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Complexes of two mannose α-amino acid derivatives with zinc and cadmium
Polyhedron Vol. 12, No. 20, pp. 2519-2523. Printed in Great Britain
1993 0
0277-5387/93 $6.00+.00 1993 Pergamon Press Ltd
COMPLEXES OF TWO MANNOSE a-AMINO ACID DERIVATIVES WITH ZINC AND CADMIUM M. A. DiAZ-DiEZ” Departamento
de Quimica Analitica y Electroquimica, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain and
F. J. GARCIA-BARROS, F. J. HIGES-ROLANDO, A. BERNALTE-GARCIA and C. VALENZUELA-CALAHORRO Departamento de Quimica InorgBnica, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain (Received 7 May 1993 ; accepted 3 June 1993)
Abstract-Complexes of zinc(I1) and cadmium(I1) with 2-amino-2-deoxy-D-glycero-D-talo heptonic acid (HMa) and 2-(benzylamino)-2-deoxy-D-glycero-D-tale heptonic acid (BnMa) have been obtained. The complexes were characterized by elemental analysis, IR spectroscopy and X-ray powder diffraction. These complexes have a 1 : 2 metal-to-ligand ratio and an octahedral structure. Coordination occurs through the nitrogen atom of the amino group and oxygen atoms of the bridging carboxylate group. The thermal behaviour of the complexes has also been studied.
Studies of the interactions of carbohydrates and their derivatives with metal ions have increased during the last few years, mainly due to the possible importance of such interactions in a variety of industrial, pharmaceutical and biological processes. ‘,2 The ability of sugar derivatives to sequester metal ions can be utilized for the extraction of metals which are economically important and for the development of new classes of metal-based affinity catalysts. Furthermore, carbohydrates are often highly soluble in water and are usually only weakly immunogenic and of low toxicity. These properties are very useful in developing pharmaceutical agents for the removal of toxic metals or the uptake of essential metals. Finally, the complexation of metal ions by several carbohydrates derivatives is of great interest in view of their biological role, particularly in the availability of nutrients to plants and in the regulation of the flow of metal ions across cell walls. 3 *Author to whom correspondence should be addressed.
It is worth noting that on introduction of a carboxy or amino group (or both) into a sugar molecule the complex-forming ability is enhanced by several orders of magnitude, even in acidic or neutral solution.“6 Our interest in the coordination chemistry of carbohydrate cl-amino acids7-9 prompted us to prepare and characterize the zinc(I1) and cadmium(I1) complexes of 2-amino-2-deoxy-D-glycero-D-talo heptonic acid (HMa) and 2-(benzylamino)-2deoxy-D-glycero-D-talo heptonic acid (BnMa) in order to investigate the mode of attachment of the ligand molecules to the metal ions. The ligands used in this study have the structure shown in Fig. 1. EXPERIMENTAL Preparation
of the ligands and complexes
The ligands 2-amino-2-deoxy-D-glycero-D-talo heptonic acid (HMa) and 2-(benzylamino)-2deoxy-D-glycero-D-talo heptonic acid (BnMa) were prepared according to the method of Galbis et al.”
2519
M. A. DiAZ-DiEZ
2520
YytJH3
HO-rH HO-r-H H-C-Cl-l I
H-C-a-l I Cba-1 I
r”F";j"& m-T-” Ho-r-H H-rOH H-C-Ctl I
obtained through a Philips PW- 1700 diffractometer using Cu-K, radiation. RESULTS
AND DISCUSSION
The analytical data and proposed formulae for the complexes are summarized in Table 1. Analyses for nitrate proved negative.
CH@l II
Fig. 1. Structural formulae of the ligands HMa (I) and BnMa (II).
and recrystallized twice from doubly-distilled water. All the remaining chemicals proved to be sufficiently reliable to be used without further purification. The complexes were synthesized as follows: A freshly prepared aqueous solution of the metal nitrate was added to a hot aqueous solution of the ligand in the metal: ligand stoichiometric ratio of 1 : 2. The pH of the whole solution was then
adjusted at a pH value lower than that of precipitation of the correspondent hydroxide, by dropwise addition of dilute NaOH. When the resulting solutions were stirred during the next few hours and they were either concentrated or cooled, microcrystalline solids were isolated. All compounds were filtered off by suction, washed consecutively with water, ethanol and diethylether, air-dried and stored in Z~UCUO over anhydrous CaCl 2 Apparatus
et al.
