biltz, Annali Chim. 31,349 (1903). M. Lederer, C. r. hebd. S~anc.Acad. Sci. Revs 236, 1557 0953). R. G. Charles and E. P. Riedel, J. inorg, nucl. Chem. 28, 3005 (1966). R. E. Sievers et al., Advances in Chemistry Series Vol. 71, p. 141. American Chemical Society, Washington, D.C. (1967); and literature therein. E.W. Berg and J. J. C. Acosta, A nalytica chim. A cta 40, 101 ( 1968); and literature therein. G. K. Schweitzer and W. Van Willis, Analytica Chim. Acta. 36, 77 (1966); and references therein. T. R. Sweet and H. W. Parlett, Analyt. Chem. 40, 1885 (1968); and references therein, L. R. Melby, N. J. Rose, E. Abramson and J. C. Caris, J. Am. chem. Soc. 86, 5117 (1964). J. A. Cunningham, D. E. Sands and W. F. Wagner, lnorg. Chem. 6, 499 (1967). G . W . Pope, J. F. Steinbach and W. F. Wagner, J. inorg, nucl. Chem. 20, 304 (1961). 817
818
M . A . G O U V E I A , M. De JESUS T A V A R E S and R. G. De C A R V A L H O
work [6], by choosing ligands sufficiently bulky, the steric crowding inhibits the bonding of water molecules and the chelates formed are anhydrous. These authors found all the chelates of fl-diketones with C, or higher, are anhydrous. The substitution of hydrogen by fluorine atoms in the molecule of the ligand tends to produce less hydrated compounds. Many adducts with fl-diketonates and a variety of donor molecules (alcohols, dioxan, pyridines, dimethylformamide, etc.) have been described in the literature. However, it was recently concluded [12] that when water and an organic donor are both present, only the water is coordinated to the lanthanide ion, the organic donor molecules being hydrogen-bonded or held in the crystal by lattice forces. No references were found about the influence of the donor molecule of the adduct, in an anhydrous medium, on the volatility of the compound. Although the tetrakis chelates of lanthanides have not been so extensively studied as the tris compounds, Lippard[l 3] recently prepared a volatile hexafluoroacetylacetonate of yttrium and caesium (Cs[Y(HFA)4]) and other volatile tetrakis chelates of lanthanides and alkali metals were prepared by Belcher et a/.[14]. The/3-diketones most extensively studied have been pentan-, hexan-, heptanand octan-diones and their methyl, benzoyl and fluorinated derivatives. The main purpose of the present work is to prepare and to study the properties of some lanthanide chelates of a fl-diketone with more than C8, in order to compare its behaviour with other chelates already studied. EXPERIMENTAL Synthesis o f decan-2,4-dione (Hdd). The diketone was prepared by a Claisen condensation [ 15, 16]. 100g of Na metal cut in small pieces was placed in a Quickfit three necked flask and absolute ethanol was added dropwise with vigorous stirring until the Na was converted to the white ethoxide. To the gelatinous precipitate were added 750 ml of ethyl acetate. The mixture was stirred during 20 min. Then the reactor was cooled to 0°C in an ice-bath and 250 ml of n-hexyl methyl ketone were added dropwise, during 1 hr, with constant stirring, which was continued for 3 hr at 0°C and for 48 hr at room temperature. Then the same volume of iced water and 283 ml of glacial acetic acid (65 ml acetic acid per mole o f N a ethoxide) were added and stirring continued. The organic phase was separated and washed twice with dilute acetic acid and distilled in a fractionation column, under 15 mm Hg. The main fraction distilled at 108 °- 112°C and a small fraction at 114°-118°C. The gas chromatography of these fractions revealed two close peaks. After two fractional distillations of the first fraction using a 13 cm Vigreux column a colourless liquid (B.P.~5 = 108° - 112°C) was obtained which exhibited only one peak in gas chromatography. I.R. spectrum of this fraction and the agreement of its boiling point with the value given by Weygand[17] (B.P.1a = 108°-112°C) were additional tests of purity. Density at 20°C (d20o= 0-9076) and refractive index (no~°° = 1"4553) were also determined. The yield was 54 per cent. Preparation oftris chelates M(dd)a. All the chelates were prepared by the method cited by Sievers et al.[5]. Lanthanide oxide (1 lmM) was dissolved in conc, HNO3 and the solution was evaporated to dryness. The pH of the solution was adjusted to 5 (pH paper) with 4.26M methanolic NaOH. 33mM of Hdd were dissolved in 20 ml of methanol in a separate funnel and the solution neutralized with 7.75 ml of 4.26M methanolic NaOH. This solution was added dropwise with stirring to the methanolic 12. 13. 14. 15. 16. 17.
