Effect of ligand substituent coordination on the geometry and the electronic structure of Cu(II)-diradical complexes

Article abstract of DOI:10.1021/ic402612v

Two organic moieties, known as ligands, having -OMe and -SePh as the ortho substituent attached to the aniline moiety of the parent 2-anilino-4,6-di-tert- butylphenol ligand, were synthesized. The ligands reacted with CuCl ₂·2H₂O in a 2:1 ratio in CH₃CN in the presence of Et₃N and provided the corresponding mononuclear Cu(II)-diradical complexes 1 (-OMe) and 2 (-SePh). Complex 1 was square planar, while complex 2 was in distorted square planar geometry due to the secondary coordination between the Se atom and the central Cu(II) center. Both complexes were comprised of multi-paramagnetic centers and exhibited an S_t = 1/2 ground state as established by variable-temperature magnetic susceptibility measurements. X-band electron paramagnetic resonance measurements indicated the presence of an unpaired electron at the Cu(II) center in complex 1 and at the ligand center (π-radical) in complex 2. The extent of the secondary interaction was found to be dependent on the softness of the donor atom belonging to the ortho substituent.

Full text of DOI:10.1021/ic402612v

Article
pubs.acs.org/IC
Effect of Ligand Substituent Coordination on the Geometry and the
Electronic Structure of Cu(II)-Diradical Complexes§
Richa Rakshit,†,⊥ Samir Ghorai,†,⊥ Soumava Biswas,‡ and Chandan Mukherjee*,†
†Department of Chemistry, Indian Institute of Technology, Guwahati 781039, Assam, India
‡Indian Institute of Science Education and Research Bhopal, Bhopal 462023, Madhya Pradesh, India
S
* Supporting Information
ABSTRACT: Two organic moieties, known as ligands, having −OMe
and −SePh as the ortho substituent attached to the aniline moiety of the
parent 2-anilino-4,6-di-tert-butylphenol ligand, were synthesized. The
ligands reacted with CuCl2·2H2O in a 2:1 ratio in CH3CN in the
presence of Et3N and provided the corresponding mononuclear Cu(II)-
diradical complexes 1 (−OMe) and 2 (−SePh). Complex 1 was square
planar, while complex 2 was in distorted square planar geometry due to
the secondary coordination between the Se atom and the central Cu(II)
center. Both complexes were comprised of multi-paramagnetic centers
and exhibited an St = 1/2 ground state as established by variable-
temperature magnetic susceptibility measurements. X-band electron
paramagnetic resonance measurements indicated the presence of an
unpaired electron at the Cu(II) center in complex 1 and at the ligand
center (π-radical) in complex 2. The extent of the secondary interaction
was found to be dependent on the “softness” of the donor atom belonging to the ortho substituent.
Scheme 1. Schematic Representations of (a) the Ligand and
the Corresponding Cu(II) Complex Reported by Kaim and
Coworkers, (b) Synthetic Route for H2LOMe and H2LSePh and
Their Corresponding Cu(II)-Diradical Complexes, and (c)
the Possible Different Redox-States of the Ligands
INTRODUCTION
■
Mononuclear Cu(II) ion containing metalloenzyme galastose
oxidase (GOase) selectively catalyzes aerial oxidation of
primary alcohols to their corresponding aldehydes, with
concomitant reduction of molecular oxygen to H2O2.1 Because
of the structural simplicity and high utility as oxidation catalyst,
synthesis of radical(s)-containing Cu(II) complexes as
structural and/or functional models of GOase has drawn
considerable attention.2 In this regard, several Cu(II)-diradical
complexes were synthesized.2a
In those complexes the
,g,i−k
ground state is predominated by a Cu(II)-centered unpaired
electron, which was caused by the stronger antiferromagnetic
coupling between the two radical centers than that between the
Cu(II) and a radical center. Although incorporation of different
functional groups or steric crowding at the ligand backbone
changes the dihedral angle (i.e., the angle between two ligating
O−Cu−N planes, and will be noted here as distortion) around
the Cu(II) center up to 35.5°,2i no alteration in the coupling
,j
fashion between the radicals and the Cu(II) and a radical
centers are known.
