Fluorinated phenolates in monomeric and dimeric Co(II) compounds

Article abstract of DOI:10.1016/j.poly.2012.09.032

Five structures of two monometallic cobalt aryloxide compounds and two bimetallic cobalt-thallium compounds with bridging fluorinated aryloxide ligands (OC₆F₅ = OAr^F, OC₆H ₃(CF₃)₂ = OAr′) are presented with magnetic susceptibility and spectroscopic characterization data. The monometallic compounds, [Co(OAr^F)₂(DME)]₂, 1, and [Co(OAr′)₂(DME)]₂, 2, are prepared by metathesis reactions between two equivalents of TlOAr and one of CoI₂. The heterobimetallic compounds [Tl₂Co(OAr^F) ₄]·2 toluene, 3a, and [Tl₂Co(OAr′) ₄]₂·2 toluene, 4, were prepared with a 4:1 ratio of the thallium aryloxide to CoI₂. An unsolvated form of [Tl ₂Co(OAr^F)₄], 3b, was also structurally characterized. Magnetic susceptibility studies revealed that 3b is a simple, isolated high-spin Co^II with Curie-Weiss behavior. Dimeric compounds 1 and 2 are also high-spin Co^II but exhibit antiferromagnetic coupling, via superexchange through two μ₂-OAr^F ligands, as supported by DFT calculations. Compound 4 exhibits ferromagnetic behavior which is ascribed to the presence of μ₃-OAr ligands, instead of μ₂-OAr groups.

Full text of DOI:10.1016/j.poly.2012.09.032

Polyhedron 52 (2013) 276–283
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Fluorinated phenolates in monomeric and dimeric Co(II) compounds
Montana V. Petersen a, Amber H. Iqbal a, Lev N. Zakharov b, Arnold L. Rheingold c, Linda H. Doerrer d,
⇑
a Barnard College, Chemistry Department, 3009 Broadway, New York, NY 10027, United States
b University of Oregon, 1253 University of Oregon, Eugene, OR 97403-1253, United States
c Department of Chemistry and Biochemistry, MC 0358, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
d Boston University, Chemistry Department, 590 Commonwealth Ave., Boston, MA 02215, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 27 September 2012
Five structures of two monometallic cobalt aryloxide compounds and two bimetallic cobalt-thallium
compounds with bridging fluorinated aryloxide ligands (OC6F5 = OArF, OC6H3(CF3)2 = OAr0) are presented
with magnetic susceptibility and spectroscopic characterization data. The monometallic compounds,
[Co(OArF)2(DME)]2, 1, and [Co(OAr0)2(DME)]2, 2, are prepared by metathesis reactions between two
equivalents of TlOAr and one of CoI2. The heterobimetallic compounds [Tl2Co(OArF)4]ꢀ2 toluene, 3a,
and [Tl2Co(OAr0)4]2ꢀ2 toluene, 4, were prepared with a 4:1 ratio of the thallium aryloxide to CoI2. An
unsolvated form of [Tl2Co(OArF)4], 3b, was also structurally characterized. Magnetic susceptibility studies
revealed that 3b is a simple, isolated high-spin CoII with Curie–Weiss behavior. Dimeric compounds 1 and
Dedicated to Alfred Werner on the 100th
Anniversary of his Nobel prize in Chemistry
in 1913.
Keywords:
Phenoxide
Cobalt
Thallium
2 are also high-spin CoII but exhibit antiferromagnetic coupling, via superexchange through two
ligands, as supported by DFT calculations. Compound 4 exhibits ferromagnetic behavior which is ascribed
to the presence of 3-OAr ligands, instead of 2-OAr groups.
l
2-OArF
Bridged
l
l
Fluorinated aryloxide
Ferromagnetic antiferromagnetic
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
observed differences in coordination number at the transition
metal as a function of the aryloxide ligand.
