Synthesis, Characterization, and Magnetic Properties of a Series of Copper(II) Chloride Complexes of Pyridyliminebenzoic Acids

Article abstract of DOI:10.1002/ejic.201701391

A series of Cu^II halide complexes, Cu(HL1)Cl₂·CH₃OH (1), [Cu(L1)Cl]₂·H₂O (2), [Cu(HL2)Cl₂]₂·2DMF (3), [Cu(HL2)₂Cl]_nCl_n·2nH₂O (4), and

Full text of DOI:10.1002/ejic.201701391

A Journal of
Accepted Article
Title: Synthesis, Characterization, and Magnetic Properties of a Series
of Copper(II) Chloride Complexes of Pyridyliminebenzoic Acids
Authors: Elena Buvaylo, Vladimir Kokozay, Valeriya Makhankova,
Andrii Melnyk, Maria Korabik, Maciej Witwicki, Brian Skelton,
and Olga Vassilyeva
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201701391
Link to VoR: http://dx.doi.org/10.1002/ejic.201701391

10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
Synthesis, Characterization, and Magnetic Properties of a Series
of Copper(II) Chloride Complexes of Pyridyliminebenzoic Acids
Elena A. Buvaylo,[a] Vladimir N. Kokozay,[a] Valeriya G. Makhankova,[a] Andrii K. Melnyk,[b] Maria
Korabik,[c] Maciej Witwicki,[c] Brian W. Skelton,[d] and Olga Yu. Vassilyeva*[a]
Dedicated to Professor Julia Jezierska in honour of her seventieth anniversary
Abstract: A series of Cu(II) halide complexes, Сu(HL1)Cl2∙CH3OH
(1), [Сu(L1)Cl]2∙H2O (2), [Сu(HL2)Cl2]2∙2DMF (3),
molecular devices and machines.1 However, substitution
reactions at the bipyridine backbone to tune the desired
properties of the resulting complexes are challenging from a
synthetic viewpoint and -iminopyridines serve an attractive
[Cu(HL2)2Cl]nCln·2nH2O (4) and [Cu(L3)Cl]n (5), containing
pyridyliminebenzoic acids HL1, HL2 and HL3 derived from o-, m-
and p-aminobenzoic acids, respectively, have been obtained as
single crystals and characterized by elemental analysis, IR, EPR
spectroscopy, magnetic measurements and single-crystal X-ray
diffraction techniques. The results obtained show the formation of
molecular (1), dimeric (2, 3) and polymeric structures (4, 5) based on
chloride (1–4) and carboxylate bridges (5) with copper(II) atoms in
the square-pyramidal geometry of varying degrees of distortion. In
the case of 2 and 5 the ligand deprotonation was completely
achieved even in the absence of a base. The closest Cu···Cu
separations are found in the crystal lattices of the polymer 5 (3.33 Å)
and dimers 2 (3.35 Å) and 3 (3.38 Å). The X-band polycrystalline
EPR spectra of 1–3 with typical axial patterns show no indication of
exchange interactions between copper ions in the range 295–77 K.
The observed rhombic features of the EPR spectra of 4 arise from
the coupling of g-tensors from differently oriented Cu(II) coordination
alternative in this respect.
A
facile preparation of -
iminopyridines by simple
condensation between 2-
pyridinecarbaldehyde (2-PCA) and primary amine have afforded
a number of metal complexes that were screened for catalytic,
luminescent, photophysical, electrochemical and magnetic
properties.2–5 Nevertheless, iminopyridine compounds remain
less explored than bipyridine complexes.
Alpha-iminopyridines bearing free carboxylate ends are
considered highly useful due to their simultaneous activities as
both chelator and
a
bridging ligand adopting various
coordination modes. Aromatic amino acids have proven
themselves very efficient in the design of carboxylate
incorporated Schiff base ligands.6
Metal complexes with halide bridges have been structurally
and magnetically characterized in detail. Over the past several
decades, interest in low-dimensional Cu(II) molecular magnetic
systems in which superexchange pathways involve diamagnetic
halide ions has had a revival in large part owing to the advent of
high-temperature superconductors.7 As the structural variety is
very large, the metal atoms show a wide range of values for the
polyhedra in the solid state.
A characteristic spin-triplet EPR
spectrum of 5 at 77 K was simulated using the spin-Hamiltonian
parameters for S = 1, gx = 2.08, gy = 2.11, gz = 2.37 and the value of
the zero-field splitting parameter
D
of 0.137 cm–1. Magnetic
susceptibility measurements revealed antiferromagnetic (1–3, 5) and
ferromagnetic coupling (4) between the metal atoms at low
temperatures. Theoretical methods were employed to provide
additional insight into magnetic interactions in the studied
compounds.
coupling constant. As
a
result, the magnetostructural
correlations for halide-bridged Cu(II) dimers and polymers are
less obvious than those for hydroxo- and alkoxo bridged copper
compounds. DFT calculations have proven to be a powerful tool
when applied to the field of molecular magnetism. Theoretical
methods can provide significant support for magnetic-exchange
pathways developed from experimental data.8
We have been exploring the chemistry of the Schiff-base
ligands that originate from the condensation of 2-PCA and
amino benzoic acids towards 3d metals (Cr, Mn, Co, Ni, Zn) with
the aim of producing novel complexes with diverse potential
advantages.9 We have now extended our investigations to
copper and describe herein the formation and crystal structures
of five new copper(II) complexes, Сu(HL1)Cl2∙CH3OH (1),
Introduction
Alpha-iminopyridine Schiff base ligands whose nitrogen atoms
are perfectly placed to act cooperatively in cation binding are
electronically similar to classic bipyridines. Metal complexes of
the latter have shown remarkable properties in photochemistry,
photophysics, electrochemistry, supramolecular chemistry,
[Сu(L1)Cl]2∙H2O
(2),
[Сu(HL2)Cl2]2∙2DMF
(3),
[Cu(HL2)2Cl]nCln·2nH2O (4) and [Cu(L3)Cl]n (5), containing
pyridyliminebenzoic acids HL1, HL2 and HL3 derived from o-, m-
and p-aminobenzoic acids, respectively (Scheme 1, DMF – N,N-
dimethylformamide). The position of the carboxylate group in the
structural isomers HL1–HL3 influences the amount of chloride
ligands in the coordination environments around the copper
atoms in 1–5 what imposes the particular bridging pattern
between metal centers. Magnetic susceptibility measurements
revealed antiferromagnetic (1–3, 5) and ferromagnetic coupling
(4) between the Cu atoms. The data obtained were compared to
the exchange parameters of other Cu(II) dimers and polymers
[a]
Department of Chemistry, Taras Shevchenko National University of
Kyiv,
64/13 Volodymyrska str., Kyiv 01601, Ukraine.
Phone +380 44 235 4371
E-mail: vassilyeva@univ.kiev.ua
www.chem.univ.kiev.ua
[b]
Institute for sorption and problems of endoecology, the National
Academy of Sciences of Ukraine,
13 Generala Naumova str., Kyiv 03164, Ukraine
Faculty of Chemistry, University of Wroclaw,
F. Joliot-Curie 14, Wroclaw 50-383, Poland
School of Molecular Sciences, M310, University of Western
Australia, Perth, WA 6009, Australia
[c]
[d]
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
with chloro bridges to assess their consistency with known
magnetostructural J-correlations. Moreover, theoretical methods
were employed to provide a detailed analysis of the electronic
structures of the complexes and independent evaluation of the
magnetic coupling constants.
Scheme 1. Formation of Schiff base ligands HL1, HL2 and HL3 and respective copper(II) complexes 1–5.
Results and Discussion
coordination for 2 and 5, respectively.10 Medium intensity bands
that appear at 1614 (1), 1624 (2), and 1598 cm–1 (3, 4) are
attributed to the imine bonds of HL1 and HL2, respectively. In
the case of 5, the characteristic ν(C=N) absorptions of HL3
merged into the higher energy COO– band. Broad bands
observed in the O–H stretching region (3600–3400 cm–1) of the
spectra of 1–5 with relatively sharp maxima at 3502 and 3428
(1), 3524 and 3447 (2), 3412 and 3458 cm–1 (4) are indicative of
the presence of carboxylic acid and alcohol OH functional
groups along with lattice and adsorbed water molecules with an
extensive network of hydrogen bonds. The sharp multiple
absorption bands with medium to high intensity that appear
Synthesis and IR spectroscopy
Novel Cu(II) chloride complexes 1–5 were synthesized from the
reactions of the pre-formed Schiff base ligands and CuCl2·2H2O
in methanol or a methanol/DMF mixture and isolated by the
solution evaporation method at room temperature.
Compounds with neutral (1, 3 and 4) and deprotonated (2, 5)
Schiff base ligands can be easily distinguished based on their
infrared spectra (Figs S1–S5). The spectra of 1, 3 and 4 are
dominated by sharp absorptions at 1654 (1), 1692 (3) and 1708
cm–1 (4), which are attributed to a C=O stretching vibration of the
carboxylic groups. Two strong bands observed at 1596, 1351 (2)
and 1594, 1392 cm–1 (5) are due to as(COO) and s(COO)
vibrations of the metal coordinated carboxylate functionalities of
HL1 and HL3, respectively. The coordination mode of the
carboxylate can be assigned on the basis of the difference of
these two frequencies [Δ = 245 (2); 202 (5) cm–1], which
indicates the presence of monodentate and bridging
around 1600–1360 cm–1 correspond to the (CC
+ CN)
stretching of the aromatic rings; (CH) and out-of-plane bending
(CH) vibrations of the rings are found at 3100–3000 cm–1 and
786–773 cm–1, respectively. Several peaks arising below 3000
cm–1 on a broad band in the spectra of all complexes are
ascribed to CH stretching of the –HC=N– groups of the ligands
and alkyl groups of the solvents.
