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Complex chromium and uranyl isocyanates
J. inorg, nucl. Chem., 1972, Vol. 34, pp. 2935-2937.
Pergamon Press.
Printed in Great Britain
NOTES Complex chromium and uranyl isocyanates (Received 7 December 1971 ) THE LIGAND behavior of the cyanate ion is of interest because of its potential ambidentate character. Normally, coordination is through nitrogen[l, 2], but a few examples have been prepared which may be oxygen bound on the basis of the behavior of the Vco band in the i.r. spectra[3, 4]. This is shifted to lower energies in these cases, while in authentic N-bonded systems the shift is the other way. The other bands in the near i.r. region show no systematic differences. Oxygen bonding is not proved in any of the examples in which it is suggested, and in view of the unfavorable charge distribution [5], its occurrence would be notable. We have investigated several systems in which the metal ion shows a strong affinity for oxygen donors to see if O-bound cyanates would be formed. This report describes new cyanato complexes of Cr(III) and U(IV), both of which favor oxygen in other systems (the former is also a d 3 ion, analogous to Mo(III) and Re(IV) which are among the other possible Obonded compounds). Although these show no evidence of the hoped for oxygen bonding mode, they are interesting additions to the known cyanato complexes. Several uranyl cyanates have been reported, but these were not characterized structurally [6]. EXPERIMENTAL Tetraphenylarsonium hexaisocyanatochromium(II1) was prepared by mixing 0"25 g CrCl3, 2 g tetraphenylarsonium chloride and a trace of zinc dust to 75 ml reagent acetone and stirring until solution was essentially complete. The solution was filtered, 1.65 g AgCNO added, and the mixture stirred vigorously for 30 min. This was again filtered, and a large quantity of ether added to separate the product as a green oil. Purification was accomplished by redissolving the oil in a 50:50 acetonenitromethane mixture and reprecipitating with ether. The oil crystallized on drying under vacuum. Analytical results: found; Cr, 3.2%; N, 5.6%; H, 4.0%. [(C6Hs)4As]3[Cr(NCO)6] requires Cr, 3'6%; N, 5'8%, H, 4.1%. C analysis was unreliable. A uranyl cyanate complex was formed by reacting 4"5 g AgNCO with 6"3 g tetraethylammonium bromide in 50 ml. ethanol. The AgBr was filtered off, and 2.5 g of uranyl nitrate hexahydrate in 25 ml. acetone added. A yellow precipitate formed which was washed with acetone and dried under vacuum. Analysis; found; U, 33"2%; N (from N C O only) 7.9%. Calculated for [(C2Hs)4N]2[UO2(NCO)4(H20)., U; 33.4% N (from NCO); 7.8%. Presence of water is shown by the i.r. spectrum as discussed below. Nitrogen analyses were performed by a Kjeldahl technique in which decomposition was brought about by HCI which converts only cyanate nitrogen to NH3. Chromium was analyzed colorimetrically as C r O c , U gravimetrically as the 8-hydroxyquinolinate. I.R. spectra were taken on Perkin-Elmer models 621 and 301 spectrophotometers using KBr pellets and Nujol mulls. Electronic reflectance spectra were taken on a Beckman D U instrument. RESULTS AND DISCUSSION The chromium(III) complex prepared appeared to be a hexacyanate, and represents the first such with this coordination among the first row transition elements. The other hexacyanate complexes are those for which the i.r. spectra are suggestive of O-bonding. The i.r. spectrum in this case showed no such indications (Table 1). The vco band is assigned to 1335 cm -1, a region free from tetraphenyl1. 2. 3. 4. 5. 6.
