Single end to end azido bridged adduct of a tridentate schiff base copper(II) complex: Synthesis, structure, magnetism and catalytic studies

Article abstract of DOI:10.1016/j.ica.2013.09.032

Copper(II) azido complex [CuL(μ_-1,3-N₃)] _n (1) of a NNO donor tridentate Schiff base (HL = 2-[1-(methylamino-ethylimino)-methyl]-phenol containing single end-to-end μ_-1,3-azido bridged 1D infinite chain has been synthesized and characterized by elemental analysis, FT-IR spectroscopy. X-ray single crystal structure analysis reveals that in 1, the central copper(II) ion displays a distorted square pyramidal coordination geometry and are linked by single EE azide bridges forming chains running parallel to the crystallographic b axis. The magnetic interaction revealed that 1 is antiferromagnetic in nature (J = -19.5 (±0.2) cm^-1). The catalytic activity of the complex is investigated in a series of solvents for the oxidation of olefins using tert-butyl-hydroperoxide as oxidant. The results showed highest selectivity for 1 in acetonitrile medium.

Full text of DOI:10.1016/j.ica.2013.09.032

Accepted Manuscript
Single end to end azido bridged adduct of a tridentate schiff base copper (II)
complex: synthesis, structure, magnetism and catalytic studies
Sourajit Banerjee, Chandan Adhikary, Corrado Rizzoli, Rammohan Pal
PII:
S0020-1693(13)00515-X
http://dx.doi.org/10.1016/j.ica.2013.09.032
ICA 15660
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
23 July 2013
6 September 2013
17 September 2013
Please cite this article as: S. Banerjee, C. Adhikary, C. Rizzoli, R. Pal, Single end to end azido bridged adduct of a
tridentate schiff base copper (II) complex: synthesis, structure, magnetism and catalytic studies, Inorganica Chimica
Acta (2013), doi: http://dx.doi.org/10.1016/j.ica.2013.09.032
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Single end to end azido bridged adduct of a tridentate schiff base copper
(II) complex: synthesis, structure, magnetism and catalytic studies
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Sourajit Banerjeea, Chandan Adhikarya,*, Corrado Rizzolib, Rammohan Palc
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aDepartment of Chemistry, Governement College of Education, Burdwan, 713102, India
bDepartimento di Chimica, Parco Area delle Scienze 17/A, 43124, Parma, Italy
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cDepartment of Chemistry, Acharya Jagadish Chandra Bose College, Kolkata 700020, India
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Abstract
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Copper (II) azido complex [CuL(µ-1,3-N3)]n (1) of a NNO donor tridentate Schiff base
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(HL = 2-[1-(Methylamino-ethylimino)-methyl]-phenol containing single end-to-end µ-1,3-
azido bridged 1D infinite chain has been synthesized and characterized by elemental analysis,
FT-IR spectroscopy. X-ray single crystal structure analysis reveals that in 1, the central
copper (II) ion displays a distorted square pyramidal coordination geometry and are linked by
single EE azide bridges forming chains running parallel to the crystallographic b axis. The
magnetic interaction revealed that 1 is antiferromagnetic in nature (J = -19.5 ( 0.2) cm-1).
The catalytic activity of the complex is investigated in a series of solvents for the oxidation of
olefins using tert-butyl-hydroperoxide as oxidant. The results showed highest selectivity for 1
in acetonitrile medium.
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Keywords: Copper(II)-azido complex; Schiff-base ligand; X-ray crystal structure; Magnetic
study; Olefin oxidation
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*Corresponding author. Tel: +91-0342-2656853; e-mail. cadhikary123@gmail.com
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1. Introduction
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The Schiff bases derived from the mono-condensation of diamines with carbonyl
compounds (salicylaldehyde, o-hydroxyacetophenone, acetylacetone or benzoylacetone) are a
group of mono-negative NNO donor ligands which readily react with transition metal ions
