Inorg. Chem. 1988. 27. 3614-3619
3614
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-0.548 V, respectively. The replacement of T E A P by tetraethylammonium chloride has no significant effect on voltammograms obtained in 0.1 M S D S (Figure 7), and thus the effect induced by NaCl clearly results from the replacement of the tetraethylammonium cation by the sodium cation. This effect on the electrochemistry in S D S micellar solution is attributed to changes induced in the micellar environment by the cations from the supporting electrolyte; the cmc values of 0.1 M S D S in the presence of 0.1 M NaCl and 0.1 M T E A P are 1.5 and 0.1 mM, respectively. The 15-fold decrease in cmc reflects a greater tendency for surfactant aggregation in the presence of the tetraethylammonium cation. The larger tetraethylammonium cation presumably ion-pairs more effectively with the dodecyl sulfate anion than does the smaller, more hydrophilic, sodium cation. The effect of this tetraethylammonium ion-pairing on the structure of the S D S micelles should be similar to the effect engendered by the incorporation of heptanol?' i.e., increased distances between the anionic S D S head groups, which result in a tighter, more closely packed, micellar environment. The more tightly packed TEAP/SDS micelles apparently allow for more efficient electron transfer between the electrode and solubilized complexes than do the more loosely packed N a / S D S micelles.
a reduction in Faradaic current for all complexes; in fact, the
Acknowledgment. Financial support by the National Institutes of Health, Grant No. HL21276 and CA42179 (E.D.), and the Department of Energy, Grant No. DE-FG02-86ER60487 (W. R.H.), is gratefully acknowledged. J.R.K. also wishes to thank Dr. Hendrik Emons of Karl-Man-University Leipzig and Dr. Jim Sullivan of Argonne National Laboratory for many helpful discussions.
current is reduced to such an extent that reliable voltammetric information can be obtained only for [Re(dmpe)2C12]+ and [ R e ( d m ~ e ) ~ B r ~which ] + , exhibit peak potentials of -0.608 and
(37) Russell, J. C.; Whitten, D. G . J. Am. Chem.Soc. 1982,104,5937-5942.
E (VOLT)
Figure 7. Cyclic voltammograms of [Re(dmpe)2Clz]+in aqueous solution: (a) 0.1 M SDS/O.I M TEAP, [Re] = 1.51 mM; (b) 0.1 M SDS/O.l M (TEA)CI, [Re] = 1.50 mM; (c) 0.1 M SDS/O.l M NaCI, [Re] = 1.61 mM. The scan rate is 100 mV/s.
Contribution from the Biomedical Chemistry Research Center, Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, Department of Chemistry, Rosary College, River Forest, Illinois 60305, and Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439
Structural and Kinetic Investigations of a Tc(III)/Tc(II) Redox Couple. X-ray Crystal and trans -[Tc"'( DPPE),C12]N03*HN03,Where Structures of trans -[TC~~(DPPE)~CI,] DPPE = 1,2-Bis(dipheny1phospbino)ethane' Karen Libson,2 Mary Noon Doyle,2 Rudy W. Thomas,2 Theodore Nelesnik,2 Mary Woods,3 James C. S ~ l l i v a nR. , ~ C. Elder,2 and Edward Deutsch*,2 Received January 11 1988 The components of a reversible Tc(III/II) redox couple have been characterized by single-crystal X-ray analysis. The Tc(I1) com lex ~ ~ ~ ~ ~ - [ T C ( D P P E(fw ) ~=C966.67) I,] crystallizes in the monoclinic space group P2]/u with u = 17.821 (4) A,6 = 11.187 (2) c = 23.572 (4) A,8 = 103.55 (l)", and 2 = 4; 4945 observed reflections were refined to a weighted R factor of 0.029. (fw = 1091.69) crystallizes in the triclinic space group PT with a = 10.083 The Tc(II1) salt C~~~~-[TC(DPPE)~CI,]NO~-HNO~ (2) A. 6 = 11.119 (4) A,c = 12.767 (1) A,a = 71.80 (l)", j3 = 73.68 (l)", y = 69.35 ( 1 ) O , and Z = 1; 5697 observed reflections were refined to a weighted R factor of 0.035. Oxidation of the Tc(I1) complex to the Tc(II1) form causes a shortening of the T c C l bond by 0.105 (2) A, consistent with the ionic nature of this interaction. Conversely, oxidation from Tc(I1) to Tc(II1) causes a lengthening of the Tc-P bond by 0.072 (2) A, consistent with the domination of this interaction by 7-back-bonding from Tc to P. The magnitudes of these bond length changes are used to predict the inner-sphere reorganizational barrier to electron transfer of the c ~ ~ ~ ~ - [ T c ( D P P E ) couple ~ C ~ ~to] +be/ "only ca. 2.6 kcal/mol. Preliminary kinetic studies in nonaqueous media confirm that ~ ~ U ~ S - [ T C " ( D P P E(X ) ~=XC1, ~ ] Br) complexes are facile electron-transfer partners for a variety of 1-equiv oxidants. The rate of reduction of [(en)2Co(S(CH2C6H4CH,)CH2CH,NH2)]3+ by ~ ~ u ~ ~ - [ T c ~ * ( D P P in E )acetonitrile ~CI,] (25 "C; p = 0.10 M) is 3.0 (7) x 104 M-1 sLl. I
1,
Introduction Redox-active technetium complexes are of considerable interest for nuclear medicine applications.5,6 Technetium(III/II) corn(1) Abstracted in part from: (a) Libson, K. Ph.D. Thesis, University of Cincinnati, 1981. (b) Noon, M. Ph.D. Thesis, University of Cincinnati,
1984. (2) University of Cincinnati. (3) Rosary College. (4) Argonne National Laboratory.
