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DaltonTransactions
PAPER
Cite this: DOI: 10.1039/c8dt01829d
Received 7th May 2018,Accepted 7th June 2018
DOI: 10.1039/c8dt01829d
rsc.li/dalton
High-coordinate CoII and FeII compoundsconstructed from an
asymmetric tetradentateligand show slow magnetic relaxation
behavior†
Xing-Cai Huang, *a Zi-Yi Qi,a Cheng-Long Ji,a Yi-Ming Guo,a
Shi-Chang Yan,a
Yi-Quan Zhang, *b Dong Shao c and Xin-Yi Wang *c
Using an asymmetric tetradentate ligand
N-((6-(1H-pyrazol-1-yl)pyridin-2-yl)methylene)benzohydrazide
(pypzbeyz), two high-coordinate 3d transition metal compounds
[CoII(pypzbeyz)(NO3)2] (1) and
[FeII(pypzbeyz)2](BF4)2(CH3CN) (2) have been synthesized and
characterized by structural and magnetic
measurements. X-ray crystallographic analyses revealed that
compound 1 is seven-coordinate with a dis-
torted pentagonal bipyramidal geometry (pseudo-D5h) and compound
2 is eight-coordinate with a tri-
angular dodecahedral geometry (pseudo-D2d). Direct current (dc)
magnetic susceptibilities revealed that
compound 1 shows easy-plane magnetic anisotropy (D = +29.9 cm−1,
E = 0.31 cm−1) and 2 shows easy-
axis magnetic anisotropy (D = −6.6 cm−1, E = 0.02 cm−1).
Alternating current (ac) magnetic measure-ments indicate that both
compounds exhibit field-induced slow magnetic relaxation
behavior.
Furthermore, ab initio calculations also demonstrate that
compound 1 presents a strong easy-plane mag-
netic anisotropy and 2 presents an easy-axis magnetic
anisotropy, which are further identified by the cal-
culated orientations of the local magnetic axes. These results
demonstrate an effective way to achieve the
targeted synthesis of high-coordinate 3d SIMs.
Introduction
Since the first discovery of 3d single-ion magnets (SIMs,
K[(tpaMes)FeII]) in 2010,1 many efforts have been devoted to
pur-suing these interesting molecular nanomagnets due to
theirpromising potential for enhancing the energy barrier (Ueff
)and blocking temperature (TB).
2 For the reported 3d SIMs, it isworth mentioning that the
coordination geometry and metalcentre are two key factors to affect
their slow magnetic relax-ation. With a particular combination of
the electronic con-figuration and coordination mode, 3d transition
metal ionscan achieve large magnetic anisotropy (determined by
using
the zero-field splitting parameters, D and E). Considering
themetal centres, the reported 3d SIMs have been expanded toV(IV),3
Cr(II),4 Mn(III/IV),5 Fe(I/II/III),6 Co(I/II),7 Ni(I/II),8 and
Cu(II)9
centres. With different coordination numbers ranging from 2to 8,
the reported mononuclear 3d SIMs have various coordi-nation
geometries, including linear, trigonal planar, tetra-hedron, square
pyramid, trigonal prism, octahedron, trigonalbipyramid, pentagonal
bipyramid and triangular dodecahe-dron. Representatively, Long et
al. reported a two-coordinatelinear FeI complex
[K(crypt-222)][FeI(C(SiMe3)3)2] (crypt-222 =2.2.2-cryptand), which
possessed an excellent effective spin-reversal barrier of 226(4)
cm−1.6a Recently, Gao et al. have alsoreported a two-coordinate
linear CoII imido complex [(sIPr)CoNDmp] (Dmp =
2,6-dimesitylphenyl), which featured therecord effective relaxation
barrier of 413 cm−1 for 3d SIMs todate.7f Significantly, the axial
ligand field imposed at theselow-coordinate 3d metal centres (FeI
and CoII) leads to thelarge magnetic anisotropy of these ions and
the observed highUeff or TB values.
On the other hand, high-spin Co(II) and Fe(II) compoundswith
high coordination numbers (CN = 7, 8) are relatively rarecompared
to the widely reported compounds with CNnumbers of 5 or 6. To
obtain high-coordinate 3d transitionmetal compounds, appropriate
chelate ligands should bedesigned. Generally speaking, high-spin
seven-coordinate
†Electronic supplementary information (ESI) available: 1H, 13C,
HSQC andHMBC NMR of the ligand, detailed structural parameters, the
continuous shapemeasures, other magnetic plots and fitting
parameters of the Cole–Cole plots for1 and 2. CCDC 1831200–1831202.
For ESI and crystallographic data in CIF orother electronic format
see DOI: 10.1039/c8dt01829d
aSchool of Chemistry and Environmental Engineering, Yancheng
Teachers University,
Yancheng, 224007, China. E-mail: [email protected] Key
Laboratory for NSLSCS, School of Physical Science and
Technology,
Nanjing Normal University, Nanjing 210023, China.
E-mail: [email protected] Key Laboratory of
Coordination Chemistry, Collaborative Innovation Centre of
Advanced Microstructures, School of Chemistry and Chemical
Engineering,
Nanjing University, Nanjing, 210093, China. E-mail:
[email protected]
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Co(II) and Fe(II) compounds with a distorted pentagonal
bipyr-amidal geometry can be constructed by using
pentadentateligands. These compounds usually have very large
magneticanisotropy. Therefore, we have reported the first
observation ofthe field-induced SIM behavior in the
seven-coordinate Co(II)compounds with a distorted pentagonal
bipyramidal geometry(pseudo-D5h) constructed with microcyclic
pentadentateligands.10 Furthermore, the seven-coordinate Fe(II)
SIMs withthe distorted pentagonal bipyramidal geometry showed
easy-axis magnetic anisotropy with negative D value (D < 0) by
usingsimilar pentadentate ligands.11 Despite the fact that the
nearlyplanar five-membered coordination ring has been fixed by
thepentadentate ligands, the coordination environment in
thepentagonal bipyramidal geometry can be tuned using
auxiliaryligands in the axial positions. To understand the
influence ofthe coordination environment on the magnetic
anisotropy, aseries of Co(II) SIMs with the auxiliary ligands of
differentdonor atoms (C, N, O and S atoms)12 or halogen ions (Cl−,
Br−
and I−)13 in the axial positions of the pentagonal
bipyramidalgeometry have been investigated. Besides the
pentadentateligands, the heptadentate macrocyclic ligand
(py2-15-pyN3O2)and the monodentate pyridine derivatives can also be
used toobtain the seven-coordinate Co(II) SIMs with distorted
pentago-nal bipyramidal geometries.14 Moreover, the
seven-coordinatecompounds [Co(NO3)4]
2− having no organic ligand also showeasy-plane magnetic
anisotropy and SIM behavior.15 So far,eight-coordinate 3d
transition metal compounds have beenrarely reported.16–20 From a
synthetic point of view, to obtaineight-coordinate 3d transition
metal compounds, tetradentateligands are preferred.16d To the best
of our knowledge, severaleight-coordinate mononuclear 3d transition
metal compoundsshowing SIM behaviors were constructed using the
symmetrictetradentate ligands (Scheme 1). It has also been reported
thatthe first eight-coordinate Co(II) SIMs constructed
from12-crown-4 (La) with a distorted square antiprismatic
geometry(pseudo-D4d) exhibited large and negative magnetic
an-isotropy.17 Very recently, the eight-coordinate Fe(II)
SIMs[FeII(Lb)2](ClO4)2
18 and [FeII(Lc)2](BF4)2·1.3H2O19 (ligands b
and c in Scheme 1) with the pseudo-D2d symmetry have
beenconstructed from the symmetrical tetradentate ligands.
