Electron-spin exchange coupling transmitted by58,60Ni (I = 0) and59Co (I = 7/2): Does the nuclear magnetic moment of the spacer atom show?

Article abstract of DOI:10.1021/om058027k

The trinuclear complexes {(Me₂P-η⁶-C ₆H₅)₂M}₂Ni 7^.. (M = V), 8 (M = Cr), {(Me₂P-η⁶-C₆H₅) ₂M}₂CoH 10^.. (M = V), 11 (M = Cr), and {(Me₂P-η⁶-C₆H₅) (η⁶-C₆H₆)M}₂Ni(CO)₂ 14^.. (M = V) and 15 (M = Cr) have been prepared and characterized by means of X-ray crystal structure analysis in two representative cases (11, 15). The closed complexes 7^.., 8, 10^.., and 11 are semirigid, and the open species 14 and 15 are conformationally flexible. Magnetocommunication has been studied for the diradicals 7 ^.., 10^.., 14^.., and 15^.+.- by fluid solution EPR spectroscopy. Comparison of 7^.. with 10^.. shows that the magnetic moment of the nucleus ⁵⁹Co fails to shape the ⁵¹V hyperfine structure in any discernible way. The flexibility of 14^.. furnishes this complex with the largest exchange coupling constant J in the series and is responsible for a pronounced temperature dependence, as demonstrated by alternating EPR line widths upon lowering the temperature. Isoelectronic replacement of V^. by Cr^.+ in the terminal sandwich units yielding 15^.+.+ profoundly attenuates the exchange coupling. Cyclic voltammetry reveals that the complex 10^.. engages in a five-step redox chain 2-|-|0|+|2+|3+. Since the central couple 0|+ represents the oxidation of the spiro cobalt atom, the redox splitting δE_1/2(0| -,-|2-) is governed by a neutral spacer and δE_1/2(3+|2+,2+|+) by a cationic spacer. The positive charge on the spacer exerts a leveling effect in that δE_1/2(reduction) = δE_1/2(oxidation), contrary to spacers of constant charge, for which δE_1/2(reduction) > δE_1/2(oxidation) is commonly observed.

Full text of DOI:10.1021/om058027k

Organometallics 2005, 24, 5509-5517
5509
Articles
Electron-Spin Exchange Coupling Transmitted by 58,60Ni
59
(I ) 0) and Co (I ) 7/2): Does the Nuclear Magnetic
Moment of the Spacer Atom Show?†,1
Christoph Elschenbroich,* Martin Wu¨nsch, Andreas Behrend, Bernhard Metz,
Bernhard Neumu¨ller, and Klaus Harms
Fachbereich Chemie der Philipps-Universita¨t, D-35032 Marburg, Germany
Received May 12, 2005
The trinuclear complexes {(Me2P-η6-C6H5)2M}2Ni 7•• (M ) V), 8 (M ) Cr), {(Me2P-η6-
C6H5)2M}2CoH 10•• (M ) V), 11 (M ) Cr), and {(Me2P-η6-C6H5)(η6-C6H6)M}2Ni(CO)2 14•• (M
) V) and 15 (M ) Cr) have been prepared and characterized by means of X-ray crystal
structure analysis in two representative cases (11, 15). The “closed” complexes 7••, 8, 10••,
and 11 are semirigid, and the “open” species 14 and 15 are conformationally flexible.
Magnetocommunication has been studied for the diradicals 7••, 10••, 14••, and 15•+•+ by fluid
solution EPR spectroscopy. Comparison of 7•• with 10•• shows that the magnetic moment of
the nucleus 59Co fails to shape the 51V hyperfine structure in any discernible way. The
flexibility of 14•• furnishes this complex with the largest exchange coupling constant J in
the series and is responsible for a pronounced temperature dependence, as demonstrated
by alternating EPR line widths upon lowering the temperature. Isoelectronic replacement
of V• by Cr•+ in the terminal sandwich units yielding 15•+•+ profoundly attenuates the
exchange coupling. Cyclic voltammetry reveals that the complex 10•• engages in a five-step
redox chain 2-|-|0|+|2+|3+. Since the central couple 0|+ represents the oxidation of the
spiro cobalt atom, the redox splitting δE1/2(0|-,-|2-) is governed by a neutral spacer and
δE1/2(3+|2+,2+|+) by a cationic spacer. The positive charge on the spacer exerts a leveling
effect in that δE1/2(reduction) ) δE1/2(oxidation), contrary to spacers of constant charge, for
which δE1/2(reduction) > δE1/2(oxidation) is commonly observed.
Introduction
spin interaction on EPR and magnetic properties.5 In
all these variants, the intervening medium, commonly
called the “spacer”, is of utmost importance, and there-
fore generalizations as to the propagating properties of
certain spacer components are in high demand. In this
endeavor, because of their well-defined redox and
magnetic properties, sandwich complexes serve admi-
rably as probes. The investigation described in the
present paper deals with paramagnetic bis(η6-benzene)-
vanadium (1•) as terminal units in trinuclear complexes
and how an intervening complex unit containing Co or
Ni as central metal atom influences the interaction
Intramolecular communication may be mechanical,
as demonstrated by the cooperativity of the four heme
groups in hemoglobin,2 electronic, as exhibited by the
mixed/intermediate valence phenomenon,3 electrochemi-
cal, as in the mutual influence multiple redox sites exert
on each other’s potentials,4 or magnetochemical, which
manifests itself in the effect of electron-electron spin-
† Dedicated to bis(benzene)chromium on the occasion of its 50th
birthday.20b
* To whom correspondence should be addressed. E-mail: eb@
chemie.uni-marburg.de.
(1) Metal π Complexes of Benzene Derivatives, LVIII. Part LVII:
Elschenbroich, Ch.; Pietras, M.; Harms, K. J. Organomet. Chem. 2003,
684, 359.