Crystal Structures
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
the ideal values of 1 for an equilateral bipyramid and 0 for a
square pyramid,11 is equal to 0.42 (Table 1). A distorted square
pyramidal description is preferred, however, because it better
describes the copper coordination geometry in the related
compounds 1–5 (Table 1). The Cu–N/O bond lengths in 1 follow
a pattern similar to that observed in 2–5 and other square-
pyramidal copper(II) complexes with the axial bond always being
longer than the corresponding basal bonds due to Jahn-Teller
distortion of the copper(II) ion.12 Two basal Cu–Cl bonds in 1
Сu(HL1)Cl2∙CH3OH (1)
The compound crystallizes in the monoclinic space group P21/n;
the asymmetric unit consists of one neutral Cu(HL1)Cl2 molecule
and
a
solvent molecule of crystallization. The copper
coordination sphere, CuN2Cl2O, has a five-coordinate structure
intermediate between a trigonal bipyramid (chlorine atom Cl2
axial) and a square pyramid (carboxylic oxygen O21 apical) and
can be described as a distortion of either (Fig. 1). The angular
structural index parameter,  = (β – α)/60, evaluated from the
two largest angles (α < β) in the five-coordinated geometry with
show
a
traditional
bonding
distance.
1
2
3
4
Figure 1. Structures and principal labelling of the molecules of 1–4. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level. Structure of
one of the dimeric molecules is given for 2.
The lengths of the two carboxylic C–O bonds of 1.225(4) and
1.314(4) Å for 1 unequivocally confirm a molecular form of the
Schiff base. The deprotonated tridentate ligand L1– usually
occupies coordination sites in the basal plane of Cu(II) ion
forming one five- and one six-membered chelate rings with the
metal.13 With carboxylic oxygen O21 placed at the apical
position in 1, HL1 undergoes considerable strain so that the two
fused ring systems are folded along the common Cu(1)−N(10)
axis by 52.55°. This greatly distinguishes complex 1 from 2 and
other copper compounds of the same Schiff base ligand and
different counteranions which show the folding angle of 1.47 (2),
There is a hydrogen bond between the OH hydrogen on the
carboxylic group to the oxygen atom of the methanol solvent
molecule (Table 2). A further, but weaker hydrogen bond,
between the methanol OH hydrogen atom and Cl2 of the
molecule related by a cell translation along the c-axis generates
a hydrogen-bonded dimer (Fig. 2). Another chloride atom
attached to the metal centre, Cl1, very weekly interacts with a π-
system of the neighbouring pyridyl ring with the Cl1···centroid
distance of 4.04 Å. The parallel pyridyl rings of the adjacent
molecules of 1 also display π∙∙∙π stacking with the ring centroid
distance of 3.54 Å (Fig. 2). The hydrogen bonding, π∙∙∙Cl and
π∙∙∙π noncovalent interactions afford Cu···Cu separations in the
crystal lattice equal to 8.69, 6.34 and 7.65 Å, respectively.
−
14.6 (F3CCO2 ),13a 15.28 (NCS−),13b 23.58 (C2O42−),13c and
−
−
28.60° (NO3 , N3 ).13a
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
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Table 1. Geometrical parameters (bond distances, Å, and angles, °) of the
distorted square-pyramidal coordination environment of Cu(II) in 1–5[a]
Cu–Xbasal
Cu–Xax
trans angles
cis angles at
at Cu(II)
Cu(II)
Сu(HL1)Cl2∙CH3OH (1)
Cu(1)–N(10)
Cu(1)–N(11)
Cu(1)–Cl(1)
Cu(1)–Cl(2)
Cu(1)–O(21)
2.005(2)
2.030(2)
2.2601(8)
2.2485(7)
142.13(7);
167.03(7)
79.82(10)–
113.85(8)
2.250(2)
[Сu(L1)Cl]2∙H2O (2)
Cu(1)–N(10)
Cu(1)–N(11)
Cu(1)–O(21)
Cu(1)–Cl(1)
2.024(3)
2.001(3)
1.891(3)
2.3028(10)
169.07(9);
171.89(13)
82.02(13)–
99.11(9)
Cu(1)–Cl(1)1
Cu(2)–N(30)
Cu(2)–N(31)
Cu(2)–O(41)
Cu(2)–Cl(2)
2.7062(11)
2.6561(10)
Figure 2. Fragment of crystal packing of 1 showing the hydrogen bonding,
πCl and ππ noncovalent interactions between Сu(HL1)Cl2 molecules. The
intermolecular H bonds as well as noncovalent interactions are shown as
dashed lines; H atoms are omitted.
2.003(3)
1.997(3)
1.906(3)
2.2898(10)
169.14(13);
173.05(10)
82.72(13)–
95.21(3)
Cu(2)–Cl(2)2
[Сu(HL2)Cl2]2∙2DMF (3)
Table 2. Geometry of hydrogen bonds for 1–4 (Å and °)[a]
Cu(1)–N(1)
Cu(1)–N(20)
Cu(1)–Cl(1)
Cu(1)–Cl(2)
Cu(1)–Cl(1)3
2.0329(16)
155.05(5);
173.05(5)
80.61(6)–
2.0420(16)
2.2767(5)
2.2501(5)
109.390(18)
D–H∙∙∙A
d(D–H)
d(H∙∙∙A)
d(D∙∙∙A)
(DHA)
Сu(HL1)Cl2∙CH3OH (1)
O(22)–H(22)∙∙∙O(1)
O(1)–H(1)∙∙∙Cl(2)1
0.835(19)
0.828(19)
1.76(2)
2.31(2)
2.587(3)
3.129(2)
171(4)
170(4)
2.6258(5)
2.4079(15)
2.4099(18)
[Cu(HL2)2Cl]nCln·2nH2O (4)
[Сu(L1)Cl]2∙H2O (2)
O(1)–H(1A)∙∙∙O(42)
O(1)–H(1B)∙∙∙O(42)2
Cu(1)–N(11)
Cu(1)–N(21)
Cu(1)–N(120)
Cu(1)–Cl(1)
Cu(1)–N(220)
2.0267(15)
175.53(6);
173.67(4)
75.26(6)–
0.81(2)
2.06(2)
2.07(2)
2.864(4)
2.891(5)
169(7)
176(5)
2.0133(15)
2.0643(15)
2.2569(5)
107.72(6)
0.821(19)
[Сu(HL2)Cl2]2∙2DMF (3)
O(21)–H(21O)∙∙∙O(10)
0.811(17)
1.773(16)
2.555(2)
162(3)
[Cu(L3)Cl]n (5)
Cu(1)–N(1)
[Cu(HL2)2Cl]nCln·2nH2O (4)
O(121)–H(121)∙∙∙O(2)
O(221)–H(221)∙∙∙Cl(2)
O(1)–H(1AO)∙∙∙Cl(2)3
O(1)–H(1BO)∙∙∙Cl(2)
2.016(6)
2.069(5)
1.979(4)
1.980(4)
157.24(18);
164.97(19)
79.7(2)–
0.82
1.79
2.592(2)
2.9899(15)
3.172(2)
3.193(2)
163.9
163.7
168(4)
167(4)
Cu(1)–N(20)
Cu(1)–O(21)4
Cu(1)–O(22)5
Cu(1)–Cl(1)
101.95(13)
0.82
2.19
0.808(18)
0.832(17)
2.38(2)
2.38(2)
[a] Symmetry transformations used to generate equivalent atoms: 1 –x, –y, 1–
z; 2 1–x, –y, 2–z , 3 1–x, 2–y, –z.
[a] Symmetry transformations used to generate equivalent atoms: 1 -x,-y,1-z;
2 1-x,1-y,2-z; 3 1-x,2-y,1-z; 4 x-1/2,1/2-y,z-1/2; 5 3/2-x,1/2-y,1-z.
The Cu–Cl bonds to those Cl atoms [2.7062(11), 2.6561(10) Å]
are longer than bonds to the Cl atoms in the basal planes
[2.3028(10), 2.2898(10) Å]. The bond distances and angles are
within the usual range for this type of compound (see
Discussion). The fused five- and six-membered rings of L1–
groups for both dimers in 2 are virtually coplanar [dihedral
angles for Cu1 and Cu2 are 3.31 and 1.47°, respectively].
Cu···Cu separations in the dimers are about 3.51 Å (Cu1) and
3.35 Å (Cu2).
[Сu(L1)Cl]2∙H2O (2)
The compound crystallizes in the triclinic space group P1;
the unit cell contains two independent dimeric molecules, both of
which lie on crystallographic inversion centers. There are no
significant differences between the two molecules (Fig. 1, Table
1). The copper atoms are square pyramidal ( = 0.05 and 0.07),
with N10, N11, Cl1 and O21 (Cu1) and N30, N31, Cl2 and O41
(Cu2) in the basal planes with the apical atoms being the
centrosymmetrically related Cl atoms.
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
are situated between the stacks of dimers; there is a hydrogen
bond between the carboxylic acid group of HL2 and the oxygen
atom of the DMF molecule (Table 2).
