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Spectral and magnetic properties of phenylazo-6-aminouracil complexes
Spectrochimica Acta Part A 60 (2004) 77–87
Spectral and magnetic properties of phenylazo-6-aminouracil complexes Mamdouh S. Masoud a,∗ , Saeda A. Abou El-Enein b , Mohamed E. Ayad b , Ahmed S. Goher b a b
Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt Chemistry Department, Faculty of Science, Minufiya University, Shebin El-Kome, Egypt Received 6 January 2003; accepted 17 March 2003
Abstract Complexes of CoII , NiII and CuII with substituted phenylazo-6-aminouracils containing (-H, p-OH, p-CH3 , p-OCH3 p-COOH) have been synthesized and characterized by elemental analysis, magnetic measurements and spectral measurements (IR, UV–Vis, ESR). Infrared spectra assigned the fundamental bands of the major groups, O–H, N–H, C–H, C=O, C=N, N=N, C–N and C–O (, ␦ and ␥ modes of vibrations). The absence of OH and the appearance of C=O in the infrared spectra of the free ligands of 5-(p-tolyl and p-anisylazo)-6-aminouracil, assigned the keto structure, whereas in cases of 5-(phenyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracil ligands, the data showed strong OH and C=O bands to assign keto–enol tautomerisms. The modes of interactions between the ligands and the metals were discussed, where oxygen and nitrogen atoms (of amino–amide groups) are involved in chelation. The azo group was not involved in chelation for all the prepared complexes except those of copper complexes derived from 5-(phenyl, p-tolyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracils. The room temperature effective magnetic moment values, the Nujol mull spectra and ESR proved that all the prepared complexes were of octahedral geometry, except the nickel complex derived from 5-(phenylazo)-6-aminouracil and cobalt complex derived from 5-(p-carboxy-phenylazo)-6-aminouracil were square planar. © 2003 Elsevier B.V. All rights reserved. Keywords: Spectra; Magnetism; Structures; Complexes; Azouracil
1. Introduction Barbiturates display a wide variety of responses in the body depending on the nature of substituted groups [1–4]. The properties vary from simple sedation to hypnosis, probably due to the susceptibility of the acidic hydrogen to rapid metabolic attack and subsequent degradation of the compounds within the body [5–8]. In our laboratory [9–43], much work has been carried out on the chemistry of such important biological pyrimidine compounds. In this paper, the interest is focused to study the chelating properties of 6-aminouracils and their azo compounds based on elemental analysis, magnetic moments, spectral methods (UV–Vis, IR) and ESR for copper complexes. 2. Experimental The azo compounds (I) were prepared by the usual diazotization process [44] of 6-aminouracil. ∗
Corresponding author. E-mail address: [email protected] (M.S. Masoud).
1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00226-9
The amines used were aniline, p-aminophenol, p-touldine, p-anisidine and p-carboxy aniline. The following abbreviations are given for the compounds under investigation: 5-(phenylazo)-6-aminouracil (H2 L1 ), 5-(p-hydroxyphenylazo)-6-aminouracil (H2 L2 ), 5-(p-tolylazo)-6-aminouracil (H2 L3 ), 5-(p-anisylazo)-6-aminouracil (H2 L4 ), 5-(p-carboxy phenylazo)-6-aminouracil (H2 L5 ). Eighteen transition metal (CoII , NiII and CuII ) complexes of the stoichiometries 1:1, 1:2, 1:3 and 2:3 (M:L ratio) were prepared and analyzed. All the complexes were prepared in a similar way as follows: 0.01 mol of the metal chloride salt in 50 ml ethanol was added to 0.02 mol of the ligand in presence of 50 ml ethanol. The reaction mixture was refluxed for 2 h. The complex was filtered off, washed several times with water–ethanol and dried in a vacuum desiccator over CaCl2 for 1 day. The preparation of
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Table 1 Color, elemental analysis, Nujol mull electronic absorption spectra (max , nm) and the room temperature effective magnetic moment values (eff , 298 K) Compound
Color
% Calculated (% found)
H2 L1 Co–H2 L1 Ni–H2 L1 Cu–H2 L1 H 2 L2 Co–H2 L2 Ni–H2 L2 Cu–H2 L2 H 2 L3 Co–H2 L3 Ni–H2 L3 Cu–H2 L3 H 2 L4 Co–H2 L4 Ni–H2 L4 Cu–H2 L4 H 2 L5 Co–H2 L5 Ni–H2 L5 Cu–H2 L5
Yellow Brown Orange Brown Brown Brown Brown Brown Yellow Yellowish–green Yellow Grey Brown Brown Orange Brown Yellow Orange Orange Brown
52.0 39.5 44.8 42.4 48.6 38.1 41.1 34.2 53.9 43.1 48.9 40.5 50.6 41.6 38.3 42.6 48.0 36.8 37.7 39.8
C
H (51.9) (39.4) (44.5) (42.6) (48.5) (38.0) (41.2) (34.0) (53.8) (43.2) (48.8) (40.4) (50.4) (41.5) (38.3) (42.8) (47.9) (36.8) (37.7) (39.5)
3.9 3.9 3.6 3.9 3.7 3.5 3.1 4.7 4.5 4.9 4.1 5.2 4.2 3.7 4.2 5.3 3.3 3.6 4.1 4.2
N (3.9) (4.1) (3.4) (4.1) (3.6) (3.4) (3.2) (4.5) (4.3) (4.9) (3.9) (5.5) (4.2) (3.5) (4.2) (5.1) (3.2) (3.6) (4.0) (4.2)
30.3 22.7 25.5 24.1 28.3 22.2 24.0 14.2 28.6 22.9 25.9 21.5 26.8 22.1 20.4 17.1 25.4 17.9 16.9 18.6
(30.2) (22.7) (25.4) (24.0) (28.1) (22.4) (24.0) (13.8) (28.5) (22.7) (26.0) (21.5) (26.7) (22.2) (20.4) (17.0) (25.3) (17.8) (16.9) (18.5)
M
Cl
– 12.7 (12.6) 10.7 (10.6) 10.9 (10.9) – 12.5 (12.3) 13.4 (13.5) 12.9 (12.7) – 6.4 (6.5) 7.2 (7.3) 6.5 (6.3) – 12.4 (12.3) 8.5 (8.4) 7.8 (7.8) – 15.1 (15.2) 14.2 (14.1) 8.4 (8.3)
– – – – – – – 14.4 (14.2) – – – – – – 5.2 (5.0) 8.5 (8.6) – – – –
eff 298 K
max (nm)
– 4.9 Diamagnetic 2.52 – 5.2 3.12 2.82 – 5.5 3.15 2.8 – 4.6 3.21 1.54 – 2.5 3.22 0.5
– 407, 586, 864, – 423, 583, 583, – 652, 469, 435, – 401, 517, 507, – 468, 517, 436,
357, 318 435, 316 545, 415, 390 323, 276, 231 841, 413, 393, 316, 270 503, 432, 318 484, 416, 279, 237 412, 287, 600 409, 401, 312 296, 279, 244 440, 401, 310, 280, 245 403, 309, 274, 238 410, 354, 322, 276 413, 257, 283 315, 286, 253, 218
All the complexes are with m.p. > 300 ◦ C.
5-(phenylazo)-6-aminouracil complexes were prepared in an ammoniacal-ethanolic medium. The C, H and N analytical data of the compounds, (Table 1) were carried out at the central microanalytical laboratory, Chemistry Departments, Faculties of Sciences, Cairo and Alexandria Universities. The metal contents were determined by EDTA complexometric titration [45] and atomic absorption technique. Spectrophotometric measurements were recorded on a UV–Vis double beam spectrophotometric—ratio recording Microcomputer Control, Model Lambda 4B, Perkin Elmer covering the wavelength range 190–850 nm. The spectra of the ligands solutions at different pHs (2–12) were carried out. The electronic absorption spectra of the solid complexes were measured in Nujol mull following the method described by Lee et al. [46]. The KBr infrared spectra of the ligands and their metal complexes were recorded using Infrared Spectrophotometer Model 1430 Perkin Elmer, covering the range 4000–200 cm−1 .
