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Silver(I) complexes of selenourea (13C and 15N labeled); characterization by 13C,15N and 107Ag NMR
Inorganic Chemistry Communications 5 (2002) 355–357 www.elsevier.com/locate/inoche
Silver(I) complexes of selenourea (13C and 15N labeled); characterization by 13C; 15N and 107Ag NMR Saeed Ahmad, Anvarhusein A. Isab
*
Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Received 15 December 2001; accepted 12 March 2002
Abstract Silver(I) complexes of selenourea (Seu), Ag(Seu)NO3 and AgðSeuÞ2 NO3 have been prepared and characterized by elemental analysis, IR and NMR ð1 H; 13 C; 15 N and 107 AgÞ spectroscopy. An upfield shift in 13 C NMR and downfield shifts in 1 H and 15 N NMR for selenourea resonances are consistent with the selenium coordination to Ag(I). In 107 Ag NMR, the AgNO3 signal is deshielded by more than 600 ppm on its coordination to selenourea. Ó 2002 Published by Elsevier Science B.V. Keywords: Silver(I); Complexes; Selenourea; NMR
1. Introduction Selenourea, [SeCðNH2 Þ2 ] (Seu) has a high nucleophilicity, caused by the strong electron donating effect of the amino groups, which is comparable to that of thiourea [1]. Some metal complexes of Seu are already reported in the literature [2–4], but there is no known report describing the complexation of AgNO3 with selenourea or other selenones. In this work we report the synthesis of the 1:1 and the 1:2 complexes of silver(I) with selenourea (10% 13 C and 15 N labeled) and their characterization by 1 H; 13 C; 15 N and 107 Ag NMR spectroscopy. Characterization of silver(I) complexes of such small ambidentate ligands would provide a basis for understanding and predicting the interaction with more complex selenone ligands. Recently, we reported the similar studies for silver(I) complexes of thiourea (Tu) [5].
2. Experimental 2.1. Preparation of the complexes The complexes were prepared by mixing the solutions of Seu and AgNO3 in acetonitrile in the molar ratios of *
Corresponding author. Fax: +9663-860-4277. E-mail address: [email protected] (A.A. Isab).
1387-7003/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII: S 1 3 8 7 - 7 0 0 3 ( 0 2 ) 0 0 4 0 5 - 7
1:1 or 2:1 and stirring for 15 min. The resulting white precipitates were filtered and washed with acetone. After preparation the complexes were stored in refrigerator. Yield ¼ 85%. Melting points; AgðSeuÞNO3 ¼ decomposed at 108 °C; AgðSeuÞ2 NO3 ¼ 157–158 °C. Anal. Found (Calc): C, 4.46 (4.10); H, 1.43 (1.38); N 14.82 (14.35) for AgðSeuÞNO3 and C, 5.99 (5.77); H, 1.99 (1.94); N, 16.97 (16.84) for AgðSeuÞ2 NO3 . 2.2. Instrumentation The solid-state IR spectra were recorded on a Perkin– Elmer FTIR 180 spectrophotometer using KBR pellets. All NMR measurements were carried out on a Jeol JNM-LA 500 NMR spectrophotometer at 297 K using 0.25 M solution of the complexes in DMSO-d6 . Since both complexes give black deposits in solution after some time therefore, spectra were measured within 30– 40 min. The 13 C NMR spectra were obtained at the frequency of 125.65 MHz with 1 H broadband decoupling and relative to TMS. The 15 N NMR spectrum were recorded at 50.55 MHz using NH4 15 NO3 as an external reference, which lies at 375.11 ppm relative to pure CH3 NO2 . The 107 Ag NMR was obtained at 20.13 MHz using 10 mm low frequency probe with 9.1 M aqueous AgNO3 as an external reference. The spectral conditions were: 1.02 s acquisition time, 6.0 s delay time, 45° pulse angle and approximately 500 scans. The 77 Se
356 Table 1 1 H; 13 C; 15 N and
S. Ahmad, A.A. Isab / Inorganic Chemistry Communications 5 (2002) 355–357
107
Ag NMR chemical shifts (in ppm) and coupling constants of various species in DMSO-d6
Species
d ð1 HÞ
1
AgNO3 Seua AgðSeuÞ1 NO3 AgðSeuÞ2 NO3 Tub AgðTuÞ1 NO3 b AgðTuÞ2 NO3 b
– 7.60 8.64 8.25 7.05 8.18 7.88
– 144.9 37.8 112.2 91.5 151.3 217.2
a b
JNAH ðHzÞ
d ð13 CÞ
d ð15 NÞ
1
– 179.99 167.16 172.07 183.81 176.53 179.10
– 116.48 124.12 120.63 107.52 115.00 112.52
– 13.6 16.7 15.2 14.0 17.1 16.5
JCAN ðHzÞ
d ð107 AgÞ 165.96 – 810.46 784.34 – 685.93 671.77
d ð77 SeÞ ¼ 1854:5 ppm (relative to SeO2 in D2 O at 1301.4 [15]). Values taken from [5].