0020-1669/88/1327-3614$01.50/0
plexes of the general formula trans-[TcD2X2]+lo(where D represents a chelating bis(tertiary phosphine or arsine) ligand and x represents a halide or Feudohalide ligand) are of special interest since some of the Tc(II1) cations are taken up by the heart7-10 (5)
Deutsch, E.; Libson, K.; Jurisson, S.; Lindoy, L. F.Prog. Inorg. Chem.
1983, 30, 75. ( 6 ) Deutsch, E.; Libson, K. Comments Inorg. Chem. 1984, 3, 8 3 . (7) Deutsch, E.; Bushong, W.; Glavan, K. A.; Elder, R. C.; Sodd,V. J.;
Scholz, K. L.; Fortman, D. L.; Lukes, S. J. Science (Washington, D.C.) 1981, 214, 8 5 .
0 1988 American Chemical Society
A T c ( I I I ) / T c ( I I ) Redox Couple
Figure 1. Perspective drawing of the Tc(1I) cation trans-[Tc(DPPE)2C12]+,showing 50% probability ellipsoids and spheres. Hydrogen atoms are omitted for clarity.
and some of the neutral Tc(I1) species cross the blood-brain barrier."J2 Moreover, reduction of the Tc(II1) cation trans[Tc(DMPE)$12]+ (where D M P E represents 1,2-bis(dimethylphosphino)ethane) to the neutral Tc(I1) form has been shown to occur in vivo.I3 The structural and kinetic studies reported herein have been undertaken in order to better define the inorganic chemistry that underlies these biological p r o c e s s e ~ . ~ , ~ , ~ ~ Structural studies on the components of inorganic redox couples are, in their own right, of fundamental importance in inorganic chemistry. Such investigations detail the structural effects engendered by simple changes in the electronic configuration of the central metal and thus help elucidate the nature of the bonding forces within the overall complex.l5 Structural characterizations have been reported for many first-row transition-metal couples: e.g., Cr(III[,II/I/O),I6 F ~ ( I I I / I I ) , ~C~OJ (~I I / I ) , ~C~O ( I I I / I I ) , ~ ~ Ni(III/II), and C U ( I I / I ) . ~ ~ -Similar ~~ characterizations of second-row Ru(III/II) couples have recently been the focus of (8) Deutsch, E.; Glavan, K. A.; Sodd, V. J.; Nishiyama, H.; Ferguson, D. L.; Lukes, S. J . Nucl. Med. 1981, 22, 897. (9) Deutsch, E.; Glavan, K. A.; Bushong, W.; Sodd, V. J. In Applications of Nuclear Chemistry and Radiochemistry; Lambrecht, R., Marcos, N., Eds.; Pergamon: New York, 1982; p 139. (10) Gerson, M.; Deutch, E.; Nishiyama, H.; Libson, K.; Adolph, R.; Grossman, L.; Sodd, V.; Fortman, D.; Vanderheyden, J.-L.; Williams, C.; Saenger, E. Eur. J . Nucl. Med. 1983, 8, 371. (1 Neves. M.:Libson. K.: Deutsch. E. In Technetium in Chemisfrv and . 