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Synthesis and characterization of a technetium nitrido dimer
www.elsevier.nl/locate/ica Inorganica Chimica Acta 316 (2001) 110– 112
Note
Synthesis and characterization of a technetium nitrido dimer Terrence Nicholson a,b,*, Daniel J. Kramer a, Alan Davison a, Alun G. Jones b a
Room 6 -433, Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts A6enue, Cambridge, MA 02139, USA b Department of Radiology, Har6ard Medical School, Boston, MA 02116, USA Received 10 October 2000; accepted 12 January 2001
Abstract In 1993, Baldas et al. [1] reported the synthesis of the technetium(VI) nitridodi (m-oxo) dimer (AsPh4)2[{TcNCl2}2(m-O)2], which was synthesized from methanesulfonic acid and Cs2[TcNCl5] in water with heating. We report here, the facile synthesis and characterization of the tetrabutylammonium analog, (Bu4N)2[{TcNCl2}2(m-O)2] (1), which is synthesized from (Bu4N)[TcNCl4] and water in acetone at room temperature. This may have important ramifications for technetium based radiopharmaceutical development, since [99mTcNCl4]− is frequently employed at the tracer level as a technetium nitrido synthon, and technetium nitrido chemistry continues to be a rapidly developing area in radiopharmaceutical research [1]. The infrared spectrum of 1 displays a pronounced absorption at 1062 cm − 1, attributed to the TcN bond. The FAB(−) mass spectrum displays the parent ion of 642 m/z which corresponds to {(Bu4N)[{TcNCl2}2(m-O)2]}−. The X-ray crystal structure of 1 is similar to the previously reported tetraphenylarsonium analog [2]. The technetium nitrogen triple bond lengths are 1.601(7) and 1.597(7) A, . The X-ray structure solution for C32H72Cl4N2O4Tc of molecular weight 886.72 g mol − 1: Monoclinic space group P21/n, a= 15.2894(12), b=16.4321(12), c=17.9311(14) A, , i = 105.5100(10)°, volume = 4340.9(6) A, 3. Solution based on 6212 independent reflections to give a final R value of 0.0701 and GOF = 1.124. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Crystal structures; Technetium complexes; Nitrido complexes; Dimer complexes
1. Introduction With the increased scrutiny technetium nitrido chemistry is being afforded of late, due to the development of various reagents which effectively introduce the nitrido ligand at the tracer level (99mTc), the behavior of the nitrido core in aqueous media is an important topic. The fact that 1 has been synthesized from two different precursors in good yields suggests that it might be an important intermediate or a by-product in nitrido based radiopharmaceutical development.
done in laboratories approved for the use of low levels of radioactive materials. Precautions have been detailed elsewhere [3]. Reagents and solvents were used as received unless otherwise stated. Routine infrared spectra were obtained on a Perkin –Elmer 1600-FTIR Spectrometer. Analytical results were obtained from Atlantic Microlab Inc., Norcross, GA. Fast atom bombardment (FAB) ( + /− ) spectra of samples dissolved in p-nitrobenzyl-alcohol matrix were recorded with a MAT 731 mass spectrometer equipped with an Ion Tech B11N FAB gun, operating at an accelerating voltage of 8 kV. The FAB gun produced a beam of 6–8 keV xenon neutrals.
2. Experimental Caution! Technetium-99 is a weak b−-emitter (E= 0.292 MeV, t1/2 = 2.12 ×105 years). All work has been * Corresponding author. Fax: + 1-617-258 6989.
2.1. X-ray crystallographic data collection parameters The crystal data and some experimental details of the structure determination are given in Table 1. The crystal exhibited no significant decay under X-irradiation.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 3 7 3 - 5
T. Nicholson et al. / Inorganica Chimica Acta 316 (2001) 110–112
A yellow prismatic crystal of 1 was isolated from the acetone–water mixture as described below. The crystals dimensions were 0.13×0.16 ×0.17 mm3. The diffractometer employed was a Siemens platform goniometer with a CCD detector with the data set collected at Table 1 X-ray data for structure determination of 1 Empirical formula Formula weight Temperature (°K) Crystal system Space group a (A, ) b (A, ) c (A, ) i (°) V (A, 3) Z Dcalc (mg m−3) v (mm−1) Radiation (l, A, )3 a R, Rw Goodness-of-fit on F 2 a
C32H72Cl4N2O4Tc2 886.72 293 monoclinic P21/n 15.289(1) 16.432(1) 17.931(1) 105.510(1) 4340.9(6) 4 1.357 0.915 Mo Ka (0.71073) 0.0701, 0.1285 1.124
Graphite monochromated.