Our laboratory has been investigating homoleptic and
heteroleptic transition metal complexes of highly perfluorinated
aryloxide [1–4] and alkoxide [2,5] ligands including pentafluoro-
phenoxide (OC6F5 = OArF) and bis-3,5-trifluoromethylphenoxide
(OC6H3(CF3)2 = OAr0). We are interested in effects of extensive fluo-
rination on the reactivity of the phenoxide oxygen atom, how the
types of compounds formed with these fluorinated ligands differ
from their protio analogs, and how these ligand differences affect
reactivity of the transition metal complexes. Spectroscopic studies
[2] have shown that these fluorinated oxygen donor ligands act as
medium field ligands similar to F- or OH- and are therefore
compatible with high oxidation state transition metals. We have
previously reported the synthesis of homoleptic anions of the form
[M(OAr)4]2ꢁ for Fe(II) [4], Co(II) [1], Ni(II) [2], and Cu(II) [1,3]. In
each case we have prepared the heterobimetallic thallium deriva-
tives [Tl2M(OAr)4] because of the subsequent ease of metathesis of
the thallium cation for less-coordinating cations. We now report
the structural, electronic, and magnetic characterization of the
[Tl2Co(OAr)4] compounds, whose preliminary characterization
has been reported [1]. As is often the case with cobalt, the connec-
tivity and electronic structure were observed to be different than
other late metals and more varied. For the first time, we have
Structural studies [2] for the Ni(II) compound [Tl2Ni(OArF)4]
indicated a monomeric pseudo-tetrahedral S = 1 species with Tl
atoms bridging two edges of the tetrahedron, as shown in
Scheme 1. In contrast, the [Tl2Cu(OAr)4] complexes [3] with both
OArF and OAr0 exhibited extended structures in which approxi-
mately square planar Cu(II) centers were bridged to one another
through two thallium centers forming {Tl2O4} octahedra as also
shown in Scheme 1. Solution susceptibility studies suggested that
these extended structures did not persist in solution.
Herein we report the solid state structures of the [Tl2Co(OAr)4]
compounds for both the OArF and OAr0 ligands, including unsolvat-
ed and toluene solvate forms of the former. We have also prepared
two neutral {(DME)Co(OAr)2} synthons for potential use in prepar-
ing other heterobimetallic complexes.
2. Experimental
2.1. General conditions
All studies were carried out at room temperature on a Schlenk
line or in a nitrogen-filled glovebox. Bulk solvents (hexanes,
CH2Cl2, THF, and toluene) were dried in a nitrogen-filled MBraun
SPS (solvent purification system) using Al2O3, and CD2Cl2 was
distilled from CaH2. Celite was dried overnight in vacuo while
⇑
Corresponding author.
E-mail address: doerrer@bu.edu (L.H. Doerrer).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.09.032

M.V. Petersen et al. / Polyhedron 52 (2013) 276–283
277
F
2.3. X-ray diffraction data
F
F
F
F
F
F
F
Crystallographic data are collected in Table 1. Data were col-
lected on APEX-CCD-detector equipped Bruker diffractometers,
and were corrected for absorption using semi-empirical, multi-
scan methods. All structures were solved by heavy-atom methods
and the remaining non-hydrogen atoms were located from subse-
quent difference maps. All structures were refined with anisotropic
thermal parameters for all non-hydrogen atoms; hydrogen atoms
were treated as idealized contributions. All software is contained
F
F
F
F
F
F
Tl
F
F
F
F
F
F
O
F
F
F
O
F
O
F
F
O
O
F
O
O
Tl
Tl
F
F
F
F
Cu
F
F
O
Ni
Cu
F
O
O
O
F
F
F
O
F
F
F
F
F
F
F
Tl
F
F
F
F
F
F
F
F
F
F
F
F
F
in various libraries (SHELXTL, SMART and SAINT) maintained by Bruker
F
F
F
AXS, Madison, WI.
[Tl2Ni(OArF)4]
[Tl2{Cu(OArF)4}2]2-
Scheme 1. Previously observed [Tl2M(OArF)4] structural motifs.
2.4. Synthetic procedures
2.4.1. {Co(OArF)2(DME)}2, 1
heated to 125 °C with an oil bath. All other reagents were obtained
commercially and were not purified further. NMR spectra were
measured on a Varian 300 MHz spectrometer. 1H chemical shifts
were referenced to (CH3)4Si via the resonance of residual protiosol-
vent and 19F shifts were referenced to internal CFCl3. UV–Vis data
were collected utilizing a Shimadzu 3600 UV–Vis–NIR spectropho-
tometer. Solution phase magnetic susceptibilities were determined
by Evans’ method [6,7] in d6-acetone, CD3CN, or CD2Cl2 with 10%
(Me3Si)2O and the same solution as internal reference and are
reported after correction using appropriate diamagnetic terms
[8,9]. SQUID data were collected with a Quantum Design MPMS
SQUID susceptometer by loading powdered samples into gel cap-
sules placed in plastic straws, and the resulting susceptibilities
were corrected for diamagnetic contributions [10]. Microanalyses
were performed by Kolbe Microanalytisches Laboratorium,
Mülheim an der Ruhr, BRD.
A portion of TlOArF (4.476 g, 11.55 mmol) dissolved in 4 mL THF
was added to one half equiv CoI2 (1.806 g, 5.777 mmol) in 50 mL
THF forming a dark purple solution with yellow (presumed TlI pre-
cipitate. After stirring overnight, the reaction mixture was filtered
through Celite, removing the yellow precipitate, and the product
was concentrated to dryness. The product was recrystallized from
a 2:1 ratio of DME:THF and hexanes affording X-ray quality block-
habit purple crystals in 17.6% yield (after three recrystallizations).