D. Forster and D. M. L. Goodgame, J. chem. Soc. 2790 (1964). D. Forster and D. M. L. Goodgame, J. chem. Soc. 262,454 (1965). R. A. Bailey and S. L. Kozak, J. inorg, nucl. Chem. 31,689 (1969). J. L. Burmeister, E. A. Deardorff, A. Jensen and V. M. Christiansen, lnorg. Chem. 9, 58 (1970). E. L. Wagner, J. chem. Phys. 43, 2728 (1965). P. Pascal, Bull. Soc. chim. Fr. 15, 11 (1914). 2935
2936
Notes
arsonium ion bands. A band in the same position was observed in a sample of the tetraethylammonium salt, confirming its association with the anion. This value is in the range usual for Vco in N-bonded cyanates. Evidence for Fermi resonance splitting as is found in the free cyanate ion and in the Obonded cases is not present. Positions of YeN and 8NCOare normal, but not diagnostic. In the far i.r. region, a strong band at 345 cm -x is assigned to the VM-L frequency. In the analogous N-bonded thiocyanate complex, VML lies at 364 cm -1 [7]. In complexes of other metals, VM-NCO> VM-MCS,and although these are of tetrahedral geometry, it is surprising to find the order reversed. It could be argued that the low VMLvalue here suggests oxygen rather than nitrogen bonding, but in view of the near i.r. results, this seems improbable. The visible reflectance spectrum is readily assignable oe the basis of an octahedral d 3 ion (Table 2). The value of Dq is lower than that for N-bonded thiocyanate; 1640 cm -~ vs. 1770 cm -~ [8]. Oxygen bonding would be expected to produce a smaller crystal field splitting than N-bonding, but at the same time previous work has shown that N-bound cyanate is weaker than N-bound thiocyanate in tetrahedral species[9, 10], so that the value observed here is quite consistent with the N-bound mode. The magnetic susceptibility at room temperature, measured by the Gouy method, was 3.77 B.M. This is normal for Cr(III). The i.r. spectrum of the uranium complex is given in Table 3. Assignment of the important Vco frequency is difficult as it is located in a region containing cation bands of considerable intensity and which are shifted appreciably from their positions in other salts. The band at 1322 cm -~ is tentatively assigned to this band, although this could be 2~co. If the latter is the case, Fermi resonance as found for the possible O-bonded cyanates is absent, and since it is unlikely that any band below 1322 cm -~ can be the Vco band, N-bonding again seems most probable. The ~ c o frequency is split. This is similar in magnitude to that found for bridging cyanate[1], but the energy of the bands is higher and the geometry is no doubt responsible for this. Assignment of the symmetric and asymmetric Vuo bands is based on the observation by Jones [12, 13] that the U - O bond length and force constants are related to the other ligands present. Using Table 1. I.R. spectrum of [(CeH5)4As]3[CF(NCO)6] Vmax(cm -1)
Assignment
2205 (s) 1335 (m) 619 (m) 601 (m) 345 (s) 151 (br, m) 99 (br, w)
VCN Vco ~Nco ~co I-IML
Table 2. Electronic spectrum of [(C6Hs)4As]3[Cr(NCO)d VmaI(cm -~)
Assignment
16,390 22,950
4A2o---> 42r~ 4A~o ~ 4Tlo (F)
Dq (era -1) B (cm -~) 1640
656
7. D. Forster and D. M. L. Goodgame, lnorg. Chem. 4, 715 (1965). 8. C. K. Jorgensen, Absorption Spectra and Chemical Bonding in Complexes. Pergamon Press, Oxford (1962). 9. F. A. Cotton, D. M. L. Goodgame, M. Goodgame and A. Sacco, J. Am. chem. Soc. 83, 4157 (1961). 10. F . A . Cotton and D. M. L. Goodgame, J.Am. chem. Soc. 83, 1777 (1961). 11. J. Nelson and S. M. Nelson, J. chem. Soc. (A), 1597 (1969). 12. L. H. Jones, Spectrochim.Acta 10, 395 (1958). 13. L. H. Jones, Spectrochim. Acta 11,409 (1958).
Notes
2937
Table 3. I.R. spectrum of [(C2Hs)4N]~[UO2(NCO)4(H20)] (cm -~)
Assignment
3570 (s) 3500 (s) 3380 (s) 3440 (s) 2193 (s) 2118 (sh) 1615 (br, m) 1322 (W) 887 (S) 854 (s) 656 (s) 623 (s) 522 (s) 489 (s) 276 (s) 262 (S) 221 (m) 201 (m) 125 (w, br)
yon yon yon yon vcN vcN VHOH Vco VtJO(assym.) Voo (sym.) /SNco 6NCO Vv-on, vu-on, VU-NCO UU-NCO 8ovo 8ouo
Vma x
his correlations, the force constants aad bond lengths suggested here (6"71 mdyn/A; 1.71 A) are reasonable. McGlynn, Smith and Neel~ [ 14] demonstrated a further relationship between vuo assym. and the spectrochemical series for some uranyl complexes. Our value of 887 cm -1 is appropriate for nitrogen coordinated ligands. In the far i.r. region Vt:-NCOis at a higher energy than the corresponding band in the analogous N-bonded thiocyanate (259 cm-l), as would be expected for N-bonded cyanate. It is difficult to predict where this frequency would lie if the cyanate were O-bonded; one would anticipate a similar value if the U - O bond were similar in strength to the U - N , but the charge distribution could make it much weaker and therefore lower in energy. Again, splitting may be a result of symmetry. Bands at 489 cm-I and 522 cm -1 are in the vu-mo region. Two bands here are difficult to explain from the proposed formula. The presence of two water molecules would have little effect on the composition and is a possibility. However, assignments here are based only on analogy with other compounds. Department o f Chemistry Rensselaer Polytechnic Institute Troy New York 12181 14. S. P. McGlynn, J. K. Smith and W. C. Neely, J. chem. Phys. 35, 105 (1961 ).
