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Contribution from the Laboratoire de Chimie Bioorganique et Bioinorganique, URA 1384, Universit€ Paris-Sud XI, Bat. 420, 91405 Orsay, France, Institut for Physik, Medizinische Universitiit zu Lilbeck, 2400 Lilbeck, FRG, and Laboratoire de Chimie des EEments de Transition, URA 419, Universite Pierre et Marie Curie Paris VI, 4 Place Jussieu, 75005 Paris, France
Magnetic Susceptibility, EPR, Mossbauer, and X-ray Investigations of Heteropolynuclear Clusters Containing Iron(111) and Copper(11) Ions: (Cu(Mesalen)J2Fe(acac) (NO3)2 and {Cu(Mesalen)I3Fe(acac)(PF,J2+ Irene Morgenstern-Badarau,**l*Daniel Laroque,la Eckhard Bill,lb Heiner Winkler,lb Alfred X. Trautwein,*Jb Francis Robert,Ic and Yves JeanninlC Received June 2X 1990 Magnetic susceptibility, EPR, Mkbauer, and X-ray studies have been performed on heteropolynuclear clusters containing iron(II1) and (C~(Mesalen))~Fe(acac)( PF,), (Mesalen = 1,2-bis((methyland copper(I1) ions: (Cu(Me~alen)}~Fe(acac)(NO~)~ sa1icylidene)amino)ethane; acac = acetylacetonato(I-)). The spectroscopic results obtained for the trinuclear system (2CuFe) suggest strong antiferromagnetic coupling of iron(II1) to the two copper(I1) ions to yield a S = 3/2 ground-state system. X-ray studies reveal that the tetranuclear system (3CuFe)crystallizes in the hexagonal space group H 1 2 2 with 2 = 6, a = b = 14.471 (3) A, and c = 50.372 (2) A; it consists of a trinuclear unit (2CuFeJplus a mononuclear Cu(Mesalen) molecule, arranged in helicoidal polymeric chains. Magnetic susceptibility,EPR, and Mhsbauer studies under moderate fields consistently show that the (2CuFeJand Cu(Mesa1en) moieties are weakly interacting. Under high-field and low-temperatureconditions, this interaction is not observable in Messbauer spectroscopy. Since the Mhsbauer spectra under these conditions are identical for the tri- and tetranuclear clusters, we conclude that the I2CuFe) moieties are very similar in both cluster types. The presence of the additional Cu(Mesalen) molecule in the tetranuclear cluster expresses itself in the Mhsbauer spectra only at elevated temperatures by an enhancement of the spinspin relaxation rates of nearly 1 order of magnitude larger compared to the trinuclear cluster.
Introduction Few heteropolynuclear molecules that contain spin-coupled iron(II1) and copper(I1) ions have been reported until now.2 Within those studied so far, the focus has been on properties that are related to the antiferromagnetically coupled iron-copper pair of cytochrome c o x i d a ~ e . ~In addition to the current interest in analogue compounds for the redox center of the enzyme, such hetero di- and polynuclear systems display interesting magnetic properties dependent upon intramolecular and intermolecular
interaction^.^ To elucidate the magnetic properties, complementary methods such as magnetic susceptibility and Mbsbauer and EPR spectroscopy may be applied to these systems. Magnetic susceptibility, EPR, and preliminary zero-field M8ssbauer experiments of the noted as trinuclear cluster {C~(Mesalen))~Fe(acac)(NO~)~, { ZCuFe), have been previously reported.5 The temperature dependence of the effective magnetic moment over the temperature interval 4.2-300 K unambiguously demonstrates the presence of exchange coupling between the metal ions, with the two copper(I1) and the iron(II1) ion (S = 5/2) being antiferroions (S = magnetically coupled to a S = 3/2 ground-state system. The EPR