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Magnetic and spectral properties of Cu(II) cyanobenzoates
,: ino~, nucl ('hem Vol 4'L pp. 51-55 Pergamon Press Ltd 1981 Printed in Great Britain
MAGNETIC AND SPECTRAL PROPERTIES OF Cu(II) CYANOBENZOATES K. S. PATEL* and P. O. IKEKWERE Department of Chemistry, University of Ibadan, Ibadan, Nigeria
(First received 2 July 1979; received for publication 6 March 1980) Abstract--The cyanobenzoates of Cu(lI) have been prepared and their magnetic and spectral properties examined. Although Cu(lI) compounds of ortho-substituted benzoic acids crystallise from aqueous solutions mostly as monohydrates with dimeric structure, Cu(lI) o-cyanobenzoate precipitated out as a dihydrate with the magnetic and spectral properties of a monomer whilst its anhydrous form has the characteristics of a dimer. Anhydrous Cu(lI) m-cyanobenzoate behaves as a dimer and was isolated from the same solution along with the monohydrate which consists of a mixture of dimer and or polymer. Dihydrated Cu(ll) p-cyanobenzoate and the basic salt, Cu(p-CNC~H4COO) (OH), comprise monomeric or polymeric molecules.
INTRODUCTION Although numerous reports are available on the magnetic and spectral properties of Cu(II) substituted arylcarboxylates[1-3], it appears from the literature that very little is known on Cu(II) cyanobenzoates. In 1%7, W h y m a n et aL[4] characterised a basic Cu(II) p-cyanobenzoate, [Cu(p-CNC6H4COO)(OH)],, on the basis of magnetic and IR spectral properties. It would be of further interest to isolate, if possible, two pure forms of the same compound from a single preparation as obtained for some of the Cu(II) arylcarboxylates [1,5]. In this paper we report the preparation of Cu(II) compounds of ortho-, recta- and para-cyanobenzoic acids and their probable structures are discussed on the basis of their magnetic and spectral properties.
Cu(lI) sulphate while stirring. The precipitated product was filtered, washed with water and dried at room temperature over anhydrous calcium chloride in a vacuum desiccator. Cu(I1) o-, and p-cyanobenzoates were obtained as dihydrates while the corresponding m-cyanobenzoate was isolated as a monohydrate. In addition to these compounds, a crystalline green anhydrous Cu(m-CNC6H4CO0)2 was also isolated on standing the mother liquor for several days. Consistent results were obtained on repeating the preparations. The anhydrous Cu(o-CNC6H4COO), was obtained by drying the dihydrated compound in a vacuum pistol at 90°C over P~,(L. The basic compound. Cufp-CNC6H4COO)fOH) was prepared by using the method of Whyman et al.[4]. All the sodium salts of the acids were synthesized by reacting stoichiometric amounts of the relevant acid and caustic soda in methanol. The resulting solution was filtered and evaporated and the crystals were dried as previously described. Elemental analyses for C, H and N were carried out by the Microanayltical Laboratories at the Universities of Leeds and Ibadan. Copper was determined by using standard solution of EDTA with murexide as indicator[7]. The analytical results along with colours of the compounds and the pK,, values of the parent acids are presented in Table I. Physical measurements. The magnetic susceptibilties were determined over the temperature range 320-80 K by the Gouy method using apparatus from Newport Instruments Ltd. Mercurytetrathiocyanmocobaltate(II) was used as a calibrant. Diamagnetic corrections were calculated from Pascal's constants[Sl. The results are presented in Table 2. The electronic spectra of the complexes in dioxan solution were recorded on a Unicam SP 700 spectrophotometer. The
EXPERIMENTAL o-Cyanobenzoic acid was obtained from K & K Laboratories, Inc., while the m-, and p-cyanobenzoic acids were available from Aldrich Chemical Co. Ltd. The solvents were purified by the standard methods [6]. Preparation of the compounds. The Cu(II) cyanobenzoates were isolated by adding an aqueous solution of the sodium salt of the appropriate acid to a slight excess of an aqueous solution of
*.Author to whom correspondence should be addressed.
Table 1. Micro analytical data of Cu(lI) cyanobenzoates
Compound
Found
Colour
Cu(o-CNC6H4CO0) oo2!{20 ''
*Lt . blue
(%) N
Calc.