R. A. BAILEY T. W. M I C H E L S E N
Pergamon Press.
Printed in Great Britain
NOTES Complex chromium and uranyl isocyanates (Received 7 December 1971 ) THE LIGAND behavior of the cyanate ion is of interest because of its potential ambidentate character. Normally, coordination is through nitrogen[l, 2], but a few examples have been prepared which may be oxygen bound on the basis of the behavior of the Vco band in the i.r. spectra[3, 4]. This is shifted to lower energies in these cases, while in authentic N-bonded systems the shift is the other way. The other bands in the near i.r. region show no systematic differences. Oxygen bonding is not proved in any of the examples in which it is suggested, and in view of the unfavorable charge distribution [5], its occurrence would be notable. We have investigated several systems in which the metal ion shows a strong affinity for oxygen donors to see if O-bound cyanates would be formed. This report describes new cyanato complexes of Cr(III) and U(IV), both of which favor oxygen in other systems (the former is also a d 3 ion, analogous to Mo(III) and Re(IV) which are among the other possible Obonded compounds). Although these show no evidence of the hoped for oxygen bonding mode, they are interesting additions to the known cyanato complexes. Several uranyl cyanates have been reported, but these were not characterized structurally [6]. EXPERIMENTAL Tetraphenylarsonium hexaisocyanatochromium(II1) was prepared by mixing 0"25 g CrCl3, 2 g tetraphenylarsonium chloride and a trace of zinc dust to 75 ml reagent acetone and stirring until solution was essentially complete. The solution was filtered, 1.65 g AgCNO added, and the mixture stirred vigorously for 30 min. This was again filtered, and a large quantity of ether added to separate the product as a green oil. Purification was accomplished by redissolving the oil in a 50:50 acetonenitromethane mixture and reprecipitating with ether. The oil crystallized on drying under vacuum. Analytical results: found; Cr, 3.2%; N, 5.6%; H, 4.0%. [(C6Hs)4As]3[Cr(NCO)6] requires Cr, 3'6%; N, 5'8%, H, 4.1%. C analysis was unreliable. A uranyl cyanate complex was formed by reacting 4"5 g AgNCO with 6"3 g tetraethylammonium bromide in 50 ml. ethanol. The AgBr was filtered off, and 2.5 g of uranyl nitrate hexahydrate in 25 ml. acetone added. A yellow precipitate formed which was washed with acetone and dried under vacuum. Analysis; found; U, 33"2%; N (from N C O only) 7.9%. Calculated for [(C2Hs)4N]2[UO2(NCO)4(H20)., U; 33.4% N (from NCO); 7.8%. Presence of water is shown by the i.r. spectrum as discussed below. Nitrogen analyses were performed by a Kjeldahl technique in which decomposition was brought about by HCI which converts only cyanate nitrogen to NH3. Chromium was analyzed colorimetrically as C r O c , U gravimetrically as the 8-hydroxyquinolinate. I.R. spectra were taken on Perkin-Elmer models 621 and 301 spectrophotometers using KBr pellets and Nujol mulls. Electronic reflectance spectra were taken on a Beckman D U instrument. RESULTS AND DISCUSSION The chromium(III) complex prepared appeared to be a hexacyanate, and represents the first such with this coordination among the first row transition elements. The other hexacyanate complexes are those for which the i.r. spectra are suggestive of O-bonding. The i.r. spectrum in this case showed no such indications (Table 1). The vco band is assigned to 1335 cm -1, a region free from tetraphenyl1. 2. 3. 4. 5. 6.
