Both end-on and end-to-end azide bridged tetranuclear ferromagnetic nickel(II) Schiff base complexes

Article abstract of DOI:10.1039/c7nj00852j

Variable temperature magnetic measurements of a novel tetranuclear nickel(ii) complex, consisting of two pseudo-dinuclear entities bridged by an end-to-end azide, indicate the presence of both intra- and inter-dinuclear ferromagnetic interactions (J₁ = 16.48 cm^-1 and J₂ = 24.17 cm^-1, respectively), as also corroborated by DFT calculations (J₁ = 12.0 cm^-1 and J₂ = 29.2 cm^-1).

Full text of DOI:10.1039/c7nj00852j

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A. Bhattacharyya, M. Das, A. Bauza, S. Herrero, R. González-Prieto and A. Frontera, New J. Chem., 2017,
DOI: 10.1039/C7NJ00852J.
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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Both end-on and end-to-end azide bridged tetranuclear
ferromagnetic nickel(II) Schiff base complex
Anik Bhattacharyyaa, Mithun Dasa, Antonio Bauzáb, Santiago Herreroc, Rodrigo
González-Prietoc, Antonio Fronterab,* and Shouvik Chattopadhyaya,*
aDepartment of Chemistry, Inorganic Section, Jadavpur University, Kolkata ꢀ 700032, India.
Tel: +913324572941; eꢀmail: shouvik.chem@gmail.com
bDepartamento de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma
(Baleares), Spain.
c Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense de
Madrid, Ciudad Universitaria, 28040 Madrid, Spain.
Variable temperature magnetic measurement of a novel tetranuclear
nickel(II) complex, consisted of two pseudoꢀdinuclear entities bridged by an endꢀ
toꢀend azide, indicates the presence of both intra and inter dimer ferromagnetic
interactions (
J
1 = 16.48 cmꢀ1 and J2 = 24.17 cmꢀ1, respectively), as also corroborated
1 = 12.0 cmꢀ1 and 2 = 29.2 cmꢀ1).
by DFT calculations (
J
J
Keywords: Nickel(II); Tetranuclear; EO and EE azide; Ferromagnetic; DFT study;
O•••π hole interaction.
Introduction
A rich diversity of architectures of coordination polymers could be produced
by linking transition and nonꢀtransition metal centres with bridging ligands.1 The
exploration of magnetic properties of these polynuclear
d and f block metal
complexes with exchangeꢀcoupled magnetic centres is an important research topic
nowꢀaꢀdays.2 These coordination polymers could have potential applications in
molecularꢀbased ferromagnets, e.g. single molecule magnets (SMM) and single chain
magnets (SCM), which are promisingly used as data storage devices, nanoscale tools,
quantum computing systems etc.3 In order to prepare nanoscale molecular magnets,
nickel(II) is a preferred spin carrier due to its large singleꢀion zeroꢀfield splitting.4
1

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On the other hand, the flexidentate azide ligand is frequently being used as a
bridging ligand, since it provides coordination complexes with great structural
variety and efficiently mediates different kinds of magnetic exchange depending on
its mode of coordination.5 Thus, the endꢀon (EO) bridging mode gives rise to
ferromagnetic coupling, as far as the Ni–N–Ni angle is below ca. 104°, whereas the
endꢀtoꢀend (EE) bridges generate strong antiferromagnetic coupling. Triply or
quadruply bridging azide coordination modes (such as ꢀ3ꢀ1,1,1, ꢀ3ꢀ1,1,3, ꢀ4ꢀ1,1,1,1 or ꢀ4ꢀ
1,1,3,3) are relatively scarce.6 However, they are also of particular interest for the
construction of polynuclear complexes. N2O2 donor tetradentate Schiff bases are
popularly used as blocking ligands in preparing such azide bridged polyꢀnuclear
complexes, because of their wideꢀranging stability and also for the ease of their
synthesis.7 The fascinating bridging ability of phenoxo oxygen atoms also favours
the formation of such high nuclearity complexes.8 In the present work, we have
used a salicylaldimine Schiff base to prepare an interesting tetranuclear nickel(II)
complex, consisting of azide/phenoxo bridged pseudoꢀdinuclear nickel(II) moieties,
bridged by an EE azide. The variable temperature magnetic susceptibility
measurement indicates the existence of ferromagnetic interactions not only inside
the pseudoꢀdinuclear moieties, but also in between these dinuclear moieties through
the EE azide bridge. DFT calculations corroborate the findings.
