Identification of [M(II)(arene)2]2+ (M = V, Cr) as the key intermediate in the formation of V[TCNE](x)(·)ySolvent magnets and Cr[TCNE](x) (·) Solvent

Article abstract of DOI:10.1021/ja9929741

To elucidate the mechanism of the reaction between V⁰(C₆H₆)₂ and tetracyanoethylene (TCNE) that leads to the room-temperature magnet V[TCNE]](x)(·)yCH₂Cl₂ (x ~2; y ~ 1/2 ), reactions between bis(arene)- vanadium (arene = 1,3,5-trimethylbenzene, 1,3,5-tri-tert-butylbenzene) and its cations and TCNE and its anion were studied. The reaction of V°(arene)₂ with TCNE yields magnets with critical temperatures ranging from 28 to 400 K. Products from the reaction of [V(I)(arene)₂]⁺ with [TCNE](·)^-) were not magnets; however, reaction of [V(I)(arene)₂]⁺ with [TCNE](·)^-) in the presence of TCNE forms a magnetically ordered material. The reaction of V⁰(1,3,5-C₆H₃Me₃)₂ with 2 equiv of one-electron oxidant [Fe(III)(C₅H₅)₂]⁺, and subsequently with [TCNE](·)^-, also leads to a magnetic material. The results of these investigations suggest that V⁰(arene)₂ undergoes two one-electron oxidation reactions with TCNE to form sequentially [V(I)(arene)₂]⁺ and '[V(II)(arene)₂]²⁺', the latter being the key intermediate that reacts with [TCNE](·) ^- to produce the magnetic product. [V(I)(arene)₂]⁺ has been isolated, whereas and '[V(II)(arene)₂]²⁺' has not. The one-electron oxidation of V⁰[C₆H₃(t- Bu)₃]₂ with Ag-[BPh₄] produces {V(I)[C₆H₃(t-Bu)₃]₂}⁺[BPh₄]^-. The stoichiometric reaction of V⁰[C₆H₃(t-Bu)₃]₂ with TCNE leads to paramagnetic {V(I)[1,3,5-C₆H₃(tBu)₃]₂}⁺[TCNE](·) ^-. {V(I)[C₆H₃(t- Bu)₃]₂}⁺[BPh₄]^- and {V(I)[1,3,5-C₆H₃-(tBu)₃]₂}⁺[TCNE](·) ^- have been structurally characterized. When [V(II)(NCMe)₆]{B[3,5- C₆H₃(CF₃)₂]₄}₂ is reacted with [TCNE](·) ^-, a route that does not use bis(arene)vanadium complexes, a magnetic precipitate is also produced. As established earlier, the reaction of Cr⁰(arene)₂ with TCNE forms nonmagnetically ordered [Cr(I)(arene)2](·)⁺-[TCNE](·) ^-. Reaction of lower oxidation potential Cr⁰Np₂ (Np = naphthalene) with TCNE putatively forms '[Cr(II)Np₂]²⁺' which reacts with [TCNE](·)^- to form Cr[TCNE](x)·yS, which was isolated and, unexpectedly, does not magnetically order. Similar results are obtained when [Cr(II)(NCMe)₄][BF₄]₂ or [Cr(II)(NCMe)₆][B(3,5-C₆H₃(CF₃)₂)₄]₂ is reacted with [n-Bu₄N][TCNE].

Full text of DOI:10.1021/ja9929741

290
J. Am. Chem. Soc. 2000, 122, 290-299
Identification of [MII(Arene)2]2+ (M ) V, Cr) as the Key Intermediate
in the Formation of V[TCNE]x‚ySolvent Magnets and
Cr[TCNE]x‚Solvent
Douglas C. Gordon,1 Laura Deakin, Atta M. Arif, and Joel S. Miller*
Contribution from the Department of Chemistry, UniVersity of Utah, 315 South 1400 East RM Dock,
Salt Lake City, Utah 84112-0850
ReceiVed August 16, 1999
Abstract: To elucidate the mechanism of the reaction between V0(C6H6)2 and tetracyanoethylene (TCNE)
1
that leads to the room-temperature magnet V[TCNE]]x‚yCH2Cl2 (x ∼2; y ∼ /2), reactions between bis(arene)-
vanadium (arene ) 1,3,5-trimethylbenzene, 1,3,5-tri-tert-butylbenzene) and its cations and TCNE and its anion
were studied. The reaction of Vo(arene)2 with TCNE yields magnets with critical temperatures ranging from
28 to 400 K. Products from the reaction of [VI(arene)2]+ with [TCNE]•- were not magnets; however, reaction
of [VI(arene)2]+ with [TCNE]•- in the presence of TCNE forms a magnetically ordered material. The reaction
of V0(1,3,5-C6H3Me3)2 with 2 equiv of one-electron oxidant [FeIII(C5H5)2]+, and subsequently with [TCNE]•-,
also leads to a magnetic material. The results of these investigations suggest that V0(arene)2 undergoes two
one-electron oxidation reactions with TCNE to form sequentially [VI(arene)2]+ and “[VII(arene)2]2+”, the latter
being the key intermediate that reacts with [TCNE]•- to produce the magnetic product. [VI(arene)2]+ has been
isolated, whereas and “[VII(arene)2]2+” has not. The one-electron oxidation of V0[C6H3(t-Bu)3]2 with Ag-
[BPh4] produces {VI[C6H3(t-Bu)3]2}+[BPh4]-. The stoichiometric reaction of V0[C6H3(t-Bu)3]2 with TCNE
leads to paramagnetic {VI[1,3,5-C6H3(tBu)3]2}+[TCNE]•-. {VI[C6H3(t-Bu)3]2}+[BPh4]- and {VI[1,3,5-C6H3-
(tBu)3]2}+[TCNE]•- have been structurally characterized. When [VII(NCMe)6]{B[3,5-C6H3(CF3)2]4}2 is reacted
with [TCNE]•-, a route that does not use bis(arene)vanadium complexes, a magnetic precipitate is also produced.
As established earlier, the reaction of Cr0(arene)2 with TCNE forms nonmagnetically ordered [CrI(arene)2]•+-
[TCNE]•-. Reaction of lower oxidation potential Cr0Np2 (Np ) naphthalene) with TCNE putatively forms
“[CrIINp2]2+” which reacts with [TCNE]•- to form Cr[TCNE]x‚yS, which was isolated and, unexpectedly,
does not magnetically order. Similar results are obtained when [CrII(NCMe)4][BF4]2 or [CrII(NCMe)6][B(3,5-
C6H3(CF3)2)4]2 is reacted with [n-Bu4N][TCNE].
3
1
Introduction
between S ) /2 V(II) and two S ) /2 [TCNE]•- ligands,
forming a ferrimagnet.2c,4 Despite the unusual magnetic proper-
ties of this material, the mechanism of the reaction, as well as
the structure of the magnetic product, remains to be elucidated.
In an attempt to address the chemistry and physics associated
with for the room-temperature V[TCNE]x‚yCH2Cl2 (x ∼2; y
∼0.5) magnet, TCNE has been used to synthesize a variety of
molecule-based magnets as electron-transfer salts. Examples of
structurally characterized TCNE-based molecular magnets
include the 1-D chains containing metallocene repeat units, such
as [MIII(C5Me5)2]+[TCNE]•- (M ) Cr, Fe, Mn)2c,6 that ferro-
magnetically order below 8.8 K and the linear chain coordination
polymers with [TCNE]•- bridging manganoporphyrins.2a TCNE-
The development and understanding of new materials with
technologically important properties is a contemporary research
area. One aspect is aimed at the development2 and exploitation3
of molecule-based materials exhibiting technologically important
bulk magnet behavior, e.g., ferro- or ferrimagnetism. The
molecule-based magnet with the highest ordering temperature
(Tc ∼400 K), namely, V[TCNE]x‚yCH2Cl2 (x ∼2; y ∼0.5),
results from the reaction of V0(C6H6)2 (1) with tetracyanoeth-
ylene (TCNE) in dichloromethane.4 Variations in x, y, and Tc
were observed to be dependent upon reaction conditions.5 The
saturation magnetization for V[TCNE]x‚yCH2Cl2 (x ∼2; y ∼0.5)
is consistent with the presence of antiferromagnetic coupling
(1) Deceased October 16, 1998 while exploring the Tangspo river in
Tibet. Chem. Eng. News 1998, 76 (51), 44. Balf, T. Men’s J. 1998, 8 (2),
106. McRae, M. Nat. Geogr. AdV. 1999, 1 (1), 97.
(4) (a) Manriquez, J. M.; Yee, G. T.; McLean, R. S.; Epstein, A. J.;
Miller, J. S. Science 1991, 252, 1415. (b) Miller, J. S.; Yee, G. T.;
Manriquez, J. M.; Epstein, A. J. Conjugated Polymers and Related
Materials: The Interconnection of Chemical and Electronic Structure;
Proceedings of Nobel Symposium NS-81; Oxford University Press: New
York, 1993; p 461. (c) Epstein, A. J.; Miller, J. S. Conjugated Polymers
and Related Materials: The Interconnection of Chemical and Electronic
Structure; Proceedings of Nobel Symposium NS-81; Oxford University
Press: New York, 1993; p 475.
(5) (a) Zhou, P.; Epstein, A. J.; Miller, J. S. Phys. Lett. A 1993, 181, 71.
(b) Zhou, P.; Morin, B. G.; Miller, J. S.; Epstein, A. J. Phys. ReV. B 1993,
48, 1325. (c) Epstein, A. J.; Miller, J. S. Mol. Cryst., Liq. Cryst. 1993, 233,
171. (d) Long, S. M.; Zhou, P.; Epstein, A. J.; Zhang, J.; Miller, J. S. Mol.
