A polynuclear helical and two dinuclear copper(II) complexes of a monocondensed N,N,O donor Schiff base with pseudohalides as co-ligand

Article abstract of DOI:10.1016/j.ica.2012.10.020

Three copper(II) complexes, [Cu₂L₂(μ _1,1-NCO)(NCO)] (1), [Cu₂L₂(μ_1,3- NCS)(NCS)] (2) and [CuL(μ_1,5-dca)]_n- ·nH ₂O (3), where HL = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, have been prepared and characterized by elemental analysis, IR and UV-Vis spectroscopy, single crystal X-ray diffraction studies and by cyclic voltammetry. Complexes 1 and 3 crystallize in monoclinic space group P2 ₁/n and complex 2 in monoclinic P2₁/c. In complex 1, OCN^- shows μ_1,1 bridging mode; in complex 2, SCN ^- shows μ_1,3 bridging mode whereas in complex 3, N(CN)^-₂ shows μ_1,5 bridging mode. The tridentate Schiff base ligand reacts with copper(II) to occupy its three equatorial positions. The coordination polyhedra around one of the copper center in compounds 1 and 2 are best described as an elongated (4 + 1) square pyramid, whereas the coordination polyhedra around other copper center is square planer. The copper atom in compound 3 has a slightly distorted square pyramidal environment. Significant C-H/π interactions are observed in both complexes 1 and 2. Complex 3 is an example of MOFs containing penta-cordinated Cu(II) ions linked together by N(CN)^-₂ to yield 1D infinite P and M-helical chains.

Full text of DOI:10.1016/j.ica.2012.10.020

Inorganica Chimica Acta 395 (2013) 24–32
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Inorganica Chimica Acta
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A polynuclear helical and two dinuclear copper(II) complexes of a monocondensed
N,N,O donor Schiff base with pseudohalides as co-ligand
Pallab Bhowmik a,b,c, Shouvik Chattopadhyay a, , Michael G.B. Drew , Ashutosh Ghosh
⇑
d
c,
⇑
a
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
Department of Chemistry, Sundarban Mahavidyalaya, Kakdwip, West Bengal, India
b
c
Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India
d
School of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG 66AD, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 June 2012
Received in revised form 9 October 2012
Accepted 17 October 2012
Available online 2 November 2012
2 2 2 2
Three copper(II) complexes, [Cu L (l1,1-NCO)(NCO)] (1), [Cu L (l1,3-NCS)(NCS)] (2) and [CuL(l1,5-dca)]n-
ꢀ
nH
2
O (3), where HL = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, have been prepared and char-
acterized by elemental analysis, IR and UV–Vis spectroscopy, single crystal X-ray diffraction studies and
by cyclic voltammetry. Complexes 1 and 3 crystallize in monoclinic space group P2
1
/n and complex 2 in
ꢁ
ꢁ
monoclinic P2
mode whereas in complex 3, NðCNÞ2 shows
1
/c. In complex 1, OCN shows
l
1,1 bridging mode; in complex 2, SCN shows
l1,3 bridging
ꢁ
l1,5 bridging mode. The tridentate Schiff base ligand reacts
Keywords:
Crystal structure
Copper(II)
Schiff base
Pseudo-halide
Polynuclear
with copper(II) to occupy its three equatorial positions. The coordination polyhedra around one of the
copper center in compounds 1 and 2 are best described as an elongated (4 + 1) square pyramid, whereas
the coordination polyhedra around other copper center is square planer. The copper atom in compound 3
has a slightly distorted square pyramidal environment. Significant C–H/
p interactions are observed in
both complexes 1 and 2. Complex 3 is an example of MOFs containing penta-cordinated Cu(II) ions linked
together by NðCNÞꢁ2 to yield 1D infinite P and M-helical chains.
Ó 2012 Elsevier B.V. All rights reserved.
