Structurally well-characterized new multinuclear Cu(II) and Zn(II) clusters: X-ray crystallography, theoretical studies, and applications in catalysis

Article abstract of DOI:10.1039/c6nj02150f

Two new trinuclear Cu(ii) and dinuclear Zn(ii) clusters are crystallized out by reacting the metal salts with the triethanolamine (H₃tea) ligand in the presence of benzoic acid (Hba). The complexes are characterized by elemental, thermal, magnetic, spectral (FTIR, UV-Visible, EPR, and photoluminescence) and single crystal X-ray studies. Single crystal X-ray crystallography reveals the composition of the complexes to be [Cu₃(H₂tea)₂(ba)₂(NO₃)₂] (1) and [Zn₂(H₂tea)(ba)₃]H₂O (2). FTIR ascertains the binding modes of H₂tea^-, ba^- and NO₃^-. Triethanolamine binds in both the complexes in the monoanionic (H₂tea^-) mode. ba^- is present as an anchoring auxiliary to generate di- and trinuclear clusters. The Cu(ii) ion is present as a distorted octahedral center in the Cu₃ cluster (1), while the two Zn(ii) ions in 2 have been reported for the first time to possess distorted octahedral as well as tetrahedral geometry in the same molecule. The intriguing features of the non-covalent supramolecular interactions have been investigated and supported theoretically by using Hirshfeld surface analysis and ab initio methods. The solid state photoluminescence (PL) spectra of 1 and 2 disclose the luminescence property of the complexes. Due to the closed or nearly closed shell configuration (d⁹ or d¹⁰), the present complexes are screened for catalytic properties in the hydrocarboxylation of alkanes and cycloalkanes. The catalytic activity data are indicative of the potential catalytic properties of 1 and 2.

Full text of DOI:10.1039/c6nj02150f

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: I. A. Ansari, F.
Sama, M. Raizada, M. Shahid, M. Ahmad and Z. A. Siddiqi, New J. Chem., 2016, DOI:
10.1039/C6NJ02150F.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/njc

Please do not adjust margins
New Journal of Chemistry
Page 1 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
New J. Chem.
ARTICLE
Structurally wellꢀcharacterized new multinuclear Cu(II) and Zn(II)
clusters: Xꢀray crystallography, theoretical studies, and applications
in catalysis
Received 00th January 20xx,
Accepted 00th January 20xx
Istikhar A. Ansaria, Farasha Samaa, Mukul Raizadaa, M. Shahida, Musheer Ahmadb, Zafar A. Siddiqia*
DOI: 10.1039/x0xx00000x
Two new trinuclear Cu(II) and dinuclear Zn(II) clusters are crystallized out by reacting the metal salts with
triethanolamine (H3tea) ligand in the presence of benzoic acid (Hba). The complexes are characterized by
elemental, thermal, magnetic, spectral (FTIR, UVꢀVisible, EPR, and photoluminescence) and single
crystal Xꢀray studies. Single crystal Xꢀray crystallography reveals the composition of the complexes to be
www.rsc.org/
[Cu3(H2tea)2(ba)2(NO3)2] (1) and [Zn2(H2tea)(ba)3]H2O (2
). FTIR ascertains the binding modes of H2tea‒,
‒
ba‒ and NO3 . Triethanolamine binds in both the complexes as mono anionic (H2tea‒) mode. ba‒ is
present as an anchoring auxiliary to generate diꢀ and trinuclear clusters. Cu(II) ion is present as distorted
octahedral center in Cu3 cluster (1), while the two Zn(II) ions in 2 have been reported for the first time to
possess distorted octahedral as well as tetrahedral geometry in a same molecule.The intriguing features
of the nonꢀcovalent supramolecular interactions have been investigated and supported theoretically by
using Hirshfeld surface analysis and abꢀinitio methods. The solid state photoluminescence (PL) spectra
of
1 and 2 disclose the luminescence property of the complexes. Due to the closed or nearly closed shell
configuration (d9 of d10), the present complexes are screened for the catalytic properties in the
hydrocarboxylation of alkanes and cycloalkanes. The catalytic activity data is indicative of the potential
catalytic
properties
of
1
and
2.
molecules.[2] Besides copper, the coordination chemistry of d10
systems like zinc(II) complexes has also attracted much attention
owing to their versatile role in various metalloenzymes like
carbonic anhydrase. Zn(II) complexes have been proven better
enzymatic mimics in the recent years. Specially the polynuclear
zinc complexes are explored as efficient catalysts e.g. zinc cluster
is used in direct conversion of ester, carboxylic acids and lactones
to oxazolines.[3] Simultaneously, Cu(II) catalysts have been
reported in literature to catalyse a number of organic reactions.[4]
In designing polynuclear clusters of Cu(II) and Zn(II) metal ions, it
is important to select the ligands which decide the structural
Introduction
The designing of polynuclear transitionꢀmetal complexes
bearing unique structural features has become a challenge in the
past decade due to their broad applications such as in catalysis,
biochemistry, materials science and medicinal chemistry. The topology and nuclearity of the resulting clusters.[4]
reason for the wide utility of the high nuclearity metal complexes
Flexible aminoꢀpolyalcohols are recognized as useful
is their complex molecular structures, topology and electronic
versatility. Though several transition metal ions yield polynuclear
clusters, special emphasis has always been given to the Cu(II)
and Zn(II) chemistry.[1]
ligands in coordination chemistry and related areas, and have
ability to show a variety of coordination modes being broadly used
for the preparation of diverse materials with monoꢀ and specially
polynuclear metal complexes.[5]
The chemistry of polynuclear copper complexes is a topic of great
scientific interest due to its relevance to many areas, including
bioinorganic chemistry and materials science. Copper complexes
have recently attracted increasing attention as alternative O2
reduction catalysts. Among numerous copperꢀcontaining enzymes
such as hemocyanin, cytochrome c oxidase, and nitrous oxide
reeducates, few molecular examples play a variety of critical roles
in biology responsible for activation and transformation of small
Aminoꢀalcohol derivative ligands are useful in the synthesis of
polynuclear coordination clusters by chelating to one metal centre
and bridging other metal centres through the alkoxide arms.
Furthermore, the introduction of the auxiliary ligands like
carboxylic acid, plays a key role in maintaining the structural
topology and integrity of the cluster exhibiting unusual
coordination modes (Scheme S1).[5,6]
Triethanolamine (H3tea) is an ideal amino alcohol ligand
which acts as deprotonated multidentate in the area of clusters
chemistry with its [N,O,O,O] donor sites. This ligand exhibits
versatile bridging and chelating modes, as it can, in theory, bind to
upto a number of metals at a time. Its flexibility in cluster science
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 2 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Journal Name
‒
gives rise to various deprotonated forms as: H3tea, H2tea‒, Htea2
EPR spectrum of the complexes was acquired on a Perkinꢀ
‒
and tea3
, which further provides numerous different types of Elmer spectrometer using Xꢀband frequency (9.1 GHz) at
bonding modes. The flexible nature of the H3tea is what makes it room temperature in solid. Thermal gravimetric analysis
so much promising and has thus far been known to display eight (TGA) data were recorded from room temperature up to 600
°
different modes of bonding (Scheme S2).[7]
°C at a heating rate of 20 C/min. The data were obtained
using
a
Shimadzu TGAꢀ50H instrument. Magnetic
For 3d metal ions these amino alcohols and carboxylate
susceptibility was measured by magnetic susceptibility
balance, Sherwood scientific Cambridge U. K. at room
temperature. Cyclic voltammetry (CV) was performed on
EG&G PAR 273 Potentiostat/Galvanostat an IBM PS2
computer with EG&G M270 software for data acquisition. The
threeꢀelectrode cell configuration comprised of, a platinum
sphere, a platinum plate and Ag(s)/AgNO3 were used as
working, auxiliary and reference electrodes, respectively. The
supporting electrolyte used was [nBu4N]ClO4. Platinum
sphere electrode was sonicated for 2 min in dilute nitric acid,
dilute hydrazine hydrate and then in double distilled water to
remove the impurities. The solutions were deoxygenated by
bubbling research grade nitrogen gas and an atmosphere of
nitrogen was maintained over the solution during
measurements.
units can combine in more interesting ways and yield more
‒
elaborate products. When fully deprotonated (tea3 ), the tendency
of the three alkoxide arms of the triꢀanion generally directs the
formation of dinuclear [M2] and triangular [M3] units where each
arm of the ligand bridges produces edge of the triangle. In the
presence of coꢀligands such as carboxylates or β diketonates etc,
these smaller units can combine to produce complexes whose
structures range from ‘simple’ [M2], [M3] or [M4] (centered)
triangles to rodꢀlike complexes describing ‘1ꢀD’ arrays of edgeꢀ
sharing triangles; planar discꢀlike complexes describing ‘two
dimensional’ arrays of edgeꢀsharing triangles; and more
complicated ‘three dimensional’ arrays commonly based on
tetrahedra, octahedra and icosahedra. These ligands are
excellent candidates for use in paramagnetic cluster synthesis as
they have the ability to act as both terminal and bridging ligands.