Cryst., Liq. Cryst. 1995, 272, 195. (e) Brinckerhoff, W. B.; Zhang, J.; Miller,
J. S.; Epstein, A. J. Mol. Cryst., Liq. Cryst. 1995, 272, 207.
(2) Recent reviews: (a) Miller, J. S.; Epstein, A. J. J. Chem. Soc., Chem.
Commun. 1998, 1319. (b) Miller, J. S.; Epstein, A. J. Chem. Eng. News
1995, 73 (40), 30. (c) Miller, J. S.; Epstein, A. J. Angew. Chem. 1994, 106,
399. (d) Kinoshita, M. Jpn. J. Appl. Phys. 1994, 33, 5718. (e) Chiarelli, R.;
Rassat, A.; Dromzee, Y.; Jeannin, Y.; Novak, M. A.; Tholence, J. L. Phys.
Scr. 1993, T49, 706. (f) Kahn, O. Molecular Magnetism; VCH Publishers:
New York, 1993; p 373. (g) Caneschi, A.; Gatteschi, D. Prog. Inorg. Chem.
1991, 37, 331. (h) Plass, W. Chem. Ztg. 1998, 32, 323.
(3) (a) Miller, J. S. AdV. Mater. 1994, 6, 322. (b) Landee, C. P.; Melville,
D.; Miller, J. S. In NATO ARW Molecular Magnetic Materials; Kahn, O.,
Gatteschi, D., Miller, J. S., Palacio, F., Eds. 1991, E198, 395. (c) Morin,
B. G.; Hahm, C.; Epstein, A. J.; Miller, J. S. J. Appl. Phys. 1994, 75, 5782.
10.1021/ja9929741 CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/31/1999

V[TCNE]X‚ySolVent Magnets
J. Am. Chem. Soc., Vol. 122, No. 2, 2000 291
for the underlying diamagnetism of the sample from Pascal constants
and of the airtight Delrin or nongelatin capsule sample holder. The
critical temperature, Tc, is determined as the intersection of the steepest
slope of the magnetization curve with the temperature axis, when
warming is done under low applied fields. Samples were cooled in
zero applied field to 2 K and then warmed under an applied field. Low-
field magnetization measurements (3 Oe) were done after degaussing
the shield and resetting the magnet. Powder EPR spectra were recorded
using a Bruker EMX X-band spectrometer with 1,1-diphenyl-2-
picrylhydrazyl (Sigma) as an external standard (g ) 2.0037).
X-ray crystallography studies were done using a Nonius Kappa CCD
diffractometer. The positions of non-hydrogen atoms were obtained
by the direct method using SIR-9717 and were assigned anisotropic
thermal parameters. Hydrogen atom positions were determined by
isotropic refinement. Structure refinement was done using SHELXL
9718a and ORTEP 3.18b Structures 3+[BPh4]- and 3+[TCNE]•- displayed
disorder in the THF solvent molecules. Analysis of crystals of 3 (dark
red prisms) revealed a unit cell with a ) 29.1871(6) Å, b ) 17.3849-
(6) Å, c ) 9.9041(3) Å, V ) 5012.3(3) Å3, and Z ) 6. The refinement
converged to R1 ) 0.0895, wR2 ) 0.2467, and goodness of fit ) 1.079
for 5308 reflections. Axial photographs and systematic absences were
consistent with the compound having crystallized in the monoclinic
space group C2/m. There are two disordered molecules of V(1,3,5-tri-
t-butylbenzene)2 in an asymmetric unit. The first molecule is sitting
on a 2/m symmetry site while the second molecule is sitting on an m
symmetry site. The tert-butyl groups in both molecules are orienta-
tionally disordered, and the second molecule has additional disorder
resulting from three different orientations of the complex.
V0(1,3,5-C6H3Me3)2 (2). A recently reported procedure19 was modi-
fied as follows. A Schlenk tube was loaded with VCl3 (1.26 g, 8.01
mmol), AlCl3 (0.343 g, 13.9 mmol), and aluminum powder (0.343 g,
12.7 mmol). 1,3,5-Trimethylbenzene (15 mL, 0.11 mol) was added via
syringe, and the tube was heated in an oil bath at 100 °C for 2 h. After
cooling to room temperature, 20 mL of THF was added and the reaction
mixture was stirred for an additional 72 h. The solvent was removed
in vacuo and the residue extracted with hexanes. The solution was then
filtered and cooled to 195 K, producing dark red needles (yield: 1.91
g, 82%). IR (KBr, cm-1): 2960-2872 (s), 1655-1596 (m), 1450 (m),
1372 (s), 1146 (m), 1028 (s), 986 (s), 812 (m), 444 (vs). Anal. Calcd
for V(1,3,5-C6H3Me3)2‚0.75(C4H8O), C21H30O0.75V: C, 73.02; H, 8.75.
based magnets containing late first-row transition metals (M )
Mn, Fe, Co, Ni) have also been prepared and display spontane-
ous magnetization below 100 K and coercive fields ranging from
300 (M ) Ni) to 6500 Oe (M ) Co).7
Herein we elucidate the mechanism of the reaction between
V0(arene)2 and TCNE that produces V[TCNE]x‚yS (S ) solvent)
magnets using arene ) 1,3,5-trimethylbenzene and 1,3,5-tri-
tert-butylbenzene. Furthermore, we report the structural char-
acterization of [VI(C6H3(t-Bu)3)2]+ as 3+[BPh4]- and 3+[TCNE]•-,
which represents not only the first characterizations of an early
transition metal bis(arene) complex with this bulky ligand but
also the first bis(arene)vanadium [TCNE]•- complex. In addi-
tion, the preparation and magnetic properties of Cr[TCNE]x‚
yS, which unexpectedly do not display spontaneous magneti-
zation, is presented.
Experimental Section
All experimental procedures were carried out under inert atmosphere
conditions using either Schlenk or glovebox techniques. All solvents
used were dried and degassed before use. Tetrahydrofuran (THF), 1,3,5-
trimethylbenzene, diethyl ether, toluene, and n-hexane were distilled
from sodium benzophenone ketyl and dichloromethane was distilled
from CaH2. [n-Bu4N]+[TCNE]•-,8 [Fe(C5H5)2]{B[3,5-C6H3(CF3)2]4},9
[VII(NCMe)6]{B[3,5-C6H3(CF3)2]4}2,10 Cr0Np2 (Np ) naphthalene),11
[CrII(NCMe)4][BF4]2,12 and [CrII(NCMe)6]{B[3,5-C6H3(CF3)2]4}210 were
synthesized according to previously published procedures. Ag[BPh4]
was obtained from the stoichiometric aqueous reaction of AgNO3
(Johnson-Matthey) and Na[BPh4] (Strem). Aluminum powder (ACROS),
VCl3 (ACROS), and vanadium foil (Aldrich, 99.7%, 5 × 20 × 0.5
mm) were used as received. AlCl3 (ACROS) was purified by sublima-
tion before use. TCNE13 and 1,3,5-tri-tert-butylbenzene14 were syn-
thesized according to literature methods and purified by sublimation.
Elemental analyses were carried out by Atlantic Microlab Inc. (Nor-
cross, GA). The thermal properties were studied on a TA Instruments
model 2050 thermogravimetric analyzer (TGA) equipped with an
electron spray mass spectrometer, located in a Vacuum Atmospheres
DriLab glovebox under argon. Samples were heated from room
temperature to 450 °C at 20 °C/min. Infrared spectra were taken on a
BioI-Rad FTS-40 spectrophotometer using Nujol mulls on NaCl plates
or as KBr pellets, both prepared in a glovebox. Cyclic voltammetry
studies were done in a glovebox under nitrogen using a glassy carbon
working electrode, a Ag wire counter electrode, and a Ag/Ag2O
reference electrode. Ferrocene was used as an external standard {Fe-
(C5H5)2/[Fe(C5H5)2]+: E1/2 ) +0.46 V vs SCE, CH2Cl2}.15 Scans of 2
and 3 (1 mmol) were done in CH2Cl2 at 25 °C at 50 mV/s with
supporting electrolyte [n-Bu4N][PF6] (0.1 mol).
Found: C, 72.75; H, 8.41. EPR (9.785 GHz):
g
) 1.989;
300 K
A51V
) 6.10 mT.
300 K
[VI(1,3,5-C6H3Me3)2]+[BPh4]-, 2+[BPh4]-. A slurry of Ag[BPh4]
(30 mg, 0.70 mmol) in CH2Cl2 (20 mL) was cooled to -78 °C, a 20-
mL CH2Cl2 solution of 2 (0.141 g, 0.484 mmol) was added dropwise,
and the reaction mixture was stirred for 1 h, then warmed slowly to
room temperature, and stirred for an additional 18 h. The reaction
mixture was filtered through Celite on a medium frit and the solid
washed with CH2Cl2. The filtrate was then concentrated to ∼10 mL
and layered with hexanes (20 mL), which produced orange/red
microcrystals (yield: 0.177 g, 60%). IR (KBr, cm-1): 3048-2921 (s),
1580 (m), 1479 (s), 1453 (s), 1427 (s), 1379 (s), 1030 (s), 742 (vs),
731 (vs), 709 (vs), 603 (s). Anal. Calcd for [V(1,3,5-C6H3Me3)2]-
[BPh4]‚1.15CH2Cl2, C43.15H46.3BCl2.26V: C, 73.18; H, 6.59. Found: C,
73.10; H, 6.62.