111
−90°C. The scan mode used was 2q/ , with a maximum 2q of 46.5°. A total of 17 359 reflections were collected of which 6212 were of I\ 2|(I) and were used in the final refinement. The technetium atom was located using the Patterson method, with full-matrix least-squares refinement on F 2. (G.M. Sheldrick and Siemens Industrial Automation, SHELXTL V 5.0, 1995.). Neutral atomic scattering factors were used throughout the analysis. Extinction effects were not observed. Final hydrogen atom positions were calculated. All non-hydrogen atoms were refined anisotropically.
2.2. Synthesis Preparation of (Bu4N)2[{TcNCl2}2(m-O)2] (1): to a stirred solution of (Bu4N)[TcNCl4] in 65 ml acetone, was added 15 ml deionized water. The bright orange color darkens before turning yellow–brown. This solution was allowed to sit at room temperature (r.t.) in an open flask, which deposited yellow crystals within 24 h. The air stable crystals were isolated and air-dried on a fine fritted funnel. The yellow–brown filtrate was set aside, which produced a second crop of crystalline complex 1. Analytical results for 1: Anal. Found: C, 43.56; H, 8.20; N, 6.37. Calc. for [C32H72Cl4N2O4Tc]: C, 43.46; H, 8.20; N, 6.33%. IR (KBr, cm − 1): w(TcN), 1062. FAB(− ) MS: (in p-nitro-benzylalcohol) m/z: ({(Bu4N)[Tc2N2O2Cl4]}−, 642); ([Tc2N2O2Cl3]−, 365); ([Tc2N2O2Cl2]−, 328).
3. Discussion
Fig. 1. ORTEP diagram for the oxo-bridged dianion, showing 15% thermal ellipsoids. Table 2 Selected bond lengths (A, ) and angles (°) for 1 Tc1N4 Tc1O1 Tc1O2 Tc1Cl3 Tc1Cl4 Tc1Tc2 Tc1O1Tc2 N3Tc2O1 N3Tc2Cl5 N4Tc1O1 N4Tc1Cl3 N4Tc1Tc2 O1Tc1O2 Cl3Tc1Cl4
1.601(7) 1.909(4) 1.930(5) 2.416(2) 2.382(2) 2.5493(10) 83.6(2) 107.3(3) 102.3(3) 109.2(3) 99.1(3) 101.9(3) 92.9(2) 85.04(10)
Tc2N3 Tc2O1 Tc2O2 Tc2Cl5 Tc2Cl6 Tc1O2Tc2 N3Tc2O2 N3Tc2Cl6 N4Tc1O2 N4Tc1Cl4 N3Tc2Tc1 O1Tc2O2 Cl5Tc2Cl6
1.597(7) 1.915(5) 1.923(5) 2.388(2) 2.379(2) 82.8(2) 108.7(4) 100.8(3) 107.6(3) 103.8(3) 101.3(3) 93.9(2) 85.01(9)
High oxidation state chemistry of the Group 7 transition metals is dominated by oxo complexes. We report here the synthesis of an oxo bridged, dimeric technetium(VI) nitrido complex which forms at room temperature in an acetone–water mixture. Upon the dropwise addition of H2O to a stirred solution of TBA[TcNCl4] in acetone, the solution’s color changes from the bright orange nitrido precursor to a dark purple–brown before lightening to a golden yellow. The intermediate color(s) probably reflect reaction intermediates containing aquo and/or hydroxy groups, which are subsequently deprotonated to form the bridging oxo groups that are observed in the structurally characterized product. An ORTEP diagram of the edge sharing square pyramidal structure of the dianion with a syn orientation of nitrido groups is shown in Fig. 1. The structural aspects of this complex are quite unexceptional, with bond lengths and angles well within the expected ranges (see Table 2). What is exceptional however is the similarity between the [Tc2N2O2]2 + core and the isoelectronic [Mo2O4]2 + core. This easily syn-
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T. Nicholson et al. / Inorganica Chimica Acta 316 (2001) 110–112
thesized dimeric technetium nitrido complex is isoelectronic to the oxo-molybdenum dimer [Mo2O4Cl4], which has proved to be a very useful synthon. The substitution chemisty of this complex is currently being examined.
Acknowledgements We would like thank Dr. William M. Davis of the MIT Department of Chemistry for his assistance with the X-ray data collection and Li Li of the MIT Depart-
.
ment of Chemistry Instrumentation Facility for the fast atom bombardment mass spectrometry results.
References [1] (a) M. Nicolini, G. Bandoli, U. Mazzi. Technetium and Rhenium in Chemistry and Nuclear Medicine, Cortina Int. 3 (1990). (b) Verona. R. Pasqualini, A. Duatti. J. Chem. Soc. Chem. Commun. (1992) 1354 – 1360. [2] J. Baldas, J.F. Boas, S.F. Colmanet, Z. Ivanov, G.A. Williams, Radiochim. Acta 63 (1993) 111. [3] A. Davison, C. Orvig, H.S. Trop, M. Sohn, B.V. DePamphilis, A.G. Jones, Inorg. Chem. 19 (1980) 1988.
