Coordination of diorganotellurides to cobalt(III) in cobaloximes

Article abstract of DOI:10.1016/j.poly.2012.08.017

The unexpectedly aqueous stable bis-tellurium cationic complex [Co(dmgH)₂{PhTe(CH₂)₃SO₃Na} ₂]⁺(1⁺) (dmgH^- = dimethylglyoximate) has been fully characterized in the solid state and in solution. The UV-Vis spectrum of 1⁺ differs from that of earlier cobaloximes, exhibiting a new low energy band centered at λ_max = 425 nm (ε ～ 26155 dm³ mol^-1 cm^-1) and assigned with DFT calculations to allowed LMCT transitions. ¹H, ¹³C, and ¹²⁵Te NMR spectra show unequivocally that two diastereomers exist equally in water, 50% of the achiral C_2h meso-[Co(dmgH) ₂{R,S-PhTe(CH₂)₃SO₃Na} ₂]⁺ and 50% of the chiral C₂ rac-[Co(dmgH) ₂{PhTe(CH₂)₃SO₃Na}₂] ⁺ (25% of each enantiomer [Co(dmgH)₂{R,R-PhTe(CH ₂)₃SO₃Na}₂]⁺ and [Co(dmgH)₂{S,S-PhTe(CH₂)₃SO₃Na} ₂]⁺). The solid-state structure of the meso diastereomer has been solved. Neutral mono-tellurium complexes [CoCl(dmgH) ₂{Te(p-MeO-C₆H₄)₂}](2) and [CoCl(dpgH)₂ {Te(p-MeO-C₆H₄)₂}](3) (dpgH^- = diphenylglyoximate) have also been characterized in the solid (3) state and in solution (2 and 3). The structural results provide the first examples of Co(III)-Te bonds. The solid-state structure of the related cobaloxime salt [Co(dmgH)₂(py)₂][CoCl₂(dmgH) ₂] obtained during one synthesis is also reported.

Full text of DOI:10.1016/j.poly.2012.08.017

Polyhedron 58 (2013) 39–46
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Coordination of diorganotellurides to cobalt(III) in cobaloximes
Gabriel García-Herbosa 1, William R. McNamara, William W. Brennessel, José V. Cuevas,
⇑
Sandip Sur, Richard Eisenberg
Department of Chemistry, University of Rochester, Rochester, NY 14627, United States
a r t i c l e i n f o
a b s t r a c t
The unexpectedly aqueous stable bis-tellurium cationic complex [Co(dmgH)2{PhTe(CH2)3SO3Na}2]+(1+)
(dmgHꢀ = dimethylglyoximate) has been fully characterized in the solid state and in solution. The
UV–Vis spectrum of 1+ differs from that of earlier cobaloximes, exhibiting a new low energy band cen-
Article history:
Available online 18 August 2012
Dedicated to the memory of Michelle Millar
whose enthusiasm and spirit brought joy to
inorganic chemists everywhere.
tered at kmax = 425 nm (
e
ꢁ 26155 dm3 molꢀ1 cmꢀ1) and assigned with DFT calculations to allowed LMCT
transitions. 1H, 13C, and 125Te NMR spectra show unequivocally that two diastereomers exist equally in
water, 50% of the achiral C2h meso-[Co(dmgH)2{R,S-PhTe(CH2)3SO3Na}2]+ and 50% of the chiral C2
rac-[Co(dmgH)2{PhTe(CH2)3SO3Na}2]+ (25% of each enantiomer [Co(dmgH)2{R,R-PhTe(CH2)3SO3Na}2]+
and [Co(dmgH)2{S,S-PhTe(CH2)3SO3Na}2]+). The solid-state structure of the meso diastereomer has been
solved. Neutral mono-tellurium complexes [CoCl(dmgH)2{Te(p-MeO–C6H4)2}](2) and [CoCl(dpgH)2
{Te(p-MeO–C6H4)2}](3) (dpgHꢀ = diphenylglyoximate) have also been characterized in the solid (3) state
and in solution (2 and 3). The structural results provide the first examples of Co(III)–Te bonds. The
solid-state structure of the related cobaloxime salt [Co(dmgH)2(py)2][CoCl2(dmgH)2] obtained during
one synthesis is also reported.