3. Results and discussion 3.1. Stereochemistry of the metal complexes 3.1.1. Cobalt complexes The analytical data, (Table 1) gave that the cobalt complexes separated from—(phenyl, p-anisyl and p-hydroxyphenylazo)-6-aminouracils are with mol ratio 2Co:3L to give Co2 (HL)2 L·nH2 O·mC2 H5 OH, where n=6, 3, 5, m=0.25, 0 and 0, respectively. However, the complexes of (p-tolyl and p-carboxyphenylazo)-6-aminouracils are with the formula Co(HL)2 H2 L·7H2 O (1:3) and CoL·2H2 O·0.5C2 H5 OH (1:1), respectively. The Nujol mull electronic absorption spectra
revealed that the complexes of phenyl, anisyl, tolyl and hydroxy ligands have maximum electronic spectral bands at 407, 401, 484 and 423 nm with magnetic moment values 4.9, 4.6, 5.5 and 5.2 B.M., respectively, consistent with the octahedral and pseudo octahedral structures [47]. However, the 5-(p-carboxyphenylazo)-6-aminouracil cobalt complex has Nujol mull spectral bands at 468 (w.b) and 410 (s) nm with eff of 2.52 B.M., to assign square planar structure [48]. 3.1.2. Nickel complexes The analytical data, (Table 1) revealed that these complexes are with the mole ratios 1:1, 1:1, 1:2, 1:3 and 2:3 from 5-(p-carboxyphenyl, phenyl, p-anisyl, p-tolyl and p-hydroxyphenylazo)-6-aminouracil, respectively. The Nujol mull electronic spectral features gave doublet bands in the wavelength range 401–496 and 517–583 nm due to 3 A2g →3 T1g (p) and 3 A2g →3 T1g transitions, respectively, gathered with magnetic moment values (3.15–3.22 B.M.) to assign a high spin octahedral structure [49]. The slightly higher eff values above that for the spin-orbit only arises from slight mixing of multiplet excited state in which spin-orbit coupling is appreciable [50]. However, the Nujol mull electronic spectra of the diamagnetic nickel 5-(phenylazo)-6-amino-uracil complex showed bands at 435 (w.b) and 586 (b) nm due to 3 A2g →3 T1g (p) and 3 A →3 T 2g 1g transitions in a square planar geometry [51], respectively. The strong band at 316 nm is due to n–* transition. 3.1.3. Copper complexes The analytical data, (Table 1) gave 1Cu:2L mol ratio for the complexes separated from 5-(phenyl, p-anisyl and p-carboxyphenylazo)-6-aminouracil compounds with
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formula: Cu(HL)2 ·0.5H2 O·0.25C2 H5 OH, Cu(H2 L)2 ·2Cl· 3.5C2 H5 OH and Cu(HL)2 ·4H2 O·1.5C2 H5 OH, respectively. However, the copper(II) complex of the p-hydroxyphenylcompound in the 1Cu:1L mol ratio, (Table 1) of the formula: Cu(H2 L)·H2 O·2C2 H5 OH·2Cl. In a similar way, the copper(II) of 5-(p-tolylazo) 6-aminouracil compound having the formula Cu(HL)2 ·H2 L·10H2 O. The Nujol mull electronic absorption spectra of copper complexes; display the spectral bands at 309–390, 409–451, 503–583, 683 and 864 nm. The first band assigned to intraligand charge transfer transition [50]. The latter four bands are due to complex formation. The fourth and fifth spectral bands appeared only in the 5-(phenylazo)-6-aminouracil copper complexes, of a square pyramidal or distorted octahedral configuration of the transition 2 Eg →2 T2g (D) [51,52]. The prepared copper complexes
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derived from p-anisyl- and p-hydroxyphenyl-compounds gave weak bands centered at 507, 583 and 503 nm with the presence of strong bands at 403 and 432 nm referring to the d–d transition of CuII in a tetragonal field [51,52]. The p-tolyl- and p-carboxyphenyl–copper complexes showed very weak bands at 401, 409, 435 and broad band at 436 nm, respectively, to typify d–d transition of copper complex in a tetragonal distorted octahedral geometry about CuII ion. The magnetic moment values of all the prepared copper complexes are in the range 2.3–2.86 B.M., while those of p-anisyl and p-carboxy-compounds are with eff 1.54 and 0.5 B.M., respectively. The higher value is probably assigned to the absence Cu–Cu interaction and due to the creation of highly positive centers, e.g. in the form of alloyed structures. The lower values less than the spin only
Table 2 Fundamental infrared bands (cm−1 ) of 5-(phenylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3420 (b) 3350 (w) 3280 (w) 3190 (w) 3100 (w) 3040 (sh.w) 2960 (v.w) 2780 (v.w) 1785 (w) 1735 (s.sh) 1720 (w) 1650 (v.s) – 1585 (m) 1540 (v.w) 1505–1495 (m) 1450 (s) (b) 1420 (s) (b) 1370 (m.sh) 1330 (sh), 1320 (w) 1300 (sh.s) 1260 (sh.s) – – 1175 (v.w) 1150 (w) 1080 (s) – 1010 (v.w) 990 (v.w) 910 (m.sh) 875 (w.sh) 850 (w.sh) 810 (s) 755 (s.sh) 710 (w) 680 (s) 650 (w) 630 (w) 610 (v.w) 515 (m) (sp) 495 (m) (sp) 410 (s)
3430 (b) 3320 (v.w) 3200 (v.w) – – 3060 (w) 2910 (v.w.sh) – – 1720 (w) 1710 (w) 1665 (w) 1620 1590 (w) 1540, 1530 (w.sp) 1485 (s), 1500 (sh.w) 1450 (w) 1415 (m.b) 1360 (v.w) – 1280 (v.s) 1280 (sh.w) 1240 (sh.w) 1210 (sh.w) 1160 (sp) 1150, 1135 (sp) 1070 (v.w) – 1020 (v.w) 1000 900 (v.w) – 830 (v.w) – 755 (s.sh) – 690 (s.sh) 670 (w.sh) 655 (w.sh) 570 (v.w) 500 (m.sh)
3440 (b) 3300 (w) – 3150 (v.w, b) 3110 (w.b) 3000 2920 (v.w) 2800 (sh) – 1735 (s.sh) 1695 (v.w) 1630 ( m) – 1600 (m) 1545, 1535, 1525 1510 (w), 1495, 1475 1450 (w) 1415 (w), 1390 1390 – 1300 (m) 1270 (d) 1250 (d) 1205 (d) 1160 (sp.w) 1120 (sp.w) 1070 (v.w) 1040–1020 (sp) – 995 (w) 950 (w) 880 (v.w) – 825 (b) 755 (s.sh) 705 (w) 680 (v.w) 660 (v.w) – 560 (v.w) 520 (sp) 500 (sp) 440 (b)
3420 (b) 3300 (m) – 3160 (sh.w) 3100 (b) 3000 2920 (w.sh) 2840 (b.w) – 1735 (s.sh) – 1640 (s) – 1595 (s) 1545, 1550 (sp.w) 1490, 1475 (v.w.sp) 1420 (w) 1415 (v.w) 1380 (sh) – 1300 (m.sh) 1270 (sp.s) 1240 (sp.s) 1205 (sp.s) 1165 (w) 1140 (w) 1070 (v.w) 1040 (w.sh) 1020 995 (w) 950 (w.sh) – – 825 (b)765 (s.sh) 700 (s) 680 (v.w) 640 (sh) – 570 (s) 510 (sp) 493 (sp) 435 (sh)
OH NH of amino NH of amino NH of amide NH of amide NH in H.b amide, CH of aryl NH in H.b amide, CH of aryl
430 (w.b)
C=O C=O ␦NH of amino C=N C=N ␦NH amide ␦NH amide N=N N=N C–N amide ␦OH ␦OH C–N of amino C–N of amino C–N of amino C–OH C–OH C–OH C–OH Ring vibration Ring vibration ␥–OH ␥–OH ␥N–H (amino) ␥N–H (amino) ␥N–C=O ␥N–C=O ␥C–OH ␥C–OH NH (amino) NH (amino) NH of amide
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder; (h.b) hydrogen bonded.
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value (1.73 B.M) indicate magnetic exchange interaction between adjacent CuII . 3.2. Infrared spectra of the metal complexes The infrared spectra of the free 5-(phenylazo)-6-aminouracil ligand and its complexes, Table 2, gave that the ligand gave strong and weak carbonyl bands at 1735 and 1720 cm−1 . The first one is unaffected on complexation with NiII and CuII and is shifted to 1720 cm−1 with CoII . The second one disappeared in copper complex and shifted to lower frequency (1710 and 1695 cm−1 ) in presence of CoII and NiII , respectively. The ligand bands at {1330 (sh), 1320 (w), 1300 (s)} and {910 (m), 875 (w), 850 (w) cm−1 } assigned to ␦OH and ␥OH , respectively [53]. These bands are absent and shifted to lower frequencies, respectively, on complexation with CoII . However, the first and second ␦OH ligand bands are disappeared, while the third one still remains at the same positions in NiII and CuII complexes. The ␥OH ligand at 910 cm−1 shifted to 950 cm−1 in CuII and NiII complexes, while the ligand bands at 875 and 850 cm−1 are absent in the CuII complex and the second one is absent in NiII complex. The and ␥ C–OH bands of free ligand at {1150 (w), 1080 (s)} and {650 (w), 630 (w)} cm−1 are strongly affected on complexation in their shapes and positions [53,54]. The weakly broad OH ligand band at 3420 cm−1 is shifted to lower frequency by chelation. However, the free ligand exhibits bands at 3350 (w), 3280 (w); 1650 (s); 810 (s), 515 (m) and 495 (m) cm−1 [55], due to different modes of vibrations of NH2 group, namely , ␦, ␥ and . On complexation, these bands show the following remarks: (i) the first NH (amino) band becomes more distinctive and shifted to 3300 cm−1 in CuII and NiII complexes. The second NH (amino) is absent in copper(II) and nickel(II) complexes. Meanwhile, such region in cobalt(II) complex appeared at lower frequency with a very weak feature overlapped with OH band in a broad feature. The presence of six water molecules explained such broadness; (ii) the ␦NH (amino) ligand band is shifted from its position and changed in appearance by complexation; (iii) the ␥NH (amino) of ligand is shifted by 15 cm−1 with some broadening in case of copper and nickel complexes. In case of the cobalt complex, this band is absent. So, the NH2 group is of great importance on chelation with CoII rather than NiII and CuII . The appearance of broad bands, at 2840 and 2800 cm−1 in copper(II) and nickel(II) complexes are due to strongly associated hydrogen bonded complexes. The two weak NH (amide) ligand bands are at 3190 and 3100 cm−1 . The first one is shifted to lower frequency with very weak feature in nickel(II) and copper(II) complexes. The second one is unaffected and shifted to 3110 cm−1 in copper(II) and nickel(II) complexes, respectively, and becomes more sharp. However, the NH (amide) ligand bands disappeared in cobalt complexes due to its existence in the enol form. This is established by the presence of the broad band at 1620 cm−1 due to C=N in cobalt spectrum. The ␦NH (amide) ligand bands changed in their positions and shapes by complex-
ation. More support for the contribution of the nitrogen atom of the amide group of the ligand on chelation, where strong ␥(N–C=O) [56] and NH band appeared at {710 (w), 680 (s)} and 410 (s) cm−1 , respectively. The latter band is shifted to higher frequency in all complexes. The ␥(N–C=O) bands changed only in their positions in nickel(II) complex. In the copper complex, the first band is shifted to lower frequency by 10 cm−1 and the second band is unaffected. In the cobalt complex, the first band is absent and the second one is shifted to higher frequency. The strong ligand azo group bands at 1450 and 1420 cm−1 are shifted from their positions by (30 and 5 cm−1 ) accompanied with a weak appearance, in copper complex and unaffected in both cobalt(II) and nickel(II) complexes. So, the azo group is involved in the structural configuration with CuII rather than NiII and CoII . The 2:3 cobalt complex derived from 5-(phenylazo)-6-aminouracil exists as octahedral geometry, where two ligands of these are of tridentate, while the third is tetradentate attachment. The mainly groups used for chelation with cobalt(II) are OH, NH of (amino and amide groups). The square planar and distorted octahedral 1:2 nickel and copper complexes, respectively, are assigned. The ligand bounds to the metal via bidentate attachment OH and NH (amide). The infrared spectra showed that the azo group takes place in chelation with CuII . The following structures are given as follows:
The absence of OH and the appearance of C=O (1805, 1750 cm−1 ) and C–OH (1170, 1145 cm−1 ) in the infrared spectra of 5-( p-tolylazo)-6-aminouracil, (Table 3) assigned
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Table 3 Fundamental infrared bands (cm−1 ) of 5-(p-tolylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3430 (b) 3180 (b) 3020 (v.w) 2920 (w.sh) 2850 (w.sh) 2800 (w.sh) 1805 (w) 1750 (s) 1625 (s) 1535 (s) 1490 (sh) 1455 (m) 1410 (s) 1395 (v.w.sh) 1300 (w.b) 1260–1275 (b) 1215 (s) 1170 (v.w) (sp) 1145 (v.w) (sp) 1105 (mb) – 1020 (m) 825 (s) 760 (s) 675 (w) 635 (b) 535 (s) 470 (m) – –
3440–3330 (b.sh) 3210 (s) 3020 (sh) 2920 (sh) 2850 (sh) 2780 (w) 1805 (w) 1740 (s) 1625 (s) 1530 (s) 1495 (sh.w) 1450 (s) 1410 (sp.s) 1390 (sp.s) 1315 (w) 1305 (w) 1260–1270 (w.b) 1210 (m) 1165 (sp) (w) 1145 (sp) (w) 1100 (m) – 1020 (m) 815 (s) 760 (m) 680 (m) 625 (b) 530 (s) 475 (m) 410 –
3460–3320 (b.sh) – – – – – 1805 (w) – – 1530 (s) 1495 (sh.w) 1450 (s) 1415 (sp.s) 1390 (sp.s) 1305 (w) 1260–1270 (b.s) 1215 (s) 1165 (w.sp) 1145 (w.sp) 1100 (m) – 1020 (m) 820 (s) 760 (m) 680 (m) 625 (b) 530 (s) 475 (m) 415 –
3400 (m) – 3010 (sh) 2950, 2900 2830 (w) 2750 (sh.w) – 1705 (m) 1625 (m), 1570 (w) 1525 (w) 1500 (v.w.sh) 1465 (w.b) – 1390 (s) – 1285 (s) 1230 (s) – – 110 (s) 1050 (m) 1020 (m) 810 (sh) 775 (m) 670 (m) 625 (s) 545, 515 (sp.m) – 425 355 (w.b)
NH (amino) NH (amide) NH (amide) C–H C –H C=O C=O ␦NH (amino), C=C ␦NH (amide) N=N N=N ␦OH ␦C–N (amide) C–N (amino) C–N (amino) C–OH C–OH C–OH C–OH Ring vibration ␥NH2 + CH out of plane bend ␥NH2 + CH out of plane bend Ring bend and C–OH twist (broad) ␥N–C=O ␥C=O NH (NH2 ) NH (amide)
Abbreviations, (s) strong; (m) medium; (w) weak; (v.w) very weak; (b) broad; (sp) splitted; (sh) shoulder.