Another interesting observation is the existence of Oꢁꢁꢁπ hole interaction in
the complex. It is well known to supramolecular chemists that electron rich entities
interact with an ‘σꢀhole’ (a positive electrostatic potential along the vector of the
covalent bond), as in hydrogen and halogen bonding interactions.9 Although less
common, positive electrostatic potentials can also be found on electron deficient πꢀ
systems and these ‘πꢀholes’ can also attract electron rich species in a directional
manner in the solid state.10 Conventional πꢀacidic systems are aromatic rings
substituted with electron withdrawing substituents.10 More unconventional and
minimalist πꢀholes are, for instance, the nitrogen atom in nitroꢀcompounds such as
2

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nitromethane and nitroaromatics, the carbon atom in carbonyl groups (e.g. amides)
or cyanide, the sulphur atom in SO3, etc.10 In the present paper, the interaction of
the oxygen atom of the perchlorate anion with the imidic carbon atom has been
analysed using the Molecular Electrostatic Potential (MEP) mapped onto the van der
Waals surface. Herein, we report the synthesis, characterization, Xꢀray structure,
magnetic properties and DFT study of a novel, ferromagnetic, tetranuclear
nickel(II) complex and the existence of Oꢁꢁꢁπ hole interaction in it. The interaction
energy has also been calculated.
Experimental Section
All chemicals were of reagent grade and used as purchased from Sigmaꢀ
Aldrich without further purification.
Caution!!! Although no problems were encountered in this work, metal complexes
containing organic ligands in presence of azides are potentially explosive. Only a
small amount of the material should be prepared and it should be handled with care.
Preparation
CH3OH
of
[{Ni2(L)2(µ1,1-N3)(H2O)}(µ1,3-N3){Ni2(L)2(µ1,1-N3)(H2O)}]ClO4·
A methanol solution (20 ml) of 3ꢀmethoxysalicyldehyde (152 mg, 1 mmol) and
N,Nꢀdimethylꢀ1,3ꢀdiaminopropane (0.12 ml, 1 mmol) was refluxed for ca. 1 h. A
methanol (10 ml) solution of nickel(II) perchlorate hexahydrate (370 mg, 1 mmol)
was added and stirred for 15 min. A methanolꢀwater (2:1) solution (10 ml) of sodium
azide (70 mg, 1 mmol) was then added to it. The stirring was continued for an
additional 1 h. A parrot green precipitate was filtered off and the filtrate was left
to stand in the air. Single crystals, suitable for Xꢀ Ray diffraction, were obtained
after few days on slow evaporation of the filtrate.
Yield: 283 mg, (77%, based on nickel). Anal. Calc. for C53H84N17Ni4O15Cl
(1469.59): C, 43.32; H, 5.76; N, 16.20. Found: C, 43.2; H, 5.5; N, 16.4. FTꢀIR (KBr,
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cmꢀ1): 1091 (ClꢀO); 1631 (C=N); 2054, 2078 (N3); 3444 (OꢀH). λmax (nm) [εmax(lit molꢀ1
cmꢀ1)] (DMSO): 994 (17.7); 893 (9.3); 647 (15.4); 384 (2341.5); 262 (3156.9).