Magnetic data were acquired on a Quantum Designs MPMS-5XL
SQUID magnetometer as previously described16 and were corrected
(6) (a) Miller, J. S.; Epstein, A. J. In Molecular Magnetism: From
Molecular Assemblies to the DeVices; Coronado, E., Delhae`s, P., Gatteschi,
E., Miller, J. S., Eds.; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1996; Vol. E321, p 379. (b) Miller, J. S.; Calabrese, J. C.;
Rommelmann, H.; Chittipeddi, S. R.; Zhang, J. H.; Reiff, W. M. Epstein,
A. J. J. Am. Chem. Soc. 1987, 109, 769.
(7) Zhang, J.; Ensling, J.; Ksenofontov, V.; Gu¨tlich, P.; Epstein, A. J.;
Miller, J. S. Angew. Chem., Int. Ed. Engl. 1998, 37, 657.
(8) Webster, O. W.; Mahler, W.; Benson, R. E. J. Org. Chem. 1960, 25,
1470.
(9) Calderazzo, F.; Pampaloni, G.; Rocchi, L.; Englert, U. Organome-
tallics 1994, 13, 2592.
(10) Buschmann, W. E.; Miller, J. S. Chem. Eur. J. 1998, 4, 1731.
(11) (a) Kundig, E. P.; Timms, P. L. J. Chem. Soc., Dalton Trans. 1980,
991. (b) Kundig, E. P.; Timms, P. L. J. Chem. Soc., Chem. Commun. 1977,
912.
Reaction of 2 with TCNE (1:1) (CH2Cl2, 25 °C) (4). A solution
of 2 (53.5 mg, 0.184 mmol) dissolved in CH2Cl2 (15 mL) was added
to a 15-mL CH2Cl2 solution of TCNE (23.9 mg, 0.187 mmol), which
immediately formed a black precipitate (yield: 46.5 mg). The reaction
mixture was stirred for an additional 24 h and then filtered, washed
with CH2Cl2, and dried in vacuo. IR (NaCl/Nujol, cm-1) νCtN: 2197
(m), 2097 (s, br). Tc ) 160 K.
Reaction of 2 with TCNE (1:2) (toluene, -78 °C) (5). A solution
of 2 (58 mg, 0.20 mmol) dissolved in toluene (15 mL) was added to a
(12) Heintz, R. A.; Smith, J. A.; Szalay, P. S.; Weisgerber, A.; Dunbar,
K. R., submitted.
(13) Carboni, R. A. Org. Synth. 1959, 39, 64.
(14) Ditto, S. R.; Card, R. J.; Davis, P. O.; Neckers, D. C. J. Org. Chem.
1979, 44, 894.
(15) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877.
(16) Brandon, E. J.; Rittenberg, D. K.; Arif, A. M.; Miller, J. S. Inorg.
Chem. 1998, 37, 3376.
(17) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo,
C.; Guagliardi, A.; Moliteni, A. G. G.; Polidori, G.; Spagna, R. (Release
1.02).
(18) (a) Sheldrick, G. M. SHELX97. Programs for Crystal Structure
Analysis (Release 97-2). University of Go¨ttingen, Germany, 1997. (b)
Farrugia, L. J.; J. Appl. Crystallogr. 1997, 30, 565.
(19) Calderazzo, F.; Pampaloni, G. J. Organomet. Chem. 1995, 500, 47.

292 J. Am. Chem. Soc., Vol. 122, No. 2, 2000
Gordon et al.
5-mL CH2Cl2 solution of TCNE (33.4 mg, 0.261 mmol), which
immediately formed a precipitate. The reaction mixture was stirred for
1 h, warmed to room temperature, then filtered, washed with toluene,
and dried in vacuo, producing a blue/black powder (yield: 68.4 mg).
IR (NaCl/Nujol, cm-1) νCtN: 2190 (m), 2147 (s), 2101 (w). Tc ) 260
K.
producing a cherry-red solution, and the solvent was removed in vacuo.
The resulting product was redissolved in 3 mL of THF, and vapor
diffusion of hexane into the solution at 220 K for 3 days resulted in
formation of dark red crystals (yield: 37 mg, 87%). Single crystals
(plates) of 3+[BPh4]- suitable for X-ray crystallography were obtained
by crystallization at -35 °C from a THF/hexanes (1:1) solution. IR
(KBr, cm-1): 3124 (w), 3057-2873 (s), 1581 (m), 1480 (s), 1461 (m),
1366 (s), 1240 (s), 1136 (m), 993 (w), 878 (w), 732 (s), 703 (vs). µeff-
(300K) ) 2.85 µB. Anal. Calcdd for C60H80BV: C, 83.50; H, 9.34.
Found: C, 83.52; H, 9.32.
{VI[C6H3(t-Bu)3]2}+[TCNE]•-, 3+[TCNE]•-. A solution of TCNE
(5.2 mg, 0.041 mmol) dissolved in THF (15 mL, -78 °C) was added
dropwise to a solution of 3 (23.0 mg, 0.042 mmol) in THF (15 mL,
-78 °C). The reaction mixture was stirred at -78 °C for 4 h, then
slowly warmed to room temperature, and concentrated under vacuum
to ∼15 mL. The suspension was then filtered, and the orange powder
washed with THF and dried in vacuo (yield: 20 mg, 73%). Vapor
diffusion of n-hexane into a THF solution at -35 °C over several days
produced red prisms suitable for single-crystal X-ray crystallographic
analysis. IR (NaCl/Nujol, cm-1) νCtN: 2185 (s), 2146 (s).
Reaction of 2 with TCNE (1:2) (CH2Cl2, -25 °C) (6). A solution
of 2 (30.8 mg, 0.106 mmol) dissolved in CH2Cl2 (15 mL) was added
to a cooled (-25 °C) 15-mL CH2Cl2 solution of TCNE (44.7 mg, 0.349
mmol), which immediately formed a fine blue/black precipitate. The
reaction mixture was then warmed to room temperature, filtered, washed
with CH2Cl2, and dried in vacuo (yield: 23.0 mg). IR (NaCl/Nujol,
cm-1) νCtN: 2218 (m), 2152 (s,br). Tc ) 138 K.
Reaction of 2+[BPh4]- with TCNE (1:1) (CH2Cl2, 25 °C) (7). A
5-mL CH2Cl2 solution of 2+[BPh4]- (27.5 mg, 0.045 mmol) was added
to a 5-mL CH2Cl2 solution of TCNE (5.6 mg, 0.044 mmol), which
immediately formed a black precipitate. The reaction mixture was stirred
for 24 h, then the solid was filtered and dried in vacuo (yield: 15.6
mg). IR (NaCl/Nujol, cm-1) νCtN: 2200 (m), 2104 (s, br). Tc ) 28 K.
Reaction of 2+[BPh4]- with [n-Bu4N]+[TCNE]•- (1:1) (CH2Cl2,
25 °C) (8). A 15-mL CH2Cl2 solution of [n-Bu4N]+[TCNE]•- (19.4
mg, 0.052 mmol) was added to a 15-mL CH2Cl2 solution of 2+[BPh4]-
(30.9 mg, 0.051 mmol), which immediately formed a black precipitate.
The reaction mixture was then stirred at room temperature for an
additional 60 min, filtered, washed with CH2Cl2, and dried in vacuo
(yield: 11.2 mg). IR (NaCl/Nujol, cm-1) νCtN: 2201 (m), 2146 (m),
2110 (s). TGA/MS, m/z+: 71 (BuN+), 57 (Bu+), 56 (BuN+ -Me), 42
(BuN+ -Et), no observed solvent loss. θ ) -28 K (T > 100 K) and θ
) -570 K (200 < T < 300 K).
Reaction of 2+[BPh4]- with (1:1) [n-Bu4N]+[TCNE]•- and TCNE
(CH2Cl2, 25 °C) (9). A solution of 2+[BPh4]- (14.7 mg, 0.025 mmol)
dissolved in CH2Cl2 (5 mL) was added to a 5-mL CH2Cl2 solution
containing TCNE (3.4 mg, 0.027 mmol) and [n-Bu4N][TCNE] (9.9 mg,
0.027 mmol), which immediately formed a blue/black precipitate. The
reaction mixture was stirred for 15 min, and then the solid was filtered
and dried in vacuo (yield: 6.8 mg). IR (NaCl/Nujol, cm-1) νCtN: 2188
(m), 2146 (m), 2101 (w). Tc ) 265 K.
Reaction of 3 with Excess TCNE (11). A solution of 3 (17 mg,
0.031 mmol) dissolved in 5 mL of CH2Cl2 was added to a 5-mL CH2-
Cl2 solution of TCNE (10 mg, 0.078 mmol) in CH2Cl2 at room
temperature, producing a dark blue precipitate within a few minutes.
The solution was stirred for 18 h, and the precipitate was then filtered
and dried under vacuum (yield: 2.5 mg). IR (NaCl/Nujol, cm-1
CtN: 2218 (m), 2194 (m), 2155 (s), 2100 (sh). Tc ) 203 K.
Attempts to make 32+[BPh4-]2. A 15-mL solution of 3 (34 mg, 0.063
)
ν
mmol) in THF was added dropwise to a cooled (-78 °C) slurry of
Ag[BPh4] (87 mg, 0.204 mmol) in 15 mL of THF. The reaction mixture
was stirred for 1 h, warmed to room temperature over 3 h, and then
filtered through Celite, producing an orange/red solution that was
subsequently pumped to dryness and redissolved in 1 mL of THF,
layered with diethyl ether (2 mL), and placed in the freezer (-40 °C).