C
H
Cu
49.11
3.10
7.05
16.10
C
49.05
H
o
(%) N
pK a at 25 C Cu
3.10
7.15
16,Z12
3.24 [12]
CU ( o-CNC6!{4COO ) ~
Green
53.25
2.30
7.55
17.98
54.01
2.27
7.87
17.86
3.14
C/( m- CNC6HdCOO) 2 "H2r
Lt. Greet
51.48
2.68
7.37
16.90
51.41
2.70
7.50
17.00
3.60 f 1 3 7
CU (m - C N C 6 H 4 C O O ) 2
Green
54.06
2.30
7.65
17.60
54.01
2.27
7.87
17.66
3.60 [137
tU ( p-C~]C6H4COO ) 2 " 2![?C
Lt. blue
49.00
3.20
7.~0
16.66
49.05
3.10
7.15
1d.22
3.ss [~3]
Cu. ( p-CNC6H4CO0 ) (O][)
Lt. blue
42.45
2.35
6.10
27.92
42.39
2.22
6.18
2:.02
3.55 [13]
*LT.
.
Light
[~21
52
K.S. PATEL and P. O. IKEKWERE Table 2. Magnetic data for Cu(II) cyanobenzoates
Xcu
Temp,
x lo 6
(cm 3 mo1-1)
(K)
~-u -I x ao - 2
Uef~ a
(mol cm "3)
(B,M.)
CU(O-CNC6H4COO)2.2H20 Diamagnetic correction . -174 x 10 -6 cm 3 mol -I 299.1
I~493
6.70
1.89
270.3
1,643
6.09
1.89
240.6
1,843
5.43
1.88
210.2
2,094
4.78
1.88
180.0
2t451
4.08
1.88
150.5
2,908
3.44
1.87
125.8
3p410
2.93
1.85
I00,2
4~276
2.34
1.85
82.1
5,292
1.89
1.86
(%b
.
6 o)
CU(O-CNC6H4CO0) 2 Diamagnetic correction ~ -148 x 10~6cm 3 mol "I 319.5
868
11.52
1.49
299.1
879
11.38
1.45
270.0
895
11.18
1.39
240.0
879
11.38
1.30
210.2
840
11.90
1.19
180.3
764
13,08
1.05
150.2
672
14,88
0.90
125.9
568
17.60
0.76
I00.5
409
24.48
0.57
82.4
316
31.64
0.46
(Cq - 2,16; J - 291 cm -I) Cu(m-CNC6H4COO)2-H20 Diamagnetic correction - -161 x 10-6 cm 3 mol -I
298.9
1,088
9.19
1.61
265.0
1,195
8.37
1.59
224.4
1,330
7.52
1.54
184.1
1,524
6.56
1.50
155.5
1,714
5.84
1.46
125.9
1,966
5.09
1.41
~03.1
2,221
4.50
1.35
84.0
2~599
3.85
1.32
Cu(m-CNC6H4CO0) 2 Diamagnetic correction ~ -148 x 10-6 c m3 mol -I 299.3
845
11.83
1.42
269.8
834
11.99
1.34
240.0
821
12.18
1.26
210.0
762
13.12
1.13
180.0
669
14.95
0.98
150.5
533
18.76
0.80
126.4
393
25.45
0.63
100.2
312
32.05
0.50
82.6
267
37.45
0.42
(g
=
2.15;
J - 309 cm -I)
Magnetic and spectral properties of Cu(II) cyanobenzoates
53
Table 2. (Contd) CU(p-CNC6H4COO)2.2H20 Diamagnetic correction . -174 x 10 -6 cm 3 mol -I 299.9
1,676
5.97
2.00
265.6
1,898
5.27
2.01
225.5
2,264
4.42
2.02
185.0
2,789
3.59
2.03
160.6
3,248
3.08
2.04
134.8
3,889
2.57
2.05
116.0
4,589
2.18
2.06
95.6
5,695
1.76
2.09
87.8
6,762
1.48
2.18
(8 - -I0 °)
Cu[(p--CNC6H4COO)(OH)] Diamagnetic correction . -86 x 10 -6 cm 3 mol -I 299.~
1,583
6.32
~.95
270.0
1,770
5.65
1.95
240.0
2,044
4.89
1.98
210.I
2,352
4.25
1.99
~80.0
2,887
3.46
2.04
150.2
3,602
2.78
2.08
126.6
4,468
2.24
2.13
I00.5
6,073
1.65
2.21
82.4
8,083
1.24
2.31
(8 - -32 °) a Calculated from ~eff " 2.828 (XA T) ~.