Todemonstrate the effect of an 8-coordinate coordinationenvironment
on the SIM behavior, a series of eight-coordinateFeII and CoII SIMs
based on the derivatives of Lb have beeninvestigated.20
Following the approach as mentioned above, we haverecently
addressed our interest in high-coordinate 3d tran-sition metal
compounds for constructing 3d SIMs by using tet-
radentate ligands. The asymmetric tetradentate ligands
withdifferent functional groups have been rarely reported
fordesigning high-coordinate 3d transition metal compounds.Due to
the steric effect, the asymmetric tetradentate ligandscan
coordinate to different 3d transition metal centres withdifferent
coordination modes. In this work, we have reportedtwo
high-coordinate 3d transition metal compounds[CoII(pypzbeyz)(NO3)2]
(1) and [Fe
II(pypzbeyz)2](BF4)2(CH3CN)(2) based on an asymmetric
tetradentate ligand pypzbeyz(Scheme 2). Interestingly, based on the
same ligand, the CoII
compound 1 is seven-coordinate with a distorted
pentagonalbipyramidal geometry (pseudo-D5h) and Fe
II compound 2 iseight-coordinate with a triangular dodecahedral
geometry(pseudo-D2d). Both of them exhibited slow magnetic
relaxationunder a dc field, a characteristic of SIMs. Furthermore,
mag-netic measurements and theoretical calculations revealed
thatcompound 1 features easy-plane magnetic anisotropy, while
2features easy-axis magnetic anisotropy.
Experimental
All preparations and manipulations were performed underaerobic
conditions. All chemicals and solvents were obtainedfrom commercial
sources and used without further purifi-cation.
6-(Pyrazol-1-yl)pyridine-2-carbaldehyde was preparedaccording to
the reported procedure.21
Physical measurements
Elemental analyses for C, H and N were carried out on a VarioEL
II Elementar. Infrared spectra were obtained on a NicoletiS50
spectrometer with pressed KBr pellets in the range400–4000 cm−1 at
room temperature. 1H, 13C, HSQC andHMBC NMR were obtained with a
Bruker AVIII 400 MHzBBFO1 spectrometer at 298 K unless otherwise
stated.
Scheme 1 Selected ligands used for eight-coordinate FeII and
CoII
SIMs.
Scheme 2 The synthesis of the ligand pypzbeyz and its crystal
struc-ture, and the schematic representations of the Co(II) and
Fe(II)compounds.
Paper Dalton Transactions
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Chemical shifts (δ) are given in ppm and the coupling constantJ
is given in Hz. NMR multiplicities are abbreviated as follows:s =
singlet, t = triplet, and m = multiplet. Magnetic measure-ments
were performed on polycrystalline samples by using aQuantum Design
SQUID VSM magnetometer at temperaturesranging from 1.8 K to 300 K
under a dc field up to 7 T. All thedata were corrected for
diamagnetism of the sample holderand of the constituent atoms using
Pascal’s constants.22
Synthesis of the ligand pypzbeyz
A 30 mL MeOH solution of 6-(pyrazol-1-yl)
pyridine-2-carbalde-hyde (0.35 g, 2 mmol) and benzoyl hydrazine
(0.27 g, 2 mmol)was refluxed for 2 h. The resulting clear colorless
mixture wasslowly cooled to room temperature, affording the ligand
N-((6-(1H-pyrazol-1-yl)pyridin-2-yl)methylene)benzohydrazide
(pypz-beyz) as white crystals suitable for X-ray diffraction
studies.The white crystals were filtered off, washed with methanol
anddried in air. Yield: 0.39 g, ca. 75%. Elemental analysis (%)
cal-culated for C17H17N5O2: C 63.15, H 5.30, N 21.66; found:
C63.11, H 5.41, N 21.62. IR (KBr, cm−1): 3509(m), 3403(s),3169(m),
2984(m), 1640(s), 1603(w), 1589(w), 1560(s), 1523(m),1474(s),
1436(w), 1418(w), 1397(s), 1347(w), 1328(s), 1310(m),1287(s),
1231(w), 1203(m), 1182(w), 1151(m), 1134(m), 1104(w),1081(w),
1053(s), 1043(s), 1000(w), 990(w), 956(w), 944(m),922(s), 887(w),
864(w), 851(s), 762(s), 738(w), 708(s), 689(m),678(w), 655(w),
645(w), 637(w), 619(w), 601(w), 522(w), 500(w).1H NMR (DMSO-d6, 400
MHz, 298 K): δ 12.17 (s, 1H, NH), 8.63(s, 1H, pyrazole–H), 8.51(s,
1H, pyrazole–H), 8.06 (t, J = 8.0 Hz,1H, Py–H), 7.95–7.91 (m, 4H,
Py–H and Ph–H), 7.85 (s, 1H,PyCHN), 7.62 (t, J = 8.0 Hz, 1H, Ph–H),
7.55 (t, 2H, J = 8.0 Hz,Ph–H), 6.60 (s, 1H, pyrazole–H); 13C{1H}
NMR (DMSO-d6,100 MHz, 298 K): δ 163.4 (OvC), 152.2 (Py–C), 150.8
(Py–C),147.0 (pyrazole–C), 142.4 (PyCHN), 140.2 (Py–CH), 133.1
(Ph–C), 132.1 (Ph–CH), 128.6 (Ph–CH), 127.8 (Ph–CH), 127.1
(pyra-zole–CH), 117.8 (Py–CH), 112.4 (Py–CH), 108.4
(pyrazole–CH).