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10.1021/om058027k CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/05/2005

5510 Organometallics, Vol. 24, No. 23, 2005
Elschenbroich et al.
between the terminal units. While being isovalence
electronic in the complexes to be studied, the central
metals Co (I ) 7/2) and Ni (I ) 0) differ in their nuclear
magnetic moment. This couple may therefore reveal
whether nuclear magnetism of a bridging atom affects
the extent of intramolecular communication or mani-
fests itself in the EPR hyperfine pattern which is
diagnostic of electron-electron spin-spin exchange
coupling in a biradical complex.
for a more formal treatment invoking singlet-triplet
state mixing, which also forms the basis for the spectral
simulation routines.5c,14e
Adhering to the electron transfer interpretation of
exchange coupling, one may pose the question whether,
just like in the “chemical mechanism” of inner sphere
ET,8 the electrons “on their way” interact with magnetic
nuclei of the bridge, in the present case possibly giving
rise to 59Co in addition to 51V hyperfine structure. To
test this notion, the organometallic biradicals [(Me2P-
η6-C6H5)2V•]2M (7••, M ) Ni; 10••, M ) CoH) will be
described and their EPR spectra compared. Since all
three metal centers V, Ni, and Co in the target com-
plexes are redox active, the study of magnetocommu-
nication will be complemented by cyclic voltammetry,
which should shed light on electrocommunication present
in these trinuclear complexes.
Intramolecular magnetocommunication clearly ex-
presses itself in the spin-exchange coupling J of two
unpaired electrons that reside on the central metal
atoms of two bis(benzene)vanadium units separated by
a spacer.6 We have studied the spacer dependence of
the magnitude of J extensively in recent years, employ-
ing as a probe (η7-C7H7)V(η5-C5H5), trovacene(3•), rather
than the symmetrical complex (η6-C6H6)V(η6-C6H6) (1•)
because the synthesis of derivatives is somewhat more
tractable for the former, compared to the latter.7a
Furthermore, the lower symmetry of trovacene consti-
tutes an additional source of information since the spin
densities in the five- and seven-membered rings differ;
this governs the intensity of exchange coupling in
isomeric dinuclear complexes that are linked via the
five- or the seven-membered rings, respectively.7b For
the synthesis of chelating sandwich complexes, bis-
(benzene)vanadium is to be preferred, however, because
a chelating ligand based on unsymmetrical trovacene
can introduce problems caused by isomerism. The work
described in this paper deals with the coordination of
the “ligands” bis(dimethylphosphano-η6-benzene)vana-
dium (4•) and bis(dimethylphosphano-η6-benzene)chro-
mium (5) to the spacer atoms 58,60Ni (I ) 0) and 59Co (I
) 7/2) (present in the unit Co-H), the question being
raised whether the presence of a nuclear spin I ) 7/2
in the case of cobalt exerts an influence on the magni-
tude of the exchange coupling constant J. In a physically
descriptive sense, spin exchange in a typical biradical,
which is defined by a very low value of J, is often
rationalized in terms of two concerted intramolecular
electron transfer processes whose rate governs the EPR
hyperfine pattern. In this picture, the “slow” (weak)
exchange limit implies coupling of each individual
electron spin to a single nuclear spin only. The magni-
tude of hyperfine coupling a then is identical to that in
a localized monoradical. Conversely, in the “fast” (strong)
exchange limit electron spin coupling to the nuclear
spins on both sites arises and the 51V hyperfine splitting
is halved, causing the hyperfine pattern to mimic that
of a delocalized dinuclear monoradical. This visualiza-
tion gives a feel for the borderline cases and serves to
justify the term “exchange” in the name for the param-
eter J. It also provides a conceptual link between
exchange coupling and intramolecular electron and
energy transfer. Yet, the more informative EPR hyper-
fine patterns in the intermediate exchange region call
Results and Discussion
Synthesis. Di[bis(dimethylphosphano-η6-benzene)-
vanadium]nickel (7••) was prepared by lithiation of bis-
(benzene)vanadium (1•) and reaction with dimethylchlo-
rophosphane and then bis(1,5-cyclooctadiene)nickel (6).
Reaction of bis(dimethylphosphano-η6-benzene)vana-
dium (4•) with (η3-cyclooctenyl)(η4-cycloocta-1,5-diene)-
cobalt (9) yielded di[bis(dimethylphosphano-η6-benzene)-
vanadium]cobalt hydride (10••) (Scheme 1). The analogous
diamagnetic chromium complexes 89 and 11 were
prepared accordingly; they formed superior crystals for
X-ray crystallography, and their structural features are
considered to be representative for the vanadium con-
geners as well.
While the trinuclear complexes 7••, 8,9 10••, and 11
feature a nearly rigid frame, the intermetallic distances
being fixed, it was desirable to dispose of complexes with
identical coupling paths which are flexible, however. We
therefore also prepared the compounds 14•• and 15, in
which the sandwich units are part of monodentate
phosphane ligands. In this case, rather than by a spiro
nickel center, the ligands are connected by a Ni(CO)2
unit (Scheme 1).
X-ray Crystallography. Drawings of the molecular
structures of the complexes 11 and 15 in the crystal are
depicted in Figures 1 and 2; pertinent distances and
angles are given in the captions. The geometries of the
central MP4 cores in the trinuclear complexes 11 and
89 are contrasted in Figure 3. Despite the vicinity of the
heavy metal atom cobalt, the hydrogen atom of the
Co-H bond could be located; additionally, its presence
can be inferred from the structural features of the CoP4
core.10 The positions of the four P atoms in 11 deviate
markedly from tetrahedral in that they are part of a
distorted trigonal bipyramid in which the atoms P2, P3,
and P4 occupy the equatorial positions and P1 and the
hydride ligand reside at the apical position. This de-
(6) (a) Elschenbroich, Ch.; Heck, J. Angew. Chem., Int. Ed. Engl.
1981, 20, 267. (b) Nowotny, M.; Elschenbroich, Ch.; Behrendt, A.;
Massa, W.; Wocadlo, S. Z. Naturforsch. 1993, 48 b, 1581. (c) Elschen-
broich, Ch.; Metz, B.; Neumu¨ller, B.; Reijerse, E. Organometallics 1994,
13, 5072. (d) Elschenbroich, Ch.; Bretschneider-Hurley, A.; Hurley, J.;
Behrendt, A.; Massa, W.; Wocadlo, S.; Reijerse, E. Inorg. Chem. 1995,
34, 743.
(7) (a) Elschenbroich, C.; Schiemann, O.; Burghaus, O.; Harms, K.
Chem. Commun. 2005, 2149, and previous papers in the series
“Trovacene Chemistry”. (b) Elschenbroich, Ch.; Plackmeyer, J.; Harms,
K.; Burghaus, O.; Pebler, J. Organometallics 2003, 22, 3367.
