Copper(II) α-hydroxycarboxylate complexes of bis(2-pyridylcarbonyl)amine ligand: From mononuclear complex to one-dimensional coordination polymer

Article abstract of DOI:10.1016/j.poly.2009.06.087

The coordination geometry and supramolecular structures of three copper(II) complexes of two α-hydroxycarboxylates and one α-methoxycarboxylate with nitrogen donor co-ligands are discussed. The complexes have been characterized by elemental analysis, ESI-MS, IR and electronic spectroscopy, thermogravimetric analysis and magnetic measurements. The X-ray structure analysis of all the complexes, namely [(BPCA)Cu^II(MA)] (1), [(BPCA)Cu^II(MPA)(H₂O)] (2) and [(BPCA)Cu^II(BA)]_n (3), where BPCA = bis(2-pyridylcarbonyl)amidate, MA = racemic mandelate, MPA = racemic α-methoxy phenylacetate and BA = benzilate anion, shows the copper(II) ion in a distorted square-pyramidal geometry. In 1 the mandelate anion is coordinated to the copper(II) center in a bidentate fashion while in 2 the α-methoxycarboxylate is monodentate. In both cases a one-dimensional supramolecular array is formed through hydrogen bonds: the mononuclear units are directly connected in 1 by the MA hydroxyl group, whereas in 2 is the coordinated water that operates as H donor towards the MPA carboxylate group and the BPCA carbonyl oxygens of nearby complexes. In 3 the benzilate anion, acting as bridging ligand between copper ions, gives rise to a one-dimensional coordination polymer. In the latter, intra- and inter-chain π?π stacking interactions between pyridines and one phenyl ring of benzilate anions are observed in the packing.

Full text of DOI:10.1016/j.poly.2009.06.087

Polyhedron 29 (2010) 434–440
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Copper(II)
a-hydroxycarboxylate complexes of bis(2-pyridylcarbonyl)amine
ligand: From mononuclear complex to one-dimensional coordination polymer
Partha Halder a, Ennio Zangrando b, Tapan Kanti Paine a,
*
a Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S.C. Mullick Road, Jadavpur, Kolkata 700032, India
b Dipartimento di Scienze Chimiche, University of Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 7 August 2009
The coordination geometry and supramolecular structures of three copper(II) complexes of two
hydroxycarboxylates and one a-methoxycarboxylate with nitrogen donor co-ligands are discussed. The
a-
complexes have been characterized by elemental analysis, ESI-MS, IR and electronic spectroscopy, ther-
mogravimetric analysis and magnetic measurements. The X-ray structure analysis of all the complexes,
namely [(BPCA)CuII(MA)] (1), [(BPCA)CuII(MPA)(H2O)] (2) and [(BPCA)CuII(BA)]n (3), where BPCA = bis(2-
Keywords:
Copper
Hydroxy acids
Hydrogen bonds
Coordination polymer
Solid-state structure
pyridylcarbonyl)amidate, MA = racemic mandelate, MPA = racemic
BA = benzilate anion, shows the copper(II) ion in a distorted square-pyramidal geometry. In 1 the man-
delate anion is coordinated to the copper(II) center in a bidentate fashion while in 2 the -methoxycarb-
a-methoxy phenylacetate and
a
oxylate is monodentate. In both cases a one-dimensional supramolecular array is formed through
hydrogen bonds: the mononuclear units are directly connected in 1 by the MA hydroxyl group, whereas
in 2 is the coordinated water that operates as H donor towards the MPA carboxylate group and the BPCA
carbonyl oxygens of nearby complexes. In 3 the benzilate anion, acting as bridging ligand between copper
ions, gives rise to a one-dimensional coordination polymer. In the latter, intra- and inter-chain
stacking interactions between pyridines and one phenyl ring of benzilate anions are observed in the
p p
ꢀ ꢀ ꢀ
packing.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
in complex synthesis and, to a certain extent, also on the ratio of
the reactants. Moreover, the
forms can act as source of H-bonds and are suitable for
ing and/or C–Hꢀ ꢀ ꢀ interactions with aromatic nitrogen donor
ligands. It is also possible to fine tune such non-covalent interac-
tion by suitable functionalization on -hydroxy acids.
In spite of a large number of copper(II) -hydroxycarboxylates
reported in literature [17–22,24–29,31–33], study on the effect of
ligand functionality in directing the self-assembled product is rare
[20,31]. We decided to investigate copper(II) complexes of
a
-hydroxy acids or their monoanionic
Coordination compounds of appropriate metal–ligand combina-
tion are used as molecular building blocks for self-organized struc-
tures with diverse topologies and potential application [1–8].
