Formation of bis(μ-tetrazolato)dinickel(ii) complexes with N,N,O-donor Schiff bases via in situ 1,3-dipolar cyclo-additions: Isolation of a novel bi-cyclic trinuclear nickel(ii)-sodium(i)-nickel(ii) complex

Article abstract of DOI:10.1039/c3dt52796d

A dinuclear and a novel bi-cyclic hetero trinuclear bis(μ-tetrazolato) bridged nickel(ii) Schiff base complexes [Ni₂(L¹) ₂(PTZ)₂] (1) and [Ni₂(L²) ₂(PTZ)₂Na(H₂

Full text of DOI:10.1039/c3dt52796d

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PAPER
Formation of bis(μ-tetrazolato)dinickel(II)
complexes with N,N,O-donor Schiff bases
via in situ 1,3-dipolar cyclo-additions: isolation of
a novel bi-cyclic trinuclear nickel(II)–sodium(I)–
nickel(II) complex†
Cite this: DOI: 10.1039/c3dt52796d
Mithun Das,a Sudipta Chatterjee,b Klaus Harms,c Tapan Kumar Mondala and
Shouvik Chattopadhyay*a
A dinuclear and a novel bi-cyclic hetero trinuclear bis(μ-tetrazolato) bridged nickel(II) Schiff base com-
plexes [Ni2(L1)2(PTZ)2] (1) and [Ni2(L2)2(PTZ)2Na(H2O)]ClO4·H2O (2) {where HL1 = 2-((2-(dimethylamino)-
ethylimino)methyl)-6-methoxyphenol, HL2 = 2-((2-(methylamino)ethylimino)methyl)-6-methoxyphenol
and HPTZ = 5-(2-pyridyl)tetrazole} have been synthesized by in situ 1,3-dipolar cyclo-addition and
characterized by spectral analysis, X-ray crystallography, and variable-temperature magnetic susceptibility
measurements. Both the complexes crystallize in monoclinic space group P21/c. Both the complexes
feature double µ-NN’-tetrazolato bridged dinickel(II) structures, in which each nickel(II) is coordinated
meridionally by a depronated terdentate Schiff base [(L1)− for 1 and (L2)− for 2] and two nitrogen atoms of
−
−
the (PTZ) . A nitrogen atom from a symmetry related bridging (PTZ) coordinates to complete the distorted
octahedral geometry of nickel(II). The phenoxo and methoxo oxygen atoms from two [NiL2] units and a
water molecule coordinate to a sodium(I) to form the unique bi-cyclic trinuclear nickel(II)–sodium(I)–
nickel(II) core in complex 2. Very strong π⋯π stacking is observed in complex 2 to form a supramolecular
chain. The variable-temperature (1.8–300 K) magnetic susceptibility measurements show the presence of
anti-ferromagnetic coupling between two nickel(II) centers for both complexes with J = −2.14(1) cm−1 (for
1) and J = −1.20(2) cm−1 (for 2). To obtain a better understanding of the magnetic exchange mechanism,
quantum mechanical (DFT) calculations have been performed. The calculated J values [Jtheo = −4.53 cm−1
(for 1) and Jtheo = −2.48 cm−1 (for 2)] are in agreement with the values obtained experimentally.
Received 7th October 2013,
Accepted 19th November 2013
DOI: 10.1039/c3dt52796d
www.rsc.org/dalton
catalysis.8 Current interests in the magnetic study of poly-
nuclear nickel(II) complexes with a variety of bridging groups
Introduction
Encouragement for the syntheses of polynuclear complexes of come from their potential use as a single molecule magnet
transition metals is provided by their potential use as (SMM).9 SMMs are molecules which contain a small number
materials with ferromagnetic properties,1 as materials for non- of magnetic ions with large magnetic interactions between
linear optics,2 as catalysts for diverse reactions3 and as suitable them (J ∼ 10–100 K). In this context, the polynuclear nickel(II)
models for the active sites of many enzymes.4 Among them, di- complexes bridged by azides deserve special mention as they
or poly-nuclear complexes of nickel(II) have been extensively are capable of transmitting ferromagnetic interactions.10
investigated due to their potential applications in bioinorganic These metal ligated azides can be made to undergo 1,3-dipolar
chemistry,5 magneto-chemistry,6 materials chemistry7 and cyclo-addition with a suitable carbonitrile to form tetrazoles,
of which the diazene moiety (–NvN–) may again be used to
bridge nickel(II) to form new dinuclear complexes.11 Diazene
bridged polynuclear complexes of nickel(II) have been studied
in recent years.12 Among them, the pyradizine, pyrazole, tri-
azole and tetrazole groups have been used largely due to their
versatility as ligands (CSD search, ESI†). The coordination
ability of the tetrazolate ligand through the four nitrogen
atoms allows it to serve as a multidentate or a bridging build-
ing block in the field of metal–organic frameworks.13 Among a
aDepartment of Chemistry, Inorganic Section, Jadavpur University, Kolkata –
700 032, India. E-mail: shouvik.chem@gmail.com; Tel: +91-33-24572941
bDepartment of Chemistry, Serampore College, Serampore, Hooghly-712201, India
cFachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse,
D-35032 Marburg, Germany
†Electronic supplementary information (ESI) available. CCDC 942816 and
960204. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3dt52796d
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number of coordination modes of tetrazolates, the 1,2-coordi- H, 4.97; N, 23.01%. Found: C, 50.5; H, 4.7; N, 23.3%. FT-IR
nation mode to produce bis(μ-tetrazolato) bridged complexes (KBr, cm−1): 1638 (CvN), 1446 (tetrazolate), 1402 (tetrazolate).
is relatively common in the literature.14 The structural features, UV-Vis, λmax (nm) [εmax(dm3 mol−1 cm−1)] (DMSO): 390 (3512),
i.e. bridging angles and distances of all these complexes, are 553 (36), 786 (45), 892 (55).
very similar as are the magnetic properties; all of them show
Synthesis of [Ni2(L2)2(PTZ)2Na(H2O)]ClO4·H2O (2). A metha-
weak anti-ferromagnetic coupling.15 In order to introduce nol solution (10 ml) of N-methyl-1,2-diaminoethane (1 mmol,
more variations in the structures and magnetic properties, we 0.08 ml) and 3-methoxysalicylaldehyde (1 mmol, 150 mg) was
have used N,N,O-donor Schiff bases as the blocking ligands.
refluxed for ca. 1 h to produce the ligand 2-((2-(methylamino)-
The chemistry of Schiff-base ligands has received continu- ethylimino)methyl)-6-methoxyphenol (HL2). A methanol solu-
ous and intensive attention in many fields of research because tion (5 ml) of 2-cyanopyridine (1 mmol, 105 mg) was then
of their unique coordination and structural properties.16 added to it, followed by the addition of a methanol solution
Among them, definitely the salen type Schiff bases are being (5 ml) of nickel(II) perchlorate hexahydrate (1 mmol, 365 mg)
paid the most attention, because of the ability of the phenoxo with constant stirring. A solution of sodium azide (1 mmol,
oxygen atoms to form μ2-bridges, thus forming high-nuclearity 65 mg) in a methanol–DMSO (1 : 2) mixture (15 ml) was then
complexes.17 N,N,O-donor terdentate Schiff bases can also added and stirred for 2 h. X-ray quality single crystals were
be easily prepared on refluxing N-substituted diamines with obtained after several weeks on slow evaporation of the mother
different substituted salicylaldehydes.6a,16c These ligands can liquor in a refrigerator. Yield: 350 mg (71%, based on nickel).
then be used to form complexes with several transition Anal. Calc. for C34H42N14NaNi2O10Cl (982.62): C, 41.56; H, 4.31;
metals.4b,9a Tetrazolato bridged dinuclear nickel(II) complexes N, 19.96%. Found: C, 41.7; H, 4.5; N, 19.8%. FT-IR (KBr, cm−1):
containing Schiff bases as the blocking ligands are very rare. 3426 (OH), 3274 (NH), 1646 (CvN), 1431 (tetrazolate), 1408 (tet-
Only one such complex is reported in the literature.18 The mag- razolate), 1082 (perchlorate). UV-Vis, λmax (nm) [εmax(dm3 mol−1
netic properties of such complexes have also not been reported cm−1)] (DMSO): 389 (11 459), 560 (34), 776 (48), 854 (66).
to date. In the present paper, we would like to report the syn-
theses, structures, magnetic properties and DFT studies of two
bis(μ-tetrazolato) bridged nickel(II) complexes, of which one is Physical measurements
the first example of a bi-cyclic trinuclear nickel(II)–sodium(I)–
nickel(II) complex.