1), Nuclear iedicine;'Nicolini, M.,'Bandoli, G., Mazzi, U., Eds.; Cortina International: Verona, Italy, 1986; p 123. (12) Neves, M.; Libson, K.; Deutsch, E. Nucl. Med. Eiol. 1987, 14, 503. (13) Vanderheyden, J.-L.; Heeg, M. J.; Deutsch, E. Inorg. Chem. 1985,24, 1666. (14) Deutsch, E.; Libson, K.; Vanderheyden, J.-L.; Ketring, A. R.; Maxon, H. R. Nucl. Med. Eiol. 1986, 13, 465. (15) Cotton, F. A.; Falvello, L. R.; Najjar, R. C. Znorg. Chem. 1983, 22,770. (16) Bohling, D. A.; Mann, K. R. Znorg. Chem. 1984, 23, 1426. (17) (a) Beattie, J. K.; Moore, C. J. Znorg. Chem. 1982, 21, 1292. (b) Smith, D. A.; Heeg, M. J.; Heineman, W. R.; Elder, R. C. J . Am. Chem. SOC. 1984, 106, 3053. (18) (a) Zalkin, A,; Templeton,D. H.; Ueki, T. Znorg. Chem. 1973,12, 1641. (b) Baher, J.; Englehardt, L. M.; Figgis, B. N.; White, A. H. J . Chem. SOC.,Dalton Trans. 1975, 530. (c) Hair, N. J.; Beattie, J. K. Znorg. Chem. 1977, 16, 245. (d) Beattie, J. K.; Best, S. P.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalron Trans. 1981,2105. (e) Brunschwig, B. S.; Creutz, C.; McCartney, D. H.; Sham, T.-K.; Sutin, N. Faraday Discuss. Chem. SOC.1982, 74, 113. (19) Szalda, D. J.; Creutz, C.; Mahajan, D.; Sutin, N. Znorg. Chem. 1983, 22, 2372. (20) Hammershoi, A.; Geselowitz, D.; Taube, H. Znorg. Chem. 1984,23,979. (21) Szalda, D. J.; McCartney, D. H.; Sutin, N. Inorg. Chem. 1984, 23, 3473. (22) Dagdigian, J. V.; McKee, V.; Reed,C. A. Inorg. Chem. 1982, 21, 1332. (23) Diaddario, L. L., Jr.; Dockal, E. R.; Glick, M. D.; Ochrymowycz, L. A.; Rorabacher, D. B. Znorg. Chem. 1985, 24, 356. (24) Bharadwaj, P. K.; Johm, E.; Xie, C.-L.; Zhang, D.; Hendrickson, D. N.; Potenza, J. A.; Schugar, H. J. Znorg. Chem. 1986, 25, 4541.
Inorganic Chemistry, Vol. 27, No. 20, 1988 3615 Table I. Fractional Atomic Positional Parameters','
for
tran~-[Tc~~(DPPE),C1,1 atom X Tc 0.29556 (2) Cl(1) 0.33032 (5) Cl(2) 0.25078 (5) P(1) 0.42991 (5) P(2) 0.35926 (5) P(3) 0.16522 (5) 0.23207 (5) P(4) C(l) 0.4871 (2) C(2) 0.4654 (2) 0.1017 (2) C(3) C(4) 0.1257 (2) C(11) 0.4629 (2) C(12) 0.4673 (2) 0.4870 (2) C(13) C(14) 0.5038 (2) C(15) 0.4998 (2) C(16) 0.4801 (2) C(21) 0.4811 (2) 0.5604 (2) C(22) C(23) 0.5995 (2) C(24) 0.5613 (3) 0.4841 (3) C(25) C(26) 0.4445 (2) 0.3571 (2) C(31) C(32) 0.3804 (2) C(33) 0.3847 (3) C(34) 0.3653 (3) C(35) 0.3439 (3) C(36) 0.3401 (3) C(41) 0.3367 (2) C(42) 0.3764 (2) C(43) 0.3547 (3) C(44) 0.2936 (3) 0.2532 (3) C(45) C(46) 0.2744 (2) C(51) 0.1333 (2) C(52) 