and methods
Chemical analysis of carbon, hydrogen and nitrogen were performed by means of microanalytical methods using a Perkin-Elmer 240 microanalyser. The metal content was determined by thermogravimetry. IR spectra were obtained from KBr pellets (4000450 cm- ‘) using a Perkin-Elmer FT-IR 1720 spectrophotometer. Thermoanalytical data were obtained from TG, DTG and DSC curves. These were recorded on a Mettler TA-3000 system provided with a Mettler TG 50 thermobalance and a Mettler DSC 20 differential scanning calorimeter. The atmospheres used were air (flow = 200 cm3 min- ‘) or nitrogen (flow = 200 cm3 min-‘, purity = 99.99% v.v.) for TG and DSC runs. The heating rate was 10°C min- ’ and the weight of the samples was between 3and 13mg. The X-ray powder diffraction patterns were
IR spectra
The bonding sites of the ligands that are involved in coordination with the metal ion have been examined by a careful comparison of the IR spectra of the free ligands and their complexes. Besides, the IR spectra of the complexes have been analysed, paying attention to the bands due to the carboxylate and amino groups. The position in the bands corresponding to the stretching vibrations of these groups can illustrate its coordination to the metal ions, because its energy depends on the degree of symmetry of these groups. The IR spectra of HMa complexes are almost identical, showing their similarity in structure and the type of bonding present. Compared with the spectrum of the free ligand, ’ ’ in the high frequency IR region they show an absorption centred at 3502 [zinc(II) complex] and 3504 cm-’ [cadmium(II) complex], which has been identified as being due to the stretching vibrations in hydroxyl groups with intramolecular hydrogen bonds. Besides, the absorption band observed for HMa at 3124 cm- ’ assigned to the v(NH3+) stretching vibration is absent in the spectra of the complexes, indicating that the amino group participates in the coordination. On the other hand, the asymmetric COO- stretching frequency (v,,& of the amino acids occurs at 158&1660 cm-’ when the group is coordinated to metals. whereas. a non-coordinated COO- group
Table 1. Analytical data [Found (Calc.)] and proposed formulae for the complexes Compound
C(%)
H(%)
N(%)
M(%)
ZnMa,
32.4 (32.7) 30.5 (30.0) 45.6 (46.1) 43.0 (43.3)
5.4 (5.5) 5.1 (5.0) 6.1 (6.1) 5.8 (5.7)
5.3 (5.4) 4.9 (5.0) 3.8 (3.8) 3.6 (3.6)
13.0 (12.7) 19.7 (20.0) 9.2 (8.9) 14.5 (14.5)
CdMa, Zn(BnMa)2*2Hz0 Cd(BnMa),*2H,O
Mannose u-amino acid derivatives with Zn and Cd
2521
quencies, are known in order to decide the coorhas the v,,,,(COG) stretching at lower frequencies.‘2”3 The bands at 1606 [zinc(II) complex] dination behaviour of the carboxylate group. On and 1587 cm-’ [cadmium(II) complex] therefore the basis of these criteria, the carboxylate group indicates that COO- is also coordinating in the coordinates as a bridging bidentate ligand in both complexes. Likewise, coordination of the amino complexes. The presence of the coordinated carboxylate group is supported by the disappearance of the group is supported by similar previous assign- absorption band assigned to N-H bonding with respect to same band in the free ligand. ments14 in the complexes of analogous a-amino In this case the Av values are greater than those acids with zinc(I1) and cadmium(II), in which the observed for HMa complexes. This behaviour is amino group and one oxygen of the carboxylate usual in N-protected amino acids with N-protecting moiety provide a chelate ring in the equatorial plane with carbonyl substituents at axial positions. groups showing an electron-withdrawing effect, It is generally observed that the value of Av cor- because these groups reduce the basicity of the amino group. This implies a weakness of the nitroresponding to (v,,,,,,,- vSym)of the carboxylate group change in the order zinc(I1) > cadmium(I1). In our gen-metal bond and a concomitant increase in the case the same occurs and thus the values are 185 strength of the oxygen-metal bond C-0.. . M, and 178 cm- ’ for the zinc(I1) and cadmium(I1) com- therefore, resulting in greater values.16 plexes, respectively. This could be explained on the From these considerations it could be concluded basis that as the relation charge/ratio decreases for that the coordination behaviour of BnMa in these cadmium(I1) with regard to zinc(I1) the metaloxycompounds is the same as that of HMa. gen bond [C-O.. * M] is weakened and C-O is strengthened and, consequently, Av decreases too. Thermal study With regard to the IR spectra data of the BnMa complexes with zinc(I1) and cadmium(II) it is worth The TG and DSC curves of complexes of the noting that the same criteria : (a) position of v,~~,.,,_same ligand are very similar, which, having in mind (COO-) stretching” and (b) Av difference between the similar molecular structures, also suggests a asymmetric and symmetric carboxylate stretching fre- similar thermal decomposition mechanism. Table 2
Table 2. Thermoanalytical
Complex
Process
ZnMa,
Pyrolysis Combustion of the rest
CdMa,
Pyrolysis Combustion of the rest
Zn(BnMa),*2H,O
Dehydration” Pyrolysis Combustion of the rest
Cd(BnMa),*2H,O
Dehydration” Pyrolysis Combustion of the rest
data of the metal complexes
Temperature (“C)
Weight loss (%)
200-300 (257, endo) 30&500 (355, exo) (484, exo)
43.0
Residue Weight (%) Calc. Found
327 40.6 251 263
2 15-294 (255, endo) 300-550 (450, exo)
39.8
75-160 160-240 (170, 181, endo) 24&520 (486, exo)
4.7 (4.9 talc.) 35.7
6&154 154210 (165, endo) 21&555 (463, exo)
4.7 (4.6 talc.) 23.6
“This step overlaps with the start of the pyrolysis.
