The spin-allowed transitions in the visible spectra of some
rr.onoacidopentaammine and diacidotetraammine complexes of
Co(III), with the acido groups being C03z--, H20, N02-, 02C3H5-,
p-, No3-, ci-, and Br-, have been resolved and the relevant crystal
field and Racah parameters determined with a modified version of
the model originally proposed by Wentworth and Piper. The tesults
appear to be consistent within the series and agree well with those
reported in the literature for structurally related systems

Suk-Yee Chan

Wai-Kee Li

Hrčak - Portal of scientific journals of Croatia

CROATICA CHEMICA ACTA CCACAA 52 (1) 11-16 (1979) CCA-1136 YU ISSN 0011-1643 546.733 Originai Scientific Paper Visible Spectra of Some Monoacidopentaammine and Diacidotetraammine Complexes of Cobalt(Ill) Suk-Yee Chan and Wai-Kee Li* Department of Chemistry,. The Chinese University of Hong Kong Shatin, N. T. Hong Kong Received September 8, 1978 The spin-allowed transitions in the visible spectra of some rr.onoacidopentaammine and diacidotetraammine complexes of Co(III), with the acido groups being C03z--, H20, N02-, 02C3H5-, p-, No3-, ci-, and Br-, have been resolved and the relevant crystal field and Racah parameters determined with a modified version of the model originally proposed by Wentworth and Piper. The tesults appear to be consistent within the series and agree well with those reported in the literature for structurally related systems. INTRODUCTION In two previous notes1•2, the visible spectra of the complexes [Co(RNH2) 3X]2\ where R = H, Me, Et, n-Pr, and n-Bu and X =Br and Cl, were analyzed in terms of a crystal field model. This model was a modified version of that originally devised by Wentworth and Piper3. In order to test this newly pro-posed model further, the following investigations have been carried out and are reported in this note: (1) The visible spectra of some monoacidopentaamminecobalt(III) com-plexes, w,ith the acido groups being C032- , H 20, No 2- , 0 2C3H 5- , F-, and N03 - , are analyzed. This part is similar to what has been done before1•2 except that the range of the acido groups has been expanded considerably. (2) The visible spectra of some trans-diacidotetraamminecobalt(III) com-plexes, with the acido groups being c1- and Br-, are analyzed. This provides a good test since, according to the model, the values of the crystal field para-meters Ds and Dt for these D4 h systems should be twice as large as those for the analogous C4 v complexes. EXPERIMENTAL The methods of synthesis for the complexes [Co(NH3)sC03] + 4, [Co(NH3)5H20J3+ 5, [Co(NH3)sN02J2• 6, [Co(NH3)502CaHsJ+~ 7, [Co(NHs)5F]2+ 8, [Co(NHa)sN03]2+ 9, trans--[Co(en)2Cl2]' 10, and trans-[Co(en)2Br2]' 11 can be readily found in the literature and are not described here. The spectra of the complexes were recorded by a Hitachi 323 UV-VIS-NIR recording spectrophotometer in the 210-700 nm range at room tempe-rature. Reagent grade methanol was used as solvent for the diacido complexes since they are known to ·be unstable towards hydrolysis and isomerization in water. For * To whom correspondence should be addressed. 12 S.-Y. CHAN AND W.-K. LI other complexes water was used. All the spectra were recorded as soon as the complexes had been dissolved. Repeated recordings showed no change in the spectra. 