0.0672 (3) C(53) 0.0474 (3) C(54) 0.0895 (4) C(55) 0.1536 (3) C(56) 0.1765 (3) C(61) 0.1240 (2) C(62) 0.1458 (2) C(63) 0.1149 (3) C(64) 0.0633 (3) C(65) 0.0427 (3) C(66) 0.0724 (3) C(71) 0.2512 (2) C(72) 0.2160 (2) C(73) 0.2299 (3) C(74) 0.2798 (3) 0.3148 (3) C(75) C(76) 0.3007 (2) C(81) 0.2417 (2) C(82) 0.2999 (2) C(83) 0.3098 (3) C(84) 0.2621 (4) 0.2074 (3) C(85) 0.1958 (3) C(86)
Y
z
0.44320 (2) 0.62965 (7) 0.26783 (7) 0.45387 (8) 0.33961 (8) 0.45030 (8) 0.55064 (8) 0.4626 (3) 0.3576 (3) 0.4409 (3) 0.5269 (3) 0.5828 (3) 0.5756 (3) 0.6742 (4) 0.7809 (4) 0.7893 (3) 0.6927 (3) 0.3325 (3) 0.3396 (4) 0.2453 (5) 0.1455 (4) 0.1362 (3) 0.2288 (4) 0.1787 (3) 0.1355 (3) 0.0155 (4) 0.0646 (4) 0.0255 (3) 0.0961 (3) 0.4033 (3) 0.4999 (4) 0.5518 (4) 0.5087 (5) 0.4112 (4) 0.3591 (3) 0.5852 (3) 0.6484 (4) 0.7410 (5) 0.7878 (4) 0.7246 (5) 0.6245 (4) 0.3316 (3) 0.2145 (3) 0.1219 (4) 0.1467 (5) 0.2603 (5) 0.3532 (4) 0.5168 (3) 0.5833 (3) 0.5596 (4) 0.4698 (5) 0.4025 (4) 0.4270 (3) 0.7135 (3) 0.7657 (3) 0.8877 (4) 0.9591 (4) 0.9124 (4) 0.7884 (4)
0.25808 (1) 0.21982 (4) 0.30197 (3) 0.31312 (4) 0.19099 (4) 0.19862 (4) 0.32215 (4) 0.2573 (1) 0.2163 (1) 0.2494 (1) 0.3002 (1) 0.3604 (1) 0.4200 (2) 0.4556 (2) 0.4334 (2) 0.3744 (2) 0.3385 (1) 0.3581 (1) 0.3826 (2) 0.4146 (2) 0.4236 (2) 0.4001 (2) 0.3675 (2) 0.1751 (1) 0.1263 (2) 0.1164 (2) 0.1536 (2) 0.2024 (2) 0.2128 (2) 0.1170 (2) 0.1027 (2) 0.0487 (2) 0.0018 (2) 0.0210 (2) 0.0755 (2) 0.1554 (2) 0.1583 (2) 0.1254 (2) 0.0874 (2) 0.0834 (2) 0.1167 (2) 0.1460 (2) 0.1604 (2) 0.1224 (2) 0.0711 (2) 0.0568 (2) 0.0938 (2) 0.4010 (1) 0.4370 (2) 0.4955 (2) 0.5191 (2) 0.4844 (2) 0.4252 (2) 0.3251 (2) 0.3675 (2) 0.3711 (2) 0.3322 (3) 0.2899 (2) 0.2853 (2)
'The estimated error in the last digit is given in parentheses. This form is used throughout. *The atom-numbering scheme is as shown in Figure considerable for two related reasons. First, these couples are widely used in investigating the kinetics and mechanisms of electron-transfer reactions, and in these studies the effect (25) Stynes, H. C.; Ibers, J. A. Inorg. Chem. 1971, I O , 2304. (26) Bernhard, P.; Burgi, H.-B.; Hauser, J.; Lehmann, H.; Ludi, A. Inorg. Chem. 1982, 21, 3936. (27) Richardson,E. D.; Walker, D. D.; Sutton, J. E.; Hodgson, K. 0.;Taube, H. Znorg. Chem. 1979, 18, 2216. (28) Gress, M. E.; Creutz, D.; Quicksall, C. 0. Inorg. Chem. 1981,20, 1522. (29) Eggelston, D. S.; Goldsby, K. A,; Hodgson, D. J.; Meyer, T. J. Inorg. Chem. 1985, 24, 4573.
Libson et al.