NMR for the complexes could not be recorded because the complexes give black deposits in the solution after some time. However, we were able to obtain the 77 Se NMR of the ligand. All NMR (1 H; 13 C; 15 N and 107 Ag) chemical shifts and coupling constants for selenourea, its complexes and their thiourea analogues are given in Table 1.
3. Results and discussion In IR, a decrease in the m(C@Se) mode from 736 cm1 for free Seu to 714 and 724 cm1 in AgðSeuÞNO3 and AgðSeuÞ2 NO3 , respectively, is indicative of reduction in C@Se bond order on selenium coordination to Ag(I). However, intensity of the band was very low in complexes. Three mðNH2 Þ bands around 3200 cm1 are observed at comparatively higher frequency for complexes compared to those for the free ligand. A sharp band for NO 3 bending was observed at 824 cm1 for both complexes [6]. In 1 H NMR, a downfield shift of about 1 ppm was observed for NAH proton of Seu on its complexation with AgNO3 . The deshielding is related to an increase in p electron density in the CAN bond [7]. The signal appeared as a doublet showing coupling with nitrogen (which is 15 N labeled). As shown in Table 1, there is a significant change in the 1 JNAH coupling constant on coordination of Seu with AgNO3 . In 13 C NMR, the > C@Se resonance of Seu in AgðSeuÞNO3 was found 12 ppm upfield compared to free Seu resonance, while in AgðSeuÞ2 NO3 , the upfield shift was of 7 ppm. The upfield shift is attributed to a lowering of > C@Se bond order upon coordination and a shift of N ! C electron density producing a partial double bond character in the CAN bond, as observed in metal complexes of thiourea [5,8]. A downfield shift of 5 ppm in AgðSeuÞ2 NO3 compared to AgðSeuÞNO3 is because of the increase in number of electronegative groups attached to Ag(I) ion. The coupling constant, 1 JCAN could not be obtained by 13 C NMR since the expected triplet could not be resolved properly in 13 C NMR. However, we were able to resolve the 1 JCAN coupling constant by 15 N NMR. The greater shifts in the
13
C NMR for Seu complexes compared to Tu analogues (Table 1) suggests that Seu binds more strongly to silver(I) compared to Tu [9]. In 15 N NMR, the free Seu resonance appeared as a doublet by coupling with labeled 13 C. The 15 N NMR signal in the complexes shifted downfield consistent with an increase in double bond character of the CAN bond. The 15 N NMR of the two complexes shows an opposite trend to that which was observed in 13 C NMR. A similar trend was observed in silver(I) of thiourea. A smaller downfield, instead of a large upfield shift in 15 N NMR rules out the binding of Seu to silver(I) via nitrogen. The metal binding through nitrogen involves an upfield shift of at least 50 ppm as it is observed in some Pt(II) complexes [10,11]. The 107 Ag signal for AgNO3 in DMSO-d6 was observed downfield by 166 ppm compared to that in D2 O. The complexation with Seu shifts the signal further downfield by more than 600 ppm. This very large reduction in shielding appears to be the characteristic of silver(I) binding to the selenium of Seu. The nitrogen-bonded complexes possess a shift of around 100 ppm in 107 Ag NMR [12]. This provides a clear evidence that Seu binds to silver(I) only through selenium atom. The 107 Ag chemical shifts for Seu complexes are found approximately 100 ppm downfield than for Tu complexes. The greater shift is because Se more polarizable compared to sulfur. For Tu complexes, which exist in the form of polymers, it was observed that the 107 Ag resonance for AgðTuÞ2 NO3 appears upfield compared to that for AgðTuÞNO3 [5,13,14]. A similar trend is observed for Seu complexes, which suggests that these compounds should also be polymeric. Further confirmation of their polymeric nature comes from their solubility; when dissolved in DMSO, they give black deposits indicating the breakage of polymers.