Crystal data and refinement details: Formula = C53H84N17Ni4O15Cl; Formula
Weight = 1469.59; Temperature(K) = 150(2); Crystal system = Monoclinic; Space
group = P21; a(Å) = 11.494(7); b(Å) = 21.318(3); c(Å) = 14.593(5); β(deg) = 111.24(4);
Z = 2;
d F (000) = 1540; Total Reflections =
calc(g cmꢀ3) = 1.464; ꢂ(mmꢀ1) = 1.227;
37853; Unique Reflections = 15355; Observed data [I > 2σ(I)] = 13149; No. of
parameters = 809; R(int) = 0.0259; R1, wR2 (all data) = 0.0570, 0.1230; R1, wR2 [I >
2σ(I)] = 0.0450, 0.1158.
Results and Discussion
Synthesis
Scheme 1. Synthetic route to the complex.
The Schiff base, HL, was prepared by the condensation of N,Nꢀdimethylꢀ1,3ꢀ
diaminoproane with 3ꢀmethoxysalicylaldehyde in methanol following the literature
method.11 The tetranuclear complex containing both EO and EE azide bridges was
readily obtained by stirring HL with nickel(II) perchlorate hexahydrate and sodium
azide in methanol (Scheme 1).
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Description
of
structure
of
[{Ni2(L)2(µ1,1-N3)(H2O)}(µ1,3-N3){Ni2(L)2(µ1,1-
N3)(H2O)}]ClO4·CH3OH
The complex (Fig. 1) crystallizes in the monoclinic space group P21. The
asymmetric unit contains a tetranuclear cationic species, [{Ni2(L)2(ꢂ1,1ꢀN3)(H2O)}(ꢂ1,3ꢀ
N3){Ni2(L)2(ꢂ1,1ꢀN3)(H2O)}]+ and a perchlorate anion. The tetranuclear cationic unit
(Fig. S1, ESI) consists of two pseudoꢀdinuclear [Ni2(L)2(ꢂ1,1ꢀN3)(H2O)]+ entities (Fig.
S2, ESI) bridged by an EE azide. Each pseudoꢀdinuclear unit consists of two
elongated octahedral nickel(II) centres doubly bridged by one EO azide and one
phenoxo oxygen. Ni(1) is coordinated by an amine nitrogen, N(1), an imine nitrogen,
N(2) and one phenoxo oxygen, O(1), of one deprotonated tetradentate Schiff base
ligand (L)ꢀ and phenoxo oxygen, O(2) and methoxy oxygen atom, O(3), of another
deprotonated Schiff base ligand.
Fig. 1. Perspective view of the complex with selective atom numbering scheme
highlighting only metal and bridging atoms.
The octahedral geometry of Ni(1) is completed by the coordination through
an azide nitrogen atom, N(5). This azide nitrogen, N(5), is also coordinated to Ni(2)
and act as an ꢂ1,1 azide. The remaining coordination sites of Ni(2) are occupied by
amine nitrogen, N(3), imine nitrogen, N(4) and phenoxo oxygen, O(4), of one
deprotonated tetradentate Schiff base and one water oxygen atom, O(5). The sixth
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coordination site of Ni(2) is occupied by an EE bridged azide, N(8), which links two
pseudoꢀdinuclear units. The perspective views of pseudoꢀdinuclear units are shown in
Fig. S2, ESI. Another dinuclear unit contains Ni(3) and Ni(4) and assumes identical
structure. Selected bond lengths and bond angles are gathered in Tables S1 and S2
(ESI) respectively. The separation between nickel(II) centres in the pseudoꢀ
dinuclear unit is 3.177(2) Å, which is much shorter than the EE azide bridged
nickel(II) centres in the tetranuclear unit [6.010(2) Å], as expected. The torsion
angle Ni(2)–N(8)–N(10)–Ni(3) is 153.96(2)° suggesting the trans nature of EE azide
bridge. The saturated six membered chelate rings, [Ni(1)–N(1)–C(3)–C(4)–C(5)–N(2)]
and [Ni(4)–N(13)–C(42)–C(43)–C(44)–N(14)], have twistꢀboat conformations with
puckering parameters Q = 0.783(4) Å; θ = 88.9(3)°; φ = 93.8(3)° and Q = 0.766(5) Å;
θ = 88.0(4)°; φ = 93.8(3)° respectively while the other two chelate rings, [Ni(2)–
N(3)–C(16)–C(17)–C(18)–N(4)] and [Ni(3)–N(11)–C(29)–C(30)–C(31)–N(12)], have halfꢀ
chair conformations with puckering parameters Q = 0.538(6) Å; θ = 146.4(5)°; φ =
346.2(9)° and Q = 0.545(6) Å; θ = 144.8(5)°; φ = 343.1(9)° respectively.12
There are four hydrogen atoms, H(5C), H(5D) and H(10A) and H(10B), of two
coordinated water molecules, available in the cationic unit for hydrogen bonding
interaction. The hydrogen atoms, H(5C) and H(5D), attached with O(5), of the water
molecule, are hydrogen bonded with an oxygen atom, O(12), of a perchlorate anion
and the phenoxo oxygen atom, O(1), within the pseudoꢀdinuclear unit, respectively.