In contrast to the conventional coupling fashion, in 2005
Kaim and coworkers2k showed that the presence of a −SMe
substituent at the ligand backbone (at the ortho position of the
aniline moiety, Scheme 1) in a Cu(II)-diradical complex (3)
can alter the coupling fashion; that is, antiferromagnetic
coupling between the two radicals is less than that of the
Cu(II) and a radical. It is proposed that the change in the
coupling fashion is due to the 32.2° dihedral angle between two
ligating O−Cu−N planes, caused by the weak secondary
Received: October 16, 2013
Published: March 21, 2014
© 2014 American Chemical Society
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interaction between the Cu(II) center and the S atom from the
−SMe substituent. However, it is known that Cu(II)-diradical
complex having 35.5° dihedral angle around the Cu(II) center
with no secondary interaction does not alter the coupling
fashion.2j This acute observation indicates that the alteration in
the coupling fashion might not be solely because of the
distortion around the Cu(II) center but is rather possibly due
to the secondary interaction that promotes a geometrical
change in the complex. Because of this change the couplings
fashion, and the coupling magnitude between the paramagnetic
centers might change over. To find out the actual fact, we have
employed two ligands by placing −OMe and −SePh at the
ortho position of the aniline moiety (Scheme 1). We chose
−OMe and −SePh substituted ligand because both of them
could interact with the Cu(II) center. Additionally, on going
from O to Se the “hardness” of the donor atom will decrease
and consequently the Cu−substituent interaction (secondary
coordination) should increase. Hence, the extent of interaction
and its effect on the geometry as well as electronic structure of
the corresponding Cu(II)-diradical complexes can be evaluated.
Herein, we report the synthesis and characterization of ligand
H2LOMe, H2LSePh, and their corresponding Cu(II)-diradical
complexes (Scheme 1). The effect of secondary coordination
on the geometry and the electronic structure of the Cu(II)
complexes are presented.
RESULTS AND DISCUSSION
■
Ligands H2LX (X = −OMe and −SePh) were synthesized by
reacting equimolar amounts of 3,5-di-tert-butylcatechol and the
corresponding amine in the presence of Et3N in hexane
(Scheme 1). Reaction of the individual ligand (H2LOMe or
H2LSePh) with CuCl2·2H2O in a 2:1 ratio in CH3CN in the
presence of Et3N provided the corresponding Cu(II)-diradical
complexes 1 and 2, respectively (Scheme 1). Single crystals for
1 [{CuII(LOMe·)2}·H2O] and 2 [{CuII(LSePh·)2}] were obtained
by recrystallizing the corresponding complex from a 5:2
CH2Cl2/CH3CN solvent mixture. The molecular structures
are presented in Figure 1. Selected bond distances and bond
angles are given in Table 1.
Figure 1. Molecular structure of (a) complex 1 and (b) complex 2;
thermal ellipsoids were drawn at 50% probability. Hydrogen atoms,
solvent molecules, and methyl group attached to the tert-butyl groups
(only in 2) were omitted for clarity.
actual phenyl rings. An alternating short and long C−C bond
distance showed a quinoid-type distortion. This type of
distortion was expected for phenyl ring with its oxidized
form(s) (Scheme 1). Additionally, the C(1)−N(1) = 1.341(4)
[1], 1.349(2) Å [2] and C(2)−O(1) = 1.294(4) [1], 1.293(3)
Å [2] bond distances, which were between their single bond
and double bond character, confirmed one-electron oxidized
iminobenzosemiquinone form {[LX·]−, Scheme 1} of the
In both neutral complexes (1 and 2) the central copper atom
was coordinated by two ligand-centered N as well as O atoms.