b Values of 0 indicate that
the Curie Weiss law (XA . C ) is obeyed. T ÷g C Values of g a n d J are those which best reproduce the eKperimental results when incorporated
in the Bleaney Bowers equation[10].
The value of N~ is taken as 60 x 10 -6 cm 3 mol -'[.
diffuse reflectance spectra were obtained using the reflectance attachment to the Unicam SP 500 spectrophotometer. The spectral data are shown in Table 3. The IR spectra were measured on a Perkin-Elmer Model 577 spectrophotometer as pressed potassium bromide discs. The instrument was calibrated with polystyrene. The IR spectral data are listed in Table 4. RESULTS AND DISCUSSION Magnetism. The magnetic behaviour of the anhydrous Cu(II) o-, and m-cyanobenzoates is similar to those of dimeric Cu(II) carboxylates[9, 10] and can be described by the Bleaney and Bowers model[ll]. The values of splitting factor, g, and the exchange coupling constant, J, are given in Table 2. Magnetic data for Cu(o-CNC6H4COO)2 • 2H20, Cu(pCNC6H4COO)2.2H20 and Cu(p-CNC6H4COO)(OH) obey the Curie-Weiss law and the 0 values are given in Table 2. Though Cu(m-CNC6H4COO)2. H20 obeys the Curie-Weiss law above 160°K the magnetic properties can be explained in terms of a mixture containing binuclear and or polynuclear forms. Measurements down to liquid helium temperatures will be of great help to understand the magnetic interaction in Cu(pCNC~H4COO)(OH). It is worth to note that the behaviour of Cu(II) o-cyanobenzoate dihydrate is rather unusual since Cu(II) o-substituted arylmonocarboxylates precipitate out from aqueous solution mostly as mono-
hydrates having a binuclear configuration[2,3]. Moreover, the magnetic properties of the Cu(II) cyanobenzoates differ considerably from those of the corresponding Cu(ll) nitrobenzoates[5] and no simple trend was found to exist between the pK, values of the acids[12, 13] and the magnetic moments of these compounds. Electronic spectra. All dioxan soluble complexes afforded three absorptions in the vicinity of 33.5, 26.6 and 14.5 kK (Table 3). The band at about 14.5 kK was identified as d-,:/transition of the Cu(II) ions[14], while the shoulder around 26.6kK was considered as diagnostic of the spin-spin interaction of the bridging system[14, 15]. The absorption in the region of 33.5 kK was unresolved owing to the presence of intraligand transitions, although it has been reported for Cu(II) carboxylates[16, 17]. The band around 26.0kK which is characteristic of binuclear species was found to be absent in the reflectance spectra of Cu(oCNC6H4COO)2 2H20, Cu(p-CNC6H4COO)2 . 2H20 and Cu(p-CNC6H4COO)(OH). IR spectra. The appearance of sharp absorption bands at 3576 and 35;'4cm ~ in the spectra of Cu(pCNC6H4COO)2"2H20 and Cu(p-CNC6H4COO)2(OH) (Table 4) is considered diagnostic of a basic salt or its impurity[4], while broad absorption bands between 3404 and 3280 cm ' are due to O-H stretching modes.