Synthesis of [CoII(pypzbeyz)(NO3)2] (1)
A solution of pypzbeyz (29.1 mg, 0.1 mmol) and Co(NO3)2·6H2O
(29.1 mg, 0.1 mmol) in methanol (5 mL) was sub-jected to ultrasonic
vibration for 5 minutes, followed by fil-tration. Orange red block
crystals suitable for X-ray diffractionstudies were obtained by the
slow diffusion of diethyl ethervapour into the solution after 3
days. The orange red crystalswere filtered off, washed with the
mother solution, methanoland diethyl ether, and dried in air.
Yield: ca. 40%. Elementalanalysis (%) calculated for C16H13N7O7Co:
C 40.52, H 2.76, N20.67; found: C 40.46, H 2.81, N 20.59. IR (KBr,
cm−1): 3388(vs), 3124(w), 2426(m), 1643(s), 1621(m), 1603(s),
1575(s),1540(s), 1484(vs), 1387(vs), 1348(s), 1305(s), 1282(s),
1227(w),1178(m), 1152(s), 1108(w), 1076(w), 1055(w), 1028(s),
1013(w),1000(w), 982(w), 931(s), 911(w), 888(w), 838(w), 802(w),
778(m),766(w), 730(m), 688(s), 660(s) 627(w), 580(m), 534(m).
Synthesis of [FeII(pypzbeyz)2] (BF4)2(CH3CN) (2)
A solution of pypzbeyz (58.3 mg, 0.2 mmol) and
Fe(BF4)2·6H2O(33.8 mg, 0.1 mmol) in MeCN (5 mL) was subjected to
ultra-
sonic vibration for 5 minutes, followed by filtration. Darkblack
block crystals suitable for X-ray diffraction studies wereobtained
by the slow diffusion of diethyl ether vapour into thesolution
after 2 days. The black crystals were filtered off,washed with the
mother solution, acetonitrile and diethylether, and dried in air.
Yield: ca. 30%. Elemental analysis (%)calculated for
C34H29B2F8N11O2Fe: C 47.87, H 3.43, N 18.06;found: C 47.78, H 3.52,
N 18.04. IR (KBr, cm−1): 3408(s),3271(m), 3154(m), 1648(s),
1618(w), 1603(w), 1574(s), 1545(s),1480(s), 1464(m), 1402(m),
1368(m), 1345(m), 1306(s), 1283(s),1229(w), 1117(w), 1150(s),
1084(s), 1055(m), 1042(m), 979(s),929(s), 912(w), 888(w), 800(m),
767(m), 731(w), 712(s), 689(m),653(w), 630(w), 614(w), 600(w),
586(w), 534(w), 521(w), 509(w).
X-ray data collection, structure solution and refinement
The X-ray data of pypzbeyz·CH3OH, 1 and 2 were collected on
aBruker APEX D8 QUEST diffractometer with a Photon 100CMOS detector
(Mo-Kα radiation, λ = 0.71073 Å). The APEX IIIprogram was used to
determine the unit cell parameters andfor data collection. The data
were integrated using SAINT23
and SADABS.24 The structures for all compounds were solvedby
direct methods and refined by full-matrix least-squaresbased on F2
using the SHELXL-2014/7 package.25 All the non-hydrogen atoms were
refined anisotropically. The hydrogenatoms of the organic ligands
were refined as riding on thecorresponding non-hydrogen atoms.
Additional details of thedata collections and structural refinement
parameters are pro-vided in Table 1. Selected bond lengths and
angles are listedin Table S1.†
Computational details
CASSCF with MOLCAS 8.2. Complete-active-space self-con-sistent
field (CASSCF) calculations with the MOLCAS 8.2program package26,27
were performed on individual FeII andCoII fragments (see Fig. S1†
for the calculated model structuresof complexes 1 and 2) on the
basis of the X-ray determinedgeometry of complexes 1 and 2. The
basis sets for all atoms areatomic natural orbitals obtained from
the MOLCAS ANO-RCClibrary: ANO-RCC-VTZP for FeII or CoII ions; VTZ
for close Nand O; VDZ for distant atoms. The calculations employed
thesecond order Douglas–Kroll–Hess Hamiltonian, where
scalarrelativistic contractions were taken into account in the
basisset. And then, the spin–orbit couplings were handled
separ-ately in the restricted active space state interaction
(RASSI-SO)procedure. For the fragments of individual FeII or CoII
ions,active electrons in 5 active spaces include all d electrons
(CAS(6 in 5 + 5′) for FeII and CAS(7 in 5 + 5′) for CoII) in the
CASSCFcalculations. To exclude all the doubts, we calculated all
theroots in the active space. We have mixed the maximumnumber of
spin-free states which was possible with our hard-ware (all from 5
quintets, all from 45 triplets and all from 50singlets for FeII
ions; all from 10 quadruplets and all from 40doublets for CoII
ions).
NEVPT2 with Orca 4.0. To deeply analyse the magnetic an-isotropy
of complexes 1 and 2, Orca 4.0 calculations28 were per-formed with
the N-Electron Valence State Perturbation Theory
Dalton Transactions Paper
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(NEVPT2)29 method. A spin–orbit coupling (SOC) operator wasused
for the efficient implementation of the multicentre spin–orbit
mean-field (SOMF) concept developed by Hess et al.30 Thespin–spin
contributions (SSC) to the D values were also includedalthough they
are very small for our complexes. All calculationswere performed
with triple-ζ with one polarization functionTZVP31 basis set for
all atoms. Tight convergence criteria wereused in order to ensure
that the results are well converged withrespect to technical
parameters. The effective Hamiltonianimplemented in Orca was used
to extract the ZFS parameters Dand E. We also carried out the
calculation using the first CASSCFcalculation. And then, the effect
of the dynamical electronic cor-relation was applied using the
NEVPT2 method. Our previouscalculations15,32 show that the NEVPT2
method performed wellin the calculations of zero-field splitting
(ZFS) parameters D andE for transition metal-based magnets.
Results and discussion
The two air-stable high-coordinate mononuclear transitionmetal
compounds 1 and 2 were prepared by the reaction ofpypzbeyz·CH3OH,
Co(NO3)2·6H2O and Fe(BF4)2·6H2O indifferent solvents (CH3OH for 1
and CH3CN for 2). Also, wewant to point out that attempts to
prepare the eight-coordinateCoII complexes with different ligand to
metal ratios anddifferent counter-ions such as BF4
− and ClO4− anions were not
successful.
Description of the structures of pypzbeyz and complexes 1and
2
Single crystal X-ray diffraction analyses revealed
thatpypzbeyz·CH3OH and complexes 1 and 2 crystallize in
themonoclinic space group P21/c, triclinic space group P1̄, and
theorthorhombic space group Pbca, respectively. Forpypzbeyz·CH3OH,
one pypzbeyz and one CH3OH crystallize inthe asymmetric unit (see
Scheme 2). Along the a axis,pypzbeyz·CH3OH formed a 1-D
supramolecular network viahydrogen bonds (N–H⋯O and O–H⋯O, see Fig.