After several days, red needles were isolated (yield: 31.0 mg); however,
magnetic measurements and elemental analysis characterization con-
firmed this material to be 3+[BPh4]-.
Thermolysis of 3+[TCNE]• (12). 3+[TCNE]•- (7.8 mg, 0.012 mmol)
was refluxed in toluene (15 mL) for 14 h producing a black precipitate
that was filtered, washed with hexanes (yield: 0.4 mg), and dried in
vacuo. IR (NaCl/Nujol, cm-1) νCtN: 2205 (m), 2122 (s).
Reaction of 3+[BPh4]- with TCNE and [n-Bu4N]+[TCNE]•-
(CH2Cl2, 25 °C) (13). A solution of 3+[BPh4]- (7.9 mg, 0.0091 mmol)
dissolved in CH2Cl2 (8 mL) was added to an 8-mL CH2Cl2 solution
containing TCNE (1.1 mg, 0.0085 mmol) and [n-Bu4N]+[TCNE]•- (3.9
mg, 0.010 mmol), which immediately formed a dark precipitate. The
reaction mixture was stirred for 3 h, filtered, washed with CH2Cl2, and
dried in vacuo, producing a dark blue powder (Yield: 3.4 mg). IR
(NaCl/Nujol, cm-1) νCtN: 2193 (m), 2159 (m), 2034 (w, br). Tc )
258 K.
Reaction of 2 with [FeIII(C5H5)2]{B[3,5-C6H3(CF3)2]4} and
[n-Bu4N]+[TCNE]•- (10). A 20-mL CH2Cl2 solution of [Fe(C5H5)2]-
{B[3,5-C6H3(CF3)2]4} (109.8 mg, 0.105 mmol) was added dropwise to
a 15-mL CH2Cl2 solution of 2 (15.2 mg, 0.052 mmol) at -78 °C. The
reaction mixture was stirred for 40 min, changing color from dark red
to green. A -78 °C solution of [n-Bu4N]+[TCNE]•- (39.6 mg, 0.107
mmol) dissolved in 10 mL of CH2Cl2 was added to the above solution,
immediately forming a dark blue precipitate. The reaction mixture was
stirred at this temperature for 9 h and then warmed to room temperature,
filtered, and dried in vacuo (yield: 14.2 mg). IR (NaCl/Nujol, cm-1
CtN: 2212 (m), 2192 (m), 2146 (s, br), 2100 (sh). Tc ) 200 K.
Vo[C6H3(t-Bu)3]2 (3). Vanadium vapor was co-condensed with 1,3,5-
)
ν
tri-tert-butylbenzene (∼5 g) at 77 K by resistively heating vanadium
foil at 125 A and 3.3 V for 40 min. After being warmed to room
temperature under an argon atmosphere, the product was extracted with
hexanes and the resulting solution filtered through Celite on a sintered
frit. Solvent was removed in vacuo, and the excess ligand was removed
by sublimation (50 °C, 10-3 Torr). The residue was redissolved in
hexanes, filtered, and crystallized by slow evaporation of the solvent
under argon, producing red/black prisms (yield: 120 mg, ∼10% based
on evaporated V). IR (KBr, cm-1): 3088 (w), 2956-2863 (s, br), 1478
(s), 1457 (s), 1389 (m), 1358 (s), 1287 (m), 1240 (s), 1135 (s), 993 (s),
Reaction of [VII(NCMe)6][B(3,5-C6H3(CF3)2)4]2 with [n-Bu4N]-
[TCNE] (14). A solution of [VII(NCMe)6]{B[3,5-C6H3(CF3)2]4}2 (56.2
mg, 0.0277 mmol) in CH2Cl2 (15 mL) was added to a stirring solution
of [n-Bu4N][TCNE] (20.2 mg, 0.0545 mmol) in CH2Cl2 (15 mL),
immediately forming a black solution. The reaction mixture was left
stirring at room temperature for an additional 2.5 h after which the
solution was filtered, and the precipitate was washed with CH2Cl2 and
then dried in vacuo (yield: 12.9 mg). IR (NaCl/Nujol, cm-1) νCtN
2212 (w), 2192 (m), 2154 (s), 2041 (m, br). Tc ) 188 K.
:
1
Reaction of Cr0Np2 with TCNE (Toluene, 25 °C) (15). A solution
of Cr0Np2 (52.0 mg, 0.169 mmol) dissolved in toluene (15 mL) was
added dropwise to a stirring solution of TCNE (56.0 mg, 0.438 mmol)
dissolved in 15 mL of toluene and immediately formed a black
precipitate. The reaction mixture was left stirring at room temperature
for an addition 20 h after which the solution was filtered and the
precipitate washed with toluene and then dried in vacuo (yield: 51.0
mg). IR (NaCl/Nujol, cm-1) νCtN: 2213 (m), 2110 (s). No absorptions
assignable to υCH were observed. TGA/MS: 13% weight loss between
50 and 225 °C; m/z+: 92 (PhMe+). Elemental Anal. Found: C, 44.48;
H, 2.29; N, 26.74. θ ) -75 K (T > 80 K).
876 (m), 814 (m). H NMR (300 MHz, C6D6) δ: 4.25 (s, 54H), ring
protons not observed. Anal. Calcd for C36H60V: C, 79.51; H, 11.12.
Found: C, 79.35; H, 11.06. EPR (9.785 GHz):
g
) 1.988;
300 K
A51V
) 6.72 mT.
300 K
{VI[C6H3(t-Bu)3]2}+[BPh4]-, 3+[BPh4]-. Both 3 (27 mg, 0.050
mmol) and Ag[BPh4] (44 mg, 0.10 mmol) were combined in a Schlenk
flask, cooled to -78 °C, and to this was added 20 mL of toluene. The
reaction mixture was stirred for 1 h, then slowly warmed to ambient
temperature, and stirred for 14 h. The reaction mixture was filtered
through Celite on a medium frit and the collected solid washed with
toluene and dried in vacuo. The solid was extracted with CH2Cl2,

V[TCNE]X‚ySolVent Magnets
J. Am. Chem. Soc., Vol. 122, No. 2, 2000 293
Scheme 1
Reaction of [CrII(NCMe)4][BF4]2 with [n-Bu4N]+[TCNE]•- (MeCN,
25 °C) (16). A solution of [CrII(NCMe)4][BF4]2 (78.0 mg, 0.020 mmol)
dissolved in 8 mL of MeCN was added to a stirring 8-mL MeCN
solution of [n-Bu4N]+[TCNE]•- (185.0 mg, 0.50 mmol), immediately
forming a dark precipitate. The reaction mixture was left stirring at
room temperature for an addition 6 h after which the solution was
filtered, and the precipitate washed with MeCN and then dried in vacuo
(yield: 55.4 mg). IR (NaCl/Nujol, cm-1) νCtN: 2300 (vw), 2214 (m),
2111 (s) No absorptions assignable to υCH were observed. TGA/MS:
20% weight loss between 50 and 300 °C; m/z+: 41 (MeCN+).
Elemental Anal. Found: C, 45.74; H, 3.13; N, 25.07. θ ) -70 K (T
> 80 K).
Figure 1. Cyclic voltammograms of 2 and 3 in CH2Cl2 at 25 °C, with
0.1 M [n-Bu4N][PF6] at a glassy carbon electrode versus SCE. 2: E1/2
) -0.37 V reversible; ∆Ep ) 100 mV; Epa ) +1.09 V irreversible.
E1/2 ) -0.29 V reversible; ∆Ep ) 105 mV; Epa ) +0.66 V irreversible.
Reaction of [CrII(NCMe)6]{B[3,5-C6H3(CF3)2]4}2 with [n-Bu4N]+-
[TCNE]•- (CH2Cl2, 25 °C) (17). A solution of [CrII(NCMe)6]{B[3,5-
C6H3(CF3)2]4}2 (71.3 mg, 0.035 mmol) dissolved in 8 mL of CH2Cl2
was added to a stirring 8-mL CH2Cl2 solution of [n-Bu4N]+[TCNE]•-
(25.1 mg, 0.068 mmol), immediately forming a dark precipitate. The
reaction mixture was left stirring at room temperature for an addition
30 min after which the solution was filtered, and the dark brown
precipitate was washed with CH2Cl2 and then dried in vacuo (yield:
12.6 mg). IR (NaCl/Nujol, cm-1) νCtN: 2298 (vw), 2212 (m), 2098
(s). TGA/MS: 22% weight loss between 50 and 325 °C; m/z+: 41
(MeCN+), no CH2Cl2 solvent observed. Elemental Anal. Found: C,
41.85; H, 1.87; N, 23.15. θ ) -42 K (T > 80 K).
the reaction of [VII(NCMe)6]2+ with [TCNE]•-, eq 4b, inde-
pendently has been reported to form the V[TCNE]x‚yS magnet.21
It was anticipated from the work of Cloke et al.22 that
sterically demanding arene ligands would increase the stability
of electron-deficient bis(arene)vanadium complexes and aid in
the isolation of the mono- and dication complexes. Stabilization
of an electron-deficient metal center in a sandwich complex by
a bulky arene ligand was demonstrated with the report of [TiI-
(1,3,5-triisopropylbenzene)2]+.23
To test this hypothesis, the reactions of V0(arene)2 and [VI-
(arene)2]+ [arene ) 1,3,5-trimethylbenzene (2 and 2+), 1,3,5-
tri-tert-butylbenzene (3 and 3+)] with TCNE and [TCNE]•- were
studied. 2+ and 3+ as the [BPh4]- salts were isolated from the
reaction of 2 and 3 with Ag[BPh4], and the latter was
crystallographically characterized (vide infra) and is the first
report of the structure of a transition metal sandwich complex
with this bulky 1,3,5-tri-tert-butylbenzene ligand. The reversible
one-electron reduction potential for 1+, 2+, and 3+ vs SCE are
E1/2 ) -0.36 (dimethoxyethane),24 -0.29, and -0.37 V (CH2-
Cl2), Figure 1, respectively. Furthermore, these compounds
exhibit irreversible oxidations to the 2+ state at Epa ) +0.24,25
+0.66, and +1.09 V, respectively. Hence, 1, 2, and 3 will reduce
TCNE [E-/0 ) +0.25; E2-/- ) -0.83 V (CH2Cl2)]26 to
Results and Discussion
Mechanistic investigations of the reaction of V0(C6H6)2 with
TCNE centered on the hypothesis that the first step was an
electron-transfer reaction forming [VI(C6H6)2]+ and [TCNE]•-,
eq 1, Scheme 1.