K. S. PATEL and P. O. IKEKWERE
54
Table 3. Electronic spectral data of Cu(II) cyanobenzoate
Dioxan
Coni'ound
solution
2eflectance
(~max kK)
ligand
(~max)CK)
Cu(o-CNC6H4COO)2,2H20
33.00
27.00 sh
14.40(236)
34.00
absent
13.33
Cu(o-CNC6H4COO) 2
33.50
26.30
14.70(207)
34.00
25.64
14,29
33.50
26.80
14.50
34.00
25.00
13.51
33°50
26.60
14.50(191)
34.00
25.97
14.49
33.40
26.60
14.50
33,95
absent
14.71
-
-
-
33.95
absent
14.29
*Cu(m-CNC6H4CoO)2.H20 Cu(m-CNC6H4CCO)2 *Cu(p-CNC6H4COO)2,2H2 O **Cu (D-CNC6![4CCO)(OH)
D OD
Compound is sparinqly soluble in dioxan Compound is insoluble in dioxan Figures i~ parentheses give Cmax"
Table 4. The symmetric COO (~COO-) and asymmetric COO (,,aCOO) stretching frequencies of sodium and Cu(II) cyanobenzoates VaCOO-
vsCOO-
(cm -1)
(cm-1)
CN (cm -I)
o--CNC6H4COONa
1610
1387
2235
Cu(o-CNC6H4coo)2.2H20
1635
1410
2260 2233
CU(O-CNC6H4COO) 2
1635
1403
2256 2232
m--CNC6H4COONa
1626
1399
2247 2230
Cu(m-CNC6H4COO)2.H20
1634
1405
2271 2238
Cu(m-CNC6H4COO)2
1636
1406
2270 2234
p-CNC6H4COONa
1549
1391
2234
Cu(p-CNC6H4COO)2,2H20
1549 1524
1416
2246
3576~ 3280
1549
1420
2247
3574
Compound
Cu
(p-CNC6H4coo)(OH)
The splitting of the C -= N stretching frequency could be attributed to coordination of the cyano group or cyano groups in different environments within the crystal lattice. However; such splittings are often observed in simple cyano complexes[18]. Although the symmetric and asymmetric COOstretching frequencies are given in Table 4, their assignments are only tentative.
Acknowledgement--One of us (K.S.P.) is grateful to Dr. A. Earnshaw, University of Leeds, Leeds, for allowing the use of the facilities of his laboratories. REFERENCES
1. J. Lewis, Y. C. Lin, L. K. Royston and R. C. Thompson, J. Chem. Soc. 6464 (1%5).
V O-H
(cm-I)
3375 3237
3404
2. J. Lewis, F. E. Mabbs, L. K. Royston and W. R. Smail, J. Chem. Soc. (A) 291 (1%9). 3. R. W. Jotham, S. F. A. Kettle and J. A. Marks, J. Chem. Soc., Dalton 428 (1972). 4. R. Whyman, W. E. Hatfield and C. S. Fountain, lnorg. Chim. Acta 1,429 (1%7). 5. A. Earnshaw and K. S. Patel, J. lnorg. Nucl. Chem. 27, 1805 (1%5). 6. A. I. Vogel, A Text Book o[ Practical Organic Chemistry, 3rd Edn, pp. 163-179. Longmans, London (1%1). 7. H. A. Flaschka, E. D. T. A. Titrations: (An introduction to theory and practice), 2nd Edn, pp. 64--86. Pergamon Press, Oxford (1%4). 8. A. Earnshaw, Introduction to Magnetochemistry, pp. 5-6. Academic Press, London (1%8). 9. R. J. Doedens, Prog. Inorg. Chem. 21,209 (1976). 10. K. S. Patel and B. B. Adeleke, lnorg. Nucl. Chem. Lett. 16, 57 (1980).
Magnetic and spectral properties of Cu(II) cyanobenzoates 11. B. Bleaney and K. D. Bowers, Proc. Roy. Soc. A 214, 451 (1952). 12. G. Kortum, W. Vogel and K. Andrussow, Dissociation Constants of Organic Acids in Aqueous Solution, pp. 240--400. Butterworths, London (1%1). 13. A. Albert and E. P. Serjeant, The Determination of Ionization Constants, 2nd Edn, pp. 84--85. Chapman Hall, London (1971).
54
14. M. Kato, F1. B. Jonassen and J. C. Fanning, Chem. Rev. 64, 99 (1%4). 15. L. Dubicki and R. L. Martin, Inorg. Chem. 5, 2203 (1%6k 16. E. A. Boudreaux, Inorg. Chem. 3, 506 (1%4). 17. J. Beta and D. Sen, J. Chem. Soc., Dalton 18 (1977). 18. K. Nakamoto, IR Spectra of Inorganic and Coordination Compounds, 2nd Edn, p. 179. Wiley, New York (1970).
