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Ferric Wheels and Cages Decanuclear Iron Complexes with Carboxylato and Pyridonato Ligands.

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[l] For reviews, see: a) K. C. Nicolaou, W.-M. Dai. Arigew. Chem. 1991.103.1453:
Angrii. C'h~ni.I n / . Ed. Errgl. 1991, 30. 1387; b) K. C. Nicolaou. A. L. Smith.
E. W Yue, Proc. .YutI. . 4 ~ d Scr.
. D'SA 1993, 90, 5881, c) R. Gleiter. D. Kratz.
A n p i , Chrrii 1993, 105. 884: Angeii. Chem. Int. Ed. Engl. 1993. 32. 842;
d ) M. E Maier. .'$w/ert 1995. 1 : e) J. W. Grissom. G . U. Gunawardena. D.
Klingherg. D. Huang, 7?.truhrdron 1996. 52. 6453.
[2] a) R. R. Jones. R. G. Bergman, J. Am. Chem. SOC.1972, 94. 660; b) R. G.
Bergman. ACL Chiwr. Res. 1973. 6. 5; c) T. P. Lockhart. P. B. Comita, R. G.
Bergman. J 4 n r . Chrvri. SOC. 1981. l(J3. 4082; d ) T. P. Lockhart. R. G .
Bergman. r h d 1981. 1113. 4091
[3] a) A. G Myers. E. Y. Kuo. N. S. Finney. J Am. Clrem. Soc. 1989, Iff. 8057;
h) R Nagata. H. Yamanaka, E. Okazdki, I. Saito, Tetruhedroii Lett. 1989. 30,
4995.c)A G . Myers. P. S. Dragovich. E. Y. Ku0.J. Am. Chem. Soc. 1992, 114.
9369: d ) J. W. Grissom, D. Huang. Angew Chen?. 1995, 107, 2196; Angeir.
C/rr,nr.h i t . Ed €rig/. 1995. 34, 2037. and references therein
[4] a ) L D Folnnd. J. 0. Karlsson. S. T. Perri. R. Schwabe, S L. Xu, S. Patil.
H. W. Moorc.. J Am. Chern. Soc. 1989, 111, 975; b) R. W. Sullivan, V. M.
Coghlan, S. A. Munk, M. W Reed. H. W. Moore, J Org. Cheni. 1994.59.2276.
[S] a) K Nakatani. S. Isoe. S. Maekawa. I. Saito, Tetruhedron Leu. 1994,35,605;
b) K. Nakatani. S. Maekawa. K. Tanahe, I. Saito. J. Am. Chem. Soc. 1995, 117.
[6] This work wab reported in part at the 69th Annual Meeting of the Chemical
Societ) of Japan. Kyoto (Japan). March 27. 1995, Abstract Vol. 11, p. 1131
[7] Y Wanz. M G. Finn. J. A m Chem. Sue. 1995, 117. 8045.
181 a ) F J. G . Alonso, A. Hohn, J. Wolf. H. Otto, H. Werner, Angeu-. Chern. 1985.
97, 401; Atigci~.C'hem. h t . Ed. Eng/ 1985. 24,406; b) R. Wiedemann. J. Wolf,
H. Werner. .4ngm C/icvir. 1995. 107. 1359; Angew. Cliem. Inf. Ed Engl 1995.
34, 1244.
191 This rhodium complex is known to he dimeric; see for example: a ) H. Werner.
J Wolf. A Hohn. J Orgunonrrt. C h e m 1985, 287, 395: b) P. Binger, J. Haas.
G Glaser. R Goddard. C Kriiger. Chem. Ber. 1994. 127. 1927
[lo] M. I . Bruce. Chcwr. Rnz. 1991, 91. 197.
[ I l l It is known that the addition of pyridine shifts the equilibrium between an
alkqne complex [(RC-CH)Rh) and an alkynyl(hydrid0) complex
[RC-CRhH]. uhich is converted to a vinylidene complex: J. Wolf, H. Werner,
0 Serhadli. M. 1.Ziegler. Angeir. Clrem. 1983, 95,428; Angen.. Chern. lnt. Ed.
€'rig/. 1983, 22. 414. However, pyridine deterred the present reaction. N.N-Diisopropylethylamine and tetramethylethylenediamine were moderately effective m d after two days gave 4a in 42 and 23 YOyield, respectively.