Acknowledgements This research was supported by the KFUPM Research Committee under project no. CY/NMR-STUDIES/214.
S. Ahmad, A.A. Isab / Inorganic Chemistry Communications 5 (2002) 355–357
References [1] S. Patai, Z. Rappoport, in: The Chemistry of Organic Selenium and Tellurium Compounds, vol. 1, Wiley, Chichester, 1986, p. 679. [2] S. Hauge, M. Tysseland, Acta Chem. Scand. 25 (1971) 3072. [3] O. Vikane, Acta Chem. Scand. A 29 (1975) 152, 763, 787. [4] P.G. Jones, C. Thone, Chem. Ber. 124 (1991) 2725. [5] S. Ahmad, A.A. Isab, Transition Met. Chem. (in press). [6] M.M. El-Etri, W.M. Scovell, Inorg. Chim. Acta 187 (1991) 201. [7] Z. Popovic, G. Pavlovic, D. Matkovic-Calogovic, Z. Soldin, M. Rajic, D. Vikic-Topic, D. Kovacek, Inorg. Chim. Acta 306 (2000) 142. [8] U. Bierbach, T.W. Hambly, N. Farrell, Inorg. Chem. 37 (1998) 708.
357
[9] A.A. Isab, A.R. Al-Arfaj, M.N. Akhtar, J. Coord. Chem. 33 (1994) 287. [10] T.G. Appletone, J.R. Hall, S.T. Ralph, Inorg. Chem. 24 (1985) 673. [11] F.M. Macdonald, P.J. Sadler, Magn. Res. Chem. 29 (1991) S52. [12] P.M. Henrichs, S. Sheard, J.J.H. Jackerman, G.E. Maciel, J. Am. Chem. Soc. 101 (1979) 3222. [13] M.R. Dupa, G. Henke, B. Krebs, Inorg. Chim. Acta 18 (1976) 173. [14] P.M. Henrichs, J.J.H. Jackerman, G.E. Maciel, Inorg. Chem. 16 (1977) 2544. [15] J. Milne, Mag. Res. Chem. 31 (1993) 652.
Silver(I) complexes of selenourea (13C and 15N labeled); characterization by 13C; 15N and 107Ag NMR Saeed Ahmad, Anvarhusein A. Isab
*
Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Received 15 December 2001; accepted 12 March 2002
Abstract Silver(I) complexes of selenourea (Seu), Ag(Seu)NO3 and AgðSeuÞ2 NO3 have been prepared and characterized by elemental analysis, IR and NMR ð1 H; 13 C; 15 N and 107 AgÞ spectroscopy. An upfield shift in 13 C NMR and downfield shifts in 1 H and 15 N NMR for selenourea resonances are consistent with the selenium coordination to Ag(I). In 107 Ag NMR, the AgNO3 signal is deshielded by more than 600 ppm on its coordination to selenourea. Ó 2002 Published by Elsevier Science B.V. Keywords: Silver(I); Complexes; Selenourea; NMR
1. Introduction Selenourea, [SeCðNH2 Þ2 ] (Seu) has a high nucleophilicity, caused by the strong electron donating effect of the amino groups, which is comparable to that of thiourea [1]. Some metal complexes of Seu are already reported in the literature [2–4], but there is no known report describing the complexation of AgNO3 with selenourea or other selenones. In this work we report the synthesis of the 1:1 and the 1:2 complexes of silver(I) with selenourea (10% 13 C and 15 N labeled) and their characterization by 1 H; 13 C; 15 N and 107 Ag NMR spectroscopy. Characterization of silver(I) complexes of such small ambidentate ligands would provide a basis for understanding and predicting the interaction with more complex selenone ligands. Recently, we reported the similar studies for silver(I) complexes of thiourea (Tu) [5].
2. Experimental 2.1. Preparation of the complexes The complexes were prepared by mixing the solutions of Seu and AgNO3 in acetonitrile in the molar ratios of *
Corresponding author. Fax: +9663-860-4277. E-mail address: [email protected] (A.A. Isab).