MAGNETIC AND SPECTRAL PROPERTIES OF Cu(II) CYANOBENZOATES K. S. PATEL* and P. O. IKEKWERE Department of Chemistry, University of Ibadan, Ibadan, Nigeria
(First received 2 July 1979; received for publication 6 March 1980) Abstract--The cyanobenzoates of Cu(lI) have been prepared and their magnetic and spectral properties examined. Although Cu(lI) compounds of ortho-substituted benzoic acids crystallise from aqueous solutions mostly as monohydrates with dimeric structure, Cu(lI) o-cyanobenzoate precipitated out as a dihydrate with the magnetic and spectral properties of a monomer whilst its anhydrous form has the characteristics of a dimer. Anhydrous Cu(lI) m-cyanobenzoate behaves as a dimer and was isolated from the same solution along with the monohydrate which consists of a mixture of dimer and or polymer. Dihydrated Cu(ll) p-cyanobenzoate and the basic salt, Cu(p-CNC~H4COO) (OH), comprise monomeric or polymeric molecules.
INTRODUCTION Although numerous reports are available on the magnetic and spectral properties of Cu(II) substituted arylcarboxylates[1-3], it appears from the literature that very little is known on Cu(II) cyanobenzoates. In 1%7, W h y m a n et aL[4] characterised a basic Cu(II) p-cyanobenzoate, [Cu(p-CNC6H4COO)(OH)],, on the basis of magnetic and IR spectral properties. It would be of further interest to isolate, if possible, two pure forms of the same compound from a single preparation as obtained for some of the Cu(II) arylcarboxylates [1,5]. In this paper we report the preparation of Cu(II) compounds of ortho-, recta- and para-cyanobenzoic acids and their probable structures are discussed on the basis of their magnetic and spectral properties.
Cu(lI) sulphate while stirring. The precipitated product was filtered, washed with water and dried at room temperature over anhydrous calcium chloride in a vacuum desiccator. Cu(I1) o-, and p-cyanobenzoates were obtained as dihydrates while the corresponding m-cyanobenzoate was isolated as a monohydrate. In addition to these compounds, a crystalline green anhydrous Cu(m-CNC6H4CO0)2 was also isolated on standing the mother liquor for several days. Consistent results were obtained on repeating the preparations. The anhydrous Cu(o-CNC6H4COO), was obtained by drying the dihydrated compound in a vacuum pistol at 90°C over P~,(L. The basic compound. Cufp-CNC6H4COO)fOH) was prepared by using the method of Whyman et al.[4]. All the sodium salts of the acids were synthesized by reacting stoichiometric amounts of the relevant acid and caustic soda in methanol. The resulting solution was filtered and evaporated and the crystals were dried as previously described. Elemental analyses for C, H and N were carried out by the Microanayltical Laboratories at the Universities of Leeds and Ibadan. Copper was determined by using standard solution of EDTA with murexide as indicator[7]. The analytical results along with colours of the compounds and the pK,, values of the parent acids are presented in Table I. Physical measurements. The magnetic susceptibilties were determined over the temperature range 320-80 K by the Gouy method using apparatus from Newport Instruments Ltd. Mercurytetrathiocyanmocobaltate(II) was used as a calibrant. Diamagnetic corrections were calculated from Pascal's constants[Sl. The results are presented in Table 2. The electronic spectra of the complexes in dioxan solution were recorded on a Unicam SP 700 spectrophotometer. The
EXPERIMENTAL o-Cyanobenzoic acid was obtained from K & K Laboratories, Inc., while the m-, and p-cyanobenzoic acids were available from Aldrich Chemical Co. Ltd. The solvents were purified by the standard methods [6]. Preparation of the compounds. The Cu(II) cyanobenzoates were isolated by adding an aqueous solution of the sodium salt of the appropriate acid to a slight excess of an aqueous solution of
*.Author to whom correspondence should be addressed.
Table 1. Micro analytical data of Cu(lI) cyanobenzoates
Compound
Found
Colour
Cu(o-CNC6H4CO0) oo2!{20 ''
*Lt . blue
(%) N
Calc.