[12] The heat ofthe formation ofdiradical6a isestimated to heabout 16 kcalmol-'
less than tha! ofSaI13j. This valuecorresponds to thedifference in thestrength
of the secondary alkyl (95 kcalmol-l) and aryl C - H (110 kcalmol-') bonds.
It is less likely that the rhodium center abstracts hydrogen before the benzenoid
radical does. because the bond dissociation energy of a secondary C - H bond
is greater than rliat o f a Rli-H bond (ca. 54-64 kcalmol-I) [14].
[13] N . S Issacs. Phrsiwl Orgunrc Chemistry. Wiley, New York, 1987, p. 24.
[I41 S. 1. A. Martinho, J. L. Beauchamp, Clrern. Rev. 1990, 90. 629.
[15] The incorporation of deuterium a t the metu position was confirmed by comparison oftheintensityof ' H NMRsignalsofthemetoprotons(6 =7.23-7.32)
with thoseoftheorthoandporu protons(&=7.12-7.22) inCD,CI,.Theratio
of the integrations of the signals in these two regions is which means
that one of thenwtu positions had 52% deuterium incorporation. No incorporation of deuterium in the side chain was apparent. The observation of two
isotope peaks for [ M '1 at m j s = 160 (22.8%) and 161 (24.0%) in the El mass
spectrum (70 eV) of 4aD also supports the assignment of the product (51.3%
deuterium incorporation).
[16] In the absence of molecular sieves 4 A no incorporation of deuterium into 4a
w a s observed and recovered laD had a reduced deuterium content. This IS
prohdbiy due 10 rapid D/H exchange during the isomerization between the
alkynyl(hydrido) complex and the vinylidene complex owing to trace amounts
of H,O.
[17] The reaction of l a (0.4 mmol) was carried out with 1.4-cyclohexadiene
(10 mmol) in benzene ( 3 mL) in the presence of 5 mol% Rh catalyst and Et,N
(0.5 mmol) at 50 C for 30 h. The use of greater excesses of 1.4-cyclohexadiene
deterred the cyclization.
Ferric Wheels and Cages: Decanuclear Iron
Complexes with Carboxylato and Pyridonato
Cristiano Benelli, Simon Parsons, Gregory A. Solan, and
Richard E. P. Winpenny*
The study of polymetaIlic complexes has recently begun to
lead to not only fascinating structures but also interesting properties. In particular the magnetic relaxation and hysteresis effects first shown for a dodecanuclear manganese cluster['] and
recently found in deca-12]and t e t r a n ~ c l e a r [manganese
are novel and have implications for fundamental science and
potential future applications. To understand and exploit these
phenomena more examples are required, and therefore the
greatest need in this area remains the design of reliable synthetic
routes to produce nanoscale clusters with the potential for highspin ground states.
We have developed the reaction of metal carboxylates with
pyridone ligands leading to incomplete replacement of the carboxylates and large polynuclear arrays of copper[41and nickel.r5.61We hoped that this strategy would prove general for
the 3d metals, but on examination of the reactivity of
[Fe30(02CMe),(H,0),]C1 with pyridones we isolated solids,
which on dissolution in MeOH led to the isolation of a yellow
powder that analyzed as [Fe(OMe),(O,CMe)] . This could be
recrystallized from MeOH/THF in low yield, and X-ray structure determination['] revealed the compound to be complex I,
which is very similar to the "ferric wheel" 2 reported by Lippard
and co-workers."] A centrosymmetric cyclic decanuclear array
of iron atoms is held together by twenty p,-OMe hgdnds and ten
1,3-bridging acetato ligands (Fig. 1).
Fig. 1.