M . F . Richardson, W. F. Wagner and D. E. Sands, J. inorg, nucl. Chem. 31, 1417 (1969). S.J. Lippard, J. A m. chem. Soc. 88, 4300 (1966). R. Belcher, J. Majer, R. Perry and W. I. Stephen, J. inorg, nucl. Chem. 31, 471 (1969). J. M. Sprague, L. J. Beckham and H. Adkins, J..4 m. chem. Soc. 56, 2665 (1934). C. D. Hund and C. D. Kelso, J. Am, chem. Soc. 62, 2184 (1940). C. Weygand and H. Baumg~tel, Bet. dtsch, chem. Ges. 62, 578 (1929).
Lanthanide chelates of decan-2,4-dione
819
solution of the lanthanide nitrate. The initial additions produced a precipitate which redissolves with stirring but at the end some precipitate remained undissolved. This suspension was added dropwise with stirring to ca. 400 ml of water. After 2 hr of stirring the fine granules of precipitate were suction filtered through a sintered glass filter and air dried for 1 hr. The whole precipitate was suspended in acetone and filtered. This operation was repeated twice. The precipitate was first air dried for 24 hr and then in vacuo over P205, for 7 days. The chelates were purified by dissolving in the minimum amount of chloroform and precipitating the chelate by addition of acetone. After 24 hr at 0°C the precipitate was filtered and dried in vacuo, over P205, for 24 hr. This operation was repeated twice. Analysis Carbon and hydrogen were determined by elemental analysis. The lanthanides were calculated by the weight of oxide remaining after ignition at 1000°C. Melting points Were determined by a capillary method using a Biichi apparatus. When the compound is heated it softens slowly and suddenly all the solid melts. The temperature at this moment is taken as the melting point. X-ray powder diffraction These patterns were obtained on a Philips diffractometer. Thermogravimetry The thermogravimetric data were obtained on a Ugine-Eyraud (DAM) thermoanalytical balance. The atmosphere was dry nitrogen and the heating rate was kept constant (4°C/min). RESULTS
AND DISCUSSION
From the results of the elemental analysis shown in Table 1, one may conclude that the compounds prepared are anhydrous trischelates. As observed by Newbery et al.[18] the complexes formed by lanthanides and /3-diketones fall in one of the three categories, (a) compounds incorporating hydroxy groups, (b) trischelates, usually solvated, and (c) tetrakischelates with a lanthanide and a univalent ion. R
\// C
I
0-
CH
R'
\/ C
il
0
When using a/3-diketone of the above general formula it is expected that the bulkier are the groups R and R', the more probable are anhydrous chelates. Hence all the rare earth pentan- and hexanedionates described in the literature are hydrated, the heptanedionates prepared by Sievers [5] being the first that are anhydrous. Thus it would be expected, as indeed was verified, that the decanedionates would be anhydrous. The melting points shown in Table 2 are the average of three determinations. As with the melting points of rare earth acetylacetonates [11], heptanedionates and octanedionates [5], a decreasing trend is observed on going from Nd to Lu. 18. M. Ismail, S. J. Lyle and J. E. Newbery, J. inorg, nucl. Chem. 31, 1715 (1969).
820
M.A.
G O U V E I A , M. D e JESUS T A V A R E S and R. G. D e C A R V A L H O Table 1. Analytical data and colour of some rare earth decan-2,4dionates Ln(llI) Ln(IlI)
C
(%)
Colour
H
(%)
(%)
Caled. Found Calcd. Found Caled. Found Nd Sm Gd Tb Ho Er Yb Lu
Blue Beige Beige Beige Beige Pink Beige Beige
22.1 22.9 23.7 23.8 24-5 24.8 25.4 25-6
21-7 22.4 23.7 24.1 25.3 24.6 25-2 26.1
55.3 54.8 54.2 54-1 53.6 53.4 52.9 52-8
55"1 55.5 54.6 54.1 53.9 53.5 53.3 52.9
7.88 7.81 7.73 7.71 7.64 7.62 7.55 7.53
7-95 7.86 7.63 7.55 7-49 7.45 7.46 7.43
Nd x Sm •
IOO Ixe • l l Ov ~
a Gd
W~ v ir
• Tb ,~ Ho
¢.