Although the Cu(1)−N(1) = 1.935(3) [1], 1.940(3) Å [2]
(brackets indicate the complex) bond distance was almost same
for both complexes and was in accord with the +II oxidation
state of the copper center,2i a remarkable elongation (0.055
−l
coordinating ligands in 1 and 2.2i Therefore, from the X-ray
−l
Å) in Cu−O bond distance {Cu(1)−O(1) = 1.908(3) [1],
1.963(2) Å [2]} due to secondary coordination, Cu(1)−Se(1)
= 3.076(1) Å, was observed in 2. Furthermore, the secondary
coordination caused a large deviation in the O1−Cu(1)−O(1i)
bond angle {180.00(11) [1], 143.79(5)° [2]}. The geometry
around the copper center in 1 was square planar (τ = 0.0°) with
no Cu−OMe (OMe indicates O atom from the −OMe group),
3.513(4) Å, interaction from the two oppositely (trans)
oriented −OMe groups attached at the ortho position of the
aniline moiety (Figure 1). On the contrary, a distorted square
planar geometry (τ = 26.2°), which can also be considered as
pseudo-octahedron, with a large dihedral angle (36.6°) between
the two N(1)−Cu(1)−O(1) planes was observed in 2.
Interestingly, in complex 2, two −SePh groups were situated
cis to each other.
single-crystal analysis, both complexes can be described as
Cu(II)-diradical.
Variable-temperature magnetic susceptibility measurements
for both 1 and 2 are shown in Figure 2 as a plot of μeff versus T.
Both complexes were composed of three paramagnetic centers
with one unpaired electron on each (vide supra). At 10 K, μeff =
1.82 μB (1) and μeff = 1.73 μB (2) were observed (parentheses
indicates the complex). These values were in accord with an S =
1/2 ground state for both complexes and discarded the possible
ferromagnetic coupling among the three paramagnetic centers.
A higher μeff value (>1.73 μB) in 1 was related to the higher g
value (g > 2.00) and indicated that the unpaired electron was
residing on Cu(II) center. The μeff = 1.73 μB value in 2 arose
due to the presence of radical-centered unpaired electron (g =
2.00). In 1, the μeff value remained almost constant up to 150
K, then increased slightly and gradually with the increase in
temperature, and reached at 2.06 μB at 300 K. This feature
The C−C bond distances of the tert-butyl-containing C6
rings in both 1 and 2 were not equal and were falling within the
1.39
0.01 Å range. This indicated that the rings were not
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1/2) and the higher spin state (S = 3/2) as high (>105 cm−1, as
1 K ≈ 0.7 cm−1). In the case of 2, the μeff value started
increasing gradually at 45 K and reached almost to a plateau at
300 K (μeff = 2.62 μB). This feature showed the existence of
energetically low-lying S = 3/2 spin state (∼32 cm−1, as 1 K ≈
0.7 cm−1). The experimental results were simulated (Figure 2)
using the following parameters: [1], gCu(II) = 2.10, gR = 2.00, J12
= J13 = 0.0 cm−1, J23 = −342.0 cm−1, and [2], gCu(II) = 2.03, gR =
2.00, J12 = J13 = −64.0 cm−1, J23 = −23.0 cm−1.3
Table 1. Selected Bond Distances (Å) and Angles (deg) for
Complexes 1 and 2
1
2
Cu1−N1
Cu1−O1
C1−N1
N1−C7
C2−O1
C1−C2
C2−C3
C3−C4
C4−C5
C5−C6
C6−C1
C7−C8
C8−C9
C9−C10
C10−C11
C11−C12
C12−C7
C13−C14
C14−C15
C15−C16
C16−C17
C17−C18
C18−C13
O2−C12
O2−C13
1.935(3)
1.908(3)
1.341(4)
1.421(4)
1.294(4)
1.449(4)
1.424(4)
1.363(4)
1.418(4)
1.371(4)
1.409(4)
1.381(6)
1.375(6)
1.372(7)
1.341(6)
1.390(5)
1.940(3)
1.963(2)
1.349(2)
1.411(3)
1.293(3)
1.453(3)
1.439(3)
1.374(3)
1.430(3)
1.366(3)
1.421(3)
1.404(3)
1.385(3)
1.381(4)
1.368(3)
1.386(3)
1.405(3)
1.383(3)
1.383(4)
1.388(4)
1.356(4)
1.391(4)
1.381(3)
The interactions between the three unpaired electrons will
provide electronic spin states (St, S*) = (3/2, 1), (1/2, 1), and
(1/2, 0), where St = SCu + Srad1 + Srad2 and S* = Srad1 + Srad2
.