The hydrogen atoms, H(10B) and H(10A), attached with O(10), of the water
molecule, of another pseudoꢀdinuclear unit are hydrogen bonded with phenoxo
oxygen atom, O(8), and a symmetry related (ꢀ1+x,y,ꢀ1+z) oxygen atom, O(14), of a
perchlorate anion, respectively (Fig. S3, ESI). Thus a hydrogen bonded chain has
been created. The details of hydrogen bonding are given in Table S3, ESI.
Theoretical study on supramolecular assembly
In the solid state of the complex an interesting 1D infinite chain is present
(Fig. 2a) where the tetranuclear complexes are connected by means of the
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perchlorate anions that establishes two concurrent hydrogen bonding interactions
with the coordinated water molecules. The details about hydrogen bonding are given
in the supplementary information. Interestingly, in addition to the hydrogen bonds,
an ancillary πꢀhole interaction is also established (blue dashed line in Fig. 2) between
the perchlorate anion and the carbon atom of the imine bond (the OꢁꢁꢁC distance is
shorter than the sum of the van der Waals radii, i.e. 3.22 Å). In the present
theoretical study, the interaction of the oxygen atom of the perchlorate anion with
the imidic carbon atom has been analysed using several computational tools. The
existence of a πꢀacidic region in a dimeric model of the complex has been analysed
using the Molecular Electrostatic Potential (MEP) mapped onto the van der Waals
surface. The MEP surface is shown in Fig. 2b and it can be observed that the MEP
value over the carbon atom of the imidic C=N bond is positive (5 kcal/mol) thus
highlighting its ability to interact with electron rich atoms.
Fig. 2. (a) Xꢀray fragment of the complex showing the infinite 1D chain; (b) MEP
surface of a dimeric model of the complex; (c) Theoretical model used to evaluate
the πꢀhole interaction. Distances are in Å; (d) Distribution of bond and ring critical
points (red and yellow spheres, respectively) and bond paths for a dimeric model of
the complex.
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This interaction has also been evaluated by extracting a tetranuclear
fragment from the infinite 1D chain of the Xꢀray structure (Fig. 2c). The interaction
energy of this binary complex is ΔE1 = –19.2 kcal/mol where both interactions
(hydrogen bonding and anionꢁꢁꢁπꢀhole) cooperate. In order to estimate the
contribution of the πꢀhole interaction, an additional model has been computed
eliminating the coordinated water molecule (not shown in the figure). As a result, the
hydrogen bonding interaction is not established and the interaction energy is
reduced to ΔE2 = –12.3 kcal/mol that is the contribution of the anionꢁꢁꢁπꢀhole
interaction and the difference (ΔE1 – ΔE2 = –6.9 kcal/mol) is the contribution of the
hydrogen bond. Finally, the Bader’s theory of “atoms in molecules” (AIM)13 has been
used to characterize the πꢀhole and hydrogen bond interactions. A bond critical
point (CP) and a bond path connecting two atoms is an unambiguous evidence of this
interaction. The AIM distribution of critical points and bond paths computed for a
model of the assembly are shown in Fig. 2d. The distribution reveals that the Oꢁꢁꢁπ–
hole interaction is characterized by a bond CPs (red sphere) and a bond path
connecting the O atom of the perchlorate anion to the imidic C atom, thus
confirming the existence of the interaction. The hydrogen bonding interaction is
also characterized by a bond CP (red sphere) and a bond path connecting the O atom
of the perchlorate anion to the H atom of the coordinated water molecule. As a
consequence of the formation of both interactions a ring CP (yellow sphere) also
appears upon complexation due to the creation of a supramolecular ring.