The main difference between Cu1 and Cu2 arises from the
involvement of the Cu2 based dimers in hydrogen bonds to
water molecules. The water molecule forms H-bonds with the
uncoordinated carboxylate oxygen atom O(42) and also to the
same atom on a centrosymmetrically related dimeric molecule to
form a one-dimensional hydrogen bonded polymer propagating
along the b axis (Fig. 3, Table 2). In the crystal lattice, the layers
built of hydrogen-bonding polymers in the ab plane alternate
with parallel layers of loose Cu1 based dimers along the c axis.
The offset face-centered aromatic stacking between the layers is
very weak (the ring centroid distances are around 3.62 and 3.73
Å).
[Cu(HL2)2Cl]nCln·2nH2O (4)
The compound crystallizes in the monoclinic space group P21/n;
the asymmetric unit consists of one cation [Cu(HL2)2Cl]+,
chloride anion and a water molecule of crystallization. In contrast
to 3, the copper atom in 4 accommodates two neutral Schiff
base ligands in its coordination sphere; the former are not
symmetry related. The metal atom is square pyramidal ( = 0.03),
with the Cu–N distances in the basal plane lying in the range
2.0133(15)–2.0643(15) Å and the distance to the apical atom,
Cu1-N220 = 2.4079(15) Å, being significantly elongated (Fig. 1,
Table 1). There is also a weak interaction to the coordinated Cl
atom of the molecule related by the crystallographic 21-screw
axis, Cu1–Cl1 [1/2-x, y-1/2, 1/2-z] at 2.9810(5) Å forming a one-
dimensional helical structure along the b axis (Fig. 4). The
second Cl atom, Cl2, is not bonded to the metal center. Although
the hydrogen atoms of water molecule 2 were not located, other
hydrogen bonding interactions are clearly present. The
carboxylic groups are hydrogen bonded to the uncoordinated Cl
atom, Cl2, and O2. Water molecule 1 forms hydrogen bonds to
Cl2 and to a centrosymmetrically-related Cl2. Hydrogen bonding
details are listed in Table 2. The closest Cu···Cu separation in
the crystal lattice is about 4.7 Å. Considering the ring centroid
distance of 3.97 Å between the adjacent aromatic rings in the
chain appreciable π∙∙∙π stacking can be ruled out.
Figure 3. Crystal packing of 2 showing layered arrangement of Cu1 and Cu2
based dimers in the bc plane with intermolecular hydrogen bonds between the
Cu2 based dimers and water molecules shown as dashed lines. H atoms are
omitted for clarity.
Complex 4 is distinguished by a very large difference
between the two Cu–Cl bond lengths [2.2569(5) and 2.9810(5)
Å] compared with other monochloro-bridged copper(II) chains.15
A polynuclear chain built with alternating short and long Cu–Cl
distances of 2.365 and 2.751 Å, respectively, is found in
Cu(ImH)Cl2 (ImH = imidazole).15a In [Cu(2pymehist)Cl](ClO4),
where 2pymehist is 2-(4-imidazolyl)-ethylimino-6-methylpyridine,
this difference is even smaller [2.322(2) and 2.614(2) Å].15b
Nevertheless, a magnetic exchange interaction observed for 4
(see Magnetic Studies) should be transmitted through a very
weakly coordinated µ-Cl– ligand.
[Сu(HL2)Cl2]2∙2DMF (3)
The compound crystallizes in the triclinic space group
; the
P1
dimeric molecule is situated on a crystallographic inversion. The
coordination about the Cu atom can be described as distorted
square pyramidal ( = 0.30), the base consisting of the two
chlorine atoms, Cl1, Cl2 and the two nitrogen atoms, N1, N20
from the bidentate chelate HL2 (Fig. 1, Table 1). Bond
parameters are unexceptional. The apical position is occupied
by the centrosymmetrically related chlorine Cl1’ of the dimer.
This apical Cu1–Cl1’ bond is elongated at 2.6258(5)
Å
compared to the Cu1–Cl1 bond length of 2.2767(5) Å. The trans
angles of the base are N1–Cu1–Cl2 155.05(5)° and N20–Cu1–
Cl1 173.05(5)°. The Cu···Cu separation in the dimer is about
3.38 Å. In contrast to HL1 in 1, the carboxylic group of HL2 in 3
and 4 (see below) stays uncoordinated. Among the relatively few
reported metal complexes of HL2, the ligand demonstrates the
same coordination mode both in monomeric Pd(II),14a Ru(II)14b
coordination compounds and Mn(I)14c and W(0)14d carbonyl
derivatives. In the case of the trimethyl Sn compound,
Sn(CH3)3(H2O)(L2),
the
carboxylate
group
becomes
monodentate to the tin center.14e
Figure 4. One-dimensional chain formed by weak Cu–Cl coordination bonding
in complex 4 along the b axis.
In the crystal lattice of 3, the dimers are arranged in stacks
propagating along the a axis with the minimum Cu···Cu distance
inside the stack being 5.38 Å (Fig. S6). The neighboring
benzene and pyridyl rings along the stack are twisted by 33.08°
with respect to each other with the ring centroid distance of 4.07
Å, too great for effective π–overlap. The solvent DMF molecules
[Cu(L3)Cl]n (5)
The compound crystallizes in the monoclinic space group C2/c;
it is a one-dimensional polymer in the (-1 0 1) direction. The Cu
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
atom is bound to the chlorine atom and the pyridyl and imine
nitrogen atoms of the ligand. It is also bonded to two carboxylate
oxygen atoms from the two adjacent ligands, O21 through the c-
glide and O22 through an inversion center, thus forming the
polymer. The polymer consists of double strands of 4-N-(2’-
pyridylimine)benzoic acid ligands bonded to the copper atoms.
The polymer is not linear but is bent at the copper atoms to form
a zigzag arrangement (Fig. 5). The dihedral angle between the
planes generated by each set of four copper atoms is 63.43(2)°.
The coordination around the copper atom is square pyramidal
with the chlorine at the apex; the Cu atom is displaced 0.30 Å
from the basal plane in the direction of the Cl atom (Table 1).
The two copper atoms are bridged by two bidentate-bridging
carboxylate groups in a syn–syn conformation to form a dimeric
combination of the succinamate(–1) ligand with aromatic N,N’-
chelates.16c The Cu···Cu distances in the latter, that vary from
2.98 to 3.22 Å, are somewhat shorter compared with 5. In the
case
of
Cu2(tzn)(OAc)3
[Htzn
=
1,3-bis(2-
carboxymethyl)benzene triazene,
x
=
3]16b the Cu···Cu
separation is even less than that for the “parent” dicopper
tetraacetate, 2.53 vs. 2.61 Å,17 respectively.
The double stranded polymer of 5 is reinforced by π∙∙∙π
stacking between the parallel benzene rings with the ring
centroid distance of 3.42 Å.
Remarkably,
the
known
solvatomorph
of
5,
[Cu2(L3)2Cl2]n·3nH2O (6),18 demonstrates a completely different
connectivity with the deprotonated Schiff base ligand acting as a
bridge with its two nitrogen atoms chelating to a Cu center of a
Cu2Cl2 ring and its carboxylate oxygen atom coordinating in a
monodentate mode to a copper atom of another Cu2Cl2 ring. As
a result, the four-membered Cu2Cl2 rings in 6 are linked into a
two-dimensional layer.
unit with
a Cu···Cu separation of about 3.33 Å. Partial
paddlewheel motifs Cu2(RCOO)x with x ranging from 1 to 3 have
been reported.16 Structural examples for both x = 1 and x = 2 are
found in the family of copper(II) complexes derived from the
Figure 5. Fragment of the crystal structure of 5 with principal labelling and displacement ellipsoids for non-H atoms drawn at the 50% probability level (left). One-
dimensional double stranded polymer formed by Cu–O coordination bonding in complex 5 projected oblique to the b axis (right).
EPR spectra
the copper(II) ground state.20a Hence, the ground state of Cu(II)
2
2
in 4 is expected to be dominated by the 푑푥
molecular orbital
−푦
The X-band polycrystalline EPR spectra of 1–3 (Fig. 6, Table 3)
show typical axial patterns with no resolved hyperfine structure.
The spectra are almost temperature independent with a subtle
change of their shapes seen between 295 and 77 K. The axial
symmetry characteristics of 1–3 with a gII > g relation (Table 3)
confirm a square-pyramidal coordination geometry for these
complexes suggested by the structural data. The X-band
polycrystalline EPR spectra of 4 at RT and 77 K suggest a
rhombic pattern of the g tensor (g3 > g2 > g1) (Fig. 6, Table 3) and
thus the ground state of Cu(II) with significant contribution from
the 푑푧2 molecular orbital. This does not stay in line with the
square-pyramidal copper polyhedron, for which the  value is
close to 0. Therefore, the experimental g values were tested to
decide if they are actually molecular by the parameter G:19
G = (gz  g0)/[1/2(gx + gy) – g0]
and this is further supported by DFT calculations.
Such EPR behaviour is not unique for square-pyramidal
copper(II) complexes with misaligned local molecular axes. The
X-band EPR spectrum of the polycrystalline compound
[Cu2Cl4(L)]·2CH3CN with substituted 1,3,5-triazine-2,4,6-triamine
ligand L with g1 = 2.05, g2 = 2.11 and g3 = 2.24 was interpreted
by the authors in terms of a rhombic symmetry.20b However, G
value calculated by us from these experimental data is equal to
3.06 indicating that the effective g values are not molecular. Our
inspection of the crystal structure reveals that while the two
Cu(II) centers with the same CuN3Cl2 donor set in the molecule
of [Cu2Cl4(L)]·2CH3CN are symmetry related, their local
molecular axes are profoundly misaligned. In the crystal
structure of [Cu(mpppa)Cl2] [mpppa
–
N-methyl-N-((6-
the
pivaloylamido-2-pyridyl)methyl)-N-(2-pyridylethyl)amine],
which lies in the 4.4–4.9 range when the g values are equal to
molecular values. In the case of 4, the calculated G value is 2.74
strongly implying that the observed EPR features arise from the
coupling of g-tensors from differently oriented Cu(II) coordination
polyhedra in the solid state rather than from a 푑푧2 contribution to
complex molecules with a CuN3Cl2 chromophore are arranged in
a 1D helical chain via intermolecular C–H···Cl hydrogen-bonding
interactions in the way similar to 4.20c Three distinct g values: g1
= 2.185, g2 = 2.140, and g3 = 2.068 observed in its powder EPR
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
spectrum were also interpreted as arising from a rhombic pattern.