These electronic spin states can be symbolically represented as
(↑↑↑), (↑↓↑), and (↑↑↓), respectively. The observed S = 1/2
ground state for both complexes indicated that the electronic
spin state (3/2, 1) was higher in energy compared to the
others. The S = 1/2 ground state could appear due to the
presence of an unpaired electron either on a Cu(II) center or
on a radical center. The ground state electronic configuration
(↑↑↓) would provide Cu(II)-centered electron paramagnetic
resonance (EPR) spectrum, while (↑↓↑) would provide a
radical-centered EPR spectrum. Therefore, to define the exact
location of unpaired electron and ground state electronic
configuration, X-band EPR measurements were performed for
both complexes at 77 K in a 1:1 CH2Cl2/toluene solvent
mixture and depicted in Figure 3.
1.346(5)
1.436(6)
̀
Se1−C12
Se1−C13
1.922(2)
1.923(2)
N1−Cu1−N1i
O1−Cu1−O1i
N1−Cu1−O1
N1−Cu1−O1i
Cu1−N1−C1
Cu1−O1−C2
N1−C1−C2
O1−C2−C1
C12−O2−C13
C12−Se1−C13
180.00(11)
180.00(11)
83.84(11)
96.16(11)
112.6(2)
179.30(6)
143.79(5)
83.29(6)
96.93(6)
113.10(12)
112.24(12)
113.54(16)
117.68(16)
113.20(21)
113.20(28)
117.09(26)
117.28(31)
99.78(9)
Figure 3. Experimental (Exp) X-band EPR spectrum for 1 and 2
presented with simulation (Sim). X-band microwave frequency
(GHz): 9.125 [1], 9.145 [2]; modulation frequency (kHz): 100 [1, 2].
Simulation of the experimental results provided the following
parameters: [1], (g1, g2, g3) = 2.000, 2.025, 2.170, gav = 2.065;
Cu(A1, A2, A3) = (33, 43, 173) × 10−4 cm−1, N(A1, A2, A3) =
(6, 7, 2) × 10−4 cm−1, and [2], (g1, g2, g3) = 1.964, 1.992, 1.992,
gav = 1.983; (A1, A2, A3) = (13, 30, 30) × 10−4 cm−1, Cu(A1, A2,
A3) = (10, 10, 8) × 10−4 cm−1. Complex 1 exhibited a slight
rhombic signal with g|| > g⊥ and gav = 2.065. This type of signal
2
is common for square planar Cu(II) complexes with (dx −y2)1
magnetic orbital.2i,j,l Hence, the (↑↑↓) ground state prevailed in
1 with dominating antiferromagnetic coupling between the
radicals. Unlike complex 1, an axial signal at gav = 1.983 was
observed in complex 2. This indicated a radical-centered
unpaired electron and (↑↓↑) as the ground-state electronic
configuration owning stronger antiferromagnetic coupling
Figure 2. Showing μeff vs T plots for 1 and 2.
consolidated the presence of multi-paramagnetic centers, and
indicated the energy difference between the ground state (S =
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between the Cu(II) and a radical center.2k These results agreed
well with the variable-temperature magnetic susceptibility
measurements. The lower gav value [<2.0023 (free radical)]
in 2 emphasized the fact that spin state with nonzero orbital
angular momentum situated at low energy.4 Herein, it is
important to note that gav = 1.983 in 2 was much lower than
that of gav = 2.0006 observed for the Cu(II)-diradical complex
with −SMe as the ortho substituent (3). This higher gav
deviation from 2.0023 in 2 than in 3 implicated a greater
extent of interaction, due to low energy difference, between the
ground state and the excited state with nonzero orbital angular
momentum. This was possible due to the higher “softness” of
the donor Se atom compared to the donor S atom.
promotes an alteration in the couplings fashion and their
magnitudes between magnetic orbitals.
EXPERIMENTAL SECTION
■
General Considerations. All the chemicals and solvents were
obtained from commercial sources and were used as supplied, unless
noted otherwise. The 3,5-di-tert-butylcatechol, o-anisidine, diphenyl
diselenide, and 2-fluoronitrobenzene were purchased from Sigma-
Aldrich. Solvents were obtained from Merck (India). Air-sensitive
reaction was performed under Ar atmosphere using proper glass
apparatus.