Keywords:
Cobalt
Tellurium
Cobaloximes
Stereoisomers
125Te NMR
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
studies, systems composed of a light absorber or photosensitizer
(PS), a catalyst, aqueous protons and a sacrificial electron source
In coordination chemistry, the compatibility of different metal
ions and ligands for binding has long been noted, with Pearson’s
analysis of hard and soft acids and bases (HSAB) for metal ions
and ligands, respectively, being the most widely cited and em-
ployed [1]. In this paper, we report several new Co(III) complexes
that possess a divalent telluroether ligand. In the HSAB system,
Co(III) is viewed as a ‘‘very hard’’ metal ion while telluroethers
(RR’Te) are considered as ‘‘very soft’’. Telluroethers, as well as anal-
ogous ligands with Se and S donor atoms, generally exhibit poor
ability to coordinate to medium or high oxidation states of 3d
transition metals [2]. Whereas there have been several reports pre-
viously of Co–Te bonds in organometallic compounds having Co in
the +1 oxidation state, the present systems are the first between
Co(III) and Te in telluroethers. In light of the metallic nature of tel-
lurium as an element, the Co–Te bonds in this report also represent
interesting examples of polarized metal–metal bonding [3].
Our path to the preparation and characterization of the title
complexes was circuitous and derived from work that was being
done on the visible–light driven generation of H2 from water, cor-
responding to the reductive side of water splitting [4]. In these
are examined under visible light irradiation for H2 generation.
The photosensitizers may be either metal complexes or organic
dyes having long-lived excited states for electron transfer. One
set of molecular catalysts that has been extensively studied are
cobaloxime complexes such as [Co(dmgH)2LCl], were L is a pyri-
dine or phosphine ligand; these complexes are catalysts for both
photochemical and electrochemical production of hydrogen with
relatively good levels of activity [4b,5]. In the photochemical
studies, the sacrificial donors have generally been tertiary amines
such as triethylamine (TEA), triethanolamine (TEOA) and ethylene-
diamine (tetraacetic acid) (EDTA), that upon oxidation undergo
irreversible decomposition through well established chemistry
[6]. Another sacrificial donor is ascorbic acid that is used under
more acidic conditions (pH 4–5).
The relatively small number of compounds used as sacrificial
donors, together with undesirable aspects of their decompositions
such as radical formation and/or liberation of a second highly
reducing electron prompted us to seek additional compounds that
could be easily oxidized as electron donors in hydrogen generating
systems. In this regard, Te(II) compounds proved attractive be-
cause they can be easily oxidized to Te(IV) and they have been
shown to catalytically activate hydrogen peroxide [7]. In the course
of initial studies of Te(II) compounds as potential electron sources
for hydrogen formation with catalysts such as [Co(dmgH)2LCl], the
formation of strongly colored solutions were seen. Additionally,
⇑
Corresponding author.
E-mail address: eisenberg@chem.rochester.edu (R. Eisenberg).
Permanent address: Departamento de Química, Facultad de Ciencias, Universidad
1
de Burgos, 09001 Burgos, Spain.
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.017

40
G. García-Herbosa et al. / Polyhedron 58 (2013) 39–46
when an unsymmetrical TeRR’ compound was examined, evidence
of diasteromers was seen by NMR spectroscopy. In fact, coordina-
tion of telluroethers bearing different substituents has been re-
ported previously to lead to chirality in complexes of Pd(II), Pt(II)
and Ru(II) [8]. While the objective of using Te(II) compounds as
sacrificial electron donors for efficient H2 generation was not
achieved (only small amounts of H2 were seen), the study led to
the new compounds reported herein that have the first examples
of Co(III)–Te(II) bonds.
2.3. [Co(dmgH)2{PhTe(CH2)3SO3Na}2]F.3H2O (1.F)
This compound was prepared following the same procedure as
above for 1.BF4 but using CoF2 instead of Co(BF4)2ꢂ6H2O. Yield 65%.
The compound is also a 50–50 mixture of meso and rac diastereo-
mers. 1H NMR and 13C{1H} NMR spectra are identical to that
described above for 1.BF4.
Anal. calc. for C26H42CoFN4Na2O13S2Te2: C, 29.41; H, 3.99; N,
5.28. Found: C, 29.06; H, 3.85; N, 5.25%.
2.4. [CoCl(dmgH)2{Te(p-MeO–C6H4)2}] (2)
2. Experimental section
To a solid mixture of 195 mg (0.57 mmol) of Te(p-MeO–C6H4)2,
67.8 mg (0.285 mmol) of CoCl2ꢂ6H2O, 66.4 mg (0.57 mmol) of dim-
ethylglyoxime and 24 mg (0.285 mmol) of NaHCO3 was added
10 mL of absolute ethanol. Stirring in air for 24 h led to a red pre-
cipitate that was filtered and washed with 3 mL of absolute ethanol
and then with 2 ꢃ 3 mL aliquots of diethylether. Yield 120 mg, 63%.