Elemental analysis was performed using a PerkinElmer 240C
elemental analyzer. IR spectra in KBr (4500–500 cm−1) were
recorded using a PerkinElmer Spectrum Two FT-IR spectro-
photometer. Electronic spectra in DMSO (1000–300 nm) were
Experimental section
Materials
recorded in a JASCO V-630 UV-VIS spectrophotometer. Variable
temperature magnetic susceptibilities were measured on a
Quantum Design MPMS SQUID-XL7 magnetometer. Diamag-
netic corrections were made with Pascal’s constants for all the
constituent atoms. Fluorescence spectra were obtained on a
Hitachi F-7000 Fluorescence Spectrophotometer at room temp-
erature. Fluorescence total emission intensity decay measure-
All starting materials were commercially available, reagent grade,
and used as purchased from Sigma-Aldrich without further puri-
fication. Caution!!! Although no problems were encountered in
this work, perchlorate salts containing organic ligands are
potentially explosive. Only a small amount of the material
should be prepared and they should be handled with care.
ments were carried out on
a
fluorescence lifetime
spectrometer with components from Edinburgh Analytical
Instruments (EIA, UK) and EG&G ORTEC (USA) and operated
in the time-correlated single-photon-counting mode. Exci-
tation was provided by a pulsed high-pressure (1.5 atm) nitro-
gen lamp operating at 25 kHz repetition rate, the pulse profile
having a FWHM of 1.3 ns. Slits of bandwidth 16 nm were used
in both excitation and emission channels. Intensity decay pro-
Synthesis of [Ni2(L1)2(PTZ)2] (1). A methanol solution
(20 ml) of N,N-dimethyl-1,2-diaminoethane (1 mmol, 0.1 ml)
and 3-methoxysalicylaldehyde (1 mmol, 150 mg) was refluxed
for ca. 1 h to produce the ligand 2-((2-(dimethylamino)ethyl-
imino)methyl)-6-methoxyphenol (HL1). Then a methanol solu-
tion (5 ml) of nickel(II) acetate tetrahydrate (1 mmol, 250 mg)
was added followed by the addition of a methanol–water
(2 : 1 mixture) solution of sodium azide (1 mmol, 65 mg) with
constant stirring. A green coloured solid was separated. The
resulting green solid was filtered and dried in air. The metha-
nol solution of this solid was then added to the methanol solu-
tion of 2-cyanopyridine (1 mmol, 105 mg) with stirring. The
crystalline complex started to separate on standing at room
temperature from the resulting solution and was collected by
filtration after ca. 2 days. X-ray quality single crystals were
obtained as red prisms by slow diffusion of acetonitrile into
the DMSO solution of the complex. Yield: 310 mg (73%, based
on nickel(II)). Anal. Calc. for C36H42N14Ni2O4 (852.22): C, 50.74;
files were fitted to the sum-of-exponentials series
X
IðtÞ ¼
Ai expðꢀt=τiÞ
i
where Ai was a factor representing the fractional contribution
to the time-resolved decay of the component with a lifetime of
τi. Best fit parameters were estimated using software supplied
by Edinburgh Instruments (UK), implementing a non-linear
least-squares iterative fitting procedure. Mean lifetimes were
calculated using the relation
X
X
kτl ¼
Aiτi2=
Aiτi
i
i
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Paper
Electrochemical measurements were performed using an
electrochemical analyzer CHI600C in DMSO solution under a
dry nitrogen atmosphere in conventional three-electrode con-
figurations using a Pt disk working electrode, a Pt auxiliary
electrode and an Ag/AgCl reference electrode, with tetrabutyl-
ammonium hexafluorophosphate as a supporting electrolyte
in the potential range from −1.5 to 1.5 V with 0.1 V s−1 scan
rate, and were uncorrected for junction contribution. Under
our experimental conditions the Fc–Fc+ couple, used as an
internal reference for the potential measurements, was located
at 0.39 V. E1/2 was defined as equal to (Epa + Epc)/2, where Epa
and Epc were the anodic and cathodic peak potentials,
respectively.
Table 1 Crystal data and refinement details in complexes 1 and 2
Complex
1
2
Formula
C
36H42N14Ni2O4
C34H40N14ClNaNi2O9,H2O
982.62
Formula weight
Crystal size [mm]
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
β (°)
852.22
0.06 × 0.17 × 0.25 0.11 × 0.13 × 0.14
100
150
Monoclinic
P21/c
10.8601(3)
20.9255(5)
22.4384(6)
95.719(1)
4
Monoclinic
P21/c
12.9315(15)
14.2046(12)
11.3055(13)
113.218(9)
2
1.483
1.046
888
Z
dcalc. (g cm−3
)
1.263
0.861
1992
μ (mm−1
F(000)
)
Total reflections
Unique reflections
6572
3292
66 876
8522
Crystal data collection and refinement
Crystal data of complex 1 were collected at 100 K on a STOE
IPDS 2T using graphite monochromated Mo-Kα radiation (λ =
0.71073 Å) whereas a single crystal of 2 having suitable dimen-
sions was used for data collection using a ‘Bruker SMART
APEX II’ diffractometer equipped with graphite-monochro-
mated Mo-Kα radiation (λ = 0.71073 Å) at 150 K. In both cases,
the molecular structures were solved by direct methods and
refinement by full-matrix least squares on F2 using the
SHELX-97 package.19 Non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen atoms were placed
in their geometrically idealized positions and constrained to
ride on their parent atoms. H atoms of water molecules were
located by difference Fourier maps and were kept fixed. Multi-
scan empirical absorption corrections were applied to the data
of both the complexes.20 Significant crystallographic data are
summarized in Table 1. CCDC reference numbers 942816 (1)
and 960204 (2). The unit cell of 2 includes a highly disordered
water molecule, which could not be modeled as discrete
atomic sites. So the structure was subjected to the SQUEEZE
procedure from the PLATON suite to calculate the diffraction
contribution of the solvent molecules and thereby produce a
set of solvent-free diffraction intensities.21 A void volume of
657 Å (less than 15% of the unit cell volume) contained a
minimum of 29 electrons. Prior to SQUEEZE, all non-hydrogen
Observed data [I > 2σ(I)] 2716
5871
0.064
0.0720, 0.1490
0.0495, 0.1414
−0.51, 0.77
R(int)
0.030
R1, wR2 (all data)
R1, wR2 [I > 2σ(I)]
Largest diff. in peak
0.0707, 0.1499
0.0583, 0.1444
−0.80, 1.38
and hole (e Å−3
)
For magnetic properties we used the crystallographic co-
ordinates. The magnetic exchange coupling constant was cal-
culated using the equation
Jtheo ¼ ðEBS ꢀ EHSÞ=ð2S1S2 þ S2Þ
where Jtheo was theoretically calculated magnetic exchange
coupling constant, EHS and EBS were the energy in high spin
and broken-symmetry states respectively.25 S1 and S2 were the
spins on the two nickel(II) centres (for dinuclear nickel(II) com-
plexes, S1 = S2 = 1). The approach used here for determining
the magnetic exchange coupling constants for dinuclear com-
plexes was also used by other groups.26
Results and discussion
Synthesis
atoms were made anisotropic and all hydrogen atoms were The ligands HL1 and HL2 were prepared by the 1 : 1 conden-
inserted at their calculated positions. Details of the SQUEEZE sation of 3-methoxysalicylaldehyde with the N,N-dimethyl-1,2-
procedure are given in the CIF file.
diaminoethane and N-methyl-1,2-diaminoethane respectively
in methanol following a literature method.27 The ligands were
not isolated and were used directly for the preparation of
Computational method
The geometries of 1 and 2 were fully optimized in the gas nickel(II) complexes. Addition of nickel(II) acetate in a metha-
phase without symmetry constraints starting from the crystal- nol solution of HL1 followed by the addition of sodium azide
lographic coordinates at the density functional theory (DFT) produced a green coloured complex [Ni(L1)(µ-1,1-N3)Ni(L1)-
level using the hybrid B3LYP exchange-correlation func- (N3)(OH2)], the structure of which was already reported by a
tional,22 as implemented in the Gaussian 09 program.23 The different group.27a The methanol solution of 2-cyanopyri-
triple-ξ quality basis set proposed by Ahlrichs and co-workers dine was then added to methanol solution of the complex
was used for all atoms.24 Frequency calculations on the opti- with constant stirring to produce complex 1 via 1,3-dipolar
mized geometries were performed at the same level of theory cyclo-addition. It is to be noted here that three nickel(II) azide
to confirm that the geometries corresponded to true minima. complexes, [Ni(L)(N3)], cis-[Ni(N3)2(phen)2] and cis-[Ni-
The experimental and theoretical bond distances (Table S1†) (N3)2(bipy)2], [where L = 2-((2-(dimethylamino)ethylimino)-
and angles were comparable (Tables S2 and S3†), giving the methyl)phenol, bipy = 2,2′-bipyridine, phen = 1,10-phenan-
reliability to the level of theory.
throline], have already been made to undergo 1,3-dipolar
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cyclo-addition with a suitable carbonitrile to form tetrazo-
les.11a Among them, only one complex contains Schiff base as
the co-ligand.18 On the other hand, complex 2 was prepared by
stirring a methanol solution of HL2 with 2-cyanopyridine,
nickel(II) perchlorate and sodium azide in DMSO. The differ-
ence in the compositions of the two complexes arises from the
differences in the methods of preparation. In the case of
complex 1, the azide complex was isolated first and this was
then made to react with 2-cyanopyridine. The azide complex
with HL2 could not be isolated even after several attempts.
