IC 2013 CrTol2

Full text

Bis(toluene)chromium(I) [1,2,5]Thiadiazolo[3,4‑c][1,2,5]thiadiazolidyl
and [1,2,5]Thiadiazolo[3,4‑b]pyrazinidyl: New Heterospin (S1=S2=
1/2) Radical-Ion Salts
Nikolay A. Semenov,
†
Nikolay A. Pushkarevsky,
‡,§
Elizaveta A. Suturina,
⊥,∥
Elena A. Chulanova,
§,⊥
Natalia V. Kuratieva,
‡
Artem S. Bogomyakov,
¶
Irina G. Irtegova,
†
Nadezhda V. Vasilieva,
†
Lidia S. Konstantinova,
▽
Nina P. Gritsan,*
,⊥,∥
Oleg A. Rakitin,
▽
Victor I. Ovcharenko,
¶
Sergey N. Konchenko,
‡
and Andrey V. Zibarev*
,†,∥
†
Institute of Organic Chemistry,
‡
Institute of Inorganic Chemistry,
⊥
Institute of Chemical Kinetics and Combustion, and
¶
International Tomography Center, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia
§
Department of Natural Sciences and
∥
Department of Physics, National Research University−Novosibirsk State University, 630090
Novosibirsk, Russia
▽
Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russia
*
SSupporting Information
ABSTRACT: Bis(toluene)chromium(0), Cr0(η6-C7H8)2(3),
readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1)
and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran
solvent with the formation of heterospin, S1=S2=1/2, radical-
ion salts [3]+[1]−(4) and [3]+[2]−(5) isolated in high yields.
The salts 4and 5were characterized by single-crystal X-ray
diffraction (XRD), solution and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the
temperature range 2−300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast
to 4,in5anions were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were
calculated using the CASSCF/NEVPT2 and broken-symmetry density functional theory approaches, and the complex magnetic
motifs featuring the dominance of antiferromagnetic (AF) interactions were revealed. The experimental χTtemperature
dependences of the salts were simulated using the Van Vleck formula and a diagonalization of the matrix of the Heisenberg spin
Hamiltonian for the clusters of 12 paramagnetic species with periodic boundary conditions. According to the calculations and χT
temperature dependence simulation, a simplified magnetic model can be suggested for the salt 4with AF interactions between
the anions ([1]−···[1]−,J1=−5.77 cm−1) and anions and cations ([1]−···[3]+,J2=−0.84 cm−1). The magnetic structure of the
salt 5is much more complex and can be characterized by AF interactions between the anions, [2]−···[2]−, and by both AF and
ferromagnetic (FM) interactions between the anions and cations, [2]−···[3]+. The contribution from FM interactions to the
magnetic properties of the salt 5is in qualitative agreement with the positive value of the Weiss constant Θ(0.4 K), whereas for
salt 4, the constant is negative (−7.1 K).
■INTRODUCTION
Despite rapid progress in the design, synthesis, and structural
and functional characterization of molecule-based magnetic and
conductive materials for electronics and spintronics, there is a
permanent demand for new building blocks in the field.
1
A
large number of candidate building blocks came from
chalcogen−nitrogen chemistry,
2
especially in the form of
neutral and charged π-heterocyclic radicals.
3−8
Derivatives of the 1,2,5-chalcogenadiazole ring system (Chart
1)
2
can be easily reduced into radical anions (RAs),
8
and the
latter can be isolated in the form of thermally stable crystalline
salts.
7
The salts, both homospin (where only anions were
paramagnetic) and heterospin (where both ions were para-
magnetic), revealed antiferromagnetic (AF) interactions in their
spin systems.
7
With the McConnell I model
9
dealing with spin polarization,
this result is expected for the homospin salts. In these salts, the
spin density on the van der Waals (VdW) surfaces of their RAs
is mostly positive, with only small islands of negative spin
Received: March 20, 2013
Published: May 21, 2013
Chart 1. Archetypal 1,2,5-Chalcogenadiazoles and Their
RAs, 1 and 2
Article
pubs.acs.org/IC
© 2013 American Chemical Society 6654 dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−6663

density.
10
For neighboring RAs in the crystal lattice, contacts of
like spin density are most probable to give rise to AF exchange
interactions between them, whereas for ferromagnetic (FM)
interactions, contacts of unlike spin density are required
9
[except contacts of unlike density on orthogonal molecular
orbitals (MOs) leading to AF interactions].
9a
In principle, such
a situation can be achieved with heterospin salts of the
discussed RAs, with paramagnetic cations [MCp2]+and
[MCp*2]+[M = Cr, Mn, Fe; Cp = η5-C5H5;Cp*=η5-
C5(CH3)5] possessing peripheral negative spin density on the
ligands.
11
However, heterospin, S1=3/2and S2=1/2, salt
[CrCp*2]+[1]−(for 1, see Chart 1) experimentally revealed
only AF effects.
7c
A theoretical study based on the CASSCF
and spin-unrestricted broken-symmetry (BS) density functional
theory (DFT) calculations led to the conclusion that the
magnetic properties of the salt are controlled by its crystal
packing, which is favorable for anion−anion and cation−cation
AF interactions and unfavorable for anion−cation FM
interactions.
7
For the design and synthesis of magnetic materials, it is
important that heterospin systems can also be obtained with
neutral radicals when they crystallize in the asymmetric unit
containing more than one radical. For such heterospin systems,
based on S−Nπ-heterocyclic radicals, AF and spin-canted AF
effects were observed.
3d,e
It should be noted that currently systems with AF
interactions are receiving increased attention because of the
experimental observation of the spin-liquid state, as well as their
prospects in creating nanoscale memory cells.
12
According to our calculations (see below), another group of
paramagnetic (S=1/2) cations with peripheral negative spin
density on ligands consists of [MAr2]+(M = Cr, Mo, W). In the
chemical context, it is important that (1) the ionization energy
(IE) of their precursors MAr2(reducing agents in the target
salts’preparations)
13
can be varied in a rather broad range
depending on the ring substituents (for example, the bigger the
number of methyl substituents, the lower the IE) and
14
(2)
with the same Ar ligands, the IE is practically equal for M = Cr
(3d), Mo (4d), and W (5d) (with Ar = C6H6, in 5.40−5.52 eV
range),
14
allowing one to cover the whole d block in a single
approach. In the physical context, the cations with Mo and W
are especially promising because of the strong spin−orbit
coupling inherent in these heavy atoms. The strength of the
spin−orbit coupling increases sharply with the atomic number
as Z4to be sufficient for atoms with Z> 30. In the heterospin
salts containing Mo (Z= 42) or W (Z= 74) atoms in the
cation and heavier chalcogen Se (Z= 34) or Te (Z= 52) atoms
in the anion, the strong spin−orbit coupling can lead to spin
canting to originate a FM ground state even under conditions
of AF exchange interactions between paramagnetic centers (the
Dzyaloshinsky−Moriya mechanism;
9b,15
the spin−orbit con-
tribution to spin-canted AF and FM ordering of Se−Nπ-
heterocyclic radicals was already discussed
3f,g
). An important
spectroscopic advantage is that in contrast to the [CrCp*2]+
cation, which is undetectable by electron paramagnetic
resonance (EPR) spectroscopy because of the fast relaxation
and substantial zero-field splitting,
16
[MAr2]+(M = Cr, Mo)
cations can be detected by conventional EPR techniques.