1H NMR (400 MHz, CDCl3, 25 °C): d 2.20 (s, 12H, 4Me dmgHꢀ),
3.86 (s, 6H MeO–C6H4), 6.94(d, 4H, MeO–C6H4), 7.39 (d, 4H,
MeO–C6H4). 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C): d 12.81 (CH3
dmgH-), 55.47 (MeO–C6H4), 101.87, 115.81, 136.86, 152.47 (TeC6
H4OMe), 162.23 (MeC = NOH dmgHꢀ).
2.1. Chemicals
Cobalt(II) chloride hexahydrate, cobalt(II) tetrafluoborate
hexahydrate, cobalt(II) fluoride, dimethylglyoxime (dmgH2), diph-
enylglyoxime (dpgH2), are commercially available (Aldrich) and
were used as received. Absolute ethanol and 96% ethanol were
purchased from Fisher and used without further purification. The
tellurium(II) ligands PhTe(CH2)3SO3Na (L1) [9] and Te(anisyl)2
(L2) [10] were synthesized as reported in the literature.
Anal. calc. for C22H28ClCoN4O6Te: C, 39.65; H, 4.23; N, 8.41.
Found: C, 39.41; H, 3,98; N, 8.11%.
2.2. [Co(dmgH)2{PhTe(CH2)3SO3Na}2]BF4ꢂ2H2O (1.BF4)
To a solid mixture of 200 mg (0.57 mmol) of PhTe(CH2)3SO3Na,
97 mg (0.285 mmol) of Co(BF4)2ꢂ6H2O, 66.4 mg (0.57 mmol) of
dimethylglyoxime and 24 mg (0.285 mmol) of NaHCO3 was added
5 mL of water. Heating at 60 °C for 30 min led to the formation of a
dark red solution. Filtration, concentration and addition of 15 ml of
absolute ethanol afforded a red–brown solid that was washed with
absolute ethanol (10 mL) and then with diethylether (10 mL) to
yield 230 mg of product (66% yield). The compound exists as a
50–50 mixture of meso and rac diastereomers. For X-ray character-
ization, orange needles of the meso isomer were obtained on
standing from hot saturated solutions of the compound in EtOH
(99%)–H2O (1%).
2.5. [CoCl(dpgH)2{Te(p-MeO–C6H4)2}] (3)
To a mixture of 195 mg (0.57 mmol) of Te(p-MeO–C6H4)2,
67.8 mg (0.285 mmol) of CoCl2ꢂ6H2O, 137 mg (0.57 mmol) of diph-
enylglyoxime and 24 mg (0.285 mmol) of NaHCO3 was added
10 mL of ethanol. Heating at 60 °C with stirring for 30 min led to
a brown crystalline solid that was filtered and washed with
2 ꢃ 3 mL aliquots of ethanol and 2 ꢃ 3 mL aliquots of diethyl ether.
Yield 250 mg, 96%. Yellow–orange needles for X-ray characteriza-
tion were obtained from dichloromethane solutions into which
hexane diffused slowly.
1H NMR (400 MHz, CDCl3, 25 °C): d 3.84 (s, 6H MeO–C6H4),
6.93(d, 4H, MeO–C6H4), 7.00 (d, 8H, C6H5), 7.28(m, 12H, C6H5)
7.62 (d, 4H, MeO–C6H4). 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C):
d 55.46 (MeO–C6H4), 101.50, 116.39, 137.17, 153.61 (TeC6H4OMe),
127.56, 129.31, 129.71, 129.83 (Ph dpghꢀ) 162.51 (PhC = NOH
dpgHꢀ).
2.2.1. 1H NMR of meso isomer
(400 MHz, D2O, 25 °C): d1.76 (s, 6H, 2Mea dmgHꢀ), 1.96 (m, 4H
TeCHaHbCH2CH2SO3Na), 2.04 (s, 6H, 2Meb dmgHꢀ), 2.86 (m, 2H
TeCHaHbCH2CH2SO3Na), 2.87 (t, 4H, TeCH2CH2CH2SO3Na), 3.22
(m, 2H, TeCHaHbCH2CH2SO3Na), 7.15 (m 4H, o-C6H5Te), 7.41 (m,
4H, m-C6H5Te), 7.58 (m, 2H, p-C6H5Te). 13C{1H} NMR (100.6 MHz,
D2O, 25 °C): d 12.26 (CaH3 dmgHꢀ), 12.85 (CbH3 dmgHꢀ), 14.74
(TeCH2CH2CH2SO3Na), 22.83 (TeCH2CH2CH2SO3Na), 51.11 (TeCH2
CH2CH2SO3Na), 111.75 (ipso-TeC6H5), 130.58, 131.97, 134.09 (TeC6
H5), 155.98 (MeCa = N-dmgHꢀ), 156.57 (MeCb = NOH dmgHꢀ).