V0(arene)2 + TCNE f [VI(arene)2]+ + [TCNE]•- (1)
2[VI(arene)2]+ f V0(arene6)2 + [VII(arene)2]2+ (2)
[VII(arene)2]2+ + 6S f [VIIS6]2+ + 2arene
(3)
[TCNE]•-, but not [TCNE]2-
.
[VII(arene)2]2+ + 2[TCNE]•- f [TCNE]x‚yS magnet (4a)
[VIIS6]2+ + 2[TCNE]•- f [TCNE]x‚yS magnet (4b)
The reaction of either 1 or 2 with TCNE leads to the rapid
formation of the V[TCNE]x‚yS magnets. The mechanism of this
reaction is the focus of the research reported herein. In contrast,
(21) Zhang, J.; Miller, J. S.; Vazquez, C.; Zhou, P.; Brinckerhoff, W.
B.; Epstein, A. J. ACS Symp. Ser. 1996, No. 644, 311.
(22) (a) Cloke, F. G. N.; Courtney, K. A. E.; Sameh, A. A.; Swain, A.
C. Polyhedron 1989, 8, 1641. (b) Cloke, F. G. N.; Lappert, M. F.; Lawless,
G. A.; Swain, A. C. J. Chem. Soc., Chem. Commun. 1987, 1667; the
structure of Ti0[C6H3(t-Bu)3]2 was reported as confirmed by X-ray crystal-
lography; however, these data have not been published.
(23) Calderazzo, F.; Ferri, I.; Pampaloni, G.; Englert, U.; Green, M. L.
H. Organometallics 1997, 16, 3100.
(24) Elschenbroich, C.; Hurley, J.; Metz, B.; Massa, W.; Baum, G.
Organomet. 1990, 9, 889.
(25) Elschenbroich, C.; Bar, R.; Bilger, E.; Mahrwald, D.; Nowotny, M.;
Metz, B. Organometallics 1993, 12, 3373.
This reaction was immediately followed by the disproportion-
ation of [VI(C6H6)2]+ to [VII(C6H6)2]2+ and re-forming V0-
(C6H6)2, eq 2. [VIIS6]2+ (S ) THF, MeCN) via the solvation of
[VII(C6H6)2]2+, eq 3, has been established to form from the
disproportionation of [VI(arene)2]+ in the presence of nucleo-
philes, e.g., THF, P(OMe)3, MeCN, and 1,2-dimethoxyethane.20
Either dication would be subsequently attacked by [TCNE]•-
to form the magnetic product, eq 4, Scheme 1. Furthermore,
(20) (a) Avile´s, T.; Teuben, J. H. J. Organomet. Chem. 1983, 253, 39.
(b) Calderazzo, F.; De Benedetto, G. E.; Pampaloni, G.; Mo¨ssmer, C. M.;
Stra¨hle, J.; Wurst, K. J. Organomet. Chem. 1993, 451, 73.
(26) Schiavo, S. L.; Bruno, G.; Zanello, P.; Laschi, F.; Piraino, P. Inorg.
Chem. 1997, 36, 1004.

294 J. Am. Chem. Soc., Vol. 122, No. 2, 2000
Gordon et al.
arene ring in 3+[BPh4]- and 3+[TCNE]•- is presumed to be
due to interannular repulsion driven by the presence of the bulky
t-Bu groups. The puckered C6 ring in 3+[BPh4]- and 3+[TCNE]•-
has also been noted to a lesser degree for Gd0[C6H3(t-Bu)3]2,
which has a significantly larger metal center allowing for greater
separation between the rings [average Gd-Cring bond distance
is 2.630(4) Å].28
The [TCNE]•- anion of 3+[TCNE]•- is slightly twisted about
the central CdC bond creating a dihedral angle of 5.7(2)°. The
CdC bond length is 1.389 Å, the C-C bond lengths vary
between 1.426 and 1.450 Å, and the CN bond lengths vary
between 1.119 and 1.129 Å. These bond lengths are very similar
those found in the unbound anion of [CrI(benzene)2][TCNE]•-
with reported CC, C-CN, and CN average bond lengths of
1.436, 1.414, and 1.140 Å,29 respectively, and [FeIII(C5Me5)2]-
[TCNE]•- with reported CC, C-CN, and CN average bond
lengths of 1.3926, 1.417, and 1.140 Å,6b respectively,
Table 1. Crystal and Experimental Data for
{VI[C6H3(t-Bu)3]2}[BPh4]‚THF, 3+[BPh4]- and
{VI[C6H3(t-Bu)3]2}[TCNE]‚3/2THF, 3+[[TCNE]•-
3+[BPh4]-‚THF
3+[TCNE]•-‚3/2THF
empirical formula
formula weight
temperature (K)
crystal system
space group
a (Å)
C64H84BOV
931.06
200.0(1)
monoclinic
P21/c
11.2396(1)
20.2835(4)
26.6935(4)
94.6430(10)
6065.57(16)
4
C48H72N4O1.5
780.04
V
200.0(1)
monoclinic
P21/c
11.0332(3)
18.03389(5)
22.7485(7)
92.8691(16)
4597.1(2)
4
b (Å)
c (Å)
â (deg)
V (Å3)
Z
density calc (Mg/m3)
goodness of fit on F2
final R indices
1.020
1.063
1.127
a
1.046
R1b ) 0.0638
wR2c ) 0.1750
R1b ) 0.0733
wR2c ) 0.1717
2
a Goodness of fit ) [∑(w(Fo - Fc2)/(n - p)]1/2, where n is the
Magnetic Properties. The 2-300 K magnetic susceptibilities,
ø, of 2, 3, 2+[BPh4]-, 3+[BPh4]-, and 3+[TCNE]- have been
measured, Figure 3. The S ) 1/2 V(0) complexes 2 and 3 obey
the Curie-Weiss law, ø (T - θ)-1, above 150 K with θ )
-0.40 and 1.2 K, and temperature-independent paramagnetism
(TIP) values of 200 × 10-6 and 300 × 10-6 emu/mol,
respectively. The 300 K effective moments, µeff [≡ (8øT)1/2],
are 1.81 and 1.74 µB, respectively, which are slightly higher
than that reported for 1 (1.68 µB),30 but are very close to the
spin-only value of 1.73 µB expected for a S ) 1/2 complex. The
S ) 1 V(I) monocations 2+[BPh4]- and 3+[BPh4]- also obey
the Curie-Weiss law with θ ) 3.9 and -5.9 K and TIP values
of 200 × 10-6 and 220 × 10-6 emu/mol, respectively. The 300
K µeff are 2.91 and 2.83 µB, respectively, in agreement with a
previously reported 2+[AlCl4]- (2.80 µB)30 and the spin-only
value of 2.83 µB expected for a S ) 1 complex. Due to the
paucity of variable-temperature magnetic studies of bis(arene)-
vanadium complexes, θ and TIP values are generally unavail-
able, but temperature-dependent moments characteristic of
having TIPs have been reported for low-spin d4 and d5
compounds.31 The slight increase in µeff below 10 K for both 2
and 2+[BPh4]- requires further study.
number of reflections and p the number of parameters refined. b R1 )
∑(||Fo| - |Fc||)/∑|Fo|. c wR2 ) [∑(w(Fo - Fc2)2)/∑(Fo )2]1/2
.
2
2
the 1:1 stoichiometric reaction of the easier-to-oxidize 3 with
TCNE led to the isolation of 3+[TCNE]•-. When this reaction
is undertaken in the presence of excess TCNE, then a magnetic
product, and not the electron-transfer salt, is obtained. 3+[TCNE]•-
is stable in solution with non-Lewis base solvents or in the solid
state (-78 °C) for extended periods of time but is only
moderately stable in solvents such as THF at room temperature.
Hence, the bulky 1,3,5-tri-tert-butylbenzene ligand imparts an
increased stability on 3+ with respect to nucleophilic attack
enabling the isolation and subsequent characterization of
3+[TCNE]•-.
Structures of 3+[BPh4]- and 3+[TCNE]•-. The structures
of both 3+[BPh4]- and 3+[TCNE]•- were determined by single-
crystal X-ray analyses, Table 1, Figure 2. Although M0[C6H3(t-
Bu)3]2 (M ) Y, Ti, Zr, Hf, V, Nb, Cr, W) have been synthesized
via the co-condensation of early transition metal vapor with the
arene ring,22 structures of these complexes have not been
reported. Selected bond lengths and bond angles of 3+[BPh4]-
and 3+[TCNE]•- are listed in Table 2. Both 3+[BPh4]- and
3+[TCNE]•- display near-parallel planar rings with angles
between mean ring planes of only 1.3 and 0.35°, respectively.