Magnetic properties
The temperature dependence of magnetic susceptibility of the complex has
been measured at 0.2 T between 300 and 1.8 K. The magnetic susceptibility of the
complex increases with decreasing temperature (Fig. 3) as it is typical for
paramagnetic compounds. However, the representation of
χMꢁT versus temperature
shows a continuous increase of the values with decreasing temperature until
reaching a maximum at 10 K. This increase suggests the existence of ferromagnetic
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interactions in the complex. Furthermore, a decrease of the χMꢁT values from 10 to
1.8 K points out to the preponderance of antiferromagnetic interactions or the
existence of zero field splitting, which is typical of nickel(II) complexes. Thus, the
χ
Mꢁ
The final
(6.7 cm3 K molꢀ1) is higher than the calculated spin–only value of 4 cm3 K molꢀ1
assuming = 2. The shape of this curve is similar to those observed for other ꢀꢀ
phenoxoꢀꢀ1,1ꢀazide dinickel(II) complexes.14 Nevertheless, in the present complex,
the Mꢁ value at room temperature is higher and the increase is also more
pronounced that the reported values for similar complexes.14
T
values increase from 6.7 cm3 K molꢀ1 at 300 K to 12.2 cm3 K molꢀ1 at 10 K (Fig. 3).
Mꢁ Mꢁ value at room temperature
value at 1.8 K is 10.1 cm3 K molꢀ1. The
χ
T
χ T
g
χ
T
Fig. 3. Magnetic susceptibility (□) and χMꢁT (○) versus temperature for the
complex. Solid lines indicate the best fit obtained using the PHI program.16
The measurements of the magnetization versus field at 1.8 K (Fig. 4) are in
accordance with the aboveꢀdescribed magnetic data. Thus, the magnetization at 1.8
K strongly increases until about 1 T and, for positive values of the magnetic field,
the experimental magnetization data are higher than the theoretical values
calculated by the Brillouin function considering
g = 2.22, obtained from the magnetic
fit (see below). This indicates suggests the existence of ferromagnetic interactions
in the complex. However, hysteresis is not observed, which is characteristic of soft
magnetic materials.15
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Fig. 4. Magnetization versus magnetic field at 1.8 K for the complex (red squares).
The solid green line indicates the theoretical curve based on the Brillouin function
for positive values of the magnetic field and considering
g = 2.22.
Taking into account the structure of the complex, it would be reasonable to
speculate that the interaction between two nickel(II) centres doubly bridged by an
EO azide and a phenoxide will be much stronger than the coupling through EE azide.
Therefore, the complex was initially considered as two dimers joined by a ligand and
the magnetic susceptibility was calculated per dimer unit. However, all mathematical
expressions based on this model were unsuccessful regardless of the spin system
considered. Hence, the whole tetramer molecule has been considered with two
intramolecular magnetic interactions:
J1 between the two nickel atoms of each dimer
unit and 2 between the two dimers through the azide ligand. Besides the zero field
J
splitting typical for nickel(II) complexes, two additional parameters corresponding
to an intermolecular interaction (zJ) and TIP have also been taking into account. The
parameters obtained from the best fit using the PHI program16 are
g = 2.22, D =
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4.42 cmꢀ1,
1, with σ2 = 5.23×10ꢀ5 (Fig. 3). As indicated above, both intra and interꢀdimer
magnetic interactions are ferromagnetic. J1 and values are very close to those
found for similar situations in dinuclear complexes (16.6 and 16.9 cmꢀ1 for
and 2.25
and 2.20 for
),14 and also close to the values found in theoretical calculations (14.1ꢀ
J J
1 = 16.48 cmꢀ1, 2 = 24.17 cmꢀ1, zJ = 0.01 cmꢀ1, and TIP = 3.14×10ꢀ3 mL molꢀ
g
J
g
15.8 cmꢀ1).14 The low value of
D could be explained by the small distortion of
nickel(II) centres.