(8) (a) Wilkins, R. G. Kinetics and Mechanism of Reactions of
Transition Metal Complexes, 2nd ed.; VCH: Weinheim, 1991; Chapter
5.8. (b) Jordan, R. B. Reaction Mechanisms of Inorganic and Organo-
metallic Systems, 2nd ed.; Oxford University Press: New York, 1998;
Chapter 6.4. (c) Beitz, J. V.; Miller, J. R.; Cohen, H.; Wieghardt, K.;
Meyerstein, D. Inorg. Chem. 1980, 19, 966.
(9) Elschenbroich, Ch.; Heikenfeld, G.; Wu¨nsch, M.; Massa, W.;
Baum, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 414.
(10) (a) Frentz, B. A.; Ibers, J. A. Inorg. Chem. 1970, 11, 2403. (b)
Holah, D. G.; Hughes, A. N.; Maciaszek, S.; Magnuson, V. R.; Parker,
K. O. Inorg. Chem. 1985, 24, 3956.

Electron-Spin Exchange Coupling
Organometallics, Vol. 24, No. 23, 2005 5511
Scheme 1
scription is supported by the fact that the cobalt atom
lies only 40 pm from the plane defined by P2, P3, and
P4, whereas in tetrahedral coordination this distance
would amount to 70 pm assuming identical Co-P bond
lengths. Furthermore, the angles P2CoP3 (123°) and
P2CoP4 (120°) also point to a flattening of the internal
trigonal pyramid P2P3P4Co since these angles should
amount to 109.5° if Co resided at the center of a
tetrahedron P1P2P3P4. Conversely, the angles P1CoP2
(97°), P1CoP3 (100°), and P1CoP4 (106°) are smaller
than that encountered in an undistorted tetrahedron.
The intermetallic distance of the terminal chromium
atoms is affected only marginally, though, by hydride-
ligand-induced distortion in that d(Cr‚‚‚Cr) ) 849.0 (8),
861.5 pm (11), this difference partially being attribut-
able to the larger covalent radius of Co, compared to
Ni.
In the structure of the “open” congener 15, as ex-
pected, the interchromium distance d(Cr‚‚‚Cr) ) 947 pm
exceeds that found for the “closed” trinuclear complexes
8 and 11. Of course, this gradation of intermetallic
distances is not transferable to fluid solution, where the
extent of intramolecular communication was studied by
means of EPR spectroscopy and cyclic voltammetry. The
dimensions of the bis(arene)metal units are affected
insignificantly by their incorporation into the trinuclear
complexes 8, 11, and 15.
1
NMR Spectroscopy. The most significant H NMR
feature of complex 11 is the resonance at δ -12.92,
which appears as a quintet, J(1H,31P) ) 32 Hz, and can
Figure 1. Molecular structure of di[bis(dimethylphos-
phano-η6-benzene)chromium]cobalt hydride (11), ORTEP
plot (50% probability ellipsoids). Selected bond lengths (Å)
and bond angles (deg): Co-P1 2.146(2), Co-P2 2.132(2),
Co-P3 2.136(2), Co-P4 2.138(1), P1-C5 1.843(5), P2-C6
1.846(5), P3-C7 1.836(5), P4-C8 1.860(5), P1-Co-P2
96.81(6), P1-Co-P3 100.00(6), P1-Co-P4 106.28(6), P2-
Co-P3 122.54(6), P3-Co-P4 106.97(6), P2-Co-P4 120.03-
(6), sandwich tilt angles 1.0 (Cr1), 2.0 (Cr2), intersandwich
angle 80.5, Cr1‚‚‚Co 4.472(1), Cr2‚‚‚Co 4.343(1), Cr1‚‚‚Cr2
8.615(1).
Figure 2. Molecular structure of di[bis(dimethylphos-
phano-η6-benzene)chromium]nickel (15), ORTEP plot (50%
probability ellipsoids). Selected bond lengths (Å) and bond
angles (deg): Ni1-P1 2.207(2), Ni1-P2 2.217(2), Ni1-C25
1.747(6), Ni1-C26 1.786(7), P1-C1 1.813(8), P2-C13
1.813(7), C25-O1 1.155(7), C26-O2 1.122(8), P1-N1-C25
111.9(3), P2-Ni1-C25 110.5(3), C25-Ni1-C26 114.2(3),
P1-Ni1-C26 107.0(3), P2-Ni1-C26 107.0(2), P1-Ni1-
P2 105.8(3), Cr1‚‚‚Ni1 4.9089(16), Cr2‚‚‚Ni1 4.9006(16),
Cr1‚‚‚Cr2 9.478(2).

5512 Organometallics, Vol. 24, No. 23, 2005
Elschenbroich et al.
Figure 3. Bond angles P(i)MP(j) in the central MP4 cores
of the trinuclear complexes 89 and 11. Note that in 8 the
‚
:
sums of angles ∑(<) and ∑(‚ ‚) approach those expected for
tetrahedral coordination of Ni, whereas for 11 they signal
distortion toward trigonal bipyramidal coordination.
be assigned to the metal-bonded hydrogen atom. The
absence of discernible splitting caused by scalar coupling
J(1H,59Co) must be traced to the short relaxation time
effected by the large quadrupole moment of the nucleus
59Co. 31P{1H} NMR of 11 exhibits a single resonance at
δ 11.8, which, together with the quintet structure of the
proton signal of the P4Co-H segment, signalizes ap-
parition of a dynamic process. Reversion of three-
membered interannular bridges at sandwich complexes
is a well-known phenomenon, which has been observed
in the ferrocene11a,b as well as in the bis(arene)metal11c,d
series. Apart from the equivalence of the P atoms,
cycloreversion is also responsible for that of the methyl
groups, which in the frozen configuration, present in the
crystal, adopt axial and equatorial positions. Strictly
speaking, the complexes 7••, 8, 10••, and 11 should be
designated as “semirigid”, thereby implying that some
conformational mobility is encountered, which, however,
does not grossly change the mutual disposition of the
terminal metal atoms that engage in intramolecular
communication. This contrasts with the singly bridged
complexes 14•• and 15, which possess more degrees of
conformational freedom with attendant variability of
intermetallic distances and extent of communication.