and auxiliary ligand to form mono and polynuclear complexes with varied functionalities and
applications. Depending on the number, nature and relative position of the donor atoms of a
Schiff base, the ligand allows a good control over the stereochemistry of the metallic centers
in homo- and heteropolynuclear complexes [1-3]. All these advantages make Schiff bases
privileged ligands in the effort to synthesize metal complexes having relevance to
bioinorganic chemistry, catalysis, encapsulation, transport and separation processes [4].
Copper(II) Schiff base complexes find wide applicability in the field of catalysis,
antimicrobial activities, synergistic action on insecticides, plant growth regulator, antitumor
and cytotoxic activity, harmonic generation activity etc [5]. Furthermore copper(II) azido
complexes have also received intense attention in the field of molecular magnetism [6].
Keeping such observations in mind we have directed our investigation in synthesizing Schiff
base copper(II) complexes and their azido adducts and simultaneous study of their magnetic
property and catalytic efficacy. Schiff base copper complexes can now be extensively used as
active catalysts in several oxidation reactions both in homogeneous [7-11] and heterogeneous
condition [12-16]. So far our knowledge goes, catalytic oxidations involving Schiff base
copper azido complexes have been scarcely reported in the literature [17-18]. Although
molecular oxygen and hydrogen peroxide (30%, an environmental friendly oxidant) catalyzed
epoxidation reactions are well documented in the literature yet due to the explosive nature of
hydrogen peroxide, the industrial processes still mainly have to rely on tert-butyl-
hydroperoxide (TBHP) [19].In industrial epoxidation involving Halcon-Arco and Sumitomo
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processes [20-23] alkyl-hydroperoxides are used on a large scale. The recycling of co-
products e.g. tert-BuOOH has been realized in the Sumitomo process. Notably, TBHP has
seldom been used as an oxidant in the investigations of the catalytic efficiency of copper(II)
complexes towards epoxidation/oxidation reactions in homogeneous medium. Here we report
the synthesis, characterization, X-ray single crystal structure and magnetic study of an azido
derivative of a Schiff base Cu(II) complex. The catalytic epoxidation acivity of the complex
has been investigated in a variety of alkenes using tert-butyl-hydroperoxide as an oxidant.
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2. Experimental
2.1. Materials
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All solvents used are of AR grade and were distilled and dried before use.
Salicylaldehyde, and copper(II) nitrate trihydrate were purchased from Merck (India) and
used as received. Styrene, α-methylstyrene, cyclooctene, cyclohexene, tert-BuOOH (70%
aq.), N-methylethylenediamine were purchased form Aldrich and used as received.
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2.2. Physical Measurements
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Microanalysis (CHN) was performed in a Perkin Elmer 240 elemental analyzer. IR
spectra were recorded on a Bruker Alpha T 200140 FT-IR spectrometer. Absorption spectra
were studied on Shimadzu UV2100 UV-Vis recording spectrophotometer. Magnetic
measurements of 1 were performed with a Cryogenic SQUID S600 magnetometer operating
between 2 and 300 K at an applied field of 1T. Magnetic data were corrected for the
diamagnetism of the sample holder, measured in the same range of temperature and field, and
for the intrinsic diamagnetism of the samples estimated through Pascal’s constants. GC
analysis was carried out with an Agilent Technologies 6890N network GC system equipped
with a fused silica capillary column (30 m x 0.32 mm) and a FID detector.
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2.3. Synthesis
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Caution! Although our samples never exploded during handling, azide metal
complexes are potentially explosive: only a small amount of material should be prepared and