1
. Introduction
The rational design and synthesis of polynuclear coordination
donor tridentate Schiff base, 2-[1-(2-dimethylamino-ethylimino)-
ethyl]-phenol (HL), afforded two dinuclear copper(II) complexes,
2 2 2 2
[Cu L (l1,1-NCO)(NCO)] (1) and [Cu L (l1,3-NCS)(NCS)] (2), with
complexes are of continuing interest because of their diverse struc-
tures and potential applications in magnetic materials [1]. A variety
of bridging groups have been employed for the synthesis of such
systems; among them the pseudohalide bridged complexes have
been received considerable attention because a small change in
the co-ligands can lead to a surprising difference among the struc-
tures and magnetism of the resulting complexes [1–3]. The most
comprehensive literature refers to azide ligands, but there are also
reports on the structure and magnetic properties of cyanato and
thiocyanato bridged complexes [4–12]. Coordination polymers
based on dicyanamide (dca) ligand have attracted much attention
in the past few years, not only because of their interesting extended
architectures but also they can facilitate the synthesis of metal–or-
ganic frameworks containing channels and cavities with various
sizes and shapes [13–21]. A large variety of topologies and magnetic
properties are seen in dicyanamide based complexes due to their
isocyanate or isothiocyanate bridge respectively and a polynuclear
copper(II) complex, {[CuL(
anamide bridge.
n
l1,5-dca)]} ꢀnH
2
O (3), containing a dicy-
2
. Experimental
.1. Starting materials
-hydroxyacetophenone and N,N-dimethylethelenediamine
2
2
were purchased from Lancaster and were of reagent grade. They
were used without further purification. The other reagents and sol-
vents used were of commercially available reagent quality, unless
otherwise stated.
2
2
.2. Preparations
2
different bridging modes [22–39]. Our attempts utilizing a N O
2 2
.2.1. Synthesis of [Cu L (l1,1 NCO)(NCO)] (1)
The tridentate Schiff base 2-[1-(2-dimethylamino-ethylimino)-
ethyl]-phenol (HL) was synthesized by refluxing N,N-dimethyl-
ethelenediamine (0.22 mL, 2 mmol) with 2-hydroxyacetophenone
(0.24 mL, 2 mmol) in methanol. The ligand was not isolated. A
⇑
Corresponding authors. Tel.: +91 33 2414 6666x2941 (S. Chattopadhyay).
E-mail addresses: shouvik.chem@gmail.com (S. Chattopadhyay), ghosh_59@
yahoo.com (A. Ghosh).
0
020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.10.020

P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
25
methanol solution of Cu(CH
then added to HL with constant stirring. An aqueous solution
1 mL) of NaOCN (0.130 g, 2 mmol) was added after 15 min, and
3
COO)
2
ꢀH
2
O (0.399 g, 2 mmol) was
Table 1
Crystal data and structure refinement of complexes 1–3.
(
Complex
1
2
3
stirring was continued for another 30 min. Deep green single crys-
tals, suitable for X-ray diffraction, were obtained after two days by
slow evaporation of the filtrate at room temperature.
Formula
M
Crystal system
Space group
a (Å)
C
26
H
34Cu
2
N
6
O
4
C
26
H
34Cu
2
6
N O
2
S
2
C
14 5 2
H19CuN O
621.68
monoclinic
P2 /n
11.55122(12)
20.0881(2)
11.64687(12)
93.188(1)
2698.38(5)
4
653.83
monoclinic
P2 /c
12.2936(2)
19.5877(3)
12.1908(2)
96.391(2)
2917.34(8)
4
352.88
monoclinic
P2 /n
16.8018(17)
10.7634(12)
17.9184(16)
103.855(10)
3146.1(6)
8
1
1
1
Yield 70% (Anal. Calc. for C26
3.52. Found: C, 50.2; H, 5.5; N, 13.5%). IR (KBr, cm ):1598
C=N), 2174( NCO), UV–Vis spectrum, kmax(CH CN): 604, 369, 270
and 231 nm. Magnetic moment, = 1.75 BM.
2 6 4
H34Cu N O : C, 50.23; H, 5.51; N,
ꢁ1
1
b (Å)
c (Å)
(c
c
3
l
b (°)3
V (Å )
Z
2
.2.2. Synthesis of [Cu
Complex 2 was obtained by following a similar procedure to
that of 1, but NH SCN (0.152 g, 2 mmol) used in place of NaOCN.
2 2
L (l1,3NCS)(NCS)] (2)
D
l
c
(g cmꢁ3)
(mm
1.530
2.306
1288
1.489
3.412
1352
1.490
1.403
1464
ꢁ1
)
4
F(000)
Deep-green single crystals suitable for X-ray diffraction were ob-
tained a few days by slow evaporation of the filtrate in open
atmosphere.
R
int
0.029
14673
3866
3765
0.0497, 0.1311
150
0.039
16459
4262
3926
0.0343, 0.0940
150
0.123
18996
8963
4045
0.1009, 0.1703
150
Total reflections
Unique reflections
I > 2
, wR
T/K
r
(I)
Yield 72% (Anal. Calc. for C26
2.85. Found: C, 47.7; H, 5.4; N, 12.7%). IR (KBr, cm ):1594 (
084( SNC), UV–Vis spectrum, kmax(CH CN): 594, 367, 270 and
29 nm. Magnetic moment, = 1.78 BM.