16,17
Previously, various CrAr2were used in the synthesis of
radical-ion salts with tetracyanoethylene (TCNE) and 7,7,8,8-
tetracyanoquinodimethane (TCNQ). The salts obtained were
homospin because only the [CrAr2]+cations were paramagnetic
(S=1/2), whereas the anions formed diamagnetic (S=0)
dimers.
18
This work begins the application of MAr2(M = Cr, Mo, W)
compounds to the synthesis of heterospin, S1=1/2and S2=1/2,
radical-ion salts based on 1,2,5-chalcogenadiazoles and related
chalcogen−Nπheterocycles. Herein we report on the synthesis
and structural and magnetic characterization of two salts
obtained by the reduction of [1,2,5]thiadiazolo[3,4-c][1,2,5]-
thiadiazole and [1,2,5]thiadiazolo[3,4-b]pyrazine (1and 2,
respectively; Chart 1) with bis(toluene)chromium(0) (3)as
salts bis(toluene)chromium(I) [1,2,5]thiadiazolo[3,4-c][1,2,5]-
thiadiazolidyl (4) and [1,2,5]thiadiazolo[3,4-b]pyrazinidyl (5),
respectively (Scheme 1).
■EXPERIMENTAL AND COMPUTATIONAL DETAILS
General Procedure. All operations were carried out under argon
using glovebox and Schlenk techniques. Compounds 1and 2were
prepared by literature methods.
19,20
Compound 3was synthesized by a
known procedure
21
with toluene instead of benzene. Solvents were
dried by common methods and distilled under argon.
Cyclic Voltammetry (CV). The CV measurements on degassed 2
×10−3M solutions of compound 2in MeCN were performed at 295
K in an argon atmosphere with a PG 310 USB potentiostat (HEKA
Elektronik). The measurements were carried out in a mode of a
triangular pulse potential sweep in a three-electrode electrochemical
cell (V=5cm
3) at a stationary platinum electrode (S=8mm
2), with
0.1 M Et4NClO4as the supporting electrolyte. The sweep rates were
0.01−100 V s−1, and the peak potentials were quoted with reference to
a saturated calomel electrode (SCE) used in the measurements as a
standard.
EPR Measurements. The solid-state and solution EPR spectra of
salts 4and 5were recorded on a ELEXSYS-II E500/540 spectrometer
(X-band, MW frequency 9.87 GHz, MW power 1 mW, modulation
frequency 100 kHz, and modulation amplitude 0.005 mT) equipped
with a high-Qcylindrical resonator ER4119HS. Numerical simulations
of the experimental EPR spectra were performed with the Winsim
2002 program
22
using the Simplex algorithm for optimization of
hyperfine coupling (hfc) constants and line widths.
Crystallographic Analysis. The single-crystal X-ray diffraction
(XRD) data for compound 2and salts 4and 5(Table 1) were
collected with a Bruker DUO APEX diffractometer equipped with a
4K CCD area detector at 150 K with graphite-monochromatized Mo
Kαirradiation (λ= 0.71073 Å). The φ-scan technique was employed
to measure intensities. Absorption corrections were applied using the
SADABS program.
23
The crystal structures were solved by direct
methods and refined by full-matrix least-squares techniques with use of
the SHELXTL package.
24
Atomic thermal parameters for non-H atoms
were refined anisotropically. The positions of the H atoms were
localized from the difference maps and refined using the riding model.
The obtained crystal structures were analyzed for distances between
ions by means of the PLATON and MERCURY programs.
25
The XRD
geometries were used in quantum-chemical modeling magnetic
properties of the salts.
CCDC 921742 (2), CCDC 921740 (4), and CCDC 921741 (5)
contain the supplementary crystallographic data for this paper. These
Scheme 1. Synthesis of 4 and 5
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636655

data can be obtained free of charge from The Cambridge
Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/
cif.
Magnetic Measurements and Simulations. The magnetic
susceptibility measurements on the salts 4and 5were performed
with an MPMS-XL Quantum Design SQUID magnetometer in the
temperature range 2−300 K in magnetic fields of 500, 1000, 3000, and
5000 Oe. Invariance to the field evidenced the absence of FM
impurities in the samples. To calculate the molar magnetic
susceptibility (χ) of the salts 4and 5, the diamagnetic corrections
were estimated using Pascal’s constants.
26
The temperature dependences of χwere simulated using the Van
Vleck formula and a diagonalization of the matrix of the Heisenberg
spin Hamiltonian for the clusters of 12−16 paramagnetic species.
9b,27
All Jvalues reported herein are based on the phenomenological spin
Hamiltonian of the form in eq 1.
∑
=−  
H
JSS2
ij
N
ij ij
,(1)
Quantum-Chemical Calculations. Parameters of the Heisenberg
spin Hamiltonian (eq 1), viz., the pair exchange coupling constants Jij,
were calculated quantum chemically via the energy splitting between
the singlet and triplet states of the pairs of paramagnetic species with S
=1/2. Earlier, we demonstrated that the exchange parameters Jfor the
pairs of 1,2,5-chalcogenadiazolidyl-type RAs calculated using the spin-
unrestricted BS approach
28
at the UB3LYP level of theory
29
are in
good agreement with the experiment.
7
In this paper, parameters Jwere
also calculated using the BS approach
28
at the UB3LYP level with the
def2-TZVP basis set
30
using the ORCA program package.
31
Some
estimations were done with the smaller def2-SVP basis set.
32
The J
values were calculated according to the formula (2),
33
=− −
⟨⟩ −⟨⟩
JEE
SS
()
HS
BS
LS
2HS 2
BS
LS (2)
where EHS is the energy of the high-spin state of the pair and EBS
LS is the
energy of the low-spin state within the BS approach.
28
The accuracy of
the energy calculations (self-consistent procedure) was chosen to be
10−8H, which provided values for Jwith an accuracy of 0.004 cm−1.
Previously for salt [CrCp*2]+[1]−, for the pairs formed by RAs and
cations, the Jvalues calculated using the BS approach were
nonrealistically large and the multiconfiguration CASSCF method
was employed instead.
7
In this paper, we also were unable to obtain
the correct solutions for the BS states of the anion−cation pairs. Thus,
the CASSCF and CASSCF/NEVPT2
34
procedures realized in the
ORCA suit of programs
31
were also employed for calculations of the
singlet−triplet splitting (ΔEST =2J). In these calculations, the def2-
TZVP and smaller def2-SVP bases sets were used.
The ground-state gtensor and energies of a series of electronically
excited states (doublets and quartets) of the bis(toluene)chromium(I)
[3]+were calculated at the CASSF/RASSI/SINGLE-ANISO level
35
with the ANO-RCC basis set
36
using the MOLCAS7.6 suit of
programs.
37
Relativistic effects were taken into account based on the
Douglas−Kroll Hess Hamiltonian.
38
The active space of the CASSCF
calculations (Supporting Information, Figure S1) included nine
electrons in nine orbitals: five d atomic orbitals (AOs) of Cr and
two π-bonding and two π*-antibonding MOs of the toluene ligands,
which are mixed with d AOs of Cr (3d5configuration). A total of 1
sextet, 24 quartet, and 75 doublet spin states obtained in the CASSCF
calculations were mixed by spin−orbit coupling, giving rise to 252
spin−orbit states using the RASSI module.