UV–Vis (THF) (kmax, nm (
(141) 594 (138). leff (Evans’ method) = 6.39
32H20O8F20Co2: C, 37.30; H, 1.96; F, 36.88. Found: C, 37.16; H,
e
M, Mꢁ1 cmꢁ1)):513 (120) 551 (142) 580
B. Anal. Calc. for
l
C
1.91; F, 37.05%.
2.4.2. {Co(OAr0)2(DME)}2, 2
A portion of TlOAr0 (0.218 g, 0.504 mmol) dissolved in 4 mL
DME was added to one half equiv CoI2 (0.0787 g, 0.252 mmol) in
6 mL THF forming a dark blue-green solution with yellow (pre-
sumed TlI precipitate). After stirring overnight, the reaction mix-
ture was filtered through Celite, removing the yellow precipitate,
and the product was concentrated to dryness. The product was
recrystallized from DME and hexanes affording X-ray quality
block-habit purple crystals in 50% yield after three recrystalliza-
2.2. Electronic structure calculations
A C2-symmetrized version of compound 1 was calculated using
the Amsterdam Density Functional package [11], with TZ2P basis
sets for all atoms, using all electrons, and a spin-unrestricted sys-
tem with six unpaired electrons. A comparison of the calculated
distances and angles with the single-crystal X-ray diffraction data
are presented in Table S1.
tions. UV–Vis (CH2CL2) (kmax, nm (
(255) 660 (186). leff (Evans’ method) = 5.26
e
M, Mꢁ1 cmꢁ1)) 493 (236) 587
B. Anal. Calc. for
l
Table 1
Summary of X-ray crystallographic data.
1
3a
3b
4
Formula
C
32H20Co2F20O8
C76H32Co2F40O8Tl4
2768.36
triclinic
C24CoF20O4Tl2
1199.91
monoclinic
C2/c
6.5075(5)
26.410(2)
15.7928(12)
–
90.6020(10)
–
2714.1(4)
4
C39H20CoF24O4Tl2
1476.22
triclinic
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
1030.34
monoclinic
C2/c
11.7321(5)
17.9147(8)
17.9686(9)
–
105.746(2)
–
3634.9(3)
4
ꢀ
ꢀ
P1
P1
11.7969(15)
13.9222(17)
25.231(3)
96.740(2)
102.643(2)
96.954(3)
3969.1(9)
2
2.316
8.648
218(2)
0.0549
11.835(4)
13.059(4)
15.915(5)
100.657(6)
96.325(6)
113.222(5)
2175.3(12)
2
2.254
7.910
150(2)
0.0657
a
(°)
b (°)
c
(°)
V (Å3)
Z
q
l
(calc), (g cmꢁ3
)
1.883
1.066
2.937
(Mo K
a
), (mmꢁ1
)
12.622
100(2)
0.0416
0.1048
8276
T (K)
100(2)
0.0345
0.0706
24829
3744
R (F) (%)a
R (wF2) (%)b
Collected
Unique
0.0930
26265
15513
0.1354
10728
7513
3082
Rint
Observed
0.0321
3250
0.0335
11930
0.0408
2852
0.0427
5960
a
R =
R
||Fo|ꢁ|Fc||/
R
|Fo|.
b
2
R(
x
F2) = {
R
[
x
(Fo ꢁFc2)2]/
R[x ; x = 1/[r
(Fo2)2]}1/2 2(Fo2)+(aP)2 + bP], P = [2Fc2 + max(Fo,0)]/3.

278
M.V. Petersen et al. / Polyhedron 52 (2013) 276–283
C40H32O8F24Co2: C, 39.56; H, 2.66; F, 37.54. Found: C, 39.71; H,
2.62; F, 37.33%.
3. Results and discussion
3.1. Synthesis and electronic spectra
2.4.3. [Tl2Co(OC6F5)4], 3b
Preparation of [Co2(OArF)4(DME)2], 1, and [Co2(OAr0)4(DME)2],
2, proceeds readily via metathesis of CoI2 with two equivalents
of the appropriate TlOAr in THF/DME solution. The synthesis and
some spectroscopic characterization of the [Tl2Co(OAr)4] com-
pounds 3b and 4 have been reported previously [1], as was the
same information for {K(18-crown-6)}2[Co2(OPh)6] [1]. Com-
pounds 1, 3, and 4 are presented in Scheme 2 with composition
and connectivity. Compound 2 is proposed to be very similar to
1, based on similarity of all other characterization data. All com-
pounds appear purple in the solid state and in solution. The elec-
tronic spectra in the visible region have several absorbances
between ꢂ480–600 nm with extinction coefficients less than
1000, consistent with weak LMCT (O 2p to Co 3d) or d–d transitions
for low-symmetry, high spin CoII centers.