it should be handled with care.
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2.3.1. Synthesis of [CuL(µ1,3-N3)] ( 1)
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A methanolic solution (20 ml) of N-methylethylenediamine (1mmol, 0.074g) was added to a
methanolic solution (20 ml) of salicylaldehyde (1mmol, 0.122g). The reaction mixture was
refluxed for 1h and evaporated on a water bath until the volume reduced to ca. 5 ml to
obtained a viscous yellow orange liquid. Copper (II) nitrate trihydrate (1mmol, 0.241g)
dissolved in methanol was added and the mixture was refluxed for another 30 min Finally 5
ml aqueous solution of NaN3 (2mmol, 0.130g) was added dropwise to the mixture with
continuous stirring and the resulting solution was then filtered. The green filtrate was kept in
the open atmosphere. From the green solution block pale yellow crystals were formed within
few days. (Yield ca. 80%). Anal. Calcd. for C10H13CuN5O (282.79): calcd: C, 42.4; H, 4.6;
N, 24.8. Found: C, 42.2; H, 4.8; N, 24.9. FTIR (cm-1): νas (N3), 2030; νs(N3), 1332 and 1345;
δ(N3), 620; ν(C=N), 1640 cm-1. λmax/nm (methanol), 299; 266; 360; 621.
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2.4. X-ray Crystallography
2.4.1. X-ray Crystal data of [CuL(µ1,3-N3)]n (1)
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C10H13CuN5O, M = 282.79, Orthorhombic, space group P212121, a = 7.1631(9), b = 8.3919
(10), c = 19.652 (2) Å, α = β = γ = 90˚, V = 1181.3 (2) Å3, Z = 4, Rint = 0.050, Dcalc. = 1.590
Mg m-3, F000 = 580, µ = 1.84 mm-1, dimensions = 0.16 × 0.10 × 0.07 mm, T = 295 K.
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2.4.2. X-ray single crystal structure determination of [CuL(µ1,3-N3)]n (1)
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Single crystal X-ray diffraction data for 1 were mounted on a Bruker SMART 1000
CCD diffractometer at room temperature using graphite monochromated Mo-Kα radiation (λ
= 0.71073Å) and were used to measure cell dimensions and diffraction intensities. The
crystals were found to belong to the orthorhombic system and the systematic absences
identified the correct space group as P212121. For data collection, data reduction and cell
refinement the programs APEX2 and SAINT [24] were used. The structure was solved by
direct methods using SIR97 [25] and refined by SHELX97-L [26]. The N-bound H atom was
located in a difference Fourier map and refined isotropically. All other H atoms were
positioned geometrically and refined using a riding model, with C–H = 0.93-0.97 Å and with
Uiso = 1.2 Ueq(C) or 1.5 Ueq(C) for methyl H atoms. A rotating model was used for the
methyl group.
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2.5. Catalytic reactions
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The homogeneous oxidation reactions were carried out under stirring in a two-neck
round-bottom flask fitted with a water condenser and placed in an oil bath at 333-353 K. The
proportions used were: substrate (10mmol), solvent (10 ml) and catalyst (0.005 mmol). tert-
BuOOH (20 mmol) was added immediately before the start of the reaction and the mixture
was stirred continuously for 24 h. At different time intervals, the products were collected
from the reaction mixture and analyzed by gas chromatography. The products were identified
by known standards.
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3. Results and Discussion
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3.1. Description of structure of [CuL(µ1,3-N3)]n (1)
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The structure determination reveals that the neutral [CuL(µ-1,3-N3)]n units in complex
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1 are connected by the single µ-1,3-azido ligands to form an infinite 1D polymeric chains. A
perspective view of the chain structure running parallel to the crystallographic b-axis is
depicted in Fig. 1 and an Ortep diagram of the monomer with atom labelling scheme is
shown in Fig. 2.
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In 1, each Cu(II) ion is placed in a distorted square pyramidal environment, in which