Beside covalent linkages between the building blocks, non-cova-
pꢀ ꢀ ꢀp stack-
p
a
lent intermolecular interactions, like H-bonds,
direct the formation of self-assembled structures of variable
p
ꢀ ꢀ ꢀ
p
, and C–Hꢀ ꢀ ꢀ
p
,
a
dimensions [9–13]. The coordination chemistry of metal com-
plexes containing
a-hydroxy acids has been extensively studied
over the last years for their unusual structural features as well as
various physical and chemical properties [14–31]. These carboxyl-
ate species reveal various coordination modes (i.e., denticity) since
they can behave as monodentate or bidentate chelating (through
the carboxylate group or via one oxygen of the carboxylate and
a-hydroxy acids and a-methoxy carboxylic acid with bis(2-pyri-
dylcarbonyl)amidate (BPCA) as nitrogen donor coligand (Chart 1).
We report herein the complexes [(BPCA)CuII(MA)] (1), [(BPCA)-
CuII(MPA)(H2O)] (2), and [(BPCA)CuII(BA)]n (3) [MA = racemic man-
delate,
MPA = racemic
a
-methoxy
phenylacetate
and
the
a
-OH group). In addition, different coordination patterns were
BA = benzilate anion], comparing the effect of carboxylic acids on
their solid state structure. It is expected that the tridentate bis(2-
pyridylcarbonyl)amidate ligand and packing requirements may in-
duce the hydroxy carboxylate to adopt different coordination
modes in the copper(II) complexes. Moreover, the benzilate with
reported in the same compound, as well as bridging behavior
between two metal ions as observed for simple carboxylate
ligands. The coordination mode eventually adopted by the
a-
hydroxy anions may depend on the metal ion and co-ligands used
two phenyl rings at
ing, affecting its binding mode beside the possibility to form extra
ꢀ ꢀ ꢀ interaction in comparison to mandelate. The effect of ligand
a-carbon would engender more steric crowd-
* Corresponding author. Tel.: +91 33 2473 4971; fax: +91 33 2473 2805.
E-mail address: ictkp@iacs.res.in (T.K. Paine).
p
p
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.06.087

P. Halder et al. / Polyhedron 29 (2010) 434–440
435
2.2.3. Complex [(BPCA)CuII(BA)]n (3)
The complex was synthesised according to the procedure de-
scribed for complex 1 except for benzilic acid was used instead
of mandelic acid. Yield: 0.34 g (66%). Anal. Calc. for C26H19CuN3O5:
C, 60.40; H, 3.70; N 8.13. Found: C, 59.8; H, 3.5; N, 8.2%. IR (KBr,
cmꢁ1): 3502–3406 (br), 3063 (br), 1713 (s), 1625, 1600 (s),
1382–1359 (s), 1300, 766, 704. ESI-MS (positive ion mode,
water–methanol): m/z = 1057.19 (25%, [(BPCA)2Cu2(BA)2+Na]+),
805.18 (75%, [(BPCA)2Cu2(BA)]+), 555.12 (10%, [(BPCA)Cu(BA)+K]+),
539.15 (100%, [(BPCA)Cu(BA)+Na]+), 289.04 (50%, [BPCA)Cu]+). UV–
Vis in DMF (k, nm; e
, Mꢁ1 cmꢁ1): 634 (100), 429 (sh), 342 (sh), 308
(sh), 285 (11 350), 274 (13 400).
2.3. Physical methods
Chart 1.
Fourier transform infrared spectroscopy on KBr pellets was per-
formed on a Shimadzu FT-IR 8400S instrument. Elemental analyses
were performed on a Perkin Elmer 2400 series II CHN series. Solu-
tion electronic spectra were measured on an Agilent 8453 diode ar-
ray spectrophotometer. Electro-spray mass spectra were recorded
with a Waters QTOF Micro YA263. Room temperature magnetic
data were collected on a Gouy balance (Sherwood Scientific, Cam-
bridge, UK). Diamagnetic contributions were estimated for each
compound by using Pascal’s constants. TGA measurements were
carried out on a TA instruments SDT Q 600 thermal analyzer with
the heating rate of 10 °C/min from room temperature to 800 °C un-
der nitrogen atmosphere.
functionality, coordination geometry of metal complex and other
non-covalent interactions in stabilizing such self-assembled struc-
tures is described.
2. Experimental
2.1. Chemicals
The chemicals were purchased from commercial sources and
used as received. The solvents were distilled and dried before
use. Although no problems were encountered during the synthesis
of complexes, perchlorate salts are potentially explosive and
should be handled with care. The ligand HBPCA was synthesised
according to a literature procedure [34].