S4 andTable S4 in the ESI†). For compound 1, the CoII centre
isseven-coordinated by three N atoms and one O atom from oneligand
pypzbeyz (N1, N3, N4, O1) and three O atoms from twoNO3
− (O2, O4 and O5) in a distorted pentagonal bipyramidalgeometry.
The Co–N/O bond lengths are in the range of2.088(2)–2.241(2) Å (see
Table S1 in the ESI†). Furthermore, thedistance of Co1⋯O6 is
3.070(3) Å, which is too far to be con-sidered as the Co–O bond
length. As can be seen from Fig. 1(c)and Table S1,† the five atoms,
which are from the ligand pypz-beyz (N1, N3, N4, O1) and NO3
− (O4), constituted an irregularpentagon plane. The axial bond
angle is 176.49(5)° (∠O5–Co1–O2), and the axial bond lengths are
2.0879(19) and 2.1242(19)Å (for Co1–O5 and Co1–O2, respectively).
To further evaluatethe distortion of the coordination environment
of compound1, the continuous shape measures (CShM) were
calculatedusing the SHAPE 2.1 program33 (see Table S2 in detail,
ESI†).The CShM value related to the pentagonal bipyramidal
geome-try (D5h) for 1 is 3.010. Due to the asymmetric character of
the
Table 1 Crystallographic data and structure refinement
parameters for pypzbeyz·CH3OH, 1 and 2
Compounds pypzbeyz·CH3OH 1 2
Formula C17H17N5O2 C16H13N7O7Co C34H29B2F8N11O2FeFormula weight
323.35 474.26 853.15CCDC number 1831200 1831201 1831202Crystal
system Monoclinic Triclinic OrthorhombicSpace group P21/c P1̄ Pbcaa
(Å) 6.641(2) 8.078(5) 11.092(2)b (Å) 29.396(6) 9.943(5) 19.313(4)c
(Å) 8.657(2) 13.111(5) 35.246(7)α (°) 90 76.07(2) 90β (°) 101.47(3)
74.63(4) 90γ (°) 90 66.64(3) 90V (Å3) 1656.2(7) 921.2(9) 7550(3)Z 4
2 8T, K 293(2) 293(2) 293(2)ρcalcd (g cm
−3) 1.297 1.710 1.501Crystal size (mm) 0.68 × 0.60 × 0.24 0.15 ×
0.12 × 0.10 0.56 × 0.18 × 0.10μ(Mo-Kα) (mm−1) 0.089 0.991
0.488F(000) 680 482 2888θ range (°) 3.130–27.662 2.798–27.661
2.731–27.513Refl. collected/unique 30 033/3833 9626/4196 59
769/8089R(int) 0.0425 0.0234 0.0539Tmax/Tmin 0.7456/0.6750
0.7456/0.6723 0.7456/0.6792Data/restraints/parameters 3833/0/219
4196/0/281 8089/0/524R1
a/wR2b (I > 2σ(I)) 0.0694/0.1722 0.0353/0.0911
0.0657/0.1441
R1/wR2 (all data) 0.0852/0.1816 0.0466/0.0974 0.1171/0.1672GOF
on F2 1.081 1.029 1.053Max/min (e Å−3) 0.273/−0.232 0.402/−0.467
0.569/−0.522
a R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = {∑[w(Fo2 −
Fc2)2]/∑[w(Fo2)2]}1/2.
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ligand pypzbeyz, compound 1 has a relatively large
distortionfrom the pentagonal bipyramidal geometry. From the
crystalpacking diagram of 1 (see Fig. S5, ESI†), the
intermolecularCo⋯Co distances are found to be in the range of
6.886(3)–9.943(5) Å, resulting in negligible intermolecular
magneticinteractions. For compound 2, the FeII centre is
eight-coordi-nate and adopts a distorted triangular dodecahedron
geometrywith all eight N6O2 atoms from two tetradentate ligands
ofpypzbeyz. The CShM value related to the triangular dodecahe-dron
geometry (D2d) for 2 is 1.472 (see Table S3 in detail,ESI†). The
Fe–N/O bond lengths of 2 are in the range of2.243(3)–2.327(3) Å,
which fall in the bond length region forthe reported
eight-coordinate FeII compounds. From thepacking diagram (see Fig.
S6, ESI†), the intermolecular Fe⋯Fedistances are in the range of
10.853(3)–12.296(4) Å, alsoleading to negligible intermolecular
magnetic interactions.
Magnetic properties
Direct current (dc) magnetic susceptibilities of 1 and
2.Variable-temperature dc magnetic susceptibility data (T =2–300 K
and Hdc = 1000 Oe) and isothermal magnetizationcurves (T = 2 K, Hdc
= 0–7 T) of 1 and 2 were obtained on thepolycrystalline samples
(Fig. 2). The observed χMT values at300 K were 2.58 cm3 mol−1 K for
1 and 3.20 cm3 mol−1 K for 2,which is larger than the expected
spin-only χMT values1.875 cm3 mol−1 K for 1 and 3.00 cm3 mol−1 K
for 2 (S(CoII) =3/2 and S(FeII) = 2), suggesting the significant
orbital contri-bution to the magnetic moments of the high-spin CoII
for 1and high-spin FeII for 2. The magnetization versus H curves
of1 and 2 up to 7 T at 2 K tend to be 2.56μB for 1 and 2.94μB for2,
which are lower than the theoretical spin-only value of3.00μB for
the mononuclear Co
II compound and 4.00μB for themononuclear FeII compound. The
magnetizations of 1 and 2do not saturate up to 7 T at 2 K,
suggesting the presence of sig-nificant magnetic anisotropy.
To gain a better understanding of the magnetic anisotropyof CoII
and FeII centres for 1 and 2, respectively, the mag-netic
susceptibility data and also the magnetization data ofcompound 1
were simultaneously fitted by using the PHIprogram34 with the
anisotropic spin Hamiltonian as given ineqn (1),
H ¼D½Ŝz2 � S Sþ 1ð Þ=3� þ EðŜx2 � Ŝy2Þþ μBðgxŜxBx þ gyŜyBy
þ gzŜyBzÞ
ð1Þ
where D, E, Si, gi and Bi represent the uniaxial ZFS
parameter,transverse ZFS parameter, spin operator, g tensor and
mag-netic vector, respectively, and μB is the Bohr magneton.