These coordination clusters selfꢀassemble through syn syn
carboxylate and / or nitrate bridges, often supported to form poly
systems, 1D tapes, 2D sheets, and 3D networks which have been
constructed through nonꢀcovalent interactions. Among others,
carboxylic acids have been successfully used in crystal
engineering to generate a variety of 3D bridged architectures.[7]
Crystallographic data collection and refinements
Single crystal Xꢀray diffraction of the compounds (
1 and
2
) were performed at 296 K on a Bruker SMART APEX CCD
diffractometer, X–ray data was collected using graphite
monochromated MoꢀKα radiation (λ = 0.71073 Å). The linear
absorption coefficients, scattering factors for the atoms, and
the anomalous dispersion corrections were taken from the
International Tables for X–ray Crystallography.[8] The data
integration and reduction were processed with SAINT
Software.[9] An empirical absorption correction was applied to
the collected reflections with SADABS[10] and the space
group was determined using XPREP.[11] The structures were
solved by direct methods using SIRꢀ97[12] and refined on F2
by full matrix least squares using the SHELXSꢀ97 program
package.[13] All nonꢀhydrogen atoms were refined with
anisotropic displacement parameters. A summary of the
crystallographic data and the structure refinement for the
complexes is given in Table S1. CCDC reference numbers
In view of the above and due to our ongoing interest for
new preparative routes to polynuclear complexes of various
transition metal complexes, we chose to investigate the
coordination chemistry of copper and zinc with triethanolamine
(H3tea) in the presence of benzoic acid as the ancillary ligand.
This combination of aminoalcoholate and benzoate with Cu(II)
and Zn(II) results in the trinuclear (Cu3) and dinuclear (Zn2)
complexes which are further proven to be efficient catalysts for
the conversion of alkanes to carboxylic acids.
Experimental
for
1 and 2 are 1474749 and 1474750, respectively.
Hirshfeld surface analysis
Materials and methods
Hirshfeld surfaces mapped with various properties and
2D fingerprint plots were generated using Crystal Explorer
3.0.[14]This have been proven to be a useful visualization tool for
the analysis of intermolecular interactions in the crystal packing.[15]
The Hirshfeld surface can be defined in a crystal as the region
around a molecule where the ratio of the electron distribution of a
sum of spherical atoms for the molecule (the promolecule) to the
corresponding sum over the crystal (the procrystal) equals to 0.5.
The shape and nature of the surface is directly influenced by the
surrounding environment of the molecule in the crystal.
All reagents of analytical grade were obtained from
commercial sources and used without further purification.
The infrared (IR) spectra of the compound were recorded
within the range 4000–400 cm‒1 using KBr pellets on Perkin
Elmer Model spectrum GX spectrophotometer. Melting points
were determined by open capillary method and are
uncorrected. Electronic spectrum and molar conductivity of
10‒3 M solution in MeOH was recorded on Perkin Elmer λꢀ
850 UVꢀvisible spectrophotometer at various temperatures
with cuꢀvettes of 1 cm path length and Systronicsꢀ305 digital
conductivity bridge, at room temperature respectively. The
elemental C, H and N analyses were obtained from Microꢀ
Analytical Laboratory of Central Drug Research Institute
(CDRI), Lucknow, India. Fluorescence measurements were
determined on Hitachi Fꢀ2700 spectrophotometer. Solid state
fluorescence spectra were recorded on Jobin Yvon Horiba
Fluorologꢀ3 spectro fluorimeter at room temperature. The
For each point on the Hirshfeld iso surface, two
distances de, the distance from the point to the nearest nucleus
external to the surface, and di, the distance to the nearest nucleus
internal to the surface, are defined.
The normalized contact distance (dnorm) based on de and di is
given by
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 3 of 14
Journal Name
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
dꢄ − rꢄꢅꢆꢇ dꢈ − rꢈꢅꢆꢇ
= +
Synthesis
dꢀꢁꢂꢃ
rꢄꢅꢆꢇ
rꢈꢅꢆꢇ
Synthesis of [Cu3(H2tea)2(ba)2(NO3)2] (1)
vdW
Where rivdW and re
are the van der Waals radii of the atoms.
A mixture of Cu(NO3)2—3H2O (0.03 g, 0.13 mmol) and
benzoic acid (Hba) (0.016 g, 0.13 mmol) in MeCN (20 mL)
was stirred for 10 min at 80 °C producing a blueꢀgreen
solution. A solution of H3tea (0.298 g, 2 mmol) in CH3CN (10
mL) was added dropwise to the above mixture. The reaction
was then stirred for 5 h after addition of 10 drops of NEt3.
The resulting green solution was allowed to evaporate
slowly. After being at room temperature, green block crystals
The value of dnorm may be negative or positive depending on the
intermolecular contacts being shorter or longer than the van der
Waals separations.[16] The parameter dnorm displays a surface with
a redꢀwhiteꢀblue colour scheme, where bright red spots highlight
shorter contacts, white colour areas represent contacts around
the van der Waals separation, and blue colour regions are devoid
of close contacts.
of
1 were collected, which were suitable for Xꢀray
The electrostatic potential (ESP) were mapped on the
Hirshfeld surface[17]over the range −0.139 au (red), through 0
(white), to 0.225 au (blue) and −0.161 au (red), through 0 (white),
to 0.208 au (blue) respectively, for, 1 and 2. For this purpose, ab
initio wave functions were obtained at HF/STOꢀ3G** using Crystal
Explorer 3.0 software. Molecular geometries were taken directly
from the relevant crystal structure with H atoms at their neutron
distances. 3Dꢀdeformation density (DD) maps were also plotted
for the molecule at the crystal geometry over the electron density
isoꢀsurface (the value is 0.008 e/au3) using Crystal Explorer 3.0.
For this purpose, ab initio wave functions were also obtained at
HF/ STOꢀ3G.
crystallographic study in 70% yield based on the added
amounts of metal salt. Elemental analysis: Calcd: for
C26H34Cu3N4O16 (M = 795): C, 36.74; N, 6.59; H, 4.00%.
Found: C, 36.92; N, 6.78; H, 4.12%. Molar conductance, Λm
(10‒3 M, methanol): 35.0 ꢂ‒1cm2mol‒1. FT–IR (as KBr, ν/cm‒
1): 1572/1386s νas/νs(COO‒), 3400 (O–H), 945s (Cu–O–Cu).
Synthesis of [Zn2(H2tea)(ba)3]—H2O (2)
2
was synthesized by similar procedure to that used for 1
except that equal amount of Zn(NO3)2—4H2O was used in
place of Cu(NO3)2—3H2O. Yield: 65.0% based on the added
amounts of metal salt. Elemental analysis: Calcd: for
C27H31NO10Zn2 (M = 660): C, 49.10; N, 2.12; H, 4.69%. Found:
C, 49.80; N, 2.20; H, 4.50%. Molar conductance, Λm (10‒3 M,
methanol): 50.0 ꢂ‒1cm2mol‒1. FT–IR (as KBr, ν/cm‒1):
Catalytic activity
In a typical experiment, the reaction mixtures were
prepared as follows: to 4.0 ꢁmol of the copper promoter (1) or zinc
promoter (2) contained in a 13.0 mL stainless steel autoclave,
equipped with a Teflonꢀcoated magnetic stirring bar, were added
1.00–1.50 mmol of K2S2O8, 2.0 mL of H2O, 4.0 mL of MeCN
(typical total solvent volume was 6.0 mL) and 1.00 mmol of alkane
(if liquid). Then the autoclave was closed and flushed with CO
three times to remove the air, and finally pressurized with
0.75−1.0 atm of alkane (if gaseous) and 10−20 atm of CO. The
reaction mixture was stirred for 6 h at 60 °C using a magnetic
stirrer and an oil bath, whereupon it was cooled in an ice bath,
degassed, opened and transferred to a flask. Diethyl ether (9.0–
11.0 mL) and 90 ꢁL of cycloheptanone (GC internal standard)
were added. The obtained mixture was vigorously stirred for 10
min, and the organic layer was analyzed by gas chromatography
(internal standard method), revealing the formation of the
corresponding monocarboxylic acids as the dominant products. In
the reactions with cycloalkane substrates, cyclic ketones and
alcohols were also formed as byꢀproducts of partial alkane
oxidation, whereas in the transformations of linear alkanes the
generation of the corresponding oxygenates was negligible (their
overall yields were not exceeding 1.0%). Blank tests indicated that
the hydrocarboxylations also proceed in the metalꢀfree
systems,[18] although typically leading to 3ꢀ5 times inferior yields of
carboxylic acids in comparison with the Cu3/Zn2ꢀpromoted
transformations. Additional experiments were performed under
the typical reaction conditions in the presence of the carbonꢀ
centred radical trap CBrCl3, revealing the suppression of the
formation of carboxylic acids. The acetonitrile solvent is
nonreactive in the present systems, since no generation of acetic
or propionic acids from MeCN was detected when the reactions
were repeated in the absence of alkane. Furthermore, the alkane
hydrocarboxylations do not proceed either in sole H2O or MeCN
solvent.