Physical Methods. X-ray crystallographic data were collected
using a Bruker SMART APEX-II CCD diffractometer, equipped with a
fine focus 1.75 kW sealed tube Mo Kα radiation (λ = 0.71073 Å) at
296(2) K, with increasing w (width of 0.3° per frame) at a scan speed
of 3 s/frame. Structures were solved by direct methods using
SHELXS-97 and refined with full-matrix least-squares on F2 using
SHELXL-97.5 All the non-hydrogen atoms were refined anisotropi-
cally.
CONCLUSIONS
■
To conclude, two Cu(II)-diradical complexes were synthesized
by placing −OMe and −SePh as the ortho substituents. Hard
donor O atom did not undergo secondary coordination with
the Cu(II) center, while soft donor Se atom did. Because there
was no secondary coordination, complex 1 was square planar. A
distorted square planar or a pseudo-octahedral geometry was
found in 2 because of the secondary coordination. It was
observed that the higher softness of the donor atom caused (i)
higher secondary coordination [Cu−S = 3.336(av), Cu−Se =
3.076 Å], (ii) more distortion [τ(1, 3, 2) = (0, 32.2,2k 36.6)°],
and (iii) elongation in the Cu−O bond distance with higher
deviation in the O−Cu−O bond angle [{1} = 1.908, 180.0; {3}
= 1.923 (av), 149.7; {2} = 1.963 Å, 143.8°]. Interestingly, no
significant deviation was caused by the secondary coordination
in the N−Cu−N bond angle [{1} = 180.0; {3} = 172.0; {2} =
179.3°].
IR spectra were recorded on Perkin-Elmer instrument at normal
temperature with KBr pellet by grinding the sample with KBr (IR
grade). UV−visible spectra were recorded on Perkin-Elmer, Lamda
750, UV−vis−near-IR spectrometer by preparing a known concen-
tration of the samples in high-performance liquid chromatography
(HPLC) grade CH2Cl2 at room temperature using a cuvette of 1 cm
width. EPR spectra were measured on X-Band Microwave unit, JES-
FA200 ESR spectrometer. Mass spectral (MS) data were obtained
from quadrupole time-of-flight (QTOF)-MS spectrometer. Variable-
temperature magnetic susceptibility measurements were performed
using superconducting quantum interference device (SQUID)
magnetometer at 1 T (1) and 0.1 T (2).
Synthesis of [C21H29NO2], H2LOMe. Synthesis of this ligand was
reported previously.6
Synthesis of [C26H31NOSe], H2LSePh. To a solution of 3,5-di-tert-
butylcatechol (2.54 g, 11.47 mmol) and 2-(phenylselanyl)aniline (2.85
g, 11.47 mmol) in hexane (25 mL), Et3N (0.05 mL) was added. The
resulting solution was stirred for 48 h at room temperature (30 °C). A
dark brown solution was obtained with an orange precipitate. The
mixture was filtered and washed with hexane (10 mL). The brown
filtrate was evaporated in vacuo to give a viscous brown liquid as crude
product. The crude product was purified by column chromatography
on silica gel (60−120 mesh) with ethyl acetate−hexane (1:9) as the
eluent. The product was afforded as yellow viscous liquid. Yield: 2.78
g, 54%. Fourier transform infrared (FTIR) (KBr pellet cm−1): 3433,
In the square planar complex 1 (τ = 0.0°), the radical-
centered magnetic orbitals (pz orbitals) were orthogonal to the
2
Cu(II) {dx −y2} orbital. The two radicals were coupling to each
other through the Cu(II)-centered t2g orbital. This coupling is
strongly antiferromagnetic in nature2l and dominated over the
Cu(II) and a radical center coupling magnitude and provided
(↑↑↓) as the ground state. On the contrary, because of the
secondary interaction a remarkable deviation from the linearity
in the O−Cu−O bond angle occurred in 2 (Table 1). Because
of this deviation, the orthgonality between the radical-centered
and the Cu(II)-centered magnetic orbitals was lost. Thus, an
antiferromagnetic coupling between the magnetic orbitals
appeared. Furthermore, the extent of antiferromagnetic
interaction between the two radical centers was diminished
due to the deviation in the O−Cu−O bond angle. In complex 2
(∠ O−Cu−Oi = 149.7°), the ligand-centered radicals
interacted strongly with the Cu(II)-centered magnetic orbital
and underwent a higher extent of coupling (antiferromagnetic)
than did the two radicals. This caused (↑↓↑) to be the ground
state. Herein, it is important to note that the previously
reported Cu(II)-diradical complex2j having (i) 35.5° dihedral
angle, (ii) no secondary interaction, and (iii) (↑↑↓) as the
ground state shows two cross angles (cross angle = the two
largest angles around the central metal atom in a square planar
complex) as 155.1 and 157.4°. These indicate an almost same
deviation from the linearity in both cross angles, while we
observed almost linearity in one of the two cross angles (Table
1); the other was <150°, to have (↑↓↑) as the ground state.