The calculated G value of 1.80 does not support this assignment.
* these are not the molecular g parameters, see text for details
The polycrystalline powder EPR spectrum of 5 at room
temperature is dominated by a broad isotropic signal centered at
about geff = 2.16 (Hpp ≈ 1500 G) (Fig. 7). At 77 K 5 shows a
characteristic spin-triplet EPR spectrum with four well-resolved
features at 1400, 2600, 3200 and 3800 cm–1. The feature at
3200 G most certainly originates from a monomeric Cu(II)
impurity, which is always present in dinuclear species and the
absorption at low field (1400 G) is the MS = ±2 transition. The
fine structure components of the spin-triplet state coming from
the first excited state of the antiferromagnetic di-copper entity
were simulated using the spin-Hamiltonian parameters for S = 1,
gx = 2.08, gy = 2.11, gz = 2.37 and the value of the zero-field
splitting parameter D of 0.137 cm–1 (1470 G). The contribution of
paramagnetic impurities was estimated by the magnetic data
fitting.
Figure 6. X-band powder EPR spectra of Сu(HL1)Cl2∙CH3OH (1),
[Сu(L1)Cl]2∙H2O (2), [Сu(HL2)Cl2]2∙2DMF (3) and [Cu(HL2)2Cl]nCln·2nH2O (4)
at 77 K.
The polycrystalline Cu(II) complex of the asymmetric Schiff
base ligand derived from 2-(2-aminoethyl)pyridine and 3,5-di-
Figure 7. X-band EPR spectra of the polycrystalline sample [Cu(L3)Cl]n (5) at
room temperature and 77 K, sim – simulated spectrum for S = 1 with
parameters given in the text.
tert-butyl-4-hydroxybenzaldehyde with
a CuN2O3 donor set
showed three signals in the Q-band EPR spectrum with
observed g values of 2.180, 2.115 and 2.059.20d The spectrum
was considered a result of cooperative effects due to magnetic
exchange between the non-equivalent paramagnetic centers
with the observed values of g components caused by coupling of
the g matrixes. The calculated G value of 2.10 is in accord with
the conclusion made by the authors.
The EPR data show no indication of exchange interactions
between copper ions in 1–4 in the range 295–77 K in agreement
with the experimental magnetic data and calculated exchange
coupling constants (see below).
Magnetic studies
The results of susceptibility measurements of complexes 1–5
are illustrated in Fig. 8 in the form χm, χmT versus T (χm being the
corrected molar magnetic susceptibility per one metal ion and T
is absolute temperature). Temperature dependences of
reciprocal susceptibility χm–1 are also presented in the insets.
Experimental data fitting results for 1–4
Magnetic properties of 1–4 at higher temperatures are very
similar, the χmT values at the room temperature are almost
Table 3. Parameters of powder EPR spectra of 14 at 77 K
Complex
g1
g2
g3
equal:
0.428 (μeff = 1.85 B.M.),
0.422 (μeff = 1.84
B.M.),
0.440 (μeff = 1.88 B.M.) and 0.427 cm3 K mol–1 (μeff = 1.85 B.M.)
for 1–4, respectively. These values practically do not change
with lowering temperature down to 25 K, and then decrease (1–
3) or increase (4) sharply reaching 0.220 (μeff = 1.33 B.M.), 0.286
(μeff = 1.51 B.M.), 0.165 (μeff = 1.15 B.M.) and 1.15 cm3 K mol– 1
(μeff = 3.04 B.M.) for 1–4, respectively, at 1.8 K. This behavior
indicates the occurrence of weak antiferromagnetic (1–3) and
1
2.078
2.061
2.069
2.053
2.078
2.061
2.069
2.103
2.243
2.235
2.252
2.210
2
3
4*
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10.1002/ejic.201701391
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ferromagnetic (4) interactions between copper ions at very low
temperatures.
K and C = 0.464 cm3 K mol–1, θ = –3.07 K for 1, 2 and 3,
respectively. Magnetization data for 3 at 2 K were collected in
the range 0–50 000 G. The experimental data lie below the
M/N calculated value for an isolated S = 1/2 ion, thus
confirming the antiferromagnetic coupling in the complex (Fig.
S7).
Taking into account the dimeric structure of 2 and 3 their
magnetic data have been analyzed using Bleaney-Bowers
equation based on the Hamiltonian H = ∑ Jij Si Sj:
−1
2
2
푁훽
푔
휒푚
=
[1 + 1 푒푥푝 (−퐽)]
(1)
3푘푇
3
푘푇
The magnetic data of compound 4 have been fitted to the
numerical expression of Baker et al.21 for a ferromagnetic S =
where the J value (singlet-triplet energy gap) characterizes
intradimer interactions, N is the Avogadro number, g is the
spectroscopic splitting factor,  is the Bohr magneton, and k is
the Boltzmann constant. While the molecular structure of
complex 1 is monomeric, there are several possible pathways
for magnetic exchange in the crystal through noncovalent
interactions (Fig. 2). The susceptibility versus temperature plot
of 1 was thus fitted with a dimer model. The best-fit parameters
obtained are: g = 2.12, J = –2.3 cm–1, R = 1.2  10–3; g = 2.15, J
= –1.4 cm–1, R = 3.6  10–5 and g = 2.16, J = –4.0 cm–1, R = 7.9
 10–5 for 1, 2 and 3, respectively. Magnetic susceptibilities for
these compounds obey Curie-Weiss low with the parameters: C
= 0.431 cm3 K mol–1, θ = –1.9 K; C = 0.424 cm3 K mol–1, θ = –0.9
1/2 regular chain:
2/3
Ng2 2
4kT
A
 
m 
 
(2)
B
 
where A = 1.0 + 5.7979916y + 16.902653y2 + 29.376885y3 +
29.832959y4
+ B = 1.0 + 2.7979916y +
14.036918y5,
7.0086780y2 + 8.6538644y3 + 4.5743114y4 with y = J/2kT and
with the spin Hamiltonian defined as 퐻 = −퐽 푛−1 푆푖 푆푖+1. J is the
∑
푖=1
intrachain magnetic coupling parameter and other symbols have
their usual meaning. A least-squares fit of the susceptibility data
for complex 4 gives g = 2.16, J = 3.27 cm–1, R = 2.0  10–3.
(1)
(2)
(3)
(4)
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10.1002/ejic.201701391
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(5)
Figure 8. Temperature dependences of χm (□) and χmT (○) for Сu(HL1)Cl2∙CH3OH (1), [Сu(L1)Cl]2∙H2O (2), [Сu(HL2)Cl2]2∙2DMF (3), [Cu(HL2)2Cl]nCln·2nH2O (4)
and [Cu(L3)Cl]n (5). Solid lines represent the best fit, insets show χm–1 vs. T relation.
2
2
Experimental data fitting results for 5
SOMO of 1 is only 51% of 푑푥
in character. This result is
−푦
consistent with data obtained for square-planar [CuCl4]2–
(61%),19 although it is lower due to the distorted structure of 1
allowing for small contributions from the other d-type orbitals.
The substantial contributions from the orbitals of ligands to the
SOMOs of 1–5 bring about the significant spin density flow from
the central copper(II) ions towards the donor atoms of ligands.
This is illustrated with the Löwdin spin populations in Fig. 9.
In a dinuclear Cu(II) complex with the magnetic orbitals
The susceptibility data for 5 show a broad maximum at about
100 K, then decrease gradually till 25 K and further increase
abruptly at lower temperatures (Fig. 7). Such a dependence is
characteristic of two antiferromagnetically coupled copper(II)
ions. The increase of susceptibility below 25 K suggests the
presence of a monomeric impurity in 5. The χmT values of 0.232
(μeff = 1.36 B.M.) at room temperature is lower than the
theoretical value corresponding to S = 1/2 (1.73 B.M.) and drops
down to 0.0124 cm3 mol–1 K (μeff = 0.32 B.M.) at 1.8 K confirming
antiferromagnetic exchange between the copper ions. The
modified Bleaney-Bowers equation (3) that takes into account
the presence of a monomeric impurity was used to fit the
susceptibility data:
(SOMOs) being of the 푑푥
2
2 type, the symmetric and
−푦
antisymmetric combinations of these orbitals are possible and
the singlet–triplet energy gap, hence the J parameter, becomes
dependent on the relative stability of the two combinations.24
The magnetic orbitals predicted at the B3LYP level for dinuclear
2, 3 and 5 are in accord with these expectation. For each of
these three complexes the SOMO#1 is the antisymmetric and
the SOMO#2 the symmetric combination (Fig. 9). Only for 4 the
two combinations were not predicted. Instead, each of the
magnetic orbitals is located on one Cu atom. These can be
explained by the noticeably larger Cu···Cu distance in 4 (4.669
Å) in comparison with 2 (3.506 Å), 3 (3.377 Å) and 5 (3.327 Å).