2 6 2 2
H34Cu N O S : C, 47.76; H, 5.24; N,
R
1
2
[I > 2
r(I)]
ꢁ
1
1
2
2
cC=N),
c
3
l
equivalent to 1.2 times those of the atom to which they were at-
tached. Hydrogen atoms for the water molecules in 3 were located
in a difference Fourier map. Absorption corrections were carried
2
.2.3. Synthesis of [CuL(
Complex 3 was also obtained by following a similar procedure
to that of 1, but NaN(CN) (0.178 g, 2 mmol) was used in place of
NaOCN. After the solution was stirred at room temperature for
h, brown precipitation was obtained from the mother liquor. Sin-
gle crystals suitable for X-ray diffraction were grown in a CH CN
l
1,5-dca)]
n
ꢀnH
2
O (3)
2
out using the ABSPACK program [42]. The structures were refined
2
on F to R
1
0.0497, 0.0343, 0.1009; wR
2
0.1311, 0.0940, 0.1703
(I).
1
for 3765, 3926, 4045 data, respectively with I > 2
r
3
solution of the brown mass by a slow diffusion of ether in a sealed
tube.
3
. Results and discussion
Yield 65% (Anal. Calc. for C14
9.85. Found: C, 47.8; H, 5.2; N, 19.7%). IR (KBr, cm ):1595
C=N), 2175, 2292 ( NCNCN), UV–Vis spectrum, kmax(CH CN): 596,
69, 269 and 230 nm. Magnetic moment, = 1.72 BM.
5 2
H19CuN O : C, 47.65; H, 5.43; N,
ꢁ1
3.1. Syntheses
1
(c
c
3
The mono-condensed ligand (HL) was prepared by 1:1 conden-
sation of N,N-dimethylethelenediamine and 2-hydroxyacetophe-
none in methanol following the literature method [43].
3
l
2
.3. Physical measurements
The complexes were synthesized simply by allowing the Schiff
base to react with Cu(CH
lowed by the addition of NaOCN (for 1), NH
NaN(CN)2 (for 3) in 1:1:1 M ratio. The mononegative tridentate
Schiff base ligand along with cyanate or thiocyanate or dicyanam-
ide anion balances the charge of the complex species (1, 2, and 3)
but the metal ion remains coordinately unsaturated. In such a sit-
3
COO)
2
ꢀH
2
O in a methanol solution fol-
SCN (for 2) and
Elemental analysis (carbon, hydrogen and nitrogen) were per-
formed using a Perkin–Elmer 2400 series II CHN analyzer. IR spec-
tra in KBr (4500–500 cm ) were recorded using a Perkin–Elmer
RXI FT-IR spectrophotometer. Electronic spectra in acetonitrile
4
ꢁ
1
(
1200–350 nm) were recorded in a Hitachi U-3501 spectropho-
tometer. Electrochemical studies were carried out using a Sycopel
model AEW2 1820F/S instrument. The measurements were per-
formed at 300 K in acetonitrile solutions containing 0.2 M TEAP
ꢁ
ꢁ
ꢁ
uation, anions such as OCN , SCN and NðCNÞ group can exhibit
2
their well-known bridging properties to result in dinuclear (1, 2)
ꢁ
ꢁ3
and 1D helical chain (3) complexes. In complex 1, OCN shows
and 10 M complex deoxygenated by bubbling with nitrogen.
The working, counter, and reference electrodes used were a plati-
num wire, a platinum coil, and an SCE, respectively. Magnetic sus-
ceptibility measurements at 300 K were carried out with a
Sherwood Scientific Co., UK, magnetic susceptibility balance and
diamagnetic corrections were made using Pascal’s constants.
ꢁ
l1,1 bridging mode; in complex 2, SCN shows
l
1,3 bridging mode
ꢁ
where as in complex 3, NðCNÞ shows
l1,5 bridging mode. The for-
2
mations of the complexes are shown in Scheme 1.