The average VC bond distance in 3+[BPh4]- is 2.301(3) Å and
in 3+[TCNE]•- is 2.297(3) Å, and both are significantly larger
than the average VC bond distance reported for 2+ [2.231(10)
Å].27 This is consistent with the presence of increased steric
repulsion between rings for the 3+ cations, due to the bulkier
t-Bu groups with respect to Me groups. The arene rings in
3+[BPh4]- and 3+[TCNE]•- are puckered. For 3+[BPh4]-, the
VCBu bond distances to vary between 2.299(3) and 2.341(3) Å
while the VCH bond distances range from 2.288(3) to 2.340(3)
Å. For 3+[TCNE]•-, the VCBu bond distances to vary between
2.263(3) and 2.299(3) Å while the VCH bond distances range
from 2.257(3) to 2.295(3) Å, Table 2. The t-Bu groups of
3+[BPh4]- and 3+[TCNE]•- are eclipsed, and the t-Bu carbon
atoms deviate from the mean plane of the ring by 0.259(4)-
0.349(4) and 0.308(5)-0.391(5) Å, respectively, and therefore
lie bent away from the metal center by approximately 14.5 (
0.5° in relation to the mean ring plane. In comparison, the t-Bu
groups of Gd0[C6H3(t-Bu)3]2 are bent out of the plane of the
arene ring by 6-10°.28 This distortion from planarity of the
The susceptibility of 3+[TCNE]•- above 100 K obeys the
Curie-Weiss law with θ ) -0.7 K and a TIP of 200 × 10-6
emu/mol and has a 240 K32 µeff of 3.28 µB, Figure 3. This
moment is consistent with the expected spin-only moment of
1
3.32 µB for an independent S ) /2 plus S ) 1 spin system.
The magnetically ordered V[TCNE]x‚yS materials, prepared
from the reaction of (a) V0(arene)2 with TCNE, (b) [VI(arene)2]+
with 1:1 TCNE/[TCNE]•-, (c) 1:2 V0(arene)2/[FeIII(C5H5)2]•+
with [TCNE]•-, (d) or [VII(NCMe)6][B(3,5-C6H3(CF3)2)4]2 with
[TCNE]•-, display the presence of spontaneous magnetization
below a critical temperature, Tc. Tc is determined as the
intersection of the steepest slope of the magnetization curve
with the temperature axis, when the sample is cooled in the
absence of a field and warming is done under low applied fields.
From the field dependence of the magnetization it is known
that these V[TCNE]x‚yS materials are bulk ferrimagnets whereby
antiferromagnetic interactions between the metal and ligand lead
(29) Miller, J. S.; O’Hare, D. M.; Chakraborty, A.; Epstein, A. J. J. Am.
Chem. Soc. 1989, 111, 7853.
(30) Fischer, E. O.; Joos, G.; Watson, H. Z. Naturforsch. 1958, 13b,
456.
(27) Calderazzo, F.; Pampaloni, G.; Rocchi, L.; Marchetti, F. J. Orga-
nomet. Chem. 1991, 417, C16.
(28) Brennan, J. G.; Cloke, F. G. N.; Samah, A. A.; Zalkin, A. J. Chem.
Soc., Chem. Commun. 1987, 1668.
(31) Figgis, B. N. Introduction to Ligand Fields; Interscience Publ.: New
York, 1966; p 351.
(32) This material was only measured up to 240 K due to instrumental
difficulties.

V[TCNE]X‚ySolVent Magnets
J. Am. Chem. Soc., Vol. 122, No. 2, 2000 295
Figure 2. ORTEP (ellipsoids at 30% probability) and atom-labeling diagram for {VI[C6H3(t-Bu)3]2}[TCNE], 3+[TCNE]•-. The same cation labeling
scheme is used for 3+[BPh4]-.
for coordinated and noncoordinated [TCNE]•- occur between
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for
{VI[C6H3(t-Bu)3]2}[BPh4]‚THF, 3+[BPh4]-, and
these values.34 Therefore, from the υCN stretching frequencies
{VI[C6H3(t-Bu)3]2}[TCNE]‚3/2THF, 3+[TCNE]•-
of the magnetic precipitates, typically around 2210(m), 2190-
3+[BhPh4]-
3+[TCNE]•-
(m) and 2146(s), it is concluded that [TCNE]•- is present as
coordinated [TCNE]•-. Two bands are expected for either
isolated or trans-µ bonded [TCNE]n (n ) 0, 1-, 2). The presence
of the additional bands suggest the presence of µ3-, and µ4-
[TCNE]n, as reported for [Mn(C5Me5)(CO)2]3[TCNE],36a [Mn(C5-
Me5)(CO)2]4[TCNE],36a and [Ru(NH3)5]4[TCNE][PF6]8.36b Ad-
ditionally, cis-µ bridging may be present and lead to additional
absorptions. Furthermore, the complex and broad nature of the
absorptions suggest that mixtures of bonding motifs are present.
Similar absorptions have been reported for V[TCNE]x.yS
prepared from V(CO)6.21 The nonmagnetic product 8 from the
reaction of 2+ with [TCNE]•- displays a very different υCN
absorption band pattern [2201(m), 2146(m), 2110(s)]. The
thermolysis of 3+[TCNE]•- (12), which presumably forms a
material of nominal V+[TCNE]•- composition, has υCN bands
[2205(m), 2122(s)] that do not resemble that for 8. Nonetheless,
like 8, 12 lacks the υCN absorption at ∼2150 cm-1 present for
all V[TCNE]x‚yS magnets, and its 2122(s) is close to the 2110-
(s) band for 8. The relationship between this spectrum and the
magnetic properties of the material has yet to be established.
All V[TCNE]x‚yS precipitates, magnetic or not, do not have
an absorption at ∼1000 cm-1 assignable to υVdO, indicating
that the material has not undergone accidental oxidation during
manipulation. In addition, a υCdC band is not observed for these
materials. Such a band (∼1400 cm-1) either may be obscured
by intense Nujol absorption in this area or may be absent due
to the TCNE adopting binding modes that lead to IR-inactive
CdC vibrations.
Bond Distances
V-Cphenyl (1-6)
V-Cphenyl (19-24)
Cphenyl-Cphenyl
2.277(3)-2.341(3) 2.272(3)-2.340(3)
2.263(3)-2.329(3) 2.257(3)-2.339(3)
1.402(4)-1.428(4) 1.406(4)-1.423(4)
1.531(4)
1.543(4)
1.537(4)
1.516(5)-1.545(5) 1.516(5)-1.529(5)
1.530(4)-1.535(4) 1.530(5)-1.541(5)
1.522(4)-1.537(4) 1.528(5)-1.534(5)
C
C
C
phenyl(1)-Cbutyl(7)
phenyl(3)-Cbutyl(11)
phenyl(5)-Cbutyl(15)
1.532(4)
1.538(4)
1.542(4)
Cbutyl(7)-Cmethyl(8-10)
C
C
butyl(11)-Cmethyl(12-14)
butyl(15)-Cmethyl(16-18)
Bond Angles
116.4(3)-122.9(3) 117.4(3)-122.5(3)
phenyl(1)-Cbutyl(7)-Cmethyl(10) 106.5(3)
phenyl(3)-Cbutyl(11)-Cmethyl(14) 105.9(2)
phenyl(5)-Cbutyl(15)-Cmethyl(16) 111.5(2)
Cphenyl-Cphenyl-Cphenyl
C
C
C
113.0(3)
109.1(3)
112.6(3)
to uncompensated spin.2a,c,4,21,33 8 formed from the reaction
between 2+ and [TCNE]•- neither orders magnetically nor
simply obeys the Curie-Weiss law. The data can be fit to the
Curie-Weiss expression with θ ) -28 K (T > 100 K) and θ
) -570 K (200 < T < 300 K).
Infrared Spectra. All magnetically ordered V[TCNE]x‚yS
precipitates display a complex, nominal three-absorption peak
pattern for υCN stretching modes as previously reported, Table
3, Figure 4.4 TCNE0 has υCN absorption bands that occur above
2200 cm-1 34 The [TCNE]2- υCN absorption bands are found
.
at 2139 (m) and 2057 (s) cm-1 34,35a and at 2176 (m) and 2097
(s) cm-1 for bound µ-[TCNE]2- 35b
The υCN absorption bands
.
(33) The magnetically ordered products of the reactions with 2n and 3n
(n ) 0, 1+) display significant variation in Tc, dependent upon reaction
temperature, solvent, and complex oxidation state, as reported earlier.4,5
The synthetic procedure that favors the formation of such a binding mode
that leads both to strongly coupled VII and [TCNE]•- radicals and to a 3-D
network will be the one that leads to the product with the highest Tc. As
the synthetic procedure used to produced these materials suffers from the
shortcoming that all solids immediately precipitate from solution, it becomes
clear that a controlled and reproducible method for magnet formation is
required in order to consistently yield the desired magnetic properties. This
is currently under further investigation in this laboratory.
The only V-containing sample that does not display this three-
banded pattern is 3+[TCNE]•-, which possesses υCN absorptions
at 2185 (s) and 2146 (s) cm-1, diagnostic of isolated unbound
[TCNE]•-.6b,34 These bands are very similar to the υCN absorp-
(35) (a) Fox, J. R.; Foxman, B. M.; Guarrera, D.; Miller, J. S.; Calabrese,
J. C.; Reis, Jr., A. H. J. Mater. Chem. 1996, 6, 1627. (b) Yee, G. T.;
Calabrese, J. C.; Vazquez, C.; Miller, J. S. Inorg. Chem. 1993, 32, 377.