The intradimer exchange couplings parameters J were
calculated for complexes 2–5 and are listed in Table 4. Usually,
Broken Symmetry (BS) DFT calculations can be reasonably
accurate when compared to the experimentally determined J
values.24c,25 Before further discussion, it is advisable to briefly
compare the performance of the three used functionals, namely
the B3LYP, TPSSh and B97D, and various basis sets. The
results obtained here with the TPSSh method clearly indicate a
stronger magnetic superexchange interaction in comparison with
the functional B3LYP. This is particularly evident if the J values
computed for 5 are compared. The functional B97D predicted
the significantly greater J values for 3, 4 and 5. Interestingly, the
predicted J values were found to change only slightly with the
basis set size, but this alteration brings the computed values
closer to the ones determined experimentally. However, even
the results obtained with use of valence double-zeta basis sets
(def2-SVP and cc-pVDZ) are reasonably accurate.
2
2
2 2
푁푔
훽
푁푔 훽
(
)
휒푚
=
1 − 푥 +
푥
퐽
4푘푇
푘푇[3+exp(− )]
푘푇
(3)
in which x is the molar fraction of noncoupled species.22
The fitting procedure using equation (3) results in J = –118
cm–1, g = 2.18, monomeric impurity x = 3%, R = 5.9  10–5. The
temperature Tmax = 112 K, which was calculated from the
obtained singlet-triplet energy gap J = –118 cm–1 using the
relation |J|/kTmax = 1.599, is in good accordance with Tmax
observed in the experimental data.
Theoretical calculations
The 3d orbitals of a copper(II) ion located in an octahedral ligand
field undergo splitting into the t2g and eg set. Allocation of nine
electrons among them places three electrons in the eg series.
Such an electronic configuration is unstable due to the Jahn-
Teller effect, which lifts the degeneracy and lowers the
molecular symmetry. If the resulting molecular structure
becomes elongated octahedral, square pyramidal or square
2
2
planar, then the unpaired electron occupies the 푑푥
orbital.19,23
−푦
As revealed by the DFT computations (Fig. 9), the singly
occupied molecular orbitals (SOMOs) for complexes 1–5 are not
2
2
2
2
pure 푑푥
but 푑푥
involved in the σ-antibonding interaction
−푦
−푦
with the orbitals of ligands. According to the Löwdin reduced
orbital populations at the B3LYP/def2-TZVP theory level the
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10.1002/ejic.201701391
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In general, all the intradimer exchange coupling constants
calculated at the hybrid DFT theory level (B3LYP and TPSSh)
stay fairly close to their experimental counterparts. In contrast,
the functional B97D, which was shown successful in the
exploration of the weak π∙∙∙π and CH∙∙∙π interactions in Cu
dimers8a, seems to lack accuracy here due to the absence of the
Hartree–Fock (HF) exchange. It appeared unsuitable for the
calculation of intradimer exchange couplings parameters in the
present study.
For complexes 2–4 only a very weak exchange interaction
between the Cu(II) ions was predicted with B3LYP and TPSSh.
Although for 2 and 3 neither of these two functionals were able
to provide the right sign of the J parameter, the absolute error of
several cm–1 in the J value can be considered most satisfactory
when the coupling is weak. In the case of 5, the J values are
noticeably overestimated, but this should be expected at the BS
DFT theory level.25a,b,g Significantly better results were obtained
for 5 with the DDCI2 and DDCI3 ab initio methods and the
combined B3LYP/DDCI3 approach.
In order to identify the paths of exchange coupling via
noncovalent intermolecular interactions in 1, three computational
models were taken under investigation, that is the mediation
through hydrogen bonds engaging the methanol molecules
(labeled as H∙∙∙O), the π∙∙∙π interaction between the HL1 ligands,
and π∙∙∙Cl interaction (Fig. 10). It is noteworthy that in this regard
the functional B97D performed satisfactorily in the prediction of J.
This supports the previous findings of Singh and Rajaraman.8a In
Fig. 10 the spin densities for noncovalently interacting dimers
are shown. Noticeably, along every one of the three interaction
pathsways, there is the spin density concentration and this
suggests that the magnetic coupling can be transmitted along
them.
Figure 9. Molecular structures of model systems used in the computational
study, Löwdin spin populations and isosurfaces of SOMOs. Hydrogen atoms
were removed for clarity.
Table 4. Exchange coupling parameters J (cm–1) computed with three density functionals, ab initio methods and combined approach, the last calculated as J =
J(B3LYP/def2-QZVPP) + [J(DDCI3/cc-pVDZ) – J(B3LYP/cc-pVDZ)]
method
B3LYP
basis set
def2-SVP
def2-TZVP
J
method
basis set
def2-SVP
def2-TZVP
J
method
basis set
def2-SVP
def2-TZVP
J
Complex 1
0.00
TPSSh
0.04
0.02
B97D
-0.04
-0.02
(H∙∙∙O)
-0.32
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10.1002/ejic.201701391
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FULL PAPER
def2-TZVPP
def2-QZVPP
-0.50
-0.26
-0.42
-0.38
-0.26
-0.14
0.74
0.52
0.50
0.52
11.0
10.6
10.6
9.6
def2-TZVPP
def2-QZVPP
def2-SVP
-0.10
-0.10
-0.34
-0.42
-0.48
-0.32
1.62
1.08
1.04
1.08
7.3
def2-TZVPP
-0.04
-0.22
-1.18
--1.22
-1.20
-1.56
2.10
def2-QZVPP
def2-SVP
Complex 1
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
def2-SVP
TPSSh
TPSSh
TPSSh
TPSSh
TPSSh
TPSSh
B97D
B97D
B97D
B97D
B97D
B97D
(π∙∙∙π)
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
Complex 1
(π∙∙∙Cl)
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
1.98
1.95
1.92
Complex 2
Complex 3
Complex 4
Complex 5
1.16
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
7.0
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
1.02
14.0
13.4
7.5
0.80
0.78
7.0
31.48
34.88
34.22
33.52
57.98
63.96
61.12
60.74
-472.61
-492.60
-499.44
-497.71
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
3.6
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
4.0
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
3.6
3.8
3.3
3.8
18.0
17.0
16.4
15.9
-211.8
-210.2
-204.1
-201.4
-209.4
-168.2
-154.0
28.2
26.5
25.4
24.9
-305.8
-297.6
-296.0
-294.2
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-SVP
def2-TZVP
def2-TZVPP
def2-QZVPP
pVDZ
def2-TZVP
def2-TZVPP
def2-QZVPP
def2-TZVP
def2-TZVPP
def2-QZVPP
DDCI2
DDCI3
pVDZ
pVDZ
B3LYP/DDC
I3
def2-
QZVPP/pVDZ
-146.0
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10.1002/ejic.201701391
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HL3, both options are possible, considering structures of 5 and
known 6,18 and, what is more, simultaneous bridging of copper
atoms through two chlorides and one carboxylate group of L3
can occur ([Cu4(L3)2(HL3)2Cl4](ClO4)2∙2CH3OH,18 7).
Magnetic properties of a large variety of mono-chloro- and
di-chloro-bridged copper(II) complexes have been studied for
over four decades with the aim to establish systematic magneto-
structural correlations. There is a large body of data for Cu(μ-
Cl)2Cu complexes with square-pyramidal (SP) and trigonal-
bipyramidal (TBP) coordination geometries. An empirical
correlation between the singlet–triplet gap in such compounds
and the /R0 ratio, where  is a bridging CuClCu angle and R0 is
the longer axial Cu–Cl distance in the SP geometry and the
equatorial distance in the TBP geometry, was proposed by
Hatfield and co-workers.26 It was found that for 32.6 < /R0
<
34.8 °/Å values, the exchange interaction is ferromagnetic and
for values beyond these limits the interactions are
antiferromagnetic. Many of the studied complexes having a
geometry of square pyramids sharing a base-to-apex edge with
parallel basal planes (SP I) are consistent with this correlation
(Table 5, compounds 1–14).27 For complex 3, /R0 value is
equal to 33.0 °/Å, and the exchange is antiferromagnetic (J = –
4.0 cm–1). The structure of SP I complex 2, that is also
antiferromagnetic (J
=
–1.4 cm–1), is complicated by the
presence of two crystallographically independent dimers with
/R0 values of 31.9 and 32.8 °/Å falling into “antiferromagnetic”
and “ferromagnetic” ranges. These results do not fit the trend of
the Hatfield’s analysis. Compounds 2 and 3 with relatively
simple structures are not unique in this respect (Table 5,
compounds 15–24)18,28 emphasizing the need to take into
consideration other structural factors to improve theoretical
models.
Figure 10. Molecular models used in the DFT studies of exchange coupling
mediated by noncovalent intermolecular interactions in 1; in addition spin
density isosurfaces are shown (calculated at the B3LYP/def2-TZVPP theory
level).
For molecular complex 1 with no bridging ligands between
copper atoms, the overall magnetic coupling throughout the
compound is weakly antiferromagnetic in nature, with a J value
of –2.3 cm–1. From the crystal structure, several possible
exchange pathways responsible for the type of magnetic
behavior observed can be inferred: the hydrogen bonding, π∙∙∙Cl
and π∙∙∙π noncovalent interactions. Surprisingly, the magnitude
of the J value obtained in the case of noncovalent interactions in
1 is larger than that for the dichloro-bridged dimer 2 bearing the
same ligand. Both hydrogen bonding29 and π-stacking8a,30 have
been reported to propagate essentially antiferromagnetic
interactions between metal centers with exchange-coupling
constants provided by theoretical calculations being in good
agreement with experimentally reported values. In recent years,
the π···halide interaction has also been recognized as a
noncovalent bonding interaction being able to mediate magnetic
coupling exhibiting a ferromagnetic sign.31 It is not obvious
whether the observed coupling in 1 is due to a particular
exchange pathway since various intermolecular interactions
usually compete in the solid state.