Thebest fit leads to D = +29.9 cm−1, E = 0.31 cm−1 gx = gy =
2.40,and gz = 2.25 for 1. For compound 2, the magnetic data
werefitted with the spin Hamiltonian as given in eqn (2),
H ¼ D½Ŝz2 � SðSþ 1Þ=3� þ EðŜx2 � Ŝy2Þ þ gμBSB: ð2ÞThe best fit
leads to D = −6.6 cm−1, E = 0.02 cm−1 and g =
2.09 for 2. The large and positive D value of 1 is well
consistentwith the values reported for the pentagonal
bipyramidalcobalt(II) compounds, which can be ascribed for the
spinorbital coupling through second-order perturbation betweenthe
ground and excited states.12,13 The negative D value andsmall E
value of 2 are in agreement with the other two reportedvalues of
eight-coordinate FeII compounds with uniaxial an-isotropy (the
calculated results D = −11.7 cm−1 of [FeII(Le)2](ClO4)2,
18 D = −6.32 cm−1 of [FeII(Lf )2](BF4)2·1.3H2O).19
Alternating current (ac) magnetic susceptibilities of 1 and 2.To
probe the dynamics of the magnetization for both com-plexes,
frequency-dependent ac susceptibility measurementswere performed
under zero and nonzero applied dc fields. Noout-of-phase (χ″M)
signal was observed for the two complexesunder zero dc field,
probably due to the fast QTM effects(Fig. S7 and S8, ESI†). In
order to determine the optimum dcfield to suppress the QTM effect,
ac measurements were per-formed on both compounds under various dc
fields at 2.0 K(Fig. S10 and S12, ESI†). As we can see, obvious
frequencydependent ac signals (in-phase (χ′M) and out-of-phase
(χ″M))were detected for both compounds 1 and 2, demonstrating
theslow magnetic relaxation of both compounds. The optimumdc field
is around 1000 Oe for both 1 and 2, which was used
Fig. 1 Crystal structures of compounds 1 (a) and 2 (b) shown
with 30%thermal ellipsoids; and the coordination polyhedron around
CoII (c) andFeII (d) centres for 1 and 2, respectively. Solvent
molecules and uncoor-dinated ions are omitted for clarity.
Fig. 2 χMT vs. T plots at 1000 Oe from 2 to 300 K and M vs. H
plots (inset)at 2 K for 1 (a) and 2 (b); the blue solid lines are
fitted by using the PHIprogram and the red solid lines are plotted
using the CASSCF calculations(CAS (7, 5 + 5’) and CAS (6, 5 + 5’)
for 1 and 2, respectively) with MOLCAS 8.2.
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for the detailed ac susceptibility measurements (Fig. 3 andFig.
S11 and S12, ESI†). The peaks of the out-of-phase signals(χ″)
appear from 1.8 to 4.4 K for 1 and 1.8 to 2.4 K for 2.
From the frequency dependent ac data at temperaturesranging from
1.8 to 5.6 K for 1 and 1.8 to 2.6 K for 2, semicircleCole–Cole
plots were constructed and fitted using the general-ized Debye
model (Fig. 4a and c).35 The obtained α values arein the range of
0.06–0.22 for 1 and 0.24–0.44 for 2 (see TablesS7 and S8 for
fitting parameters in detail, ESI†), suggesting asubstantial
broadening of the distribution of relaxation times,especially at
low temperatures for 3d SIMs. To estimate the an-isotropy energy
barrier (Ueff ), the plot of the high temperaturedata was first
fitted by using the Arrhenius law τ−1 = τ0
−1 exp
(−Ueff/kBT ). The Ueff was estimated to be (34.6 ± 2.3) cm−1
witha pre-exponential factor τ0 = (1.1 ± 0.6) × 10
−7 for 1 and (18.6 ±3.7) cm−1 with τ0 = (1.3 ± 0.4) × 10
−9 s for 2 (Fig. 4b and d, redcolour curves). For a compound
with an easy plane magneticanisotropy (D > 0), the Orbach
process should not be involvedas the direct relaxation between the
ground MS = ±1/2 levels isallowed. The mechanism for the magnetic
relaxation is some-what complicated. The transverse anisotropy
located in theeasy plane with a considerable E value was
proposed,36 whichis clearly not suitable for our compound 1 as its
E value is neg-ligible. The other mechanism could be the Orbach
relaxationpathway through the excited Ms = ±3/2 states
37 or the Ramanprocess involving a virtual state,7d,36 provided
that the directrelaxation of the ground MS = ±1/2 levels is slowed
sufficientlyfor some reasons, such as the phonon bottleneck
effect.37 Asthe above obtained Ueff is much lower than the energy
gapbetween the MS = ±1/2 and MS = ±3/2 doublets, the Orbachpathway
is not likely. Thus, the Raman process dominating athigher
temperatures should be considered.38 The relaxationtime in the high
temperature region can be fitted with a powerlaw (τ = CT−n, the
inset of Fig. 4b) affording n = 2.2, indicatinga Raman process
involving both acoustic and opticalphonons.39 For compound 2,
although the curvature of theArrhenius plot at 2 K indicates the
existence of the multiplerelaxation pathways, the few data points
in the small range of1.8–2.6 K prevent the reasonable analysis of
its multiple relax-ation processes.
Theoretical calculations
To gain insight into the origin of the magnetic anisotropy
forcompounds 1 and 2, complete-active-space self-consistent
field(CASSCF) calculations with the MOLCAS 8.2 program packagewere
performed on individual CoII and FeII fragments.
The calculated zero-field splitting parameters D (E) (cm−1)and g
(gx, gy and gz) tensors of the lowest spin–orbit state ofcomplexes
1 and 2 using CASSCF with MOLCAS 8.2 andNEVPT2 with Orca 4.0 lead
to +24.0(−2.3) cm−1 and +21.5(+2.0) cm−1 for 1 and −5.1(0.4) cm−1
and −5.7(0.3) cm−1 for 2(listed in Table 2). Both the calculated D
and E values are in
Table 2 Calculated zero-field splitting parameters D (E) (cm−1),
energybarrier (DS2 or D(S2 − 1/4)) and g (gx, gy and gz) tensors of
the lowestspin–orbit state of complexes 1 and 2 using CASSCF with
MOLCAS 8.2and NEVPT2 with Orca 4.0
1 2
CASSCF NEVPT2 CASSCF NEVPT2
CAS (7, 5 + 5′) (7, 5 + 5′) (6, 5 + 5′) (6, 5 + 5′)Spin 3/2
2D/cm−1 24.0 21.5 −5.1 −5.7E/cm−1 −2.3 2.0 0.4 0.3DS2 or D(S2 −
1/4)/cm−1 48.0 43 20.4 22.9gx 2.385 2.333 2.047 2.039gy 2.330 2.284
2.062 2.052gz 2.139 2.122 2.112 2.109Ueff 34.6 18.6
Fig. 3 Frequency dependence of the in-phase (χ’M) and out-of
phase(χ’’M) parts of the ac susceptibility for compounds 1 (a) and
2 (b) in therange of 1.8–6.0 K and 1.8–3.0 K under a 1000 Oe dc
field.