2.3.1. X-ray crystallographic data collection and refinement of the
structures
Crystallographic data for the complexes are summarized in
Table 1. Diffraction data for 1 were collected at RT on a Nonius
2.2. Syntheses
DIP-1030H system (Mo K
data collections for 2 and 3 were performed on a Bruker Smart APEX
II (Mo K radiation, k = 0.71073 Å) at 150 K. Cell refinement, index-
a radiation, k = 0.71073 Å). Intensities
2.2.1. Complex [(BPCA)CuII(MA)] (1)
a
To a methanolic solution (20 mL) of HBPCA ligand (0.227 g,
1 mmol) was added Cu(ClO4)2ꢀ6H2O (0.37 g, 1 mmol). To the
resulting solution was added a methanolic solution (3 mL) of man-
delic acid (1 mmol) and triethylamine (1 mmol). The solution
turned immediately to blue and was stirred further for 3 h to yield
a pale blue solid. The solid was isolated by filtration and air-dried.
The filtrate was kept at room temperature for a week to isolate
blue single crystals suitable for X-ray crystallography. Yield:
0.26 g (59%). Anal. Calc. for C20H15CuN3O5: C, 54.48; H, 3.43; N,
9.53. Found: C, 54.5; H, 3.3; N, 9.7%. IR (KBr, cmꢁ1): 3423 (br),
3101–3032 (br), 1705 (s), 1599 (s), 1355–1342 (s), 1093, 1043,
766, 704. ESI-MS (positive ion mode, water–methanol):
m/z = 751.02 (20%, [(BPCA)2Cu2(MA)+Na]+), 479.01 (25%, [(BPCA)-
Cu(MA)+K]+), 463.04 (100%, [(BPCA)Cu(MA)+Na]+), 289.00 (70%,
ing and scaling of the data sets were carried out using Denzo and
Scalepack packages [35], and the APEX2 v2.1-0 software [36]. The
structure was solved by direct methods and subsequent Fourier
Table 1
Crystallographic data for complexes 1–3.
1
2ꢀ0.5MeOHꢀ0.5H2O
3
Empirical formula
Formula weight
Crystal system
Space group
C20H15CuN3O5 C21.50H22CuN3O7
C26H19CuN3O5
516.98
monoclinic
P21/c
440.89
495.95
triclinic
monoclinic
P21/n
P 1
a (Å)
b (Å)
c (Å)
5.515(3)
9.402(3)
18.333(4)
90.49(3)
98.47(3)
108.21(3)
891.6(6)
2
10.0649(4)
15.4982(6)
14.6418(5)
8.8400(11)
12.7073(17)
19.617(3)
[BPCA)Cu]+). UV–Vis in DMF (k, nm; , Mꢁ1 cmꢁ1): 629 (100), 429
e
a
(°)
(sh), 342 (sh), 309 (sh), 285 (11 300), 274 (13 400).
b (°)
108.692(1)
100.998(4)
c
(°)
2.2.2. Complex [(BPCA)CuII(MPA)(H2O)] (2)ꢀ0.5 MeOHꢀ0.5 H2O
V (Å3)
2163.48(14)
4
1.529
1.059
1028
2163.2(5)
4
1.587
1.056
1060
The complex was synthesised according to the procedure de-
Z
Dcalc (Mg/m3)
1.642
1.265
450
scribed for complex 1 except for
a-methoxy phenylacetic acid
l
(Mo K
a
) (mmꢁ1
)
was used instead of mandelic acid. The solution was kept at room
temperature for slow evaporation of solvent for 5 days to isolate
dark blue needles. Yield: 0.35 g (70%). Anal. Calc. for C21.5H22Cu-
N3O7: C, 51.86; H, 4.45; N, 8.44. Found: C, 51.9; H, 4.4; N, 8.7%.
IR (KBr, cmꢁ1): 3448 (br), 2931, 1713 (s), 1635 (s), 1599 (s),
1363(s), 1097, 1029, 761, 704. ESI-MS (positive ion mode,
water–methanol): m/z = 931.51 (50%, [(BPCA)2Cu2(MPA)2+Na]+),
743.43 (25%, [(BPCA)2Cu2(MPA)]+), 477.28 (100%, [(BPCA)Cu(M-
PA)+Na]+), 312.14 (70%, [BPCA)Cu+Na]+), 289.05 (50%, [BPCA)Cu]+).