[*] Dr. R. E. P. Winpenny, Dr. S. Parsons, Dr. G. A. Solan
Department of Chemistry, The University of Edinburgh
West Mains Road, Edinburgh, EH9 3JJ (UK)
Fax. Int. code +(131)667-4743
Prof. C. Benelli
Dipdrtimento di Chimica, Universita degli Studi di Firenze (Italy)
Angew. Clrlmi. lnr. Ed. Engl. 1996. 35, No. 16
This work was supported by the Engineering and Physical Sciences Research
Council and the Leverhulme Trust.
c? VCH Vrrlugsgeseilschuft mbH. 0-69451
Wernheim. 1996
0570-0833/96/3S16-1825 S 1S.W
+ .2SIO
Yellow powders with identical elemental composition can be
produced from many reactions involving iron(Ir1) and acetate in
methanol, for example by mixing ferric chloride with sodium
acetate in this solvent, or by refluxing a solution of [Fe,O(0,CMe)6(H,0)3]C1 in methanol. Whether the unrecrystallized
powder contains exclusively cyclic oligomers is unclear; unfortunately powder diffraction studies failed as the powder is amorphous. We suspect that a polymeric material may be present and
that cyclization occurs during crystallization; however, mass
spectrometric studies of the powder show a n intense high-mass
peak at m/z 1710 corresponding to [l - O,CMe]+. Only one
significant peak is observed at a mass above that of 1, at m / z
1831, which arises from [l O,CMe]+. This cut-off in the mass
spectrum may be coincidental.
The magnetic behavior of the yellow powder is similar to that
reported for 2IS1down to about SOK, but below this temperature the magnetic susceptibility increases dramatically. Such behavior is not compatible with the existence of rings with an even
number of ions having a magnetic moment if only one type of
magnetic interaction is present, as would be expected from the
molecular structure of 1. Probably the powder contains some
oligomeric impurities that prevent detailed analysis of the lowtemperature data at this time. Similar yellow powders result
from reactions of other iron carboxylates in MeOH; however,
their exact nature is currently unclear.
To synthesize acyclic polynuclear iron complexes we have
utilized other precursors and other solvents. The salt
[NEt4],[Fe,0C16][91 has proved ideal for such studies.[”. ‘I
Dissolution of this salt with two molar equivalents of sodium
benzoate in acetonitrile, followed by addition of three equivalents of sodium 6-chloro-2-pyridonate, Na(chp), gives a red solution, which we believe contains a dinuclear species of approximate formula [F~ , O ( O, C P~ ) , ( C ~ ~) , ( C H, C.[’N) Filtration
of the solution followed by mixing with acetone gives, after one
week, orange-brown crystals suitable for diffraction studies!’]
The structure in the crystal (Fig. 2) corresponds to a decanuclear iron complex capped by two sodium atoms with the stoichiometric formula 3.
1,1‘,3-bridging and 1,3-bridging benzoates, and chp ligands
bridging in a p,-fashion through the exocyclic 0 atom. Terminally bound water molecules are attached to Fe4 and Fe4a, and
acetone molecules are bound to the Na atoms. The iron-oxo
core can be considered t o contain two distorted Fe60, hexagonal prisms sharing one “square” face containing Fe4,04, Fe4a,
and 0 4 a (Fig. 3). Similar hexagonal prisms are found as seg-
Fig. 3 . The central Fe,,O,, core of 3 showing the atom numbering scheme. Only
pr-oxo, p,-oxo. and it,-hydroxo groups are shown. Selected bond angles [’I: Fe201-Fe3 128.7, Fe2-01-Fel 91.4, Fe2-01-Fel 97.4. Fel-02-Fe4 130.2. Fei-02-Fe2
100.8. Fe2-02-Fe4 127.0. Fe-4-03-Fe3a 130.2, Fe4-03-FeSa 126.9, Fe3a-03-FeSa
100.6. Fe4a-04-FeSa 126.8. Fe4a-04-Fe2 129.0. Fe2-04-FeSa 100.6 (average esd
0.3 ).