Fig. 4 Cole–Cole plots of 1 (a) and 2 (c) measured under a 1000
Oe dcfield from 1.8 to 5.6 K for 1 and from 1.8 to 2.6 K for 2. The
red solid linescorrespond to the best fit obtained with a
generalized Debye model. Therelaxation time of the magnetization
ln(τ) vs. T−1 for 1 (b) and 2 (d). Thered line corresponds to the
Arrhenius fit in the high temperature regionand the inset (b):
power law analysis in the form of ln(τ) vs. ln(T ).
Paper Dalton Transactions
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good agreement with the experimental results, fitted using
thePHI program. Consequently, the positive D value for 1 and
thenegative D value for 2 suggest that compounds 1 and 2
possesscharacteristics of easy-plane anisotropy and easy-axis
an-isotropy, respectively. Furthermore, the energy barrier (Ueff )
ofcompound 1 for the Orbach process is lower than the
valuescalculated from CASSCF with MOLCAS 8.2 (48.0 cm−1) andNEVPT2
with Orca 4.0 (43 cm−1) followed by D(S2 − 1/4).Similar to compound
1, the experimental energy barrier (Ueff )of compound 2 for the
Orbach process is also smaller than thecalculated values according
to DS2. The distinct differencesbetween the experimental and
calculated energy barriers canbe ascribed to the QTM existing in
most SMMs.
The calculated orientations of the gx, gy and gz on CoII and
FeII of compounds 1 and 2 using CASSCF calculations (CAS(7,5 +
5′) and CAS(6, 5 + 5′) for 1 and 2, respectively) are shown inFig.
5. For 1, the hard axis (gz) is almost along the direction ofthe
two axial atoms, while the easy axes (gx and gy) are verti-cally
located in the plane of the ligand pypzbeyz. Furthermore,the
transverse g values (gx and gy) are visibly larger than theaxial g
value (gz), further supporting the easy-plane anisotropyof
seven-coordinate CoII ions for 1 in the pseudo-D5h sym-metry. For
2, the easy axis (gz) is along the direction of thecrossing planes
between two ligands, while the hard axes(gx and gy) are located in
the middle positions of the crossingplanes. Obviously, gz is larger
than gx and gy, confirming theeasy-axis anisotropy of the
eight-coordinate FeII ions in 2 inthe pseudo-D2d symmetry.
Conclusions
In summary, we have successfully designed and synthesizedtwo
high-coordinate 3d compounds [CoII(pypzbeyz)(NO3)2] (1)and
[FeII(pypzbeyz)2](BF4)2(CH3CN) (2) based on an asym-metric
tetradentate ligand pypzbeyz. The crystal structures ofthe
compounds indicate that the cobalt centre in 1 is in
thehepta-coordinated environment with a distorted
pentagonalbipyramidal geometry (pseudo-D5h), while the iron centre
in 2has an eight-coordinated environment with a triangular
dode-cahedral geometry (pseudo-D2d). Magnetic measurementsreveal
that both compounds 1 and 2 exhibit slow magnetic
relaxation behaviour due to their magnetic anisotropy in
thespecific symmetry for the mononuclear 3d centers. The easy-plane
magnetic anisotropy for 1 and easy-axis magnetic an-isotropy for 2
were confirmed by the experimental and theore-tical results. This
work will pave an avenue to rationally designand develop
high-coordinate CoII and FeII SIMs in the future.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We thank the National Natural Science Foundation of
China(21601153, 21522103, 21471077, and 11774178). X.-C. Huangalso
thanks the Scientific Research Staring Foundation ofYancheng
Teachers University. We also thank Dr Yuanting Sufrom Nanyang
Technological University (Singapore) for hiskind help in the NMR
analysis.
Notes and references
1 D. E. Freedman, W. H. Harman, T. D. Harris, G. J. Long,C. J.
Chang and J. R. Long, J. Am. Chem. Soc., 2010, 132,1224.
2 (a) G. A. Craig and M. Murrie, Chem. Soc. Rev., 2015, 44,2135;
(b) S. Gómez-Coca, D. Aravena, R. Morales andE. Ruiz, Coord. Chem.
Rev., 2015, 289–290, 379;(c) A. K. Bar, C. Pichon and J.-P. Sutter,
Coord. Chem. Rev.,2016, 308, 346; (d) Y.-S. Meng, S.-D. Jiang,
B.-W. Wang andS. Gao, Acc. Chem. Res., 2016, 49, 2381.
3 M. Atzori, L. Tesi, S. Benci, A. Lunghi, R. Righini,A.
Taschin, R. Torre, L. Sorace and R. Sessoli, J. Am. Chem.Soc.,
2017, 139, 4338.
4 (a) Y.-F. Deng, T. Han, Z. Wang, Z. Ouyang, B. Yin,Z. Zheng,
J. Krzysteke and Y.-Z. Zheng, Chem. Commun.,2015, 51, 17688; (b) W.
Wang, J. Li, L. Yin, Y. Zhao,Z. Ouyang, X. Wang, Z. Wang, Y. Song
and P. P. Power,J. Am. Chem. Soc., 2017, 139, 12069.
5 For examples of Mn(III) SIMs, see: (a) J. Vallejo, A.
Pascual-Alvarez, J. Cano, I. Castro, M. Julve, F. Lloret, J.
Krzystek,G. De Munno, D. Armentano, W. Wernsdorfer, R. Ruiz-Garcia
and E. Pardo, Angew. Chem., Int. Ed., 2013, 52,14075; (b) G. A.
Craig, J. J. Marbey, S. Hill, O. Roubeau,S. Parsons and M. Murrie,
Inorg. Chem., 2015, 54, 13;(c) S. Realista, A. J. Fitzpatrick, G.
Santos, L. P. Ferreira,S. Barroso, L. C. J. Pereira, N. A. G.
Bandeira,P. Neugebauer, J. Hrubý, G. G. Morgan, J. van Slageren,M.
J. Calhorda and P. N. Martinho, Dalton Trans., 2016, 45,12301. For
an example of an Mn(IV) SIM, see: (d) M. Ding,G. E. Cutsail, D.
Aravena, M. Amoza, M. Rouzières,P. Dechambenoit, Y. Losovyj, M.
Pink, E. Ruiz, R. Cléracand J. M. Smith, Chem. Sci., 2016, 7,
6132.
Fig. 5 Calculated orientations of the local magnetic axes of the
grounddoublet on the CoII and FeII ions of complexes 1 (a) and 2
(b) withCASSCF calculations. CAS (7, 5 + 5’) and CAS (6, 5 + 5’)
for compounds 1and 2, respectively.