3.2. Description of the structures of 1, 2 and 3
2.4. X-ray crystallography
3.2.1. Complex 1
2 2 1,1
The structure of complex 1 consists of the dinuclear [Cu L (l -
Crystal data for the three crystals are given in Table 1. Single
crystals for complexes 1, 2 and 3 were used for data collection
using the Oxford Diffraction X-Calibur CCD System at 150 K, data
for 1 and 2 with Cu Ka and for 3 with Mo Ka radiation. The crystals
were positioned at 50 mm from the CCD. 1780 frames were mea-
sured with a counting time of 3 s for 1 and 2, while 321 frames
were measured with a counting time of 10 s for 3. Data analyses
NCO)(NCO)] species. An ORTEP diagram with the atom-labeling
scheme is shown in Fig. 1. Two copper(II) atoms [Cu(1) and
Cu(2)] are bridged by cyanate ion in an end-on fashion, giving the
dinuclear structure with a Schiff base as the co-ligand attached
to each copper centers. The coordination polyhedron around the
Cu(1) is best described as an elongated (4 + 1) square pyramid.
Two nitrogen atoms, N(19) and N(22), and one oxygen atom,
O(11), from the deprotonated Schiff base ligand L and one nitrogen
were carried out with the CRYS
were solved using direct methods with the SHELXS97 program
41]. The non-hydrogen atoms were refined with anisotropic
ALIS program [40]. The structures
ꢁ
atom N(1) from a terminal OCN ligand define the equatorial
plane, having bond lengths to the Cu(1) atom at 1.959(3),
[
thermal parameters. The hydrogen atoms bonded to carbon were
included in geometric positions and given thermal parameters
2.067(3), 1.908(3) and 1.974(5) Å, respectively. One nitrogen atom,
ꢁ
N(2) of a bridging
l1,1 NCO is coordinated to the Cu(1) in the axial

2
6
P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
Scheme 1. Synthesis of ligand and complexes 1, 2 and 3.
Fig. 1. The structure of 1 with ellipsoids at 30% probability. Hydrogen atoms omitted for clarity.
position at distance of 2.553(4) Å. There is a slight distortion to the
square plane and the deviations of the coordinating atoms N(19),
N(22), O(11), N(1) from the least-square mean plane through them
are ꢁ0.059(3), 0.056(3), 0.058(2) and ꢁ0.055(6) Å, respectively,
and that of the copper atom from the same plane is ꢁ0.178(4) Å,
towards the axially coordinated N(2) atom. This deviation from
planarity of the equatorial plane is also manifest in the trans angles
[O(11)–Cu(1)–N(22), N(19)–Cu(1)–N(1)], which are 166.1(1) and
172.3(2)°, respectively. So Cu(1) ion has a distorted square pyrami-
4
dal geometry with a CuN O chromophore and a s value of 0.10

P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
27
Table 2
which bridges two copper(II) ions in an end-on coordination mode.
Bond lengths to the Cu (2) are 1.972(3) Å to the imino nitrogen
N(39), 2.043(3) Å to the amino nitrogen N(42), 1.888(3) Å to the
phenoxo oxygen O(31) of the Schiff base and 1.977(3) Å to the
nitrogen atom N(2) of the bridging OCN anion. The deviation of
the coordinating atoms N(2), N(39), N(42) and O(31) from their
least-squares mean plane are ꢁ0.146(4), ꢁ0.155(3), 0.146(3) and
Selected bond lengths (Å) and bond angles (°) for complexes 1 and 2.
Atoms
1
2
Cu(1)–O(11)
Cu(1)–N(19)
Cu(1)–N(1)
Cu(1)–N(22)
Cu(2)–O(31)
Cu(2)–N(39)
Cu(2)–N(2)
Cu(2)–N(42)
O(11)–Cu(1)–N(19)
O(11)–Cu(1)–N(1)
N(19)–Cu(1)–N(1)
O(11)–Cu(1)–N(22)
N(19)–Cu(1)–N(22)
N(1)–Cu(1)–N(22)
O(31)–Cu(2)–N(39)
O(31)–Cu(2)–N(2)
N(39)–Cu(2)–N(2)
O(31)–Cu(2)–N(42)
N(39)–Cu(2)–N(42)
N(2)–Cu(2)–N(42)
1.908(3)
1.959(3)
1.973(5)
2.066(3)
1.888(3)
1.972(3)
1.977(3)
2.043(3)
91.1(1)
1.883(2)
1.951(2)
1.958(2)
2.050(1)
1.888(2)
1.962(2)
1.966(2)
2.062(2)
92.20(7)
89.68(8)
176.27(9)
169.61(7)
86.78(7)
91.95(7)
92.37(2)
89.91(8)
172.8(1)
169.0(8)
85.61(8)
90.87(9)
0
.155(3) Å, respectively, and that of the copper atom from the
same plane is ꢁ0.043(3) Å. The two trans angles, O(31)–Cu(2)–
N(42) and N(2)–Cu(2)–N(39) are 168.1(1) and 173.7(2) Å, respec-
tively. From the crystallographic literature, it is seen that Cu(II)
91.2(2)
ꢁ
dinuclear
l
1,1 NCO bridged compounds have a Cu–NNCO–Cu angle
172.3(2)
166.1(1)
85.3(1)
90.8(2)
91.6(1)
in the narrow range 92.3–96.3° [45–51]. However in 1, this angle is
far greater at 114.6(2)° which is, to the best of our knowledge, the
largest Cu–NNCO–Cu angle for this type of dinuclear compound so
far observed. The Cu(1) and Cu(2) separation is 3.826(1) Å. The
five-membered ring Cu(1)–N(19)–C(20)–C(21)–N(22) has an enve-
lope conformation on C(21) with puckering parameters
Q(2) = 0.416(4) Å and Q = 105.1(5)° while ring Cu(2)–N(39)–
C(40)–C(41)–N(42) has an half chair conformation with puckering
parameters Q(2) = 0.443(4) Å and Q = 300.7(4)° [52]. Selected bond
lengths and bond angles are given in Table 2.