Anal. calc. for C42H37ClCoN4O6Te: C, 55.09; H, 4.07; N, 6.12.
Found: C, 54.90; H, 3.85; N, 6.06%.
2.6. Characterization
1H and 13C NMR spectra were recorded on a Bruker Avance 400
spectrometer (400.1 MHz). 59Co (I = 7/2, 100%), 125Te (I = ꢀ1/2,
6.99%) were measured on a Bruker model Avance 500 NMR spec-
trometer operating at 500.13 MHz proton NMR frequency. The
59Co NMR was measured at 118.67 MHz and the 125Te NMR was
measured at 157.79 MHz. For 125Te the sweep width was
1624 ppm and about 16 K transients were accumulated. All NMR
spectra were recorded at room temperature (296 K). The 125Te
NMR chemical shifts are referenced with Te2Ph2 in toluene-d8 as
an external reference at 418.0 ppm [11]. All 59Co NMR chemical
shifts are reported with aqueous K3[Co(CN)6] sample as an external
reference at 0.0 ppm [12].
2.2.2. 1H NMR of rac isomer
(400 MHz, D2O, 25° C): d1.90 (s, 12H, 4Me dmgHꢀ), 1.96 (m, 4H
TeCHaHbCH2CH2SO3Na), 2.86 (m, 2H TeCHaHbCH2CH2SO3Na), 2.87
(t, 4H, TeCH2CH2CH2SO3Na), 3.22 (m, 2H, TeCHaHbCH2CH2SO3Na),
7.15 (m 4H, o-C6H5Te), 7.41 (m, 4H, m-C6H5Te), 7.58 (m, 2H,
p-C6H5Te). 13C{1H} NMR (100.6 MHz, D2O, 25 °C): d 12.55 (CH3
dmgHꢀ), 14.74 (TeCH2CH2CH2SO3Na), 22.83 (TeCH2CH2CH2SO3Na),
51.11 (TeCH2CH2CH2SO3Na), 111.75 (ipso-TeC6H5), 130.58, 131.97,
134.09 (TeC6H5), 156.27 (MeC = NOH dmgHꢀ).
125Te NMR (500 MHz, D2O, 25 °C): d 712.3(s, 1Te), 713.3(s, 1Te).
Under the same experimental conditions the 125Te NMR of the free
ligand PhTe(CH2)3SO3Na (L1) showed one singlet at 449.1 ppm.
Anal. calc. for C26H40BCoF4N4Na2O12S2Te2: C, 28.09; H, 3.63; N,
5.04. Found: C, 28.26; H, 3.86; N, 4.63%.
2.7. Electrochemistry
Cyclic voltammetry experiments were conducted on an EG&G
PAR 263A potentiostat/galvanostat using a three-electrode single-
compartment cell including a glassy carbon working electrode, a
UV–Vis (H2O): kmax = 425 nm (
e
ꢁ 26155 dm3 molꢀ1 cmꢀ1
)

G. García-Herbosa et al. / Polyhedron 58 (2013) 39–46
41
Pt wire auxiliary electrode, and a Ag wire pseudo-reference elec-
trode. For all measurements, samples were degassed by purging
with argon. Tetrabutylammonium hexafluorophosphate (Fluka)
was used as the supporting electrolyte (0.1 M), and ferrocene
was employed as an internal reference. All redox potentials were
measured relative to the ferrocenium/ferrocene (Fc+/Fc) couple
(0.40 V vs SCE) [13] that was used as an internal standard and then
adjusted to NHE assuming an SCE potential of 0.24 V. All scans
[NBu4][Co(dmgH)2Cl2], TeCl2(4-MeO-Ph) [18] and [Co(dmgH)2(-
py)Cl] [19], as well as the not yet reported [Co(dmgH)2py2][-
Co(dmgH)2Cl2], were obtained. In recognition of the fact that the
intense red species formed only in protic solvents, a water soluble
telluroether, PhTe(CH2)3SO3Na, was employed for additional syn-
thesis [9].