(36) (a) Gross-Lannert, R.; Kaim, W.; Olbrich-Deussner, B. Inorg. Chem.
1990, 29, 5046. (b) Moscherosch, M.; Waldhor, E.; Binder, H.; Kaim, W.;
Fiedler, J. J. Inorg. Chem. 1995, 34, 4326.
(34) Dixon, D. A.; Miller, J. S. J. Am. Chem. Soc. 1987, 109, 3656.

296 J. Am. Chem. Soc., Vol. 122, No. 2, 2000
Gordon et al.
Figure 3. Magnetic moment and reciprocal susceptibility of 2 (2, 4), 3 (1, 3), 2+[BPh4]- ([, ]), 3+[BPh4]- (b, O), and 3+[TCNE]•- (9, 0).
Table 3. Summary of the υCN IR Absorption Data
compd
υ
CN, cm-1
4
5
6
2197 (m), 2097 (s, br)
2190 (m), 2147 (s), 2101 (w)
2218 (m), 2152 (s,br)
7
8
9
10
2200 (m), 2104 (s, br)
2201 (m), 2146 (m), 2110 (s)
2188 (m), 2146 (m), 2101 (w)
2212 (m), 2192 (m), 2146 (s, br), 2100 (sh)
2185 (s), 2146 (s)
3+[TCNE]•-
11
12
13
14
15
16
17
2218 (m), 2194 (m), 2155 (s), 2100 (sh)
2205 (m), 2122 (s)
2193 (m), 2159 (m), 2034 (w, br)
2212 (w), 2192 (m), 2154 (s), 2041 (m, br)
2213 (m), 2110 (s)
2300 (vw), 2214 (m), 2111 (s)
2298 (vw), 2212 (m), 2098 (s)
tions at 2183 and 2144 cm-1 reported for, e.g., [n-Bu4N]+-
[TCNE]•- 8 and [FeIII(C5Me5)2]+[TCNE]•-,6b confirming that
isolated [TCNE]•- is present.
VII Identified as the Key Intermediate. As noted for 1,4
the reactions of 2 and 3 with TCNE lead to the rapid formation
of black insoluble precipitates 5 and 11 that magnetically order
at ∼260 and ∼205 K, respectively. These Tc’s are lower than
that reported from the reaction with 1 with a Tc ∼400 K,4 but
as noted for the reactions with 1, the Tc’s are highly sensitive
to reaction conditions (temperature and solvent), ranging from
∼28 to ∼400 K.4,5,33 These differences are attributed to a
variation in [TCNE]•- bonding motifs leading to different
connectivities, which directly affects the magnetic coupling
between metal centers as well as the υCN absorptions.
The determination of a viable mechanism, either the dispro-
portionation reaction (Scheme 1) or the electron-transfer reaction
(Scheme 2) (vide infra), for the formation of the V(TCNE)x
magnet is the question that the following reactions address.
Central to this issue is the importance of the presence of a VII
species, which the results support as being the key intermediate
toward magnet formation. Once produced, the [VII(arene)2]2+
species reacts with either (a) [TCNE]•-, producing the magnetic
product, or (b) a coordinating solvent (S) to form the well-known
[VIIS6]2+, which reacts with [TCNE]•- to form the magnetic
Figure 4. υCN IR absorptions for representative V[TCNE]x‚yS materi-
als.
product. It will be demonstrated that the disproportionation
reaction is not a kinetically important mechanism. The oxidation
of [VI(arene)2]+ by TCNE will be discussed as the likely path
for formation of the magnet. It is important to note that as the

V[TCNE]X‚ySolVent Magnets
J. Am. Chem. Soc., Vol. 122, No. 2, 2000 297
Scheme 2
ficiently rapid to observe the formation of a magnetic precipitate.
For complexes containing less hindered arene rings, such as
2+I- and 2+[AlBr4]-, this reaction has been reported as very
rapid and plays an important role in the formation of a VII
species.20b Since a magnetic product is not obtained from the
reaction between 2+[BPh4]- and [TCNE]•-, this reaction does
not appear to play an important role in the reaction of less
hindered arenes, including the reaction of 1 that leads to the
room-temperature V[TCNE]x‚yS magnet.
Due to V0(arene)2 being redox active in the presence of
TCNE, we hypothesize that the VII species could alternatively
be formed from a second one-electron oxidation with another
TCNE molecule, Scheme 2, eq 5.
V(TCNE)x product precipitates from solution, the oxidation
reactions that form the V2+ species must be considered as
irreversible. The product insolubility can therefore drive the
oxidation reaction to completeness despite the formal reduction
potential of TCNE having more negative potentials than the
oxidation potential of [VI(arene)2]+.15
[VI(arene)2]+ + TCNE f [VII(arene)2]2+ + [TCNE]•- (5)
[VI(arene)2]+ + [TCNE]•- f [VII(arene)2]2+ + [TCNE]2-
(6)
The reactions of [VI(arene)2]+ with [TCNE]•- directly address
the importance of the disproportionation mechanistic step in the
formation of a magnetic precipitate and would suggest that the
formation of a “[VII(arene)2]2+” species in situ has occurred.
Attempts to isolate [VII(arene)2]2+ as the [BPh4]- salt were
unsuccessful. Importantly, there is no reaction observed nor
precipitate produced from the stoichiometric reaction between
3+[BPh4]- and [n-Bu4N]+[TCNE]•- either at -78 °C or at room
temperature for one week in CH2Cl2. Redox chemistry was not
anticipated to occur between 2+ or 3+ and [TCNE]•-. This
demonstrates the stability of the 3+ cation under these conditions
toward decomposition in the presence of nucleophiles such as
[TCNE]•-. In contrast to this reaction, the reaction of 2+[BPh4]-
with [n-Bu4N]+[TCNE]•- leads to the immediate formation of
black insoluble precipitate 8, which does not exhibit a spontane-
ous magnetization. This result is consistent with the rapid
decomposition of the cation 2+ in the presence of the nucleophile
[TCNE]•-, leading to the precipitate, but not the V[TCNE]x‚yS
magnet as an oxidant to oxidize VI to VII is not present. The
presence of a magnetic product would only be expected should
the disproportionation of the monocation be sufficiently rapid
to produce [VII(arene)2]2+ before precipitate formation, and this
does not occur. Therefore, since the IR spectrum for this material
does not display aromatic υCH bands (∼3060 cm-1) and the
υCN bands [2201 (m), 2146 (m), 2110 (s)] are consistent with
µn (n > 2) bound [TCNE]•-,36 we attribute this insoluble
material as a [n-Bu4N]x-1VI[TCNE]x•-‚yS-containing polymeric
material. As 8 does not display magnetic ordering, it was not
studied in greater detail.
In contrast, addition of 1 equiv of both TCNE and [n-Bu4N]+-
[TCNE]•- to the reaction with either 2+[BPh4]- or 3+[BPh4]-
leads to the rapid formation of magnetically ordered 13 and 9,
respectively. Likewise, addition of 2 equiv of the one-electron
oxidant, [FeIII(C5H5)2]+, to 2 and the immediate reaction of this
product with [n-Bu4N]+[TCNE]•- leads to the formation of
magnetically ordered 10. The production of magnetic product
in the former reaction is attributed to the oxidation of 2+ or 3+
by TCNE, confirming that [TCNE]•- is an insufficient oxidant
to oxidize VI to VII. The magnetic product from the latter
reaction is attributed to the oxidation of 2+ or 3+ by [FeIII-
(C5H5)2]+, further confirming that [TCNE]•- is an insufficient
to oxidize VI to VII.
[VI(arene)2]+ + [TCNE]•- f [VI(arene)2]+[TCNE]•- (7)
As previously discussed, [TCNE]•- is too weak of an oxidant
to oxidize [VI(arene)2]+ to ‘[VII(arene)2]2+’, which reduces
[TCNE]•- to [TCNE]2-, eq 6. The reaction of [VI(arene)2]+ and
[TCNE]•-, eq 7, does not produce a magnetic material, but leads
either to the stable 3+[TCNE]•- or to the nonmagnetic precipi-
tate, of putative [n-Bu4N]1-xVI[TCNE]x‚yS composition when
1,3,5-trimethylbenzene is used as the ligand. Therefore “[VII-
(arene)2]2+” is hypothesized to be the key intermediate in the
formation of the V[TCNE]x‚yS magnet from the reaction of bis-
(arene)vanadiums and TCNE, Scheme 2. However, its formation
may additionally include the kinetically slower disproportion-
ation of [VI(arene)2]+.
Scheme 2 is consistent with all the reactions between
V-arene complexes and TCNE and correctly predicts which
reactions lead to magnetically ordered or nonordered products.
The magnetic behavior of several representative compounds is
shown in Figure 5. As reported for 1,4 reactions between the
V0(arene)2 complexes, 2 or 3, and TCNE both lead to magnetic
materials, 5 and 11, respectively. For these reactions, the excess
TCNE serves to doubly oxidize V0(arene)2, and form the
V[TCNE]x‚solvent magnets. Recall that it is the irreversible
reaction from eq 5 that drives this electron-transfer reaction.
As with 1,4 the stoichiometric (1:1) reaction between 2 and
TCNE also yields a magnet (7), whereas unlike for 1,4 the same
reaction between 3 and TCNE yields the stable salt 3+[TCNE]•-.
This is attributed to the kinetic stabilization of 3+ with respect
to 1+ and 2+ due to the bulkier arene ligand. 7, however, may
include material in which spontaneous moment does not occur,
since vanadium in oxidation states lower than two may be
present.