Thus we are compelled to prepare complex 2 in situ by the reac-
tion of the Schiff base (HL2), nickel(II), sodium azide and 2-
cyanopyridine in a DMSO–methanol mixture. The orientation
of the Schiff base in complex 2 is the reverse to that in
complex 1, and this reversal of orientation is directed by the
presence of sodium(I) in it (Scheme 1).
Structure description
Fig. 1 The ORTEP view of complex 1 showing 30% probability thermal
ellipsoids. H atoms are not shown for clarity. Only the relevant atoms
are leveled. Symmetry element * = 1 − x + 1, −y, −z + 1.
Complex [Ni2(L1)2(PTZ)2] (1). Complex 1 crystallizes in the
monoclinic space group P21/c. The perspective view is shown
in Fig. 1. Selected bond lengths and bond angles are given in
Tables S1 and S2† respectively. The complex features a double
µ-NN′-tetrazolato bridged nickel(II) dimer, in which two dis-
torted octahedral nickel(II) centers are bridged by the two
centrosymmetrically related tetrazolate ions. Within the
dimeric unit, each of the two distorted octahedral nickel(II)
centers is coordinated meridionally by an oxygen atom O(14)
and two nitrogen atoms N(1) and N(4) of a depronated terden-
tate Schiff base (L1)− and two nitrogen atoms, N(17) and N(23)
coordinates to complete the distorted octahedral geometry of
nickel(II). The Ni–N bond lengths fall within the range
1.999(3)–2.193(5) Å as was also observed in similar tetrazolato
nickel(II) Schiff base systems.18 It should be noted that the
µ-NN′ bridging geometry of the (PTZ)− is considerably asym-
metric, which can be seen from the inequality in the bridging
angles (Ni(1)–N(17)–N(18) = 140.1(3) and Ni(1)*–N(18)–N(17) =
124.7(2)), as was also observed in similar complexes.18 The
saturated five membered ring [Ni(1)–N(1)–C(2)–C(3)–N(4)] has
an envelope conformation on C(2) with puckering parameters
−
of the 5-(2-pyridyl)tetrazolate, (PTZ) . A nitrogen atom, N(18),
from a symmetry related (1 − x + 1, −y, −z + 1) bridging (PTZ)−
Scheme 1 Synthetic route for the preparation of complexes 1 and 2.
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Fig. 2 Perspective view of a 1D array in crystal packing of 1 via C–H⋯π interactions. Different intra- (sky blue) and inter-molecular (light green)
interactions are highlighted. Cg(2) = centre of gravity of the ring R1 [Ni(1)–N(17)–C(21)–C(22)–N(23)], Cg(4) = centre of gravity of the ring R2 [Ni(1)–
O(14)–(7)–C(6)–C(5)–N(4)], Cg(5) = centre of gravity of the ring R3 [Ni(1)–N(17)–N(18)–Ni(1)*–N(17)*–N(18)*] and Cg(7) = centre of gravity of the
ring R4 [C(6)–C(7)–C(8)–C(9)–C(10)–C(11)].
Q(2) = 0.437(5) Å and ϕ(2) = 252.3(2)°.28 There are no signifi- perspective view is shown in Fig. 3. Selected bond lengths and
cant H-bonding interactions in the complex.
bond angles are given in Tables S1 and S3† respectively. The
The hydrogen atoms, H(13A) and H(13C), attached with asymmetric unit consists of a cationic trinuclear cation
C(13) of (L1)− form intra-molecular C–H⋯π interaction with [Ni2(L2)2(PTZ)2Na(H2O)]+, an ionic perchlorate and a crystal
the chelate ring R1 [Ni(1)–N(17)–C(21)–C(22)–N(23)]. One aro- water. The lattice water molecule was highly disordered and
matic hydrogen, H(24), attached with C(24) forms intra-mole- was removed using PLATON/SQUEEZE. Each nickel(II) is co-
cular C–H⋯π interaction with the chelate ring R2 [Ni(1)–O(14)– ordinated meridionally by one phenolic oxygen atom and two
(7)–C(6)–C(5)–N(4)]. The hydrogen atom, H(12A), attached with nitrogen atoms [O(1), N(1) and N(2) for Ni(1) and O(2), N(8)
C(12) of (L1)− forms intra-molecular C–H⋯π interaction with and N(9) for Ni(2)] of one depronated terdentate ligand, (L2)−,
the ring R3 [Ni(1)–N(17)–N(18)–Ni(1)*–N(17)*–N(18)*]. The along with two nitrogen atoms [N(3) and N(10) for Ni(1); N(7)
−
hydrogen atom, H(26), attached with C(26) is involved in inter- and N(14) for Ni(2)] of 5-(2-pyridyl)tetrazolate, (PTZ) . The
molecular C–H⋯π interactions with the phenyl ring R4 [C(6)– sixth coordination site of each nickel(II) is occupied by a
C(7)–C(8)–C(9)–C(10)–C(11)] of a symmetry (−x, −y, 1 − z) nitrogen atom [N(6) for Ni(1) and N(13) for Ni(2)] of another
related (L1)− forming one dimensional supramolecular chain (PTZ) bonded to the second nickel(II), constructing a double
−
structure (Fig. 2). Geometric features of the C–H⋯π inter- µ-NN′-tetrazolato bridged nickel(II) complex. It should be
−
actions are given in Table 2.
noted that the µ-NN′ bridging geometry of the (PTZ) is con-
Complex [Ni2(L2)2(PTZ)2Na(H2O)]ClO4·H2O (2). Complex 2 siderably asymmetric, which can be seen from the inequality
crystallizes in the monoclinic space group P21/c. The
Table 2 Geometric features (distances in Å and angles in degrees) of
the C–H⋯π interactions obtained for 1 and 2
Complexes C–H⋯Cg(ring)
H⋯Cg (Å) C–H⋯Cg (°) C⋯Cg (Å)
1
2
C(12)–H(12a)⋯Cg(5) 2.87
3.318(4)
2.984(5)
2.984(5)
3.275(6)
3.627(7)
3.232(5)
3.699(5)
3.039(5)
3.039(5)
109
96
88
101
160
97
139
94
C(13)–H(13a)⋯Cg(2) 2.72
C(13)–H(13c)⋯Cg(2) 2.85
C(24)–H(24)⋯Cg(4) 2.96
C(26)–H(26)⋯Cg(7) 2.72
C(1)–H(1c)⋯Cg(8)
2.96
C(12)–H(12)⋯Cg(13) 2.93
C(18)–H(18a)⋯Cg(4) 2.80
C(18)–H(18b)⋯Cg(4) 2.95
86
Cg(2) = centre of gravity of the ring R1 [Ni(1)–N(17)–C(21)–C(22)–N(23)],
Cg(4) = centre of gravity of the ring R2 [Ni(1)–O(14)–(7)–C(6)–C(5)–
N(4)], Cg(5) = centre of gravity of the ring R3 [Ni(1)–N(17)–N(18)–Ni(1)*–
N(17)*–N(18)*] and Cg(7) = centre of gravity of the ring R4[C(6)–C(7)–
C(8)–C(9)–C(10)–C(11)] for 1 and Cg(4) = centre of gravity of the ring R2
[Ni(2)–N(10)–C(33)–C(34)–N(14)], Cg(8) = centre of gravity of the ring R4
[Ni(1)–N(7)–N(6)–Ni(2)–N(14)–N(13)] and Cg(13) = centre of gravity of
the ring R7 [C(22)–C(23)–C(24)–C(25)–C(26)–C(27)] for 2. Symmetry
element: * = 1 − x + 1, −y, −z + 1.