In the dry box four equivalents of Tl (OC6F5)4 (1.29 g,
3.33 mmol) were dissolved in THF and one equivalent of CoI2
(0.261 g, 0.833 mmol) was added while the solution was stirring.
A dark deep blue colored solution with yellow precipitate was
formed. After the solution was stirred overnight, it was filtered
through Celite and the solvent was removed in vacuo. A dark
purple solid remained, which was triturated three times with
2 mL of hexane. The product was dissolved in a minimum amount
of toluene, filtered and layered with hexane for recrystallization.
The recrystallization was left in the refrigerator and after one
day the solvents were pumped off. The product was filtered
leaving
a purple colored solid with a
73% yield. 1H NMR
(d, ppm, C6H5Br): 2.64 (s, 3H, C6H5–CH3), 7.79 (b, 5H, C6H5–CH3)
13C NMR (d, ppm, C6H5Br): 22.15(s, C6H5–CH3), 139.76 (ipso,
C6H5–CH3), 129.87 (ortho, C6H5–CH3), 130.70 (meta, C6H5–CH3),
126. 94 (para, C6H5–CH3) 19F NMR (d, ppm, C6H5Br): ꢁ162.64 (s,
OC6F5). UV–Vis (toluene) [kmax, nm (eM, Mꢁ1 cmꢁ1)]: 584.9 (530),
511 (320), 530 (350) UV–Vis (THF) [kmax, nm (eM, Mꢁ1 cmꢁ1)]:
533 (230), 586 (340).
3.2. Structural
Crystallographic data collection parameters are presented in Ta-
ble 1. The dimeric [(DME)(ArFO)Co( 2-OArF)2Co(OArF)(DME)], 1,
l
consists of two highly distorted trigonal bipyramidal centers as
shown in Fig. 1, with important distances and angles collected in
Table 2. The two cobalt atoms are 3.1392(3) Å apart (Co–Co in co-
balt metal = 2.50 Å [13]) and related by a twofold axis running
2.4.4. [Tl2Co(OC8F6H3)4ꢀtoluene]2, 4
In the dry box four equivalents of Tl(OC8F6H3)4 (3.76 g,
8.68 mmol) were dissolved in THF and one equivalent of CoI2
(0.679 g, 2.17 mmol) was added while the solution was stirring.
A dark blue colored solution with yellow precipitate was formed.
After the solution was stirred overnight, it was filtered through
Celite and the solvent was removed in vacuo. The dark blue solid
was triturated three times with 2 mL of hexane. The product was
dissolved in a minimum amount of toluene, filtered and layered
with hexane for recrystallization. The recrystallization was left in
the refrigerator and after one day the solvents were pumped off.
The product was filtered leaving a purple colored crystalline solid
with a 52% yield. Crystals were suitable for X-ray crystallography.
1H NMR (d, ppm, CD2Cl2): 2.64 (s, 3H, C6H5–CH3), 7.79 (br, 5H,
C6H5–CH3) 13C NMR (d, ppm, CD2Cl2): 22.15(s, C6H5–CH3), 139.76
(ipso, C6H5–CH3), 129.87 (ortho, C6H5–CH3), 130.70 (meta, C6H5–
CH3), 126. 94 (para, C6H5–CH3) 19F NMR (d, ppm, CD2Cl2): ꢁ73.74
(S, CF3). UV–Vis (toluene) [kmax, nm (eM, Mꢁ1 cmꢁ1)]: 547 (300),
598 (430) UV–Vis (THF) [kmax, nm (eM, Mꢁ1 cmꢁ1)]: 479 (110),
482 (110), 522 (200), 544 (230), 599 (300). Anal. Calc. for C35.5H16
O4F24CoTl2: C, 29.81; H, 1.13; F, 31.88. Found: C, 30.28; H, 1.61;
F, 29.34%. The lack of agreement in the F analysis is likely due to
poor combustion, not uncommon in highly fluorinated species.
along the O(2)–O(3) vector, through the two
l2-bridging arylox-
ides. The axis of the trigonal bipyramid is the O(3)–Co(1)–O(4) vec-
tor (corresponding angle is 167.55(5)°) and the equatorial plane
corresponds to that containing the O(1), O(2), and O(5) atoms in
which the O–Co–O angles are 110.40(4)°, 111.82(5)°, and
136.86(4)°. The two largest O–Co–O angles around cobalt give a
s5 value of 0.53, calculated as shown in Equation 1, where
b are the largest and second largest O–M–O angles respectively.