Treatment of aqueous cobalt(II) salts with PhTe(CH2)3SO3Na in
the presence of dimethylglyoxime and sodium bicarbonate in
aerobic conditions afforded highly colored solutions of the com-
plex [Co(dmgH)2{PhTe(CH2)3SO3Na}2]+ (1+). However, attempts to
prepare the neutral mono-tellurium substituted complex [CoCl
(dmgH)2{PhTe(CH2)3SO3Na}] proved unsuccessful in yielding a
pure product. On the other hand, analogous reactions with
Te(p-anisyl)2 that were carried out in absolute ethanol, did indeed
lead to the neutral mono-tellurium complexes [CoCl(dmgH)2
{Te(p-MeO–C6H4)2}] (2) and [CoCl(dpgH)2{Te(p-MeO–C6H4)2}] (3).
The different results of the reactions for the two different Te ether
compounds appear to correlate with solvent polarity with the
more polar aqueous medium favoring the cationic bis telluroether
complexes, and the less polar EtOH affordiing the neutral mono
telluroether product.
were performed at 100 mV sꢀ1
.
2.8. X-ray structural determination of complexes 1.BF4, 3 and
[Co(dmgH)2(py)2]–[CoCl2(dmgH)2]
Orange needles of [meso-1.BF4ꢂ3EtOH], yellow-orange needles
of 3 and orange needles of [Co(dmgH)2(py)2][CoCl2(dmgH)2] suit-
able for single crystal X-ray diffraction were maintained at
100.0(1) K, on a Bruker SMART platform diffractometer equipped
with an APEX II CCD detector. The X-ray source, powered at
50 kV and 30 mA, provided Mo Ka radiation (k = 0.71073 A°, graph-
ite monochromator). Space groups were determined based on sys-
tematic absences, intensity statistics, and space group frequencies.
Direct methods were used to solve the structures [14]. Full-matrix
least-squares/difference Fourier cycles were performed, which lo-
cated the remaining non-hydrogen atoms. All non-hydrogen atoms
were refined with anisotropic displacement parameters. All hydro-
gen atoms were given riding models and refined with relative iso-
tropic displacement parameters.
4.1. Structural characterization in solution
4.1.1. 1H and 13C NMR
The 1H NMR spectrum of complex 1.BF4 in D2O is shown in
Fig. 1. The methyl groups of the dmgH ligands appear as three sing-
lets in a 1:2:1 ratio at d 1.76 1.90 and 2.04 ppm. To understand the
nature of these resonances, it is necessary to consider that coordi-
nation of L1 through tellurium leads to chirality as shown in
Scheme 1 and that for a Te center having three different groups
bonded to it, pyramidal inversion is extremely slow on the NMR
timescale. Note that as a consequence of the chirality, the protons
of the methylene bonded to Te are diasterotopic.
3. Computational details
Density functional theory (DFT) calculations were carried out
using Gaussian 03 (GAUSSIAN, Inc.) [15]. Time-dependent (TD) calcu-
lations were performed on the optimized ground-state structures
in gas phase. All calculations employed the B3LYP [16] functional
using the 6-31G(d,p) basis set for H, C, N and O, while Co and Te
were approximated using LANL2DZ effective core potentials [17].
The synthesis and stereochemistry of optically active tricoordi-
nate tellurium compounds, such as telluroxides, telluronium salts
and telluronium ylides were reviewed in 1997 (see Scheme 2)
[20]. Configurationally stable telluroxides were only obtained with
bulky groups, but the mechanism for racemization in the presence
of water were thought to involve an achiral hydrate rather than
simple pyramidal inversion at Te. The pyramidal inversion energy
for Me2TeO was estimated to be about 64 kcal molꢀ1 based on an
ab initio MO study. Enantiomerically pure (R)-telluronium salts
[MeEtPhTe]X (X = BF4ꢀ, ClO4ꢀ) were found to be stable toward
pyramidal inversion, with no racemization taking place even after
refluxing in methanol for 3 days [20].
4. Results and discussion
When studying the reactivity of diaryltelluroethers Ar2Te
(Ar = Ph, 4-MeO–Ph, 4-NH2–Ph) with solid [Co(dmgH)2(py)Cl] in
dry organic solvents such as dichloromethane or acetone, no reac-
tion was observed. However, after the addition of water, these mix-
tures developed intense red colors. Despite the absence of well
characterized examples of Co(III)–tellurium compounds, we pre-
sumed that the deep color was due to cobalt(III)–tellurium bonded
species. Unfortunately, initial attempts to isolate these deeply col-
ored compounds failed. Only crystals of known compounds like
In the present study, coordination of two chiral ligands in the
trans axial positions of the octahedral [CoIIIL2(dmgH)2]+ complex
Fig. 1. 1H NMR spectrum of 1.BF4. Signal due to residual H2O at 4.72 ppm has been removed for clarity.