Fig. 3 The ORTEP view of complex 2 showing 30% probability thermal
ellipsoids for all non-hydrogen atoms. H atoms are shown as spheres of
an arbitrary radius. Only non-carbon bonded H atoms are shown for
clarity. Only the relevant atoms are leveled.
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in the bridging angles (Ni(1)–N(7)–N(6) = 141.4(2), Ni(2)–N(6)– tetrazolato) bridging ring R4 [Ni(1)–N(7)–N(6)–Ni(2)–N(14)–
N(7) = 124.3(2) and Ni(1)–N(13)–N(14) = 126.3(2), Ni(2)–N(14)– N(13)] between two nickel(II) centres respectively. Three intra-
N(13) = 141.2(2)), as was also observed in complex 1. The satu- molecular cation⋯π interactions are observed involving Na(1)
rated five membered ring, Ni(1)–N(1)–C(2)–C(3)–N(2), has an and the rings R3 [N(4)–N(5)–N(6)–N(7)–C(17)], R4 [Ni(1)–N(7)–
envelope conformation on C(2) with puckering parameters Q(2) N(6)–Ni(2)–N(14)–N(13)] and R1 [Ni(1)–N(3)–C(16)–C(17)–N(7)].
= 0.462(4) Å and ϕ(2) = 245.3(4)°, whereas the Ni(2)–N(8)–C(19)– These intra-molecular C–H⋯π and cation⋯π interactions are
C(20)–N(9) ring has twisted geometry over C(19) and C(20) with shown in Fig. 5. There is significant π⋯π interaction between
puckering parameters Q(2) = 0.440(6) Å and ϕ(2) = 81.5(5)°.28
the ring R5 [N(3)–C(12)–C(13)–C(14)–C(15)–C(16)] with a sym-
The sodium(I) centre is penta-coordinated. The geometry of metry related (−x, 1/2 + y, 1/2 − z) ring R6 [N(10)–C(29)–C(30)–
the penta-coordinated metal center may conveniently be C(31)–C(32)–C(33)] forming a supramolecular chain (Fig. 6),
measured by the Addison parameter (τ), which is 0.133 in this with Cg(10)⋯Cg(11), Cg(10)⋯PerpR6 and Cg(11)⋯PerpR5
case [τ = (α − β)/60, where α and β are the two largest ligand– [Cg(ring)⋯PerpR = perpendicular distance of the centre of
metal–ligand angles of the coordination sphere], suggesting a gravity on the corresponding ring] distances being 3.697(2),
slightly distorted square pyramidal geometry (τ = 0 for a 3.359(2) and 3.355(2) respectively and the dihedral angle
perfect square pyramid and τ = 1 for a perfect trigonal bipyra- between R5 and R6 is 0.7(2)°. The chain is further assisted by
mid). The sodium centre, Na(1), is bonded to phenoxo and the inter-molecular C–H⋯π interactions between one aromatic
methoxo oxygen atoms O(1), O(2), O(3) and O(4) from two hydrogen, H(12), attached with C(12) of the ring R5 with the
[NiL2] units, forming the basal plane of the square pyramid. symmetry related (−x, 1/2 + y, 1/2 − z) phenyl ring R7 [C(22)–
The apical fifth coordination site of the sodium(I) centre is C(23)–C(24)–C(25)–C(26)–C(27)] of (L2)−. The perchlorate
occupied by a coordinated water molecule. Thus a bi-cyclic tri- oxygen atom, O(6), is involved in anion⋯π interaction with the
nuclear nickel(II)–sodium(I)–nickel(II) core is produced (Fig. 4). ring R5 (Fig. 6), with the O(6)⋯Cg(10) and Cl(1)⋯Cg(10) dis-
The two µ-oxo bridges present in the trinuclear structure of 2 tances being 3.532(5) Å and 4.942(2) Å respectively and the Cl
is asymmetric, which can be seen from the inequality in the (1)–O(6)⋯Cg(10) angle is 167.6(3)°. Geometric features of the
angles involving the bridging oxygen atoms Ni(1)–O(1)–Na(1) = C–H⋯π and cation⋯π interactions are given in Tables 2 and 3
112.53(11); Ni(2)–O(3)–Na(1)
= 117.66(11). The sodium(I) respectively.
centre, Na(1), is pulled out of the mean square plane towards
the apical donor atom O(5) by 0.5215(16) Å as is usual for a
square pyramidal structure.
IR and electronic spectra and photo-physical studies
The distinct bands at 1638 and 1646 cm−1 due to the azo-
methine (CvN) group are noticed in the IR spectra of com-
plexes 1 and 2 respectively.16 The bands at 1446, 1402 cm−1
(for 1) and 1431, 1408 cm−1 (for 2) are due to the tetrazolate
moiety and also observed in other tetrazolate-based metal
complexes in previous reports.29 A broad band at 3426 cm−1 in
the IR spectrum of 2 indicates the presence of water molecules
in the complex.16c Another broad band at 1082 cm−1 indicates
The hydrogen H(1N), attached with N(1) of (L2)−, is
H-bonded with the oxygen atom, O(6), of an ionic perchlorate
(Fig. 3). The N(1)–H(1N), H(1N)⋯O(6) and N(1)⋯O(6) distances
are 0.92(6), 2.51(6) and 3.415(6) Å respectively; the N(1)–
H(1N)⋯O(6) angle is 169(4)°.
The complex shows cation⋯π, C–H⋯π, anion⋯π inter-
actions and π⋯π stacking. H(18A) and H(18B), attached with
C(18) of (L2)−, are involved in C–H⋯π interactions with the
chelate ring R2 [Ni(2)–N(10)–C(33)–C(34)–N(14)] of (PTZ)− with
metal and H(1C) attached with C(1) of (L2)− and the bis(µ-NN′-
Fig. 5 Perspective view of intra-molecular C–H⋯π and cation⋯π inter-
actions in complex 2. Cg(2) = centre of gravity of the ring R1 [Ni(1)–
N(3)–C(16)–C(17)–N(7)], Cg(4) = centre of gravity of the ring R2 [Ni(2)–
N(10)–C(33)–C(34)–N(14)], Cg(5)
= centre of gravity of the ring
Fig. 4 Perspective view of coordination geometry around sodium(I) and
the bi-cyclic trinuclear nickel(II)–sodium(I)–nickel(II) core in complex 2.
R3 [N(4)–N(5)–N(6)–N(7)–C(17)] and Cg(8) = centre of gravity of the ring
R4 [Ni(1)–N(7)–N(6)–Ni(2)–N(14)–N(13)].
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Fig. 6 Perspective view of a 1D array in crystal packing of 2 via π⋯π stacking and inter-molecular C–H⋯π interaction (intra-molecular interactions
have been omitted for clarity). An anion⋯π interaction has also been shown. Cg(10) = centre of gravity of the ring R5 [N(3)–C(12)–C(13)–C(14)–
C(15)–C(16)]; Cg(11) = centre of gravity of the ring R6 [N(10)–C(29)–C(30)–C(31)–C(32)–C(33)] and Cg(13) = centre of gravity of the ring R7 [C(22)–
C(23)–C(24)–C(25)–C(26)–C(27)].
Table 3 Geometrical parameters (Å, °) for the cation⋯π interactions for
complex 2
Table 4 Spectroscopic and photo-physical data of complexes 1 and 2
in DMSO solutions
Cg(Ring I)⋯M
Cg(I)⋯M (Å)
β (°)
M⋯Perp (Å)
Absorption λmax (nm)
Emission
λmax (nm)
〈τ〉
(ns)
Complexes
[εmax (dm3 mol−1 cm−1)]
Cg(2)⋯Na(1)
Cg(5)⋯Na(1)
Cg(8)⋯Na(1)
3.627
3.626
3.018
32.72
35.96
8.49
3.052
2.935
2.984
1
2
390 (3512), 553 (36), 786 (45),
892 (55)
389 (11 459), 560 (34), 776 (48),
854 (66)
412
437
413
437
0.996
1.008
0.992
0.777
β = Cg(I)⋯M vector and normal to the plane of ring(I); M⋯Perp =
perpendicular distance of M (metal) on ring(I); Cg(2) = centre of gravity
of the ring R1 [Ni(1)–N(3)–C(16)–C(17)–N(7)], Cg(5) = centre of gravity
of the ring R3 [N(4)–N(5)–N(6)–N(7)–C(17)] and Cg(8) = centre of gravity
of the ring R4 [Ni(1)–N(7)–N(6)–Ni(2)–N(14)–N(13)].
lifetime 〈τ〉 of the complexes has been summarised in Table 4.