the keto structure. The compared data of the free ligand and its complexes showed that: (i) the azo group bands of the ligand (1455, 1410 cm−1 ) are unaffected in presence of CoII and NiII . In the case of the CuII complex, the first one shifted to 1465 cm−1 in a weak broad feature, and the second one is absent. So, the azo group is involved in chelation with CuII and not in CoII and NiII ; (ii) the first C=O ligand band (1805 cm−1 ) appeared at the same position in presence of CoII and NiII , and is absent in case of CuII , while the second C=O (1750 cm−1 ) ligand band showed blue shift through complexation. The C–OH (1170, 1145 cm−1 ) and ␥C=O (535 cm−1 ) ligand bands are unaffected on chelation to CoII and NiII , but are affected on complexation to CuII . The data typified that the enolic oxygen is involved in the structure of the CuII complex. This is confirmed with the strong band at 1390 cm−1 and the appearance of the new band at 1050 cm−1 , due to C–OH , while the keto form is more predominant in the NiII and CuII complexes; (iii) the NH , C–N , ␥N–C=O , NH modes of the vibration of ligand NH amide bands at 3180, 3100, 1300, 635 cm−1 , respectively, are affected on complexation with different degrees in the shape and the position, i.e. the nitrogen atom of the amide takes place on complexation; (iv) the different modes of vibrations of NH (amino) ligand bands of free ligand are unaffected on complexation with CoII and NiII , except the NH appeared in a broad shoulder, possibly due to the hy-
drogen bonding. In the CuII complex, the NH2 and ␥NH2 and C–N (amino) bands showed change in the shape and the position on complexation (Table 3). The infrared spectra of complexes deduced that the ligand is of bidentate attachment through nitrogen atom of amide and the adjacent oxygen atom in case of NiII and CoII . The azo group and the oxygen atom in position [4] are involved in coordination with CuII . So, the NH of amide groups of the ligand is changed on chelation, i.e. both groups are involved on chelation, probably due to some intermolecular hydrogen bond with some water molecules. All the measurements suggested the following structures:
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(s) cm−1 }, respectively, are blue-shifted on complexation except the 1480 cm−1 band is red-shifted. The C–N ligand amide band (1370 cm−1 ) is blue-shifted by 20 cm−1 in a very weak feature. In general, all data pointed that both nitrogen (amino and amide) and oxygen atoms are active sites for complexation. The weak splitted bands at 1435, 1415 cm−1 assigned the azo group in the free ligand not involved in chelation. The presence of a band at 1395 cm−1 assigned to ␦OH through hydrogen bond with azo group. So, the following structures could be deduced as follows:
The infrared spectra of the 5-( p-anisyl-azo)-6-aminouracil acid complexes, (Table 4) gave the keto tautomer is predominant for this ligand assigned by the absence of OH and the presence of keto bands at (1870, 1740 and 1680 cm−1 ). The 1870 cm−1 ligand band is absent in all complexes. The strong and ␥ C=O ligand bands at 1740, 1680 and 515 cm−1 , respectively, are affected with different degrees on complexation (Table 4). Similarly, the ␦OH (1325, 1300 cm−1 ), ␥OH (885 cm−1 ) and ␥C–OH (635 cm−1 ) ligand bands revealed the change in their positions and shapes on chelation. The infrared spectrum of ligand reveals the , ␦, ␥ and NH (amino) at 3440 (w), {1635 (s) and 1590 (w)}, 855 (w) and 440 (m) cm−1 . The first band is absent in nickel complex and blue-shifted by 40 cm−1 in CuII and still remained at the same position in CoII with change in feature. The second and fourth bands are blue-shifted in all complexes. The third band is absent on chelation. The broad NH and ␦NH (amide) ligand bands at (3210–3250 cm−1 ) and {1535 (m), 1480 Table 4 Fundamental infrared bands (cm−1 ) of 5-(p-anisylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3440 (w) 3210–3250 (sp) 3070 (w) 2930 (w) 2840 (w) 2790 (w) 1870 (m.b) 1740 (s) 1680 (s) 1635 (s) 1590 (w) 1535 (m) 1480 (s.b) 1435 (sp.w) 1415 (sp.w)
3440 3180 3020 2950 2825 2780 – 1730 1710 1620 1580 1525 1495 1445 1415
– 3200 3010 2950 2850 2770 – 1755 – 1620 1585 1525 1495 1445 1415
3400 3180 3020 2910 2825 2780 – 1740 1710 1620 1585 1525 1495 1450 1415
NH of amino NH of amide NH in hydrogen bond CH of aryl CH of OCH3 CH of OCH3 Diketone C=O C=O ␦NH of NH2 NH of amino + C=C ␦NH of amide ␦NH of amide N=N N=N
(sh.w) (b) (sh.w) (sh.w) (w) (sh.w) (sh) (s) (sh.w) (b.m) (m) (w) (w)
(s) (sh.w) (sh.w) (w) (w) (s.w.b) (s) (sh.w) (m) (s) (w) (w)
(v.w.b) (b) (sh.w) (sh.w) (w) (sh.w) (v.w.sh) (w) (s) (sh.w) (b.m) (m) (w) (w.b)
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Table 4 (Continued ) Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
– 1370 1325 (w) 1300 (s) 1260 (v.w.sh) 1240 (s) 1200 (w.sh) 1175 (v.s) 1115 (w) 1100 (s) 1020 (s) 985 (sh.w) 885 (s) 855 (w) 825 (s) 775 (v.w) 765 (s) 680 (sp.w) 670 (sp.w) 635 (v.w.sh) 515 (v.s) 480 (w) 440 (m) 415 (w) 390 (sh.w) –
1395 (w) 1350 (sh.w) 1345 (v.w.sh) 1305 (sh.w) 1285 (v.w) 1240 (s) 1210 (m) 1170 (m) 1145 (m) 1100 (m) 1020 (s) 930 (sh.w) – – 825 (s) 780 (w) 755 (s.b) – 670 (m) 615 (s.b) 530 (v.s) 475 (m) 430 (w) 405 (w) – –
1395 (w) 1350 (sh.w) 1345 (v.v.w.sh) 1305 (w.sh) 1285 1240 (s) 1210 (m) 1170 (m) 1145 (m) 1100 (s) 1020 (s) 930 (sh.w) – – 825 (s) 780 (w) 755 (s.b) – 670 (m) 610 (s.b) 530 (v.s) 470 (m) 430 (w) 405 (w) – 350 (sh.w)
1395 (w) 1350 (sh.w) – 1305 (w.sh) 1285 1245 (s) 1210 (m) 1175 (m) 1145 (m) – 1020 (s) 930 (sh.w) – – 830 (s) – 755 (s.b) – 670 (w) 615 (b) 530 (m) 475 (w) 430 410, 405 (sh) 395 (v.w) 350, 340 (sp.w)
␦OH C–N of ␦OH ␦OH C–N of C–N of C–N of C–OH C–OH C–OH
amide
amino amino amino
␥OH ␥OH ␥NH of NH2 ␥NH of NH2 ␥NH of NH2 C–H out of plane ␥C–OH ␥C–OH ␥C–OH ␥C=O ␥C=O NH amino NH amino M–Cl
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
However, the C=O of 5-(p-hydroxyphenylazo)-6-aminouracil ligand bands at 1750 (w), 1720 (w), 1705 (s) and 1690 (m) cm−1 are affected on chelation with different degrees. Only one carbonyl group is affected on chelation with CuII , while in presence of CoII and NiII , the two carbonyl groups
are tautomerised to the enol skeleton where one of them is utilized for chelation. This is supported by the presence of OH at 3500 cm−1 in cobalt and nickel complexes. The data for the ␥C=O , ␦OH , ␥OH and C–OH typified that the oxygen atom is a center for complexation (Table 5).