1542/1390s νas/νs(COO‒), 3450w (O–H), 940s (Zn
–O
–Zn).
NO2
O
O
O
O
HO
OH
2
2
O
O
H
3
O
Cu
N
O
N
OH
NO2
O
OH
N
HO
OH
+
O
(1)
OH
MeCN
HO
O
O
O
Zn
OH
N
O
O
3
2
O
O
2
(2)
Scheme 1. Synthetic procedure for 1 and 2.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 4 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Journal Name
Results and discussion
coordination modes with ∆ values observed at ̴
170 cm−1,which is
in the region close to that found in the precursor copper(II)
acrylate a dinuclear [Cu2(CH2=CHCOO)4(H2O)2]. The magnitudes
of ∆ν indicating that both the complexes are consist asymmetric
bidentate mode (mode d) in addition to the anionic monodentate
mode (mode a) in 2, which is also confirmed from the Xꢀray
crystallography of the complexes.
Synthesis
The synthetic procedure and structures of new trinuclear
Cu(II)ꢀ and binuclear Zn(II)ꢀtriethanolamine complexes anchored
by aromatic carboxylate bridging has been presented in Scheme
1. The trinuclear Cu(II) complex (1) bears distorted octahedral
geometry around the Cu(II) metal ions while 2 has unusual
geometry, as two zinc metal ions are present in different
coordination environment. One of the Zn(II) adopts distorted
tetrahedral and other Zn(II) has distorted octahedral geometry
with same oxidation state i.e., +2. Both tetrahedral and octahedral
Zn(II) ions are joined with the synꢀsyn ba‒ and H2tea‒ bridges.
General synthetic approach was employed in the formation of
trinuclear (1), and dinuclear (2) complexes. The formation of 1
and 2 can be represented by equations (i) and (ii). The single
crystal Xꢀray determination revealed that both the complexes
consist of neutral trinuclear and neutral binuclear entities as
Absence of any sharp band at 1385 cm−1 confirmed that anion is
not present in the complexes (1 and 2). It was further confirmed
by the magnitude of molar conductance.[19] The presence of the
coordinated nitrates in 1 is ascertained by two bands; the
asymmetric stretching vibration of nitrate νas(–ONO2) at 1479 cm−1
and the symmetric stretching vibration, νsym(–ONO2) at 1299 cm−1.
−
These vibrations do not occur in the ionic nitrates (NO3 ) in lattice
and the frequency difference ∆ν(νas−νsym) = 180 cm−1 (in 1) is
indicative of syn−syn bidentate coordination mode of the nitrate
ions (Scheme S3),
and is in line with already reported
examples.[20] The band appearing at 945 cm−1 is characteristic of
M–O–M bridging in both the complexes.
[Cu3(H2tea)2(ba)2(NO3)2] (1) and[Zn2(H2tea)2(ba)3]—H2O
(2).
Molar conductivity measurements of the complexes reveal the
nonꢀelectrolytic nature of 1 and 2 in CH3CN solution, with molar
The bands in 600–800 cm−1 region are associated with
conductivity values Λm 35 and 50 ꢂ‒1cm2mol‒1. The results agree deformation modes of benzoate (ba−) group. The medium to weak
with the nonꢀionic nature of the compounds in solution.
intensity bands at 873–950 cm−1 are attributed to the C–C
vibrations. The strong to medium bands in the region 955–1253
cm−1 may be due to the C–O stretching vibrations of O–CH2. The
bands in the region 469–499 cm−1 and 575–570 cm−1 are ascribed
to ν(M–N) and ν(M–O) vibrations, respectively.
Bonding modes (FTIR Spectral studies)
Geometry and electronic properties (UVꢀvisible and EPR
Spectral Studies)
The FTIR spectra of newly synthesized complexes have
been recorded in the region 4000−400 cm−1 (Fig. S1). The band
at ~3400 cm−1 was assigned to OH(H2O) stretching vibrations.
Bands due to triethanolamine ion (H2tea−) are investigated in
three regions in both 1 and 2: (a) medium band at 3400 cm−1
assignable to the stretching vibrations of OH groups; (b) at about
2944 cm−1 and 2904, due to the νas(C–H) and νs (C–H),
respectively; and (c) three bands in the region of 1058 cm−1 are
attributed to the ν(C–Ο) stretching vibrations.[19] The bands in the
region 1607–1598 cm1 are attributed to ν(C–C) of the aromatic
moiety.
The electronic spectra of 1 (d9, trinuclear) and 2 (d10,
dinuclear) were recorded in 10−3
M methanol at various
temperatures. Absorption spectra of the complexes exhibited (Fig.
1), well resolved absorption bands at 224, 240, 270 and 363 nm in
1 and 228, 242, 332 and 338 nm in 2. The first three well resolved
π*, π→π* and
bands are assignable to intraligand transitions, n→
CT in 1 and n→π*, π→π* transitions in 2. The broad absorption
bands below 400 nm are characteristic of the ligandꢀtoꢀmetal
charge transfer (LMCT) (in 1) and are consistent with the distorted
octahedral geometry about the metal ion. Blue methanolic solution
showed a broad low intensity band at 660 nm (1) which can be
assigned to d–d transitions band,[21] while this type of band above
400 nm was absent in the Zn(II) complex (2).
The bands at 1572/1386 cm−1 in 1 and 1557/1398 cm−1
in 2 are characteristic of νas(COO) / νs(COO) vibrations of the
carboxylic acid. In particular, taking into account that the
carboxylates can coordinate to the metal ions in a bidentate or
monodentate fashion (Scheme S1), on the basis of ∆ν criterion
[∆ν = νas(COO)–νs(COO)], we can conclude that in 1 and 2, one or
both unsaturated carboxylates adopt bridging monoꢀ or bidentate,
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 5 of 14
Journal Name
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Fig. 1(a). Absorption spectra for (a) 1 and (b) 2.
The EPR spectrum of 1 is consistent with the paramagnetic
nature with the expected three lines at lower field. From the
magnitude of g1, g2 and g3, it is clear that g1> (g2 + g3)/2 which is
Fig. 2. Atomic labelling diagram (a) and core diagram (b) for 1 (Hydrogen atoms
are omitted for clarity).
characteristic of Cu(II) complex in dx2 2ground state and
−y
elongation of the axial bonds.[22] The distorted octahedral
geometry of 1 and 2 are consistent with the above data (Fig. S2)
The equatorial plane of the central copper atom is formed by two
oxygens provided from the carboxylate ligand (1.944(3) Å) and
two oxygens from the oxide bridge of H2tea− (1.959(2) Å) while the
apical positions are occupied by two oxygens from the oxide
Crystal structure description of 1
The single crystal Xꢀray determination results revealed
that 1 consists of neutral trinuclear entity. Molecular structure of
the complex is given as Fig. 2. Selected bond distances and
angles are listed in Table S2. The trinuclear copper complex is
monoclinic with space group P 21/c. In the trinuclear (Cu1–Cu2–
Cu1) system, Cu2 ion is present in octahedral environment on the
center of inversion with half a population so that a linear trinuclear
copper entity is equivalently furnished. The central Cu2 ion is
triply bridged to both of the terminal copper atoms (Cu1) through
one alkoxide bridge of the single deprotonated triethanolamine
–
bridge of –ONO2 (2.584(2) Å). The terminal copper ions contain
the equatorial plane, from two oxygens provided by the
carboxylate ligands (1.911(3) and 1.911(3) Å), the oxygen from
–
the alkoxide bridge of –ONO2 (2.750(3) Å), the oxygen from the
oxide bridge of H2tea– (1.938 (3) and 1.959 Å) and the nitrogen
atom of H2tea– (2.019(3) Å). The basal plane is composed the two
free alkoxide oxygen atoms, defined as Cu–O(H), (Cu1–O2 =
1.912(2) and Cu1–O3 = 2.071(3) Å), while the apical positions are
occupied by the nitrogen atom of H2tea– (Cu1–N = 2.008(3)Å )
and the carboxylate oxygen (Cu1–O12 = 1.912(2) Å )(Fig. S3).