These bands can be attributed to intra-ligand fluorescent
1(π→π*) emission of the coordinated ligands. The room-
temperature lifetimes of the complexes lay between
0.996–1.008 ns (1) and 0.992–0.777 ns (2). The lifetime data
and photoluminescence spectra are given in Table S4 and
Fig. S2 (ESI†) respectively.
the presence of ionic perchlorate in 2.17c The sharp band due
to the amino NH group appears at 3274 cm−1 in the spectrum
of 2.30
The electronic spectra of the complexes are similar to each
other in DMSO at room temperature (Table 4). The spectra of
complexes 1 and 2 display absorption bands within the range
of 555–559 nm and 854–892 nm with a shoulder band in the
Electrochemical studies
region 776–786 nm. These bands are assigned to the spin The redox properties of complexes 1 and 2 were explored by
allowed transitions 3A2g→3T1g(F), 3A2g→3T2g(P) and spin for- cyclic voltammetry. Each of the two complexes shows one oxi-
bidden transition 3A2g→1Eg (shoulder band) respectively.9a dative quasi-reversible Ni(III)/Ni(II) couple at E1/2 = 0.78 V (for
The higher energy d–d transitions, corresponding to 1) and 0.69 V (for 2) (vs. Ag/AgCl) which corresponds to the
3A2g→3T1g(P) are obscured by strong ligand to metal charge first electron abstraction from the corresponding complex. The
transfer transitions at 389 nm (for 1) and 390 nm (for 2), reductive quasi-reversible Ni(II)/Ni(I) couple at E1/2 = −0.82 V
which are characteristic of transition metal complexes with (for 1) and −0.74 V (for 2) can be assigned to the electron
Schiff base ligands.17
addition to nickel(II) complex to form Ni(I) species. The E1/2
The emission spectral behavior of complexes 1 and 2 has and ΔEp values for these redox couples are given in Table 5. It
been studied at room temperature using DMSO solutions. has been observed that no well defined oxidative or reductive
Complex 1 on excitation at 389 nm exhibits luminescent bands responses could be observed on running further in the positive
at 412 and 437 nm, whereas 2 on excitation at 390 nm exhibits or negative potential. The single-electron nature of the voltam-
bands at 413 and 437 nm as shown in Fig. S1.† Other related mograms has been confirmed by the comparison of current
complexes also show emissions in a similar wavelength heights for the complexes and that of a simple [Fe(bipy)3]2+
region.31 The absorption and emission maxima and mean complex under identical conditions.32 The criteria of
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Table 5 Electrochemical data for the oxidation and reduction of the nickel(II) centre of complexes 1 and 2
NiIII/NiII
NiII/NiI
Complexes
Epa (V)
Epc (V)
E1/2 (V)
ΔEp (mV)
Epa (V)
Epc (V)
E1/2 (V)
ΔEp (mV)
1
2
0.97
0.87
0.58
0.51
0.78
0.69
390
360
−1.11
−0.99
−0.52
−0.48
−0.82
−0.74
590
510
E1/2 is calculated as the average of anodic (Epa) and cathodic (Epc) peak potentials; ΔEp = (Epa − Epc).
reversibility were checked by observing constancy of peak–peak
separation (ΔEp = Epa − Epc) and the ratio of peak heights (ipa/
ipc ∼ 1) with the variation of scan rates. E1/2 values for Ni(II)/Ni
(I) couples in both the complexes fell within the range −0.7 to
−0.9 V, as were also observed in related complexes.33 Similarly,
E1/2 values for Ni(III)/Ni(II) couples fell within the range 0.6–0.9
V. The values closely resembled those of similar reported com-
plexes, which serve as further evidence for similar structural
and electronic properties.33 All the redox signals remain vir-
tually invariant under different scan rates (0.01–1.0 V s−1) in
the temperature range 300–280 K. Solvent dependent shift and
change in electrochemical reversibility of redox couples are not
noteworthy.
Magnetic properties
The variable-temperature magnetic properties (at 2 kOe in the
Fig. 8 χMT vs. T and χM vs. T (inset) plots of complex 2 are shown
between 1.8 K and 300 K. The experimental data are shown as circles
and the red lines correspond to theoretical values.
range 300–1.8 K) of 1 and 2 in the form of χMT vs. T (χM vs.
T inset) plots are illustrated in Fig. 7 and 8 respectively (χMT is
the molar susceptibility for two nickel(II)). Both complexes
show similar χMT vs. T plots. At room temperature (300 K), the
χMT values for the two complexes are 2.13 cm3 mol−1 K (for 1)
and 1.97 cm3 mol−1 K (for 2), which are almost the values
expected for a pair of uncoupled octahedrally coordinated
nickel(II) (the expected spin only value is 2.0 cm3 mol−1 K). The
χMT value decreases in both cases smoothly to a value of 2.04
(for 1) and 1.82 (for 2) cm3 mol−1 K at 60 K. As the temperature
continues to decrease, it begins to decrease more steeply to the
lowest value of 0.14 (for 1) and 0.29 (for 2) cm3 mol−1 K at
1.8 K.
This behavior is typical of a system exhibiting dominant
intra-molecular antiferromagnetic exchange coupling for both
the complexes. The magnetic data of complex 1 have been
interpreted using the expression for the molar magnetic sus-
ceptibility for S = 1 dimers (the Hamiltonian is always written
as H = −2JS1S2),
2 ꢁ
ð1Þ
2Ng2β
kT
e2J=kT þ 5e6J=kT
χM
¼
1 þ 3e2J=kT þ 5e6J=kT
In eqn (l), N, g, β, k and T have their usual meanings. A
good fit for the χMT versus T data has been obtained for the
parameters J = −2.14(1) cm−1 and g = 2.092(1) with R = 3.4 ×
10−4 {R is the agreement factor and is defined as: R =
∑[(χMT)exp − (χMT)calcd]2/∑(χMT)exp2}. Including additional
parameters such as zero-field splitting (D) for nickel(II) and/or
inter-cluster exchange (zJ′) did not improve the fit to the experi-
mental data.
Fig. 7 χMT vs. T and χM vs. T (inset) plots of complex 1 are shown
between 1.8 K and 300 K. The experimental data are shown as circles
and the red lines correspond to theoretical values.
To fit the data of complex 2, we have proceeded in the fol-
lowing way. In the first step, we have fitted the magnetic
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properties of the complex to a simple S = 1 dinuclear model
(the Hamiltonian is always written as H = −2JS1S2).
The spin delocalization mechanism, among several other
mechanisms, successfully explains nature and extent of mag-
netic interaction through spin distribution analysis between
the paramagnetic centers. It describes the delocalization of
spin of the paramagnetic centers over the whole system. The
spin-density distribution plots for 1 and 2 in broken-symmetry
and high spin states are shown in Fig. 9 and 10 respectively,
whereas the corresponding Mulliken spin-density values are
given in Table S5.† The first thing to notice in all these plots is
that the metal ions have decreased spin populations and the
bridging atoms have considerable amounts of spin popu-
2Ng2β
kT
e2J=kT þ 5e6J=kT
χdim
¼
2 ꢁ
ð2Þ
1 þ 3e2J=kT þ 5e6J=kT
In the second step, we have used the molecular field
approximation expression to reproduce the antiferromagnetic
coupling among the dinickel(II) moieties.
χdim
χM
¼
ð3Þ
1 ꢀ ð2zj′=Ng2β2Þχ
where N is Avogadro’s number, β is the B.M. and k is the Boltz- lations on them (spin delocalization), which illustrates the
mann constant. g, J and zj′ are adjustable parameters (zj′ is the spin exchange pathways. Mulliken spin density distribution
inter-molecular exchange interaction) and χdim is the analysis (Table S5†) of both the complexes also reveals that
expression for the dinickel(II) S = 1 system (eqn (3)). Strong (µ-NN′) bridges transmit weak anti-ferromagnetic interaction
π⋯π interactions between the dinickel(II) moieties force us to which is supported by the low spin densities on the bridging
consider this intra-molecular interaction in complex 2. This atoms of the tetrazolate ligand.37
model reproduces satisfactorily the magnetic data in the whole
The magnetic orbitals are composed of dx2−y2 and dz2 orbi-
temperature range with the following parameters: J = −1.20(2) tals of nickel(II) and suitable orbitals of ligands. Also, from the
cm−1, g = 1.987(2), zj′ = −0.27(3) cm−1 with R = 1.8 × 10−4 {R is spin density plots it can be easily seen that the lobes of the
the agreement factor and is defined as: R = ∑[(χMT)exp
(χMT)calcd]2/∑(χMT)exp2} for complex 2.