the basal plane is made up by two nitrogens, N(1) and N(2), one deprotonated phenoxo
oxygen O(1), of the tridentate Schiff base ligand HL and one azido nitrogen, N(3). A second
azido nitrogen, N(5)i from a symmetry related unit (symmetry operation, i = −x+1, y+1/2,
−z+1/2) at the apical position occupies the remaining fifth position of the coordinated
polyhedron. Thus the azido nitrogen N(5) bridges two copper(II) centers. Selected bond
lengths and angles are listed in Table 1.
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The basal Cu-N(3)(azido) distance [1.973(4)Å] is an intermediate between the other
two basal Cu-N(1) and Cu-N(2) distances [1.940(4), 2.054(4)Å, respectively], while the
apical Cu-N(5)i (symmetry operation i = −x+1, y+1/2, −z+1/2) distance [2.506(4)Å] is
remarkably longer, indicating a rather weak axial coordinative interaction. The axial Cu-N
distance is significantly longer than those observed in other similar single end-to-end azido
bridged 1D copper(II) complexes [6].
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The diagonal basal angles, N(1)-Cu(1)-N(3) = 165.54(16)° and N(2)-Cu(1)-O(1) =
176.51(15)° and the basal-apical angles, O(1)-Cu(1)-N(5)i = 87.66(12)° and N(1)-Cu(1)-N(5)i
= 94.61(5)° (symmetry operation i = −x+1, y+1/2, −z+1/2) significantly deviate from the ideal
values. The trigonality index τ (0.18) [= Φ1−Φ2)/60, where Φ1, Φ2 are the two largest L-M-L
angles of the coordination sphere] as calculated for the pentagonal copper site [27] confirms
the square pyramidal environment. The Cu(1)-N(3)...N(5)-Cu(1)ii torsion angle (symmetry
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operation ii = 1-x, -1/2+y, 1/2-z) is -90.3(2)° and the angle formed by the lines through the
Cu(1)-N(3) and N(5)-Cu(1)ii (symmetry operation ii = 1-x, -1/2+y, 1/2-z) bonds is
99.73(13)°. The Cu···Cu distance is 5.0748(8) Å.
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In 1, the hydrogen atom H(2N) bonded to the sp3 hybridized amino nitrogen N(2) is
involved in a weak hydrogen bond contact with an adjacent phenoxo oxygen atom, O(1)i
(symmetry operation i = −x+1, y+1/2, −z+1/2). The hydrogen atom H(9B) bonded to the sp3
hybridized C(9) methylene carbon atom is also involved in hydrogen bonding with the
terminal azide nitrogen N(5)iii (symmetry operation iii = x, y+1, z).
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3.2. Magnetic study of complex [CuL(µ1,3-N3)]n (1)
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The temperature dependence of the molar magnetic susceptibility, χM, for 1 in the 2-
300 K temperature range was measured with a Cryogenic SQUID S600 magnetometer
operating between 2 and 300 K at an applied field of 1T and is shown in Fig. 3. The χM value
of 5.5×10-3 cm3mol-1 at 300 K is slightly higher than the value expected for an isolated
magnetically uncoupled copper(II) ion (χM = 1.25×10-3 cm3mol-1 for g = 2.0). Upon cooling
the χM value increases gradually with temperature until ca. 125 K, and then rapidly, reaching
a maximum of 3.7×10-2 cm3mol-1 at ca. 22 K. The χM versus T curve explains a bulk
antiferromagnetic interaction prevailed. An isotropic infinite chain model of equally spaced
copper (II) ions bridged through µ-1,3-azido ligands with S = ½ local spins has been
considered to explain the magnetic properties of 1. The spin Hamiltonian of such a system
considering isotropic interaction between nearest neighbouring ions is
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n−1
H = −J S ⋅ S
∑
A
A
i+1
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…(1)
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where summation runs over the n site of the chain. For the condition n → ∝ no analytical
method is available so as to determine the energies of low-lying states and magnetic
susceptibility. The ring structure permits the limiting condition as follows [28-29]:
SA = SA
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for any n
…(2)
i+n
i
Finally, to fit magnetic susceptibility data a numerical expression can be used as follows [30]:
Ng2 β 2
0.25 + 0.074975x + 0.075235x2