90.1(1)
173.7(2)
168.1(1)
85.6(1)
94.0(1)
Table 3
The complex shows significant C–H/
p interactions. One of the –
Geometric features (distances in Å and angles in degrees) of the C–H/
obtained for 1–2.
p interactions
CH
2
–groups, namely, C (381) of the Schiff base is involved in two
3
Csp –H/p interactions (Table 3) with phenyl group of other two
C–HꢀꢀꢀCg(Ring)
HꢀꢀꢀCg (Å) \C–HꢀꢀꢀCg (°) CꢀꢀꢀCg (Å)
adjacent moieties (Fig. 2) where the H(38B)ꢀꢀꢀCg(R5) and
H(38C). . .Cg(R6) distances are 2.75 Å and 2.76 Å, respectively, the
C(381)–H(38B)ꢀꢀꢀCg(R5) and C(381)–H(38C)ꢀꢀꢀCg(R6) angles are
Complex 1 C(181)-H(18A)ꢀꢀꢀCg(6) 2.77
126
137
135
3.425(5)
3.512(5)
3.503(5)
C(381)-H(38B)ꢀꢀꢀCg(5)
C(381)-H(38C)ꢀꢀꢀCg(6)
2.75
2.76
137° and 135°, respectively. There is also another C–H/
p interac-
Complex 2 C(20)-H(20B)ꢀꢀꢀCg(6)
C(23)-H(23B)ꢀꢀꢀCg(5)
2.74
2.57
151
174
3.620(3)
3.529(8)
tion among C(181)–H(18A). . .Cg(R6) with H(18A). . .Cg(R6) dis-
tance at 2.77 Å and at a angle of 126° (Cg: centroid of the phenyl
ring). Geometric features of the C–H/p interactions are given in Ta-
ble 3. So each dinuclear unit of the complex 1 has three C–H/
p
interactions to form 2D array of the molecules.
(s
= 0 for a square pyramidal geometry, and
s
= 1 for a trigonal
bipyramidal geometry) [44].
The coordination environment around Cu(2) is square planar
being bonded to three atoms of ligand L, namely O(31), N(39)
and N(42), together with a nitrogen atom (N2) from a OCN ligand,
3
.2.2. Complex 2
The structure of complex 2 is very similar to that of 1, the only
ꢁ
ꢁ
differences are that here SCN is the bridging ligand in place of
Fig. 2. (a) The C–H/
respectively. (b) 2D array of the complex containing C–H/
p
interactions in dinuclear complex 1 are highlighted. Cg(6) and Cg(5) are the centroids of phenyl ring containing atoms C(32) to C(37) and C(12) to C(17),
interactions.