EPR Spectroscopy. Oligoradical complexes based on
bis(η6-benzene)vanadium(d5) (1•) or its unsymmetrical
isomer (η7-tropylium)vanadium(d5)(η5-cyclopentadienyl),
trovacene (3•), as paramagnetic probes give rise to 51V
hyperfine patterns from which the magnitude of the
exchange coupling constant J can be extracted if the
latter falls in the range 5 × 10-4 j |J| j 1.5 cm-1 or 0.1
a(51V) j |J| j 300 a(51V).5c,12 In this regime the EPR
spectra significantly deviate from the borderline cases
Figure 4. EPR spectrum (X-band) of di[bis(dimethylphos-
phano-η6-benzene)vanadium]nickel (7••), toluene, 298 K, g
) 1.988, |J| ) 0.29 cm-1; temperature dependence of the
51V hyperfine pattern.
Figure 5. EPR spectrum (X-band) of di[bis(dimethylphos-
phano-η6-benzene)vanadium]cobalt hydride (10••), toluene,
298 K, g ) 1.987, |J| ) 0.33 cm-1
.
of an octet of lines of equal intensity spaced by a(51V)
and a quindecet of relative intensities 1:2:3:4:5:6:7:8:7:
6:5:4:3:2:1, spaced by a(51V)/2. The EPR spectra of 7••
(Figure 4), 10•• (Figure 5), and 14•• (Figure 6) clearly
reflect situations between these limiting cases and
therefore are amenable to interpretation and computer
simulation (Figure 7). In this way the exchange coupling
constants |J(7••)| ) 0.29, |J(10••)| ) 0.33, and |J(14••)| )
0.42 cm-1 are determined for the spectra recorded at
298 K. Most importantly, hyperfine coupling to 59Co is
absent in the spectrum of 10•• and the ability of the units
P4Ni and P4CoH to promote exchange coupling is very
similar; the slightly larger value of J(10••) compared to
J(7••) may be traced to the larger atomic radius and
higher electron density on Co-I compared to Ni0.
(11) (a) Davison, A.; Smart, J. C. J. Organomet. Chem. 1979, 174,
321. (b) Abel, E. W.; Long, N. J.; Orrell, K. G.; Osborne, A. G.; Sik, V.;
Bates, P. A.; Hursthouse, M. B. J. Organomet. Chem. 1989, 367, 275.
(c) Benn, R.; Blank, N. E.; Haenel, M. W.; Klein, J.; Koray, A. R.;
Weidenhammer, K.; Ziegler, M. L. Angew. Chem., Int. Ed. Engl. 1980,
19, 44. (d) Elschenbroich, Ch.; Burdorf, H.; Mahrwald, D.; Metz, B. Z.
Naturforsch. 1992, 47b, 1157.
(12) Elschenbroich, Ch.; Plackmeyer, J.; Nowotny, M.; Behrendt, A.;
Harms, K.; Pebler, J.; Burghaus, O. Chem. Eur. J. 2005, in press.

Electron-Spin Exchange Coupling
Organometallics, Vol. 24, No. 23, 2005 5513
Figure 8. EPR spectrum (X-band) of the di[(η6-benzene)-
(dimethylphosphano-η6-benzene)chromium(I)]di(carbonyl)-
nickel dication (15•+•+), DMF/CHCl3 (1:1), 298 K, g )
1
1.9859, a(11 H) ) 0.341 mT, a(1 53Cr) ) 1.83 mT. High-
field 53Cr satellites broadened beyond recognition due to
large molecular size and small tumbling rate.
implying that J(8•+•+) , a(1H, 8•+•+), a(53Cr, 8•+•+).
Conversely, EPR had revealed that, despite the grada-
tion a(51V, 7••) > a(53Cr, 8•+•+), a(1H, 8•+•+) for the neutral
diradical J(7••) > a(51V, 7••) holds. Therefore, the two
isoelectronic species exhibit strongly differing extents
of exchange coupling in that J(7••) . J(8•+•+). Irrespec-
tive of the intimate coupling mechanism, this finding
can be rationalized by the contracted nature of the
singly occupied metal orbital in a cation compared to a
neutral species. For the same reason J(14••) (Figure 6)
implies intermediate exchange and J(15•+•+) (Figure 8)
weak exchange coupling on the hyperfine time scale.
The relation J(14••) > J(10••) may initially come as a
surprise since, rather than two as in 10••, only one link
PNiP connects the two paramagnetic sandwich units in
14••. However, the high conformational flexibility of
“open” 14•• must be invoked, which enables the molecule
to adopt momentary structures favorable for exchange
coupling, including the case of collisional encounter of
the two paramagnetic sandwich units with the effect
that direct exchange (through-space) can add to or
compete with superexchange (through bond).
Figure 6. EPR spectrum (X-band) of di[(η6-benzene)-
(dimethylphosphano-η6-benzene)vanadium]di(carbonyl)-
nickel (14••), toluene, 298 K, g ) 1.9843, |J| ) 0.42 cm-1
;
temperature dependence of the 51V hyperfine pattern.
Conformational rigidity of 7•• versus flexibility of 14••
serves to explain the disparate response of the EPR
spectra to temperature change (Figures 4 and 6). While
the spectrum of 7•• apart from slight general line
broadening is essentially unaffected, the spectrum of
14•• changes significantly in increasingly reverting to
an alternating line widths pattern as the temperature
is lowered; the effect expresses itself more clearly in
alternating amplitudes of consecutive lines. Superim-
posed on this pattern is the familiar low-|center-|high
field line widths variation which results from tumbling
motion insufficient to average g and hyperfine anisotro-
pies.13 Alternating line widths in exchange coupled EPR
spectra are caused by fluctuations of the coupling
constant J about its static value, which accompanies
intramolecular conformational changes.14 They were
first observed for bisnitroxides14a,b and later for di-
nuclear paramagnetic transition metal complexes,14d no
example having been found for organometallic species
yet as far as we know. In the present case 14•• modula-
Figure 7. Simulations14e of the EPR spectra (298 K) of
the organometallic biradical species 7•• (|J| ) 0.29 cm-1
,
Figure 4), 10•• (|J| ) 0.33 cm-1, Figure 5), and 14•• (|J| )
0.42 cm-1, Figure 6).