An ideal square pyramid has a value
a and
s
j
a
ꢁ bj
s5
¼
60ꢃ
of zero [14] and a trigonal bipyramid has a s5 value of 1.0. The an-
gles (°) at the bridging oxygen atoms are 99.39(7) (Co(1)–O(2)–
Co(1_2)) and 104.46(7) (Co(1)–O(3)–Co(1_2)). The terminal Co–O
bond length of 1.9267(12) Å is slightly shorter than those previ-
ously reported (1.937(2) and 1.962(2) Å) for the OArF ligand with
Co [1]. No Co-l
2-OArF linkages have been structurally characterized
previously but the longer Co–O(3) and Co–O(2) distances of
2.0582(10) and 1.9857(10) Å, respectively, are reasonable com-
pared to the terminal linkage. Only five other Co(DME) adducts,
F
F
F
F3C
CF3
F
F
F
F
F
CF3
F
Tl
Tl
F
F3C
CF3
F
F
F
O
F
CF3
CF3
O
F
O
Co
O
F
O
F
F
F
O
Tl
F
F3C
F3C
CF3
F
O
CH3
Co
Co
O
Co
O
F
F
CH3
Tl
F
F C
O
3
O
O
O
O
O
O
O
F
O
F
H C
3 Co
F
F3C
F
CF3
O
Tl
Tl
F
F
F
F3C
CF3
O
F
F
F
F
F
H3C
F
F3C
F
F
F
[Co(OArF)2(DME)]2, 1
[Co(OAr′)2(DME)]2, 2
[Tl2Co(OArF)4], 3
′
4
[Tl2Co(OAr )4],
Scheme 2. Co(II) fluorinated aryloxide compounds.

M.V. Petersen et al. / Polyhedron 52 (2013) 276–283
279
Table 2
Selected interatomic distances, bond lengths and angles.a
Compound Distances
(Å)
Angles
(°)
1
Co(1)–O(1)
Co(1)–O(2)
Co(1)–O(3)
Co(1)–O(4)
Co(1)–O(5)
O(1)–C(1)
O(2)–C(7)
O(3)–C(11)
1.9267(12) O(1)–Co(1)–O(2)
1.9857(10) O(1)–Co(1)–O(3)
2.0582(10) O(1)–Co(1)–O(4)
2.2073(12) O(3)–Co(1)–O(4)
2.0346(12) O(1)–Co(1)–O(5)
135.86(4)
101.58(5)
88.59(5)
167.55(5)
111.82(5)
110.40(4)
78.08(5)
106.42(4)
89.64(5)
75.82(5)
104.46(7)
99.39(7)
127.27(12)
127.77(4)
130.31(3)
63.35(11)
65.16(12)
63.33(12)
63.89(12)
111.94(16)
131.16(19)
90.91(16)
91.46(16)
131.78(19)
104.37(15)
136.7(2)
90.96(17)
108.18(17)
105.62(16)
92.00(17)
129.2(2)
101.65(15)
126.8(4)
127.6(4)
127.3(4)
129.3(3)
103.24(16)
118.3(3)
65.47(11)
1.315(2)
1.339(3)
1.337(3)
O(2)–Co(1)–O(5)
O(3)–Co(1)–O(2)
O(3)–Co(1)–O(5)
O(4)–Co(1)–O(2)
O(4)–Co(1)–O(5)
Co(1)–O(2)–Co(1_2)
Co(1_2)–O(3)–Co(1)
C(1)–O(1)–Co(1)
C(7)–O(2)–Co(1)
C(11)–O(3)–Co(1)
O(1)–Tl(1)–O(4)
O(2)–Tl(2)–O(3)
O(5)–Tl(4)–O(8)
O(7)–Tl(3)–O(6)
O(1)–Co(1)–O(2)
O(1)–Co(1)–O(3)
O(1)–Co(1)–O(4)
O(2)–Co(1)–O(3)
O(2)–Co(1)–O(4)
O(3)–Co(1)–O(4)
O(5)–Co(2)–O(7)
O(5)–Co(2)–O(8)
O(7)–Co(2)–O(8)
O(5)–Co(2)–O(6)
O(6)–Co(2)–O(7)
O(6)–Co(2)–O(8)
Co(1)–O(1)–Tl(1)
Co(1)–O(1)–C(1)
C(1)–O(1)–Tl(1)
C(7)–O(2)–Co(1)
C(7)–O(2)–Tl(2)
Co(1)–O(2)–Tl(2)
C(13)–O(3)–Co(1)
O(1_2)–Tl(1)–
3a
Tl(1)–O(1)
Tl(1)–O(4)
Tl(2)–O(2)
Tl(2)–O(3)
Tl(3)–O(6)
Tl(3)–O(7)
Tl(4)–O(5)
Tl(4)–O(8)
Co(1)–O(1)
Co(1)–O(2)
Co(1)–O(3)
Co(1)–O(4)
Co(2)–O(5)
Co(2)–O(6)
Co(2)–O(7)
Co(2)–O(8)
2.6754)
2.614(4)
2.548(4)
2.656(4)
2.717(4)
2.611(4)
2.631(4)
2.650(4)
1.949(4)
1.936(4)
1.980(4)
1.953(4)
1.949(4)
1.971(4)
1.950(4)
1.940(4)
Fig. 1. ORTEP diagram of [Co(OArF)2(DME)]2, 1. Hydrogen atoms and DME methyl
groups have been omitted for clarity. Ellipsoids are shown at the 50% probability
level.