p

2
8
P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
ꢁ
0.150(1) Å from the plane containing O(31), N(39), N(42), N(2)
in the direction of the bound sulfur atom. The value of two trans
angles N(42)–Cu(2)–O(31) and N(2)–Cu(2)–N(39) are 169.0°(8)
and 172.8°(1), respectively. So Cu(2) ion has a distorted square
3
pyramidal geometry with a CuN OS chromophore and a s value
of 0.06. In the dinuclear complex Cu(1) and Cu(2) are joined by
ꢁ
one end-to-end bridging SCN (isothiocyanate) group by N(1) and
S(1) atoms, respectively. The coordination polyhedron around the
Cu(1) is square planar with the metal bonded to three atoms of li-
gand Schiff-base, O(11), N(19) and N(22) together with a nitrogen
ꢁ
atom, N(1) from an bridging SCN ligand. Bond lengths to Cu(1) are
1
1
.951(2) Å to the imino nitrogen, 2.050(1) Å to the amino nitrogen,
.883 (2) Å to the phenoxo oxygen of Schiff base and 1.958(2) Å to
the nitrogen atom of the bridging SCN anion. The deviations of the
coordinating atoms N(19), N(22), N(2) and O(11) from their least-
squares mean plane are 0.119(2), ꢁ0.114(1), 0.115(2) and
0
.120(2) Å, respectively, and that of the copper atom from the
same plane is 0.059(1) Å. Two trans angels [O(11)–Cu(1)–N(22),
N(1)–Cu(1)–N(19)] are 169.61(7)° and 176.27(9)°. The Cu(1) and
Cu(2) separation is 6.225 Å. The five-membered ring Cu(1)–
N(19)–C(20)–C(21)–N(22) has an envelope conformation on
C(21) with puckering parameters Q(2) = 0.430(2) Å and
Q = 289.3(2)° and ring Cu(2)–N(39)–C(40)–C(41)–N(42) has an
envelope conformation on C(41) with puckering parameters
Q(2) = 0.408(2) Å and Q = 294.6(3)°. Selected bond parameters are
given in Table 2.
Fig. 3. The structure of 2 with ellipsoids at 30% probability. Hydrogen atoms
omitted for clarity.
The complex shows significant C–H/
ety, two –CH – groups, namely C(20) and C(23) of Schiff base are
engaged in two Csp –H/p interactions (Table 3) with the two phe-
p interactions. In each moi-
2
3
ꢁ
OCN and it shows end-to-end bridging mode. An ORTEP diagram
nyl rings of neighboring dinuclear unit as shown Fig. 4 to form a 1D
array.
with the atom-labeling scheme is shown in Fig. 3. The coordination
environment around Cu(2) is best described as an elongated (4 + 1)
square pyramid. The basal plane is formed by one amine nitrogen
N(42), one imino nitrogen N(39), an oxygen atom O(31) from the
3.2.3. Complex 3
ꢁ
Schiff base and a nitrogen atom N(2) from the terminal NCS group
The structure of 3 contains two CuL(NCNCN) moieties in the
asymmetric unit together with two solvent water molecules. How-
having bond lengths to Cu(2) are 2.062(2), 1.962(2), 1.888(2) and
1
.966(2) Å, respectively. The apical position is occupied by a sulfur
ever, unlike 1 and 2, the molecules form two distinct 1D polymers
ꢁ
ꢁ
S(1) atom from a bridging SCN (isothiocyanate) group with rather
long bond length of 2.932(7) Å. The copper atom is displaced by
bridged by the NðCNÞ ligands. Fig. 5 shows the polymer formed
2
with Cu(1); that formed with Cu(2) is equivalent. The metal atoms
Fig. 4. (a) The C–H/
respectively, (b) 1D array of the complex via C–H/
p
interactions in dinuclear complex 2 are highlighted. Cg(6)and Cg(5) are the centroids of phenyl rings containing atoms C(32)–C(37) and C(12)–C(17),
interaction.
p

P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
29
Fig. 5. The structure of the 1-D chain formed with Cu(1) in 3. Hydrogen atoms omitted for clarity An equivalent polymer is formed with Cu(2). Ellipsoids are at 10%
0
probability. Symmetry element = 1/2 ꢁ x, y ꢁ 1/2, 1/2 ꢁ z.
occupy five-coordinate environments that are close to square pyra-
midal with the three donor atoms from the Schiff base occupying
ꢁ
the equatorial plane together with one end of a bridging NðCNÞ .
2
Table 4
The axial position is occupied by the other end of a second bridging
ꢁ
Selected bond lengths (Å) and bond angles (°) for
complex 3.