Table 5 Fundamental infrared bands (cm−1 ) of 5-(p-hydroxyphenylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
– 3400 (s) 3310 (sh) 3120–3180 (b) 3050 (sh.w) 2960 (sh) 2900 (sh) 2830 (w) 2760 (w) 1750 (w) 1720 (sh.w) 1705 (m) 1690 (sh.w) 1670 (v.w) 1630 (m) 1590 (w) 1510 (m) 1460 (m) 1430 (w) 1395 (s) 1310 (w) 1280 (v.s)
3500 (w) 3420 (m) 3280 (sh) 3190 (sh), 3110 (w) 3000 (w) 2910 (sh.w) 2880 (sh w) 2840 (sh) 2770 (w) – – 1705 (sh.w) 1690, 1675 (sp.w) – 1620 (m.b) 1580 (v.w) – 1460 (w) 1400 (w) 1375 (s) – 1290 (s)
3500 (w) 3420 (m) – 3120–3180 (b) 3000 (w) 2910 (sh) 2880 (sh w) 2840 (sh) 2760 (w) – – 1705 (v.w.sh) 1690, 1670 (w.sp) – 1620 (m) 1580 (v.w) – 1460 (w) 1400 (w) 1375 (s) – 1290 (s)
– 3400 (s) 3330 (sh) 3120–3180 (b) 3050 (sh) 2960 (sh) 2900 (sh) 2830 (sh) 2760 (sh.w) – – 1705 (m) 1690 (v.w) – 1625 (m) 1580 (sh.w) 1510 (w) 1465 (m) – 1395 (s) – 1290 (s)
OH NH (amino), OH phenol NH=amino NH amide CH-aryl CH-aryl
C=O C=O C=O C=O C=C NH (NH2 ) NH (NH2 ) ␦NH amide ␦NH amide N=N ␦OH (enol, phenol) ␦OH C–N amine and ␦OH of phenol
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Table 5 (Continued ) Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
1235 (s) 1140 (sp.m) 1110 (sp.m) 1050 (m) 1015 (v.w) 985 (v.w) 825 (w) 770 (s) 760 (v.w.sh) 715 (w) 680 (v.w), 665 (v.w.sp) 650 (w.sh) 625 (m) 545 (sp.s) 515 (sp.s) 425 (w) –
1230 (b.m) 1120 (m) – 1060 (w) 1015 – 850 (sh) 780 (sp.s) 765 (sp.s) 725 (w.b) 675 (s) – 625 (s) 550 (w) (s) (sp) 515 (w) (s) (sp) 450 (b) –
1230 (b.m) – 1115 (m.b) 1060 (w) 1015 (w) – 850 (s) 780 (sp.s) 765 (sp.s) 725 (w.b) 675 (s) – 625 (s) 550 (w) (s) (sp) 515 (w) (s) (sp) 450 (b) –
1235 (s) 1165 (w.b) 1115 (m) 1055 (m) 1020 (w) 985 (w) 845 (b) 775 (sp.w) 765 (sp.w) 715 (w) 675, 685 (sp.w) – 625 (s) 545 (sp.s) 515 (sp.s) 470 (sh.w), 430 (sh.w) 350 (s)
C–N amine and ␦OH of phenol C–OH C–OH C–OH Ring vibration Ring vibration ␥OH ␥NH (NH2 ) ␥NH (NH2 ) NH amide ␦–C–OH ␦–C–OH N–C=O ␥C=O ␥C=O NH amino M–Cl
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
The , ␦, ␥ and and NH (amino) ligand bands are affected in position and shape on complexation with CoII and NiII . However, these bands are unaffected in presence of CuII . So, according to these data the nitrogen atom is involved for structural configuration in both cobalt and nickel complexes. Such conclusion is not valid in the copper complex (Table 5). The ligand broad NH (amide) bands at 3120–3180 cm−1 are shifted from its position in the cobalt complex. However, this band still remains at the same position in the nickel and copper complexes. The ␦NH (amide) bands at 1510 (m) and 1460 (m) cm−1 are affected by complexation in CoII , NiII and not changed in CuII . The ␥NH (amide) of ligand at 715 cm−1 is red-shifted by 10 cm−1 with a broad nature in cobalt and nickel complexes and not affected in copper complex. So, the nitrogen atom (amide) is involved on chelation with CoII and NiII only. The N=N at 1430 cm−1 , is absent in presence of CuII and blue-shifted by 30 cm−1 in the cases of NiII and CoII . The ␦OH (1395) cm−1 is shifted to 1375 cm−1 in CoII and NiII assigned to hydrogen bond with azo group [54]. The 2:3 cobalt and nickel complexes are in an octahedral geometry, where two ligands of the three are of tridentate attachment, while the third is pentadentate attachment. For the 1:1 octahedral copper complex, the ligand is of bidentate geometry using azo and one of carbonyl groups. The 5-(p-carboxyphenylazo)-6-aminouracil, (Table 6) gave strong bands at 3480 and 1720 cm−1 for OH and C=O [55], respectively, i.e. keto–enol structure. The OH , C=O , ␥OH , ␥C=O and C–OH ligand bands are affected with different degrees on complexation. So, the oxygen atom is considered for complexation. The ligand NH (amino) at 3230 cm−1 remains at the same position in the copper complex and red-shifted by 10 cm−1 with weak nature in the nickel complex and is absent in cobalt complex. Meanwhile, the strong ␦NH (amino) ligand band is absent in presence of CoII and not changed in the NiII and CuII cases. The strong
␥NH (amino) Bands of the ligand at 795 and 770 cm−1 are of weak splitted nature became at 775 and 760 cm−1 in cobalt complex. The first band is only affected in nickel and copper complexes. The data depicted that the amino group
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Table 6 Fundamental infrared bands (cm−1 ) of 5-(p-carboxyphenylazo)-6-amino-uracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3480 (b.s) 3230 (b.m) 3140 (sh.w) 3100 (sh.v.w) 3030 (w) 2920 (sh.v.w) 2810 (w) 1720 (sharp) – 1645 (sp) 1630 (sp) 1590 (m.sharp) 1545 (s.p) 1485 (v.w), 1465 (m) 1415 (sharp) 1385 (sharp) – 1265 (b.m) 1215 (w) 1160 (w) 1105 (w) 1095 (w) 1025 (v.w) 1000 (v.w) – 850 (s) 825 (v.w) 795 (m) 770 (s) 705 (w) 680 (w) 655 (v.w.sh) 615 (b.m) 555 (w) 520 (w) 480 (w) 430 (w)
3440 (b) – 3160 – 3020 (sh) 2920 (sh) 2840 (sh) 1730 1710 (sh.w) 1670 (v.w.sh) 1625 (s) – 1545 (s) 1480 (w), – 1410 (w) 1380 (m.b) 1290 (sh) 1255 1210 (w) 1165 (s) 1100 – – 1005 (w) – 845 (w) 815 (w) 775 (sp.w) 760 (sp.w) 700 (m) – 650 (w.b) 605 (sh.b) 550 (sh.w) 520 (m) 550 (sh.w) 520 (m) 475 (w) 430 (s)
3380, 3440 (w.b.sp) 3240 (sp.b) 3180 – – 2920 2840 1740 (m) 1705 (sh.w) 1665 (m) 1610 (sh.w) 1590 (m) 1545 (s) 1500 (sh.w), – 1410 (w) 1395 (m.b) 1290 (sh.w) 1265 – 1155 (b) 1100 – – 1010 (w) – 840–815 (b) – 780 (sh.v.w) 770 (m) 705 (w) – 660 (sh.w) 605 (m) – 520 (m) 475 (w) 430 (s)
3420 (w.b) 3230 (m) – – 3020 (sh.w) 2920 (v.w) 2840 (v.w) 1720–1735 – 1660–1690 (b) 1625 (sh.v.w) 1590 (v.s) 1545 1495 (s),– 1430, 1410 (w.sp) 1390 (w) 1300 (s) 1260 1225 (s) 1155 (sharp) 1125 (m) 1100 (w) 1040 (v.w) 1000 (v.w) 960, 920 (v.w) 840–820 (b) – – 765 (m) 720 (w) (sp) 695 (w) (sp) 650 (m) 580 (s) 550 (w) 520 (w) 490 (s) 420 (s)
OH NH (amino) NH (amide) NH (amide) Aryl Aryl OH of COOH C=O C=O–COOH C=C ␥NH of NH2 as COO ␥NH (amide) N=N SY COOH, C-N ␦OH ␦OH C–N (NH2 ) C–N (amide) C–OH C–OH C–OH Ring vibration ␥OH ␥OH ␥NH ␥NH ␥C–OH ␥C–OH ␥O–C=O ␥N -C=O ␥C=O NH (amide)
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
is strongly contributed with CoII and not with CuII and NiII complexes. The NH and ␦NH (amide) ligand bands are at {3140, 3100} and 1485 cm−1 , respectively [56]. The data pointed to the following structure:
3.2.1. Electron spin resonance of copper complexes The ESR spectral pattern of (p-tolyl, p-anisyl and p-carboxyphenylazo)-6-aminouracil copper complexes, (Table 7), gave anisotropy natural with axial compressed symmetry, where g > g⊥ > ge (free-electron spin 2.003) indicating a dx2 −y2 ground state in an octahedral geometry [57]. These complexes gave two g-values: g =2.23, 2.26
and 2.11, respectively, g⊥ =2.05, 2.05 and 2.03, respectively. The calculated g =(g + 2g⊥ )/3 are 2.11, 2.12 and 2.06, respectively. Deviation of g from that of free electron (2.0023) suggests the high covalence property of these
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Table 7 ESR parameters for copper(II) 5-(p-substituted phenylazo)-6-aminouracil complexes Substituents
ESR parameters g
g⊥
gs
g
G
5-(Phenylazo)-6-aminouracil 5-(p-Tolylazo)-6-aminouracil 5-(p-Anisylazo)-6-aminouracil 5-(p-Carboxyphenylazo)-6-aminouracil
– 2.23 2.26 2.11
– 2.05 2.05 2.03
2.05 – – –
– 2.11 2.12 2.06
– 4.60 5.20 3.66
complexes with distorted symmetry [58]. The g and hyperfine coupling constant (A) components indicate dynamic tetragonal distortion for (dx2 −y2 ground state) [59]. The g value in copper(II) complexes can be used as a measure of the covalent character of metal–ligand bond [60]. If this value is more than 2.3, the environment is essentially ionic, but if it is less than this limit, assigned the covalent environment. The g values of these complexes show considerable mixed ionic–covalent character. The g-values are taken to calculate the exchange interg −2 action [61]: G= g⊥|| −2 . If G > 4, the local tetragonal axes are aligned parallel, or only slightly misaligned, i.e. the exchange coupling is negligible, and if G < 4 significant exchange coupling is present, (considerable interaction in the solid complexes occurs). The G value of 3.66 for the p-carboxy–copper complexes leads to spin exchange interaction between CuII ions in the solid state. The p-tolyl and p-anisyl, complexes are with G=4.6 and 5.2, respectively, to assign tetragonal distortion geometry [61]. The ESR spectrum of the p-anisyl complex showed some broadness, due to the presence of some polymeric nature. This is convenient with eff 1.6 B.M. The ESR spectrum of the 5-(phenylazo)-6-aminouracil copper complex shows an isotropic behavior with g=2.05. The spectrum is characteristic of dx2 −y2 octahedral geometry around CuII ion with covalent bond [55]. It is possible to measure the -bond parameter, ␣2 , where ␣ is the coefficient of the ground state dx2 −y2 orbital, from the approximate expression [62–64]: ␣2 =
A|| 3 + (g|| − 2.0023) + (g⊥ − 2.00233) + 0.04 0.036 7
A is the parallel coupling constant expressed in cm−1 . The ␣2 values for copper complexes of 5-(p-tolylazo)-6-aminouracil, 5-(p-anisylazo)-6-aminouracil and 5-(p-carboxyazo)6-aminouracil are 0.91, 0.94 and, 0.67, respectively. The reported ␣2 value for CuII complexes with tetragonal distortion lie in the range 0.63–0.84 for nitrogen-donor ligands, and 0.84–0.94 for oxygen-donor ligands [65,66]. The axial ligands will bring changes in the equatorial bond length, and hence in g and A values [67]. The bonding between apical ligands and CuII occurs through the interaction between the metal 4s and 4p orbitals, and the ligand orbitals. So, the presence of apical ligands introduces 4s-character in the ground state, which is in turn will
A
A⊥
␣2
f2
– 225.0 225.0 185.00
– 20.00 25.00 18.50
– 0.91 0.94 0.67
– 1.00 1.44 0.98
decrease the contact hyperfine interaction. Therefore, if the 4s-character in the ground state is known, it is possible to know the axial field strength. In the presence of a small percentage of 4s-character in the ground state, the fraction of the 3d-character in the CuII 3d–4s ground state, f, can be determined from the following equation [63]: 7 A|| 5 6 A 2 − + g|| − g⊥ − ␣2 f 2 = 4 0.036 0.036 3 21 7 The f2 values for the previous complexes are 1.0, 1.44 and 0.98, respectively. The corresponding equation for obtaining ␣2 from the isotropic A value is: ␣2 =
|A| g − 2.0023 + PK K
where P is the free-ion dipole term proportional to 1/r3 and is given a value of 0.036 cm−1 , K is the Fermi constant term and is usually given a value of 0.43 [63]. The ␣2 value for 5-(phenylazo)-6-aminouracil copper complex is 0.918. The values of ␣2 of the mentioned copper complexes prove that these complexes are in tetragonal distorted structures and the ligands behave as nitrogen and oxygen donors [65,66] through chelation.