35a,b
Finally, the gtensor of
the lowest Kramers doublet was computed using the SINGLE ANISO
module
35c
of the MOLCAS7.6 program package.
37
The gtensors for
all paramagnetic species under study were also computed by the
B3LYP/DKH method using the EPR/NMR module
39
of the ORCA
program package.
31
Syntheses. Compound 4.At −30 °C, a solution of 0.177 g (0.75
mmol) of 3in 5 mL of tetrahydrofuran (THF) was added dropwise for
10 min to a stirred solution of 0.108 g (0.75 mmol) of 1in 5 mL of
THF. The precipitate was filtered off, washed with cold THF, and
dried under vacuum. Compound 4was obtained in the form of dark-
red crystals, 0.246 g (86%). Found (calcd for C16H16CrN4S2): C, 49.9
(50.5); H, 4.3 (4.2); N, 14.3 (14.7); S, 16.5 (16.9). Single crystals
suitable for XRD were picked from the bulk of the crystals.
Compound 5.At 0 °C, a solution of 0.095 g (0.40 mmol) of 3in 5
mL of THF was gradually added for 10 min to a stirred solution of
0.055 g (0.40 mmol) of 2in 5 mL of THF. The olive-green solution
Table 1. Crystallographic Data for Compounds 2, 4, and 5
245
chemical formula C4H2N4SC
16H16CrN4S2C18H18CrN4S
fw 138.16 380.45 374.42
T(°C) −123 −123 −123
λ(Å) 0.71073 0.71073 0.71073
space group P21/n(No. 14) C2/c(No. 15) C2/c(No. 15)
a(Å) 11.8139(12) 12.3474(5) 20.2956(7)
b(Å) 3.8646(3) 9.9269(4) 7.2961(2)
c(Å) 23.228(2) 13.0243(5) 14.5246(9)
β(deg) 95.985(2) 105.934(1) 131.325(1)
V(Å3) 1054.70(17) 1535.07(11) 1615.19(12)
Z,dcalc (g cm−3) 8, 1.740 4, 1.646 4, 1.540
μ(cm−1) 0.499 1.021 0.844
final Rindices [I
>2σ(I)]
a
R1 = 0.0595,
wR2 = 0.1632 R1 = 0.0228,
wR2 = 0.0656 R1 = 0.0276,
wR2 = 0.0752
a
R1 = ∑||Fo|−|Fc||/∑|Fo|;wR2={∑[w(Fo2−Fc2)2]/
∑[w(Fo2)2]}1/2.
Figure 1. CV of compound 2at a potential sweep rate of 0.1 V s−1(left) and experimental (1) and simulated (2) EPR spectra of its RA in
acetonitrile (right). Experimental (calculated at the UB3LYP/def2-TZVP level) hfc constants (mT): aH(H4,H5) = 0.338 (0.302), aN1(N2,N7) = 0.332
(0.271), aN2(N3,N6) = 0.325 (0.229); g= 2.002863 (2.0055). Previously reported hfc constants (mT) from reduction with elemental K: aH(2H) =
0.325, aN1(2N) = 0.340, aN2(2N) = 0.325.
8f
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636656

was filtered and slowly evaporated. Compound 5was obtained in the
form of dark needlelike crystals suitable for XRD, 0.140 g (95%).
Found (calcd for C18H18CrN4S): C, 57.1 (57.7); H, 4.7 (4.9); N, 14.6
(15.0); S, 8.3 (8.6).
■RESULTS AND DISCUSSION
Compounds 1
7
and 2(Supporting Information, Figure S2) are
10π-electron heteroaromatics possessing planar molecular
structures. They easily form persistent RAs
8f
under conditions
of chemical or electrochemical reduction. In MeCN, the
electrochemical −1/0 potentials of 1and 2vs SCE are −0.59
7
and −0.87 V (Figure 1), respectively. The electrochemically
generated RAs of 1
7
and 2(Figure 1) are persistent and are
characterized by EPR in combination with DFT calculations.
Reduction of heterocycles 1and 2with compound 3
(Scheme 1) gave the salts 4and 5, respectively, whose
structures were confirmed by XRD (Figures 2 and 3).
Bis(benzene)chromium(0) reacted similarly; however, single
crystals suitable for XRD were not obtained in both cases.
The structure of salt 4is composed of pillars of alternating
cations and RAs, spread along the (1, 0, −1) direction (Figure
2). The anions as well as toluene ligands of the cations are
nearly perpendicular to the pillar axis, with their mean planes
deflecting by less than 5.2°from the perpendicular plane.
Similar moieties in a pillar are symmetrically equivalent, and the
distance between the cation (centroid of the toluene C6 ring)
and RA (middle of the C−C bond) is 3.53 Å. The centers of
the RAs lie on the mean pillar axis, while the cations are shifted
to the side of it in an alternating manner (0.67 Å to the Cr
atoms). The pillars are stacked in a hexagonal motif across their
spreading direction, whereupon the RAs adjoin the cations of
four of six adjacent pillars, and vice versa.
Despite the fact that molecule 2has nearly the same size and
volume as molecule 1, the stacked motif is absent in the crystal
lattice of 5; instead, the cations and RAs alternate in a layered
motif across the caxis (Figure 3). The RAs lie close to the
mean plane of the layer: individual molecules are inclined by
∼10°offthe plane. In contrast, the toluene ligands form an
angle of ∼63°with this plane, thus forming a relatively loose
cationic layer. The anionic layer is packed in a square-tiled
motif, which reminds us that of anion packing in 4, but unlike
the structure of 4, the cations are out of the plane,
approximately over the centers of the squares, formed by four
adjacent RAs. The RAs of two adjacent layers are not placed
over one another (as in 4) but taking two alternating positions;
Figure 2. Crystal structure of the salt 4(H atoms are not shown).
Pillars of cations and RAs alternating along the (1, 0, −1) axis (a) and
view across the pillar axis (b; only one layer of ions is shown).
Figure 3. Crystal structure of the salt 5(H atoms are not shown;
disordered RAs are shown in arbitrary directions). Layers of cations
and RAs alternating across the caxis (a; rear molecules are faded) and
view across the layers (b; only one layer of RAs is shown, and
foreground cations are faded).
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636657

the interlayer distance is ∼7.26 Å. Hence, the energy of the
crystal packing may be less in 5compared with that in 4, which
is indirectly supported by noticeably better solubility of 5in
organic solvents such as THF and MeCN. The RAs are
statistically disordered by the inversion centers located in the
center of the middle C−C bond.
Salts 4and 5are EPR-active in both the solid state and
solution. Solutions in N,N-dimethylformamide (DMF) and
MeCN are stable for several days at ambient temperature, both
paramagnetic ions are seen in a 1:1 molar ratio, and the g-factor
and hfc constants obtained for cation [3]+are close to the
values measured previously
40
(Figures 4 and 5). In contrast, in
better-resolved spectra of the salts’solutions in THF, the
intensity of the RA signals decreases relatively fast (Supporting
Information, Figure S3), and the salts cannot be recovered from
the solutions by precipitation with hexane. The reasons for this
are unclear. The solvent-dependent disproportionation, for
example, 2[1]−↔1+[1]2−, is hardly possible because the
equilibrium constant estimated under CV conditions in MeCN
is extremely low.