42
G. García-Herbosa et al. / Polyhedron 58 (2013) 39–46
is no symmetry element that interchanges these two methyl
groups on each dmgH. However, in the case of the rac isomer, a
C2 axis yields equivalence of the methyl groups (see Scheme 3
where A, B, C denotes different substituents on tellurium), leading
to only one Me resonance (the symmetry of the meso diastereomer
ignoring the methyl protons is C2h).
Hence, the central signal of the three Me singlets at 1.90 ppm
(that belongs to the rac-diastereomer) integrates to exactly double
the value of the two signals at 1.76 and 2.04 ppm (that belong to
the meso-diastereomer). The same explanation applies to what is
observed in the 13C NMR spectrum. The explanation indicates that
both meso- and rac-isomers are in equal amounts, indicating that
the reaction yields a purely statistical result. There is no preference
for binding of a prochiral ligand to the Co center for which the
trans ligand has a specific chirality. The diastereotopic methylene
group attached directly to Te shows separate –CH2– signals at
3.22 ppm and 2.86 ppm, the latter overlapping with the signal of
the methylene directly attached to the sulfonate S atom.
Scheme 1.
Scheme 2.
These stereochemical results are in agreement with the re-
ported presence of meso and dl diastereomers in square planar
complexes [MX2{PhTe(CH2)3TePh}] (M = Pd, Pt; X = Cl, Cr, I) and
in ruthenium(II) complexes that were properly established by
NMR spectroscopy [8]. Nevertheless, the discussion about the ste-
reochemistry in systems containing coordinated asymmetric tellu-
roethers has often been overlooked. For instance, the coordination
chemistry of the arylalkyltellurium ligand 2-[2-(4-methoxyphe-
nyltelluro)ethyl]thiophene has been reported but neither the ex-
pected chiral nature of the ligand after coordination nor its
influence on the 1H NMR spectrum (i.e., the diastereotopic nature
of the methylene group attached to tellurium) was mentioned
[21]. The same applies to the 4-MeOC6H4TeCH2CH2SEt (L) and its
complex [PdCl2L] whose structure, with both Te and S having three
different substituents plus the lone pair, was published, but with
no mention of its stereochemistry [22]. Likewise, the complex
[Pd{4-MeC6H4TeCH2CH2-2-(C5H4N)}Cl2] was structurally charac-
terized, but no stereochemical discussion was included [23].
Fig. 2. The R, S or meso-isomer of the cation {CoIII(dmgH)2[PhTe(CH2)3SO3Na]2}+
which has point symmetry C2h and is therefore achiral. This meso isomer has two
chemically inequivalent methyl groups.
4.1.2. 125Te NMR spectroscopy
The 125Te NMR of 1.BF4 in D2O was readily observed and the
spectrum show two resonances at 713.4 and 712.3 ppm as ex-
pected from the presence of two diastereomers. The 125Te NMR
lines are considerably broader compared to the ca. 1.5 Hz line-
width of the reference peak of Te2Ph2. In many tellurium com-
pounds, 125Te often shows spin-spin couplings to other nuclei
such as proton, carbon and phosphorus [24]. We were therefore
interested in the observation of its one-bond spin-spin coupling
(1JCo–Te) to the 59Co (I = 7/2) nucleus present in 100% natural abun-
dance. However, due to the rapid quadrupolar relaxation of the
59Co nucleus, we were unable to observe any spin-spin coupling
of 125Te to the cobalt nucleus in all the complexes studied here.
Additionally, the large linewidths of the 125Te resonances of the
Fig. 3. The S,S enantiomer of the cation rac-[CoIII(dmgH)2{PhTe(CH2)3SO3Na}2]+-
which has point symmetry D2 with all dmgH methyl groups equivalent.
leads to diastereomers as shown in Figs. 2 and 3. This consists of a
50% achiral meso isomer and a 50% chiral rac isomer. The rac iso-
mer is 25% S-S and 25% R–R. In the meso isomer, there is a mirror
plane coincident with the CoIII(dmgH)2 moiety but the methyl
groups on each dmgH ligand remain distinct, Mea and Meb. There
Scheme 3.