−
orbitals on the metal ions containing the unpaired electrons
are directed along the bonding axes, which indicates that the
Nickel(II) has two magnetically equivalent orbitals, dx2−y2 magnetic orbitals on the metal ions must be of eg symmetry
and dz2. The pathway for magnetic exchange is propagated (this is normally expected for the octahedral geometry for a d8
through pπ orbitals of two N atoms of the bridging tetrazole system, as the dx2−y2 and dz2 orbitals contain the unpaired
ligand. The significant overlap between these magnetic orbi- electrons).
tals accounts for the antiferromagnetic coupling observed. The
number of double tetrazolato bridged dinuclear nickel(II) com-
plexes is limited; only three such complexes have been
reported so far.16,18,34 Among them, the magnetic characteriz-
ation is done for only one complex.15 So, in order to get a fruit-
ful comparison, we have collected the data for some
related dinuclear nickel(II) complexes bridged by two diazene
(–NvN–) moieties. It has already been pointed out that the
exchange coupling interaction depends on various factors
such as bridging bond distances, bond angles and Ni–N–N′–
Ni* torsion angle.35 So, we have gathered the magnetic data
and the main structural parameters of these complexes along
with our complexes (Table 6). The J values indicate that all are
Fig. 9 Spin density plots of 1 correspond to (a) the broken-symmetry
state and (b) the high spin state. The isodensity surfaces represented
correspond to a cutoff value of 0.004 e bohr−3. Blue and green colours
antiferromagnetically coupled. The Ni⋯Ni distances in all the
complexes are ∼4 Å. Thus this distance hardly has any pro-
nounced effect on the coupling constant, J. Rather, the Ni–N–
N′–Ni* torsion angle is varied widely in the complexes and
may play an important role in the exchange coupling
interactions.
correspond to positive and negative values respectively.
DFT calculations
To obtain a better understanding of the magnetic exchange
mechanism through the bis(µ-NN′) bridging pathways in com-
plexes 1 and 2, quantum mechanical DFT calculations were
performed using the Gaussian 09 package with broken sym-
metry formalism. The calculated exchange coupling constants
(Jtheo) −4.53 cm−1 (J = −2.14(1) cm−1) and −2.48 cm−1 (J =
−1.20(2) cm−1) for 1 and 2 respectively are slightly overesti-
mated but the negative sign indicates that they are weakly anti-
ferromagnetically coupled.
Fig. 10 Spin density plots of 2 correspond to (a) the broken-symmetry
state and (b) the high spin state. The isodensity surfaces represented
correspond to a cutoff value of 0.004 e bohr−3. Blue and green colours
correspond to positive and negative values respectively.
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Table 6 Main structural and magnetic parameters for dinuclear octahedral nickel(II) complexes with double µ-NN’ moieties. δ = ∠N–Ni–N’, θ =
∠Ni–N–N’ and § = ∠Ni–N–N’–Ni*
Complexes
Ni⋯Ni (Å)
δ (°)
θ (°)
§ (°)
0.4(6)
3.0(2)
5.8(1)
−1.6(6),
6.9(6)
−J (cm−1
)
Ref.
[Ni2(MOBPT)2Cl2(H2O)2]Cl2·7H2Oa
[Ni2(abpt)2Cl2(H2O)2]Cl2·4H2Ob
[Ni2(ppd)2(H2O)4]Cl4·2H2Oc
4.189(5)
4.1348(3)
3.920(1)
92.05(13)
93.00(4)
105.8(1)
96.36(17),
96.43(17)
96.87(7)
101.5(2),
101.7(2)
106.2(1)
94.9(2)
92.12(10)
94.60(7),
93.30(6)
92.57(12)
95.81(10)
95.14(14)
92.03(11),
92.16(11)
134.2(3), 133.7(3)
132.63(8), 134.22(8)
127.3(2), 126.9(2)
136.2(3), 136.7(3),
127.6(3), 126.1(3)
138.8(1), 124.3(1)
128.2(4), 128.9(5),
128.4(4), 128.8(4)
127.1(1), 126.7(1)
132.7(4), 132.4(4)
133.3(2), 134.4(2)
132.84(13), 133.64(12),
132.56(13), 133.05(13)
134.4(2), 132.3(2)
141.6(2), 122.0(2)
140.1(3), 124.7(2)
141.4(2), 141.2(2),
124.3(2), 126.3(2)
8.43(6)
12.5(2)
14.8
36a
36b
35a
36c
[{(L)Ni(μ-L′)}2][ClO4]2·MeCNd
4.0765(10)
20.6
e
[Ni2(Hpt)2(H2O)6I(NO3)4
[Ni2(L″)2(H2O)4][BF4]4
4.098(1)
4.056(2)
3.5(2)
4.65(5)
21.6
36d
36e
f
−19.1(7),
−13.0(8)
1.8(3)
0.5(8)
6.3(4)
0.1(3),
1.4(3)
12.7(5)
8.5(5)
3.9(6)
20.4(5),
12.4(5)
[Ni2(dcpz)2(H2O)4]g
3.824(1)
4.046
4.1429(16)
4.1031(3)
33.6
35b
36f
36g
36h
h
[Ni2(Hdcp)2(H2O)4](Im)2
18.97
17.62
22.6
[Ni2(bpt)2(SCN)2(H2O)2]·2H2Oi
[{Ni(N3)(MeOH)}2(µ-bpypz)2]·2MeOHj
[Ni2(MOBPT)2(N3)4]·2H2Oa
[Ni(tzf)(H2O)3]2·2H2Ok
4.169(5)
2.1(7)
2.88
2.13824
1.20355
36i
15
This work
This work
4.0884(12)
4.0994(10)
4.2367(6)
[Ni2(L1)2(PTZ)2]l
[Ni2(L2)2(PTZ)2Na(H2O)]ClO4·H2Om
a (MOBPT) = 4-(p-methoxyphenyl)-3,5-bis(pyridine-2-yl)-1,2,4-triazole. b (abpt) = 4-amino-3,5-bis(pyridin-2-y1)-1,2,4-triazole. c (ppd) = 3,6-bis-
(l′-pyrazoly1)pyridazine. d (L′) = [2-[3-(2′-pyridyl)-pyrazol-1-ylmethyl]pyridine], (HL′) = 3-(2-pyridyl)pyrazole. e (Hpt) = 3-(pyridin-2-yl)-l,2,4-triazole.
f (L″) = N-((6-(4-methoxyphenylimino)methyl)pyridazin-3-yl)methylene-4-methoxybenzenamine. g (dcpz) = 1,4-dicarboxylatopyridazine. h (H3dcp) =
3,5-pyrazoledicarboxylic acid and Im = imidazole. i (Hbpt) = 3,5-bispyridyl-1,2,4-triazole. j (Hbpypz) = 3,5-bis(2-pyridyl)pyrazole. k (H2tzf) = 1H-
tetrazole-5-formic acid. l (L1)
= 2-((2-(dimethylamino)ethylimino)methyl)-6-methoxyphenol, (HPTZ) = = 2-((2-
5-(2-pyridyl)tetrazole. m (L2)
(methylamino)ethylimino)methyl)-6-methoxyphenol.
Table 7 Experimental and DFT calculated exchange coupling constants J for 1 and 2
Complexes
EHS (a.u.)
EBS (a.u.)
EBS − EHS (a.u.) [(cm−1)]
Jtheo (cm−1
)
Jexp (cm−1
)
1
2
−5481.71815802
−5641.58155552
−5481.71821995
−5641.58158947
−0.00006193 (−13.59)
−0.00003395 (−7.45)
−4.53
−2.48
−2.14(2)
−1.20(2)
Although theoretical calculations corroborate well with the complexes would, therefore, afford a convenient synthetic
experimental findings that the anti-ferromagnetic interaction route for these types of complexes and opens up new possibili-
between the nickel(II) centers in complexes 1 and 2 takes place ties for the syntheses of tetrazolato bridged transition metal
through the double µ-NN′-tetrazolato bridges, the magnitudes complexes with Schiff bases as co-ligands. The variable-temp-
of J values obtained by DFT calculations are slightly higher erature magnetic susceptibility measurements for bis(µ-NN′-
than the experimental ones (Table 7). This may be attributed tetrazolato) bridged Schiff base complexes of nickel(II) show
to either the intrinsic limitations of the method or the flexi- the presence of antiferromagnetic coupling between two
bility of the structures that allow structural changes when the nickel(II) centers for both complexes. The experimental mag-
sample is cooled.16c
netic behaviors of the complexes were corroborated by DFT cal-
culations, which serve as an efficient tool for understanding
the magnetic interaction pathways of the complexes. The cal-
culated J values are in agreement with the values obtained
experimentally.