ments of other iron-oxo complexes such as [Fe, l(0)6(OH)6(0,CPh),,][’31 and [Fe16Co0,0(OH),,(0,CPh)20J;[’41
however, in these complexes the hexagonal prisms d o not share
faces. Both of these complexes were also synthesized in CH,CN,
starting with [NEt,],[Fe,OCI,] and iron benzoate, respective~ F e , , N a 2 i ~ 4 - O ) , ( ~ 3 - O ) ~ ~ ~ 3 - O H ) , ( O 2 C P h ) ,3, ~ ~ ~ ~ ~ly,[”,
~ ~ ~ ~14]~ possibly
~ 2 ( ~ e 2indicating
~ ~ ~ 2 l an important role for this solvent in
the formation of such cage structures. We have not yet been able
The metal atoms in 3 are held together by a combination of
to produce 3 from the reaction of preformed iron benzoate, for
p4-oxo groups each bridging three Fe atoms and one Na atom,
example [Fe,O(O,CPh),(H,O),]Cl with pyridonate precursors.
p3-oxo and p3-hydroxo units bridging exclusively Fe centers,
Cluster 3 contains three chemically distinct octahedral iron
centers, all of which are bound exclusively to oxygen donors.
The first group comprises Fe4 and Fe4a, and they are bonded to
oxygen atoms from two benzoato ligands, two p3-oxo groups,
one p4-oxo group, and one terminal aqua ligand. The second
group consists of Fel, Fela, Fe3, and Fe3a, each of which is
bonded to three benzoato ligands and one p3-oxo and two
p3-OH units. The remaining iron atoms, Fe2, Fe2a, Fe5, and
FeSa, are bonded to one benzoate oxygen, two p,-oxygens from
chp, and one of each of p3-oxo, p4-oxo, and p3-OH units. The
sodium sites are six-coordinate with 0-donors derived from one
p,-0x0, two p2-chp ligands, two benzoate groups, and a terminal acetone ligand.
The assignment of groups as 0x0 or hydroxo was made on the
basis of bond length considerations. Fe -O(hydroxo) bonds are
known to be significantly longer than Fe-O(oxo) bonds, and in
3 we find that F e - 0 distances to such groups fall into two
distinct regions. Fe-O(oxo) bonds vary from 1.900 to 1.951 A,
while Fe-O(hydroxo) bonds span the range 2.017 to 2.13SA
(average estimated standard deviation 0.005 A). The shortest
Fe . . . Fe contact found in 3 is 2.974(2) A between Fe3 and FeS.
Further evidence of the identity of the 0 atoms comes from their
Fig. 2. The structure of the Fe,,,Na, cage complex 3 in the crystal
VCH Verlu~sgrsrllsc.Iiaft
mhH, D-69451 Wuinheim,I996
B I5.00+ .25!0
Angcw. Clirm. I t i f . Ed Engl. 1996, 35, N o . I 6
coordination geometry; the pL,-oxogroups are planar while the
p,-hydroxides are not. The pc,-oxo groups have a trigonal-pyramidal geometry and are planar with respect to the three nearest
Fe atoms; a Na atom occupies an apical position.
The temperature dependence of the magnetic susceptibility x,
of 3 was measured between 260 and 2.5 K. The values of x, were
calculated on the basis of the elemental analysis of the crystals
used (C.H, N, Fe), which indicate that the sample has desolvated; hence the molecular weight is about 2900 u rather than
3347 u as indicated in the crystal structure. The observed hightemperature value of the product x,T of approximately
35 emu K mol- I is lower than that calculated for ten noninteracting S = 5/2 centers with a g-value of 2 (calcd
43.75 emuKrno1-I) (Fig. 4 top). However, the value of x,T
increases steadily down to 40K, where a plateau is reached at a
x,T value of roughly 64 emuKmol-'. Such a value is close to
that expected for an S = l l spin state (calcd x,T=
66 emuKmol- '). Below 20K a slight fall in x,T is observed,
possibly due to zero-field splitting within the spin ground state
o r due to intermolecular coupling. This decrease is largely independent of the magnitude of the external magnetic field. In an
attempt to clarify the nature of the spin ground state the magnetization of 3 was measured at 2.26K in an external magnetic
field from 0.5 to 7 T. The magnetization shows an increase with
the field up to 21.85 ptgper molecule (Fig. 4 bottom). For a
ground state with S = 11 a value of 22 pB is expected.