F(0 0 0)
h Range data collection (°)
Reflections collected
Reflections unique
Rint
1.12–26.37
10 742
3184
0.0378
1952
1.97–24.06
18 765
3420
0.0525
2752
1.92–27.60
22 238
4917
0.0810
3794
Data [I > 2r(I)]
Parameters
265
298
317
Goodness-of-fit (GOF) on
0.846
1.048
1.031
F2
R1 [I > 2
r
(I)]
0.0387
0.0781
0.0371
0.0877
0.0488
0.1204
1.240, ꢁ0.838
UV–Vis in MeOH (k, nm; e
, Mꢁ1 cmꢁ1): 632 (115), 303 (sh), 274
(15 600).
wR2
Residuals (e Åꢁ3
)
0.202, ꢁ0.248 0.724, ꢁ0.327

436
P. Halder et al. / Polyhedron 29 (2010) 434–440
analyses and refined by the full-matrix least-squares method
based on F2 with all observed reflections [37]. H atoms bonded to
carbon (and to hydroxyl group in 3) were included at calculated
positions, those of the hydroxyl group in 1 and of the aquo ligand
in 2 were located from electron density map and refined. In the
DF
map of 2 an area of disordered solvent was interpreted as occupied
by a molecule of MeOH and of water, both at half occupancy (H
atoms not assigned). All the calculations were performed using
the WinGX System, Ver 1.70.01 [38].
3. Results and discussion
3.1. Syntheses and characterization
The complexes 1–3 were synthesised by reacting HBPCA ligand
with copper(II) perchlorate and appropriate acids in methanol in
the presence of one equivalent of triethylamine (Scheme 1).
The IR spectra of copper(II) complexes exhibit bands at around
1600 cmꢁ1, and in the range of 1330–1380 cmꢁ1, attributable to
m
asym(OCO) and
m
sym(OCO), respectively. Complexes 1 and 3 show
-hy-
sharp bands in the 3050–3470 cmꢁ1 due to OH stretching of
a
droxy acid anion and for complex 1 weak broad band is observed
around 2600 cmꢁ1, due to hydrogen bonded OH stretching fre-
quency. In addition, sharp bands are observed at 1705 cmꢁ1 for 1
Fig. 1. Molecular structure of [(BPCA)CuII(MA)] (1).
and at 1712 cmꢁ1 for 2 and 3 corresponding to
m(C@O) vibrations
Table 2
Selected bond distances (Å) and angles (°) for complexes 1–3.
of BPCA ligand [39]. ESI-MS in positive ion mode (in water–meth-
anol) shows peaks at m/z = 479.01 (25%), 463.04 (100%), and
289.00 (70%) for 1 with isotope distribution patterns calculated
for [(BPCA)Cu(MA)+K]+, [(BPCA)Cu(MA)+Na]+, and [(BPCA)Cu]+,
respectively. Apart from this, a peak observed at m/z = 751.03
(20%) can be assigned to [(BPCA)2Cu2(MA-H)+Na]+. Similar mass
spectral pattern (in methanol) is observed for complex 2 which
shows peaks in the ESI-MS at m/z = 931.51 (50%), 743.43 (25%),
477.28 (100%), 312.14 (70%) and 289.05 (50%) with isotope
distribution patterns calculated for [(BPCA)2Cu2(MPA)2+Na]+,
[(BPCA)2Cu2(MPA)]+, [(BPCA)Cu(MPA)+Na]+, [BPCA)Cu+Na]+ and
[BPCA)Cu]+, respectively. The presence of higher molecular weight
mass peaks suggests that in solution the mononuclear copper(II)
units of complexes 1 and 2 are arranged in polymeric fashion
through some intermolecular interactions. The ESI-MS of 3 shows
peaks at m/z = 1057.19 (25%), 843.13 (10%), 827.16 (60%), 805.18
(75%), 555.12 (10%), 539.15 (100%) and 289.04 (50%) with expected
isotope distribution patterns calculated for [{(BPCA)Cu(BA)}2+Na]+,
[(BPCA)2Cu2(BA-H)+K]+, [(BPCA)2Cu2(BA-H)+Na]+, [(BPCA)2Cu2
(BA)]+, [(BPCA)Cu(BA)+K]+, [(BPCA)Cu(BA)+Na]+ and [(BPCA)Cu]+,
respectively. This indicates the polymeric nature of complex 3.