1.0 + 0.9931x + 0.172135x2 + 0.757825x3
χM =
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…(3)
kT
where
x = J / kT
…(4)
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Fitting of the magnetic susceptibility data considering the equation (3) yielded the parameter
values J = -19.5( 0.2) cm-1, g = 2.2( 0.01). A comparative account of structural and
magnetic parameters of the similar End to End azido bridged 1D chain copper(II) complexes
[31-38] are collated in the Table 2. Even a cursory look at the Table 2 it is evident that most
of the complexes listed there are ferromagnetic in nature. However, the coupling parameters
are small. For copper(II) systems, the magnitude of the super exchange parameter J is
strongly dependent on main two factors, viz. the atomic orbitals of the copper atoms involved
and the ∠Cu–N–N and Cu–N3–Cu torsion angle in the bridging region. The coupling may be
strongly AF when the end-to-end azido ligands are bonded to the equatorial coordination sites
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of the two copper atoms, in which case two dx – y orbitals is involved in the super exchange
mechanism. In contrast, very weak coupling should be expected when the interaction is axial-
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equatorial in nature involving dx – y2 and dz atomic orbitals.
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The different magnetic behavior is related to the low unpaired electronic density
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found in the dz atomic orbital in the square pyramidal or octahedrally coordinated copper
atoms. Classical attempts to relate the magnitude of the super exchange coupling and the
structural data for the axial-equatorial case conclude a greater AF coupling for the trigonal
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bipyramidal arrangement which is in agreement with the greater mixing of the dx -y and dz2
atomic orbitals in such cases [6]. In a recent study the electronic structures of two
asymmetrical EE azido-bridged copper(II) complexes [Cu(L2)(N3)]n(ClO4)n and
[Cu(L3)(N3)]n(ClO4)n [32] were studied. The result shows that the spin population in these
two complexes is largely distributed on the equatorial plane of the square pyramid
surrounding the copper(II) ions. Ferromagnetic coupling through the asymmetrical azido
ligand in these two complexes has been mainly attributed to the spin delocalization and weak
spin polarization effect.
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3.3. Catalytic activities
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The catalytic activity of 1 in the epoxidation of various olefins in homogeneous medium
is summarized in table 3.The graphical representation of different alkene conversion for 1
is shown in Fig. 4. For 1 the conversion trend of alkenes follows the order α–methyl
styrene ~ styrene > cyclooctene > cyclohexene while the observed epoxide selectivity is
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cyclooctene (73%) > α–methyl styrene(62%) > styrene(54%) ̴ cyclohexene (54%). From
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this observation it is evident that epoxide selectivity is higher in cyclooctene due to its
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active double bond and the relative stability of 1,2- epoxy cyclooctene. For cyclohexene,
epoxide selectivity was least since its active allylic site could also be activated in the
process of oxidation. When styrene is considered, 100% styrene conversion occurred with
54% epoxide selectivity. The remaining 46% products were benzaldehyde and benzoic
acid. The yield of epoxide increases from 54% to 62% when an electron donating methyl
group was introduced at the ortho position of styrene. Along with the epoxide 4-methyl
benzaldehyde and 4-methyl benzoic acid were also formed. The difference in the
conversion between styrene and α–methyl styrene may be attributed to the electronic
effect of the substituent [39]. It is known that copper (II) can bind peroxo- groups on
treatment with peroxides [40] and the pre-catalyst species containing LxCu-OOR (where