A high-spin ground state for 3 could be predicted based on
known magneto-structural correlations. Previous work"
demonstrates that antiferromagnetic exchange between Fe"'
centers is stronger when mediated by 0x0 rather than hydroxo
groups. This allows us to assume that antiferromagnetic exchange through 0 2 , 0 3 , and 0 4 , and their symmetry equivalents will be dominant, and exchange through 0 1 and 0 5 will be
of secondary importance (Fig. 3). Secondly, we can assume that
the magnitude of the exchange interaction will be related to the
Fe-0-Fe angles a t these bridging 0x0 units; the more obtuse the
angle the larger the antiferromagnetic exchange." 61 All the most
obtuse angles at 0x0 groups involve either Fe4 or Fe4a. For
example, at 0 4 a the two angles involving Fe4 are roughly 130 ;
the Fe2a-04a-Fe5 angle is 100.6(3)". Therefore we assume the
strongest antiferromagnetic exchange interactions within this
Fe, triangle are between Fe4. . Fe2a and Fe4. . Fe5. Similar
considerations lead to all the largest antiferromagnetic exchange
interactions coupling Fe4 and Fe4a antiparallel with the other
eight spin centers in the molecule.
Although the magnetic susceptibility and magnetization experiments are in good agreement with an S = 11 ground state,
on the basis of these results we cannot rule out the possibility of
a ground state with a higher spin value. The magnetization
curve did not reach a saturation plateau and, in any case, in the
presence of significant zero-field splitting of ground states with
a high spin value the magnetic susceptibility might not attain the
expected upper limit. The spin value of the ground state is far
from that expected in the presence of simple antiferromagnetic
exchange (which would give S = 15 and S = 10 for a total of six
and four S = 5/2 centers, respectively). Therefore we believe
that some level of spin frustration must exist to explain these
preliminary results. Confirmation of the exact spin ground state
will require further experiments which we are presently undertaking.
Experimental Procedure
I.2THF: A solution of [Fe30(0,CMe),(H,0),C1]-5H,0 [17] (0.63 g, 0.9 mmol) in
MeOH (30 mL) was stirred at reflux for 3 h to give a yellow precipitate (0.276 g).
Yield: 18%. The yellow solid was extracted with a Soxhlet apparatus (40mL
MeOH. 10 mL THF) for 12 h, and the resulting solution was allowed to stand for
several weeks to give pale yellow crystals of I-2THF. Both the yellow precipitate
and crystals analyze satisfactorily for [{Fe(OMe),(O,CMe)j ,o]. FAB-MS. mi::
1832 [Fe,,(OMe),,(O,CMe),,]+, 1739 [Fe,,(OMe),,(O,CMe),,]+, 1711 [Fe,,(OMe),,(O~CMe),]+, 1386 [Fe,(OMe),,(O,CMe),Jt.
1357 [Fe,(OMe),,(O,CMe),] 1208 [Fe,(OMe),,(O,CMe),]+. 1180 [Fe,(OMe),,(O,CMe),]+. 1031
1003 [Fe,(OMe),,(O,CMe),]+, 854 [Fe,(OMe), ,[Fe,(OMe),,(O,CMe),]'.
(O,CMe),]+. 826 [Fe,(OMe),,(O,CMe),]i, 675 [Fe,(OMe), , I + .
3-8MeCN.2Me2CO: A solution of [NEt,],[Fe,OCI,] (0.25 g. 0.4 mmol) and
Na(0,CPh) (0.12 g. 0.8 mmol) in MeCN (30 mL) was stirred for 15 mm before
Na(chp) (0.19g. 1.2mmol. 3equiv) was added. The resultant red solution was
stirred for 2 h then filtered and acetone (4 mL) was added. After one week at 253K
orange-brown rhombic prisms of 3-8MeCN.2Me2COhad formed. Yield. 15%.