results at 4.2 K have been shown to be consistent with the magnetic susceptibility data, with the effective g values similar to those expected for a single-ion S = 3/2 system subject to zero-field splitting of rhombic symmetry. The preliminary Miissbauer studies yielded unresolved hyperfine patterns, which suggested to us to perform a low-temperature, high-field investigation of the (2CuFe) complex. Additionally, we have succeeded in the meantime in stabilizing the I2CuFe)complex in the solid state and we have obtained single crystals of a tetranuclear compound {C~(Mesalen))~Fe(acac)(PF6)2rnoted as (3CuFe1, which contains the trinuclear unit (2CuFe)packed within the crystallographic cell together with the monomer Cu(Mesa1en). We now report on the X-ray crystal structure of this new 12CuFe)-containing system together with magnetic susceptibility, Mcssbauer, and EPR investigations, and we compare the properties of the {ZCuFe)and (3CuFe)systems. Experimental Section Synthesis. The synthesis of the complex (2CuFe)has been previously publi~hed.~ The complex (3CuFeJ was prepared from solutions of (2CuFeJin dichloromethane in presence of NaPF,. I2CuFeJ(0.002 mol)
’
Abbreviations: Mesalen, 1,2-bis((methylsalicy1idene)amino)ethane;acac, acetylacctonate(1-). 0020-1669/91/1330-3180$02.50/0
Table I. Crystallographic Data
formula fw
cryst system space group a=b,A c, A
v,A’ Z p(calcd), g cryst dimens, mm F( 000)
system absences diffractometer radiation (graphite monochromator) linear abs coeff, cm-’ scan type scan range, deg 0 limits, deg octants collcd no. of data collcd no. of unique data collcd no. of unique data used decay, ?’ 6
(C59H6108N6FeCu3)n(PF6)~
1518.56 hexagonal P6,22 14.471 (3) 50.372 (2) 9135.2 6 1.66 0.35 X 0.22 X 0.18 4644 001; I # 6n Enraf-Nonius CAD-4 Mo Ka (A = 0.71069 A) 14.15 420
0.80 + 0.345 tan 0 1-23 +h,+k,+l
4856 2591 1933 (Fa)2> 34F2)) (lob)
where wo = 2 7 r / h Z (Baj d
+ J,j)ZP,(E)
(11)
contains the dipole-dipole and exchange-coupling constants Baj and Ja, respectively, of the Massbauer ion "awwith all its neighbors "jwas well as its level density Pa(E), while P(hfb) are the Boltzmann populations of the magnetic substrates of any neighbor labeled by *b*. This model assumes that the transitions are due (20) Blume, M.Phys. Reo. 1968, 174, 351. (21) (a) Winkler, H.; Schulz. C.; Debrunner, P. G. Phys. Lett. 1979,69A, 360. (b) Winkler, H. HabilitationThais, University of Hamburg, 1983. (22) Boyle, A. J. F.;Gabriel, J. R. Phys. Lerr. 1965, 19, 451.
- 10
-5
0 Velocity [mms
5
10
-'I Figure 9. Relaxation spectra of I3CuFe) under 6.21 T parallel to the y-ray in a temperature range between 4.2 and 50 K simulated with the spin-relaxation model using the parameters of Table IV.
to an energy-conserving cross-relaxation process with a paramagnetic neighbor ion. The level spacing between all substrates of b is taken equidistant and equal to that of the Mossbauer ion so that a specific transition in a can be induced by any transition in b as inferred by the sum over Mb.This is different from the case where the zero-field splitting is comparable to or even greater than the Zeeman splitting because under that condition only transitions between equivalent pairs of levels can take place and one getsz3
w ( M - M f 1) = Wf).1/41(M f IIS*IM)l'p(M
* 1) (12)
For the interpretation of our spectra, we have used the Boyle and Gabriel expressions (loa), (lob), and (1 I), which seemed to come (23) Blume, M. Phys. Rev. Lett. 1967, 18, 305.