'l'HEORY Within the framework of crystal field theory, the energies of low-lying singlet states above the ground state (Figure 1) for a dti ion in a strong octahedral field are1- 3 E (1Ti'g) - E (1A1g) = 10 Dq - C , E ( 1 T~g)- E (1A1g) = 10 Dq + 16 B-C, where Dq, B , and C are the usual parameters encountered in crystal field theory. On decrease in symmetry to C .v or D, h, corresponding to tetragonal distortion, the degeneracy of the excited states in partially lifted as shown in Figure 1. Referring to ,the labelling given in the figure, the energies of the transitions are ~ ~ II IIB II A --...---- .. ,--- --- - -- -I I A IB Figure 1. Tetragonal splitting of the ex cited states of Co(III). E (IA) = 10 Dq - (35/4) Dt - C, E (IB) = 10 Dq - C, E (IIA) = 10 Dq - 4 Ds - 5 Dt + 16 B - C, E (IIB) = 10 Dq + 2 Ds - (25/4) Dt + 16 B - C. The additional parameters Ds and Dt have been defined elsewhere3• The only differences between the C4 v and D.,h complexes are D s (D_,h) = 2 Ds (C_" ,), Dt (D, 1) = 2 Dt (C.v). In the original model of Wentworth and Piper3, a key assumption is that the energy of the IB band of the distorted system is identical to the I band for the parent octahedral complex. VISIBLE SPECTRA OF Co(III) COMPLEXES 13 For the present work, where possible, the absorption bands of the spectra are resolved into four Gaussian curves, assuming a sloping baseline12 • Since, at most, only four transitions may be resolved from the spectra and there are five parameters to be determined, an additional assumption has to be made. It is known that, among the five parameters, C is the one that remains remarkably constant over a wide range of crystal field strength. For example, the C values in [Co(NH3).J 3+, [Co(en)3) 3+, and [Co(CN) ,.)3- have been reported as 3825, 3835, and 3650 cm-1 respectively3. Therefore, it should be reasonable to assign that, for the complexes under study, C = 3800 cm-1• In another model, Ban and Csaszar13 proposed that band II does not split so that E (II) ·= E (IIA) = E (IIB). Then, Ds = (5/24) Dt, B = (1/16) [E (II) -- 10 Dq + C + 5 Dt + 4 Ds]. The results of the analyses are given in the next section, along with a comparison among the results based on the three models described here. RESULTS AND DISCUSSION The wavelengths, intensities, and half-widths of the resolved bands of the complexes are given in Table I , together with those reported by other workers for comparison. The crystal field parameters calculated from the experimental results along with those obtained by other workers are summarized in Table II , including those of [Co(N:fl3 ) 5Cl)2+ and [Co(NH3),,Br)2+ obtained previouslyt.2 . The second bands of [Co(NH3) 5C03)+, [Co(NH3),,N0,) 2+, and the two diacido complexes have not been resolved due to the onset of the charge transfer bands and therefore the values of Ds and B are missing. Upon examining the results, the following remarks can be made: (1) The order of the values of Dq obtained from the present treatment is No,,- > en > NH3 > C4H50 2- > N03- > H"O > CO/ - > F- > Cl- > Br-, an arrangement in good agreement with that normally listed. (2) Comparing the values of Dq(Cl) and Dq(Br) of the trans-disubstituted complexes with those of the monosubstituted complexes reported by Book et al.1•2, it is found that these values remain fairly constant in C,v and D,h complexes. Also, the values of Dq(en) and Dq(NH:i) are almost unchanged irrespective of the particular substituted complex ion in which they are found. Thus the assumption that the crystal strength is characteristic of the ligand itself (for the same metal ion) is justified. (3) The comparison of the parameters Dt and Ds of the C,v and D4 h com-plexes indicates that the values of the latter are about twice as large as those of the former as predicted by the electrostatic model of the crystal field theory. (4) In the case where the IA and IB