Note
Synthesis and characterization of a technetium nitrido dimer Terrence Nicholson a,b,*, Daniel J. Kramer a, Alan Davison a, Alun G. Jones b a
Room 6 -433, Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts A6enue, Cambridge, MA 02139, USA b Department of Radiology, Har6ard Medical School, Boston, MA 02116, USA Received 10 October 2000; accepted 12 January 2001
Abstract In 1993, Baldas et al. [1] reported the synthesis of the technetium(VI) nitridodi (m-oxo) dimer (AsPh4)2[{TcNCl2}2(m-O)2], which was synthesized from methanesulfonic acid and Cs2[TcNCl5] in water with heating. We report here, the facile synthesis and characterization of the tetrabutylammonium analog, (Bu4N)2[{TcNCl2}2(m-O)2] (1), which is synthesized from (Bu4N)[TcNCl4] and water in acetone at room temperature. This may have important ramifications for technetium based radiopharmaceutical development, since [99mTcNCl4]− is frequently employed at the tracer level as a technetium nitrido synthon, and technetium nitrido chemistry continues to be a rapidly developing area in radiopharmaceutical research [1]. The infrared spectrum of 1 displays a pronounced absorption at 1062 cm − 1, attributed to the TcN bond. The FAB(−) mass spectrum displays the parent ion of 642 m/z which corresponds to {(Bu4N)[{TcNCl2}2(m-O)2]}−. The X-ray crystal structure of 1 is similar to the previously reported tetraphenylarsonium analog [2]. The technetium nitrogen triple bond lengths are 1.601(7) and 1.597(7) A, . The X-ray structure solution for C32H72Cl4N2O4Tc of molecular weight 886.72 g mol − 1: Monoclinic space group P21/n, a= 15.2894(12), b=16.4321(12), c=17.9311(14) A, , i = 105.5100(10)°, volume = 4340.9(6) A, 3. Solution based on 6212 independent reflections to give a final R value of 0.0701 and GOF = 1.124. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Crystal structures; Technetium complexes; Nitrido complexes; Dimer complexes
1. Introduction With the increased scrutiny technetium nitrido chemistry is being afforded of late, due to the development of various reagents which effectively introduce the nitrido ligand at the tracer level (99mTc), the behavior of the nitrido core in aqueous media is an important topic. The fact that 1 has been synthesized from two different precursors in good yields suggests that it might be an important intermediate or a by-product in nitrido based radiopharmaceutical development.
done in laboratories approved for the use of low levels of radioactive materials. Precautions have been detailed elsewhere [3]. Reagents and solvents were used as received unless otherwise stated. Routine infrared spectra were obtained on a Perkin –Elmer 1600-FTIR Spectrometer. Analytical results were obtained from Atlantic Microlab Inc., Norcross, GA. Fast atom bombardment (FAB) ( + /− ) spectra of samples dissolved in p-nitrobenzyl-alcohol matrix were recorded with a MAT 731 mass spectrometer equipped with an Ion Tech B11N FAB gun, operating at an accelerating voltage of 8 kV. The FAB gun produced a beam of 6–8 keV xenon neutrals.
2. Experimental Caution! Technetium-99 is a weak b−-emitter (E= 0.292 MeV, t1/2 = 2.12 ×105 years). All work has been * Corresponding author. Fax: + 1-617-258 6989.
2.1. X-ray crystallographic data collection parameters The crystal data and some experimental details of the structure determination are given in Table 1. The crystal exhibited no significant decay under X-irradiation.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 3 7 3 - 5
T. Nicholson et al. / Inorganica Chimica Acta 316 (2001) 110–112
A yellow prismatic crystal of 1 was isolated from the acetone–water mixture as described below. The crystals dimensions were 0.13×0.16 ×0.17 mm3. The diffractometer employed was a Siemens platform goniometer with a CCD detector with the data set collected at Table 1 X-ray data for structure determination of 1 Empirical formula Formula weight Temperature (°K) Crystal system Space group a (A, ) b (A, ) c (A, ) i (°) V (A, 3) Z Dcalc (mg m−3) v (mm−1) Radiation (l, A, )3 a R, Rw Goodness-of-fit on F 2 a
C32H72Cl4N2O4Tc2 886.72 293 monoclinic P21/n 15.289(1) 16.432(1) 17.931(1) 105.510(1) 4340.9(6) 4 1.357 0.915 Mo Ka (0.71073) 0.0701, 0.1285 1.124
Graphite monochromated.
111
−90°C. The scan mode used was 2q/ , with a maximum 2q of 46.5°. A total of 17 359 reflections were collected of which 6212 were of I\ 2|(I) and were used in the final refinement. The technetium atom was located using the Patterson method, with full-matrix least-squares refinement on F 2. (G.M. Sheldrick and Siemens Industrial Automation, SHELXTL V 5.0, 1995.). Neutral atomic scattering factors were used throughout the analysis. Extinction effects were not observed. Final hydrogen atom positions were calculated. All non-hydrogen atoms were refined anisotropically.