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closer to the truth because D is comparatively small. In the simulations wo has been treated as empirical parameter. It is expected to be independent of temperature and field strength as long as the latter is high enough to justify the Boyle and Gabriel model despite of a finite zero-field splitting. Due to the zero-field splitting the level spacings are of course not really equidistant, but this may be compensated in part by an inhomogeneous broadening of the levels. For the spectra of the trinuclear complex recorded under 6.21 and 2.47 T it was indeed possible to get satisfactory simulations for the whole temperature range from 4.2 to 50 K with one single value for w,. The zero-field splitting, rhombicity, and hyperfine parameters were taken as determined from the low-temperature spectra except that, for the sake of simplicity, the Euler angles CY and @ of the efg tensor have been disregarded. The solid lines in Figure 8 show the simulations obtained for S = 3/2 and the parameters of Table IV with wo = 2.6 X IO8 s-l. The estimated uncertainty of this value is about 20%. The relaxation rate in the tetranuclear complex is obviously faster. The solid lines through the spectra in Figure 9 are simulations obtained for S = 3/2 and the parameters of Table IV with wo = 2.2 X 109 s-l. Direct comparison with the trinuclear complex
is possible, since the applied field of 6.21 T is so strong that the spin of the monomeric Cu(Mesa1en) is coupled in a kind of Paschen-Back effect much stronger to the external field than to the spin 3/2 of the trimer. The monomer may, however, mediate the cross-relaxation between two trimers, thus enhancing the relaxation rate by about 1 order of magnitude. This finding is not unexpected because it is well-known, e.g. from the work of Bhargava et al.,24 that the presence of other paramagnetic ions shortens the spin-spin relaxation times substantially. Such an explanation is also consistent with the X-ray structure of the crystalline tetranuclear entity described in the preceding section. Acknowledgment. This research was supported in part by NATO Research Grant No. 330/87. Supplementary Material Available: Tables S1 and S2,listing interatomic distances and bond angles for the PF, anions and anisotropic thermal parameters (2 pages); a listing of observed and calculated structure factors (19 pages). Ordering information is given on any current masthead page. (24) Bhargava, S.C.; Knudsen, J. E.; Morup, S. J. Phys. Chem. Solids 1979, 40, 45.
Contribution from the Departments of Chemistry, Loyola University of Chicago, Chicago, Illinois 60626, and University of Coimbra, 3000 Coimbra, Portugal, and Laboratory of Organic Chemistry, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
Multinuclear NMR Study of the Interaction of the Shift Reagent Lanthanide(II1) Bis( triphosphate) with Alkali-Metal Ions in Aqueous Solution and in the Solid State7 Ravichandran Ramasamy,”f Duarte Mota de Freitas,*vt Carlos F. G. C. Geraldes,” and Joop A. Peters**l Received January 4, 1991 The paramagnetic ion-induced relaxation rate enhancementsof 6Li in adducts of Li+ and Ln(PPP)J- complexes (Ln = Dy,Tm) in aqueous solution show that up to seven monovalent counterions can coordinate in the second coordination sphere of the Ln(II1) ion to the outer oxygens of the triphosphate ligands. However, the pseudocontact ’Li NMR shift data suggest that in the second coordination sphere some preference of the counterions for the axial region opposite the water ligand may exist. The estimated Ln3+-Li+distances range from 5.1 to 5.9 A for [Li+]/[Ln(PPP)J-] ratios of 0.2-7. This is supported by a two-dimensional nutation spectrum of a polycrystalline sample of Na,La(PPP),, which indicates coordination of all Na+ ions to phosphate oxygens.
Introduction Several aqueous shift reagents (SRs) for metal cation N M R spectroscopy have been reported.’” They have been shown to be useful in membrane transport biochemistry, for example in studies of alkali-metal ion transport across ~esicles’~~ and red blood cell membranes.’**l2 However, only two of them, DY(TTHA)~and Tm(DOTP)s-, have found useful practical application for perfused heart studiesI3J4 and in vivo rat brain 23Na N M R spectroscopy.1s*16 Despite considerable discussion, there seems still to be some controversy regarding the mode of interaction of one of the SRs most widely used for N M R studies in cell systems, namely Dy(PPP)J-, with alkali-metal ions in aqueous s o l ~ t i o n . ” - ~ Moreover, it has been shown recently that Dy(PPP)J- can change ion distribution and transport across red blood cell membranes as well as membrane potential.u.25 These effects may be related to the mode of binding of alkali metal cations to Dy(PPP)?-. In
*Authors to whom correspondence should be addressed. ‘Abbreviations used in this paper are as follows: PPPs, tripolyphosphate; SRs, shift reagents; TTHAb, tetraethylenetetraminehexaacetate;DOTP-,
tet~aa~cyclododecane-N,N’,N”,N‘’’-tetrakis(methanephosphonate); MAS, magic angle spinning; NMR, nuclear magnetic resonance; LnIRE, lanthan-
ide-induced relaxation rate enhancement. Loyola University. 1Present address: Department of Chemistry, University of Texas at Dallas, Richardson, TX 75083. I University of Coimbra. * Delft University of Technology.