Discussion
Both the chloride ion and carboxylate group are especially
prominent bridging species. Compounds 1–5 are peculiar
examples where substituted benzoic acids and chloride ligands
are combined to produce mono-, di- and polymeric complexes in
which dimeric or polymeric structures are realized through
bridging functions of solely chloride ligands (2–4) or carboxylate
groups (5). While polynuclear and polymeric copper complexes
of deprotonated L1 with bridging carboxylate groups are
known,13 compound 2 demonstrates that in competition with
chloride anions, the latter are in favour of bridging the metal
atoms. At the same time, HL1 in the neutral form seems to
preclude formation of a chloro-bridged species in complex 1 by
occupying the apical position at the copper atom with its
carboxylic oxygen. In the case of HL2, the tridentate-chelate
coordination mode cannot be realized due to sterical reasons.
To the best of our knowledge copper complexes of HL2 have not
been reported, however, 3 and 4 show chloro bridges to prevail
over bridging through carboxylic groups as well. In the case of
Magneto-structural correlations for copper(II) mono-chloro-
bridged chain compounds have not been developed in the same
detail as those for the dichloro-bridged dimers due to the
insufficient amount of both structurally and magnetically
characterized examples.15,28c The relevance of various
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Table 5. Structural and magnetic data for some di-µ-chloro-bridged Cu(II) complexes with SPI geometry[a]
Complex
 [°]
/R0 [°/Å]
29.30
29.91
31.95
32.29
32.59
32.62
32.77
33.1
J [cm–1
–16.0
–7.4
]
d(Cu–Clbasal) [Å]
2.280
R0 [Å]
Ref.
1
[Cu(TMSO)2Cl2]2
88.5
3.020
3.364
2.737
2.766
2.6894
2.698
2.735
2.832
2.657
2.770/2.735
2.846
2.844
2.581
2.675
[27a]
[27b]
[27c]
[27d]
[27e]
[27f]
2
[Cu(2-methylpyridine)2Cl2]2
[Cu(apyhist)Cl]2(ClO4)2
[Cu(pmpe)Cl]2
100.63
87.46
89.31
87.66
88.00
87.10
93.6
2.287
3
–3.09
–4.54
–1.16
+0.62
+5
2.271
4
2.298
5
[Cu(pdon)Cl2]22DMF
[Cu(dmg)Cl2]2
2.2651
2.238
6
7
[Cu(dbea)Cl2]2
2.298
[27g]
[27h]
[20i]
8
[Cu(pzPh)(opo)Cl]2
[Cu(iydio)Cl]2(ClO4)2
[Cu(dien)Cl]2(ClO4)2
[Cu(Hfsaaep)Cl]2
+8.72
+1.16
+0.4
2.289
9
88.81
92.0/92.1
95.27
96.68
88.2
33.4
2.3248
2.313/2.266
2.308
10
11
12
13
14
33.5av
33.6
[27j,k]
[27l]
+0.30
+4.87
+2.28
–3.7
[Cu(bpdio)Cl2]2
33.99
34.17
34.82
2.273
[27m]
[27n]
[27o]
[Cu(pmdio)Cl]2(ClO4)2
[Cu(2,2-dimethylaziridine)2Cl2]2
2.291
93.14
2.347
15
16
17
18
19
20
21
22
23
[Cu(aamo)Cl]2
82.9
29.52
30.49
31.9/ 32.8
32.2
+12.0
+27.46
–1.4
2.329
2.217
2.303/2.290
2.286
2.285
2.292
2.28
2.808
2.906
2.706/2.656
2.732
2.653
2.918
2.64
[28a]
[Cu(pytn)Cl2]2
88.6
[28b]
[Сu(L1)Cl]2∙H2O (2)
[Cu(pbpe)Cl]2(ClO4)2
[Cu2(L3)2Cl2]n·3nH2O (6)
[Cu(Hbpmdio)Cl2]2(ClO4)2
[Cu2(pmdip)2Cl2](ClO4)2
[{Cu(terpy)Cl}2](PF6)2
[Сu(HL2)Cl2]2∙2DMF (3)
[Cu(mebta)2Cl2]2
88.47/ 84.79
88.09
85.61
94.7
This work
[28c]
+6.0
32.3
+4.95
+10.70
–1.95
–5.9
[18]
32.43
32.74
33.0
[28d]
86.44
89.9
[28d]
2.218
2.277
2.302
2.723
2.626
2.629
[28e]
86.76
88.1
33.0
–4.0
This work
[28f]
24
33.5
+6.7
[a]
Ligand abbreviations: TMSO = tetramethylene sulfoxide; apyhist = (4-imidazolyl)ethylene-2-amino-1-ethylpyridine; Hpmpe = N-(1H-pyrrol-2-ylmethylene)-2-
pyridineethanamine; pdon = 1,10-phenanthroline-5,6-dione; dmg = dimethylglyoxime; dbea = N,N-dimethyl,N'-benzyl-ethylenediamine; pzPh = 3-phenylpyrazolyl;
Hopo = 2-hydroxypyridine-N-oxide; iydio = 1-(imidazol-4-ylmethyl)-1,5-diazacyclooctane; dien = diethylenetriamine; H2fsaaep = 3-[N-2-(pyridylethyl)formimidoyl]
salicylic acid; bpdio = 2,2-bis-(2-pyridyl)-1,3-dioxolane; pmdio = 1-(2-pyridylmethyl)-1,5-diazacyclooctane; Haamo = 8-amino-5-aza-4-methyl-3-octene-2-one;
pytn
=
2-(pyrazol-1-yl)-2-thiazoline; pbpe
=
N-{(pyrazol-1-yl)methyl}-N-benzyl-2-(pyridin-2-yl)ethanamine; bpmdio
=
1,5-bis(pyridin-4-ylmethyl)-1,5-
diazacyclooctane; pmdip = 1-(pyridin-2-ylmethyl)-1,4-diazacycloheptane; terpy = 2,2':6',2"-terpyridyl; mebta = methylbenzotriazole.
*J, H = ∑ Jij Si Sj
geometrical aspects in the magnetic behavior of mono-μ-chloro–
copper chains has been considered. Hatfield32a pointed out that
overall ferromagnetic behavior can be expected for values of the
/R0 ratio lower than approximately 40 and higher than 57,
whereas antiferromagnetic character appears when this ratio is
between these two values. Landee and Greeney32b suggested
that the Ltrans–Cu–halide bond angle,, is a better parameter to
assess the magnetic interaction strength. It was further shown
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
that  values close to 180° favour the ferromagnetic behaviour,
while an antiferromagnetic behaviour is observed for the angles
smaller than 167°.15f It is important to note that the above
correlations are valid for mono-chloro-bridged copper(II)
compounds which exhibit geometries comprised between
square-pyramidal and trigonal-bipyramidal. That is not the case
for complex 4 in which the bridging Cl ion occupies an
equatorial coordination site for one Cu(II) ion and the sixth, axial,
position for the symmetry-generated metal center. Nevertheless,
the ferromagnetic coupling in 4 seems to be accounted for by
the  value of 173.67(4)° (N120–Cu1–Cl1). It will be possible to
establish the apparent magneto-structural correlation as further
magnetic and structural data concerning new compounds of this
kind become available.
in 2–4 there is no efficient path for superexchange and thus the
observed magnetic couplings are of minor magnitude. This is
understandable since in these complexes the bridging chlorine
atoms that are in the equatorial position of one Cu(II) ion occupy
the axial position of the other one. Therefore, for each Cu(II) the
different d orbitals participate in the interactions inside the Cu–
Cl–Cu bridge, namely 푑푥
2
2
and 푑푧2 . The latter is not
−푦
magnetically active and thus the exchange interactions between
the two Cu(II) ions are efficiently blocked. The superexchange
interaction in 2–4 could be more thrivingly mediated through the
Cu–Cl–Cu bridge if the magnetic orbitals had noticeable
contribution from 푑푧2 . This, however, was not found in the
Löwdin reduced orbital populations and the EPR spectra
recorded for 2–4 revealed the gz >> gx ≈ gy > 2.0023 relation,
While the majority of the compounds with copper-chloride
bridges usually show small ferromagnetic or antiferromagnetic
coupling constants (Table 5),7,15,18,27,28 copper-carboxylato
which excludes significant 푑푧
orbitals.
2
contribution to the magnetic
As discussed above, the copper-carboxylato bridges in 5
lead to much stronger magnetic interaction and this is well
reproduced in the DFT calculations (significantly negative J
values). In general, the structure of the dimeric unit (Fig. 9)
suggests two possible paths for the observed antiferromagnetic
coupling, that is superexchange through the two carboxylato
bridges provide
a pathway for much stronger magnetic
superexchange. Cu(II) is known to form molecular
tetracarboxylate clusters, which contain the characteristic
paddlewheel dimer. The nature of the group bonded to the
carbon atom in the carboxylato bridge has a dramatic effect on
the coupling constant. When the methyl group in acetate is
replaced by CCl3 J is reduced from –296 to less than –200 cm–1,
whereas its replacement with SiR3 enhances the
antiferromagnetic coupling up to –1000 cm–1 determined from
variable-temperature ESR studies.33 Copper paddlewheels are
also ubiquitous in copper coordination polymers and MOFs.34
The paddlewheel copper(II) carboxylate dimers based on N-(3-
propanoic acid)-1,8-naphthalimide with highly organized,
extended structures are diamagnetic solids at and above room
temperature with J values that must be more negative than –600
cm–1.34a
bridges and the  overlap between the 푑푥
2
2-like SOMOs. The
−푦
analysis of the respective orbitals exposed only one non-
orthogonal magnetic pair with the spatial overlap S = 0.086 (Fig.