Ferromagnetic interactions are also suggested by the fitting of the
reciprocal susceptibility versus temperature to the CurieꢀWeiss law. Fig. S4 (ESI)
shows the variation of 1/χ vs. T and the linear fit in the range 50ꢀ300 K, which
gives a positive value for the Weiss constant (θ = 18.7 K).
Other authors have used ESR studies to complement the magnetic
characterization of polynuclear dꢀmetal complexes in polyoxometalates.17 However,
in our case, an ESR study has been discarded due to the agreement found between
the results obtained by the fit of the experimental data and the results obtained
by the theoretical study on the magnetic properties discussed in the following
section.
Theoretical study on magnetic properties
The magnetic behaviour of this type of complexes has been previously
rationalized in terms of magneto structural correlation.18 In contrast to diꢀ
(phenoxo)ꢀbridged complexes, in dissimilar phenoxo/azide bridged complexes there
are many parameters that influence the magnitude of
J
.19 The exchange interaction
is propagated through the phenoxo and azide bridges and the structural parameters
related to these bridges are used to rationalize the magnetic behaviour of a system
having a ꢂꢀphenoxoꢀꢂ1,1ꢀazide bridging moiety. For the Ni–phenoxo–Ni bridging angle,
values greater than 96–98°, antiferromagnetic behaviour is expected. In sharp
contrast, the interaction is expected to be ferromagnetic for the EO azide bridged
nickel(II) complexes, increasing the
J as the angles increases (up to 104°).
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Therefore, in this ferromagnetic complex the magnetic coupling is dominated by the
ꢂ1,1ꢀazide bridge since the Ni–phenoxo–Ni bridge angle is ~102°. In fact, most of
reported ꢂꢀphenoxoꢀꢂ1,1ꢀazide nickel(II) complexes show ferromagnetic coupling.19
Two different theoretical models have been used to evaluate each magnetic
coupling, as shown in Fig. 5. First, one dimeric unit to evaluate J1 (Fig. 5a) and then
the whole tetramer has been used to (Fig. 5b) to evaluate J2 where two nickel(II)
have been replaced by zinc(II). This procedure has been previously described by
Alvarez group20 and it is a convenient and easy approach to evaluate individual
pairwise coupling in polynuclear complexes.
Fig. 5. Theoretical models used to evaluate J1 (a) and J2 (b) for the complex.
The calculated J1 value is found to be 12.0 cm–1 and is in reasonable
agreement with the experimental value 16.48 cm–1 and confirms the ferromagnetic
coupling. To further examine the magnetic coupling mechanism, the spin density
distribution has been analysed and the Mulliken spin population analysis indicates
that a significant spin (ca. 0.70 e) is delocalized through the ligands, and the rest
(3.30 e) is carried by the central nickel atoms. The spin density plot is shown in Fig.
6a for the high spin state of the complex. The spin density shape located in both
2
2
metal centres evidence that dx –y and dz2 orbitals contain the unpaired electrons as
2
2
in common in octahedral nickel(II) complexes.21 However only the dx –y orbitals of
the metal atom along with the local orbitals of the bridging ligands are involved in
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the superꢀexchange pathway of J1 (Fig. 7). Some spin density values are indicated in
the Figure. Here, the spin carried by the phenoxo oxygen atom is ca. 0.09 e in the
highꢀspin state and the spin carried by the azide bridge is considerable higher (0.16
e).