The sample analyzed well for [Fe,,Na,(jL,-O),(jL,-O)~(jL,-OH), (O,CPh),,(chp),(H,O),(Me,CO),]-MeCN. No significant peaks were observed in the FAB mass
Received: January 15. 1996 [Z8726IE]
German version: Angen. Chem. 1996. 108, 1967- 1970
Keywords: complexes with oxygen ligands
magnetic properties
. iron compounds
[l] a) R. Sessoli, D. Gatteschi. A. Caneschi. M. A Novak, Nature 1993. 365. 141;
Fig. 4. Top- The temperature dependence of 1,Tfor 3. Bottom: Magnetizat~onM
o f 3 at 2.26K against magnetic field strength. M / N = reduced magnetic moment.
Angeis.. Chem. I n / . Ed. Engl. 1996, 35. No. 16
b) H. J. Eppley, H.-L. Tsai. N. de Vries, K. Folting, G. Christou, D. N. Hendrickson, J. Am. Chem. Soc. 1995, 11 7, 301.
[2] D. P. Goldberg, A. Caneschi, S. J. Lippard, J Am. Chem. Soc. 1993, f 15.9299.
I31 M. W Wemple, D. Adams. K. S. Hagen, K. Folting, D. N. Hendrickson, G.
Christou, J. Chem. Soc. Chem. Commun. 1995. 1591.
[4] A. J. Blake, C M. Grant, C. I. Gregory, S. Parsons, J. M. Rawson, D. Reed,
R. E. P. Winpenny, J Chem. Sor. Dalton Trans. 1995. 195
IS] A. J. Blake. C. M. Grant, S. Parsons, J. M. Rawson. R E. P. Winpenny, J
Chem. SOC.Chem. Commun. 1994, 2363.
[6] A. J. Blake, E.K. Brechin, A. Codron. R. 0. Could, C. M. Grant. J M. Rawson, R. E P. Winpenny, J Chern. So<. Chem. Commun. 1995. 1983.
171 Crystdl data for I . 2 TH F (C48HLo6Fe,o0.,,):monoclinic. P2,'n. (I = 9 027(3).
h=22.101(8), ~=20.159(12)A. /{=102.54(3)', V = 3926A3, M=1914.
Z = 2 (the molecule lies on an inversion center), pcalcd
= 1 619 gem--'. T =
150.0(2)K.crystalsizeO35xO 15x0.05mm,j~(Mo,,) = 1 879mm-I. Crystal
triclinic. Pi,
data for 3-8MeCN.2Me2C0(C,,,H,,,CI,Fe,,N,,Na,O,,):
a =16.195(12), b =17.604(14). c =17.593(14) A, 1 = 61 48(5),
.., - 62.72(5)', V = 3740 A
'. M = 3347, Z = 1 (the molecule lies on an inver-
VCH Verlagsgesellschajt mbH, 0-69451 Weinheim, 1996
0870-0833/96/3516-l827$lS.OO+ .25/0
COMMUNICATIONS sion center), pCalcd
=1.487 g ~ m - ~T=l50.0(2)K,
crystal size 0.78 ~ 0 . 5 x8
0.35 mm, p(MoKJ = 1.134 mm-! Data were collected with a Stoe-Stadl-4 diffractometer. graphite monochromator, Mo,,, w - 20 scans with on-line profile-fitting (W. Clegg, Acfu Crysfullogr. Seer. A 1981. 37, 22). An absorption
correction was applied using Y-scan data for 3 (min./max. transmission 0.392.
0.560). For both 1 and 3 the crystals were cooled using an Oxford Cryosystems
low-temperature device (J. Cosier, A. M. Glazer, J. Appl. Crjsrullogr. 1986, 19,
105). Both structures were solved by direct methods and completed by iterative
cycles of difference Fourier syntheses and full-matrix least-squares refinement
against F 2 (G. M. Sheldrick, SHELXL-93, University of Gottingen, 1993).