11), clearly indicating that the magnetic interaction in 5 is solely
meditated through the two carboxylato bridges. This finding is in
line with the previous study of Rodríguez-Fortea et al.24c It
should be emphasized that accurate inclusion of electron
correlation effects via DDCI2 and DDCI3 significantly improves
the predictions, i.e. the triplet state is closer in energy to the
singlet ground state. This demonstrates how important these
effects are for an accurate estimation of magnetic coupling. The
downside of the MRCI-type methods is their high and steeply
rising computational cost. In this context, it seems important to
notice that the combined B3LYP/DDCI3 approach has been
demonstrated here to work well for the studied dinuclear system,
allowing for recovery of at least a fraction of improvement that
the DDCI3 calculations with a larger basis set could provide.
A
partial paddlewheel structure of
5 suggests that
competitive coordination of chloride ligands precludes formation
of the full copper paddlewheel. Structures of closely related
compounds 6 and 7 support this observation although other
possibilities such as steric constraints cannot be dismissed. The
magnitude of the intramolecular exchange interaction in 5 is
lower compared with that for known full paddlewheels, which is
consistent with the theoretical calculations that a lesser number
of the carboxylato bridges and a larger distance between the two
bridged Cu2+ ions lead to a decrease in the magnetic coupling
intensity.33
An efficient way to interpret results of the BS DFT
calculations is to perform the corresponding orbital
transformation of BS determinant. This assigns the orbitals into
three categories which can be chemically interpreted,25f,35 that is
(i) doubly occupied spin α and β pairs with their spatial overlap
close to unity (S ≈ 1); (ii) non-orthogonal magnetic spin α and β
pairs with their overlap clearly smaller than one (S < 1), and (iii)
unpaired spin α orbitals. The non-orthogonal magnetic orbitals
provide an image of magnetic interaction while the spatial
overlap for each magnetic pair indicates the strength of the
interaction that this pair mediates. The inspection of the
corresponding orbitals obtained for the BS solution for 2–4 did
not reveal the non-orthogonal magnetic pairs. This indicates that
Figure 11. Pair of non-orthogonal magnetic orbitals of complex 5.
The DFT calculations provided revealing insight into the role
of three noncovalent interactions that can possibly mediate the
exchange interaction in 1. The J parameters in Table 4
demonstrate that these interactions route different types of
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
magnetic coupling in accordance with the literature data. The
network of hydrogen bonds is predicted to introduce
antiferromagnetic spin ordering (J < 0). The same type of
magnetic coupling is transmitted by the π∙∙∙π interaction,
however the latter pathway is noticeably more efficient (|JH∙∙∙O| <
|Jπ∙∙∙π|). On the other hand, the π∙∙∙Cl interaction mediates
ferromagnetic coupling between neighbouring Cu(II) ions.
According to the DFT calculations the net value of J is slightly
positive, for instance at the B97D/QVZPP it amounts to 0.14 cm–
1. This is very close to experimentally determined –2.3 cm–1. The
deviation between the theory and experiment of a few cm–1 at
the DFT level is easily acceptable, but at the same time it shows
that in the DFT calculations the role of H∙∙∙O and π∙∙∙π is
design of low-dimensional systems with specific magnetic
lattices.
Experimental Section
Materials and Instrumentations
Commercially available chemicals were used as received; all
experiments were carried out in air. Elemental analysis for Cu were
performed by atomic absorption spectroscopy. Elemental analyses for
CHN were performed using a Perkin-Elmer 2400 series analyzer. The IR
spectra were recorded on a Perkin-Elmer 1600 FT–IR spectrometer (KBr
pellet, 4000–400 cm–1).
powdered samples over the temperature range 1.8–400
Magnetic susceptibility measurements of
at the
underestimated,
while
the
π∙∙∙Cl
interaction
seems
K
overestimated. All in all, the DFT calculations demonstrated that
the value of J observed for 1 is a subtle interplay of three paths
of magnetic exchange. Unfortunately, for such a large scale
molecular models the application of multireference methods is a
computationally prohibited task.
magnetic field of 5000 G and magnetization measurements at 2 K,
between 0 and 50 000 G, were carried out with a SQUID magnetometer
(Quantum Design MPMSXL-5). Corrections for the sample holders were
applied. Diamagnetic corrections for the molecule were determined from
Pascal’s constants. X-band (9.8 GHz) EPR spectra were recorded on a
Bruker ELEXSYS E500 instrument equipped with an NMR teslameter
(ER 036TM) and a frequency counter (E 41 FC) and operating at
microwave power of 10 mW, modulation amplitude of 0.5 mT and 2048
data points per spectrum. The experimental spectra were simulated
using the program SPIN (S = 1/2, S > 1/2) written by Dr Andrew
Ozarowski from NHMFL, University of Florida, with resonance field
calculated by full diagonalization of energy matrix.
Conclusion
We explored coordination abilities of Schiff base ligands HL1,
HL2 and HL3 derived from 2-pyridinecarbaldehyde and o-, m-
and p-aminobenzoic acids, respectively, towards copper(II)
chlorides in methanol and dmf. The results show that the
position of the carboxylate group in the structural isomers HL1–
HL3 influences the amount of chloride ligands in the
coordination environments around copper atoms in 1–5, which
imposes the particular bridging pattern between metal centers.
Combination of substituted benzoic acids and chloride ligands
produced mono-, di- and polymeric complexes in which dimeric
or polymeric structures are realized through bridging functions of
solely chloride ligands (2–4) or carboxylate groups (5). The X-
band polycrystalline EPR spectra of 1–4 confirm a square-
pyramidal coordination geometry for these complexes suggested
by the structural data. The EPR data show the absence of
exchange interactions between copper ions in 1–4 in the range
295–77 K in accord with the experimental magnetic data and
calculated exchange coupling constants. Complex 5 exhibited a
characteristic spin-triplet EPR spectrum at 77 K that was
simulated using the spin-Hamiltonian parameters for S = 1, gx =
2.08, gy = 2.11, gz = 2.37 and the value of the zero-field splitting
parameter D of 0.137 cm–1. As expected, compounds 2–4 with
copper-chloride bridges showed small coupling constants, while
Synthesis
Syntheses of the Schiff base ligands
A methanol solution (10 ml) of 2-PCA (0.19 ml, 2 mmol) and the
respective aminobenzoic acid (0.28 g, 2 mmol) in a 50 ml conic flask was
heated to 50 °C and magnetically stirred for half an hour. The resultant
yellow (HL1 and HL2) or brown (HL3) solution (with partially deposited
Schiff base in the case of HL3 that was dissolved by adding 5 ml of DMF)
was left in open air overnight and used as the ligand without further
purification. HL2 was partially deposited overnight.
Syntheses of Сu(HL1)Cl2∙CH3OH (1) and [Сu(L1)Cl]2∙H2O (2)
To a stirred methanol solution of the ligand from the previous preparation
(0.23 g, 1 mmol) CuCl2·2H2O (0.17 g, 1 mmol) dissolved in methanol (10
ml) was added. The solution that immediately turned blue-green, was
heated to 50 °C and magnetically stirred for 20 minutes. The blue-green
powder of 1 started to precipitate during the synthesis and was filtered off.
Crystals suitable for crystallographic determination were formed by the
next day. They were collected by filter-suction, washed with dry PriOH
and finally dried in air. Total yield: 66% (0.26 g). Elemental analysis calcd
(%) for C14H14Cl2CuN2O3 (392.71): C, 42.97; H, 3.58; N, 7.16; Cu, 16.11;
copper-carboxylato bridges in
5 lead to much stronger
antiferromagnetic superexchange. The latter was well
reproduced in the DFT, DDCI2 and DDCI3 calculations. For
complexes 2–4 small values of exchange interactions but the
sign of the J parameter (in the case of 2 and 3) were predicted
at the DFT theory level. Moreover, the DFT calculations
demonstrated that in complex 1 the H∙∙∙O and π∙∙∙π interactions
transmit antiferromagnetic coupling, while π∙∙∙Cl brings about
ferromagnetic coupling. Further theoretical work is needed for
such calculations to reach a level at which they can guide the
found: C, 43.31; H, 3.62; N, 7.45, Cu 16.34%. Complex
2 was
synthesized as described above by employing the crystalline copper salt
and double amounts of the latter and HL1. Total yield: 72% (0.48 g).
Elemental analysis calcd (%) for C26H20Cl2Cu2N4O5 (666.44): C, 46.85; H,
3.02; N, 8.40; Cu, 19.69; found: C, 46.76; H, 3.12; N, 8.48, Cu 19.50%.