AH (J g- ‘) Compound
ZnO
15.8
16.4
Cd0
22.9
22.5
ZnO
11.1
11.5
Cd0
16.4
16.6
330 37.7 529
360 48.1 1057
326 55.1 990
M. A. DiAZ-DiEZ
2522
Table 3. X-ray powder diffraction
do&) 11.55 9.94 7.97
Zn(BnMa) *2Hz0 L,, (A) 11.56 9.95 7.98
et al.
data of Zn(BnMa)z.2H,0
and Cd(BnMa),*2H,O Cd(BnMa) -2H,O &,c (A,
III0
hkl
dabs (A)
14 100 17
020 011 021 031 200 210 040 002,220 012 211 041 022 112,221 230 032 231 051 240 202 151,202 212 042 24i 060 222 250 061 013 052 25i, i6i 023 242, 123 033 260 062,322 213 043 420 4ii 233 053 271 243,43i 172 004 104,024 253 034 082 091 45i 073 442,224 282 092 46i 0100 273 470,083
11.86 10.00 8.07 6.43 6.24 6.03 5.93 5.52 5.37 5.32 5.22 5.00 4.91
II.84 10.00 8.07 6.42 6.24 6.03 5.92 5.52, 5.52 5.37 5.31 5.22 5.00 4.92, 4.92
11 100 13 7 19 2 5 36 7 6 8 19 6
4.52 4.48 4.35 4.29 4.15 4.11 4.06
4.52 4.48 4.35 4.29 4.15 4.12,4.11 4.05
14 6 44 3 29 12 3
3.997 3.948 3.906 3.771 3.715 3.636 3.595 3.567 3.511 3.394 3.333
3.994 3.946 3.914 3.771 3.716 3.634 3.593 3.563, 3.563 3.512 3.397, 3.387 3.333
5 4 3 5 9 3 9 12 3 2 12
3.207 3.152 3.121 3.018 2.972
3.209, 3.208 3.150 3.123 3.015 2.971
8 16 21 3 16
2.907 2.873 2.800
2.904 2.873 2.800, 2.800
17 7 5
2.758 2.687 2.642
2.758 2.688, 2.686 2.639
4 9 7
2.610 2.560 2.532 2.490 2.461 2.409
2.608 2.559 2.531 2.489 2.461, 2.460 2.409
11 8 3 21 11 4
2.386 2.368 2.317
2.385 2.368 2.316
7 12 5
6.26 6.05 5.78 5.51 5.36
6.26 6.04 5.78 5.51, 5.51 5.36
12 1 6 25 9
5.12 4.98 4.91 4.85 4.48
5.12 4.98 4.91, 4.90 4.86 4.48
17 19 7 3 15
4.26
4.27
65
4.16
4.17
24
3.988 3.949 3.853
3.990 3.951 3.854
8 6 14
3.719 3.636
3.720 3.639
4 17
3.540
3.543
15
3.317 3.279
3.317 3.282
9 2
3.159 3.100
3.159 3.101
19 17
2.975 2.945 2.877 2.832
2.975 2.946 2.877 2.829
6 3 11 5
2.770 2.758 2.682 2.627 2.595 2.561 2.502
2.768 2.756 2.684, 2.681 2.625 2.595 2.560 2.503
5 5 3 12 3 13 7
2.458
2.457
34
2.374 2.329
2.375 2.329
24 8
2.314 2.294 2.273
2.313 2.294 2.272, 2.272
7 3 5
z/z0
Mannose
cc-amino acid derivatives
lists the most important features of these diagrams. The TG curves of ZnMa, and CdMa, show an abrupt weight loss which starts at about 200°C and finishes at 300°C; this effect is accompanied by a sharp endothermic effect, at 257°C clearly differentiated in the DSC plots of the complexes ; the relative values of their energies suggest that such pyrolytic processes are similar. The combustion of the remaining sample, in the 30&5Oo”C temperature range, yields the ZnO and Cd0 residues, respectively. The thermal behaviour of the zinc(I1) and cadmium(I1) complexes with BnMa is very similar to that mentioned above for the HMa complexes. The first pyrolytic effect begins at approximately 70°C finishing around 230°C; it is centred at 168°C for both complexes and with very similar energy. However, in the TG plots, especially in the one corresponding to cadmium(II), a shoulder of this first main effect can be observed that incorporates a weight loss of the order 4.7%, corresponding to the loss of two H,O molecules. At temperatures above this first effect, combustion of the sample takes place, finally giving the corresponding oxides that were characterized by IR spectroscopy and X-ray powder diffraction patterns.