1387-7003/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII: S 1 3 8 7 - 7 0 0 3 ( 0 2 ) 0 0 4 0 5 - 7
1:1 or 2:1 and stirring for 15 min. The resulting white precipitates were filtered and washed with acetone. After preparation the complexes were stored in refrigerator. Yield ¼ 85%. Melting points; AgðSeuÞNO3 ¼ decomposed at 108 °C; AgðSeuÞ2 NO3 ¼ 157–158 °C. Anal. Found (Calc): C, 4.46 (4.10); H, 1.43 (1.38); N 14.82 (14.35) for AgðSeuÞNO3 and C, 5.99 (5.77); H, 1.99 (1.94); N, 16.97 (16.84) for AgðSeuÞ2 NO3 . 2.2. Instrumentation The solid-state IR spectra were recorded on a Perkin– Elmer FTIR 180 spectrophotometer using KBR pellets. All NMR measurements were carried out on a Jeol JNM-LA 500 NMR spectrophotometer at 297 K using 0.25 M solution of the complexes in DMSO-d6 . Since both complexes give black deposits in solution after some time therefore, spectra were measured within 30– 40 min. The 13 C NMR spectra were obtained at the frequency of 125.65 MHz with 1 H broadband decoupling and relative to TMS. The 15 N NMR spectrum were recorded at 50.55 MHz using NH4 15 NO3 as an external reference, which lies at 375.11 ppm relative to pure CH3 NO2 . The 107 Ag NMR was obtained at 20.13 MHz using 10 mm low frequency probe with 9.1 M aqueous AgNO3 as an external reference. The spectral conditions were: 1.02 s acquisition time, 6.0 s delay time, 45° pulse angle and approximately 500 scans. The 77 Se
356 Table 1 1 H; 13 C; 15 N and
S. Ahmad, A.A. Isab / Inorganic Chemistry Communications 5 (2002) 355–357
107
Ag NMR chemical shifts (in ppm) and coupling constants of various species in DMSO-d6
Species
d ð1 HÞ
1
AgNO3 Seua AgðSeuÞ1 NO3 AgðSeuÞ2 NO3 Tub AgðTuÞ1 NO3 b AgðTuÞ2 NO3 b
– 7.60 8.64 8.25 7.05 8.18 7.88
– 144.9 37.8 112.2 91.5 151.3 217.2
a b
JNAH ðHzÞ
d ð13 CÞ
d ð15 NÞ
1
– 179.99 167.16 172.07 183.81 176.53 179.10
– 116.48 124.12 120.63 107.52 115.00 112.52
– 13.6 16.7 15.2 14.0 17.1 16.5
JCAN ðHzÞ
d ð107 AgÞ 165.96 – 810.46 784.34 – 685.93 671.77
d ð77 SeÞ ¼ 1854:5 ppm (relative to SeO2 in D2 O at 1301.4 [15]). Values taken from [5].
NMR for the complexes could not be recorded because the complexes give black deposits in the solution after some time. However, we were able to obtain the 77 Se NMR of the ligand. All NMR (1 H; 13 C; 15 N and 107 Ag) chemical shifts and coupling constants for selenourea, its complexes and their thiourea analogues are given in Table 1.