L = ligand) type moieties seemed to be capable of transferring oxo functionality to the
organic substrates to give the corresponding oxidized products [41-42]. We speculate
that, in our case, a similar kind of mechanism is operative.
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The effect of various reaction media on epoxidation of cyclooctene catalyzed by 1 has
been compared. The graphical representation of catalytic efficacy in different solvent
media for 1 is shown in Fig. 5. The best performance of the catalyst was observed in the
acetonitrile medium. The efficiency of the catalyst followed the order acetonitrile >
dichloromethane >methanol >chloroform which is consistent with the earlier report of
cyclooctene catalyzed epoxidation of single end on azido bridged Schiff base copper (II)
complexes [17]. A comparison of the catalytic efficiency of 1 with copper salt (copper(II)
nitrate trihydrate) in homogeneous medium involving acetonitrile (Table 4) solvent
clearly indicates that complex 1 performs as a more efficient catalyst than simple copper
salt.
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4. Conclusion
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In summary, we have synthesized and characterized a 1D chain copper(II) azide
complex with NNO donor ligands. The magnetic interaction revealed that 1 is
antiferromagnetic (J = -19.5 ( 0.2) cm-1) in nature. The complex also showed moderate
catalytic activity in acetonitrile compared to the other solvents in homogeneous alkene
oxidation.
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Appendix A. Supplementary data
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CCDC 937470 contains the supplementary crystallographic data for 1. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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Acknowledgement
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The work is financially supported by the Department of Science and Technology,
Government of India, by a grant (SR/S1/IC-13/2010) (to CA).
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P. S. Mukherjee, T. K. Maji, A. Escuer, R. Vicente, J. Ribas, G. Rosair, F. A. Mautner, N.
R. Chaudhuri, Eur. J. Inorg. Chem. (2002) 943.
S. Sarkar, A. Mondal, J. Ribas, M. G. B. Drew, K. Pramanik, K. K. Rajak, Inorg. Chim.
Acta 358 (2005) 641.
35.
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H.-R. Wen, C.-F. Wang, Y. Song, J.-L. Zuo, X.-Z. You. Inorg. Chem. 44 (2005) 9039.
P. S. Dalai, P. S. Mukherjee, T. Mallah, M. G. B. Drew, N. R. Chaudhuri, Inorg. Chim. Acta
5 (2002) 472.
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37.
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X.-Z. Li, L.-N. Zhu, C.-Q. Li, D.-Z. Liao, Inorg. Chem. Commun. 9 (2006) 1297.
C. Adhikary, D. Mal, K.-I. Okamoto, S. Chaudhuri, S. Koner, Polyhedron 25 (2006) 2191.
J. Zhang, A.V. Biradar, S. Pramanik, T.J. Emge, T. Asefa, J. Li, Chem. Commun.
48 (2012) 6541.
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T. Osako, S. Nagatomo, Y. Tachi, T. Kitagawa, S. Itoh, Angew. Chem., Int. Ed. Eng. 41
(2002) 4325.
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R. A. Ghiladi, K. R. Hatwell, K. D. Karlin, H.-W. Huang, P. Moënne-Loccoz, C. Krebs, B.
H. Huynh, L. A. Marzilli, R. J. Cotter, S. Kaderli, A. D. Zuberbühler, J. Am. Chem. Soc. 123
(2001) 6183.
242
243
244
Legends to the figures
245
246
247
Fig. 1. The polymeric chain in complex [CuL(µ-1,3-N3)]n (1) running parallel to the b axis.
Symmetry codes: (i) 1-x, -1/2+y, 1/2-z; (ii) 1-x, 1/2+y, 1/2-z; (iii) x, -1+y, z; (iv) x,
1+y, z; (v) 1-x, 3/2+y, 1/2-z.
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249
Fig. 2. ORTEP diagram of the asymmetric unit of complex [CuL(µ-1,3-N3)]n (1), with
displacement ellipsoids drawn at the 50% probability level.
250
251
Fig. 3. χΜ versus T (∆) plot for complex [CuL(µ-1,3-N3)]n (1). Solid lines represent the best fit
of the data with the model described in the text.
252
253
Fig. 4. Reaction profile for the oxidation of olefins with tert-BuOOH in presence of complex
[CuL(µ-1,3-N3)]n (1).
14