The complexes show effective magnetic moments between 1.79
and 1.84 BM (per copper) at room temperature, as expected for
Cu(II) ion in d9 electronic configuration. The thermogravimetric
behavior of 1 and 3 is very similar. Decomposition of the hydroxy
carboxylate ligands begins at about 200 °C and continues up to
300 °C. A further weight loss takes place in the range 300–390 °C
and then very slowly up to 800 °C, which corresponds to the
decomposition of the tridentate BPCA ligand. Complex 2 contains
1
2
3a
Cu–N(1)
Cu–N(2)
Cu–N(3)
Cu–O(1)
Cu–O(2)
1.999(3)
2.005(3)
1.931(3)
2.297(3)
1.945(2)
2.014(3)
2.009(3)
1.933(3)
2.255(2)
1.947(2)
1.983(2)
1.979(2)
1.935(2)
2.482(2)
1.959(2)
N(1)–Cu–N(2)
N(1)–Cu–N(3)
N(1)–Cu–O(1)
N(1)–Cu–O(2)
N(2)–Cu–N(3)
N(2)–Cu–O(1)
N(2)–Cu–O(2)
N(3)–Cu–O(1)
N(3)–Cu–O(2)
O(2)–Cu–O(1)
C(13)–O(2)–Cu
163.32(11)
82.64(11)
91.20(11)
100.05(10)
82.04(12)
98.94(11)
95.26(11)
104.31(10)
177.30(10)
76.01(9)
163.45(10)
81.73(10)
90.13(10)
97.19(10)
81.75(10)
93.88(10)
98.72(10)
100.70(10)
167.42(10)
91.82(9)
164.09(10)
82.18(10)
91.23(8)
96.43(9)
82.41(10)
92.73(8)
99.40(9)
118.80(9)
160.08(9)
81.04(7)
121.4(2)
114.3(2)
112.79(18)
a
In 3 O(1) represents the symmetry related hydroxyl oxygen at ꢁx + 1, yꢁ1/2,
ꢁz + 1/2 (see Fig. 5).
lattice solvent that is lost at 140 °C, while the loss of a coordinated
water molecule is observed at 220 °C. The
tate ligand (MPA) decomposes at ca. 310 °C and then BPCA ligand
decomposes slowly up to 800 °C.
a-methoxy phenylace-
3.2. X-ray structures
3.2.1. Crystal structure of [(BPCA)CuII(MA)](1)
The X-ray structural determination of
copper(II) center is surrounded by the chelating MA anion and
1 reveals that the
Scheme 1. Syntheses of complexes 1–3.

P. Halder et al. / Polyhedron 29 (2010) 434–440
437
Fig. 2. Crystal packing of 1 shows linear one-dimensional polymer along axis a formed by H-bonds (O30 at 1 + x, y, z).
Fig. 3. ORTEP drawing of the molecular structure of [(BPCA)CuII(MPA)(H2O)] (2).
the tridentate BPCA ligand in a distorted square-pyramidal coordi-
nation geometry ( = 0.233) [40], indicating that the amide nitro-
tion at least in the solid state. The mononuclear units are con-
nected through hydrogen bonds involving the MA hydroxyl
group with the carboxylate oxygen of another symmetry related
unit to form a one-dimensional polymer developing along axis a,
as shown in Fig. 2 (O(1)ꢀ ꢀ ꢀO(3) distance = 2.630(4) Å, the collinear
metal ions being separated by 5.515(3) Å). The crystal packing
shows also non-conventional C–Hꢀ ꢀ ꢀO hydrogen bond interactions
(Cꢀ ꢀ ꢀO distance of ca. 3.2 Å) occurring between BPCA carbonyl oxy-
gens O4 and O5 and pyridyl H atoms of an adjacent array. Since the
chain construction is merely due to crystallographic translation,
each array contains mandelate anions of same chirality.
s
gen undergoes deprotonation upon complexation (Fig. 1). The
imido and two pyridyl nitrogen donors from BPCA ligand and the
carboxylate oxygen atom O2 from MA form the basal plane
whereas the hydroxyl oxygen atom (O1) is located at the apical po-
sition of the distorted square pyramid. Among the Cu–N bond dis-
tances, that involving the amide nitrogen (Cu–N(3) = 1.931(3) Å) is
slightly shorter in comparison with the Cu–N(py) distances of
1.999(3) and 2.005(3) Å (Table 2). The basal Cu–O bond length is
1.945(2) Å, while the apical hydroxyl oxygen donor is located, as
expected, at considerably longer distance 2.297(3) Å, forming an
O(2)–Cu–O(1) angle of 76.01(9)°.
Table 3
The Cu–N and Cu–O bond length values are in agreement with
those found in other BPCA-containing copper(II) complexes [39,41]
and among these it is of interest the close comparable values found
in the complex containing an oxalate anion double bridging two
Cu(BPCA) entities [42].
The atoms in BPCA are practically coplanar and the dihedral an-
gle between the pyridine planes is 4.8(2)°. The phenyl ring is ori-
ented to form an angle of 21.51° with the pyridine N(2). These
aromatic rings with a distance of 4.193 Å between their centroids
H-bond parameters for complexes 1–3.