A drastic weakening of the exchange interaction is
observed if in the neutral diradical 7•• in the terminal
sandwich units V0 is replaced by Cr•+ to yield the
isoelectronic diradical dication 8•+•+. This species has
been studied previously, and the most important result,
within the context of this discussion, was the detection
1
of H and 53Cr hyperfine structure caused by a(153Cr)
(13) (a) Wilson, R.; Kivelson, D. J. Chem. Phys. 1966, 44, 154. (b)
Atkins, P. W.; Kivelson, D. J. Chem. Phys. 1966, 44, 169. (c) Chasteen,
N. D.; Hanna, M. W. J. Phys. Chem. 1972, 76, 3951.
) 17.7 G and a(101H) ) 3.23 G.9 Theses parameters
mimic those of the mononuclear species 5•+, thereby

5514 Organometallics, Vol. 24, No. 23, 2005
Elschenbroich et al.
of the diradical cation 18••+, however, as zero-field
splitting and the observation of a ∆Ms ) 2 signal.15b
These observations agree with the habit of the spectrum
of 10•• in that the small magnitude of the coupling
constant a(59Co) fails to cause discernible splitting of
each of the 51V components. The small exchange cou-
pling constant J(10••) and the distribution of total
intensity over 15 lines render the ∆Ms ) 2 transition
too weak for observation (fluid solution), and the large
interspin distance of 860 pm in the point dipole ap-
proximation gives rise to a zero-field splitting parameter
D that is too small to shape the rigid solution spectrum.
Although the presence of magnetic 59Co in the spacer
is not obvious from the EPR spectrum of 10••, it is
tempting to speculate about the nature of exchange
coupling operative in the diradicals 7••, 8•+•+, 10••, and
11•+•+. The information from the EPR spectrum of 16•
that finite spin density is transferred from vanadium
(d5) to manganese (low-spin d6) and the fact that in the
trinuclear diradicals Mn is replaced by Ni (7••, 8•+•+) or
Co-H (10••, 11•+•+) in a spiro disposition suggest that
two orthogonal orbitals at the connecting central metal
atom are polarized in a parallel fashion. The P4M linker
in these diradicals should therefore mediate weak
ferromagnetic coupling, albeit of minute size, given the
small spin density transferred to the linker metal atom,
as demonstrated by the small hfc constant a(55Mn) in
16•+.
Scheme 2
tion of J is effected by time-dependent changes of the
intervanadium distance. From the aforesaid it is clear
that a large number of parameters would enter into
spectral simulation because the influence of tumbling
motion as well as that of conformational change on the
line widths must be included. The requisite expressions
are given in a paper by Mabbs.14d This paper also
features the EPR spectrum of an acetylene dicarboxylic
acid-bridged oxovanadium(IV) dimer that strongly re-
sembles that of the organometallic biradical 14••; the
interpretations should be closely related in both cases.
Accordingly, the simulations in the present work have
been performed with a program based on the Mabbs
approach.14e
Returning to the initial question whether a magnetic
nucleus as part of a bridge that mediates exchange
coupling gives rise to EPR hyperfine structure, the
absence of discernible 59Co splitting in the spectrum of
10•• should be commented on. Isotropic hyperfine inter-
action requires finite s orbital spin density at the
magnetic nucleus. In paramagnetic transition metal
complexes this usually arises from spin polarization of
inner s shells, brought about by partially occupied d
orbitals of the central metal atom. Bis(arene)metal
complexes that bear a metal atom with a magnetic
moment in an interannular link have been studied
previously with the aim of assessing interaction between
the two types of metal atoms present (Scheme 2).
Whereas the EPR spectrum of complex 16• reveals 51V
hyperfine structure only, no indications for 55Mn split-
ting being detectable, from the spectrum of the isoelec-
tronic cation 17•+ the value a(55Mn) ) 0.8 G can be
extracted.15a The lack of resolution of 55Mn hyperfine
splitting in the case of 16• is probably caused by the
larger intrinsic line width for 1• (≈5 G) compared to 2•+
(≈0.5 G), under which spectral detail may be hidden.
No a priori decision as to the mechanism of spin transfer
to the nucleus 55Mn in 17•+ can be offered; both a direct
mechanism (through-space) and a superexchange path
(through-bond) can operate, although the large distance
d(Cr‚‚‚Mn) ) 453 pm disfavors the former. In a similar
vein, no 53Cr satellites in addition to 95,97Mo satellites
are seen in the EPR spectrum of 18•; intermetallic
interaction reveals itself in the rigid solution spectrum
Electrochemistry. The complexes 7••, 8, 10••, 11, 14••,
and 15 contain three redox-active metal atoms, which
occur as a pair in the terminal sandwich units and a
single atom in the spacer. Whereas the presence or
absence of a magnetic moment of course is immaterial
for the redox properties, it is worthwhile to search for
electrocommunication in these species because the
variation of charge of a spacer is a novel feature. The
results of an examination of the complexes 7••, 8, 10••,
and 11 by cyclic voltammetry are collected in Table 1.
Assignment of the waves is assisted by reference to the
redox properties of the parent complexes 1• and 216 and
of mononuclear complexes that are representative for
the spacers:17
irrev.
-e-
+e-
-e-
+e-
(dppe)2CoH y
z [(dppe)2CoH]+ y
z
-0.60 V
0.32 V
[(dppe)2CoH]2+
irrev.
-e-
-e-
+e-
(dmpe)2Ni0 y
z [(dmpe)2Ni]+ y
z
+e-
-0.64 V
-0.18 V
[(dmpe)2Ni]2+
The most complete picture is drawn by complex 10••
in that five reversible waves spread over a potential
range of 2.5 V are observed (Figure 9). The central wave
at -0.91 V represents the Co+/2+ couple of the P4CoH
link; the cathodic shift of -0.31 V relative to the
(14) (a) Luckhurst, G. R. Mol. Phys. 1966, 10, 543. (b) Glarum, H.
S.; Marshall, J. H. J. Chem. Phys. 1967, 47, 1374. (c) Hudson, A.;
Luckhurst, G. R. Chem. Rev. 1969, 69, 191. (d) Collison, D.; Mabbs, F.
E.; Turner, S. S. J. Chem. Soc., Faraday Trans. 1993, 89, 3705. (e)
Burghaus, O. EPR fitting and simulation program “SIMEPR”; Uni-
versity of Marburg, available on request; Burghaus, O. Proceedings of
the Joint 29th AMPERE-13th ISMAR International Conference;
Technische Universita¨t Berlin, 1998; Magnetic Resonance and Related
Phenomena, Vol. II, p 1186. See also ref 5c.