all octahedral with chelating DME, have been crystallographically
characterized with Co–O distances (Å) of 2.120(6) and 2.140(7)
[15] in [Co(DME)(hfac)2] (RADJIQ; hfac = hexafluoroacetylace-
tonate), distances 2.141(8) and 2.179(8) [16], in [Co(DME)
{(tBuCO)2As}2] (ECUGIS), distances 2.10(1) and 2.08(1) [17], in
3b
Tl(1)–
O(1_2)
Tl(1)–
2.628(4)
2.672(4)
O(2_2)
[Co3(
l
3-Cl)(
l
3-SO4)(O2CCF3)3] (EFASCO) distances 2.127(7) and
O(1)–Co(1)––O(1_2) 117.8(2)
2.210(6) [18], in [Co(DME)2(
j
2-CoCl4)] (ENOQII), and an average
O(2_2)
of 2.105(8) [17] in [Co(DME)2(OH2)2]2+ (ENOQOO) respectively.
The Co–O(5) distance (Å) in 1 is slightly longer at 2.0346(12) and
the Co–O(4) noticeably longer at 2.2073(12). This very long contact
to DME suggests that 1 may be considered a four-coordinate com-
plex with very weak interaction with the second DME oxygen atom.
The heterobimetallic [Tl2Co(OArF)4] was crystallized in a sol-
vated form with two equivalents of toluene per cobalt center, 3a,
and in an unsolvated form, 3b. The solvated form 3a is very similar
to the previously characterized [Tl2Ni(OArF)4]ꢀ2 toluene. This sol-
vate, [Tl2Co(OArF)4]ꢀ2 toluene, 3a, also exhibits close contacts in
the solid state between thallium and oxygen atoms and is depicted
in Fig. 2. In this case, two complementary contacts effectively
dimerize the compound in the solid state, and the toluene mole-
Co(1)–O(1)
Co(1)–O(2)
O(1)–C(1)
O(2)–C7
1.941(4)
1.977(4)
1.321(7)
1.329(7)
O(1)–Co(1)–O(2_2)
O(1)–Co(1)–O(2)
O(2_2)–Co(1)–O(2)
C(1)–O(1)–Co(1)
C(1)–O(1)–Tl(1_2)
Co(1)–O(1)–Tl(1_2)
C(7)–O(2)–Co(1)
C(7)–O(2)–Tl(1_2)
Co(1)–O(2)–Tl(1_2)
O(1)–Tl(1)–O(2)
O(1)–Tl(1)–O(4)
O(2)–Tl(1)–O(4)
O(1)–Co(1)–O(2)
O(1)–Co(1)–O(2B)
O(1)–Co(1)–O(3)
O(2)–Co(1)–O(2B)
O(2)–Co(1)–O(3)
O(3)–Co(1)–O(2B)
O(4B)–Co(1)–O(1)
O(4B)–Co(1)–O(2)
O(4B)–Co(1)–O(3)
123.90(16)
94.05(15)
105.1(2)
126.5(3)
129.9(3)
101.14(15)
120.4(3)
128.1(3)
98.70(15)
65.97(17)
88.89(18)
63.24(16)
89.8(2)
84.7(2)
98.1(2)
80.7(2)
101.7(2)
176.3(2)
148.0(3)
115.8(2)
95.2(2)
4
Tl(1)–O(1)
Tl(1)–O(2)
Tl(1)–O(4)
Tl(2)–O(3)
Co(1)–O(1)
Co(1)–O(2)
Co(1)–O(3)
2.548(6)
2.645(5)
2.607(5)
2.502(6)
1.988(6)
2.017(5)
2.017(6)
Co(1)–O(2B) 2.244(5)
Co(1)–O(4B) 1.977(6)
cules surround the dimer via M-to-p-arene interactions to Tl(1)
and Tl(4), with Tlꢀ ꢀ ꢀC distances averaging 3.48(6) Å, as shown in
Fig. S1. Only two of the four thallium atoms participate in the
dimerization, namely Tl(2) and Tl(3). Whereas the intramolecular
Tl-O bonds have similar lengths to those in 3b and average
2.64(5) Å, the dotted contacts in 3a are noticeably longer at
3.005(5) and 3.223(5) Å. The other two thallium atoms, Tl(1) and
Tl(4) each bond to two toluene molecules as shown in the
Supplementary material, Fig. S1.