X-ray dzflraction The X-ray powder patterns of Zn(BnMa), - 2H20 and Cd(BnMa), - 2H20 (Table 3) show that these compounds are isomorphous and crystallize in the monoclinic system. The systematic extinctions, (OkO) absent for k = odd and (h01) for I = odd, indicate that the most probable space group is P2,/c. The unit cell data were refined by a classical least-squares method, minimizing the x (sin* f30- sin’ 0,)’ expression. The refined parameters are : a = 12.521(4), b = 23.126(4), c = 11.024(2) A ; /i’ = 89.23(3)” ; V = 3192(l) A’ for Zn(BnMa),*2H,O; and a = 12.474(3), b =
with Zn and Cd
2523
23.687(5), c = 11.032(2) 8,; /3 = 89.57(2)‘; V = 3259(l) A” for Cd(BnMa), * 2H,O. The greater volume of the unit cell of Cd(BnMa),* 2H,O is consistent with the greater size of the cadmium(I1) ion compared with the zinc(I1) ion. REFERENCES 1. S. Yano, Coord. Chem. Rev. 1988,92, 113. 2. D. M. Whitfield, S. Stojkovski and B. Sarkar, Coord. Chew Rev. 1993,122, 171. 3. V. Sauchelli, Trace Elements in Agriculture. Van Nostrand Reinhold, New York (1969). 4. D. T. Sawyer, Chem. Rev. 1964,64,633. 5. Z. Tamura and M. Miyazaki, Chem. Pharm. Bull. 1965, 13, 333. 6. G. Micera, S. Deiana, A. Dessi, P. Decock, B. Dubois and H. Kozlowski, Znorg. Chim. Acta 1985, 107,45. M. A. Diaz-Diez, E. 7. C. Valenzuela-Calahorro, Sabio-Rey, F. J. Garcia-Barros and E. Roman Galan, Polyhedron 1992, 11, 563. 8. M. A. Diaz-Diez, F. J. Garcia Barros, E. Sabio Rey and C. Valenzuela Calahorro, J. Znorg. Biochem. 1992,48, 129. 9. M. A. Diaz-Diez, F. J. Garcia Barros, E. Sabio Rey and C. Valenzuela Calahorro, J. Znorg. Biochem., in press. J. C. Palacios and E. Roman, 10. J. A. Galbis, Carbohydr. Res. 1983, 114, 158. de coordination de 11. M. A. Diaz-Diez, Compuestos iones de metales de transition con cc-aminoacidos derivados de Manosa, PhD Thesis. Universidad de Extremadura, Badajoz (1992). M. R. Udupa and G. Ara12. M. Chandrasenkharan, vamudan, Znorg. Chim. Acta 1973, 77, 88. 13. W. Levason and C. A. McAuliffe, Znorg. Nucl. Chem. Lett. 1977, 13, 123. 14. C. A. McAuliffe and W. D. Perry, J. Chem. Sot. 1969,4, 634. 15. L. P. Battaglia, A. Bonamartini Corradi, G. Marcotrigiano, L. Menabue and G. C. Pellacani, J. Am. Chem. Sot. 1980,102,2663. 16. R. Battini, G. G. Battistuzzi, G. Grandi, L. Menabue, G. G. Pellacani, M. Saladini and A. Bonamartini Corradi, J. Chem. Sot., Dalton Trans. 1981, 8, 1665.