(16) Elschenbroich, Ch.; Bilger, E.; Metz, B. Organometallics 1991,
10, 2823.
(17) The redox properties of these reference molecules have been
redetermined in the medium dimethoxyethane/(n-Bu)4NClO4. Different
behavior has been reported for the more strongly solvating medium
toluene/acetonitrile (1:1): Pilloni, G.; Schiavon, G.; Zotti, G.; Zecchin,
S. J. Organomet. Chem. 1977, 134, 305.
(15) (a) Elschenbroich, Ch.; Isenburg, T.; Metz, B.; Behrendt, A.;
Harms, K. J. Organomet. Chem. 1994, 481, 153. (b) Elschenbroich, Ch.;
Isenburg, T.; Behrendt, A. Inorg. Chem. 1995, 34, 6565.

Electron-Spin Exchange Coupling
Organometallics, Vol. 24, No. 23, 2005 5515
Table 1. Cyclovoltammetric Data for the
Trinuclear Complexes 7••, 8, 10••, and 11a
and δE1/2(oxidations) parameters is discomforting in
view of previous interpretations, which had traced the
gradation δE1/2(reductions) > δE1/2(oxidations) to metal
orbital contraction with attendant attenuation of metal-
ligand interaction.7b Why, then, is the Co2+ spacer a
more efficient mediator of electrocommunication than
the Co+ spacer?
[V]
7••
8b
10••
11
E1/2 (3+|2+)
-0.05
0.115
0.5d
-0.18
0.115
1
-0.59
0.112
1
-0.52
0.065
1
-0.08
0.061
1
0.20
0.088
1
-0.91
0.055
1
-2.24
0.055
1
∼-0.48g
∼0.08
1
∆Ep
rc
E1/2(2+|+)
-0.70e
0.065
1
∼-0.58g
∼0.08
1
∆Ep
If the peripheral sandwich units contain chromium
instead of vanadium as the central metal atom (11), only
oxidations are registered since reduction would entail
generation of a 19 VE configuration, which, because of
the extremely negative requisite potential, is way
beyond the electrochemical window. The chain of oxida-
tion steps is again started with the Co+/2+ couple,
followed by barely resolved oxidations Cr0/+ within the
terminal sandwich units. A very similar sequence of
redox steps arises if CoH in the spacer is substituted
by Ni. As for CoH in the complexes 10•• and 11, primary
oxidation of the spiro-Ni atom in 7•• occurs at a more
negative potential, compared to the reference molecule
(dmpe)2Ni. Establishment of a positive charge on the
spiro-Ni+ ion then causes anodic shifts of the subsequent
rc
E1/2(+|0)
-0.70e
0.065
1
-0.85
0.086
1
∆Ep
rc
E1/2(0|-)
-2.66
0.074
∼1
∆Ep
rc
E1/2(-|2-)
-2.80f
-2.36
0.085
1
∆Ep
r
a DME/(n-Bu)4ClO4, 221 K (7••, 10••), 293 K (8, 11), 100 mV/s at
glassy carbon vs SCE, E1/2 ) (Epa + Epc)/2, ∆Ep ) Epa Epc, r )
-
Ipa/Ipc
.
b Additional wave Epa ) -0.12 V (irrev, 293 K), -0.16 V
(rev, 248 K), ref 9. c The r values are estimates because in the
majority of cases overlapping, partially resolved waves are ob-
tained. d Dependent on scan rate. e n ) 2 (electrons transferred).
f Epc, irrev process. g Barely resolved.
V
0/+ oxidations, compared to parent 1•, and they exhibit
a redox splitting δE1/2 of 130 mV. This value, which has
been encountered repeatedly in the series under inves-
tigation, appears to be characteristic for a tetrahedral
P4M spacer unit, irrespective of the nature of M and of
that of the interacting peripheral metal atoms. While
this invariance could trivially be rationalized under the
assumption of through-space electrostatic interactions
between the redox sites, the large intermetal distance
of 860 pm renders this approach unrealistic and an
alternative through-bond mechanism of electrocommu-
nication should be searched for. This is devised easily
since primary metal-centered oxidation of one sandwich
unit will decrease the donor and increase the acceptor
character of this metal with attendant change of the
donor/acceptor ratio of η6-arylphosphane with regard to
the spacer metal atom. Propagation of this effect across
the molecule will ultimately lower the electron density
on the second peripheral metal atom, thereby causing
an anodic shift of the potential E1/2(M0/+).
Figure 9. Cyclovoltammetric traces for {(Me2P-η6-
C6H5)2V}2CoH (10••) and {(Me2P-η6-C6H5)2Cr}2CoH (11),
DME, 0.1 M (n-Bu)4NClO4, 221 K, and assignment of the
redox sites. Reduction of the chromium atoms in 11 is
beyond the cathodic border of the medium.
By way of conclusion and in response to the quest of
this paper it can be stated that the magnetic moment
of the nucleus 59Co, which is part of the spacer in the
trinuclear complex 10••, is unnoticed in that neither the
magnitude of exchange coupling J of the peripheral
paramagnetic bis(benzene)vanadium units is affected
nor does the hyperfine pattern show resolved 59Co
reference complex (dppe)2CoH reflects the well-known
electron-donating character of bis(arene)metal(0) units.
The central wave is flanked by two clearly resolved pairs
of waves that indicate vanadium-centered consecutive
reductions and oxidations, respectively, showing redox
splittings δE1/2 of 120 mV. This is remarkable since
interaction occurs across a seven-bond separation, in-
cluding orbital orthogonality at the central spiro junc-
tion. It comes as a surprise, however, that the redox
splitting δE1/2 of the two peripheral reductions and
oxidations for 10•• are of equal magnitude because in
7
splitting. In fact, the EPR spectra of the 59Co (I ) /2)-
and 58,60Ni (I ) 0)-containing species are almost identi-
cal. Access to the oxidation states Co+ and Co2+ in 10••
permits a study of the influence of a change of charge
in the spacer on the extent of electrocommunication. It
is found that a positive charge in the spacer exerts a
leveling effect on the redox splittings δE1/2(10•• 0|-,-
|2-) and δE1/2(10•• 3+|2+,2+|+) in that both values are
equal. This contrasts with the usual observation in cases
where the spacer is uncharged that δE1/2(reductions)
exceeds δE1/2(oxidations) by ≈50%, a disparity that
remains to be explained.