D. Forster and D. M. L. Goodgame, J. chem. Soc. 2790 (1964). D. Forster and D. M. L. Goodgame, J. chem. Soc. 262,454 (1965). R. A. Bailey and S. L. Kozak, J. inorg, nucl. Chem. 31,689 (1969). J. L. Burmeister, E. A. Deardorff, A. Jensen and V. M. Christiansen, lnorg. Chem. 9, 58 (1970). E. L. Wagner, J. chem. Phys. 43, 2728 (1965). P. Pascal, Bull. Soc. chim. Fr. 15, 11 (1914). 2935
2936
Notes
arsonium ion bands. A band in the same position was observed in a sample of the tetraethylammonium salt, confirming its association with the anion. This value is in the range usual for Vco in N-bonded cyanates. Evidence for Fermi resonance splitting as is found in the free cyanate ion and in the Obonded cases is not present. Positions of YeN and 8NCOare normal, but not diagnostic. In the far i.r. region, a strong band at 345 cm -x is assigned to the VM-L frequency. In the analogous N-bonded thiocyanate complex, VML lies at 364 cm -1 [7]. In complexes of other metals, VM-NCO> VM-MCS,and although these are of tetrahedral geometry, it is surprising to find the order reversed. It could be argued that the low VMLvalue here suggests oxygen rather than nitrogen bonding, but in view of the near i.r. results, this seems improbable. The visible reflectance spectrum is readily assignable oe the basis of an octahedral d 3 ion (Table 2). The value of Dq is lower than that for N-bonded thiocyanate; 1640 cm -~ vs. 1770 cm -~ [8]. Oxygen bonding would be expected to produce a smaller crystal field splitting than N-bonding, but at the same time previous work has shown that N-bound cyanate is weaker than N-bound thiocyanate in tetrahedral species[9, 10], so that the value observed here is quite consistent with the N-bound mode. The magnetic susceptibility at room temperature, measured by the Gouy method, was 3.77 B.M. This is normal for Cr(III). The i.r. spectrum of the uranium complex is given in Table 3. Assignment of the important Vco frequency is difficult as it is located in a region containing cation bands of considerable intensity and which are shifted appreciably from their positions in other salts. The band at 1322 cm -~ is tentatively assigned to this band, although this could be 2~co. If the latter is the case, Fermi resonance as found for the possible O-bonded cyanates is absent, and since it is unlikely that any band below 1322 cm -~ can be the Vco band, N-bonding again seems most probable. The ~ c o frequency is split. This is similar in magnitude to that found for bridging cyanate[1], but the energy of the bands is higher and the geometry is no doubt responsible for this. Assignment of the symmetric and asymmetric Vuo bands is based on the observation by Jones [12, 13] that the U - O bond length and force constants are related to the other ligands present. Using Table 1. I.R. spectrum of [(CeH5)4As]3[CF(NCO)6] Vmax(cm -1)
Assignment
2205 (s) 1335 (m) 619 (m) 601 (m) 345 (s) 151 (br, m) 99 (br, w)
VCN Vco ~Nco ~co I-IML
Table 2. Electronic spectrum of [(C6Hs)4As]3[Cr(NCO)d VmaI(cm -~)
Assignment
16,390 22,950
4A2o---> 42r~ 4A~o ~ 4Tlo (F)
Dq (era -1) B (cm -~) 1640
656
7. D. Forster and D. M. L. Goodgame, lnorg. Chem. 4, 715 (1965). 8. C. K. Jorgensen, Absorption Spectra and Chemical Bonding in Complexes. Pergamon Press, Oxford (1962). 9. F. A. Cotton, D. M. L. Goodgame, M. Goodgame and A. Sacco, J. Am. chem. Soc. 83, 4157 (1961). 10. F . A . Cotton and D. M. L. Goodgame, J.Am. chem. Soc. 83, 1777 (1961). 11. J. Nelson and S. M. Nelson, J. chem. Soc. (A), 1597 (1969). 12. L. H. Jones, Spectrochim.Acta 10, 395 (1958). 13. L. H. Jones, Spectrochim. Acta 11,409 (1958).
Notes
2937
Table 3. I.R. spectrum of [(C2Hs)4N]~[UO2(NCO)4(H20)] (cm -~)
Assignment
3570 (s) 3500 (s) 3380 (s) 3440 (s) 2193 (s) 2118 (sh) 1615 (br, m) 1322 (W) 887 (S) 854 (s) 656 (s) 623 (s) 522 (s) 489 (s) 276 (s) 262 (S) 221 (m) 201 (m) 125 (w, br)
yon yon yon yon vcN vcN VHOH Vco VtJO(assym.) Voo (sym.) /SNco 6NCO Vv-on, vu-on, VU-NCO UU-NCO 8ovo 8ouo
Vma x
his correlations, the force constants aad bond lengths suggested here (6"71 mdyn/A; 1.71 A) are reasonable. McGlynn, Smith and Neel~ [ 14] demonstrated a further relationship between vuo assym. and the spectrochemical series for some uranyl complexes. Our value of 887 cm -1 is appropriate for nitrogen coordinated ligands. In the far i.r. region Vt:-NCOis at a higher energy than the corresponding band in the analogous N-bonded thiocyanate (259 cm-l), as would be expected for N-bonded cyanate. It is difficult to predict where this frequency would lie if the cyanate were O-bonded; one would anticipate a similar value if the U - O bond were similar in strength to the U - N , but the charge distribution could make it much weaker and therefore lower in energy. Again, splitting may be a result of symmetry. Bands at 489 cm-I and 522 cm -1 are in the vu-mo region. Two bands here are difficult to explain from the proposed formula. The presence of two water molecules would have little effect on the composition and is a possibility. However, assignments here are based only on analogy with other compounds. Department o f Chemistry Rensselaer Polytechnic Institute Troy New York 12181 14. S. P. McGlynn, J. K. Smith and W. C. Neely, J. chem. Phys. 35, 105 (1961 ).
R. A. BAILEY T. W. M I C H E L S E N