1993 0
0277-5387/93 $6.00+.00 1993 Pergamon Press Ltd
COMPLEXES OF TWO MANNOSE a-AMINO ACID DERIVATIVES WITH ZINC AND CADMIUM M. A. DiAZ-DiEZ” Departamento
de Quimica Analitica y Electroquimica, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain and
F. J. GARCIA-BARROS, F. J. HIGES-ROLANDO, A. BERNALTE-GARCIA and C. VALENZUELA-CALAHORRO Departamento de Quimica InorgBnica, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain (Received 7 May 1993 ; accepted 3 June 1993)
Abstract-Complexes of zinc(I1) and cadmium(I1) with 2-amino-2-deoxy-D-glycero-D-talo heptonic acid (HMa) and 2-(benzylamino)-2-deoxy-D-glycero-D-tale heptonic acid (BnMa) have been obtained. The complexes were characterized by elemental analysis, IR spectroscopy and X-ray powder diffraction. These complexes have a 1 : 2 metal-to-ligand ratio and an octahedral structure. Coordination occurs through the nitrogen atom of the amino group and oxygen atoms of the bridging carboxylate group. The thermal behaviour of the complexes has also been studied.
Studies of the interactions of carbohydrates and their derivatives with metal ions have increased during the last few years, mainly due to the possible importance of such interactions in a variety of industrial, pharmaceutical and biological processes. ‘,2 The ability of sugar derivatives to sequester metal ions can be utilized for the extraction of metals which are economically important and for the development of new classes of metal-based affinity catalysts. Furthermore, carbohydrates are often highly soluble in water and are usually only weakly immunogenic and of low toxicity. These properties are very useful in developing pharmaceutical agents for the removal of toxic metals or the uptake of essential metals. Finally, the complexation of metal ions by several carbohydrates derivatives is of great interest in view of their biological role, particularly in the availability of nutrients to plants and in the regulation of the flow of metal ions across cell walls. 3 *Author to whom correspondence should be addressed.
It is worth noting that on introduction of a carboxy or amino group (or both) into a sugar molecule the complex-forming ability is enhanced by several orders of magnitude, even in acidic or neutral solution.“6 Our interest in the coordination chemistry of carbohydrate cl-amino acids7-9 prompted us to prepare and characterize the zinc(I1) and cadmium(I1) complexes of 2-amino-2-deoxy-D-glycero-D-talo heptonic acid (HMa) and 2-(benzylamino)-2deoxy-D-glycero-D-talo heptonic acid (BnMa) in order to investigate the mode of attachment of the ligand molecules to the metal ions. The ligands used in this study have the structure shown in Fig. 1. EXPERIMENTAL Preparation
of the ligands and complexes
The ligands 2-amino-2-deoxy-D-glycero-D-talo heptonic acid (HMa) and 2-(benzylamino)-2deoxy-D-glycero-D-talo heptonic acid (BnMa) were prepared according to the method of Galbis et al.”
2519
M. A. DiAZ-DiEZ
2520
YytJH3
HO-rH HO-r-H H-C-Cl-l I
H-C-a-l I Cba-1 I
r”F";j"& m-T-” Ho-r-H H-rOH H-C-Ctl I
obtained through a Philips PW- 1700 diffractometer using Cu-K, radiation. RESULTS
AND DISCUSSION
The analytical data and proposed formulae for the complexes are summarized in Table 1. Analyses for nitrate proved negative.
CH@l II
Fig. 1. Structural formulae of the ligands HMa (I) and BnMa (II).
and recrystallized twice from doubly-distilled water. All the remaining chemicals proved to be sufficiently reliable to be used without further purification. The complexes were synthesized as follows: A freshly prepared aqueous solution of the metal nitrate was added to a hot aqueous solution of the ligand in the metal: ligand stoichiometric ratio of 1 : 2. The pH of the whole solution was then
adjusted at a pH value lower than that of precipitation of the correspondent hydroxide, by dropwise addition of dilute NaOH. When the resulting solutions were stirred during the next few hours and they were either concentrated or cooled, microcrystalline solids were isolated. All compounds were filtered off by suction, washed consecutively with water, ethanol and diethylether, air-dried and stored in Z~UCUO over anhydrous CaCl 2 Apparatus
et al.