NðCNÞ . For the ligand, distances from the metal centers to oxygen
2
are 1.902(4), 1.898(4) Å to the imino nitrogen 1.973(6), 1.977(5) Å
Cu(1)–O(11)
1.902(4)
to the amino nitrogen 2.050(5), 2.038(5) Å and to the bridging
ꢁ
NðCNÞ , 2.000(6), 2.012(6) Å in the equatorial plane and 2.258(6),
Cu(1)–N(19)
Cu(1)–N(1)
Cu(1)–N(22)
Cu(1)–N(5)
Cu(2)–O(31)
Cu(2)–N(39)
Cu(2)–N(6)
Cu(2)–N(42)
Cu(2)–N(10)’’
O(11)–Cu(1)–N(19)
O(11)–Cu(1)–N(1)
N(19)–Cu(1)–N(1)
O(11)–Cu(1)–N(22)
N(19)–Cu(1)–N(22)
N(1)–Cu(1)–N(22)
O(11)–Cu(1)–N(5)
N(19)–Cu(1)–N(5)
N(22)–Cu(1)–N(5)
1.973(6)
2.258(6)
2.050(5)
2.000(6)
1.898(4)
1.977(5)
2.312(7)
2.038(5)
2.012(6)
91.7(2)
93.8(2)
105.7(2)
174.1(2)
83.9(2)
91.0(2)
90.6(2)
158.9(2)
92.1(2)
95.0(2)
91.1(2)
93.0(2)
104.9(2)
175.3(2)
85.0(2)
90.6(2)
90.6(2)
160.7(2)
92.2(2)
94.2(3)
2
2
.312(7) Å in an axial position around Cu(1) and Cu(2), respec-
tively. The equatorial planes show r.m.s. deviations of 0.140,
.138 Å, respectively around Cu(1) and Cu(2), respectively. The
0
0
copper atoms are 0.219(3), 0.195(3) Å from these planes in the
direction of the axial nitrogen atom. There are no atoms close to
the second axial position. Bond lengths are similar to those found
in 1 and 2. Cu(1) and Cu(2) ion has a distorted square pyramidal
4
[s = 0.25 for Cu(1) and s = 0.24 for Cu(2)] geometry with a CuN O
chromophore [44]. The five-membered ring Cu(1)–N(19)–C(20)–
C(21)–N(22) has an envelope conformation on N(22) and ring
Cu(2)–N(39)–C(40)–C(41)–N(42) has an twisted conformation on
C(41)–N(42) [51]. The two solvent water molecules in 3 each forms
just one strong hydrogen bond, to a ligand oxygen atoms, thus
0
0
0
O(1)–H(1B). . .O(31) and O(2)–H(2A). . .O(11) with O. . .O 2.791(9),
0
0
N(1)–Cu(1)–N(5)
2
.782(9) ÅA , O–H. . .O 164, 153° and H. . .O 1.96, 2.00 Å, respectively.
Selected bond parameters are given in Table 4.
Complex 3 is an example of MOF containing penta-cordinated
O(31)–Cu(2)–N(39)
O(31)–Cu(2) –N(6)
N(39)–Cu(2)–N(6)
O(31)–Cu(2)–N(42)
N(39)–Cu(2)–N(42)
N(6)–Cu(2)–N(42)
O(31)–Cu(2)–N(10)
N(39)–Cu(2)–N(10)
N(42)–Cu(2)–N(10)
S
ꢁ
Cu(II) ions linked together by NðCNÞ2 to yield 1D infinite P and M-
helical chains with pitch distances of 10.763 Å (Figs. 6 and 7). It is
noteworthy that there are various weak hydrogen bonds between
the adjacent helical chains in 3. The adjacent P-helices are inter-
connected to generate a 2D homo-chiral supramolecular sheet
structure within the bc plane through hydrogen bonds (Fig. 6).
Similarly M-helices generate a 2D homo-chiral sheet in the same
crystallographic plane by the same type of hydrogen bonds
0
00
0
0
0
0
0
N(6)–Cu(2)–N(10)
0
Symmetry elements: = 1/2 ꢁ x, y ꢁ 1/2, 1/2 ꢁ z;
0
0
= 3/2 ꢁ x, 1/2 + y, 1/2 ꢁ z.

3
0
P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
Fig. 6. Coordination P-helix of 3 and homo-chiral 2D supramolecular sheet of P-helices formed by hydrogen bonding interactions.
(Fig. 7). These sheets are packed along the crystallographic a-axis
3.3. IR, electronic spectra and magnetic moments
to form a 3D achiral structure (Fig. 8).