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Spectral and magnetic properties of phenylazo-6-aminouracil complexes Mamdouh S. Masoud a,∗ , Saeda A. Abou El-Enein b , Mohamed E. Ayad b , Ahmed S. Goher b a b
Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt Chemistry Department, Faculty of Science, Minufiya University, Shebin El-Kome, Egypt Received 6 January 2003; accepted 17 March 2003
Abstract Complexes of CoII , NiII and CuII with substituted phenylazo-6-aminouracils containing (-H, p-OH, p-CH3 , p-OCH3 p-COOH) have been synthesized and characterized by elemental analysis, magnetic measurements and spectral measurements (IR, UV–Vis, ESR). Infrared spectra assigned the fundamental bands of the major groups, O–H, N–H, C–H, C=O, C=N, N=N, C–N and C–O (, ␦ and ␥ modes of vibrations). The absence of OH and the appearance of C=O in the infrared spectra of the free ligands of 5-(p-tolyl and p-anisylazo)-6-aminouracil, assigned the keto structure, whereas in cases of 5-(phenyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracil ligands, the data showed strong OH and C=O bands to assign keto–enol tautomerisms. The modes of interactions between the ligands and the metals were discussed, where oxygen and nitrogen atoms (of amino–amide groups) are involved in chelation. The azo group was not involved in chelation for all the prepared complexes except those of copper complexes derived from 5-(phenyl, p-tolyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracils. The room temperature effective magnetic moment values, the Nujol mull spectra and ESR proved that all the prepared complexes were of octahedral geometry, except the nickel complex derived from 5-(phenylazo)-6-aminouracil and cobalt complex derived from 5-(p-carboxy-phenylazo)-6-aminouracil were square planar. © 2003 Elsevier B.V. All rights reserved. Keywords: Spectra; Magnetism; Structures; Complexes; Azouracil
1. Introduction Barbiturates display a wide variety of responses in the body depending on the nature of substituted groups [1–4]. The properties vary from simple sedation to hypnosis, probably due to the susceptibility of the acidic hydrogen to rapid metabolic attack and subsequent degradation of the compounds within the body [5–8]. In our laboratory [9–43], much work has been carried out on the chemistry of such important biological pyrimidine compounds. In this paper, the interest is focused to study the chelating properties of 6-aminouracils and their azo compounds based on elemental analysis, magnetic moments, spectral methods (UV–Vis, IR) and ESR for copper complexes. 2. Experimental The azo compounds (I) were prepared by the usual diazotization process [44] of 6-aminouracil. ∗
Corresponding author. E-mail address: [email protected] (M.S. Masoud).
1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00226-9
The amines used were aniline, p-aminophenol, p-touldine, p-anisidine and p-carboxy aniline. The following abbreviations are given for the compounds under investigation: 5-(phenylazo)-6-aminouracil (H2 L1 ), 5-(p-hydroxyphenylazo)-6-aminouracil (H2 L2 ), 5-(p-tolylazo)-6-aminouracil (H2 L3 ), 5-(p-anisylazo)-6-aminouracil (H2 L4 ), 5-(p-carboxy phenylazo)-6-aminouracil (H2 L5 ). Eighteen transition metal (CoII , NiII and CuII ) complexes of the stoichiometries 1:1, 1:2, 1:3 and 2:3 (M:L ratio) were prepared and analyzed. All the complexes were prepared in a similar way as follows: 0.01 mol of the metal chloride salt in 50 ml ethanol was added to 0.02 mol of the ligand in presence of 50 ml ethanol. The reaction mixture was refluxed for 2 h. The complex was filtered off, washed several times with water–ethanol and dried in a vacuum desiccator over CaCl2 for 1 day. The preparation of
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Table 1 Color, elemental analysis, Nujol mull electronic absorption spectra (max , nm) and the room temperature effective magnetic moment values (eff , 298 K) Compound
Color
% Calculated (% found)
H2 L1 Co–H2 L1 Ni–H2 L1 Cu–H2 L1 H 2 L2 Co–H2 L2 Ni–H2 L2 Cu–H2 L2 H 2 L3 Co–H2 L3 Ni–H2 L3 Cu–H2 L3 H 2 L4 Co–H2 L4 Ni–H2 L4 Cu–H2 L4 H 2 L5 Co–H2 L5 Ni–H2 L5 Cu–H2 L5
Yellow Brown Orange Brown Brown Brown Brown Brown Yellow Yellowish–green Yellow Grey Brown Brown Orange Brown Yellow Orange Orange Brown
52.0 39.5 44.8 42.4 48.6 38.1 41.1 34.2 53.9 43.1 48.9 40.5 50.6 41.6 38.3 42.6 48.0 36.8 37.7 39.8
C
H (51.9) (39.4) (44.5) (42.6) (48.5) (38.0) (41.2) (34.0) (53.8) (43.2) (48.8) (40.4) (50.4) (41.5) (38.3) (42.8) (47.9) (36.8) (37.7) (39.5)
3.9 3.9 3.6 3.9 3.7 3.5 3.1 4.7 4.5 4.9 4.1 5.2 4.2 3.7 4.2 5.3 3.3 3.6 4.1 4.2
N (3.9) (4.1) (3.4) (4.1) (3.6) (3.4) (3.2) (4.5) (4.3) (4.9) (3.9) (5.5) (4.2) (3.5) (4.2) (5.1) (3.2) (3.6) (4.0) (4.2)
30.3 22.7 25.5 24.1 28.3 22.2 24.0 14.2 28.6 22.9 25.9 21.5 26.8 22.1 20.4 17.1 25.4 17.9 16.9 18.6
(30.2) (22.7) (25.4) (24.0) (28.1) (22.4) (24.0) (13.8) (28.5) (22.7) (26.0) (21.5) (26.7) (22.2) (20.4) (17.0) (25.3) (17.8) (16.9) (18.5)
M
Cl
– 12.7 (12.6) 10.7 (10.6) 10.9 (10.9) – 12.5 (12.3) 13.4 (13.5) 12.9 (12.7) – 6.4 (6.5) 7.2 (7.3) 6.5 (6.3) – 12.4 (12.3) 8.5 (8.4) 7.8 (7.8) – 15.1 (15.2) 14.2 (14.1) 8.4 (8.3)
– – – – – – – 14.4 (14.2) – – – – – – 5.2 (5.0) 8.5 (8.6) – – – –
eff 298 K
max (nm)
– 4.9 Diamagnetic 2.52 – 5.2 3.12 2.82 – 5.5 3.15 2.8 – 4.6 3.21 1.54 – 2.5 3.22 0.5
– 407, 586, 864, – 423, 583, 583, – 652, 469, 435, – 401, 517, 507, – 468, 517, 436,
357, 318 435, 316 545, 415, 390 323, 276, 231 841, 413, 393, 316, 270 503, 432, 318 484, 416, 279, 237 412, 287, 600 409, 401, 312 296, 279, 244 440, 401, 310, 280, 245 403, 309, 274, 238 410, 354, 322, 276 413, 257, 283 315, 286, 253, 218
All the complexes are with m.p. > 300 ◦ C.
5-(phenylazo)-6-aminouracil complexes were prepared in an ammoniacal-ethanolic medium. The C, H and N analytical data of the compounds, (Table 1) were carried out at the central microanalytical laboratory, Chemistry Departments, Faculties of Sciences, Cairo and Alexandria Universities. The metal contents were determined by EDTA complexometric titration [45] and atomic absorption technique. Spectrophotometric measurements were recorded on a UV–Vis double beam spectrophotometric—ratio recording Microcomputer Control, Model Lambda 4B, Perkin Elmer covering the wavelength range 190–850 nm. The spectra of the ligands solutions at different pHs (2–12) were carried out. The electronic absorption spectra of the solid complexes were measured in Nujol mull following the method described by Lee et al. [46]. The KBr infrared spectra of the ligands and their metal complexes were recorded using Infrared Spectrophotometer Model 1430 Perkin Elmer, covering the range 4000–200 cm−1 .