and methods
Chemical analysis of carbon, hydrogen and nitrogen were performed by means of microanalytical methods using a Perkin-Elmer 240 microanalyser. The metal content was determined by thermogravimetry. IR spectra were obtained from KBr pellets (4000450 cm- ‘) using a Perkin-Elmer FT-IR 1720 spectrophotometer. Thermoanalytical data were obtained from TG, DTG and DSC curves. These were recorded on a Mettler TA-3000 system provided with a Mettler TG 50 thermobalance and a Mettler DSC 20 differential scanning calorimeter. The atmospheres used were air (flow = 200 cm3 min- ‘) or nitrogen (flow = 200 cm3 min-‘, purity = 99.99% v.v.) for TG and DSC runs. The heating rate was 10°C min- ’ and the weight of the samples was between 3and 13mg. The X-ray powder diffraction patterns were
IR spectra
The bonding sites of the ligands that are involved in coordination with the metal ion have been examined by a careful comparison of the IR spectra of the free ligands and their complexes. Besides, the IR spectra of the complexes have been analysed, paying attention to the bands due to the carboxylate and amino groups. The position in the bands corresponding to the stretching vibrations of these groups can illustrate its coordination to the metal ions, because its energy depends on the degree of symmetry of these groups. The IR spectra of HMa complexes are almost identical, showing their similarity in structure and the type of bonding present. Compared with the spectrum of the free ligand, ’ ’ in the high frequency IR region they show an absorption centred at 3502 [zinc(II) complex] and 3504 cm-’ [cadmium(II) complex], which has been identified as being due to the stretching vibrations in hydroxyl groups with intramolecular hydrogen bonds. Besides, the absorption band observed for HMa at 3124 cm- ’ assigned to the v(NH3+) stretching vibration is absent in the spectra of the complexes, indicating that the amino group participates in the coordination. On the other hand, the asymmetric COO- stretching frequency (v,,& of the amino acids occurs at 158&1660 cm-’ when the group is coordinated to metals. whereas. a non-coordinated COO- group
Table 1. Analytical data [Found (Calc.)] and proposed formulae for the complexes Compound
C(%)
H(%)
N(%)
M(%)
ZnMa,
32.4 (32.7) 30.5 (30.0) 45.6 (46.1) 43.0 (43.3)
5.4 (5.5) 5.1 (5.0) 6.1 (6.1) 5.8 (5.7)
5.3 (5.4) 4.9 (5.0) 3.8 (3.8) 3.6 (3.6)
13.0 (12.7) 19.7 (20.0) 9.2 (8.9) 14.5 (14.5)
CdMa, Zn(BnMa)2*2Hz0 Cd(BnMa),*2H,O
Mannose u-amino acid derivatives with Zn and Cd
2521
quencies, are known in order to decide the coorhas the v,,,,(COG) stretching at lower frequencies.‘2”3 The bands at 1606 [zinc(II) complex] dination behaviour of the carboxylate group. On and 1587 cm-’ [cadmium(II) complex] therefore the basis of these criteria, the carboxylate group indicates that COO- is also coordinating in the coordinates as a bridging bidentate ligand in both complexes. Likewise, coordination of the amino complexes. The presence of the coordinated carboxylate group is supported by the disappearance of the group is supported by similar previous assign- absorption band assigned to N-H bonding with respect to same band in the free ligand. ments14 in the complexes of analogous a-amino In this case the Av values are greater than those acids with zinc(I1) and cadmium(II), in which the observed for HMa complexes. This behaviour is amino group and one oxygen of the carboxylate usual in N-protected amino acids with N-protecting moiety provide a chelate ring in the equatorial plane with carbonyl substituents at axial positions. groups showing an electron-withdrawing effect, It is generally observed that the value of Av cor- because these groups reduce the basicity of the amino group. This implies a weakness of the nitroresponding to (v,,,,,,,- vSym)of the carboxylate group change in the order zinc(I1) > cadmium(I1). In our gen-metal bond and a concomitant increase in the case the same occurs and thus the values are 185 strength of the oxygen-metal bond C-0.. . M, and 178 cm- ’ for the zinc(I1) and cadmium(I1) com- therefore, resulting in greater values.16 plexes, respectively. This could be explained on the From these considerations it could be concluded basis that as the relation charge/ratio decreases for that the coordination behaviour of BnMa in these cadmium(I1) with regard to zinc(I1) the metaloxycompounds is the same as that of HMa. gen bond [C-O.. * M] is weakened and C-O is strengthened and, consequently, Av decreases too. Thermal study With regard to the IR spectra data of the BnMa complexes with zinc(I1) and cadmium(II) it is worth The TG and DSC curves of complexes of the noting that the same criteria : (a) position of v,~~,.,,_same ligand are very similar, which, having in mind (COO-) stretching” and (b) Av difference between the similar molecular structures, also suggests a asymmetric and symmetric carboxylate stretching fre- similar thermal decomposition mechanism. Table 2
Table 2. Thermoanalytical
Complex
Process
ZnMa,
Pyrolysis Combustion of the rest
CdMa,
Pyrolysis Combustion of the rest
Zn(BnMa),*2H,O
Dehydration” Pyrolysis Combustion of the rest
Cd(BnMa),*2H,O
Dehydration” Pyrolysis Combustion of the rest
data of the metal complexes
Temperature (“C)
Weight loss (%)
200-300 (257, endo) 30&500 (355, exo) (484, exo)
43.0
Residue Weight (%) Calc. Found
327 40.6 251 263
2 15-294 (255, endo) 300-550 (450, exo)
39.8
75-160 160-240 (170, 181, endo) 24&520 (486, exo)
4.7 (4.9 talc.) 35.7
6&154 154210 (165, endo) 21&555 (463, exo)
4.7 (4.6 talc.) 23.6
“This step overlaps with the start of the pyrolysis.