2.2. Synthesis Preparation of (Bu4N)2[{TcNCl2}2(m-O)2] (1): to a stirred solution of (Bu4N)[TcNCl4] in 65 ml acetone, was added 15 ml deionized water. The bright orange color darkens before turning yellow–brown. This solution was allowed to sit at room temperature (r.t.) in an open flask, which deposited yellow crystals within 24 h. The air stable crystals were isolated and air-dried on a fine fritted funnel. The yellow–brown filtrate was set aside, which produced a second crop of crystalline complex 1. Analytical results for 1: Anal. Found: C, 43.56; H, 8.20; N, 6.37. Calc. for [C32H72Cl4N2O4Tc]: C, 43.46; H, 8.20; N, 6.33%. IR (KBr, cm − 1): w(TcN), 1062. FAB(− ) MS: (in p-nitro-benzylalcohol) m/z: ({(Bu4N)[Tc2N2O2Cl4]}−, 642); ([Tc2N2O2Cl3]−, 365); ([Tc2N2O2Cl2]−, 328).
3. Discussion
Fig. 1. ORTEP diagram for the oxo-bridged dianion, showing 15% thermal ellipsoids. Table 2 Selected bond lengths (A, ) and angles (°) for 1 Tc1N4 Tc1O1 Tc1O2 Tc1Cl3 Tc1Cl4 Tc1Tc2 Tc1O1Tc2 N3Tc2O1 N3Tc2Cl5 N4Tc1O1 N4Tc1Cl3 N4Tc1Tc2 O1Tc1O2 Cl3Tc1Cl4
1.601(7) 1.909(4) 1.930(5) 2.416(2) 2.382(2) 2.5493(10) 83.6(2) 107.3(3) 102.3(3) 109.2(3) 99.1(3) 101.9(3) 92.9(2) 85.04(10)
Tc2N3 Tc2O1 Tc2O2 Tc2Cl5 Tc2Cl6 Tc1O2Tc2 N3Tc2O2 N3Tc2Cl6 N4Tc1O2 N4Tc1Cl4 N3Tc2Tc1 O1Tc2O2 Cl5Tc2Cl6
1.597(7) 1.915(5) 1.923(5) 2.388(2) 2.379(2) 82.8(2) 108.7(4) 100.8(3) 107.6(3) 103.8(3) 101.3(3) 93.9(2) 85.01(9)
High oxidation state chemistry of the Group 7 transition metals is dominated by oxo complexes. We report here the synthesis of an oxo bridged, dimeric technetium(VI) nitrido complex which forms at room temperature in an acetone–water mixture. Upon the dropwise addition of H2O to a stirred solution of TBA[TcNCl4] in acetone, the solution’s color changes from the bright orange nitrido precursor to a dark purple–brown before lightening to a golden yellow. The intermediate color(s) probably reflect reaction intermediates containing aquo and/or hydroxy groups, which are subsequently deprotonated to form the bridging oxo groups that are observed in the structurally characterized product. An ORTEP diagram of the edge sharing square pyramidal structure of the dianion with a syn orientation of nitrido groups is shown in Fig. 1. The structural aspects of this complex are quite unexceptional, with bond lengths and angles well within the expected ranges (see Table 2). What is exceptional however is the similarity between the [Tc2N2O2]2 + core and the isoelectronic [Mo2O4]2 + core. This easily syn-
112
T. Nicholson et al. / Inorganica Chimica Acta 316 (2001) 110–112
thesized dimeric technetium nitrido complex is isoelectronic to the oxo-molybdenum dimer [Mo2O4Cl4], which has proved to be a very useful synthon. The substitution chemisty of this complex is currently being examined.
Acknowledgements We would like thank Dr. William M. Davis of the MIT Department of Chemistry for his assistance with the X-ray data collection and Li Li of the MIT Depart-
.
ment of Chemistry Instrumentation Facility for the fast atom bombardment mass spectrometry results.
References [1] (a) M. Nicolini, G. Bandoli, U. Mazzi. Technetium and Rhenium in Chemistry and Nuclear Medicine, Cortina Int. 3 (1990). (b) Verona. R. Pasqualini, A. Duatti. J. Chem. Soc. Chem. Commun. (1992) 1354 – 1360. [2] J. Baldas, J.F. Boas, S.F. Colmanet, Z. Ivanov, G.A. Williams, Radiochim. Acta 63 (1993) 111. [3] A. Davison, C. Orvig, H.S. Trop, M. Sohn, B.V. DePamphilis, A.G. Jones, Inorg. Chem. 19 (1980) 1988.