C
H
Cu
49.11
3.10
7.05
16.10
C
49.05
H
o
(%) N
pK a at 25 C Cu
3.10
7.15
16,Z12
3.24 [12]
CU ( o-CNC6!{4COO ) ~
Green
53.25
2.30
7.55
17.98
54.01
2.27
7.87
17.86
3.14
C/( m- CNC6HdCOO) 2 "H2r
Lt. Greet
51.48
2.68
7.37
16.90
51.41
2.70
7.50
17.00
3.60 f 1 3 7
CU (m - C N C 6 H 4 C O O ) 2
Green
54.06
2.30
7.65
17.60
54.01
2.27
7.87
17.66
3.60 [137
tU ( p-C~]C6H4COO ) 2 " 2![?C
Lt. blue
49.00
3.20
7.~0
16.66
49.05
3.10
7.15
1d.22
3.ss [~3]
Cu. ( p-CNC6H4CO0 ) (O][)
Lt. blue
42.45
2.35
6.10
27.92
42.39
2.22
6.18
2:.02
3.55 [13]
*LT.
.
Light
[~21
52
K.S. PATEL and P. O. IKEKWERE Table 2. Magnetic data for Cu(II) cyanobenzoates
Xcu
Temp,
x lo 6
(cm 3 mo1-1)
(K)
~-u -I x ao - 2
Uef~ a
(mol cm "3)
(B,M.)
CU(O-CNC6H4COO)2.2H20 Diamagnetic correction . -174 x 10 -6 cm 3 mol -I 299.1
I~493
6.70
1.89
270.3
1,643
6.09
1.89
240.6
1,843
5.43
1.88
210.2
2,094
4.78
1.88
180.0
2t451
4.08
1.88
150.5
2,908
3.44
1.87
125.8
3p410
2.93
1.85
I00,2
4~276
2.34
1.85
82.1
5,292
1.89
1.86
(%b
.
6 o)
CU(O-CNC6H4CO0) 2 Diamagnetic correction ~ -148 x 10~6cm 3 mol "I 319.5
868
11.52
1.49
299.1
879
11.38
1.45
270.0
895
11.18
1.39
240.0
879
11.38
1.30
210.2
840
11.90
1.19
180.3
764
13,08
1.05
150.2
672
14,88
0.90
125.9
568
17.60
0.76
I00.5
409
24.48
0.57
82.4
316
31.64
0.46
(Cq - 2,16; J - 291 cm -I) Cu(m-CNC6H4COO)2-H20 Diamagnetic correction - -161 x 10-6 cm 3 mol -I
298.9
1,088
9.19
1.61
265.0
1,195
8.37
1.59
224.4
1,330
7.52
1.54
184.1
1,524
6.56
1.50
155.5
1,714
5.84
1.46
125.9
1,966
5.09
1.41
~03.1
2,221
4.50
1.35
84.0
2~599
3.85
1.32
Cu(m-CNC6H4CO0) 2 Diamagnetic correction ~ -148 x 10-6 c m3 mol -I 299.3
845
11.83
1.42
269.8
834
11.99
1.34
240.0
821
12.18
1.26
210.0
762
13.12
1.13
180.0
669
14.95
0.98
150.5
533
18.76
0.80
126.4
393
25.45
0.63
100.2
312
32.05
0.50
82.6
267
37.45
0.42
(g
=
2.15;
J - 309 cm -I)
Magnetic and spectral properties of Cu(II) cyanobenzoates
53
Table 2. (Contd) CU(p-CNC6H4COO)2.2H20 Diamagnetic correction . -174 x 10 -6 cm 3 mol -I 299.9
1,676
5.97
2.00
265.6
1,898
5.27
2.01
225.5
2,264
4.42
2.02
185.0
2,789
3.59
2.03
160.6
3,248
3.08
2.04
134.8
3,889
2.57
2.05
116.0
4,589
2.18
2.06
95.6
5,695
1.76
2.09
87.8
6,762
1.48
2.18
(8 - -I0 °)
Cu[(p--CNC6H4COO)(OH)] Diamagnetic correction . -86 x 10 -6 cm 3 mol -I 299.~
1,583
6.32
~.95
270.0
1,770
5.65
1.95
240.0
2,044
4.89
1.98
210.I
2,352
4.25
1.99
~80.0
2,887
3.46
2.04
150.2
3,602
2.78
2.08
126.6
4,468
2.24
2.13
I00.5
6,073
1.65
2.21
82.4
8,083
1.24
2.31
(8 - -32 °) a Calculated from ~eff " 2.828 (XA T) ~.
b Values of 0 indicate that
the Curie Weiss law (XA . C ) is obeyed. T ÷g C Values of g a n d J are those which best reproduce the eKperimental results when incorporated
in the Bleaney Bowers equation[10].