AH (J g- ‘) Compound
ZnO
15.8
16.4
Cd0
22.9
22.5
ZnO
11.1
11.5
Cd0
16.4
16.6
330 37.7 529
360 48.1 1057
326 55.1 990
M. A. DiAZ-DiEZ
2522
Table 3. X-ray powder diffraction
do&) 11.55 9.94 7.97
Zn(BnMa) *2Hz0 L,, (A) 11.56 9.95 7.98
et al.
data of Zn(BnMa)z.2H,0
and Cd(BnMa),*2H,O Cd(BnMa) -2H,O &,c (A,
III0
hkl
dabs (A)
14 100 17
020 011 021 031 200 210 040 002,220 012 211 041 022 112,221 230 032 231 051 240 202 151,202 212 042 24i 060 222 250 061 013 052 25i, i6i 023 242, 123 033 260 062,322 213 043 420 4ii 233 053 271 243,43i 172 004 104,024 253 034 082 091 45i 073 442,224 282 092 46i 0100 273 470,083
11.86 10.00 8.07 6.43 6.24 6.03 5.93 5.52 5.37 5.32 5.22 5.00 4.91
II.84 10.00 8.07 6.42 6.24 6.03 5.92 5.52, 5.52 5.37 5.31 5.22 5.00 4.92, 4.92
11 100 13 7 19 2 5 36 7 6 8 19 6
4.52 4.48 4.35 4.29 4.15 4.11 4.06
4.52 4.48 4.35 4.29 4.15 4.12,4.11 4.05
14 6 44 3 29 12 3
3.997 3.948 3.906 3.771 3.715 3.636 3.595 3.567 3.511 3.394 3.333
3.994 3.946 3.914 3.771 3.716 3.634 3.593 3.563, 3.563 3.512 3.397, 3.387 3.333
5 4 3 5 9 3 9 12 3 2 12
3.207 3.152 3.121 3.018 2.972
3.209, 3.208 3.150 3.123 3.015 2.971
8 16 21 3 16
2.907 2.873 2.800
2.904 2.873 2.800, 2.800
17 7 5
2.758 2.687 2.642
2.758 2.688, 2.686 2.639
4 9 7
2.610 2.560 2.532 2.490 2.461 2.409
2.608 2.559 2.531 2.489 2.461, 2.460 2.409
11 8 3 21 11 4
2.386 2.368 2.317
2.385 2.368 2.316
7 12 5
6.26 6.05 5.78 5.51 5.36
6.26 6.04 5.78 5.51, 5.51 5.36
12 1 6 25 9
5.12 4.98 4.91 4.85 4.48
5.12 4.98 4.91, 4.90 4.86 4.48
17 19 7 3 15
4.26
4.27
65
4.16
4.17
24
3.988 3.949 3.853
3.990 3.951 3.854
8 6 14
3.719 3.636
3.720 3.639
4 17
3.540
3.543
15
3.317 3.279
3.317 3.282
9 2
3.159 3.100
3.159 3.101
19 17
2.975 2.945 2.877 2.832
2.975 2.946 2.877 2.829
6 3 11 5
2.770 2.758 2.682 2.627 2.595 2.561 2.502
2.768 2.756 2.684, 2.681 2.625 2.595 2.560 2.503
5 5 3 12 3 13 7
2.458
2.457
34
2.374 2.329
2.375 2.329
24 8
2.314 2.294 2.273
2.313 2.294 2.272, 2.272
7 3 5
z/z0
Mannose
cc-amino acid derivatives
lists the most important features of these diagrams. The TG curves of ZnMa, and CdMa, show an abrupt weight loss which starts at about 200°C and finishes at 300°C; this effect is accompanied by a sharp endothermic effect, at 257°C clearly differentiated in the DSC plots of the complexes ; the relative values of their energies suggest that such pyrolytic processes are similar. The combustion of the remaining sample, in the 30&5Oo”C temperature range, yields the ZnO and Cd0 residues, respectively. The thermal behaviour of the zinc(I1) and cadmium(I1) complexes with BnMa is very similar to that mentioned above for the HMa complexes. The first pyrolytic effect begins at approximately 70°C finishing around 230°C; it is centred at 168°C for both complexes and with very similar energy. However, in the TG plots, especially in the one corresponding to cadmium(II), a shoulder of this first main effect can be observed that incorporates a weight loss of the order 4.7%, corresponding to the loss of two H,O molecules. At temperatures above this first effect, combustion of the sample takes place, finally giving the corresponding oxides that were characterized by IR spectroscopy and X-ray powder diffraction patterns.