7d
The EPR spectra of polycrystalline samples of the salts 4and
5are broad singlets (Figures 4 and 5).
In the crystal state (Figures 2 and 3), the structures of cation
[3]+are slightly different, possessing C2symmetry in the salt 4
and Cisymmetry in the salt 5(Figure 6). DFT calculations
reproduce fairly well the gfactors of the RAs and cations: giso is
equal to 2.0073 and 2.0055 for [1]−and [2]−, respectively, and
1.9879 and 1.9883 for the C2and Cistructures of [3]+.giso =
1.9818 calculated for the C2structure of [3]+at the CASSCF/
RASSI/SINGLE-ANISO level
35
is also in good agreement with
the experiment. To calculate this gfactor, the energies of the
ground-state and 99 excited-state multiplets were computed at
the CASSCF level. The ground state of [3]+is the doublet
state, with the main contribution from the configuration with
an unpaired electron located at the 3dz2AO (Supporting
Information, Figure S1; MO labeled as 3). The two lowest
excited doublet states are higher in energy by 10622 and 10999
cm−1. Excitations to these states consist mainly of electron
promotion from doubly occupied dxy or dx2−y2AOs mixed with
π-bonding MOs (Supporting Information, Figure S4; MOs
labeled as 2 and 5) to singly occupied dz2AOs. These low-
energy doublets are followed by four quartet states with
energies in the range 15870−16520 cm−1.
The spin-density distribution at the VdW surfaces of
paramagnetic ions [1]−,[2]−, and [3]+(with two slightly
different geometries) was calculated at the UB3LYP/def2-
TZVP level of theory (Figure 6). It is seen that the spin density
at the VdW surfaces of RAs is mostly positive with an island of
negative spin density in the vicinity of the C−C bond common
for both cycles. The spin density at the VdW surface of cations
[3]+is close to zero; however, with the cyclic islands of negative
values in the vicinity of the rings’C atoms. The magnetic
properties of the salts are therefore controlled by the way in
which these ions are packed in the crystal.
Figure 7 displays the temperature dependences of the molar
magnetic susceptibility (χ) for the salts 4and 5represented in
the form of product χT. The decrease of χTwith decreasing
temperature indicates the dominance of weak AF interactions
between the paramagnetic centers of both salts.
The effective magnetic moments of the salts (μeff) were
calculated using eq 3:
μ
βχχ=≈
⎛
⎝
⎜⎞
⎠
⎟
k
NTT
3(8 )
eff 2
1/2
1/2
(3)
For both salts at 300 K, μeff = 2.38 μB, which is close to the 2.45
μBexpected for systems of two noncorrelated spins S1=S2=
1/2and g= 2. In this case, χTapproaches the value of
[g12S1(S1+1)+g22S2(S2+ 1)]/8 ≅0.75 cm3K mol−1.
Treatment of the experimental magnetic data in terms of the
Curie−Weiss law demonstrated that for both salts the
dependence 1/χ(T) obeys the law in the temperature range
∼300−50 K and then deviates from linearity (Figure 7). The
Curie−Weiss parameters Cand Θare 0.71 cm3K mol−1and
−7.1 K for 4and 0.70 cm3K mol−1and 0.4 K for 5,
respectively. The values of Care in good agreement with the
theoretical spin-only value 0.75 cm3K mol−1for both salts 4
and 5. The positive value of Θin the case of salt 5is an
indication of the contribution of FM interactions in the spin
system of this salt.
To enable an understanding at the molecular level and
simulation of the magnetic properties of the salts 4and 5, the
pair exchange interactions between ions were calculated for the
XRD structures (Figures 2 and 3).
Figure 4. Left: Experimental EPR spectrum of the salt 4in a DMF
solution (1) and its simulation (2). Hfc constants (mT): 0.314 (4N),
0.349 (10H), 0.074 (2CH3). Line widths are 0.137 and 0.150 mT for
[1]−and [3]+, respectively, with a [1]−/[3]+molar ratio of 51:49; g=
2.0093 and 1.9884, respectively. Right: Experimental EPR spectrum in
the solid state.
Figure 5. Left: Experimental EPR spectrum of the salt 5in a DMF
solution (1) and its simulation (2). Hfc constants (mT): 0.328 (2N),
0.325 (2N), 0.328 (2H), 0.348 (10H), 0.078 (2CH3). Line widths are
0.067 and 0.094 mT for [2]−and [3]+, respectively, with a [2]−/[3]+
molar ratio of 48:52. Right: Experimental EPR spectrum in the solid
state.
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636658

In the crystals of 4, all RAs [1]−are structurally equivalent,
and every RA has 10 nearest-neighboring RAs. These 10
nearest neighbors give only five unique pairs [1]−···[1]−, with
shortest S···S distances in the range 3.98−8.21 Å (Supporting
Information, Figure S4). The calculated values of the exchange
parameters (Jij) for these pairs are presented in Table 2.
According to these data, coupling with nearest neighbors at
distances of more than 5 Å can be neglected.
Every cation [3]+has six nearest-neighboring RAs, which
give only three unique pairs [1]−···[3]+, with shortest Cr···S
distances in the range 4.76−5.94 Å (Supporting Information,
Figure S5). As mentioned above, we did not obtain correct
solutions for BS states of the pairs [1]−···[3]+, and only the
results of multiconfiguration calculations are presented in Table
3. The Jvalues for the pairs [3]+···[3]+, with the Cr−Cr
distances in the range 7.46−7.92 Å, were calculated at the
B3LYP/def2-SVP level and found to be small enough (−0.25
and 0.07 cm−1).
The calculated Jvalues for the pairs [1]−···[1]−(Table 2)
demonstrate that all methods employed here gave qualitatively
similar results because they revealed only AF exchange
interactions, with one pair being significantly stronger than
the others. As previously,
7
the CASSCF calculations predict
significantly smaller Jvalues for [1]−···[1]−pairs than B3LYP
calculations. Note that the results of more accurate CASSCF/
Figure 6. Structures (top; color code: yellow, S; blue, N; gray, C; light blue, Cr; light gray, H) and spin-density distributions at the VdW surfaces
(bottom) of the ions of salts 4(left) and 5(right) from UB3LYP/def2-TZVP calculations.
Figure 7. Experimental temperature dependences of χT(○) and 1/χ(□) for the salts 4(A) and 5(B) and theoretical approximations of χT
(smooth lines) using the Van Vleck equation for a cluster of 12 paramagnetic centers for the salts 4(Figure 8) and 5(Figure 9). The best fittings
lead to the following parameters: 4,J1=−5.77 and J2=−0.84 cm−1;5(oversimplified model consisting of two types of [2]−···[3]+pairs; see the
text), J1= 9.72 and J2=−7.96 cm−1. Approximation of the dependences 1/χ(T)(
□) of both salts with the Curie−Weiss law (straight lines) is
discussed in the text.
Table 2. Parameters Jij of the [1]−···[1]−Pair Exchange
Interactions Calculated at the UB3LYP, CASSCF, and
NEVPT2 Levels of Theory with the def2-TZVP Basis Set
J,cm
−1
d(S···S),
a
Å UB3LYP CASSCF NEVPT2
3.98 −8.25 −3.70 −7.45
5.22 −1.06 0.25 −0.45
6.93 −0.01 0.00 0.00
7.92 −0.02 0.00 −0.05
8.21 −0.03 0.00 0.00
a
The shortest S···S distance in the pair (Supporting Information,
Figure S4).