3. Results and discussion 3.1. Stereochemistry of the metal complexes 3.1.1. Cobalt complexes The analytical data, (Table 1) gave that the cobalt complexes separated from—(phenyl, p-anisyl and p-hydroxyphenylazo)-6-aminouracils are with mol ratio 2Co:3L to give Co2 (HL)2 L·nH2 O·mC2 H5 OH, where n=6, 3, 5, m=0.25, 0 and 0, respectively. However, the complexes of (p-tolyl and p-carboxyphenylazo)-6-aminouracils are with the formula Co(HL)2 H2 L·7H2 O (1:3) and CoL·2H2 O·0.5C2 H5 OH (1:1), respectively. The Nujol mull electronic absorption spectra
revealed that the complexes of phenyl, anisyl, tolyl and hydroxy ligands have maximum electronic spectral bands at 407, 401, 484 and 423 nm with magnetic moment values 4.9, 4.6, 5.5 and 5.2 B.M., respectively, consistent with the octahedral and pseudo octahedral structures [47]. However, the 5-(p-carboxyphenylazo)-6-aminouracil cobalt complex has Nujol mull spectral bands at 468 (w.b) and 410 (s) nm with eff of 2.52 B.M., to assign square planar structure [48]. 3.1.2. Nickel complexes The analytical data, (Table 1) revealed that these complexes are with the mole ratios 1:1, 1:1, 1:2, 1:3 and 2:3 from 5-(p-carboxyphenyl, phenyl, p-anisyl, p-tolyl and p-hydroxyphenylazo)-6-aminouracil, respectively. The Nujol mull electronic spectral features gave doublet bands in the wavelength range 401–496 and 517–583 nm due to 3 A2g →3 T1g (p) and 3 A2g →3 T1g transitions, respectively, gathered with magnetic moment values (3.15–3.22 B.M.) to assign a high spin octahedral structure [49]. The slightly higher eff values above that for the spin-orbit only arises from slight mixing of multiplet excited state in which spin-orbit coupling is appreciable [50]. However, the Nujol mull electronic spectra of the diamagnetic nickel 5-(phenylazo)-6-amino-uracil complex showed bands at 435 (w.b) and 586 (b) nm due to 3 A2g →3 T1g (p) and 3 A →3 T 2g 1g transitions in a square planar geometry [51], respectively. The strong band at 316 nm is due to n–* transition. 3.1.3. Copper complexes The analytical data, (Table 1) gave 1Cu:2L mol ratio for the complexes separated from 5-(phenyl, p-anisyl and p-carboxyphenylazo)-6-aminouracil compounds with
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formula: Cu(HL)2 ·0.5H2 O·0.25C2 H5 OH, Cu(H2 L)2 ·2Cl· 3.5C2 H5 OH and Cu(HL)2 ·4H2 O·1.5C2 H5 OH, respectively. However, the copper(II) complex of the p-hydroxyphenylcompound in the 1Cu:1L mol ratio, (Table 1) of the formula: Cu(H2 L)·H2 O·2C2 H5 OH·2Cl. In a similar way, the copper(II) of 5-(p-tolylazo) 6-aminouracil compound having the formula Cu(HL)2 ·H2 L·10H2 O. The Nujol mull electronic absorption spectra of copper complexes; display the spectral bands at 309–390, 409–451, 503–583, 683 and 864 nm. The first band assigned to intraligand charge transfer transition [50]. The latter four bands are due to complex formation. The fourth and fifth spectral bands appeared only in the 5-(phenylazo)-6-aminouracil copper complexes, of a square pyramidal or distorted octahedral configuration of the transition 2 Eg →2 T2g (D) [51,52]. The prepared copper complexes
79
derived from p-anisyl- and p-hydroxyphenyl-compounds gave weak bands centered at 507, 583 and 503 nm with the presence of strong bands at 403 and 432 nm referring to the d–d transition of CuII in a tetragonal field [51,52]. The p-tolyl- and p-carboxyphenyl–copper complexes showed very weak bands at 401, 409, 435 and broad band at 436 nm, respectively, to typify d–d transition of copper complex in a tetragonal distorted octahedral geometry about CuII ion. The magnetic moment values of all the prepared copper complexes are in the range 2.3–2.86 B.M., while those of p-anisyl and p-carboxy-compounds are with eff 1.54 and 0.5 B.M., respectively. The higher value is probably assigned to the absence Cu–Cu interaction and due to the creation of highly positive centers, e.g. in the form of alloyed structures. The lower values less than the spin only
Table 2 Fundamental infrared bands (cm−1 ) of 5-(phenylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3420 (b) 3350 (w) 3280 (w) 3190 (w) 3100 (w) 3040 (sh.w) 2960 (v.w) 2780 (v.w) 1785 (w) 1735 (s.sh) 1720 (w) 1650 (v.s) – 1585 (m) 1540 (v.w) 1505–1495 (m) 1450 (s) (b) 1420 (s) (b) 1370 (m.sh) 1330 (sh), 1320 (w) 1300 (sh.s) 1260 (sh.s) – – 1175 (v.w) 1150 (w) 1080 (s) – 1010 (v.w) 990 (v.w) 910 (m.sh) 875 (w.sh) 850 (w.sh) 810 (s) 755 (s.sh) 710 (w) 680 (s) 650 (w) 630 (w) 610 (v.w) 515 (m) (sp) 495 (m) (sp) 410 (s)
3430 (b) 3320 (v.w) 3200 (v.w) – – 3060 (w) 2910 (v.w.sh) – – 1720 (w) 1710 (w) 1665 (w) 1620 1590 (w) 1540, 1530 (w.sp) 1485 (s), 1500 (sh.w) 1450 (w) 1415 (m.b) 1360 (v.w) – 1280 (v.s) 1280 (sh.w) 1240 (sh.w) 1210 (sh.w) 1160 (sp) 1150, 1135 (sp) 1070 (v.w) – 1020 (v.w) 1000 900 (v.w) – 830 (v.w) – 755 (s.sh) – 690 (s.sh) 670 (w.sh) 655 (w.sh) 570 (v.w) 500 (m.sh)
3440 (b) 3300 (w) – 3150 (v.w, b) 3110 (w.b) 3000 2920 (v.w) 2800 (sh) – 1735 (s.sh) 1695 (v.w) 1630 ( m) – 1600 (m) 1545, 1535, 1525 1510 (w), 1495, 1475 1450 (w) 1415 (w), 1390 1390 – 1300 (m) 1270 (d) 1250 (d) 1205 (d) 1160 (sp.w) 1120 (sp.w) 1070 (v.w) 1040–1020 (sp) – 995 (w) 950 (w) 880 (v.w) – 825 (b) 755 (s.sh) 705 (w) 680 (v.w) 660 (v.w) – 560 (v.w) 520 (sp) 500 (sp) 440 (b)
3420 (b) 3300 (m) – 3160 (sh.w) 3100 (b) 3000 2920 (w.sh) 2840 (b.w) – 1735 (s.sh) – 1640 (s) – 1595 (s) 1545, 1550 (sp.w) 1490, 1475 (v.w.sp) 1420 (w) 1415 (v.w) 1380 (sh) – 1300 (m.sh) 1270 (sp.s) 1240 (sp.s) 1205 (sp.s) 1165 (w) 1140 (w) 1070 (v.w) 1040 (w.sh) 1020 995 (w) 950 (w.sh) – – 825 (b)765 (s.sh) 700 (s) 680 (v.w) 640 (sh) – 570 (s) 510 (sp) 493 (sp) 435 (sh)
OH NH of amino NH of amino NH of amide NH of amide NH in H.b amide, CH of aryl NH in H.b amide, CH of aryl
430 (w.b)
C=O C=O ␦NH of amino C=N C=N ␦NH amide ␦NH amide N=N N=N C–N amide ␦OH ␦OH C–N of amino C–N of amino C–N of amino C–OH C–OH C–OH C–OH Ring vibration Ring vibration ␥–OH ␥–OH ␥N–H (amino) ␥N–H (amino) ␥N–C=O ␥N–C=O ␥C–OH ␥C–OH NH (amino) NH (amino) NH of amide
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder; (h.b) hydrogen bonded.
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value (1.73 B.M) indicate magnetic exchange interaction between adjacent CuII . 3.2. Infrared spectra of the metal complexes The infrared spectra of the free 5-(phenylazo)-6-aminouracil ligand and its complexes, Table 2, gave that the ligand gave strong and weak carbonyl bands at 1735 and 1720 cm−1 . The first one is unaffected on complexation with NiII and CuII and is shifted to 1720 cm−1 with CoII . The second one disappeared in copper complex and shifted to lower frequency (1710 and 1695 cm−1 ) in presence of CoII and NiII , respectively. The ligand bands at {1330 (sh), 1320 (w), 1300 (s)} and {910 (m), 875 (w), 850 (w) cm−1 } assigned to ␦OH and ␥OH , respectively [53]. These bands are absent and shifted to lower frequencies, respectively, on complexation with CoII . However, the first and second ␦OH ligand bands are disappeared, while the third one still remains at the same positions in NiII and CuII complexes. The ␥OH ligand at 910 cm−1 shifted to 950 cm−1 in CuII and NiII complexes, while the ligand bands at 875 and 850 cm−1 are absent in the CuII complex and the second one is absent in NiII complex. The and ␥ C–OH bands of free ligand at {1150 (w), 1080 (s)} and {650 (w), 630 (w)} cm−1 are strongly affected on complexation in their shapes and positions [53,54]. The weakly broad OH ligand band at 3420 cm−1 is shifted to lower frequency by chelation. However, the free ligand exhibits bands at 3350 (w), 3280 (w); 1650 (s); 810 (s), 515 (m) and 495 (m) cm−1 [55], due to different modes of vibrations of NH2 group, namely , ␦, ␥ and . On complexation, these bands show the following remarks: (i) the first NH (amino) band becomes more distinctive and shifted to 3300 cm−1 in CuII and NiII complexes. The second NH (amino) is absent in copper(II) and nickel(II) complexes. Meanwhile, such region in cobalt(II) complex appeared at lower frequency with a very weak feature overlapped with OH band in a broad feature. The presence of six water molecules explained such broadness; (ii) the ␦NH (amino) ligand band is shifted from its position and changed in appearance by complexation; (iii) the ␥NH (amino) of ligand is shifted by 15 cm−1 with some broadening in case of copper and nickel complexes. In case of the cobalt complex, this band is absent. So, the NH2 group is of great importance on chelation with CoII rather than NiII and CuII . The appearance of broad bands, at 2840 and 2800 cm−1 in copper(II) and nickel(II) complexes are due to strongly associated hydrogen bonded complexes. The two weak NH (amide) ligand bands are at 3190 and 3100 cm−1 . The first one is shifted to lower frequency with very weak feature in nickel(II) and copper(II) complexes. The second one is unaffected and shifted to 3110 cm−1 in copper(II) and nickel(II) complexes, respectively, and becomes more sharp. However, the NH (amide) ligand bands disappeared in cobalt complexes due to its existence in the enol form. This is established by the presence of the broad band at 1620 cm−1 due to C=N in cobalt spectrum. The ␦NH (amide) ligand bands changed in their positions and shapes by complex-
ation. More support for the contribution of the nitrogen atom of the amide group of the ligand on chelation, where strong ␥(N–C=O) [56] and NH band appeared at {710 (w), 680 (s)} and 410 (s) cm−1 , respectively. The latter band is shifted to higher frequency in all complexes. The ␥(N–C=O) bands changed only in their positions in nickel(II) complex. In the copper complex, the first band is shifted to lower frequency by 10 cm−1 and the second band is unaffected. In the cobalt complex, the first band is absent and the second one is shifted to higher frequency. The strong ligand azo group bands at 1450 and 1420 cm−1 are shifted from their positions by (30 and 5 cm−1 ) accompanied with a weak appearance, in copper complex and unaffected in both cobalt(II) and nickel(II) complexes. So, the azo group is involved in the structural configuration with CuII rather than NiII and CoII . The 2:3 cobalt complex derived from 5-(phenylazo)-6-aminouracil exists as octahedral geometry, where two ligands of these are of tridentate, while the third is tetradentate attachment. The mainly groups used for chelation with cobalt(II) are OH, NH of (amino and amide groups). The square planar and distorted octahedral 1:2 nickel and copper complexes, respectively, are assigned. The ligand bounds to the metal via bidentate attachment OH and NH (amide). The infrared spectra showed that the azo group takes place in chelation with CuII . The following structures are given as follows:
The absence of OH and the appearance of C=O (1805, 1750 cm−1 ) and C–OH (1170, 1145 cm−1 ) in the infrared spectra of 5-( p-tolylazo)-6-aminouracil, (Table 3) assigned
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Table 3 Fundamental infrared bands (cm−1 ) of 5-(p-tolylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3430 (b) 3180 (b) 3020 (v.w) 2920 (w.sh) 2850 (w.sh) 2800 (w.sh) 1805 (w) 1750 (s) 1625 (s) 1535 (s) 1490 (sh) 1455 (m) 1410 (s) 1395 (v.w.sh) 1300 (w.b) 1260–1275 (b) 1215 (s) 1170 (v.w) (sp) 1145 (v.w) (sp) 1105 (mb) – 1020 (m) 825 (s) 760 (s) 675 (w) 635 (b) 535 (s) 470 (m) – –
3440–3330 (b.sh) 3210 (s) 3020 (sh) 2920 (sh) 2850 (sh) 2780 (w) 1805 (w) 1740 (s) 1625 (s) 1530 (s) 1495 (sh.w) 1450 (s) 1410 (sp.s) 1390 (sp.s) 1315 (w) 1305 (w) 1260–1270 (w.b) 1210 (m) 1165 (sp) (w) 1145 (sp) (w) 1100 (m) – 1020 (m) 815 (s) 760 (m) 680 (m) 625 (b) 530 (s) 475 (m) 410 –
3460–3320 (b.sh) – – – – – 1805 (w) – – 1530 (s) 1495 (sh.w) 1450 (s) 1415 (sp.s) 1390 (sp.s) 1305 (w) 1260–1270 (b.s) 1215 (s) 1165 (w.sp) 1145 (w.sp) 1100 (m) – 1020 (m) 820 (s) 760 (m) 680 (m) 625 (b) 530 (s) 475 (m) 415 –
3400 (m) – 3010 (sh) 2950, 2900 2830 (w) 2750 (sh.w) – 1705 (m) 1625 (m), 1570 (w) 1525 (w) 1500 (v.w.sh) 1465 (w.b) – 1390 (s) – 1285 (s) 1230 (s) – – 110 (s) 1050 (m) 1020 (m) 810 (sh) 775 (m) 670 (m) 625 (s) 545, 515 (sp.m) – 425 355 (w.b)
NH (amino) NH (amide) NH (amide) C–H C –H C=O C=O ␦NH (amino), C=C ␦NH (amide) N=N N=N ␦OH ␦C–N (amide) C–N (amino) C–N (amino) C–OH C–OH C–OH C–OH Ring vibration ␥NH2 + CH out of plane bend ␥NH2 + CH out of plane bend Ring bend and C–OH twist (broad) ␥N–C=O ␥C=O NH (NH2 ) NH (amide)
Abbreviations, (s) strong; (m) medium; (w) weak; (v.w) very weak; (b) broad; (sp) splitted; (sh) shoulder.