Hence, it is evident now that the dihedral angle is not the factor
that alters the couplings fashion. It is mainly the secondary
coordination that causes a geometrical change in terms of the
deviation only in one of the two cross angles, and consequently
1
3322, 2956, 2905, 2867, 1583, 1476, 1362, 1309, 1021, 734, 689. H
NMR (CDCl3, 399.85 MHz): δ 1.21 (s, 9H), 1.39 (s, 9H), 6.04 (s,
1H), 6.06 (s, 1H), 6.48 (dd, J = 8.4, 0.8 Hz, 1H), 6.77 (d, J = 2 Hz,
1H), 6.81 (dt, J = 7.2, 1.2 Hz, 1H), 7.19−7.30 (m, 7H), 7.71 (dd, J =
7.6, 1.6 Hz, 1H) ppm. 13C NMR (CDCl3, 75.47 MHz): δ 29.5, 31.6,
34.4, 35.0, 109.8, 114.0, 114.7, 119.8, 122.1, 122.5, 126.7, 127.1, 129.3,
129.5, 129.6, 131.3, 131.1, 135.3, 138.4, 142.3, 148.5, 149.7 ppm. ESI-
MS (+) m/z for [C26H31NOSe + H]+: Calcd, 454.1703; found,
454.1679. Anal. Calcd for C26H31NOSe: C, 68.85; H, 6.89; N, 3.10.
Found: C, 68.66; H, 7.09; N, 3.20%.
Synthesis of [C42H54CuN2O4·H2O], 1. To a stirred solution of
H2LOMe (0.328 g, 1.00 mmol) in CH3CN (20 mL), CuCl2·2H2O
(0.090 g, 0.53 mmol) and Et3N (0.2 mL) were added sequentially. The
reaction mixture was stirred for 2.5 h at room temperature. This
caused a brown-black precipitation. The precipitate was filtered and
washed with CH3CN. Recrystallization of the solid from a CH2Cl2/
CH3CN (5:2) solvent mixture provided a crystalline compound
suitable for single-crystal X-ray diffraction study. Yield: 0.204 g, 56%.
FTIR (KBr pellet, cm−1): 3434, 3071, 2956, 2906, 2867, 2853, 1580,
1508, 1490, 1463, 1435, 1422, 1387, 1360, 1333, 1301, 1256, 1244,
1204, 1174, 1113, 1043, 1025, 996, 926, 911, 881, 787, 775, 746, 693,
644, 604, 500. ESI-MS (+) m/z for [C42H54CuN2O4]+: Calcd, 713.35;
found, 713.37. UV−vis−NIR (CH2Cl2) λmax, nm (ε, M−1 cm−1):
1030(2600), 780(6750), 472(5600), 340(17 200), 305(20 050). Anal.
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Calcd for C42H54CuN2O4·0.7H2O: C, 69.43; H, 7.69; N, 3.86. Found:
C, 69.84; H, 7.47; N, 3.89%.