Dalton Transactions Paper
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6 For examples of Fe(I) SIMs, see: (a) J. M. Zadrozny,D. J.
Xiao, M. Atanasov, G. J. Long, F. Grandjean, F. Neeseand J. R.
Long, Nat. Chem., 2013, 5, 577; (b) C. G. Werncke,P. C. Bunting, C.
Duhayon, J. R. Long, S. Bontemps andS. Sabo-Etienne, Angew. Chem.,
Int. Ed., 2015, 54, 245. Forexamples of Fe(II) SIMs, see: (c) J. M.
Zadrozny,M. Atanasov, A. M. Bryan, C.-Y. Lin, B. D. Rekken,P. P.
Power, F. Neese and J. R. Long, Chem. Sci., 2013, 4,125; (d) M.
Atanasov, J. M. Zadrozny, J. R. Long andF. Neese, Chem. Sci., 2013,
4, 139; (e) X. Feng,C. Mathonière, I.-R. Jeon, M. Rouzières, A.
Ozarowski,M. L. Aubrey, M. I. Gonzalez, R. Clérac and J. R. Long,J.
Am. Chem. Soc., 2013, 135, 15880; (f ) C. Mathonière,H.-J. Lin, D.
Siretanu, R. Clérac and J. M. Smith, J. Am.Chem. Soc., 2013, 135,
19083. For examples of Fe(III) SIMs,see: (g) S. Mossin, B. L. Tran,
D. Adhikari, M. Pink,F. W. Heinemann, J. Sutter, R. K. Szilagyi, K.
Meyer andD. J. Mindiola, J. Am. Chem. Soc., 2012, 134, 13651;(h) X.
Feng, S. J. Hwang, J.-L. Liu, Y.-C. Chen, M.-L. Tongand D. G.
Nocera, J. Am. Chem. Soc., 2017, 139, 16474.
7 For an example of a Co(I) SIM, see: (a) Y.-S. Meng, Z.
Mo,B.-W. Wang, Y.-Q. Zhang, L. Deng and S. Gao, Chem. Sci.,2015, 6,
7156. For examples of Co(II) SIMs, see:(b) J. M. Zadrozny and J. R.
Long, J. Am. Chem. Soc., 2011,133, 20732; (c) Y. Rechkemmer, F. D.
Breitgoff, M. van derMeer, M. Atanasov, M. Hakl, M. Orlita, P.
Neugebauer,F. Neese, B. Sarkar and J. van Slageren, Nat.
Commun.,2016, 7, 10467; (d) E. Colacio, J. Ruiz, E. Ruiz,E.
Cremades, J. Krzystek, S. Carretta, J. Cano, T. Guidi,W.
Wernsdorfer and E. K. Brechin, Angew. Chem., Int. Ed.,2013, 52,
9130; (e) T. J. Woods, M. F. Ballesteros-Rivas,S. Gómez-Coca, E.
Ruiz and K. R. Dunbar, J. Am. Chem.Soc., 2016, 138, 16407; (f )
X.-N. Yao, J.-Z. Du, Y.-Q. Zhang,X.-B. Leng, M.-W. Yang, S.-D.
Jiang, Z.-X. Wang,Z.-W. Ouyang, L. Deng, B.-W. Wang and S. Gao, J.
Am.Chem. Soc., 2017, 139, 373.
8 For examples of Ni(I) SIMs, see: (a) R. C. Poulten,M. J. Page,
A. G. Algarra, J. J. Le Roy, I. López, E. Carter,A. Llobet, S. A.
Macgregor, M. F. Mahon, D. M. Murphy,M. Murugesu and M. K.
Whittlesey, J. Am. Chem. Soc., 2013,135, 13640; (b) W. Lin, T.
Bodenstein, V. Mereacre, K. Finkand A. Eichhöfer, Inorg. Chem.,
2016, 55, 2091. Forexamples of Ni(II) SIMs, see: (c) J. Miklovič,
D. Valigura,R. Boča and J. Titiš, Dalton Trans., 2015, 44,
12484;(d) D. Lomjanský, J. Moncol, C. Rajnák, J. Titiša andR. Boča,
Chem. Commun., 2017, 53, 6930.
9 R. Boča, C. Rajnák, J. Titiš and D. Valigura, Inorg.
Chem.,2017, 56, 1478.
10 X.-C. Huang, C. Zhou, D. Shao and X.-Y. Wang, Inorg.Chem.,
2014, 53, 12671.
11 (a) A. K. Bar, C. Pichon, N. Gogoi, C. Duhayon,S. Ramasesha
and J.-P. Sutter, Chem. Commun., 2015, 51,3616; (b) A. K. Bar, N.
Gogoi, C. Pichon, V. M. L. DurgaPrasad Goli, M. Thlijeni, C.
Duhayon, N. Suaud,N. Guihéry, A.-L. Barra, S. Ramasesha and J.-P.
Sutter,Chem. – Eur. J., 2017, 23, 4380.
12 D. Shao, S.-L. Zhang, L. Shi, Y.-Q. Zhang and X.-Y.
Wang,Inorg. Chem., 2016, 55, 10859.
13 B. Drahoš, R. Herchel and Z. Trávníček, Inorg. Chem.,
2017,56, 5076.
14 (a) P. Antal, B. Drahoš, R. Herchel and Z. Trávníček,
Inorg.Chem., 2016, 55, 5957; (b) L. Chen, S.-Y. Chen, Y.-C.
Sun,Y.-M. Guo, L. Yu, X.-T. Chen, Z. Wang, Z. W. Ouyang,Y. Song and
Z.-L. Xue, Dalton Trans., 2015, 44, 11482.
15 L. Chen, H.-H. Cui, S. E. Stavretis, S. C. Hunter,Y.-Q.
Zhang, X.-T. Chen, Y.-C. Sun, Z. Wang, Y. Song,A. A. Podlesnyak,
Z.-W. Ouyang and Z.-L. Xue, Inorg. Chem.,2016, 55, 12603.
16 (a) M. Di Vaira, F. Mani and P. Stoppioni, J. Chem.
Soc.,Dalton Trans., 1992, 1127; (b) A. K. Patra, K. S. Dube,G. C.
Papaefthymiou, J. Conradie, A. Ghosh andT. C. Harrop, Inorg. Chem.,
2010, 49, 2032; (c) M. Seredyuk,L. Piñeiro-López, M. C. Muñoz, F.
J. Martínez-Casado,G. Molnár, J. A. Rodriguez-Velamazán, A.
Bousseksou andJ. A. Real, Inorg. Chem., 2015, 54, 7424; (d) R.
Adam,R. Ballesteros-Garrido, S. Ferrer, B. Abarca, R.