Conclusion
Two new bis(µ-NN′-tetrazolato) bridged dinickel(II) Schiff base
complexes have been synthesized and characterized. The struc-
tural analyses reveal that 1 is a dinuclear complex, whereas 2 is
the first example of a bi-cyclic trinuclear nickel(II)–sodium(I)–
Acknowledgements
nickel(II) complex. Both the complexes have been prepared This work was supported by the DST, India under FAST Track
under non-hydrothermal and non-microwave reaction con- Scheme (order no. SR/FT/CS-118/2010, dated 15/02/2012). We
ditions using a simple in situ 1,3-dipolar cyclo-addition. The are thankful to Dr Saurabh Das, Department of Chemistry,
difference in the composition of the complexes was governed Jadavpur University, India for providing facilities for UV-Vis
by the reaction conditions. The facile synthesis of the spectral studies and Mr Kallol Bera for fluorescence lifetime
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measurements. We like to thank Prof. Y. Song, State Key Lab-
oratory of Coordination Chemistry, Nanjing National Labora-
tory of Microstructures School of Chemistry and Chemical
Engineering, Nanjing University, Nanjing, 210093, P. R. China
for variable temperature magnetic susceptibility measure-
ments and fitting.
W. Wernsdorfer, S. Hill and M. Murrie, Dalton Trans., 2008,
6409–6414; (c) J. Lawrence, E.-C. Yang, R. Edwards,
M. M. Olmstead, C. Ramsey, N. S. Dalal, P. K. Gantzel,
S. Hill and D. N. Hendrickson, Inorg. Chem., 2008, 47,
1965–1974.
10 (a) B.-W. Hu, J.-P. Zhao, E. C. Sanudo, F.-C. Liu,
Y.-F. Zeng and X.-H. Bu, Dalton Trans., 2008, 5556–5559;
(b) A. Escuer, C. J. Harding, Y. Dussart, J. Nelson,
V. McKee and R. Vicente, J. Chem. Soc., Dalton Trans.,
1999, 223–227.
References
1 (a) T. D. Keene, I. Zimmermann, A. Neels, O. Sereda, 11 (a) R. Nasani, M. Saha, S. M. Mobin and S. Mukhopadhyay,
J. Hauser, M. Bonin, M. B. Hursthouse, D. J. Price and
S. Decurtins, Dalton Trans., 2010, 39, 4937–4950;
(b) J. Ferrando-Soria, J. Pasán, C. Ruiz-Pérez, Y. Journaux,
Polyhedron, 2013, 55, 24–36; (b) A. J. Mota, A. Rodrıguez-
Dieguez, M. A. Palacios, J. M. Herrera, D. Luneau and
E. Colacio, Inorg. Chem., 2010, 49, 8986–8996.
M. Julve, F. Lloret, J. Cano and E. Pardo, Inorg. Chem., 12 (a) D. Savard, C. Cook, G. D. Enright, I. Korobkov,
2011, 50, 8694–8696; (c) C. L. Pereira, E. F. Pedroso,
A. C. Doriguetto, J. A. Ellena, K. Boubekeur, Y. Filali,
Y. Journaux, M. A. Novak and H. O. Stump, Dalton Trans.,
2011, 40, 746–754; (d) S. V. Kolotilov, O. Cador,
P. Pointillart, S. Golhen, Y. L. Gal, K. S. Gavrilenko and
L. Ouahab, J. Mater. Chem., 2010, 20, 9505–9514.
2 (a) L.-J. Zhang, J.-H. Yu, J.-Q. Xu, J. Lu, H.-Y. Bie and
X. Zhang, Inorg. Chem. Commun., 2005, 8, 638–642;
(b) E. A. Mikhalyova, S. V. Kolotilov, O. Cador, F. Pointillart,
S. Golhen, L. Ouahab and V. V. Pavlishchuk, Inorg. Chim.
Acta, 2010, 363, 3453–3460.
T. J. Burchell and M. Murugesu, CrystEngComm, 2011, 13,
5190–5197; (b) C. Chen, H. Qiu and W. Chen, Inorg. Chem.,
2011, 50, 8671–8678; (c) V. Colombo, S. Galli, H. Choi,
G. D. Han, A. Maspero, G. Palmisano, N. Masciocchi and
J. R. Long, Chem. Sci., 2011, 2, 1311–1319.
13 (a) S. Jeong, X. Song, S. Jeong, M. Oh, X. Liu, D. Kim,
D. Moon and M. S. Lah, Inorg. Chem., 2011, 50, 12133–
12140; (b) K. Darling, W. Ouellette, A. Prosvirin, S. Walter,
K. R. Dunbar and J. Zubieta, Polyhedron, 2013, 58, 18–29;
(c) D.-X. Xue, A. J. Cairns, Y. Belmabkhout, L. Wojtas,
Y. Liu, M. H. Alkordi and M. Eddaoudi, J. Am. Chem. Soc.,
2013, 135, 7660–7667; (d) J.-Y. Sun, L. Wang, D.-J. Zhang,
D. Li, Y. Cao, L.-Y. Zhang, S.-L. Zeng, G.-S. Pang, Y. Fan,
J.-N. Xu and T.-Y. Song, CrystEngComm, 2013, 15, 3402–
3411.
3 F. E. Jacobsen, R. M. Breece, W. K. Myers, D. L. Tierney and
S. M. Cohen, Inorg. Chem., 2006, 45, 7306–7315.
4 (a) T. Tekeste and H. Vahrenkamp, Inorg. Chem., 2006, 45,
10799–10806; (b) E. T. Papish, M. T. Taylor, F. E. Jernigan
III, M. J. Rodig, R. R. Shawhan, G. P. A. Yap and 14 (a) M.-G. Liu, P.-P. Zhang, J. Peng, H.-X. Meng, X. Wang,
F. A. Jove, Inorg. Chem., 2006, 45, 2242–2250; (c) M. Ji,
B. Benkmil and H. Vahrenkamp, Inorg. Chem., 2005, 44,
3518–3523.
5 (a) T. Chattopadhyay, M. Mukherjee, A. Mondal, P. Maiti,
A. Banerjee, K. S. Banu, S. Bhattacharya, B. Roy,
D. J. Chattopadhyay, T. K. Mondal, M. Nethaji,
E. Zangrando and D. Das, Inorg. Chem., 2010, 49, 3121–
3129; (b) R. Prabhakaran, P. Kalaivani, P. Poornima,
M. Zhu, D.-D. Wang, C.-L. Meng and K. Alimaje, Cryst.
Growth Des., 2012, 12, 1273–1281; (b) X.-L. Wang, Q. Gao,
A.-X. Tian and G.-C. Liu, Cryst. Growth Des., 2012, 12, 2346–
2354; (c) X.-L. Wang, H.-L. Hu and A.-X. Tian, Cryst. Growth
Des., 2010, 10, 4786–4794; (d) Z. Li, M. Li, X.-P. Zhou,
T. Wu, D. Li and S. W. Ng, Cryst. Growth Des., 2007, 7,
1992–1998; (e) X.-L. Tong, D.-Z. Wang, T.-L. Hu, W.-C. Song,
Y. Tao and X.-H. Bu, Cryst. Growth Des., 2009, 9, 2280–2286.
F. Dallemer, G. Paramaguru, V. V. Padma, R. Renganathan, 15 A.-Q. Wu, Q.-Y. Chen, M.-F. Wu, F.-K. Zheng, F. Chen,
R. Huange and K. Natarajan, Dalton Trans., 2012, 41, 9323–
G.-C. Guo and J.-S. Huang, Aust. J. Chem., 2009, 62, 1622–
9336.
1630.
6 (a) R. Biswas, P. Kar, Y. Song and A. Ghosh, Dalton Trans., 16 (a) X. Yang, D. Schipper, R. A. Jones, L. A. Lytwak,
2011, 40, 5324–5331; (b) S. Chattopadhyay, M. G. B. Drew,
C. Diaz and A. Ghosh, Dalton Trans., 2007, 2492–2494.
7 M. Sukwattanasinitt, A. Nantalaksakul, A. Potisatityuenyong,
T. Tuntulani, O. Chailapakul and N. Praphairakait, Chem.
Mater., 2003, 15, 4337–4339.