90
• Er
o Yb • Lu
119
e'
80
O
X,
70 •o "E 60
x
•
B
E
~o x"
so
13
X=
40
30
Theoretical Theoreticol
*
°:'"
Lu2 03 N,d2 0 3
.it v
;~ •
20
I0
I
I00
i
I
200
300
I
i
I
400 500 600 Temperoture,°C
I
700
,i
800
i
900
Fig. 1. Thermogravimetric curves of some rare earth decan-2,4-dionates.
L a n t h a n i d e chelates o f decan-2,4-dione
821
Table 2. Melting points o f some rare earth decan-2,4-dionates
Ln(IlI)
M.P.
(°C) Nd Sm Gd Tb Ho Er Yb Lu
,oo!
p°,, °° °°,~,•
123 +- 1 126.0___0-5 110.5---0"5 117.0_+0.5 110"0+-0"5 112-0_+0.5 118 _+1 96 -- 1
• °,,•°•,°•
M.P. (IIO*C) ;.
90'
80,
70 ,°
.E 60
~
50
•° °° •° •%
4O
Gd (C303)
°•
-. "°• ° %°
30
%°°,°°
Theoretical GdzO 3
....~., .
20
I0
I
I00
I
200
I
300
I
I
400 500 Temperoture, *C
I
600
I
700
I
800
'J
900
Fig. 2. T h e r m o g r a v i m e t r i c curve o f gadolinium decan-2,4-dionate.
The values are lower than all other lanthanide chelates so far reported. X-ray patterns revealed a very low order of cristallinity.
T hermogravimetry All the thermograms present the same pattern.
822
M.A.
G O U V E I A , M. De JESUS T A V A R E S and R. G. De C A R V A L H O
As shown in Fig. 1, from room temperature to 150°C the weight remains constant, which with the analysis data (Table 1) and the absence of the stretching vibrations of the O H in the i.r. spectra [ 19] are conclusive proof of the anhydrous nature of these chelates. Comparing the range of temperature where the weight losses start, with the melting points (Table 2 and arrow in Fig. 2) it is seen that generally the decomposition starts in the liquid phase, which agrees with the findings of Charles and Riedel [4]. In the thermogravimetric curves (Figs. 1 and 2) there are two decomposition regions, one going from 150°C to 280°C, the other from this temperature to about 450°C. At 550°C (Fig. 2) a first step is reached, corresponding to the formula LnC303. After 780°C there is a second step which corresponds to the theoretical weight of the metal oxide. As the oxides found in the final residue were stoichiometrically equivalent to the metals initially used it seems that, at least in the working conditions used, the lanthanide-2,4-dionates are not appreciable volatile. Acknowledgement-The authors wish to express their thanks to Mrs. Margarida Costa from the Instituto Nacional de Investiga~fio Industrial for the elemental analysis. 19. Unpublished results.
LANTHANIDE
CHELATES
OF
DECAN-2,4-DIONE
M. A. G O U V E I A , M. De J E S U S T A V A R E S and R. G. De C A R V A L H O Laborat6rio de Fisica e Engenharia Nucleates, Sacav6m, Portugal (Received 8 April 1970) Abstract--Chelates of eight rare earths with decan-2,4-dione have been prepared. The compounds were characterized by chemical and thermogravimetric analysis. INTRODUCTION
SINCE Urbain's work [ 1] on rare earth acetylacetonates, in 1896, a rather extensive literature has appeared on the/3-diketone chelate complexes of rare earths. Much of it concerns the preparation of the chelates, study of physical and chemical properties, structure, solvates, stability constants of complexes, etc. From a practical point of view, and ignoring some not very successful trials of separations based on/3-diketonate complexes [2, 3], it seems that nowadays three main subjects interest the research workers in this field: laser action of some/3-diketone chelates (namely of Eu and Tb) when dissolved in organic solvents [4], volatility of some diketonates and their fluorine derivatives with the possibility of separations based on gas chromatography [5] and fractional sublimation [6] and solvent extraction separations either with ~-diketones as chelating agent[7] or as nonaqueous solvent [8]. Concerning volatility the more promising lanthanide chelates are the tris compounds. However it has been shown[9] that the lanthanide atoms easily accommodate extra donor groups forming complexes with coordination numbers larger than six. Cunningham et al.[10] concluded from an X-ray crystallographic study of a tris yttrium acetylacetonate that the yttrium ion is 8-coordinated, by bonding to three acetylacetonate tings and two water molecules, with a third water molecule not bonded to the metal: [Y(acac)3(H~O)2] • H20. The presence of these water molecules seems to be the reason for the absence of volatility in some lanthanide chelates, there is evidence of hydrolysis occurring at high temperatures or even at room temperature when the compounds are stored in v a c u o [ 11 ]. As noted by Sievers et al.[5] and experimentally confirmed by theirs and Berg's 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 1 I.