Hydrogen atoms were included in both structures in calculated positions. riding on parent C atoms, with U(H) =1.2 Ueq(C)for chp H atoms and
U(H) = 1.5 U,,(C) for methyl H atoms. For I four bridging M e 0 groups are
disordered, and one molecule of T H F solvate is also disordered over two
positions and was refined with similarity restraints. All iron and fully weighted
oxygen atoms (with the exception of 0 1 0 which IS part of the T H F solvate)
were refined with anisotropic displacement parameters to gwe. using 349
parameters. wR2 = 0.2357 for 3651 unique data (20 I 4 0 ) [Rl = 0.0941 for
1820 observed reflections. fo > 4u(F)]. The largest residual difference peak
and hole were 0 977 and -0.749 e k ' , respectively. For 3 all non-hydrogen
atoms were refined anisotropically, except atoms in several disordered solvent
molecules, which were refined isotropically. to give, using 864 parameters.
wR2 = 0.2236 for 13 157 unique data (20 I SO.) [Rl = 0.0798 for 7629 observed reflections. Fo P 4u(F)]. The largest residual difference peak and hole
were 1.472 and - 1.349 e k 3 . Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication no.
CCDC-279-75 Copies of the data can be obtained free of charge on application to The Director, CCDC. 12 Union Road, Cambridge CB2 1EZ. UK (fax.
Int. code +(1223) 336-033; e-mail: teched(a
[XI K. L. Taft. C D. Delfs, G. C. Papefthymiou. S. Foner. D. Gatteschi. S. Lippard. J. A M . Cheii?. SOC.1994, 116, 823.
191 W. Armstrong, S. J. Lippard. Inorg. Chen?. 1985, 24, 981.
[lo] S. Parsons. G. A. Solan, R. E. P. Winpenny, J. Chein. Soc. Chcm. C'ornmun.
1995, 1987.
IChern. SOC.Dulton
[ l l ] A. J. Blake, S. Parsons, G. A. Solan. R. E. P. Winpenny, .
Trans. 1996. 321.
[I21 The related dinuclear complex [Fe,O(O,CPh),(chp),(phen),l. which we have
structurally characterized. can be isolated by addition of 1.10-phenanthroline
(phen). S. Parsons, G. A. Solan. R. E. P. Winpenny, unpublished results.
[I31 K. L. Taft. G. C. Papaefthymiou, S. J. Lippard, Science 1993, 259, 1302.
IA m . Chern. Soc. 1989, f f l , 6856.
[I41 W. Micklitz, S. J. Lippard, .
1151 A. K. Powell, S. L. Heath, D. Gatteschi, L. Pardi, R. Sessoli, G. Spina, F. Del
Giallo, F. Pieralli, J Am. Cheni Soc. 1995, 11 7, 2491.
[16] D. M. Kurtz, Jr., Chem. Rev 1990. 90, 589.
[17] A. Earnshaw, B. N. Figgis, 3 Lewis, J Chern. SOC.
A 1966. 1656.
Structural Reorganization of the Doubly
Protonated [222]Cryptand through
Cation-a and Charge-Charge Interactions:
Synthesis and Structure of Its
[CoCI,]-O.5C,H,CH, Salt
Leonard R. MacGillivray and Jerry L. Atwood*
For molecular recognition processes, understanding the influence of noncovalent interactions on the conformation and corresponding ionophoric properties of macro(po1y)cyclic receptors (e.g. crown ethers, cryptands)". 21 in solution,[3a.b1 the gas
phase,[3'] and the solid state[3d1is an area of much current interest. In this context, the cation-n i n t e r a ~ t i o n ' ~is] a stabilizing
[*I Prof. J. L. Atwood, L. R. MacGillivray
Department of Chemistry
University of Missouri-Columbia
Columbia. MO 6521 1 (USA)
Fax: Int. code +(573)884-9606
e-mail: chemja@mizzoul
[**I We are grateful for funding from the National Science Foundation, the Natural
Sciences and Engineering Research Council of Canada (NSERC) (research
fellowship for L. R. M.), and the International Centre for Diffraction Data
(research scholarship for L. R. M.).