The value of N~ is taken as 60 x 10 -6 cm 3 mol -'[.
diffuse reflectance spectra were obtained using the reflectance attachment to the Unicam SP 500 spectrophotometer. The spectral data are shown in Table 3. The IR spectra were measured on a Perkin-Elmer Model 577 spectrophotometer as pressed potassium bromide discs. The instrument was calibrated with polystyrene. The IR spectral data are listed in Table 4. RESULTS AND DISCUSSION Magnetism. The magnetic behaviour of the anhydrous Cu(II) o-, and m-cyanobenzoates is similar to those of dimeric Cu(II) carboxylates[9, 10] and can be described by the Bleaney and Bowers model[ll]. The values of splitting factor, g, and the exchange coupling constant, J, are given in Table 2. Magnetic data for Cu(o-CNC6H4COO)2 • 2H20, Cu(pCNC6H4COO)2.2H20 and Cu(p-CNC6H4COO)(OH) obey the Curie-Weiss law and the 0 values are given in Table 2. Though Cu(m-CNC6H4COO)2. H20 obeys the Curie-Weiss law above 160°K the magnetic properties can be explained in terms of a mixture containing binuclear and or polynuclear forms. Measurements down to liquid helium temperatures will be of great help to understand the magnetic interaction in Cu(pCNC~H4COO)(OH). It is worth to note that the behaviour of Cu(II) o-cyanobenzoate dihydrate is rather unusual since Cu(II) o-substituted arylmonocarboxylates precipitate out from aqueous solution mostly as mono-
hydrates having a binuclear configuration[2,3]. Moreover, the magnetic properties of the Cu(II) cyanobenzoates differ considerably from those of the corresponding Cu(ll) nitrobenzoates[5] and no simple trend was found to exist between the pK, values of the acids[12, 13] and the magnetic moments of these compounds. Electronic spectra. All dioxan soluble complexes afforded three absorptions in the vicinity of 33.5, 26.6 and 14.5 kK (Table 3). The band at about 14.5 kK was identified as d-,:/transition of the Cu(II) ions[14], while the shoulder around 26.6kK was considered as diagnostic of the spin-spin interaction of the bridging system[14, 15]. The absorption in the region of 33.5 kK was unresolved owing to the presence of intraligand transitions, although it has been reported for Cu(II) carboxylates[16, 17]. The band around 26.0kK which is characteristic of binuclear species was found to be absent in the reflectance spectra of Cu(oCNC6H4COO)2 2H20, Cu(p-CNC6H4COO)2 . 2H20 and Cu(p-CNC6H4COO)(OH). IR spectra. The appearance of sharp absorption bands at 3576 and 35;'4cm ~ in the spectra of Cu(pCNC6H4COO)2"2H20 and Cu(p-CNC6H4COO)2(OH) (Table 4) is considered diagnostic of a basic salt or its impurity[4], while broad absorption bands between 3404 and 3280 cm ' are due to O-H stretching modes.