O. Urbain, Bull. Soc. Chim. Fr. [3], 15, 347 (1896). W. Biltz, Annali Chim. 31,349 (1903). M. Lederer, C. r. hebd. S~anc.Acad. Sci. Revs 236, 1557 0953). R. G. Charles and E. P. Riedel, J. inorg, nucl. Chem. 28, 3005 (1966). R. E. Sievers et al., Advances in Chemistry Series Vol. 71, p. 141. American Chemical Society, Washington, D.C. (1967); and literature therein. E.W. Berg and J. J. C. Acosta, A nalytica chim. A cta 40, 101 ( 1968); and literature therein. G. K. Schweitzer and W. Van Willis, Analytica Chim. Acta. 36, 77 (1966); and references therein. T. R. Sweet and H. W. Parlett, Analyt. Chem. 40, 1885 (1968); and references therein, L. R. Melby, N. J. Rose, E. Abramson and J. C. Caris, J. Am. chem. Soc. 86, 5117 (1964). J. A. Cunningham, D. E. Sands and W. F. Wagner, lnorg. Chem. 6, 499 (1967). G . W . Pope, J. F. Steinbach and W. F. Wagner, J. inorg, nucl. Chem. 20, 304 (1961). 817
818
M . A . G O U V E I A , M. De JESUS T A V A R E S and R. G. De C A R V A L H O
work [6], by choosing ligands sufficiently bulky, the steric crowding inhibits the bonding of water molecules and the chelates formed are anhydrous. These authors found all the chelates of fl-diketones with C, or higher, are anhydrous. The substitution of hydrogen by fluorine atoms in the molecule of the ligand tends to produce less hydrated compounds. Many adducts with fl-diketonates and a variety of donor molecules (alcohols, dioxan, pyridines, dimethylformamide, etc.) have been described in the literature. However, it was recently concluded [12] that when water and an organic donor are both present, only the water is coordinated to the lanthanide ion, the organic donor molecules being hydrogen-bonded or held in the crystal by lattice forces. No references were found about the influence of the donor molecule of the adduct, in an anhydrous medium, on the volatility of the compound. Although the tetrakis chelates of lanthanides have not been so extensively studied as the tris compounds, Lippard[l 3] recently prepared a volatile hexafluoroacetylacetonate of yttrium and caesium (Cs[Y(HFA)4]) and other volatile tetrakis chelates of lanthanides and alkali metals were prepared by Belcher et a/.[14]. The/3-diketones most extensively studied have been pentan-, hexan-, heptanand octan-diones and their methyl, benzoyl and fluorinated derivatives. The main purpose of the present work is to prepare and to study the properties of some lanthanide chelates of a fl-diketone with more than C8, in order to compare its behaviour with other chelates already studied. EXPERIMENTAL Synthesis o f decan-2,4-dione (Hdd). The diketone was prepared by a Claisen condensation [ 15, 16]. 100g of Na metal cut in small pieces was placed in a Quickfit three necked flask and absolute ethanol was added dropwise with vigorous stirring until the Na was converted to the white ethoxide. To the gelatinous precipitate were added 750 ml of ethyl acetate. The mixture was stirred during 20 min. Then the reactor was cooled to 0°C in an ice-bath and 250 ml of n-hexyl methyl ketone were added dropwise, during 1 hr, with constant stirring, which was continued for 3 hr at 0°C and for 48 hr at room temperature. Then the same volume of iced water and 283 ml of glacial acetic acid (65 ml acetic acid per mole o f N a ethoxide) were added and stirring continued. The organic phase was separated and washed twice with dilute acetic acid and distilled in a fractionation column, under 15 mm Hg. The main fraction distilled at 108 °- 112°C and a small fraction at 114°-118°C. The gas chromatography of these fractions revealed two close peaks. After two fractional distillations of the first fraction using a 13 cm Vigreux column a colourless liquid (B.P.