VCH VerlugsgeseIlschaJtmhH. 0-69451 Weinheim. 1996
interaction for the binding of positively charged guests (e.g.
ammonium cations) by a number of preorganized electron-rich
synthetic hosts (e.g. c y ~ l o p h a n e s ) and
[ ~ ~ hydrophobic binding
sites in proteins (e.g. acetylcholine e s t e r a ~ e ) . [61~ Indeed,
experimental and theoretical studies have determined the interaction energies between N(CH,): and NHZ cations and the
quadrupole moment of benzene to be 9 and 19 kcalmol-', respectively,['] and close contacts between cationic amines and
aromatic residues in a limited number of protein structures have
been noted.I6. 81
Extensive work has demonstrated the formation of two-phase
liquid clathrate systems1'] resulting from the interaction of a
wide range of salts with aromatic solvents.["] Recently we reported the self-assembly of proton cryptate complexes of the
macrobicyclic ionophore [222]cryptand (1)
with inorganic anions isolated from such
liquid clathrate media."'". b1 In particular,
N~o.\o~, 1
we illustrated the ability of two trifurcated
intraionic N + - H . . ' 0 hydrogen bonds to
reorganize the flexible ligand to a chiral, in-in conformation
with approximate D, symmetry in the solid state.[*0b1Furthermore, we also studied its mechanism of protonation and revealed the ability of the oxonium ion (H,O+) to interact with
the [1-2HI2+ ion through two strong interionic 0'-H . - . O hydrogen
As part of our ongoing studies of liquid clathrate systems we
now report the synthesis and X-ray crystal structure of complex
2, which provides structural insight into the nature of the
[1-2H][CoC14] .O.SC,H,CH,
ammonium-n interaction. The complex includes a [l-2HjZ ion
that engages in both a cation-n interaction with a single molecule of toluene and charge-charge interaction with the [CoCI4]'- ion. Moreover, as a consequence of these interactions,
the ligand has undergone a structural reorganization from approximate D, symmetry to an elongated in- in conformation.
To our knowledge, this represents the first case in which an
ammonium-n interaction contributes to the structural stability
of an ionophore in the solid state.
Addition of anhydrous HCl(g) to a toluene solution of the
[2.2.2]cryptand 1 in the presence of an equimolar amount CoC1;6H,O and a further 2-3 equivalents of H,O immediately
yielded a two-phase liquid clathrate solution. Light blue crystals
of 2 suitable for X-ray analysis were obtained from the lower
layer by allowing the reaction mixture to stand at room temperature for approximately four weeks. The formula of 2 was confirmed by single-crystal X-ray diffraction," '] 'H N M R spectroscopy,["] and analytical data.['31
An ORTEP perspective of the [I-2HI2+ ion is shown in Figure 1. As in [H30],[1-2H][4CI].4H,O (3), endo protonation of
the macrobicycle leads to the formation of two intraionic trifur~ated['N
~ I+ - H . . .O hydrogen bonds, and hence, an in-in conformation is adopted by the cryptate. As a result, all six oxygen
atoms are directed inward toward the cavity, as illustrated by
NCCO torsion angles, which range from 51(l)O to 53(l)O for
N1-CCO and -49(1)" to -53(1)" for N2-CCO. However,
unlike the cryptates in 3, each of which lie on a crystallographic
twofold axis,['Obl all atoms of the [1-2HI2+ ion in 2 are contained within the asymmetric unit. Moreover, the intraionic N + H . . ' 0 interactions in 2 are distinct as revealed by their average
N + . . . O(cryptate) separations of 2.73(2) and 2.85(2) 8, to N1
and N2, respectively. Similarly, the average distances for the
edges of the two triangular faces formed by atoms 0 1 , 0 3 , 0 5
[3.65(2) A] and 0 2 , 0 4 , 0 6 [3.89(2) A] are also different. The
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Angeu. Chem. Inf. Ed. Engl. 1996, 35. No. 16
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ferris, wheel, iron, cage, carboxylase, complexes, pyridonato, decanuclear, ligand
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