G. García-Herbosa et al. / Polyhedron 58 (2013) 39–46
43
Fig. 4. Perspective view of complex 1.BF4 with atomic numbering scheme. All
hydrogen atoms have been omitted for clarity.
complexes examined here relative to the reference sample of
Te2Ph2 indicate that those resonances are affected substantially
by quadrupolar interaction with the 59Co nucleus.
Fig. 6. ORTEP diagrams of complex [Co(dmgH)2(py)2][CoCl2(dmgH)2] with atomic
numbering scheme.
Although 59Co has reasonably high sensitivity and cobalt(III)
NMR spectra are readily measured for most cobalt complexes with
high symmetry such as the octahedral K3[Co(CN)6], , the cobalt
NMR resonances are exceedingly broad and sometimes difficult
to observe for unsymmetrical complexes [25]. In fact, the large
electric field gradient and efficient quadrupolar relaxation in com-
plexes 1–3 cause the 59Co NMR peaks to broaden beyond detection
Fig. 5. Perspective view of complex 3 with atomic numbering scheme. All hydrogen atoms have been omitted for clarity.

44
G. García-Herbosa et al. / Polyhedron 58 (2013) 39–46
by 59Co NMR spectroscopy and we were, therefore, unable to ob-
serve 59Co resonances from the complexes containing tellurium di-
rectly bonded to Co(III).
Complex 3 has Co–N bonds with an average distance of 1.886 Å
with a corresponding chelate angle of 81.23o. For a more detailed
description of bond length and angles, please see the CIF files in-
cluded in Supporting Information.
For the ionization isomer [Co(dmgH)2(py)2][CoCl2(dmgH)2], the
separate structures of the cation [Co(dmgH)2(py)2]+ and anion
[CoCl2(dmgH)2]- had been reported previously [27], and the bond
lengths and angles found here are consistent with those reported
for the respective cationic and anionic cobalt(III) bis(dim-
ethylglyoximate) complexes. The metrical parameters for this
structure are provided in the Supporting Information in CIF format.
4.2. Structural characterization in solid
The solid-state molecular structures of the title cobalt-tellurium
compounds meso-1.BF4ꢂ3EtOIH and 3, as well as the ionization iso-
mer [Co(dmgH)2(py)2][CoCl2(dmgH)2] of [CoCl(dmgH)2(py)], were
determined by single-crystal X-ray crystallography. The structures
of these complexes are shown in Figs. 4–6 with important crystal-
lographic parameters in Table 1. All of the structures contain octa-
hedrally coordinated Co(III) with a planar Co(glyoximate)2 moiety
and trans axial ligands.
The asymmetric unit of the cationic complex meso-1.BF4ꢂ3EtOH
contains two half-molecules of the complex in which the Co(III) ion
in each is located on a crystallographic inversion center. The asym-
metric unit also contains three independent Na+ ions, two which
are in crystallographic inversion centers and one in a general posi-
tion, one tetrafluoroborate anion, and four ethanol solvent mole-
cules, two in general positions and two disordered on
crystallographic inversion centers. The neutral complex 3 shows
two coplanar diphenylglyoximate ligands and trans chloride and
Te(p-anisyl)2 ligands. The cobalt(III)-tellurium distances are
2.5872(11) Å and 2.5617(10) in complex 1.BF4 and 2.5252(5) Å in
complex 3 and, although there are no previously reported X-ray
characterized Co(III)–Te complexes, they compare very well with
the distance 2.561 Å found in TePh2 bonded to cobalt in a carbonyl
cluster [26]. In complex 1.BF4, the average Co–N bond distance was
found to be 1.884 Å with a corresponding chelate angle of 81.4o.
4.3. Electronic absorption and DFT calculations
The origin of the intense color of complex 1+, due to a low-en-
ergy band centered at 425 nm (
e
ꢁ 26155 dm3 molꢀ1 cmꢀ1, half
bandwidth ꢁ50 nm) merits some attention as complexes of the
type [Co(dmgH)2LCl], where L is a N or P donor ligand only exhibit
strongly absorbing bands with
cmꢀ1 at wavelengths below 300 nm, corresponding to spin allowed
intraligand (
p⁄) transitions [4a]. Such intense transitions had not
e -
on the order of 104 dm3 molꢀ1
p
–
been noted for reported complexes containing Co–Te bonds [28].