Material that does not display a spontaneous magnetization
(8), likely of nominal [n-Bu4N]x-1VI[TCNE]x‚yS composition,
was produced from the reaction between 2+ and [TCNE]•-. This
result is consistent with the inability of [TCNE]•- to oxidize
2+ to 22+. However, when this same reaction between 2+ and
[TCNE]•- is done in the presence of TCNE, the magnetic
precipitate 9 is formed, indicating that TCNE is a sufficiently
strong oxidant to oxidize 2+. The direct reaction of [VII(NCMe)6]-
{B[3,5-C6H3(CF3)2]4}2 and [n-Bu4N][TCNE], as expected, leads
to the magnetic product 14. Similar results were obtained from
the reaction between [VII(NCMe)6][BPh4]2 and [n-Bu4N]-
[TCNE].21 All of these reactions are consistent with both VII
and [TCNE]•- being required in order to produce a final product
that displays magnetic ordering.
Since 3+[TCNE]•- is readily isolated, the results from the
above reactions are inconsistent with the initial hypothesis that
the disproportionation reaction is a key step, Scheme 1, toward
the formation of a VII species. Thus, the kinetics of the
disproportionation of 3+[BPh4]- or 3+[TCNE]•- is not suf-

298 J. Am. Chem. Soc., Vol. 122, No. 2, 2000
Gordon et al.
Figure 6. Magnetic moment (filled symbols) and reciprocal suscep-
tibility (open symbols) of Cr[TCNE]x‚ formed from the reaction of Cr0-
Np2 and TCNE (15; 0, 9) and from the reaction of [CrII(NCMe)4][BF4]2
(16; 4, 2) and [CrII(NCMe)6][B(3,5-C6H3(CF3)2)4]2 (17; O, b) with
[n-Bu4N] [TCNE].
[n-Bu4N][TCNE], 16 and 17, respectively, and exhibits similar
spectral and magnetic properties, Figure 6.
The solvent content in the nonmagnetic Cr-containing reaction
products was determined by TGA/MS, assuming Cr[TCNE]2,
as results from elemental analysis were not readily interpretable,
possibly due to oxygen contamination. This led to the following
composition for 15, 16, and 17: Cr[TCNE]2‚0.5PhMe, Cr-
[TCNE]2‚1.9MeCN, and Cr[TCNE]2‚2MeCN, respectively.
The 2-300 K magnetic susceptibility of 15, prepared from
the reaction of Cr0Np2 and TCNE, can be fit to the Curie-
Weiss expression above 50 K with θ ) -75 K. The 300 K µeff
is 3.54 µB, Figure 6. Similar results are noted for 16 and 17,
i.e., θ ) -70 K, µeff(210 K) ) 3.75 µB and θ ) -42 K, µeff
(300 K) ) 3.37 µB, respectively. Assuming a Cr(TCNE)2‚yS
composition, this independent S ) 2, 1/2, 1/2 system should have
a moment of 5.47 µB. Strong antiferromagnetic coupling, as
evidenced by the θ values of <-42 K should lead to reduced
values of the moment, as observed. Variations between the high-
temperature µeff values may be due to residual solvent not
accounted for by TGA/MS.
Figure 5. Temperature dependence of the susceptibility, ø(T), for
representative V[TCNE]x‚yS materials.
Cr[TCNE]x‚ySolvent. In contrast to the reaction of V0-
(arene)2 and TCNE to form magnetically ordered materials of
nominal V[TCNE]x‚yS composition, the reaction of Cr0(arene)2
and TCNE forms [CrI(arene)2]+[TCNE]•-,29 which does not
magnetically order. Alternatively, reaction of MIII2‚xMeCN (M
) Mn, Fe, Co, Ni) with TCNE forms M[TCNE]x‚yS7 magnets
displaying reduced Tc’s with respect to M ) V. Due to the
greater covalency of CrIII2, Cr[TCNE]x‚yS has yet to be prepared
and was targeted for preparation.
The key intermediate in the mechanism outlined in Scheme
2 is [MII(arene)2]2+, formed from two one-electron oxidation
reactions with TCNE. This suggests that [CrII(arene)2]2+ also
needs to be generated in order to form the desired Cr[TCNE]x‚
yS. Cr0(arene)2 complexes are harder to oxidize than the
For these materials, the large negative θ value characterizes
the magnetic interaction between spin centers as strongly
antiferromagnetic, as observed for materials composed of M )
V, Mn, Fe, Co, Ni metal centers.7 Surprisingly, however,
magnetic ordering, e.g., antiferro- ferri-, metamagnetic ordering
is not observed above 2 K. This is in sharp contrast with the
magnetic behavior observed for M ) V, Mn, Fe, Co, Ni
materials, which all order as ferrimagnets with Tc’s of >44 K.7
The surprising lack of magnetic ordering is not understood at
the present time and is the subject of ongoing studies.
+/0
corresponding V0(arene)2 complexes, e. g., Cr0(C6H6)2: E1/2
) -0.69 V (vs SCE; DME).24 As the reaction of Cr0(arene)2
with TCNE leads to [CrI(arene)2]+[TCNE]•-,29 a more labile
arene ligand was sought. Cr0Np2 (Np ) naphthalene) [E1/2
+/0
2+/+
) -1.19; E1/2
) +0.20 V (vs Ag/AgNO3; THF)]37 was
identified and targeted to react with TCNE. Cr0Np2 can be
readily oxidized to the dication due to the appropriate reduction
potential for TCNE,26 and the Np ligand is more labile than
benzene-based arene ligands.38 Furthermore, these potentials
render the production of either [TCNE]2- or a CrIII metal center
unlikely.
The IR spectra of the Cr[TCNE]x‚yS materials display υCN
absorption bands that do not appear for the magnetically ordering
V[TCNE]x materials. 15, 16, and 17 exhibit υCN absorptions at
2213 (m), 2110 (s); 2300 (vw), 2214 (m), 2111 (s); and 2298
(vw), 2212 (m), 2098(s) cm-1, respectively. The lowest energy
bands at ∼2100 cm-1 are not characteristic of the spectra
observed for the magnetically ordering M[TCNE]x‚yS (M )
V, Mn, Fe, Co, Ni) class of materials.4,7 It is interesting to note
that a υCN band at 2110 cm-1 was also observed for 8 from the
reaction between 2+[BPh4]- with [n-Bu4N]+[TCNE]•- that is
a nonmagnetic black precipitate. Although these υCN bands
cannot be assigned to a particular [TCNE]•- binding mode, it
is clear that a correlation exists between the observation of these
bands and the presence of strongly antiferromagnetic coupling
As expected, a black precipitate 15 was immediately produced
upon reacting Cr0Np2 with TCNE in toluene. In addition to
supporting the proposed mechanism (Scheme 2), Cr[TCNE]x‚
yPhMe was available for study. Unexpectedly, Cr[TCNE]x‚
yPhMe does not magnetically order above 2 K (vide infra).
Cr[TCNE]x‚yS was also prepared from the reactions of [CrII-
(NCMe)4][BF4]2 and [CrII(NCMe)6][B(3,5-C6H3(CF3)2)4]2 with
(37) Bush, B. F.; Lagowski, J. J. J. Organomet. Chem. 1990, 386, 37.
(38) Elschenbroich, C.; Mockel, R. Angew. Chem., Int. Ed. Engl. 1977,
16, 870.

V[TCNE]X‚ySolVent Magnets
J. Am. Chem. Soc., Vol. 122, No. 2, 2000 299
and no magnetic ordering in the sample; however, the relation-
ship between the metal center electronic state and [TCNE]•-
binding mode that leads to this magnetic behavior remains
unclear.
the M(TCNE)x (M ) V, Mn, Fe, Co, Ni) materials, the reactions
done with Cr do not follow this trend.
Acknowledgment. We gratefully acknowledge the support
inpartfromtheNationalScienceFoundation(GrantCHE9320478).
The authors gratefully acknowledge the support from the U.S.
Department of Energy (DOE) Division of Basic Energy Sciences
(Grant DE-FG03-93ER45504) and the Division of Advanced
Materials (Grant DE-FG02-96ER12198), and the U.S. National
ScienceFoundation(NSF)(GrantsCHE9320478andCHE9807669).
The late D.C.G. thanks NSF for a predoctoral fellowship, and
L.D. thanks Fonds FCAR Que´bec for a postdoctoral fellowship.
We also thank Dr. J. Kim for studies on the reaction of [CrII-
(NCMe)6]2+ with [TCNE]•-, and Prof. K. R. Dunbar for the
preparation of [CrII(NCMe)4][BF4]2.
Conclusion
The reactions between [V(arene)2]n (n ) 0, 1+, 2+) and
[TCNE]y (y ) 0, 1-), as well as the reactions between [VII-
(NCH)6]2+ and [TCNE]•-, indicate that V2+ is a key intermediate
toward the formation of the room-temperature V[TCNE]x‚yS
magnet. The data presented support the reaction mechanism in
which two independent one-electron-transfer reactions occur
with TCNE as the oxidant, while reactions probing the possible
presence of a disproportionation reaction with [VI(arene)2]+ did
not lead to the magnetic product. The variation in magnetic
properties and IR spectra of the V[TCNE]x magnets from
different routes clearly demonstrates that control over the
structure of the magnetic precipitate is required in order to obtain
consistent material properties. Exploitation of this mechanism,
which requires formation of MII, leads to formation of previously
unreported Cr(TCNE)x. In contrast to the magnetic nature of
Supporting Information Available: Crystallographic data
including bond distances and angles and final positional and
thermal parameters for 3+[BPh4]- and 3+[TCNE]•- are provided
in PDF and CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
JA9929741