D - H
A
Symmetry
D - H/Å
H. . .A/Å
D. . .A/Å
D - H. . .A/Å
Complex 1
O1–H
O(3)
1 + x, y, z
0.92(4)
1.74(4)
2.630(4)
163(3)
Complex 2
O1–Ha
O1–Hb
O1–Hb
Complex 3
O1–H
O(2)
O(4)
O(5)
ꢁx, ꢁy, 1ꢁz
1ꢁx, ꢁy, 1ꢁz
1ꢁx, ꢁy, 1ꢁz
0.83(3)
0.82(3)
0.82(3)
2.03(4)
2.18(4)
2.37(3)
2.834(4)
2.910(3)
2.994(3)
163(3)
148(4)
133(4)
O(3)
0.84
2.07
2.587(3)
120
may be indicative of a weak intra-molecular
pꢀ ꢀ ꢀp stacking interac-

438
P. Halder et al. / Polyhedron 29 (2010) 434–440
3.2.2. Crystal structure of [(BPCA)CuII(MPA)(H2O)](2)
A perspective view of complex 2, reported in Fig. 3, indicates the
methoxy carboxylate monocoordinated to copper(II) ion. The
(Fig. 4) are related by centers of symmetry so that pairs of H-bond
interactions are operative along the chain. Finally a methanol mol-
ecule at half occupancy is H-bond appended to the uncoordinated
carboxylate oxygen (O3ꢀ ꢀ ꢀO7 = 2.616(8) Å). In the same area it
is also present a water molecule (occupancy = 0.5, O3ꢀ ꢀ ꢀOw =
2.938(9) Å, see Section 2). By means of H-bonds these solvent mol-
ecules (at half occupancy) eventually lead to a two-dimensional
sheet arrangement of the complexes, but the disorder observed
does not allow to detailing this feature further.
square-pyramidal coordination geometry (s = 0.066) [40], beside
the BPCA nitrogen donors, is completed by an aquo ligand at the
apical position. The trend of Cu–N and Cu–O coordination bond
distances is very similar to that found in 1 with a slight shortening
of the apical Cu–OH2 bond (2.255(2) Å). The C13–O2–Cu angle is
114.3(2)° (Table 2). The complex geometry is similar to the formato
[(BPCA)CuII(formato)(H2O)] [39] and to two acetato [(BPCA)CuII
(acetato)(H2O)] derivatives [43,44], where the Cu–OH2 bond was
found slightly elongated (ca. 2.33 Å).
3.2.3. Crystal structure of [(BPCA)CuII(BA)]n (3)
Complex 3 exhibits a five-coordinate distorted square-pyramidal
The conformation adopted by the methoxy carboxylate allows
the formation of infinite one-dimensional hydrogen bonded chains
where metal ions are separated by 5.51 and 6.65 Å. The aquo ligand
O1 plays a crucial role in connecting the complex units by means of
H-bonds: on one side it links a coordinated carboxylate oxygen O20
(Oꢀ ꢀ ꢀO distance = 2.834(4) Å) and in the opposite direction, the car-
bonyl BPCA oxygens of another complex through a bifurcate inter-
action (Oꢀ ꢀ ꢀO = 2.910(3), 2.994(3) Å) (Table 3). The complex units
coordination geometry (s = 0.067) [40] at copper(II) defined by
the BPCA imido and pyridyl nitrogen donors and by two oxygen
atoms coming from two different BA ligands (Fig. 5). The coordina-
tion structural features of BPCA are comparable to those observed
in complexes 1 and 2, with the Cu–N(amide) bond distance
(1.935(2) Å) slightly shorter with respect to the Cu–N(py) ones of
1.983(2) and 1.979(2) Å (Table 2). The dihedral angle between
the pyridine mean planes is 7.42(5)°. Here the benzilate acts as
Fig. 4. Crystal packing of 2 showing one-dimensional polymer running parallel to axis a formed by H-bonds (Symmetry codes: (‘) at ꢁx, ꢁy, 1ꢁz, (‘‘) at 1ꢁx, ꢁy, 1ꢁz; O7 is a
disordered methanol oxygen).
Fig. 5. ORTEP drawing of the monomeric unit forming the coordination polymer in 3 (O10 at ꢁx + 1, yꢁ1/2, ꢁz + 1/2).

P. Halder et al. / Polyhedron 29 (2010) 434–440
439
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments
We are grateful to the Department of Science and Technology
(DST), Government of India (Project: SR/S1/IC-10/2006) and PRIN
2007HMTJWP_002 (Rome) for the financial support. Crystal struc-
ture determination was performed at the DST-funded National Sin-
gle Crystal Diffractometer Facility at the Department of Inorganic
Chemistry, IACS. P.H. acknowledges Council of Scientific and Indus-
trial Research (CSIR), India for a fellowship.