the keto structure. The compared data of the free ligand and its complexes showed that: (i) the azo group bands of the ligand (1455, 1410 cm−1 ) are unaffected in presence of CoII and NiII . In the case of the CuII complex, the first one shifted to 1465 cm−1 in a weak broad feature, and the second one is absent. So, the azo group is involved in chelation with CuII and not in CoII and NiII ; (ii) the first C=O ligand band (1805 cm−1 ) appeared at the same position in presence of CoII and NiII , and is absent in case of CuII , while the second C=O (1750 cm−1 ) ligand band showed blue shift through complexation. The C–OH (1170, 1145 cm−1 ) and ␥C=O (535 cm−1 ) ligand bands are unaffected on chelation to CoII and NiII , but are affected on complexation to CuII . The data typified that the enolic oxygen is involved in the structure of the CuII complex. This is confirmed with the strong band at 1390 cm−1 and the appearance of the new band at 1050 cm−1 , due to C–OH , while the keto form is more predominant in the NiII and CuII complexes; (iii) the NH , C–N , ␥N–C=O , NH modes of the vibration of ligand NH amide bands at 3180, 3100, 1300, 635 cm−1 , respectively, are affected on complexation with different degrees in the shape and the position, i.e. the nitrogen atom of the amide takes place on complexation; (iv) the different modes of vibrations of NH (amino) ligand bands of free ligand are unaffected on complexation with CoII and NiII , except the NH appeared in a broad shoulder, possibly due to the hy-
drogen bonding. In the CuII complex, the NH2 and ␥NH2 and C–N (amino) bands showed change in the shape and the position on complexation (Table 3). The infrared spectra of complexes deduced that the ligand is of bidentate attachment through nitrogen atom of amide and the adjacent oxygen atom in case of NiII and CoII . The azo group and the oxygen atom in position [4] are involved in coordination with CuII . So, the NH of amide groups of the ligand is changed on chelation, i.e. both groups are involved on chelation, probably due to some intermolecular hydrogen bond with some water molecules. All the measurements suggested the following structures:
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(s) cm−1 }, respectively, are blue-shifted on complexation except the 1480 cm−1 band is red-shifted. The C–N ligand amide band (1370 cm−1 ) is blue-shifted by 20 cm−1 in a very weak feature. In general, all data pointed that both nitrogen (amino and amide) and oxygen atoms are active sites for complexation. The weak splitted bands at 1435, 1415 cm−1 assigned the azo group in the free ligand not involved in chelation. The presence of a band at 1395 cm−1 assigned to ␦OH through hydrogen bond with azo group. So, the following structures could be deduced as follows:
The infrared spectra of the 5-( p-anisyl-azo)-6-aminouracil acid complexes, (Table 4) gave the keto tautomer is predominant for this ligand assigned by the absence of OH and the presence of keto bands at (1870, 1740 and 1680 cm−1 ). The 1870 cm−1 ligand band is absent in all complexes. The strong and ␥ C=O ligand bands at 1740, 1680 and 515 cm−1 , respectively, are affected with different degrees on complexation (Table 4). Similarly, the ␦OH (1325, 1300 cm−1 ), ␥OH (885 cm−1 ) and ␥C–OH (635 cm−1 ) ligand bands revealed the change in their positions and shapes on chelation. The infrared spectrum of ligand reveals the , ␦, ␥ and NH (amino) at 3440 (w), {1635 (s) and 1590 (w)}, 855 (w) and 440 (m) cm−1 . The first band is absent in nickel complex and blue-shifted by 40 cm−1 in CuII and still remained at the same position in CoII with change in feature. The second and fourth bands are blue-shifted in all complexes. The third band is absent on chelation. The broad NH and ␦NH (amide) ligand bands at (3210–3250 cm−1 ) and {1535 (m), 1480 Table 4 Fundamental infrared bands (cm−1 ) of 5-(p-anisylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3440 (w) 3210–3250 (sp) 3070 (w) 2930 (w) 2840 (w) 2790 (w) 1870 (m.b) 1740 (s) 1680 (s) 1635 (s) 1590 (w) 1535 (m) 1480 (s.b) 1435 (sp.w) 1415 (sp.w)
3440 3180 3020 2950 2825 2780 – 1730 1710 1620 1580 1525 1495 1445 1415
– 3200 3010 2950 2850 2770 – 1755 – 1620 1585 1525 1495 1445 1415
3400 3180 3020 2910 2825 2780 – 1740 1710 1620 1585 1525 1495 1450 1415
NH of amino NH of amide NH in hydrogen bond CH of aryl CH of OCH3 CH of OCH3 Diketone C=O C=O ␦NH of NH2 NH of amino + C=C ␦NH of amide ␦NH of amide N=N N=N
(sh.w) (b) (sh.w) (sh.w) (w) (sh.w) (sh) (s) (sh.w) (b.m) (m) (w) (w)
(s) (sh.w) (sh.w) (w) (w) (s.w.b) (s) (sh.w) (m) (s) (w) (w)
(v.w.b) (b) (sh.w) (sh.w) (w) (sh.w) (v.w.sh) (w) (s) (sh.w) (b.m) (m) (w) (w.b)
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Table 4 (Continued ) Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
– 1370 1325 (w) 1300 (s) 1260 (v.w.sh) 1240 (s) 1200 (w.sh) 1175 (v.s) 1115 (w) 1100 (s) 1020 (s) 985 (sh.w) 885 (s) 855 (w) 825 (s) 775 (v.w) 765 (s) 680 (sp.w) 670 (sp.w) 635 (v.w.sh) 515 (v.s) 480 (w) 440 (m) 415 (w) 390 (sh.w) –
1395 (w) 1350 (sh.w) 1345 (v.w.sh) 1305 (sh.w) 1285 (v.w) 1240 (s) 1210 (m) 1170 (m) 1145 (m) 1100 (m) 1020 (s) 930 (sh.w) – – 825 (s) 780 (w) 755 (s.b) – 670 (m) 615 (s.b) 530 (v.s) 475 (m) 430 (w) 405 (w) – –
1395 (w) 1350 (sh.w) 1345 (v.v.w.sh) 1305 (w.sh) 1285 1240 (s) 1210 (m) 1170 (m) 1145 (m) 1100 (s) 1020 (s) 930 (sh.w) – – 825 (s) 780 (w) 755 (s.b) – 670 (m) 610 (s.b) 530 (v.s) 470 (m) 430 (w) 405 (w) – 350 (sh.w)
1395 (w) 1350 (sh.w) – 1305 (w.sh) 1285 1245 (s) 1210 (m) 1175 (m) 1145 (m) – 1020 (s) 930 (sh.w) – – 830 (s) – 755 (s.b) – 670 (w) 615 (b) 530 (m) 475 (w) 430 410, 405 (sh) 395 (v.w) 350, 340 (sp.w)
␦OH C–N of ␦OH ␦OH C–N of C–N of C–N of C–OH C–OH C–OH
amide
amino amino amino
␥OH ␥OH ␥NH of NH2 ␥NH of NH2 ␥NH of NH2 C–H out of plane ␥C–OH ␥C–OH ␥C–OH ␥C=O ␥C=O NH amino NH amino M–Cl
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
However, the C=O of 5-(p-hydroxyphenylazo)-6-aminouracil ligand bands at 1750 (w), 1720 (w), 1705 (s) and 1690 (m) cm−1 are affected on chelation with different degrees. Only one carbonyl group is affected on chelation with CuII , while in presence of CoII and NiII , the two carbonyl groups
are tautomerised to the enol skeleton where one of them is utilized for chelation. This is supported by the presence of OH at 3500 cm−1 in cobalt and nickel complexes. The data for the ␥C=O , ␦OH , ␥OH and C–OH typified that the oxygen atom is a center for complexation (Table 5).