~5 = 108° - 112°C) was obtained which exhibited only one peak in gas chromatography. I.R. spectrum of this fraction and the agreement of its boiling point with the value given by Weygand[17] (B.P.1a = 108°-112°C) were additional tests of purity. Density at 20°C (d20o= 0-9076) and refractive index (no~°° = 1"4553) were also determined. The yield was 54 per cent. Preparation oftris chelates M(dd)a. All the chelates were prepared by the method cited by Sievers et al.[5]. Lanthanide oxide (1 lmM) was dissolved in conc, HNO3 and the solution was evaporated to dryness. The pH of the solution was adjusted to 5 (pH paper) with 4.26M methanolic NaOH. 33mM of Hdd were dissolved in 20 ml of methanol in a separate funnel and the solution neutralized with 7.75 ml of 4.26M methanolic NaOH. This solution was added dropwise with stirring to the methanolic 12. 13. 14. 15. 16. 17.
M . F . Richardson, W. F. Wagner and D. E. Sands, J. inorg, nucl. Chem. 31, 1417 (1969). S.J. Lippard, J. A m. chem. Soc. 88, 4300 (1966). R. Belcher, J. Majer, R. Perry and W. I. Stephen, J. inorg, nucl. Chem. 31, 471 (1969). J. M. Sprague, L. J. Beckham and H. Adkins, J..4 m. chem. Soc. 56, 2665 (1934). C. D. Hund and C. D. Kelso, J. Am, chem. Soc. 62, 2184 (1940). C. Weygand and H. Baumg~tel, Bet. dtsch, chem. Ges. 62, 578 (1929).
Lanthanide chelates of decan-2,4-dione
819
solution of the lanthanide nitrate. The initial additions produced a precipitate which redissolves with stirring but at the end some precipitate remained undissolved. This suspension was added dropwise with stirring to ca. 400 ml of water. After 2 hr of stirring the fine granules of precipitate were suction filtered through a sintered glass filter and air dried for 1 hr. The whole precipitate was suspended in acetone and filtered. This operation was repeated twice. The precipitate was first air dried for 24 hr and then in vacuo over P205, for 7 days. The chelates were purified by dissolving in the minimum amount of chloroform and precipitating the chelate by addition of acetone. After 24 hr at 0°C the precipitate was filtered and dried in vacuo, over P205, for 24 hr. This operation was repeated twice. Analysis Carbon and hydrogen were determined by elemental analysis. The lanthanides were calculated by the weight of oxide remaining after ignition at 1000°C. Melting points Were determined by a capillary method using a Biichi apparatus. When the compound is heated it softens slowly and suddenly all the solid melts. The temperature at this moment is taken as the melting point. X-ray powder diffraction These patterns were obtained on a Philips diffractometer. Thermogravimetry The thermogravimetric data were obtained on a Ugine-Eyraud (DAM) thermoanalytical balance. The atmosphere was dry nitrogen and the heating rate was kept constant (4°C/min). RESULTS
AND DISCUSSION
From the results of the elemental analysis shown in Table 1, one may conclude that the compounds prepared are anhydrous trischelates. As observed by Newbery et al.[18] the complexes formed by lanthanides and /3-diketones fall in one of the three categories, (a) compounds incorporating hydroxy groups, (b) trischelates, usually solvated, and (c) tetrakischelates with a lanthanide and a univalent ion. R
\// C
I
0-
CH
R'
\/ C
il
0
When using a/3-diketone of the above general formula it is expected that the bulkier are the groups R and R', the more probable are anhydrous chelates. Hence all the rare earth pentan- and hexanedionates described in the literature are hydrated, the heptanedionates prepared by Sievers [5] being the first that are anhydrous. Thus it would be expected, as indeed was verified, that the decanedionates would be anhydrous. The melting points shown in Table 2 are the average of three determinations. As with the melting points of rare earth acetylacetonates [11], heptanedionates and octanedionates [5], a decreasing trend is observed on going from Nd to Lu. 18. M. Ismail, S. J. Lyle and J. E. Newbery, J. inorg, nucl. Chem. 31, 1715 (1969).