References
[1] J.-M. Lehn, Supramolecular Chemistry: Concepts and Perspectives, VCH,
Weinheim, 1995.
[2] R. Robson, J. Chem. Soc., Dalton Trans. (2000) 3735.
[3] Y. Rodríguez-Martín, M. Hernández-Molina, F.S. Delgado, J. Pasán, C. Ruiz-
Pérez, J. Sanchiz, F. Lloret, M. Julve, CrystEngCommun 4 (2002) 522.
[4] C. Janiak, Dalton Trans. (2003) 2781.
[5] S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem., Int. Ed. 43 (2004) 2334.
[6] G. Aromí, P. Gamez, J. Reedijk, Coord. Chem. Rev. 252 (2008) 964.
[7] C.N.R. Rao, S. Natarajan, R. Vaidhyanathan, Angew. Chem., Int. Ed. 43 (2004)
1466.
[8] T.-T. Luo, H.-L. Tsai, S.-L. Yang, Y.-H. Liu, R.D. Yadav, C.-C. Su, C.-H. Ueng, L.-G.
Lin, K.-L. Lu, Angew. Chem., Int. Ed. 44 (2005) 6063.
[9] M. Nishio, M. Hirota, Y. Umezawa, The CH/pi Interaction (Evidence, Nature and
Consequences), Wiley-VCH, New York, 1998.
[10] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond, IUCr Monographs, vol. 9,
Oxford University Press, 1999.
[11] C. Janiak, J. Chem. Soc., Dalton Trans. (2000) 3885.
[12] K. Biradha, CrystEngCommun 5 (2003) 374.
[13] A.M. Beatty, Coord. Chem. Rev. 246 (2003) 131.
[14] P.A. Agaskar, F.A. Cotton, L.R. Falvello, S. Han, J. Am. Chem. Soc. 108 (1986)
1214.
[15] M. Lanfranchi, L. Prati, M. Rossi, A. Tiripicchio, J. Chem. Soc., Chem. Commun.
(1993) 1698.
Fig. 6. Crystal packing of 3 viewed approx. down [1 0 1] direction with indication of
the intra- and inter-chain stacking interactions. The one-dimensional coordi-
nation polymers run parallel to axis b.
p–p
bridging ligand between two metal centers through a carboxylate
oxygen (Cu–O(2) 1.959(2) Å) and the hydroxyl oxygen O1 that
completes the square-pyramidal coordination sphere of the metal
(Cu–O(10) 2.482(2) Å). The hydroxyl group, which behaves as
efficient group to stabilize the supramolecular structure in 1, is
positioned at a distance of 2.587(3) Å from oxygen O3 with the
O1–Hꢀ ꢀ ꢀO3 angle of 120° (Fig. 5).
Thus in the present case the behavior of BA is responsible for
the formation of a one-dimensional zigzag coordination polymer,
running along axis b (Fig. 6). The metal ions are spaced by
7.546 Å and the intermetallic angle is 114.71°. As a matter of fact
the rather long Cu–O(10) distance (2.482(2) Å), as observed in a
coordination polymeric complex [Cu(BA)2(1,10-phen)]n [32], is
such to allow the formation of intra- and inter-chain face-to-face
ˇ
[16] I.K. Smatanová, J. Marek, P. Švancárek, P. Schwendt, Acta Crystallogr. C56
(2000) 154.
[17] R. Carballo, B. Covelo, S. Balboa, A. Castiñeiras, J. Niclós, Z. Anorg. Allg. Chem.
627 (2001) 948.
[18] R. Carballo, A. Castiñeiras, S. Balboa, B. Covelo, J. Niclós, Polyhedron 21 (2002)
2811.
[19] A. Castiñeiras, S. Balboa, E. Bermejo, R. Carballo, B. Covelo, J. Borras, J.A. Real, Z.
Anorg. Allg. Chem. 628 (2002) 1116.
[20] R. Carballo, A. Castiñeiras, B. Covelo, E. García-Martínez, J. Niclós, E.M.
Vázquez-López, Polyhedron 23 (2004) 1505.
[21] A. Beghidja, S. Hallynck, R. Welter, P. Rabu, Eur. J. Inorg. Chem. (2005) 662.
[22] L.-N. Zhu, S. Gao, L.-H. Huo, H. Zhao, Acta Crystallogr. E61 (2005) m2646.
[23] R. Carballo, B. Covelo, E.M. Vázquez-López, E. García-Martínez, A. Castiñeiras, J.
Niclós, Z. Anorg. Allg. Chem. 631 (2005) 785.