Table 5 Fundamental infrared bands (cm−1 ) of 5-(p-hydroxyphenylazo)-6-aminouracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
– 3400 (s) 3310 (sh) 3120–3180 (b) 3050 (sh.w) 2960 (sh) 2900 (sh) 2830 (w) 2760 (w) 1750 (w) 1720 (sh.w) 1705 (m) 1690 (sh.w) 1670 (v.w) 1630 (m) 1590 (w) 1510 (m) 1460 (m) 1430 (w) 1395 (s) 1310 (w) 1280 (v.s)
3500 (w) 3420 (m) 3280 (sh) 3190 (sh), 3110 (w) 3000 (w) 2910 (sh.w) 2880 (sh w) 2840 (sh) 2770 (w) – – 1705 (sh.w) 1690, 1675 (sp.w) – 1620 (m.b) 1580 (v.w) – 1460 (w) 1400 (w) 1375 (s) – 1290 (s)
3500 (w) 3420 (m) – 3120–3180 (b) 3000 (w) 2910 (sh) 2880 (sh w) 2840 (sh) 2760 (w) – – 1705 (v.w.sh) 1690, 1670 (w.sp) – 1620 (m) 1580 (v.w) – 1460 (w) 1400 (w) 1375 (s) – 1290 (s)
– 3400 (s) 3330 (sh) 3120–3180 (b) 3050 (sh) 2960 (sh) 2900 (sh) 2830 (sh) 2760 (sh.w) – – 1705 (m) 1690 (v.w) – 1625 (m) 1580 (sh.w) 1510 (w) 1465 (m) – 1395 (s) – 1290 (s)
OH NH (amino), OH phenol NH=amino NH amide CH-aryl CH-aryl
C=O C=O C=O C=O C=C NH (NH2 ) NH (NH2 ) ␦NH amide ␦NH amide N=N ␦OH (enol, phenol) ␦OH C–N amine and ␦OH of phenol
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Table 5 (Continued ) Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
1235 (s) 1140 (sp.m) 1110 (sp.m) 1050 (m) 1015 (v.w) 985 (v.w) 825 (w) 770 (s) 760 (v.w.sh) 715 (w) 680 (v.w), 665 (v.w.sp) 650 (w.sh) 625 (m) 545 (sp.s) 515 (sp.s) 425 (w) –
1230 (b.m) 1120 (m) – 1060 (w) 1015 – 850 (sh) 780 (sp.s) 765 (sp.s) 725 (w.b) 675 (s) – 625 (s) 550 (w) (s) (sp) 515 (w) (s) (sp) 450 (b) –
1230 (b.m) – 1115 (m.b) 1060 (w) 1015 (w) – 850 (s) 780 (sp.s) 765 (sp.s) 725 (w.b) 675 (s) – 625 (s) 550 (w) (s) (sp) 515 (w) (s) (sp) 450 (b) –
1235 (s) 1165 (w.b) 1115 (m) 1055 (m) 1020 (w) 985 (w) 845 (b) 775 (sp.w) 765 (sp.w) 715 (w) 675, 685 (sp.w) – 625 (s) 545 (sp.s) 515 (sp.s) 470 (sh.w), 430 (sh.w) 350 (s)
C–N amine and ␦OH of phenol C–OH C–OH C–OH Ring vibration Ring vibration ␥OH ␥NH (NH2 ) ␥NH (NH2 ) NH amide ␦–C–OH ␦–C–OH N–C=O ␥C=O ␥C=O NH amino M–Cl
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
The , ␦, ␥ and and NH (amino) ligand bands are affected in position and shape on complexation with CoII and NiII . However, these bands are unaffected in presence of CuII . So, according to these data the nitrogen atom is involved for structural configuration in both cobalt and nickel complexes. Such conclusion is not valid in the copper complex (Table 5). The ligand broad NH (amide) bands at 3120–3180 cm−1 are shifted from its position in the cobalt complex. However, this band still remains at the same position in the nickel and copper complexes. The ␦NH (amide) bands at 1510 (m) and 1460 (m) cm−1 are affected by complexation in CoII , NiII and not changed in CuII . The ␥NH (amide) of ligand at 715 cm−1 is red-shifted by 10 cm−1 with a broad nature in cobalt and nickel complexes and not affected in copper complex. So, the nitrogen atom (amide) is involved on chelation with CoII and NiII only. The N=N at 1430 cm−1 , is absent in presence of CuII and blue-shifted by 30 cm−1 in the cases of NiII and CoII . The ␦OH (1395) cm−1 is shifted to 1375 cm−1 in CoII and NiII assigned to hydrogen bond with azo group [54]. The 2:3 cobalt and nickel complexes are in an octahedral geometry, where two ligands of the three are of tridentate attachment, while the third is pentadentate attachment. For the 1:1 octahedral copper complex, the ligand is of bidentate geometry using azo and one of carbonyl groups. The 5-(p-carboxyphenylazo)-6-aminouracil, (Table 6) gave strong bands at 3480 and 1720 cm−1 for OH and C=O [55], respectively, i.e. keto–enol structure. The OH , C=O , ␥OH , ␥C=O and C–OH ligand bands are affected with different degrees on complexation. So, the oxygen atom is considered for complexation. The ligand NH (amino) at 3230 cm−1 remains at the same position in the copper complex and red-shifted by 10 cm−1 with weak nature in the nickel complex and is absent in cobalt complex. Meanwhile, the strong ␦NH (amino) ligand band is absent in presence of CoII and not changed in the NiII and CuII cases. The strong
␥NH (amino) Bands of the ligand at 795 and 770 cm−1 are of weak splitted nature became at 775 and 760 cm−1 in cobalt complex. The first band is only affected in nickel and copper complexes. The data depicted that the amino group
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Table 6 Fundamental infrared bands (cm−1 ) of 5-(p-carboxyphenylazo)-6-amino-uracil and its complexes Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3480 (b.s) 3230 (b.m) 3140 (sh.w) 3100 (sh.v.w) 3030 (w) 2920 (sh.v.w) 2810 (w) 1720 (sharp) – 1645 (sp) 1630 (sp) 1590 (m.sharp) 1545 (s.p) 1485 (v.w), 1465 (m) 1415 (sharp) 1385 (sharp) – 1265 (b.m) 1215 (w) 1160 (w) 1105 (w) 1095 (w) 1025 (v.w) 1000 (v.w) – 850 (s) 825 (v.w) 795 (m) 770 (s) 705 (w) 680 (w) 655 (v.w.sh) 615 (b.m) 555 (w) 520 (w) 480 (w) 430 (w)
3440 (b) – 3160 – 3020 (sh) 2920 (sh) 2840 (sh) 1730 1710 (sh.w) 1670 (v.w.sh) 1625 (s) – 1545 (s) 1480 (w), – 1410 (w) 1380 (m.b) 1290 (sh) 1255 1210 (w) 1165 (s) 1100 – – 1005 (w) – 845 (w) 815 (w) 775 (sp.w) 760 (sp.w) 700 (m) – 650 (w.b) 605 (sh.b) 550 (sh.w) 520 (m) 550 (sh.w) 520 (m) 475 (w) 430 (s)
3380, 3440 (w.b.sp) 3240 (sp.b) 3180 – – 2920 2840 1740 (m) 1705 (sh.w) 1665 (m) 1610 (sh.w) 1590 (m) 1545 (s) 1500 (sh.w), – 1410 (w) 1395 (m.b) 1290 (sh.w) 1265 – 1155 (b) 1100 – – 1010 (w) – 840–815 (b) – 780 (sh.v.w) 770 (m) 705 (w) – 660 (sh.w) 605 (m) – 520 (m) 475 (w) 430 (s)
3420 (w.b) 3230 (m) – – 3020 (sh.w) 2920 (v.w) 2840 (v.w) 1720–1735 – 1660–1690 (b) 1625 (sh.v.w) 1590 (v.s) 1545 1495 (s),– 1430, 1410 (w.sp) 1390 (w) 1300 (s) 1260 1225 (s) 1155 (sharp) 1125 (m) 1100 (w) 1040 (v.w) 1000 (v.w) 960, 920 (v.w) 840–820 (b) – – 765 (m) 720 (w) (sp) 695 (w) (sp) 650 (m) 580 (s) 550 (w) 520 (w) 490 (s) 420 (s)
OH NH (amino) NH (amide) NH (amide) Aryl Aryl OH of COOH C=O C=O–COOH C=C ␥NH of NH2 as COO ␥NH (amide) N=N SY COOH, C-N ␦OH ␦OH C–N (NH2 ) C–N (amide) C–OH C–OH C–OH Ring vibration ␥OH ␥OH ␥NH ␥NH ␥C–OH ␥C–OH ␥O–C=O ␥N -C=O ␥C=O NH (amide)
Abbreviations, (s) strong; (m) medium; (w) weak; (v) very; (b) broad; (sp) splitted; (sh) shoulder.
is strongly contributed with CoII and not with CuII and NiII complexes. The NH and ␦NH (amide) ligand bands are at {3140, 3100} and 1485 cm−1 , respectively [56]. The data pointed to the following structure:
3.2.1. Electron spin resonance of copper complexes The ESR spectral pattern of (p-tolyl, p-anisyl and p-carboxyphenylazo)-6-aminouracil copper complexes, (Table 7), gave anisotropy natural with axial compressed symmetry, where g > g⊥ > ge (free-electron spin 2.003) indicating a dx2 −y2 ground state in an octahedral geometry [57]. These complexes gave two g-values: g =2.23, 2.26
and 2.11, respectively, g⊥ =2.05, 2.05 and 2.03, respectively. The calculated g =(g + 2g⊥ )/3 are 2.11, 2.12 and 2.06, respectively. Deviation of g from that of free electron (2.0023) suggests the high covalence property of these
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Table 7 ESR parameters for copper(II) 5-(p-substituted phenylazo)-6-aminouracil complexes Substituents
ESR parameters g
g⊥
gs
g
G
5-(Phenylazo)-6-aminouracil 5-(p-Tolylazo)-6-aminouracil 5-(p-Anisylazo)-6-aminouracil 5-(p-Carboxyphenylazo)-6-aminouracil
– 2.23 2.26 2.11
– 2.05 2.05 2.03
2.05 – – –
– 2.11 2.12 2.06
– 4.60 5.20 3.66
complexes with distorted symmetry [58]. The g and hyperfine coupling constant (A) components indicate dynamic tetragonal distortion for (dx2 −y2 ground state) [59]. The g value in copper(II) complexes can be used as a measure of the covalent character of metal–ligand bond [60]. If this value is more than 2.3, the environment is essentially ionic, but if it is less than this limit, assigned the covalent environment. The g values of these complexes show considerable mixed ionic–covalent character. The g-values are taken to calculate the exchange interg −2 action [61]: G= g⊥|| −2 . If G > 4, the local tetragonal axes are aligned parallel, or only slightly misaligned, i.e. the exchange coupling is negligible, and if G < 4 significant exchange coupling is present, (considerable interaction in the solid complexes occurs). The G value of 3.66 for the p-carboxy–copper complexes leads to spin exchange interaction between CuII ions in the solid state. The p-tolyl and p-anisyl, complexes are with G=4.6 and 5.2, respectively, to assign tetragonal distortion geometry [61]. The ESR spectrum of the p-anisyl complex showed some broadness, due to the presence of some polymeric nature. This is convenient with eff 1.6 B.M. The ESR spectrum of the 5-(phenylazo)-6-aminouracil copper complex shows an isotropic behavior with g=2.05. The spectrum is characteristic of dx2 −y2 octahedral geometry around CuII ion with covalent bond [55]. It is possible to measure the -bond parameter, ␣2 , where ␣ is the coefficient of the ground state dx2 −y2 orbital, from the approximate expression [62–64]: ␣2 =
A|| 3 + (g|| − 2.0023) + (g⊥ − 2.00233) + 0.04 0.036 7
A is the parallel coupling constant expressed in cm−1 . The ␣2 values for copper complexes of 5-(p-tolylazo)-6-aminouracil, 5-(p-anisylazo)-6-aminouracil and 5-(p-carboxyazo)6-aminouracil are 0.91, 0.94 and, 0.67, respectively. The reported ␣2 value for CuII complexes with tetragonal distortion lie in the range 0.63–0.84 for nitrogen-donor ligands, and 0.84–0.94 for oxygen-donor ligands [65,66]. The axial ligands will bring changes in the equatorial bond length, and hence in g and A values [67]. The bonding between apical ligands and CuII occurs through the interaction between the metal 4s and 4p orbitals, and the ligand orbitals. So, the presence of apical ligands introduces 4s-character in the ground state, which is in turn will
A
A⊥
␣2
f2
– 225.0 225.0 185.00
– 20.00 25.00 18.50
– 0.91 0.94 0.67
– 1.00 1.44 0.98
decrease the contact hyperfine interaction. Therefore, if the 4s-character in the ground state is known, it is possible to know the axial field strength. In the presence of a small percentage of 4s-character in the ground state, the fraction of the 3d-character in the CuII 3d–4s ground state, f, can be determined from the following equation [63]: 7 A|| 5 6 A 2 − + g|| − g⊥ − ␣2 f 2 = 4 0.036 0.036 3 21 7 The f2 values for the previous complexes are 1.0, 1.44 and 0.98, respectively. The corresponding equation for obtaining ␣2 from the isotropic A value is: ␣2 =
|A| g − 2.0023 + PK K
where P is the free-ion dipole term proportional to 1/r3 and is given a value of 0.036 cm−1 , K is the Fermi constant term and is usually given a value of 0.43 [63]. The ␣2 value for 5-(phenylazo)-6-aminouracil copper complex is 0.918. The values of ␣2 of the mentioned copper complexes prove that these complexes are in tetragonal distorted structures and the ligands behave as nitrogen and oxygen donors [65,66] through chelation.
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