The observed coloration of the title complexes results from impor-
tant changes in the axial metal–ligand interactions that are similar
to the differences seen when going from Ru–Cl to Ru–Sn bonds as
observed in the electronic structure of d6 metal-diimine complexes
[RuCl(Me)(CO)2(iPr-DAB)] and [Ru(SnPh3)(Me)(CO)2(iPr-DAB)]
[29].
In order to shed light on the origin this low energy band
theoretical TD DFT calculations were performed using X-ray
Table 1
Crystal data and structure refinement for complexes meso-1.BF4ꢂ3EtOH, 3 and [Co(dmgH)2(py)2][CoCl2(dmgH)2].
Identification code
meso-1.BF4ꢂ3EtOH
3
[Co(dmgH)2(py)2][CoCl2(dmgH)2]
Empirical formula
Formula weight
T (K)
C32 H54 B Co F4 N4 Na2 O13 S2 Te2 C42 H36 Cl Co N4 O6 Te
C26 H38 Cl2 Co2 N10 O8
807.42
100.0(1)
0.71073
monoclinic
C2/c
1213.83
100.0(1)
0.71073
monoclinic
P2/n
914.73
173.0(5)
0.71073
triclinic
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
ꢀ
P1
13.610(6)
11.214(5)
29.219(13)
90°
97.514(5)
90
10.7835(10)
2.0447(11)
16.5094(15)
104.029(2)
106.321(2)
94.938(2)
1968.9(3)
2
26.684(3)
7.8859(9)
15.8520(19)
90
93.692(3)
90
3328.8(7)
4
a
(°)
b (°)
c
(°)
V (Å3)
4421(3)
4
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mmꢀ1
F (000)
1.824
1.543
1.611
1.220
1664
)
1.876
1.283
2416
920
Crystal color, morphology
Crystal size (mm)
h (°)
orange, needle
0.24 ꢃ 0.16 ꢃ 0.12
1.58–28.28
yellow-orange, needle
0.24 ꢃ 0.12 ꢃ 0.08
1.77–29.57
orange, needle
0.28 ꢃ 0.14 ꢃ 0.06
2.58–37.03
Index ranges
ꢀ18 6 h 6 17, 0 6 k 6 14, 0 6 l 6 38 ꢀ14 6 h 6 14, ꢀ16 6 k 6 16,
ꢀ44 6 h 6 44, ꢀ11 6 k 6 13,
ꢀ26 6 l 6 22
23808
ꢀ22 6 l 6 22
Reflections collected
108737
33520
Independent reflections (Rint
Observed reflections
)
10915 (0.0856)
9556
11029 (0.0600)
7280
8437 (0.0789)
4674
Completeness to theta = 29.57°
Absorption correction
99.1%
Multi-scan
99.9%
Multi-scan
99.4%
Multi-scan
Max. and min. transmission
Refinement method
0.8062 and 0.6616
Full-matrix least-squares on F2
10915/9/608
0.9043 and 0.7483
Full-matrix least-squares on F2
11029/0/498
0.9304 and 0.7263
Full-matrix least-squares on F2
8437/16/291
0.968
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.170
1.024
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0526, wR2 = 0.1193
R1 = 0.0634, wR2 = 0.1221
1.677 and ꢀ1.543
R1 = 0.0492, wR2 = 0.0953
R1 = 0.0844, wR2 = 0.1116
0.638 and ꢀ0.712
R1 = 0.0521, wR2 = 0.1021
R1 = 0.1154, wR2 = 0.1249
0.961 and ꢀ0.635
Largest difference in peak and hole
(e Åꢀ3
)

G. García-Herbosa et al. / Polyhedron 58 (2013) 39–46
45
experimental data of compound 1+, where substituents on tellu-
Appendix A. Supplementary data
rium atoms were simplified to methyl groups. The calculated high-
est value of oscillator strength found is 0.0076 with a transition
energy (singlet) of 457 nm which correspond to the transition LU-
MO HOMO-2. HOMO-2 has p⁄ N–O character and it is situated
on the coordination plane of glyoximate ligands (see figures in
Supplementary Material). The LUMO is mainly composed of p
atomic orbitals of tellurium and a d orbital of cobalt resulting in
r⁄ character. A similar electronic structure with slight differences
in the order of the energy levels has been reported for the d6
octahedral complex [Pt(SnH3)2(CH3)2(iPr-DAB)] [30]. In short, the
intense color of complex 1+ may be assigned to a ligand (p⁄ dmgH
centered) to metal (r⁄ Te–Co–Te centered) charge transfer LMCT
transition.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2012.08.017.
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Acknowledgment
This work was supported by the Office of Basic Energy Sciences,
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