–
(H2tea−) ion, one syn–syn oxide bridge from (–ONO2 ), and a
syn–syn carboxylato bridge provided from the deprotonated
benzoic acid (ba−). Both the central and terminal copper ions have
same coordination (distorted octahedral) environments with CuO6
and CuO5N chromophores, respectively.
The O−Cu−O angle around Cu2 center is 180°,
indicating further an octahedral environment. The shortest length
of Cu−O bond is assigned to deprotonated ꢁ2ꢀalkoxo bridging
intersections. The Cu———Cu distance within the trinuclear molecular
unit is 3.177 Å.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 6 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Journal Name
Furthermore, the Hꢀbonding and other nonꢀcovalent
interactions are also present in the molecule, which contribute to
the generation of supramolecular network. Two intramolecular
and one intermolecular O−H———O hydrogen bonds are formed
(Table 1). The intramolecular interactions involve the alkoxo OH
of the H2tea− ligand and the free nitrate oxygen (O−H———O = 1.883
Å) (Fig. S4).
Table 1. Distances and angles of nonꢀcovalent interaction in 1 and 2.
D–H···A
d(D–H) d(H···A) d(D···A) ∟(DHA)
(1)
O3‒H3···O7
O5‒H5···O4
C5‒H5···O8
0.768
0.729
0.939
1.883
2.160
2.528
2.468
2.806
3.453
174.51
147.31
173.22
C‒H···O
0.930
0.970
0.970
0.969
2.686
2.806
2.810
2.853
3.313
3.529
3.657
3.681
125
C12‒H12···π
C12‒H12···C7
C11‒H8···C8
(2)
146.20
131.85
143.98
O10‒H10a···O2 0.765
O10‒H10b···O8 0.801
2.066
2.003
2.099
2.436
2.549
2.890
2.871
2.803
2.810
2.766
2.804
3.321
3.466
3.652
3.665
3.650
164.24
158.89
167.99
159.22
168.32
140.12
144.10
151.91
O7‒H7···O2
C10‒H10…O8
C3‒H3···O3
C‒H··· π
C4‒H4···C15
C7‒H7···C19
0.717
0.930
0.931
0.930
0.931
0.930
The intermolecular O−H———O bonds are formed between two
adjacent complex units, involving the alkoxo OH of the H2tea−
ligand and the bridging oxygen (O−H———O = 2.806 Å) (Fig. S5).
A number of weak C−H———O interactions also contribute to the
crystal robustness (Table 1) and (Fig. S6), while no π———π
interactions between the aromatic rings were found. The C−H———π
interactions are also formed within the range 2.806ꢀ2.810 Å (Fig.
S7). The nonꢀcovalent interactions result in a 1 D polymeric chain
(Fig. S8). These supramolecular interactions have been verified
further by Hirshfeld surface Analysis (vide infra) (Fig. S9).
Fig. 3. Atomic labelling diagram (a) and core diagram (b) for 2 (Hydrogen atoms
and lattice molecule are omitted for clarity).
monodentate mode where it binds with Zn2 center only. The
octahedral Zn1 binds with two alkoxide of the H2tea– arms with the
distances Zn1−O7 = 2.173 and Zn1−O9 = 2.152 Å, two oxygen
atoms provided from the carboxylate (ba–) ligand attached to the
metal ion with the distances Zn1−O3 =2.124 and Zn1−O5 = 1.988
Å, the oxygen from the oxide bridge of H2tea– (Zn1−O8 = 2.708
(3) Å) and the nitrogen atom of H2tea– (Zn1−N1 = 2.139 Å) (Table
S2). The tetrahedral Zn2 binds with two oxygen atoms of
corboxylate ligand (ba–) with the metal oxygen bond distance
Zn2−O4 = 1.960 and Zn2−O6 = 1.960 Å, one oxygen atom of
corboxylate ligand in the asymmetric monodentate coordination
manner (Zn2−O1= 1.926 Å) and one oxygen atom from the oxide
bridge of H2tea– (Zn1−O8 = 2.708 (3) Å). The Zn———Zn distance
within the dinuclear moiety is 3.142 Å (Fig. S10).
Crystal structure description of 2
The single crystal Xꢀray diffraction of 2 reveals that the
binuclear zinc complex is monoclinic with same space group
similar to that of 1. It is interesting to note that two type of zinc
atoms are present in the same molecule of the dinuclear unit with
one of the zinc (Zn2) in tetrahedral and another zinc (Zn1) in
octahedral environment. Such tetra and octahedral Zn(II) systems
present in a complex, have not yet been reported so far and
constitute unique bimetallic Zn system (Fig. 3).
The asymmetric unit of
2 consists of one single
deprotonated H2tea–, two units of syn–syn carboxylateꢀbridge
provided from the deprotonated ba–, one asymmetric
monodentate coordination provided from ba–, and one water
molecule present in the lattice. The Zn1 center is distorted
octahedral with ZnO5N while Zn2 center has tetrahedral
environment with ZnO4chromophores. Three ba– anions adopt two
types of coordination modes (Scheme S1): (a) synꢀsyn bridging
mode between two metal centers on (Zn1 and Zn2) and (b)
Due to the hydrogen bonding donor atoms present in the
complex, structure shows intermolecular O−H———O hydrogen
bonds (Table 1) formed between two adjacent moieties, the
intermolecular interactions involve the alkoxo (OH) group of the
H2tea− ligand (first unit) and the oxygen atom of the asymmetric
monodentade carboxylate ligand of the second unit of the
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 7 of 14
Journal Name
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
complex with O−H———O distances to be 2.804 Å (Fig. S11). The
other intermolecular O−H———O bonds are formed with the link of
two adjacent units as shown in Fig. S12, i.e. between alkoxo
(OH) group of the H2tea− ligand (first unit) and the water
molecule (O−H———O = 2.640 Å). Two O−H———O bonds are also
formed with the interaction of water molecule with the bridging
carboxylate oxygen (O−H———O = 2.766 and 2.810 Å).
Various weak interactions such as intramolecular C–H———O and
intermolecular O–H———O, C–H———O, C–H———π contacts with the
unusual new C–H———C contacts are observed in
consolidated the crystal lattice. The presence of intermolecular
C–H———C interactions add new dimension to the
2 to
a
crystallography, which may thus be considered to support the
supramolecular network (Figs. S13 and S14).
Theoretical calculations (vide infra) support this view. There
are two kinds of C–H———C contacts between ba– ligands of
neighbouring units. Clearly, the C–H———C bridges are of
bifurcated type since C–H moiety participating in this form of
supramolecular interaction is connected to two benzoate ligand
carbon atoms. One pair of C4(sp3)–H4———C15(sp3) (C———C =
2.871Å) and another pair of C7(sp3)–H7———C19(sp3) (C———C =
2.803Å ) interactions exit in the molecular units of 2.
Fig. 4. Liquid and solidꢀstate photoluminescence (PL) spectra for 1 and 2
recorded in10ꢀ4 M MeOH. (Blue, yellow in liquid medium and violet, cyan in solid
state).
It is noteworthy that reports on C–H———C contacts are
rather scarce in published previous literature. Although such ‘nonꢀ
covalent interactions were identified early, studied theoretically,
and established crystallographically, these interactions invoked in
the description of supramolecular network of the crystal
structures.[23] The crystallographic results just discussed suggest
strongly that this form of nonꢀcovalent bonding constitutes an
important feature of the 1D supramolecular structure of the
present complexes (Figs. S15 and S16).
Cyclic voltammetric (CV) studies
The electrochemical properties of the oxo and
carboxylate bridged trinuclear Cu(II) and binuclear Zn(II)
complexes have been studied at 27 °C. The cyclic
voltammograms of 1 and 2 in the potential range +1.0 to –1.0 V
with reference to Ag/AgCl electrode in the presence of
tetrabutylammonium perchlorate were recorded to investigate the
changes in oxidation states of metal ions in solution. Although the
ligands involved are redoxꢀinactive in the applied potential range,
the electrochemical processes should arise from the metalꢀbased
redox reactions. The electrochemical redox properties of 1 and 2
are given as Fig. 5 at 300 V/s scan rate. The voltammogram for
the complexes shows a cathodic peak in the forward direction,
which is coupled with anodic peak in the reverse direction,
Photoluminescence properties
Coordination complexes with d9/d10 metal configurations
and conjugated organic linkers have become attractive as
luminescent materials because of their nearly closedor closedꢀ
shell ions. This led us to study fluorescence and solidꢀstate
photoluminescence properties of the two coordination complexes
at room temperature (Fig. 4). 1 exhibits an emission maximum at
405 nm in solution and 410 nm in microcrystalline solid state upon
excitation at 270 nm. However, 2 displays an emission maximum
at 440 in solution and 490 nm in solid state upon excitation at 330
nm. From the photoluminescence spectra recorded in the solid
state, it is clearly evident that in comparison to the solution phase,
the emissions in the solid state are relatively redꢀshifted. This red
shift in the solidꢀstate emission spectra may be attributed to the
presence of nonꢀcovalent interactions in the solid state, which are
not significant in the solution state. The emission peaks at 410
nm for 1 and 490 nm for 2 may be attributed to the ligandꢀtoꢀmetal
chargeꢀtransfer (LMCT) suggesting that the trinuclear (Cu3) and
dinuclear (Zn2) complexes could potentially be used as
luminescent materials.[24] The inconsistency in the emissions of 1
and 2 is probably attributed tothe differences in the metal ions and
their coordination environments.
forming a quasiꢀreversible redox couple at E0 = 0.23 (1) or –
1/2
0.44 V (2) (Fig. 5). The CV data indicated that there is a formation
of quasiꢀreversible redox couple in solution state of both the
complexes (1 and 2)[25]
.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 8 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Journal Name
Fig. 5.Cyclic voltammogram for (a) 1 and (b) 2 recorded at 200 mV/s scan rate
in MeOH.
Thermal analysis and phase purity
To estimate the stability of the coordination compounds,
thermogravimetric analyses (TGA) were carried out. The
compounds were heated under an N2 atmosphere in the
temperature range 27ꢀ600 °C at a heat ingrate of 20 °C min−1.
Thermal analysis of the complexes has provided enough
information regarding stoichiometry. As shown in Fig. 6a, the
thermogram of trinuclear copper cluster (1) indicates the stability
of the compound up to 180 °C but the binuclear zinc compound
(2) shows the release of the water molecule up to 150 °C (found
3.2%, calculated 3.7%), present in the lattice. Further, as the
temperature increases up to 300 °C, two nitrate and two H2tea‒
ligand eliminate (found 39%, calculated 38%) from 1, however, in
the 2, only one H2tea− alongwith one ba− ligand eliminate at this
temperature (found 45%, calculated 42%). Finally, decomposition
of organic benzoic acid linkers above 350 °C takes place.[26]
Fig. 6. Thermograms of the compounds (a), Experimental and as synthesized
PXRD patterns of 1 (b) and 2 (c).
The phase purity of the bulk samples of 1 and 2 was
also ascertained from powder Xꢀray diffraction (PXRD) analysis.
The simulated and as synthesized PXRD patterns of the present
compounds were identical indicating the purity of the crystalline
samples of 1 and 2 (Fig. 6b and c).
Fig. 7. Hirshfeld surface of (a) 1 and (b) 2 mapped with dnorm (i) di (ii) de (iii)
shape index (iv) and curvedness (v).
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 9 of 14
Journal Name
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Study of supramolecular interactions (A Hirshfeld surface
analysis)
The Hirshfeld surfaces[27] of 1 and 2 are illustrated in Figs. 7a and
b revealing surfaces mapped over dnorm, di, de, shape index and
curvedness. dnorm surface (ranged between −0.5 to 1.5 Å) is
transparently shown to visualize the moieties around which it was
calculated. The deep red depressions[28] visible on the dnorm
surfaces are indicative of hydrogen bonding contacts. The
dominant interactions viz. C–H———π, C–H———H, C–O———C, N–O———N
and N–O———Cu for 1 and C–H———π, C–H———H, C–O———H for 2 are
shown in the Hirshfeld surface plots as the redꢀshaded area in
Figs. 8a and b.
Fig. 9. (a) Hirshfeld surface mapped with electrostatic potential (ESP) for 1,
showing the σꢀhole on the nonꢀprotonated H atom of H2tea– with potential values
at two different interacting sites for O———H contacts (b) Front and rear views of
the electrostatic potential (ESP) mapped over the Hirshfeld surface for 1 over
the range −0.139 au (red) through 0.000 (white) to 0.225 au (blue).
Fig. 8. Intermolecular N–OꢃH and N–OꢃCu Interactions in 1 and C–Oꢃ
H
interactions in 2 through red spots shown at different orientations by Hirshfeld
surface.
The 2Dꢀfingerprint plots provide quantitative information about
the decomposition of the Hirshfeld surfaces into contributions from
the various intermolecular interactions present in the crystal
structures[29]The fingerprint plots are presented in Fig. S17(a) and
(b).
The intermolecular N–O———H interactions in 1 appear as two
distinct spikes of almost equal length in the 2D fingerprint plots in
the region 2.40 Å < (de + di) < 2.85 Å shown as a light skyꢀblue
pattern whereas the same pattern appears for C–O———H in 2 in the
region 2.36 Å < (de + di) < 3.40 Å. Complementary regions are
visible in the fingerprint plots where one molecule acts as a donor
(de> di) and the other as an acceptor (de< di). The fingerprint plots
can be used to highlight a particular atomꢀpair close contacts.
This enables the separation of contributions from different
interaction types, which overlap in the full fingerprint.
Fig. 10. (a) Hirshfeld surface mapped with electrostatic potential (ESP) for 2,
showing the σꢀhole on the nonꢀprotonated H atom of H2tea– with potential values
at two different interacting sites for O———H contacts (b) Front and rear views of
the electrostatic potential (ESP) mapped over the Hirshfeld surface for 1 over
the range −0.161 au (red) through 0.000 (white) to 0.208 au (blue).
The electrostatic potential (ESP) for the complexes has
also been mapped on the Hirshfeld surface displaying the
presence of a positive ESP on the H atom (σꢀhole) of H2tea‒ of
magnitude +0.164 au and +0.185 au, respectively, for 1 and 2
(Figs. 9 and 10).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 10 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Journal Name
This electropositive region on the H atom interacts with an
electronegative region over the O atom (−0.134 au for 1 and
−0.120 au for 2), resulting in the formation of the short dimeric
O———H contact in the crystal packing. Their contributions to the
Hirshfeld surface are 32.8 % (1) and 21.0 % (2) (Fig S17). A pair
μꢈꢗꢗ = 2.283 χ . ꢚ ꢛ. ꢜ.
ꢘ
ꢙ
{χg magnetic susceptibility erg.G‒2.gm‒1, χm molar susceptibility
erg.G‒2.mol‒1, and µeff effective magnetic moment B. M.}.
of spikes for the O———H contacts were observed on the Magnetic data indicates that µeff for complexes (3.9 (1) and 0.0
decomposed 2D fingerprint plots.
B.M. (2)) are suggestive of highly paramagnetic behavior of 1 and
diamagnetic nature of 2.[31]
The deformation density calculations for 1 and 2 are
also performed (Fig. S18) revealing, for 1, the presence of a Catalytic activities for hydrocarboxylation of alkanes and
charge depletion (CD) region at the nonꢀprotonated H atom of cycloalkanes
H2tea‒, which is directed towards the charge concentration (CC)
region over bridged O atom of H2tea‒, facilitating formation of the
Alkane functionalization reactions have been tested
using 1 and 2 as catalysts for the mild hydrocarboxylations of
O———H contacts in the crystal. For 2, the presence of a charge
depletion (CD) region at the nonꢀprotonated H atom of H2tea‒ is
also directed towards the charge concentration (CC) region over
nonꢀbridged O atom of benzoic acid, facilitating the formation of
the O———H contacts in 2.
[18]
alkanes (Cn) into carboxylic acids (Cn+1
)
. The promoting
behaviours of the 1 and 2 using various C2–C7 linear and C5–C7
cyclic alkanes as substrates are examined by reaction with carbon
monoxide (CO), water (H2O) and potassium peroxodisulfate
(K2S2O8) in a neutral H2O–MeCN medium at low temperature (60
°C) (Scheme S4).
Magnetic behaviour
There are a few examples of copper carboxylate bridged
Both the complexes (1 and 2) exhibited similar catalytic
complexes where antiferromagnetic interaction leads to almost behaviours except the yield of the product. The complex 1 is
diamagnetic behaviour up to room temperature. The carboxylate proven to be more efficient than 2 as can be seen from data given
linkers have been widely used to build magnetic units with in Table 2. The composition of the catalysts does not alter after
transitionꢀmetal ions. The carboxylate group of benzoic acid can the catalytic cycles (Table S3, Fig S19). For alkanes bearing a
adopt syn−syn, syn−anti, and anti−anti coordination modes, and single type of carbon atom (ethane and all cycloalkanes), the
corresponding compounds often show ferro ꢀ or antiferromagnetic formation of only one carboxylic acid product is detected as
behaviors.[30] The magnetic susceptibilities of 1 and 2 have been shown in Table 2 (entries 1ꢀ8), whereas linear C3–C8 alkanes
measured at the room temperature (300 K). Magnetic containing secondary and primary carbon atoms generate two to
susceptibility is measured using very sensitive instrument known four isomeric acid products (entries 2–6). Among them, the
as a magnetic susceptibility balance. The balance contains a pair branched acids derived from the carboxylations at different
of magnets mounted at opposite ends of a beam, initially in secondary C atoms always constitute the major products. For the
equilibrium, when sample is introduced into the balance, a linear C5–C7 alkanes, a mixture of three or four isomeric products
disruption of the magnetic field results. A current through a coil is formed.
located between the poles of a second pair of magnets returns the
Although the hydrocarboxylations can proceed to some
extent in the absence of 1 and 2 boosters[18], the yields of the
reactions promoted by 1 and 2 are typically three to four times
higher than those of the metalꢀfree systems under similar reaction
conditions. Hence, in the systems promoted by 1 and 2 (Table 2),
maximum yields (based on alkane) of carboxylic acids in the 47–
24% range are achieved in the hydrocarboxylations of C3H8
(46.2%), C5H10 (42.4%), C6H12 (40%), nꢀC6H14 (35%), nꢀC4H10
(28.6%), nꢀC2H6 (31.4%), nꢀC5H12 (25.8%), C7H14 (38.2%) and nꢀ
C7H16 (24.2%). The formation of the oxidation products (cyclic
beam to equilibrium. The current through the coil is measured and
transformed into a numerical reading. Diamagnetic materials are
weakly repelled by an external magnetic field, resulting in a
negative reading. Paramagnetic materials are attracted to an
external magnetic field and give a positive reading. The magnetic
moment of the complexes was calculated using by the formula as
follows:
χꢉꢊ ꢋꢌ
ꢖ
ꢐ
ꢐ
ꢓ
ꢓ
ꢃ
ꢑꢒꢑꢁ /ꢔꢕ
ꢍꢎꢏ
ketones and alcohols) in up to ̴10% yields also takes place when
L = height of sample in tube in units of centimetres, Cbal = balance
calibration constant = 1.0, R = reading for tube plus sample, Ro =
reading for the empty tube and m = mass of the sample in units of
grams. The molar magnetic susceptibility is then calculated from
the gram magnetic susceptibility using the following equation:
using cycloalkanes as substrates (entries 8–10). In contrast, the
yields of ketones and alcohols are negligible (typically below 1%)
in the transformations of linear C2–C7 alkanes
From the catalytic data, it is concluded that 1 and 2 are potent
catalyst for conversion of alkane/cycloalkane to carboxylic acids
under ecoꢀfriendly conditions (1 being more efficient than 2).
χꢃ = χꢉ × ꢐmolar massꢓ
χA = χm – diamagnetic correction
The magnetic susceptibility for a particular substance is not
particularly useful in itself. However, the effective magnetic
moment for a particular substance can be calculated from the
gram magnetic susceptibility using the following equation.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 11 of 14
Journal Name
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Table 2. Catalytic activity data of 1 and 2.
trinuclear complex are distorted octahedral while in dinuclear
complex the two zinc metal ions are present in tetrahedral
and distorted octahedral environment. This is a rare case of
the unique geometry of the 2. The complexes show various nonꢀ
covalent interactions like C–H———O, C–H———O, O–H———O, C–H———π
and C–H———C which have been supported by crystallographic
studies, ab-initio methods and Hirshfeld surface analysis.
Luminescent spectral studies of the complexes confirmed that 2 is
more promising luminescent material than 1. Furthermore, red
shift of the emission peaks in solid state spectra is attributed the
presence of nonꢀcovalent interactions in solid state which are
absent in solution state. The clusters synthesized herein this work
(1 and 2) are examined for catalytic property in conversion of
alkanes or cycloalkanes to carboxylic acids and it is concluded
that Cu3 cluster is more efficient for such catalytic transformations
while Zn2 cluster is slightly less potent probably due to the
different nuclearity and the structural environment around the
metal ions. The catalytic properties of the present clusters would
help improve yields in the production of carboxylic acids by
modifying the structure of the prospective di and triꢀnuclear metal
complexes.
Entrya
Alkane
Cn
Cn+1
carboxylic
acid
Cn+1
carboxylic
acid
Regioselectivityc
C(1) : C(2) : C(3)
:C(n)
(yield, %b)
(yield, %b) with 2
with 1
1
2
C2H6
C3H8
nꢀC2H5COOH (31.4)
nꢀC2H5COOH (28.5)
CH3CH(COOH)CH3
CH3CH(COOH)CH3
(38.6),
[1º:2º = 1:24] (1)
[1º:2º = 1:23] (2)
(40.5),
(6.2)
nꢀC3H7COOH
nꢀC3H7COOH (6.8)
3
4
nꢀC4H10
C2H5CH(COOH)CH3
C2H5CH(COOH)CH3
(24.6),
[1º:2º = 1:13] (1)
[1º:2º = 1:12] (2)
(25.4),
(3.2)
nꢀC4H9COOH
nꢀC4H9COOH (2.8)
nꢀC5H12
C2H5CH(COOH)C2H5
(7.4),
C2H5CH(COOH)C2H5
(8.2),
1:20:20 (1)
1:22:21 (2)
C3H7CH(COOH)CH3
(17.2)
C3H7CH(COOH)CH3
(16.4)
nꢀC5H11COOH (1.2)
nꢀC5H11COOH (1.0)
5
nꢀC6H14
C3H7CH(COOH)C2H5
(15.6)
C3H7CH(COOH)C2H5
(13.4)
1:20:19 (1)
1:22:21 (2)
Acknowledgements
C4H9CH(COOH)CH3
(18.6)
C4H9CH(COOH)CH3
(17.5)
The authors thank Chairman, Department of Chemistry,
AMU, Aligarh, for providing necessary research facilities. I. A. A.
and M. R. thanks UGC, New Delhi for providing NonꢀNET
fellowship. F. S. thanks UGC, New Delhi for Senior Research
Fellowship. Z. A. Siddiqi gratefully acknowledges UGC, New Delhi
for financial assistance as BSR Faculty Fellowship.
nꢀC6H13COOH (0.8)
nꢀC6H13COOH (0.6)
6
nꢀC7H16
C3H7CH(COOH)C3H7
(4.2)
C3H7CH(COOH)C3H7
(4.3)
1:18:16:14 (1)
1:19:17:13 (2)
C4H9CH(COOH)C2H5
(9.2)
C4H9CH(COOH)C2H5
(8.8)
C5H11CH(COOH)CH3
(9.8)
C5H11CH(COOH)CH3
(9.0)
References
1 (a) W. Hasse and S. J. Gehring, Chem. Soc., Dalton Trans.,
1985, 2609–2613; (b) The Cambridge Structural Database
(CSD), version 5.28 Jan. 2007; (c) F. H. Allen, Acta
Crystallogr., 2002, 58, 380–388; (d) U. Riaz, O. J. Curnow
and M. D. Curtis, J. Am. Chem. Soc., 1994, 116, 4357–
4363; (e) R. D. Adams and B. Captain, Angew. Chem., Int.
Ed., 2008, 47, 252–257; (f) R. E. P. Winpenny, J. A.
McCleverty and T. J. Meyer, 2004: Comprehensive
Coordination Chemistry, Pergamon Press: Oxford, Vol. 7,
Chapter 7.3, 125; (g) R. E. P. Winpenny, Adv. Inorg. Chem.,
2001, 52, 1–111; (h) Y. Hayashi, T. Ohshima, Y. Fujii, Y.
Matsushima and K. Mashima, Catal. Sci. Technol., 2011, 1,
230–233; (i) H. Li, M. Eddaoudi, T. L. Groy and O. M. Yaghi,
J. Am. Chem. Soc., 1998, 120, 8571–8572; (j) H. Li, M.
Eddaoudi, M. O’Keeffe and O. M. Yaghi, Nature, 1999, 402,
276–279.
nꢀC7H15COOH (1.0)
nꢀC7H15COOH (1.0)
7
8
C5H10
C6H12
C5H9COOH
(40.0)
C5H9COOH
(36.0)
C5H8O/C5H9OHd (2.2/0.2)
C5H8O/C5H9OHd (2.0/0.1)
C6H11COOH (28.6)
C6H11COOH (24.5)
C6H10O/C6H11OHd
(8.4/3.0)
C6H10O/C6H11OHd
(8.3/2.8)
9
C7H14
C7H13COOH (28.8)
C7H13COOH (26.4)
C7H12O/C7H13OHd
(9.4/1.6)
C7H12O/C7H13OHd
(8.2/1.3)
a
Reaction conditions: p(gaseous alkane) = 1.0 (C2H6, C3H8) or 0.75 (nꢀC4H10) atm + p(CO) = 10 and 2 atm (1 atm
= 0.266 mol); liquid alkane (1.0 mmol) + p(CO) = 20 atm; compound 1 or 2(4.0 mmol); K2S2O8= 1.0 (entries 1–3)
or 1.5 (entries 4–11) mmol; H2O (2.0 mL)–MeCN (4.0 mL); 60 °C, 6 h, 13.0 mL autoclave. bMoles of product/100
moles of alkane. cone/ol = cyclic ketones and alcohols (products of oxidation).
2 (a) Q, Jr and L. W. B.Tolman, Nature, 2008, 455, 333–340; (b)
C. Cambillau, M. Tegoni, M. Prudencio, A. S. Pereira, S.
Besson, J. J. Moura, I. Moura and K. Brown, Nat. Struct.
Biol., 2000, 7, 191–195; (c) T. D. Westmoreland, D. E.
Wilcox, M. J. Baldwin, W. B. Mims and E. I. J. Solomon, Am.
Chem. Soc., 1989, 111, 6106–6123; (d) A. Granata, E.
Monzani and L. Casella, J. Biol. Inorg. Chem., 2004, 9, 903–
913; (e) M. Costas, K. Chen and L. J. Que, Coord. Chem.
Rev., 2000, 200–202, 517–544; (f) G. T. Babcock and M.
Wikström, Nature, 1992, 356, 301–309; (g) N. Mano, V.
Soukharev and A. J. Heller, Phys. Chem., 2006, 110,
11180–11187; (h) M. A. Thorseth, C. E. Tornow, E. C. M.
Tse and A. A. Gewirth, Coord. Chem. Rev., 2013, 257, 130–
139; (i) C. C. L. McCrory, A. Devadoss, X. Ottenwaelder, R.
Conclusions
We report here in this work, two novel clusters,
[Cu3(H2tea)2(ba)2(NO3)2] (1) and [Zn2(H2tea)(ba)3]—H2O
where triethanolamine in mono deprotonated form acts as
primary ligand and benzoate ion is introduced as supporting
auxiliary to result in trinuclear (1) and dinuclear (2) clusters.
The two clusters have been characterized using various
spectral and single crystal Xꢀray studies. Bonding modes of
primary and auxiliary ligands are ascertained from FTIR data.
single crystal Xꢀray studies reveal that all the Cu(II) in
(2),
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 12 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Journal Name
D. Lowe, T. Daniel, P. Stack and C. E. D. Chidsey, J. Am. 9 SMART & SAINT Software Reference manuals, Version 6.45,
Chem. Soc., 2011, 133, 3696–3699.
Bruker Analytical Xꢀray Systems, Inc., Madison, WI, 2003.
3 (a) F. A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry: A 10 G. M. Sheldrick, SADABS, software for empirical absorption
Comprehensive Text 5th ed., vol. 1. John Wiley & Sons New
York. 1988; (b) T. Iwasaki, K. Agura, Y. Maegawa, Y.
correction, Ver. 2.05, University of Göttingen, Göttingen,
Germany, 2002.
Hayashi, T. Ohshima and K. Mashima, Chem. Eur. J., 2010, 11 XPREP, version 5.1, Siemens Industrial Automation Inc.,
16, 11567–11571; (c) Y. Maegawa, T. Ohshima, Y. Hayashi,
Madison, WI, 1995.
K. Agura, T. Iwasaki and K. Mashima, ACS Catal., 2011, 1, 12 G. M. Sheldrick, SHELXL97, Program for Crystal Structure
1178–1182.
Refinement, University of Göttingen, Göttingen, Germany
2008.
4 (a) S.ꢀQ. Bai, L. Jiang, A. L. Tan, S. C. Yeo, D. J. Young and T.
S. A. Hor, Inorg. Chem. Front., 2015, 2, 1011ꢀ1018; (b) S.ꢀ 13 A. Altomare, M. C. Burla, M. Camalli, G.L. Cascarano, C.
Q. Bai, L. Jiang, B. Sun, D. J. Young and T. S. A. Hor,
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori
CrystEngComm, 2015, 17, 3305ꢀ3311; (c) P. G. Cozzi,
and R. J. Spagna, J. Appl. Crystallogr., 1999, 32, 115–119.
Chem. Soc. Rev., 2004, 33, 410–421; (d) C. Di Nicola, Y. 14 S. K. Wolff, D. J. Grimwood, J. J. McKinnon, M. J. Turner, D.
Yu. Karabach, A. M. Kirillov, M. Monari, L. Pandolfo, C.
Pettinari and A. J. L. Pombeiro, Inorg. Chem., 2007, 46,
Jayatilaka and M. A. Spackman, Crystal Explorer, Version
3.0; University of Western Australia: 2012.
221−230; (e) S. J. Elliot, M. Zhu, L. Tso, H.ꢀH. T. Nguyen, 15 M. A. Spackman and D. Jayatilaka, CrystEngComm., 2009, 11,
Yip and S. I. J. Chan,J. Am. Chem. Soc., 1997, 119, 9949–
19−32.
9955; (f) B. Ding, L. Yi, P. Cheng, D.ꢀZ. Liao and S.ꢀP. Yan, 16 T. Dey, P. Chatterjee, A. Bhattacharya, S. Pal and A. K.
Inorg. Chem., 2006, 45, 5799–5803. Mukherjee, Cryst. Growth Des., 2016, 16, 1442–1452.
5 (a) W. Joseph and D. C. Sharples, Coord. Chem. Rev., 2014, 17 M. A. Spackman, J. J. McKinnon and D. Jayatilaka,
260, 1–20; (b) R. E. P. Winpenny, Adv. Inorg. Chem., 2001, CrystEngComm., 2008, 10, 377–388.
52, 1–10; (ed. A. G. Sykes). (c) M. Murrie, Chem. Soc. Rev., 18 (a) M. V. Kirillova, A. M. Kirillov, M. L. Kuznetsov, J. A. L. da
2010, 39, 1986–1995. (d) M. Nakano and H. Oshio, Chem.
Soc. Rev., 2011, 40, 3239–3248; (e) G. Rajaraman, M.
Murugesu, E. C. Sañudo, M. Soler, W. Wernsdorfer, M.
Helliwell, C. Muryn, J. Raftery, S. J. Teat, G. Christou and E.
K. Brechin, J. Am. Chem. Soc., 2004, 126, 15445–15457; (f)
S. Goswami, A. K. Mondal and S. Konar, Inorg. Chem.
Front., 2015, 2, 687–712.
Silva, J. J. R. Frausto da Silva and A. J. L. Pombeiro,
Chem. Commun., 2009, 2353–2355; (b) M. V. Kirillova, A.
M. Kirillov and A. J. L. Pombeiro, Adv. Synth. Catal., 2009,
351, 2936–2948; (c) M. V. Kirillova, A. M. Kirillov and A. J.
L. Pombeiro, Chem. Eur. J., 2010, 16, 9485–9493; (d) M.
V. Kirillova, A. M. Kirillov and A. J. L. Pombeiro, Appl.
Catal. A., 2011, 401, 106–113.
6 (a) G. Abbas, Y. Lan, V. Mereacre, W. Wernsdorfer, R. Clérac, 19 (a) Z.ꢀG. Li, J.ꢀW. Xu, H.ꢀQ. Jia, N.ꢀH. Hu and Hu, Inorg. Chem.
G. Buth, M. T. Sougrati, F. Grandjean, G. J. Long, C. E.
Anson and A. K. Powell, Inorg. Chem., 2009, 48, 9345–
9355; (b) A. M. Ako, V. Mereacre, R. Clérac, I. J. Hewitt, Y.
Lan, C. E. Anson and A. K. Powell, Dalton Trans., 2007,
5245–5247; (c) A. Singh and R. C. Mehrotra, Coord. Chem.
Commun., 2006, 9, 969–972; (b) Z. Boulsourani, V.
Tangoulis, C. P. Raptopoulou, V. Psycharis and C.
DendrinouꢀSamara, Dalton Trans., 2011, 40, 7946–7956;
(c) E. G. Bakalbassis, G. A. Katsoulos and C. A. Tsipis,
Inorg. Chem., 1987, 26, 3151–3158.
Rev., 2004, 248, 101–118; (d) J. G. Verkade, Coord. Chem. 20 (a) M. Gatehouse, S. E. Livingstone and R. S. J. Nyholm,
Rev., 1994, 137, 233–295; (e) A. M. Kirillov, Y. Y.
Karabach, M. Haukka, M. C. Fatima, G. da Silva, J.
Sanchiz, M. N. Kopylovich and A. J. L. Pombeiro, Inorg.
Chem., 2008, 47, 162–175.
Inorg. Nucl. Chem., 1958, 8, 75–78; (b) N. T. Madhu and
P. K. Radhakrishnan, Transition Met. Chem., 2000, 25,
287–292; (c) K. Nakamoto, Infrared and Raman Spectra of
Inorganic and Coordination Compounds, Wiley, New York
(1986); (d) K.ꢀE. Lee, S. W. J. Lee, J.Mol. Struct. 2010,
975, 247–255.
7 (a) B. L. Chen, B. L. F. Mok, K. S. C. Ng, Y. L. Feng and S. X.
Liu, Polyhedron, 1998, 17, 4237–4247; (b) Y. Li, R. Cao
and S. J. Lippard, Org. Lett., 2011, 13, 5052–5055; (c) R.
M. Escovar, J. H. Thurston, T. OuldꢀEly, A. Kumar and K.
H. Z. Whitmire, Anorg. Allg. Chem., 2005, 631, 2867–
2876; (d) O. V. Nesterova, M. V. Kirillova, M. Fatima, C. G.
da Silva, R. Boca and A. J. L. Pombeiro, CrystEngComm.,
2014, 16, 775–783; (e) S. K. Langley, K. J. Berry, B.
21 (a) R. S. Amim, M. R. L. Oliveira, G. J. Perpetuo, J. Janczak,
L. D. L. Miranda and M. M. M. Rubinger, Polyhedron,
2008, 27, 1891–1897; (b) A. B. P. Lever, Inorganic
Electronic Spectroscopy (Elsevier, Amsterdam 1984; (c)
E. G. Bakalbassis, G. A. Katsoulos and C. A. Tsipis,
Inorg. Chem., 1987, 26, 3151–3158.
Moubaraki and K. S. Murray, Dalton Trans., 2009, 973– 22 (a) K. Gudasi, R. Vadavi, R. Shenoy, M. Patil, S. A. Patil and
982; (f) E. K. Brechin, M. Soler, J. Davidson, D. N.
Hendrickson, S. Parsonsc, G. Christou, Chem. Comm.
2002, 2252–2253; (g) M. Casarin, C. Corvaja, C. di Nicola,
D, Falcomer, L, Franco, M, Monari, L, Pandolfo, C,
M. Nethaji, Inorg. Chim. Acta., 2005, 358, 3799–3806; (b)
A. Abragam, B. Bleaney, in Electron Paramagnetic
Resonance of Transition Ions, Clarendon Press, Oxford,
U. K. 1970.
Pettinari, F, Piccinelli and P. Tagliatesta, Inorg. Chem., 23 (a) U. T. MuellerꢀWesterhoff, A. Nazzal and W. Prossdorf, J.
2004, 43, 5865–5876; (h) M, Casarin, C, Corvaja, C, Di
Nicola, D, Falcomer, L, Franco, M. Monari, L. Pandolfo, C.
Pettinari and F. Piccinelli, Inorg. Chem., 2005, 44, 6265–
6276; (i) E. K. Brechin, Chem. Commun. 2005, 5141–
Am. Chem. Soc., 1981, 103, 7678–7681; (b) S. Gronert
and J. R. J. Keeffe, Am. Chem. Soc., 2005, 127, 2324–
2333; (c) S. Das and P. K. Bharadwaj, Inorg. Chem. 2006,
45, 5257–5259.
5153; (j) S. J. Shah, C. M. Ramsey, K. J. Heroux, J. R. 24 (a) S. Zhang, F. Jiang, Y. Bu, M. Wu, J. Ma, X. Shan, K. Xiong
O’Brien, A. G. DiꢀPasquale, A. L. Rheingold, E. Del Barco
and D. N. Hendrickson, Inorg. Chem., 2008, 47, 6245–
6253; (k) S. K. Langley, B. Moubaraki, C. M. Forsyth, I. A.
Gass and K. S. Murray, Dalton Trans., 2010, 39, 1705–
1708; (l) C. D. Samara, C. A. Muryn, F. Tuna and R. E. P.
Winpenny, Eur. J. Inorg. Chem., 2010, 3097–3101.
8 J. A. Ibers, W. C. Hamilton, International Tables for Xꢀray
Crystallography, Kynoch Press, Birmingham, England,
1974, vol. IV.
and M. Hong, CrystEngComm., 2012, 14, 6394–6396; (b)
Q. Guo, C. Xu, B. Zhao, Y. Jia, H. Hou and Y. Fan, Cryst.
Growth Des., 2012, 12, 5439–5446; (c) X. Guo, G. Zhu, Q.
Fang, M. Xue, G. Tian, J. Sun, X. Li and S. Qiu, Inorg.
Chem., 2005, 44, 3850–3855; (d) W. Q. Kan, J. Yang, Y.
Y. Liu and J. F. Ma, CrystEngComm., 2012, 14, 6934–
6945; (e) F. P. Doty, C. A. Bauer, A. J. Skulan, P. G. Grant
and M. D. Allendorf, Adv. Mater, 2009, 21, 95–101; (f) B.
Gole, A. K. Bar and P. S. Mukherjee, Chem. Commun.,
2011, 47, 12137–12139; (g) L. P. Zhang, J. F. Ma, J.
12 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 13 of 14
Journal Name
View Article Online
DOI: 10.1039/C6NJ02150F
ARTICLE
Yang, Y. Y. Pang and J. C. Ma, Inorg. Chem., 2010, 49,
1535–1550; (h) A. J. Lan, K. H. Li, H. H. Wu, L. Z. Kong,
N. Nijem, D. H. Olson, T. J. Emge, Y. J. Chabal, D. C.
Langreth, M. C. Hong and J. Li, Inorg.Chem., 2009, 48,
7165–7173; (i) H.ꢀF. Zhu, J. Fan, T. Okamura, W.ꢀY.
Sunand and N. Ueyama, Cryst. Growth Des., 2005, 5,
289–294.
25 (a) C. D. Samara, P. D. Janakoudakis, D. P. Kessissaglou, G.
E. Manoyussakis, D. Mentzapfos and A. Terzis, J. Chem.
Soc., Dalton Trans., 1992, 3259–3264; (b) Z. A. Siddiqi
and V. J. Mathew, Polyhedron, 1994, 13, 799–805; (c) K.
Dimitrou, A. D. Brown, T. E. Concolino, A. L. Rheingold
and G. Christou, Chem. Commun., 2001, 1284–1285; (d)
R. A. Sheldon, J. A. Kochi, Metal Catalysed Oxidations of
Organic Compounds; Academic Press: New York. 1981;
(e) N. A. ElꢀMaali, A. H. Osman, A.A.M. Aly and G.A.A. Alꢀ
Hazmi, Bioelectrochem., 2005, 65, 95 – 104; (f) M. A.
Neelakantana, F. Rusalraja, J. Dharmarajaa, S.
Johnsonrajaa, T. Jeyakumarb and M. S. Pillaic,
Spectrochim. Acta Part A, 2008, 71, 1599–1609.
26 O. Yesilel, H.J. Ölmez, Therm. Anal. Calorim., 2007, 89, 261–
265.
27 (a) S. K. Seth, D. Sarkar, A. D. Jana and T. Kar, Cryst. Growth
Des., 2011, 11, 4837–4849; (b) M. Mitra, S. K. Seth, S. R.
Choudhury, P. Manna, A. Das, M. Helliwell, A. Bauzá, A.
Frontera and S. Mukhopadhyay, Eur. J. Inorg. Chem.,
2013, 4679–4685; (c) S. K. Seth, Inorg. Chem. Commun.,
2014, 43, 60–63.
28 R. Yadav, M. Trivedi, G. KociokꢀKöhn, R. Prasad and A.
Kumar, CrystEngComm., 2015, 17, 9175–9184.
29 I. Khan, P. Panini, S. U. D. Khan, U. A. Rana, H. Andleeb, D.
Chopra, S. Hameed and J. Simpson, Cryst. Growth Des.,
2016, 16, 1371–1386.
30 (a) X.ꢀH. Bu, M.ꢀL. Tong, Y.ꢀB. Xie, J.ꢀR. Li, H.ꢀC. Chang, S.
Kitagawa and J. Ribas, Inorg. Chem., 2005, 44, 9837–
9846; (b) D. L. Reger, A. Debreczeni, B. Reinecke, V.
Rassolov, M. D. Smith and R. F. Semeniuc, Inorg. Chem.,
2009, 48, 8911–8924.
31 (a) B. N. Figgis, J. Lewis, in Modern Coordination Chemistry,
(ed. Lewis and R. G. Wilkins), Interscience Publishers Inc,New
York, 1960 400; (b) R. J. Angelici, W. B. Saunders, Synthesis and
technique in inorganic chemistry, 1977, 198; (c) C. E. Housecroft,
A. G. Sharpe, Inorg. Chem., vol. 3 Pearson Education Limited,
2008.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 13
Please do not adjust margins

New Journal of Chemistry
Page 14 of 14
View Article Online
DOI: 10.1039/C6NJ02150F
Graphical Abstract
Cu3 and Zn2 clusters with aminotriethanolate and benzoate bridging are
characterized as new catalysts for hydrocarboxylation of alkanes and cycloalkanes.