[24] R. Carballo, B. Covelo, E.M. Vázquez-López, E. García-Martínez, A. Castiñeiras,
C. Janiak, Z. Anorg. Allg. Chem. 631 (2005) 2006.
p
ꢀ ꢀ ꢀ
p
stacking interactions (Fig. 6), between the BPCA pyridine
BA phenyl ring (centroid-to-centroid distances of
N1 and
a
3.556(2), 3.600(2) Å, dihedral angles between the ring planes of
5.19 and 8.86°, respectively), that contribute in stabilizing the
coordination polymer.
[25] R. Carballo, B. Covelo, E. García-Martínez, E.M. Vázquez-López, Appl.
Organomet. Chem. 19 (2005) 394.
4. Conclusions
[26] A. Beghidja, G. Rogez, P. Rabu, R. Welter, M. Drillon, J. Mater. Chem. 16 (2006)
2715.
[27] R. Carballo, A. Castiñeiras, B. Covelo, A.B. Lago, E.M. Vázquez-López, Z. Anorg.
Allg. Chem. 633 (2007) 687.
[28] R. Carballo, B. Covelo, M. Salah El Fallah, J. Ribas, E.M. Vázquez-López, Cryst.
Growth Des. 7 (2007) 1069.
[29] R. Carballo, B. Covelo, N. Fernández-Hermida, A.B. Lago, E.M. Vázquez-López, Z.
Anorg. Allg. Chem. 633 (2007) 1791.
[30] A. Cuin, A.C. Massabni, C.Q.F. Leite, D.N. Sato, A. Neves, B. Szpoganicz, M.S.
Silva, A.J. Bortoluzzi, J. Inorg. Biochem. 101 (2007) 291.
[31] R. Carballo, B. Covelo, N. Fernández-Hermida, E. García-Martinez, A.B. Lago,
E.M. Vázquez-López, Cryst. Growth Des. 8 (2008) 995.
[32] Y. Qiu, K. Wang, Y. Liu, H. Deng, F. Sun, Y. Cai, Inorg. Chim. Acta 360 (2007)
1819.
We have isolated and structurally characterized three copper(II)
complexes supported by a tridentate nitrogen donor ligand and
a-hydroxy- or a-methoxy carboxylate anions. The anionic ligands
manifest different denticity towards the metal ions resulting in dif-
ferent supramolecular structures. The crystal packing of mandelate
and
a-methoxy phenylacetate complexes evidences one-dimen-
sional polymeric chains formed through H-bonds, but the presence
of an aquo ligand in the latter complex leads to chain of different
topology. On the other hand benzilate anions bridge copper(II) ions
obtaining coordination chain stabilized by aromatic/heteroaro-
[33] S. Balboa, R. Carballo, A. Castiñeiras, J.M. González-Pérez, J. Niclós-Gutiérrez,
Polyhedron 27 (2008) 2921.
matic
pꢀ ꢀ ꢀp interactions.
[34] A. Kamiyama, T. Noguchi, T. Kajiwara, T. Ito, Inorg. Chem. 41 (2002) 507.
[35] Z. Otwinowski, W. Minor, in: J.C.W. Carter, R.M. Sweet (Eds.), Methods in
Enzymology, vol. 276, Academic Press, New York, 1997, p. 307.
[36] APEX2 v2.1-0, Bruker AXS, Madison, WI, 2006.
[37] G.M. Sheldrick, University of Göttingen, Germany, 1998.
[38] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
Supplementary data
CCDC 724059, 724060, and 724061 contains the supplementary
crystallographic data for this paper. These data can be obtained

440
P. Halder et al. / Polyhedron 29 (2010) 434–440
[39] J. Borrás, G. Alzuet, M. González-Alvarez, J.L. García-Giménez, B. Macías, M.
Liu-González, Eur. J. Inorg. Chem. (2007) 822.
[42] I. Castro, J. Faus, M. Julve, M. Mollar, A. Monge, E. Gutiérrez-Puebla, Inorg.
Chim. Acta 161 (1989) 97.
[40] A.W. Addison, T.N. Rao, J. Reedijk, J. Rijn, G.C. Verschoor, J. Chem. Soc., Dalton
Trans. (1984) 1349.
[43] J.V. Folgado, E. Martínez-Tamayo, A. Beltrán-Porter, D. Beltrán-Porter, A.
Fuertes, C. Miravitlles, Polyhedron 8 (1989) 1077.
[41] C. Yuste, D. Cangussu de Castro Gomes, H. Adams, J.A. Thomas, F. Lloret, M.
Julve, Polyhedron 27 (2008) 2577.
[44] S.K. Padhi, V. Manivannan, Inorg. Chem. 45 (2006) 7994.