3616 Inorganic Chemistry, Vol. 27, No. 20, 1988 Table 11. Fractional Atomic Positional Parameters trans- [ T c " ' ( D P P E ) ~ C ~ ~ ] N O ~ . H N ~ ~ ~ atom X Y 0.0000 0.0000 0.23740 (6) -0.00590 (6) 0.05800 (6) -0.14370 (5) 0.02650 (6) -0.21960 (5) -0.5673 (2) 0.2205 (3) 0.1853 (2) -0.5342 (2) 0.1199 (2) -0.5476 (2) 0.3433 (2) -0.6186 (2) 0.0507 (2) -0.3104 (2) -0.0312 (2) -0.3146 (2) 0.2269 (2) -0.1856 (2) -0.2584 (2) 0.2343 (3) -0.2971 (3) 0.3622 (3) 0.4797 (3) -0.2624 (3) 0.4726 (3) -0.1904 (4) -0.1529 (3) 0.3472 (3) -0.0743 (2) -0.0888 (2) -0.0506 (3) 0.0003 (2) -0.1515 (3) 0.0489 (3) -0.2740 (3) 0.0092 (3) -0.0787 (3) -0.2979 (3) -0.1263 (3) -0.1985 (3) -0.2393 (2) -0.0800 (2) -0.1873 (3) -0.2277 (3) -0.1978 (3) -0.3102 (3) -0.2597 (3) -0.2428 (3) -0.3121 (3) -0.0971 (3) -0.3021 (3) -0.0152 (3) 0.2078 (2) -0.3168 (2) -0.4496 (3) 0.2660 (3) 0.3971 (4) -0.5221 (3) -0.4655 (3) 0.4708 (3) -0.3332 (3) 0.4151 (3) -0.2598 (2) 0.2854 (2) 0.5000 0.0
of z
0.0000
-0.08420 (4) 0.18620 (5) -0.02870 (5) 0.5006 (2) 0.5891 (2) 0.4472 (2) 0.4590 (2) 0.1956 (2) 0.1123 (2) 0.2348 (2) 0.3446 (2) 0.3843 (2) 0.3166 (3) 0.2099 (3) 0.1677 (3) 0.3050 (2) 0.3491 (2) 0.4363 (2) 0.4796 (2) 0.4370 (2) 0.3488 (2) -0.1141 (2) -0.0944 (2) -0.1610 (3) -0.2471 (2) -0.2673 (2) -0.2010 (2) -0.0792 (2) -0.0291 (2) -0.0774 (3) -0.1781 (3) -0.2298 (2) -0.1794 (2) 0.5000
"The atom-numbering scheme is as shown in Figures B46 and C.& Table 111. Selected Bond Lengths (A) and Angles (deg) for ~ ~ U ~ ~ - [ T C ~ ~ ( D Pand P E )tr~ns-[Tc~~'(DPPE)2C12]+ ~CI,] Tc(I1) Tc(II1)" Bond Lengths Tc-Ci( 1) 2.410 (1) 2.319 Tc-CI(2) 2.438 (1) Tc-P( 1) 2.444 (1) 2.509 (1)' Tc-P(3) 2.417 (1) Tc-P(2) 2.444 (1) 2.492 Tc-P(4) 2.410 (1)
Cl( l)-Tc-C1(2) C1( l)-Tc-P( 1) Cl( l)-Tc-P(3) C1(2)-Tc-P( 1) CI (2)-Tc-P( 3) CI(lkTc-P(2) ci(i~ - T c - P ( ~ C1(2)-Tc-P(2) C1( 2)-Tc-P( 4) P( l)-Tc-P(2) P( 3)-Tc-P( 4)
Bond Angles 173.5 (1) 81.41 (3) 92.92 (3) 101.03 (3) 84.65 (3) 88.24 (3) 90.14 (3) 98.10 (3) 83.51 (3) 79.68 (3) 79.54 (3)
}
6 1 8 (2)e
1
93.69 (2)' 80.57 (3)9
Table IV. Derived Second-Order Rate Constants" Governing the Reaction of ~ ~ u ~ s - [ T c ~ ~ ( D P P E(X) ~=XC1, , ] Br) with [(en)2Co(S(CH2C6H,CH3)CH2CH,NH,)I)+ solvent P, M 1O4k2, M-' s-'
ne
x = c1 CH3CN CH3CN CH3CN 0.5% H20/CH3CN 1.8% DMF/CH3CN DMF
0.10 0.08
0.05 0.10 0.10
0.10 X = Br 0.10 0.05 0.025 0.005
CH3CN CH3CN CH3CN CH3CN 0.5% H,O/CH$N 2.5% H20/CHjCN
0.10
0.10
3.0 (7) 4.2 (3) 2.5 (3) 1.6 (1) 0.68 (4) 0.0037 (7)
6d
1.2 (3)
8 3 1
2' 2 1
3 1
1.3 (3) 1.2 (2) 2.5 (2) 0.67 (2) 0.31 ( 1 )
1 1 1
Conditions (unless otherwise noted): 25 OC, ionic strength maintained with tetrabutylammonium perchlorate. * The standard deviation of the last digit is given in parentheses. 'Number of independent data sets. d T ~ out o of six data sets obtained with tetraethylammonium perchlorate to maintain ionic strength. Ionic strength maintained with tetraethylammonium perchlorate. Table V. Qualitative Rate Data Describing Outer-Sphere Electron-Transfer Reactions of trans- [Tc"(DPPE),CI,]" oxidant solvent k2, M-I s-' A6RU3+ DMF io7 ferrocenium >io7 10% DMF/CH,CN A,CoOH?+ 140 10% DMF/CH,CN 5% DMF/CHjCN 310