all previous cases the δE1/2(2+|+,+|0) values were
2
considerably smaller (≈ /3) than those for the δE1/2
-
(0|-,-|2-) pair.7b A novel aspect in the present work is
the fact that the reductions are mediated by a Co+-
containing spacer, whereas oxidations experience a Co2+
spacer. The observation that the higher positive charge
on the spacer serves to equalize the δE1/2(reductions)
Experimental Section
Methods and Materials. All manipulations were per-
formed with exclusion of air under dinitrogen or argon (CV)

5516 Organometallics, Vol. 24, No. 23, 2005
Elschenbroich et al.
matrix least squares with the programs SHELXL-9322 (11) and
SHELXL-9723 (15). The positions of the H atoms in 11 and 15
were calculated for ideal positions. A common displacement
parameter was refined in 11. The calculation of the bond
lengths, bond angles, and Ueq for 11 was performed with the
program PLATON.24 Crystallographic data for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as Supplementary Publications
Nos. CCDC 280180 (11) and CCDC 270617 (15). These data
can be obtained free of charge via www.ccdc.cam.ac.uk/data-
request/cif.
Table 2. Crystallographic Data for 11 and 15
11
15
instrument
radiation
formula
fw
cryst size (mm)
a (Å)
P3 (Siemens)
P4 (Siemens)
Mo KR
Mo KR
C
32H45Cr2CoP4
C30H34Cr2NiO2P2
651.22
716.53
0.6 × 0.4 × 0.08 0.4 × 0.3 × 0.2
17.426(5)
10.120(3)
18.737(6)
90
10.180(1)
11.369(1)
14.333(2)
111.64(1)
100.24(1)
103.59(1)
1433.1(3)
triclinic
P1h
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
cryst syst
space group
no.25
108.34(2)
90
3137(2)
monoclinic
P21/c
(Me2P-η6-C6H5)2V (4• ) and (Me2P-η6-C6H5)(η6-C6H6)V
(12•). Bis(benzene)vanadium (1•) (1.34 g, 6.5 mmol) in 120 mL
of cyclohexane is reacted at 80 °C during 2 h with n-
butyllithium (1.6 M in hexane, 9.3 mL, 14.9 mmol) and
N,N,N′,N′-tetramethylethylenediamine, TMEDA (2.2 mL, 14.9
mmol), whereby a reddish brown precipitate of lithiated 1•
forms. After cooling to room temperature a solution of di-
methylchlorophosphane (4.0 mL, 14.9 mmol) in 20 mL of
cyclohexane is added during 30 min under vigorous stirring.
Reaction is allowed to proceed for 24 h. The volatiles are
removed in vacuo, and the crude product is taken up in a
minimum amount of pentane and subjected to column chro-
matography (silanized silica gel, 40 cm, L 3 cm). The first
orange zone contains unreacted 1• (18%). The second, brown
zone is eluted with pentane to yield (Me2P-η6-C6H5)(η6-C6H6)-
V (12•, 0.56 g, 32%) as copper-colored platelets, mp 71-72 °C.
From the third, brown zone, which is eluted with toluene,
(Me2P-η6-C6H5)2V (4•, 0.69 g, 32%) is obtained as dark brown
prisms, mp 70-71 °C. Anal. Calcd for C14H17PV (267.21): C,
62.93; H, 6.41. Found: C, 62.42; H, 6.56. Calcd for C16H22P2V
(327.23): C, 58.72; H, 6.78. Found: C, 58.02; H, 6.86.
Use of tetramethyldiphosphane instead of dimethylchloro-
phosphane affords the same product distribution.
14
4
2
2
Z
F
calcd (g/cm3)
1.517
1.509
temp (K)
203
223
µ (cm-1
)
14.3
15.32
2θmax (deg)
50.00
55.00
h, k, l values
-20 e h e 19
0 e k e 2
0 e l e 22
6054
-1 e h e 12
-1 e k e 13
-18 e l e 17
3690
no. of reflns
no. of unique reflns (Rint
no. of reflns with
Fo > 4σ(Fo)
)
5511 (0.0503)
3423
3544 (0.0125)
2180
no. of params
356
338
a
R1
0.0451
0.1094c
0.86/-0.60
0.0447
0.1112d
0.46/-0.66
wR2 (all data)b
max/min resid
electron density (e/Å3)
2
2
a ∑||Fo| - |Fc||/∑|Fc|. b wR2 ) {[w(Fo - Fc )2]/[w(Fo2)2]}1/2
.
c w
) 1/[σ2(Fo2) + (0.0553P)2]; P ) [max(Fo2, 0) + 2Fc ]/3. d w )
1/[σ2(Fo2) + (0.0662)2].
2
{(Me2P-η6-C6H5)2V}2Ni (7••). To a solution of bis(cyclo-
octadiene)nickel (6, 0.27 g, 1.0 mmol) in toluene (10 mL) is
added at room temperature (Me2P-η6-C6H5)2V (4•, 0.71 g, 2.2
mmol), dissolved in 20 mL of toluene; the mixture is stirred
for 16 h. After filtration the brown solution is reduced to a
volume of 5 mL, layered with 20 mL of pentane, and cooled to
-20 °C. Crystallization affords 7•• (0.45 g, 60%) as small brown
prisms, dec 262-263 °C. Anal. Calcd for C32H44NiP4V2
(713.17): C, 53.89; H, 6.22. Found: C, 53.92; H, 6.30.
{(Me2P-η6-C6H5)2V}2CoH (10••). A solution of (η3-C8H13)-
(η4-C8H12)Co (9, 0.20 g, 0.72 mmol) and (Me2P-η6-C6H5)2V (4•,
0.50 g, 1.5 mmol) in 30 mL of toluene is stirred for 3 h at -20
°C. The solvent is removed in vacuo, and the residue is
extracted with three 30 mL portions of petroleum ether. The
remaining solid is dissolved in a minimal amount of toluene
and layered with low-boiling petroleum ether. Precipitation
at 4 °C generates 10•• (0.23 g, 45%) as a microcrystalline brown
material. Anal. Calcd for C32H45CoV2P4 (714.42): C, 53.80; H,
6.35. Found: C, 53.72; H, 6.47.
employing standard Schlenk techniques. Bis(η6-benzene)-
vanadium (1•),20a bis(η6-benzene)chromium (2),20b (Me2P-η6-
C6H5)(η6-C6H6)Cr (13),9 (Me2P-η6-C6H5)2Cr (5),9 {(Me2P-η6-
C6H5)2Cr}2Ni (8),9 and (η3-cyclooctenyl)(η4-1,5-cycloocta-
diene)cobalt (9)19 were prepared as described in the literature.