Table 3. Parameters Jij of the [1]−···[3]+Pair Exchange
Interactions Calculated at the CASSCF and NEVPT2 Levels
of Theory with the def2-TZVP Basis Set
J,cm
−1
d(S···Cr),
a
Å CASSCF(2,2) NEVPT2(2,2)
5.52 1.00 −1.55
4.76 0.25 0.05
5.94 0.05 −0.05
a
The shortest S···Cr distance in the pair (Supporting Information,
Figure S5).
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636659

NEVPT2 calculations are in good agreement with the DFT
data (Table 2).
The CASSCF and NEVPT2 calculations for pairs [1]−···[3]+
gave qualitatively different results: CASSCF calculations
predicted weak FM interactions for all pairs, while more
accurate CASSCF/NEVPT2 calculations suggested mainly AF
interactions. However, both methods agreed in that the
calculated Jvalue for one pair is significantly larger than that
for two others. In this pair, the plane of [1]−is almost parallel
to the toluene plane in [3]+(Supporting Information, Figure
S4) and the negative spin density of the toluene ligand is in
contact with both the negative spin density in the vicinity of
C−C bond and the positive spin density on the N−S−N
fragment of [1]−(Figure 6).
Taking into account the results of the calculations, we
proposed the simplified magnetic model for the salt 4with two
nonnegligible Jvalues: J1for [1]−···[1]−pairs formed by species
from neighboring pillars, and J2for [1]−···[3]+pair formed
within the pillars (Figure 8). Simulation of the χTdependence
was performed using the Van Vleck formula and a
diagonalization of the matrix of Heisenberg spin Hamiltonian
(eq 1) for a cluster of 12 paramagnetic species with periodic
boundary conditions. The best agreement between theory and
experiment was achieved at values J1=−5.77 and J2=−0.84
cm−1(Figure 7A). A comparison of these values with the data
of Tables 2 and 3 demonstrates that calculations by both the
B3LYP and NEVPT2 methods overestimate while the CASSCF
method underestimates the exchange interaction between RAs.
At the same time, all methods give a reasonable estimate (up to
a factor ∼1.5) of the exchange interaction for the [1]−···[1]−
pair. The agreement between the experimental and NEVPT2-
calculated Jvalues for [1]−···[3]+pair is also reasonable (−0.84
and −1.55 cm−1, respectively). In turn, the CASSCF
calculations predict even the wrong sign of J.
Analysis of the magnetic motif of the salt 5is much more
complicated. One of the complications is the structural disorder
of the RAs (Figure 3). For example, every unique [2]−···[2]−
pair is characterized by three different Jparameters, which
depend on the mutual orientation of the RAs (Supporting
Information, Figure S6). In turn, every cation [3]+has four
neighboring anions [2]−, with the Cr−S distance in the range
5.0−6.6 Å (Supporting Information, Figure S7). Taking into
account disorder of the RAs, four different parameters Jhave to
be calculated, and their values are dependent on the spatial
orientation of concrete RA in the crystal lattice. The calculated
values of the exchange parameters (Jij) for pairs [2]−···[2]−and
[2]−···[3]+are presented in Tables 4 and 5, respectively.
Table 4 demonstrates that the B3LYP and CASSCF/
NEVPT2 calculations gave qualitatively similar results for
pairs [2]−···[2]−because they revealed only AF interactions,
and for all mutual orientations, the calculated Jvalues for the
pair with d(N···N) of 3.86 Å were found to be much larger than
that for another one.
In contrast to the Jvalues for the [2]−···[2]−pairs, both FM
and AF interactions were predicted for the [2]−···[3]+pairs
(Table 5), with the sign of Jdependent on the orientation of
[2]−(Supporting Information, Figure S7). Note that in this
case both methods gave qualitatively similar results. The J
values for the [3]+···[3]+pairs (Supporting Information, Figure
S8) were found to be negligible (about −0.1 cm−1).
Overall, one can conclude that the salt 5has a rather complex
3D magnetic motif. To simulate correctly the χTdependence of
the polycrystalline sample of this salt, a diagonalization of the
matrix of Heisenberg spin Hamiltonian (eq 1) for a large
cluster with at least 36 paramagnetic species should be
performed. In addition, the statistical nature of the RA disorder
should be taken into account. Unfortunately, this task is
intractable, and a cluster with only 12 paramagnetic species was
used in our simulations. It was, however, found that with a
simplified magnetic model containing seven Jparameters
(Figure 9) one can obtain very good agreement of the
experimental and simulated χTdependences (Figure 7B). The J
values featuring both signs were as follows: J1= 7.82, J2=
Figure 8. Simplified magnetic model of the salt 4.
Table 4. Parameters Jij of the [2]−···[2]−Pair Exchange
Interactions Calculated at the UB3LYP/def2-TZVP,
CASSCF/def2-SVP, and NEVPT2/def2-SVP Levels of
Theory for Two Unique Pairs in Three Mutual Orientations
J,cm
−1
d(N···N),
a
Å mutual orientation UB3LYP CASSCF NEVPT2
3.86 C···C−0.06 0.30 −0.60
C···S−1.76 −0.50 −1.70
S···S−3.10 −0.80 −2.20
4.11 C···C−0.73 0.10 −0.50
C···S−0.22 0.00 −0.10
S···S−0.37 0.00 −0.20
a
The shortest N···N distance in the pair (Supporting Information,
Figure S6). In this case, the S···S distances cannot be used because the
S atoms are distributed over two positions due to disorder.
Table 5. Parameters Jij of the [2]−···[3]+Pair Exchange
Interactions Calculated at the CASSCF(2,2)/def2-SVP and
CASSCF(2,2)/NEVPT2/def2-SVP Levels of Theory
J,cm
−1
d(S···Cr),
a
Å CASSCF(2,2) NEVPT2(2,2)
5.65 2.40 2.50
5.80 −0.60 −2.40
6.11 −2.50 −8.30
6.61 0.90 0.70
a
The shortest S···Cr distance in the pair (Supporting Information,
Figure S7).
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636660

−8.33, J3= 2.26, J4= 0.52, J5= 2.65, J6=−0.89, and J7=−0.89
cm−1.
The magnetic model shown in Figure 9 is rather complex
despite its simplified nature. In any way, it is necessary to
account for both FM and AF interactions to reproduce
correctly the χTtemperature dependence of salt 5.
To further support the importance of both FM and AF
interactions, the χTtemperature dependence of salt 5(Figure
7B) was simulated using the oversimplified model composed of
two types of exchange-coupled pairs. In this case, the best
fitting led to J1= 9.72 and J2=−7.96 cm−1, i.e., with account
for both FM and AF interactions. This is in qualitative
agreement with the results of calculations (Table 3) predicting
both types of exchange interactions in the [2]−···[3]+pairs. The
contribution from the FM interactions is also in qualitative
agreement with the positive value of the Weiss constant Θin
the case of salt 5.
■CONCLUSIONS
Under mild conditions, bis(toluene)chromium(0) (3) readily
reduced 1and 2into thermally stable radical-ion salts 4and 5.
These salts represent a new family of heterospin, S1=S2=1/2,
chalcogen−Nπ-heterocyclic RA salts. The salts are magneti-
cally active, with dominance of the AF exchange interactions in
their spin systems.