254
255
Fig. 5. Effect of solvent on the conversion in olefin oxidation reactions catalyzed by complex
[CuL(µ-1,3-N3)]n (1) .
15

256
257
258
259
260
261
262
263
264
265
Fig.1.
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267
268
269
270
271
272
273
274
275
276
277
278
Fig. 2.
17

0.012
0.010
0.008
0.006
0.004
0.002
0.000
0
50
100
150
200
250
300
T / K
279
280
Fig. 3.
281
282
283
284
285
286
287
288
289
290
18

110
100
90
80
70
60
50
40
30
20
10
Styrene
Methylstyrene
Cyclohexene
Cyclooctene
0
5
10
15
20
25
Time (hour)
291
292
Fig. 4.
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294
295
296
297
298
299
300
301
302
303
19

100
80
60
40
20
0
Conversion (%)
acetonitrile
Methanol
Chloroform
Dichloromethane
0
5
10
15
20
25
Time (hour)
304
305
Fig. 5.
20

306
307
Table 1. Selected bond lengths (Å) and bond angles (°) of [CuL(µ-1,3-N3)]n (1)
Bond distances (Å)
Cu(1) –O(1)
Cu(1) –N(2)
N(3) –N(4)
Cu(1)–Cu(1)i
1.894(3)
2.054(4)
1.178 (5)
5.0748(8)
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–N(5) i
N(4)–N(5)
1.940(4)
1.973(4)
2.506(4)
1.158 (5)
Bond angles (o)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(3)
O(1)–Cu(1)–N(2)
N(2)–Cu(1)–N(3)
N(1)–Cu(1)–N(5)i
N(2)–Cu(1)–N(5)i
N(3)–N(4)–N(5)
92.46 (17)
89.78 (13)
176.51 (15)
92.57 (17)
94.61 (15)
94.27 (13)
177.1 (4)
O(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
Cu(1)–N(3)–N(4)
O(1)–Cu(1)–N(5)i
N(3)–Cu(1)–N(5)i
176.51 (15)
84.6 (2)
165.54 (16)
119.1 (3)
87.86 (12)
99.74 (13)
308
309
310
311
312
Symmetry code: (i) −x+1, y+1/2, −z+1/2
21

313
314
315
Table 2. Structural and magnetic parameters for one-dimensional systems with µ1,3-azido
unit: Cu–N bond distances (Å) , Cu–N–N bond distances (Å), Cu–N3–Cu bond angles (˚) and
J values (cm-1).
Complexes
Cu–N(Ǻ)
Cu–N–N (Ǻ)
125.6
Cu–N3–Cu (∆) J (cm-1)
Ref
[Cu(L1)(N3)]n(ClO4)
[Cu(L2)(N3)] n(ClO4)n
[Cu(L3)(N3)] n(ClO4)n
[Cu(L4)(N3)]n(ClO4)n
[Cu(L5)(N3)]n(ClO4)n
[Cu(L6)(N3)]n(ClO4)n
[Cu(L7)(N3)]n(ClO4)n
[Cu(R-L8)2(N3)]n(ClO4)n or
[Cu (S-L8)2((N3)]n(ClO4)n
[Cu(L9)2(N3)2]n
1.936, 2.486
1.991, 2.266
1.946, 2.398
1.947, 2.355
1.965, 2.311
1.951, 2.270
1.955, 2.880
1.975, 2.683
1.971, –
91.6
31.3
102.7
97.8
50.4
40.4
92
1.36
2.69
2.02
2.15
3.61
2.06
1.60
0.70
[31]
[32]
[32]
[33]
[33]
[33]
[34]
[35]
134.4,136.7
122.5,135.1
126.5,131.2
131.2,139.1
139.0,132.2
133.5,100.3
127.7,128.0
–
2.029, 2.611
1.948, 2.563
1.980, 2.473
1.973, 2.51
115.7, 123.0 –71
1.6
[37]
[Cu(L10)(N3)]n(H2O)2n
[Cu(L11)(N3)]n
129.0
–
17.0
–
– 4.30
–22.5
–19.5
[37]
[38]
143.6, 109.7 -151
[This Work]
[CuL(µ-1,3-N3)]n (1)
316
22