All other chemicals were commercially available and were used
as received.
Physical measurements were carried out with the following
instruments: mass spectrometry, CH 7 (EI-MS), Varian MAT;
cyclic voltammetry, potentiostat 552, function generator 568,
multipurpose unit 563 Amel, glassy carbon working electrode,
SCE reference electrode, Pt auxiliary electrode, solvent/
electrolyte DME/10-3 M (n-Bu)4NClO4, -35 °C, argon protec-
tion; EPR spectroscopy, ESP 300 (X-band), Bruker, frequency
counter TR 5214, Advantest.
X-ray Structure Determination of 11 and 15. The
crystals were covered with a perfluorinated polyether and
mounted at the top of a glass capillary under a flow of cold
gaseous nitrogen. The measured intensities were corrected for
Lorentz and polarization effects and by a numerical absorption
correction (cell parameters, instruments, and radiation see
Table 2). The structures were solved by direct methods
(SHELXS-8621). Refinement was performed against F2 by full-
{(Me2P-η6-C6H5)2Cr}2CoH (11). This trinuclear complex
was prepared as described for 10•• from 9 (0.22 g, 0.79 mmol)
and (Me2P-η6-C6H5)2Cr (5, 0.59 g, 1.8 mmol). In this case, the
product 11 (0.31 g, 55%) could be obtained as red crystals of
rhomboid shape. Anal. Calcd for C32H45CoCr2P4 (716.58): C,
1
53.63; H, 6.34. Found: C, 53.43; H, 6.23. H NMR (D8-THF,
300.13 MHz, 298 K): δ -12.92 (quint., 1 H, Co-H, 2JCoH ) 32
Hz), 4.22 (m, 8 H, 2,6-H), 4.90 (m, 8 H, 3,5-H), 4.22 (m, 4 H,
4-H), 1.56 (s, 24 H, CH3). 1H NMR (D8-THF, 300.13 MHz, 197
K): δ -16.35 (quint., 1 H, Co-H, 2JCoH ) 29 Hz), 4.32 (m, 8 H,
2,6-H), 5.00 (m, 8 H, 3,5-H), 4.33 (m, 4 H, 4-H), 1.62 (s, 24 H,
CH3). 13C{1H} NMR (D8-THF, 75.47 MHz, 298 K): δ 102.4 (1-
C), 78.7 (2,6-C), 75.4 (3,5-C), 75.0 (4-C), 27.0 (CH3). 31P{1H}
NMR (D8-THF, 116.7 MHz): 11.82 (297 K), 12.51 (183 K).
{(Me2P-η6-C6H5)(η6-C6H6)V}2Ni(CO)2 (14••). (Me2P-η6-
C6H5)(η6-C6H6)V (12•, 0.134 g, 0.5 mmol) is dissolved in 20 mL
of toluene, Ni(CO)4 (32 µL, 0.25 mmol) is added, and the
mixture is stirred for 12 h at room temperature. The reddish
(18) Fischer, E. O.; Reckziegel, A. Chem. Ber. 1961, 94, 2204.
(19) Otsuka, S.; Rossi, M. J. Chem. Soc. (A) 1968, 2630.
(20) (a) Fischer, E. O.; Reckziegel, A. Chem. Ber. 1961, 94, 2204.
(b) Fischer, E. O.; Hafner, W. Z. Naturforsch. 1955, 10b, 665.
(21) Sheldrick, G. M. SHELXS-86; University of Go¨ttingen: Go¨t-
tingen, Germany, 1986.
(22) Sheldrick, G. M. SHELXL-93; University of Go¨ttingen: Go¨t-
tingen, Germany, 1993.
(23) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨t-
tingen, Germany, 1997.
(24) Spek, A. L. PLATON-94, University of Utrecht: Utrecht, The
Netherlands, 1994.
(25) International Tables for Crystallography, Vol. A, 2nd ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1989.

Electron-Spin Exchange Coupling
Organometallics, Vol. 24, No. 23, 2005 5517
brown solution is filtered over a 2 cm layer of silanized silica
gel, and the volume is reduced in vacuo to 5 mL. Layering
with hexane leads to precipitation of 14•• (130 mg, 80%) as a
black microcrystalline product. Anal. Calcd for C30H34P2O2V2-
Ni (649.12): C, 55.51; H, 5.27. Found: C, 54.92; H, 5.16. IR
4.9 Hz). 13C{1H}NMR (C6D6, 75.47 MHz, 298 K): δ 77.1 (2,6-
C), 74.4 (3,5-C), 73.6 (4-C), 76.4 (C6H6), 20.8 (CH3), 202 (CO).
31P NMR (C6D6, 116.7 MHz, 298 K): δ 4.6 (s).
Acknowledgment. This work was supported by the
“Deutsche Forschungsgemeinschaft” and the “Fonds der
Chemischen Industrie”. We thank Dr. M. Nowotny for
some assistance in the preparation of the manuscript.
(toluene): νCO ) 1988, 1924 cm-1
.
{(Me2P-η6-C6H5)(η6-C6H6)Cr}2Ni(CO)2 (15). The prepara-
tion and product yield of 15 were identical to that of 14••.
However, crystallization afforded black crystals of 15, which
were suitable for X-ray diffraction. Anal. Calcd for C30H34P2O2-
Cr2 Ni (651.26): C, 55.32; H, 5.26. Found: C, 55.18; H, 5.23.
Supporting Information Available: Tables of atomic
coordinates, isotropic and anisotropic displacement param-
eters, and all bond lengths and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
IR (toluene): νCO ) 1984, 1932 cm-1. H NMR (C6D6, 300.13
MHz, 298 K): δ 4.71 (m, 4 H, 2,6-H), 426 (m, 4 H, 3,5-H), 4.21
(m, 2 H, 4-H), 4.37 (s, 12 H, C6H6), 1.30 (d, 12 H, CH3, 3JPH
)
OM058027K