3. Results and discussion In IR, a decrease in the m(C@Se) mode from 736 cm1 for free Seu to 714 and 724 cm1 in AgðSeuÞNO3 and AgðSeuÞ2 NO3 , respectively, is indicative of reduction in C@Se bond order on selenium coordination to Ag(I). However, intensity of the band was very low in complexes. Three mðNH2 Þ bands around 3200 cm1 are observed at comparatively higher frequency for complexes compared to those for the free ligand. A sharp band for NO 3 bending was observed at 824 cm1 for both complexes [6]. In 1 H NMR, a downfield shift of about 1 ppm was observed for NAH proton of Seu on its complexation with AgNO3 . The deshielding is related to an increase in p electron density in the CAN bond [7]. The signal appeared as a doublet showing coupling with nitrogen (which is 15 N labeled). As shown in Table 1, there is a significant change in the 1 JNAH coupling constant on coordination of Seu with AgNO3 . In 13 C NMR, the > C@Se resonance of Seu in AgðSeuÞNO3 was found 12 ppm upfield compared to free Seu resonance, while in AgðSeuÞ2 NO3 , the upfield shift was of 7 ppm. The upfield shift is attributed to a lowering of > C@Se bond order upon coordination and a shift of N ! C electron density producing a partial double bond character in the CAN bond, as observed in metal complexes of thiourea [5,8]. A downfield shift of 5 ppm in AgðSeuÞ2 NO3 compared to AgðSeuÞNO3 is because of the increase in number of electronegative groups attached to Ag(I) ion. The coupling constant, 1 JCAN could not be obtained by 13 C NMR since the expected triplet could not be resolved properly in 13 C NMR. However, we were able to resolve the 1 JCAN coupling constant by 15 N NMR. The greater shifts in the
13
C NMR for Seu complexes compared to Tu analogues (Table 1) suggests that Seu binds more strongly to silver(I) compared to Tu [9]. In 15 N NMR, the free Seu resonance appeared as a doublet by coupling with labeled 13 C. The 15 N NMR signal in the complexes shifted downfield consistent with an increase in double bond character of the CAN bond. The 15 N NMR of the two complexes shows an opposite trend to that which was observed in 13 C NMR. A similar trend was observed in silver(I) of thiourea. A smaller downfield, instead of a large upfield shift in 15 N NMR rules out the binding of Seu to silver(I) via nitrogen. The metal binding through nitrogen involves an upfield shift of at least 50 ppm as it is observed in some Pt(II) complexes [10,11]. The 107 Ag signal for AgNO3 in DMSO-d6 was observed downfield by 166 ppm compared to that in D2 O. The complexation with Seu shifts the signal further downfield by more than 600 ppm. This very large reduction in shielding appears to be the characteristic of silver(I) binding to the selenium of Seu. The nitrogen-bonded complexes possess a shift of around 100 ppm in 107 Ag NMR [12]. This provides a clear evidence that Seu binds to silver(I) only through selenium atom. The 107 Ag chemical shifts for Seu complexes are found approximately 100 ppm downfield than for Tu complexes. The greater shift is because Se more polarizable compared to sulfur. For Tu complexes, which exist in the form of polymers, it was observed that the 107 Ag resonance for AgðTuÞ2 NO3 appears upfield compared to that for AgðTuÞNO3 [5,13,14]. A similar trend is observed for Seu complexes, which suggests that these compounds should also be polymeric. Further confirmation of their polymeric nature comes from their solubility; when dissolved in DMSO, they give black deposits indicating the breakage of polymers.
Acknowledgements This research was supported by the KFUPM Research Committee under project no. CY/NMR-STUDIES/214.
S. Ahmad, A.A. Isab / Inorganic Chemistry Communications 5 (2002) 355–357
References [1] S. Patai, Z. Rappoport, in: The Chemistry of Organic Selenium and Tellurium Compounds, vol. 1, Wiley, Chichester, 1986, p. 679. [2] S. Hauge, M. Tysseland, Acta Chem. Scand. 25 (1971) 3072. [3] O. Vikane, Acta Chem. Scand. A 29 (1975) 152, 763, 787. [4] P.G. Jones, C. Thone, Chem. Ber. 124 (1991) 2725. [5] S. Ahmad, A.A. Isab, Transition Met. Chem. (in press). [6] M.M. El-Etri, W.M. Scovell, Inorg. Chim. Acta 187 (1991) 201. [7] Z. Popovic, G. Pavlovic, D. Matkovic-Calogovic, Z. Soldin, M. Rajic, D. Vikic-Topic, D. Kovacek, Inorg. Chim. Acta 306 (2000) 142. [8] U. Bierbach, T.W. Hambly, N. Farrell, Inorg. Chem. 37 (1998) 708.
357
[9] A.A. Isab, A.R. Al-Arfaj, M.N. Akhtar, J. Coord. Chem. 33 (1994) 287. [10] T.G. Appletone, J.R. Hall, S.T. Ralph, Inorg. Chem. 24 (1985) 673. [11] F.M. Macdonald, P.J. Sadler, Magn. Res. Chem. 29 (1991) S52. [12] P.M. Henrichs, S. Sheard, J.J.H. Jackerman, G.E. Maciel, J. Am. Chem. Soc. 101 (1979) 3222. [13] M.R. Dupa, G. Henke, B. Krebs, Inorg. Chim. Acta 18 (1976) 173. [14] P.M. Henrichs, J.J.H. Jackerman, G.E. Maciel, Inorg. Chem. 16 (1977) 2544. [15] J. Milne, Mag. Res. Chem. 31 (1993) 652.