C.; Pieper, U.; Bothe, E.; Bachler, V.; Bill, E.; Weyhermuller, T.;
Chaudhuri, P. Inorg. Chem. 2008, 47, 8943. (j) Mukherjee, C.;
̈
Synthesis of [C52H58CuN2O2Se2], 2. To a solution of H2LSePh (0.305
g, 0.67 mmol) in CH3CN (10 mL), CuCl2·2H2O (0.062 g, 0.35
mmol) was added followed by addition of Et3N (0.1 mL). The
reaction solution was then stirred for 16 h. This caused precipitation of
a black solid. The solid was washed with CH3CN and then dried under
air. The solid was then recrystallized from a 5:1 CH2Cl2/CH3CN
solvent mixture. A brown-black crystalline solid suitable for single-
crystal X-ray study appeared in 2 d. Yield: 0.200 g, 55%. FTIR (KBr
pellet, cm−1): 3429, 2949, 2904, 2866, 1462, 1424, 1250, 1022, 739,
687. ESI-MS (+) m/z for [C52H58CuN2O2Se2]+: Calcd, 965.23; found,
965.23. UV−vis−NIR (CH2Cl2) λmax, nm (ε, M−1 cm−1): 1036(2900),
806(6050), 460(5850), 342(18 250), 294(23 650). Anal. Calcd for
C52H58CuN2O2Se2: C, 64.65; H, 6.06; N, 2.90. Found: C, 64.28; H,
6.14; N, 2.73%.
Weyhermuller, T.; Bothe, E.; Chaudhuri, P. Inorg. Chem. 2008, 47,
11620. (k) Ye, S.; Sarkar, B.; Lissner, F.; Schleid, T.; van Slageren, J.;
Fiedler, J.; Kaim, W. Angew. Chem., Int. Ed. 2005, 44, 2103.
̈
(l) Chaudhuri, P.; Verani, C. N.; Bill, E.; Bothe, E.; Weyhermuller,
̈
T.; Wieghardt, K. J. Am. Chem. Soc. 2001, 123, 2213. (m) Schnepf, R.;
Sokolowski, A.; Muller, J.; Bachler, V.; Wieghardt, K.; Hildebrandt, P.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Details of crystallographic structural parameters for 1 and 2.
This material is available free of charge via the Internet at
http://pubs.acs.org. CCDC 935848 (1·1H2O) and CCDC
926557 (2) contain the supplementary crystallographic data for
this Paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
2005, 44, 5559. (w) Mukherjee, C.; Weyhermuller, T.; Bothe, E.;
̈
Chaudhuri, P. C. R. Chim. 2007, 10, 313. (x) Mukherjee, C.;
Weyhermuller, T.; Wieghardt, K.; Chaudhuri, P. Dalton Trans. 2006,
̈
2169. (y) Ghorai, S.; Mukherjee, C. Dalton Trans. 2014, 43, 2169.
(3) The simulations of the experimental results indicated that a
unique value for coupling constant J12, J13, and J23 (Figure 2, inset)
cannot be achieved; that is, J12, J13, and J23 can be varied to reproduce
the experimental result. In the case of 1 we observed Cu(II)-centered
ground state, and that is why we chose antiferromagnetic coupling (J23
= −342.0 cm−1) between two radical centers keeping J12 = J13 = 0.0
cm−1. Because we had a radical-centered ground state we kept
antiferromagnetic coupling between Cu and radicals higher than that
of radicals.
AUTHOR INFORMATION
Corresponding Author
*E−mail: cmukherjee@iitg.ernet.in.
■
Author Contributions
⊥R.R. and S.G. contributed equally.
(4) Kaim, W. Coord. Chem. Rev. 1987, 76, 187.
(5) Sheldrick, G. M. SHELXL−97;University of Gottingen:
̈
Notes
Gottingen, Germany, 1997.
̈
The authors declare no competing financial interest.
(6) Ghorai, S.; Mukherjee, C. Chem. Commun. 2012, 48, 10180.
ACKNOWLEDGMENTS
■
This project is funded by DST (SR/FT/CS−86/2011) and
BRNS (2012/37C/28/BRNS/1375). R.R. thanks IIT Guwahati
and S.G. thanks UGC (India) for doctoral fellowship.
DEDICATION
■
§Dedicated to Prof. Dr. Phalguni Chaudhuri on the occasion of
his 70th birthday.
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