K. S. PATEL and P. O. IKEKWERE
54
Table 3. Electronic spectral data of Cu(II) cyanobenzoate
Dioxan
Coni'ound
solution
2eflectance
(~max kK)
ligand
(~max)CK)
Cu(o-CNC6H4COO)2,2H20
33.00
27.00 sh
14.40(236)
34.00
absent
13.33
Cu(o-CNC6H4COO) 2
33.50
26.30
14.70(207)
34.00
25.64
14,29
33.50
26.80
14.50
34.00
25.00
13.51
33°50
26.60
14.50(191)
34.00
25.97
14.49
33.40
26.60
14.50
33,95
absent
14.71
-
-
-
33.95
absent
14.29
*Cu(m-CNC6H4CoO)2.H20 Cu(m-CNC6H4CCO)2 *Cu(p-CNC6H4COO)2,2H2 O **Cu (D-CNC6![4CCO)(OH)
D OD
Compound is sparinqly soluble in dioxan Compound is insoluble in dioxan Figures i~ parentheses give Cmax"
Table 4. The symmetric COO (~COO-) and asymmetric COO (,,aCOO) stretching frequencies of sodium and Cu(II) cyanobenzoates VaCOO-
vsCOO-
(cm -1)
(cm-1)
CN (cm -I)
o--CNC6H4COONa
1610
1387
2235
Cu(o-CNC6H4coo)2.2H20
1635
1410
2260 2233
CU(O-CNC6H4COO) 2
1635
1403
2256 2232
m--CNC6H4COONa
1626
1399
2247 2230
Cu(m-CNC6H4COO)2.H20
1634
1405
2271 2238
Cu(m-CNC6H4COO)2
1636
1406
2270 2234
p-CNC6H4COONa
1549
1391
2234
Cu(p-CNC6H4COO)2,2H20
1549 1524
1416
2246
3576~ 3280
1549
1420
2247
3574
Compound
Cu
(p-CNC6H4coo)(OH)
The splitting of the C -= N stretching frequency could be attributed to coordination of the cyano group or cyano groups in different environments within the crystal lattice. However; such splittings are often observed in simple cyano complexes[18]. Although the symmetric and asymmetric COOstretching frequencies are given in Table 4, their assignments are only tentative.
Acknowledgement--One of us (K.S.P.) is grateful to Dr. A. Earnshaw, University of Leeds, Leeds, for allowing the use of the facilities of his laboratories. REFERENCES
1. J. Lewis, Y. C. Lin, L. K. Royston and R. C. Thompson, J. Chem. Soc. 6464 (1%5).
V O-H
(cm-I)
3375 3237
3404
2. J. Lewis, F. E. Mabbs, L. K. Royston and W. R. Smail, J. Chem. Soc. (A) 291 (1%9). 3. R. W. Jotham, S. F. A. Kettle and J. A. Marks, J. Chem. Soc., Dalton 428 (1972). 4. R. Whyman, W. E. Hatfield and C. S. Fountain, lnorg. Chim. Acta 1,429 (1%7). 5. A. Earnshaw and K. S. Patel, J. lnorg. Nucl. Chem. 27, 1805 (1%5). 6. A. I. Vogel, A Text Book o[ Practical Organic Chemistry, 3rd Edn, pp. 163-179. Longmans, London (1%1). 7. H. A. Flaschka, E. D. T. A. Titrations: (An introduction to theory and practice), 2nd Edn, pp. 64--86. Pergamon Press, Oxford (1%4). 8. A. Earnshaw, Introduction to Magnetochemistry, pp. 5-6. Academic Press, London (1%8). 9. R. J. Doedens, Prog. Inorg. Chem. 21,209 (1976). 10. K. S. Patel and B. B. Adeleke, lnorg. Nucl. Chem. Lett. 16, 57 (1980).
Magnetic and spectral properties of Cu(II) cyanobenzoates 11. B. Bleaney and K. D. Bowers, Proc. Roy. Soc. A 214, 451 (1952). 12. G. Kortum, W. Vogel and K. Andrussow, Dissociation Constants of Organic Acids in Aqueous Solution, pp. 240--400. Butterworths, London (1%1). 13. A. Albert and E. P. Serjeant, The Determination of Ionization Constants, 2nd Edn, pp. 84--85. Chapman Hall, London (1971).
54
14. M. Kato, F1. B. Jonassen and J. C. Fanning, Chem. Rev. 64, 99 (1%4). 15. L. Dubicki and R. L. Martin, Inorg. Chem. 5, 2203 (1%6k 16. E. A. Boudreaux, Inorg. Chem. 3, 506 (1%4). 17. J. Beta and D. Sen, J. Chem. Soc., Dalton 18 (1977). 18. K. Nakamoto, IR Spectra of Inorganic and Coordination Compounds, 2nd Edn, p. 179. Wiley, New York (1970).