*
this work we further analyze this problem by studying the 6Li N M R spin-lattice relaxation times of Dy(PPP)J- and Tm(PPP)JGupta, R. K.; Gupta, P. J. Magn. Reson. 1982, 47, 344. Pike, M. M.; Springer, C. S., Jr. J. Magn. Reson. 1982, 46, 348. Pike, M. M.; Yarmusch, D.; Balschi, J. A.; Lenkinski, R. E.; Springer, C. S., Jr. lnorg. Chem. 1983, 22, 2388. Sherry, A. D.;Malloy, C. R.; Jeffrey, F. M. H.; Cacheris, W. P.; Geraldes, C. F. G. C. J. Magn. Reson. 1988, 76, 528. Buster, D. C.; Castro, M. M. C. A.; Geraldes, C. F. G. C.; Malloy, C. R.;Sherry, A. D.; Siemers, T. C. Magn. Reson. Med. 1990, 13, 239. Szklaruk, J.; Marecek, J. F.; Springer, A. L.; Springer, C. S.,Jr. Inorg. Chem. 1990,29,660. Pike, M. M.; Simon, S. R.; Balschi, J. A,; Springer, C. S.,Jr. Proc. Nor/. Acad. Sci. U.S.A. 1982, 79,810. Shinar, H.;Navon, G. J. Am. Chem. Soc. 1986, 108,5005. Brophy, P. J.; Hayer, M. K.; Riddell, F. G. Biochem. J. 1983. 210, 961. Ogino, T.;Shulman, G. I.; Avison, M. J.; Gullans, S.R.;den Hollander, J. A.; Shulman, R. G. Proc. Narl. Acad. Sci. U.S.A. 1985, 82, 1099. Espanol, M. C.; Mota de Freitas, D. Inorg. Chem. 1987, 26, 4356. Pettegrew, J. W.; Post, J. F. M.; Panchalingam, K.; Whiters, G.; Wocssner, D. E. J. Magn. Reson. 1987,71. 504. Pike, M. M.; Frazer, J. C.; Dedrick, D. F.; Ingwall, J. S.;Allen, P. D.; Springer, C. S., Jr.; Smith, T. W. Biophys. J . 1985, 48, 159. Malloy, C. R.; Buster, D. C.; Castro, M. M. C. A.; Geraldes, C. F. G. C.; Jeffrey, F. M. H.; Sherry, A. D. Magn. Reson. Med. 1990,15,33. Albert, M. S.;Lee, J.-H.; Springer, C. S.,Jr. Absrracrs, 9th Annual Meeting of the Society of Magnetic Resonance in Medicine, New York, NY, 1990; p 1269. Naritomi, H.; Kanashiro, M.; Sasaki, M.; Kuribayashi, Y.; Sawada, T. Biophys. J. 1987,52, 61 1. Chu, S. C.; Pike, M. M.; Fossel, E. T.; Smith, T. W.; Balschi, J. A,; Springer, C. S..Jr. J. Magn. Reson. 1984, 56, 33. Nieuwenhuizen, M. S.: Peters, J. A.: Sinnema. A.: Kieboom. A. P. G.: van Bekkum, H. J. Am. Chem. Soc. 1985, 107, 12.
0020-1669/91/1330-3188$02.50/00 1991 American Chemical Society