B. J. Holliday and S. Huang, J. Am. Chem. Soc., 2013, 135,
8468–8471; (b) S. Jana, P. Bhowmik and S. Chattopadhyay,
Dalton Trans., 2012, 41, 10145–10149; (c) R. Biswas,
S. Mukherjee, P. Kar and A. Ghosh, Inorg. Chem., 2012, 51,
8150–8160; (d) P. Bhowmik, H. P. Nayek, M. Corbella,
N. Aliaga-Alcalde and S. Chattopadhyay, Dalton Trans.,
2011, 40, 7916–7926.
8 (a) W.-H. Sun, S. Song, B. Li, C. Redshaw, X. Hao, Y.-S. Li
and F. Wang, Dalton Trans., 2012, 41, 11999–12010;
(b) Z. Chen, H. Morimoto, S. Matsunaga and M. Shibasaki, 17 (a) L. K. Das, R. M. Kadam, A. Bauzá, A. Frontera and
J. Am. Chem. Soc., 2008, 130, 2170–2171.
A. Ghosh, Inorg. Chem., 2012, 51, 12407–12418;
(b) S. Ghosh, S. Biswas, A. Bauza, M. Barcelo-Oliver,
A. Frontera and A. Ghosh, Inorg. Chem., 2013, 52, 7508–
7523; (c) P. Bhowmik, K. Harms and S. Chattopadhyay, Poly-
hedron, 2013, 49, 113–120.
9 (a) R. Biswas, Y. Ida, M. L. Baker, S. Biswas, P. Kar,
H. Nojiri, T. Ishida and A. Ghosh, Chem.–Eur. J., 2013, 19,
3943–3953; (b) A. Ferguson, J. Lawrence, A. Parkin,
J. Sanchez-Benitez, K. V. Kamenev, E. K. Brechin,
This journal is © The Royal Society of Chemistry 2014
Dalton Trans.

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Dalton Transactions
18 B. G. Mukhopadhyay, S. Mukhopadhyay, M. F. C. Guedes 28 D. Cremer and J. A. Pople, J. Am. Chem. Soc., 1975, 97,
da Silva, M. A. J. Charmier and A. J. L. Pombeiro, Dalton
Trans., 2009, 4778–4785.
19 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 2008, 64, 112–122.
20 R. H. Blessing, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 1995, 51, 33–38.
1354–1358.
29 (a) L. Ma, N. Yu, S. Chen and H. Deng, CrystEngComm,
2013, 15, 1352–1364; (b) F. Wang, X.-Y. Wu, R. Yu and
C.-Z. Lu, Inorg. Chem. Commun., 2012, 25, 21–25;
(c) C. Jiang, Z. Yu, C. Jiao, S. Wang, J. Li, Z. Wang and
Y. Cui, Eur. J. Inorg. Chem., 2004, 4669–4674.
21 P. van der Sluis and A. L. Spek, Acta Crystallogr., Sect. A: 30 M. Das, B. N. Ghosh, A. Valkonen, K. Rissanen and
Fundam. Crystallogr., 1990, 46, 194–201. S. Chattopadhyay, Polyhedron, 2013, 60, 68–77.
22 (a) A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652; 31 (a) M. Das and S. Chattopadhyay, J. Mol. Struct., 2013, 1051,
(b) C. Lee, W. Yang and R. G. Parr, Phys. Rev. B: Condens.
Matter, 1988, 37, 785–789.
23 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
250–258; (b) P. K. Bhaumik, K. Harms and S. Chattopadhyay,
Polyhedron, 2014, 67, 181–190; (c) P. K. Bhaumik, K. Harms
and S. Chattopadhyay, Polyhedron, 2013, 62, 179–187.
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, 32 K. Mitra, S. Biswas, C. R. Lucas and B. Adhikary, Inorg.
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, Chim. Acta, 2006, 359, 1997–2003.
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, 33 (a) D. Parker, E. S. Davies, C. Wilson and J. McMaster, Inorg.
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, J. J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
Chim. Acta, 2007, 360, 203–211; (b) O. Rotthaus, F. Thomas,
O. Jarjayes, C. Philouze, E. Saint-Aman and J.-L. Pierre, Chem.–
Eur. J., 2006, 12, 6953–6962; (c) R. N. Patel, K. K. Shukla,
A. Singh, M. Choudhary, D. K. Patel, J. Niclós-Gutiérrez and
D. Choquesillo-Lazarte, J. Coord. Chem., 2010, 63, 3648–3661.
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, 34 S. F. Palopoli, S. J. Geib, A. L. Rheingold and T. B. Brill,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, Inorg. Chem., 1988, 27, 2963–2971.
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, 35 (a) L. Rosenberg, E. J. Gabe, F. L. Lee and L. K. Thompson,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. Chem. Soc., Dalton Trans., 1986, 625–631; (b) A. Escuer,
R. Vicente, B. Mernari, A. E. Gueddi and M. Pierrot, Inorg.
Chem., 1997, 36, 2511–2516.
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, 36 (a) J. Zhou, J. Yang, L. Qi, X. Shen, Y. Xu, Y. Song and
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
GAUSSIAN 09 (Revision D.01), Gaussian, Inc., Wallingford
CT, 2009.
D. Zhu, Transition Met. Chem., 2007, 32, 711–715;
(b) F. S. Keij, R. A. G. de Graaff, J. G. Haasnoof and
J. Reedijk, J. Chem. Soc., Dalton Trans., 1984, 2093–2097;
(c) V. Mishra, F. Lloret and R. Mukherjee, Eur. J. Inorg.
Chem., 2007, 2161–2170; (d) P. J. V. Koningsbruggen,
24 A. Schaefer, C. Huber and R. Ahlrichs, J. Chem. Phys., 1994,
100, 5829–5835.
25 (a) L. Noodleman, J. Chem. Phys., 1981, 74, 5737–5744;
(b) L. Noodleman and D. A. Case, Adv. Inorg. Chem., 1992,
38, 423–470; (c) L. Noodleman, C. Y. Peng, D. A. Case and
J. M. Mouesca, Coord. Chem. Rev., 1995, 144, 199–
244.
26 (a) E. Ruiz, J. Cano, S. Alvarez and P. Alemany, J. Comput.
Chem., 1999, 20, 1391–1400; (b) E. Ruiz, A. Rodríguez-
Fortea, J. Cano, S. Alvarez and P. Alemany, J. Comput.
Chem., 2003, 24, 982–989; (c) E. Ruiz, S. Alvarez, J. Cano
and V. Polo, J. Chem. Phys., 2005, 123, 164110.
M.
D. Schollmeyer, G. Levchenko and P. Gtitlich, Inorg.
Chim. Acta, 1998, 273, 54–61; (e) Y. Lan,
W.
Gluth,
V.
Ksenofontov,
D.
Walcher,
D. K. Kennepohl, B. Moubaraki, K. S. Murray,
J. D. Cashion, G. B. Jameson and S. Brooker, Chem.–Eur.
J., 2003, 9, 3772–3784; (f) S.-Y. Zhang, Y. Li and W. Li,
Inorg. Chim. Acta, 2009, 362, 2247–2252; (g) M.-L. Tong,
C.-G. Hong, L.-L. Zheng, M.-X. Peng, A. Gaita-Arino and
J. M. C. Juan, Eur. J. Inorg. Chem., 2007, 3710–3717;
(h) R. Ishikawa, A. Fuyuhiro, S. Hayami, K. Inoue and
S. Kawata, J. Mol. Struct., 2008, 892, 220–224; (i) J. Yangy,
W.-W. Baoy, X.-M. Renz, Y. Xuy, X. Sheny and D.-R. Zhu,
J. Coord. Chem., 2009, 62, 1809–1816.
27 (a) S. K. Dey, N. Mondal, M. S. E. Fallah, R. Vicente,
A. Escuer, X. Solans, M. Font-Bardıa, T. Matsushita,
V. Gramlich and S. Mitra, Inorg. Chem., 2004, 43, 2427–
2434; (b) S. Hayami, S. Miyazaki, M. Yamamoto, K. Hiki, 37 (a) R. Biswas, C. Diaz, A. Bauzá, A. Frontera and A. Ghosh,
N. Motokawa, A. Shuto, K. Inoue, T. Shinmyozu and
Y. Maeda, Bull. Chem. Soc. Jpn., 2006, 79, 442–450;
(c) P. G. Sim, E. Sinn, R. H. Petty, C. L. Merrill and
L. J. Wilson, Inorg. Chem., 1981, 20, 1213–1222.
Dalton Trans., 2013, 42, 12274–12283; (b) A. Jana, S. Konar,
K. Das, S. Ray, J. A. Golen, A. L. Rheingold, L. M. Carrella,
E. Rentschler, T. K. Mondal and S. K. Kar, Polyhedron,
2012, 38, 258–266.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2014