317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
L1 = Tridentate Schiff base derived from condensation of pyridine-2-aldehyde with 1-(2-
aminoethyl)-piperidine; L2 = Tridentate Schiff base derived from condensation of pyridine-2-
aldehyde with N,N,2,2-tetramethylpropane-1,3-diamine; L3 = Tridentate Schiff base derived
from condensation of pyridine-2-aldehyde with 1-dimethylamino-2-propylamine; L4 = Schiff
bases obtained by the condensation of pyridine-2-carbaldehyde with N,N-dimethylethane-
1,2-diamine; L5 = Schiff bases obtained by the condensation of pyridine-2-carbaldehyde with
N,N-diethylethane-1,2-diamine; L6 = Schiff bases obtained by the condensation of pyridine-
2-carbaldehyde with 4-(2-aminoethyl)morpholine; L7= N-(2-pyridylmethyl)-N,N-
diethylethylenediamine; R-L8 or S-L9 = R or S-pyridine-2-carbaldehyde-imine; L9 = 4-
(dimethylamino)pyridine, L10 = The dinucleating macrocyclic ligand bis-p-xylyl-BISDIEN;
L11 = Schiff base derived from condensation of salicylaldehyde and N,N-dimethyl-
ethylenediamine.
23

342
343
344
345
346
Table 3. Homogeneous alkene oxidation catalysed by complex [CuL(µ-1,3-N3)]n (1)a in
acetonitrile medium
Catalyst
Substrate
Reaction Conversion %Yield of products
TONb
TOFc
(h-1)
651
Time (h)
24
(wt %)
100
Epoxide Others
54
62
46d
38e
15,624
[CuL(µ-1,3-N3)]n (1)
24
100
15,744
656
24
24
84
96
45
70
39f
16g
14,208
14,496
592
604
347
348
349
350
351
352
353
aReaction conditions: alkenes (10 mmol); catalysts (0.005 mmol); tert-BuOOH (20mmol);
acetonitrile (10 mL); temperature 70 °C. bTON = Turn over number = mol converted /(mol of
copper (active site) taken for reaction). cTOF = Turn over frequency = mol converted /(mol of
d
e
copper (active site) taken for reaction × reaction time). Benzaldehyde and benzoic acid. 4-
f
methylbenzaldehyde and 4-methylbenzoic acid. Cyclohex-2-en-1-ol and cyclohex-2-en-1-
one. gCyclooctane-1,2-diol.
24

354
355
356
357
358
Table 4. Homogeneous alkene oxidation catalysed by Cu(NO3)2.3H2O# in acetonitrile
medium
Catalyst
Substrate
Reaction Conversion %Yield of products
TON
6,552
TOF
(h-1)
273
Time (h)
24
(wt %)
42
Epoxide Others
Cu(NO3)2.3H2O
20
22##
24
24
25
33
25
33
-
-
3,888
4,296
162
179
359
360
361
#Reaction conditions were the same as given in the footnote of Table 3. ## Benzaldehyde and
benzoic acid.
25

362
363
364
Highlights
•
•
•
•
•
Azido bridged copper(II) complex was synthesized and characterized.
The complex shows antiferromagnetism.
365
366
367
368
The complex exhibits good catalytic activity in the oxidation of olefins.
Catalytic activity depends upon solvent media.
Catalytic efficacy is due to copper complex rather than copper salt itself.
369
370
26

371
372
Single end to end azido bridged adduct of a tridentate schiff base copper
(II) complex: synthesis, structure, magnetism and catalytic studies
373
374
Sourajit Banerjee, Chandan Adhikary*, Corrado Rizzolib, Rammohan Palc
375
376
aDepartment of Chemistry, Governement College of Education, Burdwan, 713102, India
bDepartimento di Chimica, Parco Area delle Scienze 17/A, 43124, Parma, Italy
377
378
cDepartment of Chemistry, Acharya Jagadish Chandra Bose College, Kolkata 700020, India
379
Graphical Abstract
380
381
382
383
384
Single end to end azido bridged 1D chain copper(II) complex with tridentate (NNO donor)
Schiff-base ligand has been synthesized and characterized by X-ray Crystallography. The
magnetic study revealed that the complex is antiferromagnetic in nature. Olefin epoxidation
reactions catalyzed by the complex, in different solvent media, have been studied by using
tert-BuOOH as oxidant.
385
386
27