bands were not resolved, Wentworth and Piper3 took for granted that the observed band maximum was the average of the energy of the 1T1g +-- 1 A1g transition of the parent compound and that of the 1E" state above the ground state. This approximation in effect assumes Complex [Co(NH3)sC03]• [Co(NH3)sH20J3+ [Co(NH3)5N02F • [Co(NH3)s02C3HsJ2• [Co(NH3)5F]2+ [Co(NH3)5N03]2• trans- [Co( en)2Cl2]• trans- [Co(en)2Br2J' TABLE I The Wavenumbers (vmax), Intensities (log E, c./moi-1 dm3 cm-1 being Molar Extinction Coefficient), and Half Width (1'1111.12) of the Resolved Bands Band IA Band IB Band IIA Band IIB - - - - -Vmax "' 1'1v1/2 1' max ~ A v1/2 Ymax CJ.i A v1/2 Vmax log e l'1 v1/2 Oil Oil Oil 1000 cm-1 .S 1000 cm-1 1000 cm-1 .S 1000 cm-1 1000 cm-L .S 1000 cm-1 1000 cm-1 1000 cm-1 18.90 1.74 2.91 21.10 1.68 4.13 26.88 (shoulder; not resolved) 18.90" 20.50" 27.85" (not resolved) 19.34 1.65 3.39 21.05 1.83 4.16 27.86 1.59 3.74 29.50 1.79 3.93 20.50" (not resolved) 30.40" (not resolved) 20.30b (not resolved) 30.30b (not resolved) 23.87 1.51 5.13 21.51 1.29 4.25 31.65 2.55 4.94 28.57 2.66 3_52 21.75" (not resolved) 30.80" (not resolved) 21.84b (not resolved) 30.80" (not resolved) 19.38 1.67 2.87 20.70 1.58 3.54 28.09 1.73 3.41 29.94 1.47 0.90 19.87. 21.35" 28.41" (not resolved) 19.88 21.00" 28.39" (not resolved) 19.05 1.97 2.92 21.37 1.73 3.45 27.70 1.70 3.62 29.07 1.70 3.76 19.45" 21.80" 28.27" (not resolved) 19.45° 21.47b 28.27" (not resolved) 19.,34 1.61 3.16 21.37 1.45 4.15 28.90 (shoulder; not resolved) 16.20" 21.20" 28.40" (not resolved) 16.34 1.-59 2.58 21.84 1.40 4.43 25.91 (not resolved) 19.20" 25.85" (not resolved) 16.12" 25.92b (not resolved) 16.48° 22.50° 24.25' 27.10° (not resolved) 15.24 1.72 2.20 21.69 1.39 2.95 Masked 15.25" 21.72" 26.12" 15.21 b 21.68" Maskedb • From reference 13. b FrO!ll reference 3. c From reference 15. ,_.. ~ ~ .< (l ~ ;i. z ;i. z tl ~ ~ t-' ..... VISIBLE SPECTRA OF Co(III) COMPLEXES 15 TABLE II Crystal F i eld Parameters Calculated from the Spectral Data Complexes DqXY* Dq z" Dt Ds B 1000 cm-1 1000 cm-1 1000 cm-1 1000 cm-1 1000 cm-1 [Co(NH3);C03)' 2.490 1.612 0.251 1.638' 0.246" 0.0513" [Co(NH3JsH20J3+ 2.485 1.803 0.195 0.314 0.565 2.058" 0.126" 0.0263" 0.630" 2.490" 1.888" 0.172" [Co(NH3);N02]2+ 2.531 3.476 -0.270 -0.510 0.407 3.058" -0.160" -0.0333" 0.551" 2.490" 3.120" -0.180" [ Co(NH3) s02C3H5] 2+ 2.450 1.922 0.151 0.340 0.594 2.020· 0.135" 0.028" 0.509" 2.490" 2.021 b 0.134" [Co(NH3);F]2+ 2.517 1.590 0.265 0.284 0.549 1.858" 0.183" 0.0381 a 0.518" 2.490" 1.849" 0.183" [Co(NH3)5N03]2+ 2.517 1.705 0.232 1.758" 0.211• 0.044" 0.536" trans- [Co( en)2Ch]' 2.564 1.463 0.629 1.483" 0.600" 2.530" 1.459" 0.612" 2.630° 1.426° 0.688° 0.618° trans-[Co(en)2Br2]+ 2.549 1.259 0.737 1.293" 0.709" 0.147" 0.550" 2.530" 1.277" 0.716" [Co(NH3);Cl] 2+" 2.51 1.46 0.299 0.222 0.501 [Co(NH3);Br] 2+ e 2.48 1.31 0.334 * Dq'Y denotes the Dq value of NH3 or e n ; Dq" denotes the Dq value of the remaining ligand(s) . • From reference 13. " From reference 3. c From reference 15. • From reference 2. e F rom refe-rence 1. that the intensities of IA and IB bands were equal. This assumption is not valid since band IB is symmetry forbidden in both C,v and D,1h complexes. As seen from the data given in Table I, the intensities of IA and IB bands are somewhat different. (5) In the determination of the Dt value, Wentworth and Piper3 assumed that the energy of the IB band was approximately equal to that of the I band in the parent complex, [Co(NH3) 6) 3+. However, this assumption is not always correct as seen from the results of [Co(NH3) 5F)2+ reported by them. If the energy of the IB band is used in the calculation instead of the first band of the parent complex, a value close to ours will be obtained, which is about 25°/o greater than theirs. (6) The values of Ds obtained by Ban and Csaszar13 are very much smaller than ours as a result of their neglecting the splitting of the second band. Un-fortunately, the crystal field model does not make a prediction on the magnitude of the splitting of the 1T2g level. Based on a molecular orbital model, Yamatera14 16 S.