820
M.A.
G O U V E I A , M. D e JESUS T A V A R E S and R. G. D e C A R V A L H O Table 1. Analytical data and colour of some rare earth decan-2,4dionates Ln(llI) Ln(IlI)
C
(%)
Colour
H
(%)
(%)
Caled. Found Calcd. Found Caled. Found Nd Sm Gd Tb Ho Er Yb Lu
Blue Beige Beige Beige Beige Pink Beige Beige
22.1 22.9 23.7 23.8 24-5 24.8 25.4 25-6
21-7 22.4 23.7 24.1 25.3 24.6 25-2 26.1
55.3 54.8 54.2 54-1 53.6 53.4 52.9 52-8
55"1 55.5 54.6 54.1 53.9 53.5 53.3 52.9
7.88 7.81 7.73 7.71 7.64 7.62 7.55 7.53
7-95 7.86 7.63 7.55 7-49 7.45 7.46 7.43
Nd x Sm •
IOO Ixe • l l Ov ~
a Gd
W~ v ir
• Tb ,~ Ho
¢.
90
• Er
o Yb • Lu
119
e'
80
O
X,
70 •o "E 60
x
•
B
E
~o x"
so
13
X=
40
30
Theoretical Theoreticol
*
°:'"
Lu2 03 N,d2 0 3
.it v
;~ •
20
I0
I
I00
i
I
200
300
I
i
I
400 500 600 Temperoture,°C
I
700
,i
800
i
900
Fig. 1. Thermogravimetric curves of some rare earth decan-2,4-dionates.
L a n t h a n i d e chelates o f decan-2,4-dione
821
Table 2. Melting points o f some rare earth decan-2,4-dionates
Ln(IlI)
M.P.
(°C) Nd Sm Gd Tb Ho Er Yb Lu
,oo!
p°,, °° °°,~,•
123 +- 1 126.0___0-5 110.5---0"5 117.0_+0.5 110"0+-0"5 112-0_+0.5 118 _+1 96 -- 1
• °,,•°•,°•
M.P. (IIO*C) ;.
90'
80,
70 ,°
.E 60
~
50
•° °° •° •%
4O
Gd (C303)
°•
-. "°• ° %°
30
%°°,°°
Theoretical GdzO 3
....~., .
20
I0
I
I00
I
200
I
300
I
I
400 500 Temperoture, *C
I
600
I
700
I
800
'J
900
Fig. 2. T h e r m o g r a v i m e t r i c curve o f gadolinium decan-2,4-dionate.
The values are lower than all other lanthanide chelates so far reported. X-ray patterns revealed a very low order of cristallinity.
T hermogravimetry All the thermograms present the same pattern.
822
M.A.
G O U V E I A , M. De JESUS T A V A R E S and R. G. De C A R V A L H O
As shown in Fig. 1, from room temperature to 150°C the weight remains constant, which with the analysis data (Table 1) and the absence of the stretching vibrations of the O H in the i.r. spectra [ 19] are conclusive proof of the anhydrous nature of these chelates. Comparing the range of temperature where the weight losses start, with the melting points (Table 2 and arrow in Fig. 2) it is seen that generally the decomposition starts in the liquid phase, which agrees with the findings of Charles and Riedel [4]. In the thermogravimetric curves (Figs. 1 and 2) there are two decomposition regions, one going from 150°C to 280°C, the other from this temperature to about 450°C. At 550°C (Fig. 2) a first step is reached, corresponding to the formula LnC303. After 780°C there is a second step which corresponds to the theoretical weight of the metal oxide. As the oxides found in the final residue were stoichiometrically equivalent to the metals initially used it seems that, at least in the working conditions used, the lanthanide-2,4-dionates are not appreciable volatile. Acknowledgement-The authors wish to express their thanks to Mrs. Margarida Costa from the Instituto Nacional de Investiga~fio Industrial for the elemental analysis. 19. Unpublished results.