The unsolvated form 3b exhibits distinctly different packing
such that the Tl centers do not bind to any of the arene rings
directly. On the left side of Fig. 3 only the intramolecular contacts
are shown in which the pseudo-tetrahedral cobalt center is clearly
seen. The s4 values of 0.69 and 0.67 are observed in the two
crystallographically independent Co centers, based on the
a
Numbers in parentheses are estimated deviations of the last significant figure.
360ꢃ ꢁ j
þ bj
a
s4
¼
141ꢃ
quantification described [19] for four-coordinate complexes. The
average unbridged O–Co–O angle is 116(10)° and the unique angle
bridged by thallium is much narrower at 94.05(15)°. The thallium
atom bridges on two edges of the tetrahedron have an average
Tl–O distance of 2.65(3) Å. The aryloxide ligands each in turn bridge

280
M.V. Petersen et al. / Polyhedron 52 (2013) 276–283
Fig. 2. ORTEP diagram of [Tl2Co(OArF)4]ꢀ2 toluene, 3a. Thallium oxygen contacts (Å) shown with dotted lines are Tl(2)ꢀ ꢀ ꢀO(6) 3.005(5) and Tl(3)ꢀ ꢀ ꢀO(3) 3.223(5). Toluene
molecules are removed for clarity. Ellipsoids are shown at the 50% probability level.
Fig. 3. ORTEP diagrams of [Tl2Co(OArF)4], 3b. One neutral unit is shown on the right. Intermolecular close contacts are shown on the left in which thallium-heteroatom
distances (Å) shown with dotted lines are Tl(1)ꢀ ꢀ ꢀO(2C) 3.179(3), Tl(1)ꢀ ꢀ ꢀF(1A) 3.352(3), Tl(1)ꢀ ꢀ ꢀF(4AA) 3.071(3), Tl(1)ꢀ ꢀ ꢀF(6C) 3.388(3), and Tl(1)ꢀ ꢀ ꢀF(7B) 3.461(4). Ellipsoids
are shown at the 50% probability level.
thallium and cobalt centers but the average Co–O distance of
1.96(2) Å is shorter than the terminal Co–O distance in five-coordi-
nate 1. There are also intermolecular contacts in 3b between the
thallium atoms and adjacent oxygen and fluorine atoms, depicted
on the right side of Fig. 3. These contacts are the only ones present
at less than 4 Å but are still clearly long and do not survive in solu-
tion, as indicated by solution magnetic susceptibility data [1].
In contrast, the bis-3,5-trifluoromethylphenoxide derivative 4,
{{Tl2Co(OAr0)4}2}ꢀ2 toluene crystallizes as a bridged dimer with
pyramidal geometry than trigonal bipyramidal, but again highly
distorted as in 1. The largest angle at Co(1) is that spanning
O(3)–Co(1)–O(2B) and is 176.3(2)°. Three distinct Tl-arene interac-
tions are present. The Tl(1) center binds to three carbons of the aryl
group from O(3) with an average distance (Å) of 3.67(8), while the
other sp2 hybridized carbons are all at least 3.91 Å away. The Tl(2)
atom bonds g6 to both a toluene molecule (average 3.25(9) Å) and
g6 to the aryl group connected to O(4) (average 3.36(5) Å). Unlike
in 1, which has one terminal and one bridging aryloxide per Co
atom, all aryloxides in 4 are bridging between Tl and Co. The two
aryloxides that bridge the two Co are l3 due to their interaction
with Tl(1) as shown in Fig. 4. The two clearly distinct structures
two l
2-OAr0 ligands, as shown in Fig. 4. The two cobalt atoms are
3.251(2) Å apart and related by an inversion center. The s5 value
for this cobalt center is 0.47 which is marginally closer to a square

M.V. Petersen et al. / Polyhedron 52 (2013) 276–283
281
Fig. 4. ORTEP diagram of [Tl2Co(OAr0)4]ꢀ2 toluene, 4. Thallium-arene contacts (Å)
are shown with dotted lines. Fluorine atoms are removed for clarity. Ellipsoids are
shown at the 50% probability level.
Fig. 6. Molecular orbital representation of 121B-
[Co(DME)(OArF)2]2, C2-1.
a
from C2-symmetrized
in 3 and 4 mark the first time that we have seen any substantial
structural difference in metal fluorinated phenolate compounds
that differ only in the aryloxide unit, OC6F5 versus OC6H3(CF3)2.
Analogous studies shown in Fig. 5 on the dimeric compound 1
also revealed Curie–Weiss behavior with good agreement between
room temperature solid (6.31 lB) and solution (6.39 lB) leff values.