The synthetic approach successfully applied in this work to
the preparation of new heterospin chalcogen−Nπ-heterocyclic
RA salts may be generalized for a whole d-block because IE is
practically equal for MAr2compounds (M = Cr, Mo, W) with
the same Ar ligands. Target salts with heavy atoms possessing
strong spin−orbit coupling, Mo or W atoms in the cations and
Se and/or Te atoms in the anions, may satisfy the
Dzyaloshinsky−Moriya mechanism for spin canting to originate
a FM ground state even under conditions of AF exchange
interactions between paramagnetic centers (cf. refs 3f and 3g).
Experiments with MoAr2reducing agents are already in
progress.
■ASSOCIATED CONTENT
*
SSupporting Information
Orbitals of bis(toluene)chromium(I) involved in the active
space for CASSCF calculations, XRD molecular and crystal
structure of compound 2, experimental EPR spectrum of salt 4
along with integral intensities of the anionic and cationic parts,
and unique pairs. This material is available free of charge via the
Internet at http://pubs.acs.org.
■AUTHOR INFORMATION
Corresponding Author
*E-mail: zibarev@nioch.nsc.ru (A.V.Z.), gritsan@kinetics.nsc.ru
(N.P.G.).
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
The authors are grateful to Prof. J. Derek Woollins for valuable
discussions and to the Russian Foundation for Basic Research
(Projects 10-03-00735, 12-03-31759, and 13-03-00072), the
Presidium of the Russian Academy of Sciences (Project 8.14),
the Royal Society (RS International Joint Project 2010/R3), the
Leverhulme Trust (Project IN-2012-094), and the Siberian
Branch of the Russian Academy of Sciences (Project 13) for
financial support of various parts of this work. E.A.S. is grateful
to the Russian Academy of Sciences for the Golden Medal with
Premium for Graduates 2011 and appreciates support from the
Ministry for Education and Science of the Russian Federation
(Project 14.132.21.1451), the Dynasty Foundation, the Mikhail
Prokhorov Foundation, and the International Scientific
Charitable Foundation named after K. I. Zamaraev.
■REFERENCES
(1) Relevant literature is too abundant to be cited completely.
Selected recent references: (a) Organic Spintronics; Vardeny, Z. V.,
Ed.; CRC Press/Taylor & Francis: London, 2010. (b) Stable Radicals:
Fundamentals and Applied Aspects of Odd-Electron Compounds; Hicks,
R. G., Ed.; Wiley: New York, 2010. (c) Organic Conductors,
Superconductors, and Magnets; Ouahab, L., Yagubskii, E., Eds.; Kluwer:
Dordrecht, The Netherlands, 2004. (d) Ratera, I.; Veciana, J. Chem.
Soc. Rev. 2012,41, 303−349. (e) Wang, C.; Dong, H.; Hu, W.; Liu, Y.;
Zhu, D. Chem. Rev. 2012,112, 2208−2267. (f) Zhao, Y.; Ling, W. Z.
Chem. Soc. Rev. 2012,41, 10751087. (g) Figueira-Duarte, T. M.;
Muellen, K. Chem. Rev. 2011,111, 7260−7314. (h) Anthony, J. E.;
Facchetti, A.; Heeney, M.; Marder, S. T. Adv. Mater. 2010,22, 3876−
3892 (and other acticles of this themed issue). (i) Miller, J. S. J. Mater.
Chem. 2010,20, 1846−1857. (j) Miller, J. S. Polyhedron 2009,28,
1596−1605. (k) Coropceanu, V.; Cornil, J.; Da Silva Filho, D. A.;
Olivier, Y.; Silbey, R.; Bredas, J.-L. Chem. Rev. 2007,107, 926−952.
(l) Bogani, L.; Wernsdorfer, W. Nat. Mater. 2008, 179−186. (m) Saito,
G.; Yoshida, Y. Bull. Chem. Soc. Jpn. 2007,80,1−137.
(2) (a) Todres, Z. V. Chalcogenadiazoles: Chemistry and Applications;
CRC Press/Taylor & Francis: London, 2012. (b) Chivers, T.;
Laitinen, R. S. In Handbook of Chalcogen Chemistry. New Perspectives
in Sulfur, Selenium and Tellurium; Devillanova, F., Ed.; RSC Press:
Cambridge, U.K., 2007. (c) Chivers, T. A Guide to Chalcogen−Nitrogen
Chemistry; World Scientific: Singapore, 2005.
(3) (a) Winter, S. M.; Balo, A. R.; Roberts, R. J.; Lekin, K.; Assoud,
A.; Dube, P. A.; Oakley, R. T. Chem. Commun. 2013,49, 1603−1605.
(b) Lekin, K.; Leitch, A. A.; Tse, J. S.; Bao, X.; Secco, R. A.;
Desgreniers, S.; Ohishi, Y.; Oakley, R. T. Cryst. Growth Des. 2012,12,
4676−4684. (c) Mailman, A.; Winter, S. M.; Yu, X.; Robertson, C. M.;
Yong, W.; Tse, J. S.; Secco, R. A.; Liu, Z.; Dube, P. A.; Howard, J. A.
K.; Oakley, R. T. J. Am. Chem. Soc. 2012,134, 9886−9889. (d) Yu, X.;
Mailman, A.; Lekin, K.; Assoud, A.; Robertson, C. M.; Noll, B. C.;
Campana, C. F.; Howard, J. A. K.; Dube, P. A.; Oakley, R. T. J. Am.
Chem. Soc. 2012,134, 2264−2275. (e) Yu, X.; Mailman, A.; Lekin, K.;
Assoud, A.; Dube, P. A.; Oakley, R. T. Cryst. Growth Des. 2012,12,
2485−2494. (f) Winter, S. M.; Oakley, R. T.; Kovalev, A. E.; Hill, S.
Phys. Rev. B 2012,85, 094430. (g) Leitch, A. A.; Brusso, J. L.; Cvrkalj,
K.; Reed, R. W.; Robertson, C. M.; Dube, P. A.; Oakley, R. T. Chem.
Commun. 2007, 3368−3370 (and other publications of this group).
Figure 9. Simplified magnetic model of the salt 5.
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636661

(4) (a) Haynes, D. A. Cryst. Eng. Commun. 2011,13, 4793−4805.
(b) Hicks, R. G. In Stable Radicals: Fundamentals and Applied Aspects of
Odd-Electron Compounds; Hicks, R. G., Ed.; Wiley: New York, 2010.
(c) Rawson, J. M.; Alberola, A. In Handbook of Chalcogen Chemistry.
New Perspectives in Sulfur, Selenium and Tellurium, Devillanova, F., Ed.;
RSC Press: Cambridge, U.K., 2007. (d) Awaga, K.; Tanaka, T.; Shirai,
T.; Umezono, Y.; Fujita, W. C. R. Chim. 2007,10,52−59. (e) Preuss,
K. E. Dalton Trans. 2007, 2357−2369. (f) Awaga, K.; Tanaka, T.;
Shirai, T.; Fujimori, M.; Suzuki, Y.; Yoshikava, H.; Fujita, W. Bull.
Chem. Soc. Jpn. 2006,79,25−34. (g) Okamoto, K.; Tanaka, T.; Fujita,
W.; Awaga, K.; Inabe, T. Angew. Chem., Int. Ed. 2006,45, 4516−4518.