A comparison of the three structures reveals that in all of them
the tridentate Schiff base and the N-atom of the corresponding
pseudohalide coordinate to the equatorial sites of Cu(II) to result
in a square planar structure. In complex 1, this N-atom of isocya-
nate but in 2 the S-atom of the isothiocyanate group coordinates
weakly to the axial position of the Cu(II) of another unit in end-
The IR spectrum of 1 shows the most intense absorption band at
ꢁ
1
2174 cm corresponding to the NCO ligand. For complex 2, one
ꢁ
1
sharp and strong band at 2062 cm
indicates the presence of
ꢁ
the N bonded NCS group. The dicyanamide ion in NaN(CN)
2
shows three sharp and strong characteristic bands in the frequency
ꢁ
1
region 2290–2170 cm
which are attributed to
c
asym
+ c
sym
ꢁ1
on (l1,1) and end-to-end (l1,3) bridging mode respectively to result
(C„N) combination modes (2286 cm ),
c
asym
(C„N)
sym (C„N) 2179 cm . Upon complexation,
these bands shift towards higher frequency [14]. For complex 3,
ꢁ
1
ꢁ1
in the dimeric structures. The difference in the bridging mode of
the pseudohalide is not surprising as the literature data show that
these are the common bridging modes of these two ligands. It is
also to be noted that the pseudohalide of one unit of the dimer re-
mains terminally coordinated. On the other hand, in 3 the dicyan-
amide ion of all the units coordinate to the axial cites of a
neighboring unit with the well known 1,5-bridging mode to form
the one-dimensional helical chain.
(2232 cm ) and c
ꢁ1
the split bands at 2293, 2240 and 2174 cm can be attributed
respectively to the sym (C„N), asym (C„N) and
c
asym
+
c
c
c
sym
(C„N) modes of the bridging dicyanamide ligand. In the IR spectra
of the complexes 1–3, stong and sharp bands due to azomethine
c(C=N) group of cordinating Schiff base appear at 1598, 1594 and
ꢁ
1
1596 cm , respectively.
Fig. 7. Coordination M-helix of 3 and homo-chiral 2D supramolecular sheet of M-helices formed by hydrogen bonding interactions.

P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
31
Fig. 8. 3D arrangements of complex 3.
The electronic spectra of 1, 2 and 3 in acetonitrile solution dis-
play d–d absorption bands at 604, 594 and 595 nm, respectively.
The positions of these bands are consistent with the observed
bands around the copper(II) centers [53]. The UV absorption bands
at 369, 270, 231 nm for complex 1 and 367, 270, 229 nm for com-
plex 2 and 368, 269, 230 nm for complex 3 may be assigned to the
ligand to metal charge transfer transitions.
magnetically non-coupled copper (II) system, indicating that the
Cu atoms in 1, 2 and 3 are non-coupled at room temperature.
3.4. Electrochemistry
All three complexes 1, 2 and 3 in acetonitrile solution display
irreversible reductive responses attributed to the Cu(II)/Cu(I) cou-
ple (Epc) at ꢁ1.048, ꢁ0.96, ꢁ0.882 V, respectively, whereas the cor-
responding irreversible oxidative responses for the Cu(II)/Cu(I)
The room temperature magnetic moments values of the com-
plexes are close to the spin-only value (1.73 BM) for the discrete
Fig. 9. The cyclic voltammogram of complexes 1, 2 and 3 in acetonitrile solution.

3
2
P. Bhowmik et al. / Inorganica Chimica Acta 395 (2013) 24–32
couple (Epa) are observed at 1.179, 1.204, 1.189 V for complexes 1,
, and 3, respectively (Fig. 9) during the anodic potential scan. The
potential values are within the range found for other Cu(II)-Schiff
base complexes [54–58]. There are also second oxidative responses
observed for all three complexes in the anodic potential scan at ca.
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[
13] J.M. Lehn, Supramolecular Chemistry: Concepts and Perspectives, VCH, New
York, 1995.
ꢁ
0.125, ꢁ0.228, ꢁ0.124 V respectively with a very narrow width
and high peak current. These responses are typical of the anodic
stripping of copper-Schiff base complexes [57–60]. Therefore, it
may be assumed that, on the electrode surface, Cu(II) complexes
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[
1
1, 2 and 3 are reduced to Cu(I), and these are not stable and under-
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and the instability of the Cu(I) complexes are in agreement with
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(
of one end-on (
l
1,1) cyanato bridged dinuclear, one end-to-end
1,5) dicy-
[
(l
1,3) thiocyanato bridged dinuclear and one end-to-end (l
6
anamide bridged polynuclear Cu(II) complexes with a tridentate
Schiff base {2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol} as
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1
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Acknowledgments
We thank EPSRC and the University of Reading for funds for the
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Appendix A. Supplementary material
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78542 (complex 3) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
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c.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
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