X-ray dzflraction The X-ray powder patterns of Zn(BnMa), - 2H20 and Cd(BnMa), - 2H20 (Table 3) show that these compounds are isomorphous and crystallize in the monoclinic system. The systematic extinctions, (OkO) absent for k = odd and (h01) for I = odd, indicate that the most probable space group is P2,/c. The unit cell data were refined by a classical least-squares method, minimizing the x (sin* f30- sin’ 0,)’ expression. The refined parameters are : a = 12.521(4), b = 23.126(4), c = 11.024(2) A ; /i’ = 89.23(3)” ; V = 3192(l) A’ for Zn(BnMa),*2H,O; and a = 12.474(3), b =
with Zn and Cd
2523
23.687(5), c = 11.032(2) 8,; /3 = 89.57(2)‘; V = 3259(l) A” for Cd(BnMa), * 2H,O. The greater volume of the unit cell of Cd(BnMa),* 2H,O is consistent with the greater size of the cadmium(I1) ion compared with the zinc(I1) ion. REFERENCES 1. S. Yano, Coord. Chem. Rev. 1988,92, 113. 2. D. M. Whitfield, S. Stojkovski and B. Sarkar, Coord. Chew Rev. 1993,122, 171. 3. V. Sauchelli, Trace Elements in Agriculture. Van Nostrand Reinhold, New York (1969). 4. D. T. Sawyer, Chem. Rev. 1964,64,633. 5. Z. Tamura and M. Miyazaki, Chem. Pharm. Bull. 1965, 13, 333. 6. G. Micera, S. Deiana, A. Dessi, P. Decock, B. Dubois and H. Kozlowski, Znorg. Chim. Acta 1985, 107,45. M. A. Diaz-Diez, E. 7. C. Valenzuela-Calahorro, Sabio-Rey, F. J. Garcia-Barros and E. Roman Galan, Polyhedron 1992, 11, 563. 8. M. A. Diaz-Diez, F. J. Garcia Barros, E. Sabio Rey and C. Valenzuela Calahorro, J. Znorg. Biochem. 1992,48, 129. 9. M. A. Diaz-Diez, F. J. Garcia Barros, E. Sabio Rey and C. Valenzuela Calahorro, J. Znorg. Biochem., in press. J. C. Palacios and E. Roman, 10. J. A. Galbis, Carbohydr. Res. 1983, 114, 158. de coordination de 11. M. A. Diaz-Diez, Compuestos iones de metales de transition con cc-aminoacidos derivados de Manosa, PhD Thesis. Universidad de Extremadura, Badajoz (1992). M. R. Udupa and G. Ara12. M. Chandrasenkharan, vamudan, Znorg. Chim. Acta 1973, 77, 88. 13. W. Levason and C. A. McAuliffe, Znorg. Nucl. Chem. Lett. 1977, 13, 123. 14. C. A. McAuliffe and W. D. Perry, J. Chem. Sot. 1969,4, 634. 15. L. P. Battaglia, A. Bonamartini Corradi, G. Marcotrigiano, L. Menabue and G. C. Pellacani, J. Am. Chem. Sot. 1980,102,2663. 16. R. Battini, G. G. Battistuzzi, G. Grandi, L. Menabue, G. G. Pellacani, M. Saladini and A. Bonamartini Corradi, J. Chem. Sot., Dalton Trans. 1981, 8, 1665.