The BSꢀDFT calculation in the tetramer gives the value of J2 = +29.2 cm–1,
which agrees well with the experimentally one (J
2 = +24.17 cm–1). It is clear from the
spin density plot (Fig. 6b) that the dz2 orbital of each nickel(II) along with the πꢀ
system of the azide mediate in the exchange mechanism, that is further confirmed
by the molecular orbital analysis (Fig. 8). The spin density distribution shows a
delocalization mechanism in which nickel(II) centres carry 86.0% of net spin and the
rest part is delocalized through coordinating atoms. The spin density map of the
high spin state shows that the spin density carried by the azide bridged ligand is
equally delocalized on both sides indicating a spin polarization mechanism that
facilitates the ferromagnetic interaction.
Fig. 6. Graphical representation of spin density (contour 0.004 e/Å3) plots at the
ground state (high spin) configuration of (a) dimer used to evaluate
J1 and (b)
tetramer used to evaluate 2. The spin density values (e) at selected atoms are
J
given.
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Fig. 7. Graphical representation of the molecular orbitals involved in the exchange
pathway of J1
.
Fig. 8. Pictorial representation of the SOMOs for the high spin state of the
complex corresponding to the 2 magnetic exchange.
J
There are several works in the literature dealing with similar systems which
have been also rationalized using theoretical calculations. For instance, Bonnet et
al.22 have synthesized and characterized an alternating EO and EE azide bridged
nickel(II) chain, with single EE and EO coordination modes behaving as isolated
antiferromagnetic {Ni2(ꢂ1,3ꢀN3)}. The ab initio magnetoꢀstructural study evidenced
the efficient antiferromagnetic coupling through the EE bridge and the Ni−N−Ni
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angle independent and almost null
J
EO. Moreover, it has been demonstrated23 the
direct control of magnetic interactions in copper(II) azide bridged binuclear
complexes by means of explicitly correlated ab initio calculations. Remarkably, the
shearing like asymmetry parameter
δ = dlong(Cu–N) – dshort(Cu–N) should be considered
as an important parameter in the control of the coupling constant.24
Concluding Remarks
In conclusion, the use of a potential tetradentate Schiff base as a blocking
ligand affords a novel tetranuclear nickel(II) complex, consisted of EO azide
bridged pseudoꢀdinuclear entities bridged by an EE azide. The existence of strong
ferromagnetic interactions not only inside the EO azide bridged dinuclear units but
also in between the dinuclear units through EE azide bridge is observed. The
present example is thus a new demonstration of versatility in magnetism of the
azide bridged nickel(II) complexes. Unconventional Oꢁꢁꢁπꢀhole interactions in the
solid state of the complex has also been studied by DFT calculations and
characterized using the Bader’s ‘AIM’ theory.
Acknowledgments: A.B. thanks the UGCꢀIndia, for awarding a Senior Research
Fellowship. Spanish Ministerio de Economía y Competitividad (CTQ2015ꢀ63858ꢀP,
CTQ2014ꢀ57393ꢀC2ꢀ1ꢀP MINECO/FEDER) is gratefully acknowledged. We would
like to thank Prof. Y. Song, Nanjing University, P.R. China for magnetic
measurements.
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Both end-on and end-to-end azide bridged tetranuclear
ferromagnetic nickel(II) Schiff base complex
Anik Bhattacharyyaa, Mithun Dasa, Antonio Bauzáb, Santiago Herreroc, Rodrigo
González-Prietoc, Antonio Fronterab,* and Shouvik Chattopadhyaya,*
aDepartment of Chemistry, Inorganic Section, Jadavpur University, Kolkata - 700032, India.
Tel: +913324572941; e-mail: shouvik.chem@gmail.com
bDepartamento de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma
(Baleares), Spain.
c Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense de
Madrid, Ciudad Universitaria, 28040 Madrid, Spain.
Variable temperature magnetic measurement of a novel tetranuclear nickel(II)
complex, consisted of two pseudo-dinuclear entities bridged by an EE azide,
indicates the presence of both intra and inter dimer ferromagnetic interactions, as
also corroborated by DFT calculations.
1