3.3. Magnetism
In this compound, however, the two cobalt centers are clearly
bridged and the magnitude of susceptibility indicates intramolecu-
lar antiferromagnetic coupling of the two cobalt centers via the
Variable temperature susceptibility studies carried out with a
SQUID susceptometer demonstrate that compound 3b behaves as
a simple Curie–Weiss magnet, as shown in Fig. S2, in the Supple-
mentary information. The data were fit to Eq. (2) giving a Curie
bridging aryloxide ligands in the {Co2(
l
2-OArF)2} core. Numerous
dimeric CoII
(l
2
2-X)2 compounds have been reported in the litera-
constant, C, of 2.52 K-cm3/mol and a Weiss constant,
H, of
ture, and many of these with some degree of magnetic character-
ization [20,21]. Among those antiferromagnetic behavior is often
seen, though systems with complete variable-temperature studies
and detailed fitting of the data are quite rare, perhaps due to the
challenges associated with an accurate description of CoII
magnetism.
ꢁ2.12 K, indicating slight intermolecular antiferromagnetic
coupling.
C
v
¼
ð2Þ
T ꢁ
The room temperature moments for both the solid state
eff = 4.49 B) and the solution ( eff = 4.46 B; Evans’ method [1])
H
All-electron DFT calculations were carried out an a C2-symmet-
ric version of 1 (C2-1), with six-unpaired electrons Fig. 6 shows an
occupied orbital in which Co d-orbitals from both Co atoms have
in-phase overlap with a p-orbital from the bridging aryloxide.
Other occupied orbitals also exhibiting both Co and bridging aryl-
oxide oxygen contributions are shown in Fig. 7. Attempts to calcu-
late electronic structures for different, lower spin states of C2-1
were unsuccessful, and did not lead to aufbau solutions. Rotation
(l
l
l
l
are in good agreement with one another. The individual Co centers
are effectively isolated from each other, and the susceptibility is
normal for a high-spin, tetrahedral center [12].
of the
l
2-OArF ligands about their O–Cipso axes was noticed in
geometry optimization attempts, however, suggesting that the an-
gle of the phenoxide plane with respect to the {Co2O2} core plays a
role in the magnitude of antiferromagnetic coupling.
The ferromagnetic or antiferromagnetic coupling character be-
tween two Cu centers is well-known to depend on the Cu–O–Cu
angle [22]. More acute angles are associated with ferromagnetic
coupling, whereas more obtuse angles correlate with antiferro-
magnetic coupling, as detailed in a variety of {Cu2(l2-OH)}-con-
taining compounds [22]. more recent study with Cu(II)
A
alkoxide complexes reiterated the role of the Cu–O–Cu angle (h)
while also noting the importance of the angle of the alkoxide car-
bon atom to the Cu–O–Cu plane (s) [23]. In aryloxide compounds,
Fig. 5. Variable temperature magnetic susceptibility data for [Co(DME)(OArF)2]2, 1.

282
M.V. Petersen et al. / Polyhedron 52 (2013) 276–283
Fig. 7. Molecular orbital representations of (left to right) 102B-a, 120B-b, and 122B-a
from C2-symmetrized [Co(DME)(OArF)2]2, C2-1.
the OC6H3(CF3)2 ligand has a dimeric structure in the solid state
with substantial ferromagnetic coupling.
Acknowledgements
This work was supported by the NSF (CAREER-0134817 and
CHE-0910647); NMR spectrometers via DUE-9952633 (Barnard
College) and CHE-0619339 (Boston University), and the donors of
the Petroleum Research Fund administered by the American
Chemical Society (PRF #38007-GB3). LHD thanks Prof. C.C. Cum-
mins for hospitality during a sabbatical when some of these data
were collected. We thank Drs. S.A. Cantalupo and J.S. Lum for spe-
cial assistance.
Fig. 8. Variable temperature magnetic susceptibility data for [Tl2Co(OAr0)4]ꢀ2
toluene, 4.
Appendix A. Supplementary material
CCDC 891130, 901763, 901764, and 901765 contain the supple-
mentary crystallographic data for 1, 3a, 3b, and 4, respectively.
These data can be obtained free of charge via http://www.ccdc.ca-
m.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Sup-
plementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.poly.2012.09.032.
the angle of the ipso carbon to the M–O–M plane can vary as well
as the angle of rotation about the O–Cipso bond. The 121B-b repre-
sentation in the center of Fig. 7 clear shows the overlap of the Co
3d, O 2p, and the aryl p⁄ orbitals. The relationship between this an-
gle of rotation to the type and degree of coupling will be of interest
as more magnetically characterized examples of non-chelating
aryloxide ligands in {M2(l2-OAr)2} moieties are reported.
In contrast, the variable temperature magnetic behavior of com-
pound 4, [Tl2Co(OAr0)4]2, clearly shows a different room tempera-
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