Ballesteros,J. A. Real and M. C. Muñoz, CrystEngComm, 2016, 18,
7950;(e) H. Petzold, P. Djomgoue, G. Hörner, S. Heider,C. Lochenie,
B. Weber, T. Rüffer and D. Schaarschmidt,Dalton Trans., 2017, 46,
6218; (f ) H. Petzold, P. Djomgoue,G. Hörner, C. Lochenie, B. Weber
and T. Rüffer, DaltonTrans., 2018, 47, 491.
17 L. Chen, J. Wang, J.-M. Wei, W. Wernsdorfer, X.-T. Chen,Y.-Q.
Zhang, Y. Song and Z.-L. Xue, J. Am. Chem. Soc., 2014,136,
12213.
18 J. Xiang, J.-J. Liu, X.-X. Chen, L.-H. Jia, F. Yu, B.-W.
Wang,S. Gao and T.-C. Lau, Chem. Commun., 2017, 53, 1474.
19 G.-L. Li, S.-Q. Wu, L.-F. Zhang, Z. Wang, Z.-W. Ouyang,Z.-H.
Ni, S.-Q. Su, Z.-S. Yao, J.-Q. Li and O. Sato, Inorg.Chem., 2017,
56, 8018.
20 X.-X. Jin, X.-X. Chen, J. Xiang, Y.-Z. Chen, L.-H. Jia,B.-W.
Wang, S.-C. Cheng, X. Zhou, C.-F. Leung and S. Gao,Inorg. Chem.,
2018, 57, 3761.
21 F. Zeng and Z. Yu, Organometallics, 2009, 28, 1855.22 O.
Kahn, Molecular Magnetism, VCH Publishers, Inc.,
New York, 1993.23 SAINT, Version 7.68A, Bruker AXS, Inc.,
Madison, WI, 2009.24 SADABS 2016/2; L. Krause, R. Herbst-Irmer, G.
M. Sheldrick
and D. Stalke, J. Appl. Crystallogr., 2015, 48, 3.25 G. M.
Sheldrick, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 2015, 71, 3.26 (a) F. Aquilante, L. De Vico, N. Ferré,
G. Ghigo,
P.-Å. Malmqvist, P. Neogrády, T. B. Pedersen, M. Pitonak,M.
Reiher, B. O. Roos, L. Serrano-Andrés, M. Urban,V. Veryazov and R.
Lindh, J. Comput. Chem., 2010, 31, 224;(b) V. Veryazov, P.-O.
Widmark, L. Serrano-Andres, R. Lindhand B. O. Roos, Int. J. Quantum
Chem., 2004, 100, 626;(c) G. Karlström, R. Lindh, P.-Å. Malmqvist,
B. O. Roos,U. Ryde, V. Veryazov, P.-O. Widmark, M. Cossi,B.
Schimmelpfennig, P. Neogrády and L. Seijo, Comput.Mater. Sci.,
2003, 28, 222; (d) F. Aquilante, J. Autschbach,R. K. Carlson, L. F.
Chibotaru, M. G. Delcey, L. De Vico,
Paper Dalton Transactions
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ishe
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TY
on
7/2/
2018
10:
00:0
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M.
View Article Online
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-
I. F. Galán, N. Ferré, L. M. Frutos, L. Gagliardi,M. Garavelli,
A. Giussani, C. E. Hoyer, G. L. Manni,H. Lischka, D. Ma, P. Å.
Malmqvist, T. Müller, A. Nenov,M. Olivucci, T. B. Pedersen, D.
Peng, F. Plasser,B. Pritchard, M. Reiher, I. Rivalta, I. Schapiro,
J. Segarra-Martí, M. Stenrup, D. G. Truhlar, L. Ungur, A.
Valentini,S. Vancoillie, V. Veryazov, V. P. Vysotskiy, O.
Weingart,F. Zapata and R. Lindh, J. Comput. Chem., 2016, 37,
506.
27 (a) L. F. Chibotaru, L. Ungur and A. Soncini, Angew.
Chem.,Int. Ed., 2008, 47, 4126; (b) L. Ungur, W. Van den Heuveland
L. F. Chibotaru, New J. Chem., 2009, 33, 1224;(c) L. F. Chibotaru,
L. Ungur, C. Aronica, H. Elmoll, G. Piletand D. Luneau, J. Am.
Chem. Soc., 2008, 130, 12445.
28 (a) F. Neese, ORCA–an ab initio, density functional and
semi-empirical program package, version 4.0, Max-Planck
institutefor bioinorganic chemistry, Mülheim an der Ruhr,
Germany,2017; (b) F. Neese, Wiley Interdiscip. Rev.: Comput. Mol.
Sci.,2018, 8, e1327, DOI: 10.1002/wcms.1327.
29 J. Miralles, O. Castell, R. Caballol and J. P. Malrieu,
Chem.Phys., 1993, 172, 33.
30 B. A. Hess, C. M. Marian, U. Wahlgren and O. Gropen,Chem.
Phys. Lett., 1996, 251, 365.
31 (a) A. D. Becke, J. Chem. Phys., 1993, 98, 5648;(b) A. D.
Becke, Phys. Rev. A, 1988, 38, 3098.
32 J.-M. Wei and Y.-Q. Zhang, Inorg. Chem., 2015, 54,1203.
33 M. Llunell, D. Casanova, J. Cirera, P. Alemany andS. Alvarez,
SHAPE, version 2.1, Universitat de Barcelona,Barcelona, Spain,
2013.
34 N. F. Chilton, R. P. Anderson, L. D. Turner, A. Soncini andK.
S. Murray, J. Comput. Chem., 2013, 34, 1164.
35 K. S. Cole and R. H. Cole, J. Chem. Phys., 1941, 9, 341.36 J.
Vallejo, I. Castro, R. Ruiz-García, J. Cano, M. Julve,
F. Lloret, G. De Munno, W. Wernsdorfer and E. Pardo,J. Am. Chem.
Soc., 2012, 134, 15704.
37 J. M. Zadrozny, J. Liu, N. A. Piro, C. J. Chang, S. Hill
andJ. R. Long, Chem. Commun., 2012, 48, 3927.
38 (a) S. Gomez-Coca, A. Urtizbarea, E. Cremades, P. J.
Alonso,A. Camón, E. Ruiz and F. Luis, Nat. Commun., 2014, 5,4300;
(b) S. Gómez-Coca, D. Aravena, R. Morales andE. Ruiz, Coord. Chem.
Rev., 2015, 289–290, 379.
39 (a) A. Singh and K. N. Shrivastava, Phys. Status Solidi
B,1979, 95, 273; (b) K. N. Shrivastava, Phys. Status Solidi B,1983,
117, 437.
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