(h) Fujita, W.; Awaga, K. Science 1999,286, 261−262.
(5) (a) Clarke, C. S.; Jornet-Somoza, J.; Mota, F.; Novoa, J. J.;
Deumal, M. J. Am. Chem. Soc. 2010,132, 17817−17830. (b) Deumal,
M.; Rawson, J. M.; Goetha, A. E.; Howard, J. A. K.; Copley, R. C. B.;
Robb, M. A.; Novoa, J. J. Chem.Eur. J. 2010,16, 2741−2750.
(c) Deumal, M.; LeRoux, S.; Rawson, J. M.; Robb, M. A.; Novoa, J. J.
Polyhedron 2007,26, 1949−1958. (d) Rawson, J. M.; Alberola, A.;
Whalley, A. J. Mater. Chem. 2006,16, 2560−2575. (e) Rawson, J.;
Luzon, J. M.; Palacio, F. Coord. Chem. Rev. 2005,249, 2631−2641.
(6) (a) Shuvaev, K. V.; Passmore, J. Coord. Chem. Rev. 2013,257,
1067−1091. (b) Cameron, T. S.; Decken, A.; Grein, F.; Knapp, C.;
Passmore, J.; Rautiainen, J. M.; Shuvaev, K. V.; Thompson, R. C.;
Wood, D. J. Inorg. Chem. 2010,49, 7861−7879 (and previous
publications of this group).
(7) (a) Zibarev, A. V.; Mews, R. In Selenium and Tellurium Chemistry:
From Small Molecules to Biomolecules and Materials; Woollins, J. D.,
Laitinen, R. S., Eds.; Springer: Berlin, 2011; pp 123−149. (b) Gritsan,
N. P.; Zibarev, A. V. Russ. Chem. Bull. 2011,60, 2131−2140.
(c) Semenov, N. A.; Pushkarevsky, N. A.; Lonchakov, A. V.;
Bogomyakov, A. S.; Pritchina, E. A.; Suturina, E. A.; Gritsan, N. P.;
Konchenko, S. N.; Mews, R.; Ovcharenko, V. I.; Zibarev, A. V. Inorg.
Chem. 2010,49, 7558−7564. (d) Makarov, A. Yu.; Irtegova, I. G.;
Vasilieva, N. V.; Bagryanskaya, I. Yu.; Borrmann, T.; Gatilov, Yu. V.;
Lork, E.; Mews, R.; Stohrer, W.-D.; Zibarev, A. V. Inorg. Chem. 2005,
44, 7194−7199 (and other publications of this group).
(8) (a) Vasilieva, N. V.; Irtegova, I. G.; Gritsan, N. P.; Lonchakov, A.
V.; Makarov, A. Yu.; Shundrin, L. A.; Zibarev, A. V. J. Phys. Org. Chem.
2010,23, 536−543. (b) Boere, R. T.; Roemmele, T. L. Coord. Chem.
Rev. 2000,210, 369−445. (c) Bock, H.; Haenel, P.; Neidlein, R.
Phosphorus Sulfur Relat. Elem. 1988,39, 235−252. (d) Kaim, W. J.
Organomet. Chem. 1984,264, 317−326. (e) Hanson, P. Adv. Heterocycl.
Chem. 1980,27,31−149. (f) Kwan, C. L.; Carmack, M.; Kochi, J. K. J.
Phys. Chem. 1976,80, 1786−1792. (g) Kamiya, M.; Akahori, Y. Bull.
Chem. Soc. Jpn. 1970,43, 268−271. (h) Fajer, J.; Bielski, B. H. J.;
Felton, R. H. J. Phys. Chem. 1968,72, 1281−1288. (i) Atherton, N. M.;
Ockwell, J. N.; Dietz, R. J. Chem. Soc. A 1967, 771−777. (j) Strom, E.
T.; Russell, G. A. J. Am. Chem. Soc. 1965,87, 3326−3329.
(9) (a) Hirel, C.; Luneau, D.; Pecaut, J.; O
hrstrom, L.; Bussiere, G.;
Reber, C. Chem.Eur. J. 2002,8, 3157−3161. (b) Novoa, J. J.;
Deumal, M. Struct. Bonding (Berlin) 2001,100,33−60. (c) Kahn, O.
Molecular Magnetism; VCH Publishers: New York, 1993. (d) McCon-
nell, H. M. J. Chem. Phys. 1963,39, 1910−1917. (e) It is believed the
McConnell I mechanism stands behind FM properties of a number of
the [MCp*2][X] (M = Mn, Fe, Cr; X = TCNE, TCNQ) salts. Miller,
J. S. J. Mater. Chem. 2010,20, 1846−1857 and references cited therein.
(10) Spin polarization is a consequence of the minimization of
electrostatic repulsion of two electrons of parallel spin sharing the
same space, according to the Pauli principle. A positive spin density
means that the associated magnetic moment is parallel to the net spin
moment of the molecule and a negative spin density that the moments
are antiparallel. Spin polarization is a real property and can be
observed and quantified with polarized neutron diffraction.
(11) (a) Kaupp, M.; Koehler, F. H. Coord. Chem. Rev. 2009,253,
2376−2386. (b) Heise, H.; Koehler, F. H.; Herker, M.; Hiller, W. J.
Am. Chem. Soc. 2002,124, 10823−10832. (c) Kollmar, C.; Kahn, O. J.
Chem. Phys. 1992,96, 2988−2997.
(12) (a) Han, T.-H.; Helton, J. S.; Chu, S.; Rodriguez-Rivera, J. A.;
Broholm, C.; Lee, Y. S. Nature 2012,492, 406−410. (b) Loth, S.;
Baumann, S.; Lutz, C. P.; Eigler, D. M.; Heinrich, A. J. Science 2012,
335, 196−198.
(13) Pampaloni, G. Coord. Chem. Rev. 2010,254,402−419.
(b) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996,96, 877−910.
(14) (a) Green, J. C. Struct. Bonding (Berlin) 1981,43,37−112.
(b) Cloke, F. G. N.; Green, M. L. H.; Morris, G. E. J. Chem. Soc., Chem.
Commun. 1978,72−74. (c) Evans, S.; Green, J. C.; Jackson, S. E. J.
Chem. Soc., Faraday Trans. 2 1972,68, 249−258. (d) Herberich, G. E.;
Mueller, J. J. Organomet. Chem. 1969,16,11−117.
(15) Dzialoshinski, I. J. Phys. Chem. Solids 1958,4, 241−255.
(b) Moriya, T. Phys. Rev. 1960,120,91−98.
(16) (a) Solodovnikov, S. P. Russ. Chem. Rev. 1982,51, 961−974.
(b) Warren, K. D. Struct. Bonding (Berlin) 1976,27,45−159.
(17) (a) Calucci, L.; Cloke, F. G. N.; Englert, U.; Hitchcock, P. B.;
Pampaloni, G.; Pinzino, C.; Piccini, F.; Volpe, M. Dalton Trans. 2006,
4228−4234. (b) Benetollo, F.; Grigiotti, E.; Laschi, F.; Pampaloni, G.;
Volpe, M.; Zanello, P. J. Solid State Electrochem. 2005,9, 732−737.
(c) Elschenbroich, C.; Moeckel, R.; Zenneck, U.; Clark, D. W. Ber.