-Y. CHAN AND W.-K. LI suggested that the splitting of band II should be less than that of band I , which is about 2000 cm-1. Since our results do not contradict this prediction, our values of Ds calculated from the splitting of band II do seem to be reason-able. Furthermore, the values of Ds for [Co(NH3 ) 5Cl]2+ and [Co(NH,.);.Br]2+ obtained by Book et al.1•2 and that for t-[Co(en) 2 Cl2]Cl calculated from the polarized crystal spectrum by Dingle15 are also substantially greater than those obtained by Ban and Csaszar13 . (7) Unlike other complexes the energy of the 1A 2 state above the ground state of [Co(NH"),NOJ 2+ is less than that of the 1 E" state (Figure 1) since the field strength of N02- is greater than that of NH,. In conclusion, it is b elieved that a rather simple crystal field model is successful in the interpretation of the spectra of complexes. In addition, the resolution of the bands can lead to consistent, and therefore hopefully meaning-ful, values for the crysta'l field parameters. Acknowledgement. - The authors wish to thank Dr. K. Y. Hui for his sample of [Co(NH3)aF)2+ and helpful discussions. REFERENCES 1. L. F. Book, K. Y. Hui, 0. W. Lau, and W.-K. Li, Z. Anorg. Al!g. Chem. 426 (1976) 215 . 2. L. F. Book, K. Y. Hui, 0. W. Lau, and W.-K. Li; Z. Anorg. il.ng. Chem. 426 (1976) 227. 3. R. A. D. Wentworth and T. S. Piper, Inorg. Chem. 4 (1965) 709. 4. F. Basolo and R. K. Murman, Inorg. Synth.: Vol. 4, p. 171, J.C. Bailar, Jr. (Ed.), (McGraw-Hill, 1953). 5. S. M. J 0 r gens en, Z. Anorg. Al!g. Chem. 19 (1899) 78. 6. G. Br au er, Handbook of Preparative I norganic Chemistry, 2nd ed., Vol. 2, p. 1534, (Academic Press, 1965). 7. F. Bas o 1 o and R. K. Mu rm an, ref. 4, p. 175. 8. F . Basolo and R. K . Mu rm an, ref. 4, p. 172. 9. F. Ba solo and R. K. Murman, ref. 4, p. 174. 10. J. C. Bai 1 a r, Jr., Inorg. Synth.: Vol. 2, p. 222, W. C. Ferne 1 i us (Ed.), (McGraw-Hill, 1946). 11. S. M. J 0 r gens e n , J . Prakt. Chem. 41 (1890) 440. 12. R. D. B. Fraser and E. Suzuki, Spectral Analysis, p. 174, J. A. B 1 a ck-b urn (Ed.), (Marcel Dekker, 1970). 13. M. B an and J. Csaszar, Magy. Kem. Fol.y. 73 (1967) 509 ; 74 (1968) 333, 587; Acta Chim. (Budapest) 57 (1968) 153. 14. H. Yamat er a , BuH. Chem. Soc. Jap. 31 (1958) 95. 15. R. Ding 1 e, J. Chem. Phys. 4·6 (1967) 1. SAZETAK Vidljivi spektri nekih monoacidopentaamin i diacidotetraamin kompleksa kobalta(III) Suk-Yee Chan i Wai-Kee Li Snimljeni su spinski dopusteni prijelazi u vidljivom podrucju monoacidopenta-amin i diacidotetraamin kompleksa kobalta(III) gdje su acido grupe bile: C032- , H20, N02-, 02CaH5-, F-, Noa-, c1- i Br-. Parametri kristalnog polja i Racah-ovi parametri odredeni su modificiranom metodom Wentworth-a i Piper-a. Rezultati su konzi-stentni unutar niza i u skladu s literaturnim podacima na srodnim sistemima. DEPARTMENT OF CHEMISTRY THE CHINESE UNIVERSITY OF HONG KONG SHATIN, N. T., HONG KONG Prispjelo 8. rujna 1978. 

Visible Spectra of Some Monoacidopentaammine and Diacidotetraammine Complexes of Cobalt(III)

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia