New μ-hydroxido-bridged copper nitrate dimer and μ4-oxido- bridged copper phenylacetate quasi-tetrahedron: Direct synthesis and uphill conversion

Article abstract of DOI:10.1016/j.poly.2012.08.064

Dinuclear [Cu₂(μ-OH)] fragment and its self-assembled tetranuclear part [Cu₂(μ₄-O)Cu₂] are found in two copper(II) complexes of ligand H₃bpmp: [Cu₂(μ ₂-OH)(μ-H₂bpmp)(μ

Full text of DOI:10.1016/j.poly.2012.08.064

Polyhedron 52 (2013) 370–376
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
New l-hydroxido-bridged copper nitrate dimer and l4-oxido-bridged copper
phenylacetate quasi-tetrahedron: Direct synthesis and uphill conversion
⇑
Aloke Kumar Ghosh, Debashis Ray
Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 14 September 2012
Dinuclear [Cu2(
copper(II) complexes of ligand H3bpmp: [Cu2(
4-O)(
bis-[(3-hydroxy-propylimino)-methyl]-4-methylphenol]. These complexes have been synthesized and
characterized by single crystal X-ray crystallography. Complex 1 showed unique reactivity with phenyl-
l
-OH)] fragment and its self-assembled tetranuclear part [Cu2(
2-OH)( -H2bpmp)( 1,3-NO3)][Cu2(
-H2bpmp)2( 1,3-O2CCH2Ph)4] (2) [H3bpmp = 2,6-
l
4-O)Cu2] are found in two
l
l
l
l
2-OH)( -H2bpmp)
l
(NO3)(H2O)](NO3)2ꢀ2H2O (1ꢀ2H2O) and [Cu4(
l
l
l
Keywords:
Schiff base
Imine-alcohol
Phenoxido bridge
Oxido
Hydroxido
Dinuclear
Crystal structure
acetate anions to provide 2 in which two [Cu2(
l2-OH)] units available within same crystal lattice
collapsed to give [Cu4( 4-O)] hub. Formation of the [Cu4] compound is also achieved from individual
l
components and phenylacetate ligands, which allows an effective tuning of the self-assembly of two
ligand bound [Cu2] fragments and removal of H+ from hydroxido bridges to provide oxido nucleus.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
carboxylato groups have been examined because of their versatile
bridging modes.
The design and synthesis of new family of dinuclear complexes
of copper(II) and their controlled aggregation via self-assembly
using ancillary clips to form tetranuclear complexes of varying
architecture is of recent interest [1a–f]. The choice of the ligand
and fine-tuning of reaction conditions with co-ligands are decisive
to control the aggregation process. Understanding of such aggrega-
tion reactions is crucial in developing tetra- and higher nuclearity
complexes from [Cu2] building units, which are useful model com-
pounds to get insight into the mechanism of complex biological
systems (such as in metalloenzymes) and their catalytic activity
[2]. Dinucleating ligands with central phenoxido bridging function-
ality (Scheme 1) have been used to construct structural and Func-
tional model of several metalloenzymes: HL [3], H3L [4], PD0OH [5],
and HL1 [6]. They can also be useful to examine interesting mag-
netic exchange interactions [7–9] and electron transfer behavior
due to the synergism between the adjacent metal ions [10,11].
These are also useful in studying DNA binding and cleavage [12],
oxidation of different catechol molecules [8,1d,13] and building
motifs for the higher order complexes of [14–19]. For systematic
studies on such self-assembly process, our current research fo-
cused on newer [Cu2] based aggregates. Depending on the nature
and number of secondary bridges the assembly of two [Cu2] frag-
ments leads to four types of [Cu4] aggregates: the stepped cubane,
the fused defective cubane, the cubane and the tetrahedron
(Scheme 2) [1a,b]. Among the ancillary ligands used, nitrato and
The bridging carboxylato groups from basal or apical positions
around CuII ions mediate a large diversity of magnetic exchange
interactions [20–23]. Base promoted and water-derived hydroxido
and oxido groups are most readily available connectors in the con-
struction and /or stabilization of [Cu2] and [Cu4] moieties
[12,18,24–28]. Out of these possibilities, the tetrahedral [Cu4O]
cores are important for several reasons, such as in industrial cata-
lytic oxidation of 2,3,6-trimethyl phenol to corresponding quinone
and bio-catalytic reduction of N2O to N2 [29,30]. Unlike tetrahedral
tetracoordinate oxygen (ttO) in [Cu4] chemistry, the corresponding
planar tetracoordinate oxygen (ptO) in [Cu4] compound is only
known very recently [31]. In trying to isolate and study new form
of tetrahedral aggregate and the role of the secondary connectors,
we have been engrossed in exploring the reactivity of H3bpmp
ligand (Chart 1, left; 2,6-bis-[(3-hydroxypropylimino)-methyl]-4-
methylphenol) [32] with copper(II) ions. It is worth noting that the
use of similar ligand H3bemp (Chart 1, right, 2,6-bis-[(2-hydroxy-
ethylimino)-methyl]-4-methylphenol) leads to systems, consisting
of [Co4] [33], [Ni6] [34], [Cu18] [35] complexes and a heterobimetallic
[Mn6Cu10] [36] aggregate. Herein, [Cu2] and [Cu4] complexes of H2-
bpmpꢁ are reported: [Cu2(
l
2-OH)(
l
-H2 bpmp)(
l
1,3-NO3)][Cu2(l2
-
OH)(
l
-H2bpmp)(NO3)(H2O)](NO3)2ꢀ2H2 O (1ꢀ2H2O) and [Cu4(l4
-
O)(l-H2bpmp)2(l1,3-O2CCH2Ph)4] (2). These two compounds are
new examples of copper(II) complexes where Cu(II) ions are con-
nected by two types of water-derived ligands: oxide and hydroxide.
Compound 2 contains a central
been obtained, apart from its direct synthesis, by converting com-
plex 1 bearing -hydroxido bridges by reacting with phenylacetate
l4-oxido nucleating group and has
⇑
Corresponding author. Tel.: +91 3222 283324; fax: +91 3222 82252.
E-mail address: dray@chem.iitkgp.ernet.in (D. Ray).
l
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.064

A.K. Ghosh, D. Ray / Polyhedron 52 (2013) 370–376
2.2. Syntheses
371
2.2.1. H3bpmp ligand
To a MeOH solution (20 mL) of 2,6-diformyl-4-methylphenol
(1.0 g, 6.1 mmol), 3-amino-1-propanol (0.91 g, 12.2 mmol) was
added in air at room temperature (28 °C) and stirred for 2 h to give
an orange colored semi-solid product after complete evaporation
of solvent in air for 12 h. The semi-solid product 2,6-bis-[(3-hydro-
xy-propylimino)-methyl]-4-methylphenol thus obtained was
washed with water and used directly without further purification.
Yield: 1.32 g (78%).
PY
N
N
N
N
PY
N
N
OH
HL
N
N
OH
PD'OH
PY
PY
2.2.2. [Cu2(
- NO3)(H2O)](NO3)2ꢀ2H2O (1ꢀ2H2O)
To the yellow MeOH solution (20 mL) of H3bpmp (0.278 g,
l2-OH)(l-H2bpmp)(l1,3-NO3)][Cu2(l2-OH)(l-H2bpmp)
(l
HN
OH
HL1
NH
1.00 mmol) a MeOH solution (10 mL) of Cu(NO3)2ꢀ3H2O (0.482
g, 2.0 mmol) was added slowly followed by NEt3 (0.139 mL,
0.101 g, 1.00 mmol) and stirred for 2 h at room temperature. The
solvent was evaporated in air to give a green solid, which was
isolated, washed with cold methanol and water, and finally dried,
under vacuum over P4O10. Yield: 0.423 g, 74%. The green pris-
matic-shaped crystals suitable for X-ray analysis were obtained
from a saturated MeOH solution after two weeks. Anal. Calc. for
N
OH
H3L
N
O
O
N
N
HN
HN
Scheme 1. Some phenoxido-bridging dinucleating ligands.
C
30H50Cu4N8O23 (1144.94 g molꢁ1): C, 31.47; H, 4.40; N, 9.79.
Found: C, 31.22; H, 4.32; N, 9.71%. Selected FT-IR bands: (KBr,
cmꢁ1
s = strong, vs = very strong, m = medium, br = broad)
3401(br), 1636(s), 1560(s), 1383(vs), 1062(vs), 826(m), 615(m),
Molar conductance, KM: (MeOH solution) 108.1 Oꢁ1 cm2 molꢁ1
UV–Vis spectra [kmax, nm (
, L molꢁ1 cmꢁ1)]: (MeOH solution)
677 (538), 373 (2446), 258 (12432).
;
ligands. These complexes have been isolated and crystallographi-
cally characterized, and the reactivity of 1 with phenylacetate
examined.
.
e
2. Experimental
2.2.3. [Cu4(
direct route
To the yellow MeOH solution (20 mL) of H3bpmp (0.278 g,
1.00 mmol)
MeOH solution (10 mL) of Cu(PhCH2CO2)2ꢀH2O
l4-O)(l-H2bpmp)2(l1,3-O2CCH2Ph)4] (2). Method A via
2.1. Materials and physical methods
a
2,6-Diformyl-4-methylphenol was prepared following a litera-
ture procedure [37]. The other chemicals used were obtained from
the following sources: 3-amino-1-propanol from Aldrich Chemical
Co. Inc., copper nitrate trihydrate, triethylamine, phenyl acetic
acid, from S. D. Fine Chemicals (India). All the chemicals and sol-
vents used in this work were of reagent grade materials and used
as received without further purification. The elemental analyses
(C, H, N) were performed with a Perkin–Elmer model 240 C ele-
mental analyzer. FT-IR spectra were recorded on a Perkin–Elmer
RX1 infra-red spectrometer. Solution electrical conductivity mea-
surements and electronic spectra were carried out using a Unitech
type U131C digital conductivity meter with a solute concentration
of about 10ꢁ3 M and a Shimadzu 1601 UV–Vis–NIR spectropho-
tometer using 1 cm quartz cell pairs.
(1.068 g, 2.0 mmol) was added slowly followed by NEt3
(0.139 mL, 0.101 g, 1.00 mmol) and stirred for 2 h at room temper-
ature. The green solid, which was isolated, washed with cold meth-
anol and water, and finally dried, under vacuum over P4O10. The
green needle-like crystals suitable for X-ray analysis were obtained
from a saturated DMF solution after three weeks. Yield: 0.532 g,
78%. Anal. Calc. for C62H70Cu4N4O15 (1365.38 g molꢁ1): C, 54.54;
H, 5.16; N, 4.10. Found: C, 54.43; H, 5.02; N, 3.88%. Selected FT-
IR bands: (KBr, cmꢁ1; s = strong, vs = very strong, m = medium,
br = broad) 3313(br), 2924(s), 2964(s), 1604(s), 1578(s), 1457(s),
1384(vs), 1343(s), 1087(vs), 836(m), 730(m), 696(m), 632(m). Mo-
lar conductance, KM: (MeOH solution) 6.5 Oꢁ1 cm2 molꢁ1. UV–Vis
spectra [kmax, nm (e
, L molꢁ1 cmꢁ1)]: (MeOH solution) 637 (387),
368 (1545), 259 (65101).
B
B
A
Cu
Cu
Cu
A
B
Cu
B
C
2A
2C
Cu2+
A
B
Cu
4C
A
C
Cu
Cu
Cu
Cu
Cu
B
2A+2B
[defective cubane]
4C
B
A
C
Cu
B
Cu
C
A
Cu
Cu
B
Cu
B
A
C
C
Cu
A = O2- ; B = PhO-
Cu
Cu
A
-
Cu
A
C = PhCH2CO2
C
Cu
C
[Cubane]
Cu
Cu
C
C
B
B
[Stepped Cubane]
[Tetrahedron]
Scheme 2. The possible topologies of [Cu4] aggregates.

372
A.K. Ghosh, D. Ray / Polyhedron 52 (2013) 370–376
3. Results and discussion
3.1. Synthetic considerations
H3bpmp was prepared (Scheme S1 in the Supporting Informa-
tion) following a reported procedure, [32] and its reactions with
copper(II) salts have been investigated (Scheme 3). Reaction of
N
OH
N
N
OH
N
H3bemp
Cu(NO3)2ꢀ3H2O with H3bpmp in MeOH and NEt3 gave [Cu2(l2
OH)( -H2bpmp)( -NO3)(H2O)](NO3)2.
The elemental analysis, molar conductivity and X-ray diffraction
data confirm the formation of [Cu2( 2-OH)( -H2bpmp)( 1,3-NO3)]
[Cu2( 2-OH)( -H2bpmp)(
-
H3bpmp
l
l
OH
HO
OH
HO
l
l
l
Chart 1. Ligands.
l
l
l
-NO3)(H2O)](NO3)2ꢀ2H2O (1ꢀ2H2O) (vide
infra). At room temperature and in air, a mixture of H3bpmp,
Cu(NO3)2ꢀ3H2O, and NEt3 in a 1:2:2 M ratio in MeOH when stirred
for 2 h, provided complex 1 in ꢂ74% yield (Eq. (1)).
2.2.4. Method B via conversion of 1
Addition of PhCH2CO2Na (0.158 g, 1.0 mmol) to a green solution
of 1 (0.286 g, 0.25 mmol) in MeOH (25 mL) resulted darkening of
green solution followed by separation of a green solid within
15 min which was collected by filtration, washed with cold meth-
anol and dried under vacuum over P4O10. Green needle-like crys-
tals suitable for X-ray analysis were obtained from DMF after
three weeks. Yield: 0.484 g, 71%.
2H3bpmp þ 4CuðNO3Þ2 ꢀ 3H2O þ 4NEt3
! ½Cu2ðl2 ꢁ OHÞð
ꢄ ð ꢁ H2bpmpÞð
þ 4ðNHEt3ÞðNO3Þ þ 7H2O
l
ꢁ H2bpmpÞðl1;3 ꢁ NO3Þꢃ½Cu2ðl2 ꢁ OHÞ
l
l
ꢁ NO3ÞðH2OÞꢃðNO3Þ2 ꢀ 2H2O
ð1Þ
Use of Cu(PhCH2CO2)2ꢀH2O in place of Cu(NO3)2ꢀ3H2O provided
2 as green solid in ꢂ78% yield (Scheme 3). Use of NaOH or KOH in
lieu of NEt3 provided same oxido bridge in presence of bridging
phenyl acetato ligands. The stronger bases were ineffective to
deprotonate the alcohol arms. The preparation of 2 (Eq. (2)) ac-
counts the formation of the oxido bridge from a molecule of water.
2.3. X-ray crystallography
The diffraction data of 1ꢀ2H2O and 2 were collected on a Bruker
APEX-II CCD X-ray diffractometer using single crystals t0hat uses
graphite-monochromated Mo K
a radiation (k = 0.71073 ÅA) by x-
scan method at 293 K. Information concerning X-ray data collec-
tion and structure refinement of the compound is summarized in
Table 1. For 1ꢀ2H2O, a total of 6154 reflections were recorded with
Miller indices hmin = ꢁ8, hmax = 8, kmin = ꢁ22, kmax = 22, lmin = ꢁ29,
lmax = 29. For complex 2, a total of 2116 reflections were recorded
with Miller indices hmin = ꢁ12, hmax = 12, kmin = ꢁ11, kmax = 12,
lmin = ꢁ25, lmax = 25. In the final cycles of refinement of full-matrix
least squares on F2, all non-hydrogen atoms were assigned aniso-
tropically. The structure was solved using the SHELX-97 [38] pro-
gram system.
2H3bpmp þ 4CuðPhCH2CO2Þ2 ꢀ H2O þ 4NEt3
! ½Cu4ðl4 ꢁ OÞð
l
ꢁ H2bpmpÞ2ðl1;3 ꢁ O2CCH2PhÞ4ꢃ
þ 4ðNHEt3ÞðPhCH2CO2Þ þ 3H2O
ð2Þ
Complex 2 can also be obtained from a reaction of Cu(NO3)2
ꢀ3H2O with H3bpmp in presence of NEt3 and PhCH2CO2Na as sum-
marized in Eq. (3).
2H3bpmp þ 4CuðNO3Þ2 ꢀ 3H2O þ 4NEt3 þ 4PhCH2CO2Na
! ½Cu4ðl4 ꢁ OÞð
l
ꢁ H2bpmpÞ2ðl1;3 ꢁ O2CCH2PhÞ4ꢃ
þ 4HNO3 þ 4NaNO3 þ 11H2O
ð3Þ
Table 1
Crystallographic data.
Analytical and X-ray diffraction establish the coordination of
threꢁe water based ligands H2O, HOꢁ and O2ꢁ. Weakly coordinating
Compound
1ꢀ2H2O
30H50N8O23Cu4
1144.94
P21/n
monoclinic
8.1397(10)
20.401(2)
26.751(3)
90.00
92.632(4)
90.00
4437.6(9)
293
2
NO3 anions support the
l
-OH-bridged [Cu2] units in 1. Whereas
Formula
M
Space group
Crystal system
a (Å)
C
C62H70N4O15Cu4
1365.38
P-421c
tetragonal
11.3774(12)
11.3774(12)
23.437(3)
90.0
90.0
90.0
3033.8(6)
293
ꢁ
bridging coordination of PhCH2CO2 supports the
[Cu4] core in 2.
l4-O-bridged
3.1.1. Ancillary ligand-exchange reactivity studies on complex 1
Treatment of a green solution of 1 in MeOH by sodium phenyl-
acetate shifts the reaction equilibrium in favor of 2 with noticeable
color change followed by precipitation of 2 within 15 min (Eq. (4)).
From a DMF solution green crystals of 2 grew slowly over three
weeks.
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
U (Å3)
T (K)
Z
4
2
½Cu2ðl2 ꢁ OHÞð
ꢁ H2bpmpÞð
þ 4PhCH2CO2Na ! ½Cu4ðl4 ꢁ OÞð
l1;3 ꢁ O2CCH2PhÞ4ꢃ þ 4NaNO3 þ 4H2O
The tentative mechanism of conversion of 1–2 is relatively
straightforward. In presence of phenylacetate ligands the bound
neutral alcohol OH functions in 1 transformed to non-coordinating
pendant ones and the basal coordinating sited are occupied by the
oxygen atoms of the phenylacetate groups replacing nitrato
groups. The other end of the phenyl acetate ligand occupies the
apical site of the adjacent square-pyramidal Cu centre and four such
phenylacetate ligands alternately occupy equatorial-apical sites in a
l
ꢁ H2bpmpÞðl1;3 ꢁ NO3Þꢃ½Cu2ðl2 ꢁ OHÞ
ꢁ NO3ÞðH2OÞꢃðNO3Þ2 ꢀ 2H2O
ꢁ H2bpmpÞ2
Dcalc (g cmꢁ3
F(000)
)
1.714
2344
0.41 x 0.34 x 0.19
19.83
43006
1.495
1412
0.43 x 0.31 x 0.18
14.53
29431
2116
0.1706
1575
1.74–23.00
ð
l
l
Crystal size (mm)
l
l
(Mo K )
a
) (cmꢁ1
Measured reflections
Unique reflections
Rint
Observed reflections I P 2
hmin–hmax (°)
ð
ð4Þ
6154
0.0729
r
(I)] 4207
2.14–23.00
-8,8; -22,22; -29,29 -12,12; -11,12; -25,25
0.0578
0.0949
632
hkl ranges
R (F2) (observed reflection)
wR(F2) (all reflections)
No. variables
0.0447
0.0762
195
1.026
0.339;- 0.324
Goodness of fit
D
1.067
0.999; -0.521
qmax
;
D
qmin (e Åꢁ3
)

A.K. Ghosh, D. Ray / Polyhedron 52 (2013) 370–376
373
2
N
O
N
O
O
H
OH2
Cu
Cu
O
N
H
H
O
H
NO3
O
O
O
O
O
H
N
Cu
Cu
O
H
1
N
N
OH
N
H3bpmp
OH
HO
OH
HO
Ph
N
O
N
Ph
Cu
O
O
O
Cu
O
O
O
O
Cu
Ph
O
Ph
Cu
O
N
O
N
HO
OH
2
Scheme 3. Schematic representation for the two different reaction pathways and the transformation of 1 to 2.
cyclic fashion to bring two hydroxide bridges close to each other to
form relatively basic 4-oxido bridge from two hydroxido bridges
with liberation of one molecule of water (Fig. S1 in supporting
2.979 Å than the triply bridged one in the later part with Cu3ꢀ ꢀ ꢀCu4
at 2.964 Å. The basal positions Cu1 and Cu2 are occupied by the
imine N1 (for Cu1) or N2 (for Cu2), phenoxido O1 atoms and
O2(H) (for Cu1) or O3(H) (for Cu2) from the H2bpmpꢁ ligand, a
hydroxido O4 group, [39]. In the basal plane the Cu-N and Cu–O
distances and Cuꢀ ꢀ ꢀCu separations within normal range [40]. From
difference Fourier maps the bridging OH groups (H4 and H8A)
were identified at 0.930 and 0.931 Å. The apical Cu–O bonds are
longer at 2.38–2.41 Å for the Jahn–Teller effect, with elongations
by 0.4–0.5 Å. The competitive binding of nitrato anions with water
lead to monodentate and bridging l1,3 coordination (Fig. 2). The
Cu–OPh–Cu angles around 99° are similar Cu–OOH–Cu angles
l
information). Considering the quantitative and spontaneous con-
version of 1–2 (Eq. (4)), the relative binding strength of the two
ꢁ
ancillary anionic ligands can be recognized as: PhCH2CO2ꢁ > NO3
.
The ligand exchange and core-conversion reaction has been
identified by FTIR spectral measurement, observing solubility dif-
ferences, checking of unit cell parameters and crystal system of
grown single crystals from powder samples (Fig. S2).
3.2. Description of the crystal structures
(Fig. S3) [41]. The calculated Addison parameters [42] (s = 0.035,
0.036, 0.035 and 0.027) indicate the amount of distortions. Packing
diagrams emphasize the intra and intermolecular hydrogen-bonds
near the [Cu2] complex (Fig. S4) and the network of hydrogen-
bonds within the structure (Fig. S5).
3.2.1. [Cu2(
H2bpmp)(NO3)(H2O)](NO3)2ꢀ2H2O (1ꢀ2H2O)
l2-OH)(l-H2bpmp)(l1,3-NO3)][Cu2(l2-OH)(l-
The green block-like single crystals of complex 1ꢀ2H2O obtained
by the slow evaporation of the MeOH solution of the complex.
Compound 1ꢀ2H2O crystallizes in the monoclinic, P21/n space
group with two molecule in the unit cell with three interstitial
water molecules. The molecular structure of 1ꢀ2H2O is shown in
Fig. 1, and important bond lengths and angles are given in Table 2.
3.2.2. [Cu4(l4-O)(l-H2bpmp)2(l1,3-O2CCH2Ph)4] (2)
Single crystal X-ray diffraction reveals that compound 2, which
crystallizes in tetragonal space group P-421c is a tetranuclear cop-
per(II) complex. The molecular structure of 2 is shown in Fig. 3 and
selected bond lengths and angles are given in Table 3. The [Cu4]
complex consists of two deprotonated H2bpmp– ligands, each of
them providing a N2O set of donor atoms to the [Cu4] core
Within the crystal unit-cell, one [Cu2(
(NO3)(H2O)] fragment is packed with another [Cu2(
bpmp)( 1,3-NO3)] part along with three molecules of water of crys-
l
2-OH)(
l
-H2bpmp)
l2-OH)( -H2
l
l
tallization. These two fragments differ from the water coordination
and mode of binding of the nitrate anions. In the former case the
doubly bridged Cu1ꢀꢀꢀCu2 provide longer inter-metallic separation
assembled around a tetrahedral
l4-O group. Four phenylacetato
groups complete the coordination environment (Figs. 3 and 4) with

374
A.K. Ghosh, D. Ray / Polyhedron 52 (2013) 370–376
Fig. 1. Molecular structure of 1ꢀ2H2O with atom-numbering scheme. H atoms are omitted for clarity. Color code: Cu, brown; N, blue; O, red; C, black. (Colour online.)
Table 2
Selected interatomic distances (Å) and angles (°) for complex 1ꢀ2H2O.
Distances
Cu(1)–N(1)
Cu(1)–O(4)
Cu(1)–O(2)
Cu(1)–O(1)
Cu(1)–O(2W)
Cu(1)ꢀ ꢀ ꢀCu(2)
Cu(2)–O(3)
Cu(2)–O(1)
Cu(2)–N(2)
Cu(2)–O(4)
Cu(2)–O(15)
1.935(7)
1.945(5)
1.947(5)
1.947(5)
2.391(6)
2.9796(14)
1.929(6)
1.943(5)
1.951(6)
1.954(5)
2.417(7)
Cu(3)–O(5)
Cu(3)–O(6)
Cu(3)–N(3)
Cu(3)–O(8)
Cu(3)–O(2A)
Cu(3)–Cu(4)
Cu(4)–N(4)
Cu(4)–O(7)
Cu(4)–O(8)
Cu(4)–O(5)
Cu(4)–O(1A)
1.939(5)
1.939(5)
1.941(7)
1.947(5)
2.400(10)
2.9642(14)
1.936(7)
1.959(6)
1.960(5)
1.962(5)
2.379(8)
Angles
N(1)–Cu(1)–O(4)
N(1)–Cu(1)–O(2)
O(4)–Cu(1)–O(2)
N(1)–Cu(1)–O(1)
O(4)–Cu(1)–O(1)
O(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(2W)
O(4)–Cu(1)–O(2W)
O(2)–Cu(1)–O(2W)
O(1)–Cu(1)–O(2W)
N(1)–Cu(1)–Cu(2)
O(4)–Cu(1)–Cu(2)
O(2)–Cu(1)–Cu(2)
O(1)–Cu(1)–Cu(2)
O(2W)–Cu(1)–Cu(2)
O(3)–Cu(2)–O(1)
O(3)–Cu(2)–N(2)
O(1)–Cu(2)–N(2)
O(3)–Cu(2)–O(4)
O(1)–Cu(2)–O(4)
N(2)–Cu(2)–O(4)
O(3)–Cu(2)–O(15)
O(1)–Cu(2)–O(15)
N(2)–Cu(2)–O(15)
O(4)–Cu(2)–O(15)
O(3)–Cu(2)–Cu(1)
O(1)–Cu(2)–Cu(1)
N(2)–Cu(2)–Cu(1)
O(4)–Cu(2)–Cu(1)
O(15)–Cu(2)–Cu(1)
171.7(3)
94.9(3)
91.8(2)
93.0(2)
79.8(2)
169.5(3)
91.8(3)
92.2(2)
98.3(3)
88.5(2)
132.86(19)
40.28(14)
132.08(18)
39.94(15)
86.13(16)
169.8(3)
94.3(3)
92.6(2)
92.2(2)
79.7(2)
167.6(3)
97.4(3)
O(5)–Cu(3)–O(6)
O(5)––Cu(3)–N(3)
O(6)–Cu(3)–N(3)
O(5)–Cu(3)–O(8)
O(6)–Cu(3)–O(8)
N(3)–Cu(3)–O(8)
O5–Cu3–O2A
O(6)–Cu(3)–O(2A)
N(3)–Cu(3)–O(2A)
O8–Cu3–O2A
O(5)–Cu(3)–Cu(4)
O(6)–Cu(3)–Cu(4)
N(3)–Cu(3)–Cu(4).
O(8)–Cu(3)–Cu(4)
O2A–Cu3–Cu4
N(4)–Cu(4)–O(7)
N(4)–Cu(4)–O(8)
O(7)–Cu(4)–O(8)
N(4)–Cu(4)–O(5)
O(7)–Cu(4)–O(5)
O(8)–Cu(4)–O(5)
N(4)–Cu(4)–O(1A)
O(7)–Cu(4)–O(1A)
O(8)–Cu(4)–O(1A)
O(5)–Cu(4)–O(1A)
N(4)–Cu(4)–Cu(3)
O(7)–Cu(4)–Cu(3)
O(8)–Cu(4)–Cu(3)
O(5)–Cu(4)–Cu(3)
O(1A)–Cu(4)–Cu(3)
171.2(2)
92.4(3)
96.1(3)
81.0(2)
90.5(2)
173.4(3)
82.7(4)
100.0(4)
88.0(4)
Fig. 2. Atom connectivity within the two Cu2 fragments showing the apical–apical
bridging from the NO3 group in one unit.
ꢁ
90.3(3)
40.83(16)
131.08(17)
132.6(2)
40.81(15)
79.9(3)
94.9(3)
170.6(3)
92.2(2)
92.9(3)
172.2(2)
80.1(2)
90.2(3)
93.3(3)
89.6(2)
94.3(3)
95.3(2)
132.22(18)
40.06(14)
132.6(2)
40.07(15)
88.91(17)
95.5(3)
86.3(3)
133.1(2)
131.98(18)
40.49(16)
40.26(16)
85.8(2)
Fig. 3. Molecular structure of 2 with atom-numbering scheme. H atoms are omitted
for clarity. Color code: Cu, brown; N, blue; O, red; C, grow: (⁄=ꢁy, x, ꢁz; ⁄⁄=ꢁy, x,
ꢁz). (Colour online.)
two types of Cuꢀ ꢀ ꢀCu distances of 3.029 and 3.175 Å, which are sig-
nificantly longer than other dimers (a . 2.645 Å) (Fig. S6) [43]. The
The apical Cu–Opa (pa = phenylacetate) distance at 2.31 Å is
longer that the basal distance of 1.95 Å, and all four coordinate uni-
formly via apical–basal sequence (Figs. 3 and S8). The latter is long-
v
NO4 coordination sphere around each Cu(II), consisting of two O
atoms from the bridging phenylacetato groups, one phenoxido O
and imine N atoms from the H2bpmpꢁ ligand, and one central
O2ꢁ anion, adopts distorted square-pyramid geometry due to the
Jahn–Teller effect expected for 3d9 copper(II) ion (Fig. S7).
er than the Cu-(l4-O) distance (1.91 Å) but close to the Cu–OPh
(OPh = ligand phenoxido O) (1.97 Å) length. The apical–basal
sequence is complementary in nature. (Fig. S9) The Cu–O–C–O/
O–C–O–Cu torsion angles (6.89°/40.82°) indicate that the pheny-

A.K. Ghosh, D. Ray / Polyhedron 52 (2013) 370–376
375
of [Cu4O] core [24,45,46]. In 1, the broad band near 3401 cmꢁ1 is ob-
Table 3
Selected inter-atomic distances (Å) and angles (°) for complex 2.
ꢀ
served for mOH stretching mode [47]. The stretching frequencies at
1383 and 826 cmꢁ1 are observed for msymðN—OÞ and masðN—OÞ modes
[48]. The conversion of 1ꢀ2H2O to 2 in solution has been well mon-
itored using FT-IR spectroscopy (Fig. S2).
ꢀ
ꢀ
Distances
Cu(01)–O(3)
Cu(01)–O(4)
Cu(01)–N(1)
1.9149(8)
1.957(4)
1.963(6)
1.971(4)
2.316(4)
3.0291(15)
O(1)**–Cu(01)
O(3)–Cu(01)*
O(3)–Cu(01)**
O(3)–Cu(01)***
O(5)–Cu(01)
1.971(4)
1.9149(8)
1.9149(8)
1.9149(8)
2.316(4)
Cu(01)–O(1)
Cu(01)–O(5)***
Cu(01)ꢀ ꢀ ꢀCu(01)***
3.4. Electronic UV–Vis spectra
The ligand field spectra of the complexes show broad absorption
Angles
bands (k), with maxima at 677 nm (e
= 535 L molꢁ1 cmꢁ1) and
O(3)–Cu(01)–O(4)
O(3)–Cu(01)–N(1)
O(4)–Cu(01)–N(1)
O(3)–Cu(01)–O(1)
O(4)–Cu(01)–O(1)
N(1)–Cu(01)–O(1)
O(3)–Cu(01)–O(5)***
O(4)–Cu(01)–O(5)***
95.53(14)
167.71(17)
95.0(2)
77.52(14)
172.95(19)
92.1(2)
N(1)–Cu(01)–O(5)***
O(1)–Cu(01)–O(5)***
O(3)–Cu(01)–Cu(01)*
O(4)–Cu(01)–Cu(01)*
N(1)–Cu(01)–Cu(01)*
O(1)–Cu(01)–Cu(01)*
O(5)***–Cu(01)–Cu(01)*
88.37(19)
94.05(13)
37.73(2)
133.24(13)
131.55(18)
39.80(14)
98.30(11)
637 nm (
e
= 387 L molꢁ1 cmꢁ1) for 1ꢀ3H2O and 2, respectively. The
intense absorptions below 400 nm at 258 nm (e
= 12432 L molꢁ1
cmꢁ1) and 259 nm ( = 65101 L molꢁ1 cmꢁ1) are dominated by me-
e
tal–ligand charge transfer transitions for 1ꢀ3H2O and 2, respec-
98.78(12)
85.80(18)
tively. Spectra of these complexes also show shoulders at 373 nm
(e
= 2446 L molꢁ1 cmꢁ1
)
and 368 nm
(e )
= 1545 L molꢁ1 cmꢁ1
respectively, due to weak HOꢁ ? CuII and PhOꢁ ? CuII ligand-to-
*
=(ꢁx, ꢁy, z).
=(ꢁy, x, ꢁz).
**
metal charge transfer (LMCT) transitions [49] (Fig. S12).
***
=(y, ꢁx, ꢁz).
4. Concluding remarks
The coordination chemistry of the H2bpmpꢁ ligand to Cu(II)
ions has been examined in this work which establishes crucial role
of the phenylacetate co-ligands for the clean and straightforward
transformation of two unit-cell packed hydroxido-bridged Cu2
lacetato groups bridge in a syn–syn arrangement in out-of-plane
mode. The coordination geometry about the metal ions is very
close to a square pyramid (Addison parameter
s is 0.087) [42].
The four phenylacetato bridges connect the Cu(II) ions along the
four edges of the [Cu4O] tetrahedron while the ligand PhOꢁ groups
bridge along the other two edges (Figs. 3 and S9). The basal–apical
and apical–basal binding combination for four carboxylate groups
is responsible for the formation of an interdimer cavity between
complexes into a
l4-oxido-bridged Cu4 cluster. The nature of the
water derived bridging co-ligands (HOꢁ or O2ꢁ) seems to dictate
the final structure of the complexes. The dinucleating ligand H2-
bpmpꢁ bearing alcoholic pendant arms facilitates the binding of
two Cu(II) ions by phenoxido and hydroxido bridges and left be-
hind apical sites open per metal ion for binding of phenylacetate
co-ligands, which displace the coordinated water and nitrate
ligands, to facilitates the collapse of two Cu(OH)Cu units into Cu2
(O)Cu2 core.
[Cu2(
from the condensation of two HOꢁ bridges in 1. The basal–basal
phenoxido O bridge squeeze the Cu–( 4–O)–Cu to 104.5° (a ) than
the other angles at 112° (a ). The crystal packing along the c-axis
l
-H2bpmp)]3+ halves which nicely traps the O2ꢁ ion formed
l
v
v
showed regular placement of the tetra-nuclear units () and phenyl
rings of the bridging phenylacetate groups remain quite far to
show any kind of
information).
p–p interactions (Figs. S10 and S11 in supporting
Acknowledgements
AKG is thankful to the Council of Scientific and Industrial Re-
search, New Delhi for the financial support. The authors also thank
to DST, New Delhi, for providing the Single Crystal X-ray Diffrac-
tometer facility to the Department of Chemistry, IIT Kharagpur un-
der its FIST program.
3.3. FT-IR Spectroscopy
C@N stretching frequencies are observed at 1604–1637 cmꢁl
ꢀ
m
The
ꢀ
for 1ꢀ3H2O, 2 and the transformed 2 from 1ꢀ3H2O. For 2, the masðCOOÞ
ꢀ
and msðCOOÞ stretching vibrations are detected at 1578 and
1384 cmꢁ1, respectively. The difference,
= 194 cmꢁ1, is in accord
1,3-bridging carboxylates. For non-bridging
ꢀ
Dm
Appendix A. Supplementary data
with the presence of
l
ꢀ
Dm
carboxylato coordination, this
separation is usually larger (ca.
350 cmꢁ1) [44]. For 2, the band at 632 is assigned for
Cu—O vibration
CCDC 868328 and 868327 contain the supplementary crystallo-
graphic data for 1ꢀ2H2O and 2, respectively. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
ciated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.poly.2012.08.064.
ꢀ
m
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