Bunsen-Ges. 1979,83, 1008−1018. (d) Prins, R.; Reinders, F. J. Chem.
Phys. Lett. 1969,3,45−48.
(18) (a) Miller, J. S.; O’Hare, D. M.; Chakraborty, A.; Epstein, A. J. J.
Am. Chem. Soc. 1989,111, 7853−7860. (b) O’Hare, D. M.; Miller, J. S.
Mol. Cryst. Liq. Cryst. 1989,176, 381−383. (c) Zvarykina, A. V.;
Karimov, Yu. S.; Ljubovsky, R. B.; Makova, M. K.; Khidekel, M. L.;
Shchegolev, I. F.; Yagubskii, E. B. Mol. Cryst. Liq. Cryst. 1970,11, 217−
228. (d) Shibaeva, R. P.; Atovmyan, L. O.; Rozenberg, L. P. J. Chem.
Soc., Chem. Commun. 1969, 649−650. (e) Shibaeva, R. P.; Atovmyan,
L. O.; Orfanova, M. N. J. Chem. Soc., Chem. Commun. 1969, 1494−
1495.
(19) Pushkarevsky, N. A.; Lonchakov, A. V.; Semenov, N. A.; Lork,
E.; Buravov, L. I.; Konstantinova, L. S.; Silber, T. G.; Robertson, N.;
Gritsan, N. P.; Rakitin, O. A.; Woollins, J. D.; Yagubskii, E. B.; Zibarev,
A. V. Synth. Met. 2012,162, 2267−2276.
(20) Sato, N.; Mizuno, H. J. Chem. Res. Synop. 1997, 250−251.
(21) Fischer, E. O.; Seeholzer, J. Z. Anorg. Allg. Chem. 1961,312,
244−263.
(22) Duling, D. R. J. Magn. Reson. B 1994,104, 105−110.
(23) APEX2, version 2.0; SAINT, version 8.18c; SADABS, version
2.11; Bruker Advanced X-ray Solutions, Bruker AXS Inc.: Madison,
WI, 2000−2012.
(24) Sheldrick, G. M. Acta Crystallogr. 2008,A64, 112−122.
(25) (a) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool,
version 10M; Utrecht University: Utrecht, The Netherlands, 2003.
(b) Spek, A. L. J. Appl. Crystallogr. 2003,36,7−13. (c) Macrae, C. F.;
Edgington, P. R.; McCabe, P.; Pidcock, E.; Shields, G. P.; Taylor, R.;
Towler, J.; van de Stree, M. J. Appl. Crystallogr. 2006,39, 453−457.
(26) Kalinnikov, V. T.; Rakitin, Yu. V. Introduction in Magneto-
chemistry. Method of Static Magnetic Susceptibility; Nauka: Moscow,
1980; p 302 (in Russian).
(27) (a) Deumal, M.; Bearpark, M. J.; Novoa, J. J.; Robb, M. A. J.
Phys. Chem. A 2002,106, 1299−1315. (b) Thompson, L. K.;
Waldmann, O.; Xu, Z. Coord. Chem. Rev. 2005,249, 2677−2690.
(28) (a) Nagao, H.; Nishino, M.; Shigeta, Y.; Soda, T.; Kitagawa, Y.;
Onishi, T.; Yoshika, Y.; Yamaguchi, K. Coord. Chem. Rev. 2000,198,
265−295. (b) Noodleman, L.; Case, D. A.; Mouesca, J. M. Coord.
Chem. Rev. 1995,144, 199−244. (c) Noodleman, L.; Davidson, E. R.
Chem. Phys. 1986,109, 131−143. (d) Noodleman, L. J. Chem. Phys.
1981,74, 5737−5743.
(29) (a) Becke, A. D. J. Chem. Phys. 1993,98, 5648−5652. (b) Lee,
C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988,37, 785−789.
(30) (a) Schaefer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992,97,
2571−2577. (b) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys.
2005,7, 3297−3305.
(31) Neese, F. ORCAAn Ab Initio, Density Functional and
Semiempirical Program Package, version 2.8; University of Bonn:
Bonn, Germany.
(32) Schaefer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992,97,
2571−2577.
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636662

(33) (a) Soda, T.; Kitagawa, Y.; Onishi, T.; Takano, T.; Shigeta, Y.;
Nagao, H.; Yoshioka, Y.; Yamaguchi, K. Chem. Phys. Lett. 2000,319,
223−230. (b) Yamaguchi, K.; Takahara, Y.; Fueno, T. In Applied
Quantum Chemistry; Smith, V. H., Ed.; Reidel: Dordrecht, The
Netherlands, 1986; p 155.
(34) (a) Angeli, C.; Cimiraglia, R.; Evangelisti, S.; Leininger, T.;
Malrieu, J.-P. J. Chem. Phys. 2001,114, 10252−10264. (b) Angeli, C.;
Cimiraglia, R.; Malrieu, J.-P. Chem. Phys. Lett. 2001,350, 297−305.
(c) Angeli, C.; Cimiraglia, R.; Malrieu, J.-P. J. Chem. Phys. 2002,117,
9138−9153.
(35) (a) Roos, B. O.; Malmqvist, P.-A. Phys. Chem. Chem. Phys. 2004,
6, 2919−2927. (b) Malmqvist, P.-A.; Roos, B. O.; Schimmelpfennig, B.
Chem. Phys. Lett. 2002,357, 230−240. (c) Chibotaru, L. F.; Ungur, L.
J. Chem. Phys. 2012,137, 064112.
(36) (a) Roos, O.; Lindh, R.; Malmqvist, P.-A.; Veryazov, V.;
Widmark, P.-O. J. Phys. Chem. A 2005,109, 6575−6579. (b) Roos, B.
O.; Lindh, R.; Malmqvist, P.-A.; Veryazov, V.; Widmark, P.-O. Chem.
Phys. Lett. 2005,409, 295−299.
(37) Aquilante, F.; De Vico, L.; Ferre, N.; Ghigo, G.; Malmqvist, P.-
A.; Neogrady, P.; Pedersen, T. B.; Pitonak, M.; Reiher, M.; Roos, B.
O.; Serrano-Andres, L.; Urban, M.; Veryazov, V.; Lindh, R. J. Comput.
Chem. 2010,31, 224−247.
(38) Hess, B. A.; Marian, C. M.; Wahlgren, U.; Gropen, O. Chem.
Phys. Lett. 1996,251, 365−371.
(39) Neese, F.; Solomon, E. I. Inorg. Chem. 1998,37, 6568−6582.
(40) (a) Gribov, B. G.; Kozyrkin, B. I.; Krivospitskii, A. D.; Chiikin,
G. K. Dokl. Akad. Nauk SSSR 1970,193,91−93 (in Russian).
(b) Karimov, Y. U.; Chibrikin, V. M.; Shchegolev, I. F. J. Phys. Chem.
Solids 1963,24, 1683−1687. (c) Anderson, S. E.; Drago, R. S. J. Am.
Chem. Soc. 1970,92, 4244−4254. (d) Veychinkin, S. I.; Solodovnikov,
S. P.; Chibrikin, V. M. Opt. Spectrom. 1960,8, 137−142 (in Russian).
Inorganic Chemistry Article
dx.doi.org/10.1021/ic400659q |Inorg. Chem. 2013, 52, 6654−66636663