Syntheses of [Сu(HL2)Cl2]2∙2DMF (3) and [Cu(HL2)2Cl]nCln·2nH2O (4)
To a flask with the light-yellow powder of HL2 in methanol from the
previous preparation (0.45 g, 2 mmol) CuCl2·2H2O (0.34 g, 2 mmol)
dissolved in DMF (10 ml) was added. The light-green solution was
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
heated to 50 °C and magnetically stirred until total dissolution of HL2 was
observed (30 min). The resulting green solution was filtered and allowed
Crystallographic data for the structures were collected at 100(2) K on an
Oxford Diffraction Gemini (for 1, 2, 4 and 5) or Xcalibur (for 3)
diffractometers using Mo-Kα (λ = 0.71073 Å) radiation or Cu-Kα (λ =
1.5407 Å) radiation in the case of 1 and 5. Following analytical absorption
corrections and solution by direct methods, the structures were refined
against F2 with full-matrix least-squares using the program SHELXL-97.36
The hydroxyl hydrogen atoms in 1 were located and refined with O–H
distances restrained to ideal values. Water molecule and OH hydrogen
atoms in 2, 3, and 4 were refined with restrained O–H distances. Those
for water molecule 2 of 4 could not be located. All remaining hydrogen
atoms in 1–5 were added at calculated positions and refined by use of a
riding model with isotropic displacement parameters based on those of
the parent atom. Anisotropic displacement parameters were employed
for the non-hydrogen atoms. Details of the data collection and processing,
structure solution and refinement for 1–5 are summarized in Table 5.
to stand at room temperature. Green crystals of
3 suitable for
crystallographic determination were formed within several days. They
were collected by filter-suction, washed with dry PriOH and finally dried in
air. Yield: 71% (0.62 g). Elemental analysis calcd (%) for
C32H34Cl4Cu2N6O6 (867.53): C, 44.30; H, 3.95; N, 9.68; Cu, 14.64; found:
C, 44.48; H, 3.99; N, 9.84; Cu 14.77%. Complex 4 was synthesized as
described above by employing the crystalline copper salt and a double
amount of HL2. Yield: 68% (0.85 g). Elemental analysis calcd (%) for
C26H24Cl2CuN4O6 (622.93): C, 50.12; H, 3.98; N, 8.99; Cu, 10.20; found:
C, 49.69; H, 3.91; N, 8.60; Cu 10.49%.
Syntheses of [Cu(L3)Cl]n (5)
To a stirred methanol/DMF solution of HL3 from the previous preparation
(0.45 g, 2 mmol) crystalline CuCl2·2H2O (0.34 g, 2 mmol) was added.
The solution that immediately turned dark-green was heated to 50 °C and
magnetically stirred for 30 minutes. After that it was filtered and allowed
Computational details
The ORCA 4.0.0 suite of programs was employed to perform DFT
calculations.37 To facilitate the comparison between theory and
experiment, fragments of the X-ray structures were used as
computational models after optimization of the positions of all hydrogen
atoms (in the triplet state). This was accomplished with the GGA
functional BP86,38 which is known to provide accurate molecular
to stand at room temperature. Green crystals of
5 suitable for
crystallographic determination were formed within several days. They
were collected by filter-suction, washed with dry PriOH and finally dried in
air. Yield: 75% (0.49 g). Elemental analysis calcd (%) for C13H9ClCuN2O2
(324.21): C, 48.15; H, 2.79; N, 8.64; Cu, 19.59; found: C, 48.36; H, 2.98;
N, 8.39; Cu 19.47%.
structures,39
and
the
def2-TZVP
basis
set.40
Single crystal structure determination
Table 6. Crystallographic data for 1–5
1
2
3
4
5
Empirical Formula
C14H14Cl2CuN2O3
392.71
Monoclinic
P21/n
C26H20Cl2Cu2N4O5
666.44
C32H34Cl4Cu2N6O6
C26H24Cl2CuN4O6
622.93
C13H9ClCuN2O2
324.21
Monoclinic
C2/c
Formula weight
867.53
Triclinic
P1
Crystal system
Triclinic
Monoclinic
P21/n
P1
Space group
T/K
100(2)
100(2)
100(2)
100(2)
100(2)
a/Å
10.9395(4)
7.2584(2)
20.1320(6)
90
7.0361(4)
12.7579(9)
13.9481(9)
79.443(6)
88.108(5)
80.272(6)
2
8.7494(4)
10.0457(5)
10.7161(4)
81.363(4)
81.972(3)
72.249(4)
1
13.4342(3)
7.59610(10)
26.4071(4)
90
17.953(3)
8.6761(11)
16.628(8)
90
b/Å
c/Å
α/°
β/°
104.764(3)
90
98.999(2)
90
116.78(2)
90
γ/°
Z
4
4
8
V/Å3
1545.77(9)
1.687
1213.17(13)
1.824
882.45(7)
1.632
2661.61(8)
1.555
2312.2(12)
1.863
Dcal/g cm–3
No. of reflections measured
No. of independent reflections
Rint
12736
13309
18960
36411
5179
2765
6109
5779
9553
2047
0.0556
0.0460
0.0333
0.0367
0.0825
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10.1002/ejic.201701391
European Journal of Inorganic Chemistry
FULL PAPER
Final R1 values (I>2σ(I))
Final wR(F2) values (I>2σ(I))
Final R1 values (all data)
Final wR(F2) values (all data)
CCDC No.
0.0347
0.0844
0.0457
0.0910
1572285
0.0595
0.1219
0.0859
0.1309
1572286
0.0365
0.0867
0.0444
0.0905
1572287
0.0436
0.0951
0.0594
0.1024
1572288
0.0518
0.1246
0.0931
0.1511
1572289
The optimization took advantage of the Split-RI-J approximation,41 thus
the appropriate auxiliary Coulomb fitting basis set was used.42 At the DFT
Keywords: 2-pyridinecarbaldehyde • o-, m- and p-aminobenzoic
acids • Schiff base ligand • alpha-iminopyridine • Cu(II) chloride
complexes• X-ray crystal structure • X-band EPR • magnetic
measurements • DFT calculations
level the exchange coupling constants
J (H = ∑ Jij Si Sj:) were
theoretically predicted within the broken symmetry (BS) framework using
the following formula:43
퐸
−퐸
퐵푆
푇
[1]
[2]
V. Balzani, G. Bergamini, F. Marchioni, P. Ceroni, Coord. Chem. Rev.
2006, 250, 1254 – 1266.
퐽 = 2 〈
(4)
2
2
〉
〈
〉
푆
− 푆
푇
퐵푆
(a) S. Pasayat, M. Böhme, S. Dhaka, S. P. Dash, S. Majumder, M. R.
Maurya, W. Plass, W. Kaminsky, R. Dinda, Eur. J. Inorg. Chem. 2016,
1604 –1618; (b) B. C. Makhubela, A. M. Jardine, G. Westman, G. S.
Smith, Dalton Trans. 2012, 41, 10715 – 10723.
where ET and EBS are the energies of the triplet and broken symmetry
state, respectively, and 푆
2
2
〈
〉
〈
〉
and 푆
퐵푆
are the expectation values of
푇
the total square spin operator for the two states. In these calculations the
hybrid B3LYP44, hybrid meta-GGA TPSSh45 and semiempirical GGA
functional with a long-range dispersion correction B97D46 were employed
together with def2-SVP, def2-TZVP, def2-TZVPP and def2-QZVPP basis
sets.40 In the calculations with the functionals B3LYP and TPSSh the
RIJCOSX approximation was used,47 hence the appropriate auxiliary
Coulomb fitting basis set was used.42
The exchange coupling for 5 was also determined by means of
Difference Dedicated Configuration Interaction (DDCI2 and DDCI3),48 as
these methods are known to provide highly accurate values of J for
molecular and extended magnetic systems.49 In this case, the value of J
was calculated as:
[3]
[4]
(a) S. Chen, R. Q. Fan, S. Gao, X. Wang, Y. L. Yang, J. Luminesc.
2014, 149, 75 – 85; (b) X. M. Wang, S. Chen, R. Q. Fan, F. Q. Zhang,
Y. L. Yang, Dalton Trans. 2015, 44, 8107 – 8125.
(a) B. Shaabani, A. A. Khandar, M. Dusek, M. Pojarova, F. Mahmoudi,
Inorg. Chim. Acta 2013, 394, 563 – 568; (b) A. Hasheminasab, J. T.
Engle, J. Bass, R. S. Herrick, C. J. Ziegler, Eur. J. Inorg. Chem. 2014,
2643 – 2652.
[5]
[6]
[7]
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J = (ES – ET),
(5)
where ES and ET are the energies of the singlet and triplet state,
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the 푑푥
2
2 -like orbitals. The molecular orbitals employed in the DDCI
−푦
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Consistent Field (CASSCF) method for the triplet state. In these
calculations the correlation-consistent basis sets cc-pVDZ was
employed.50 In addition, a combined approach similar to the ONIOM
method was tested.51 The exchange coupling parameter J was calculated
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Acknowledgements
All the computations were performed using computers of the
Wrocław Centre for Networking and Supercomputing (Grant No.
47). MK and MW acknowledge financial support from a statutory
activity subsidy from the Polish Ministry of Science and Higher
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Entry for the Table of Contents
FULL PAPER
Five monomeric, dimeric and
polymeric Cu(II) complexes with -
iminopyridine ligands have been used
as platforms for detailed
magnetostructural analysis of low-
dimensional Cu(II) molecular magnetic
systems. Theoretical methods
supported magnetic-exchange
pathways developed from the
experimental data.
Magnetostructural correlations
Elena A. Buvaylo, Vladimir N. Kokozay,
Valeriya G. Makhankova, Andrii K.
Melnyk, Maria Korabik, Maciej Witwicki,
Brian W. Skelton, and Olga Yu.
Vassilyeva*
Page No. – Page No.
Synthesis, Characterization, and
Magnetic Properties of a Series of
Copper(II) Chloride Complexes of
Pyridyliminebenzoic Acids
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