Synthesis and characterization of some heteroleptic copper(II) complexes based on meso-substituted dipyrrins

Article abstract of DOI:10.1007/s12039-011-0169-1

The syntheses and characterizations of meso-substituted dipyrrins, 5-(4-imidazol-1-yl-phenyl)- dipyrromethene (4-impdpm), 5-(4-nitro-imidazol-1-yl- phenyl)-dipyrromethene, (4-nimpdpm), 5-(4-benzimidazol- 1-yl-phenyl)- dipyrromethene (4-bimp-dpm) and heter

Full text of DOI:10.1007/s12039-011-0169-1

c
J. Chem. Sci. Vol. 123, No. 6, November 2011, pp. 819–826. ꢀ Indian Academy of Sciences.
Synthesis and characterization of some heteroleptic copper(II) complexes
based on meso-substituted dipyrrins
RAKESH KUMAR GUPTA, MAHENDRA YADAV, RAMPAL PANDEY and
DAYA SHANKAR PANDEY∗
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India
e-mail: dspbhu@bhu.ac.in
Abstract. The syntheses and characterizations of meso-substituted dipyrrins, 5-(4-imidazol-1-yl-phenyl)-
dipyrromethene (4-impdpm), 5-(4-nitro-imidazol-1-yl-phenyl)-dipyrromethene, (4-nimpdpm), 5-(4-benzimidazol-
1-yl-phenyl)-dipyrromethene (4-bimp-dpm) and heteroleptic complexes [Cu3(4-impdpm)2(hfacac)4] 1, [Cu(4-
nimpdpm)(acac)] 2, [Cu(4-nimpdpm)(hfacac)] 3, [{Cu(4-bimpdpm)(acac)}n] 4 and [{Cu(4-bimpdpm)-
(hfacac)}n] 5, imparting acetylacetonato (acac) and hexafluoroacetylacetonato (hfacac) groups as co-ligand
have been described. The dipyrrins and complexes 1–5 have been characterized by elemental analyses and
spectral (IR ESI-MS, NMR, electronic absorption and emission) studies. Crystal structures of 1, 3 and 4 have
been authenticated by X-ray single crystal analyses. The reaction between 4-impdpm and Cu(hfacac)2 gave
a trimetallic complex, under analogous conditions 4-nimpdpm and 4-bimpdpm reacted with Cu(acac)2 and
Cu(hfacac)2·2H2O to afford mononuclear (2, 3) and 1D polymeric (4, 5) complexes.
Keywords. Coordination polymers; meso-substituted dipyrrins; heteroleptic; acetylacetonato;
hexafluoroacetylacetonato; copper complexes.
1. Introduction
Further, imidazolyl-dipyrrins are of particular inter-
est in materials chemistry and life sciences.29–31 With
an objective of developing extended architectures
based on meso-substituted dipyrrins and to examine
the role of meso-substituent on ensuing complexes,
4-impdpm, 4-nimpdpm and 4-bimpdpm have been
synthesized and their reactivity examined with Cu(II)
complexes Cu(acac)2 and Cu(hfacac)2·2H2O. Through
this contribution we present the synthesis and charac-
terization of meso-substituted dipyrrins and Cu(II)
complexes [Cu3(4-impdpm)2(hfacac)4] 1, [Cu(4-
nimpdpm)(acac)] 2, [Cu(4-nimpdpm)(hfacac)] 3,
[{Cu(4-bimpdpm)(acac)}n] 4, and [{Cu(4-bimpdpm)-
(hfacac)}n] 5. Also, we present here X-ray single
crystal structures of 1, 3 and 4.
The chemistry of coordination polymers has seen a
large surge during past couple of decades because of
their intriguing architectures, topologies, and poten-
tial application in diverse areas.1–9 With an objective
of developing functional materials possessing desir-
able properties numerous systems have been synthe-
sized through the judicious choice of ligands and metal
ions.10–15 The creation of coordination polymers largely
depend on geometry of the metal ions, nature of the
ligand, metal to ligand ratio, solvent systems, counter
anions and the pH of reaction medium.16–19 Among
these, the choice of ligand plays crucial role in the
formation of coordination polymers. In addition, the
design and synthesis of dipyrromethenes (dipyrrins)
has been attractive because of their rather easy synthe-
sis and functionalization as well as monoanionic and
chelating nature of their conjugate base and extensive
use in various areas.20–28 A large number of charge
neutral homo-/heteroleptic complexes and supramolec-
ular clusters imparting dipyrrins has been synthesized
and thoroughly studied.20,21 It has been established
that suitably designed meso-substituted dipyrrins find
wide applications in the synthesis of extended homo-/
heterometallic architectures.20–22
2. Experimental
The solvents were rigorously purified by stan-
dard procedures prior to their use.32 Imidazole, 4-
nitroimidazole, benzimidazole, 4-fluorobenzaldehyde,
trifluoroacetic acid (TFA), 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ), triethylamine, Cu(hfacac)2·-
2H2O and silica gel (200–400 mesh) were procured
from Sigma Aldrich Chemical Co., USA and used
as received without further purifications. The ligands
∗For correspondence
819

820
Rakesh Kumar Gupta et al.
4-impdpm, 4-nimpdpm and 4-bimpdpm were synthe- 2.1c 5-(4-benzimidazol-1-yl-phenyl)-dipyrromethane
sized by the procedure described by Magdolen et al. (4-bimpdpm): It was prepared by following the above
with slight modifications33 and the precursor complex procedure for 1 using 4-impdpm (4.44 g, 0.02 mol).
Cu(acac)2 following literature procedure.34 Elemen- Yield: 50% (3.85 g). Anal. Calc. for C22H18N4: C,
tal analyses for C, H and N were performed on an 78.08; H, 5.36; N, 16.56%. Found: C, 78.15; H, 5.39;
1
Exeter Analytical Inc. Model CE-440 Elemental Ana- N, 16.49%. H NMR (CDCl3, δ ppm): 5.59 (s, 1H,
lyzer. IR spectra (4000–400 cm−1) were acquired on meso-H), 5.60 (s, 2H, pyr-H), 6.18 (s, 2H, pyr-H), 6.77
a Varian 3300 FT-IR spectrometer. Electronic absorp- (s, 2H, pyr-H), 7.35-7.40 (m, 6H), 7.56 (s, 1H), 7.79 (s,
tion and emission spectra were obtained on Shimadzu 1H), 7.82 (s, 1H, imi-H), 8.58 (bs, 2H, NH), IR (KBr
UV-1701 and Varian Cary Eclipse Fluorescence pellet, cm−1): 3256, 3122, 2961, 1676, 1615, 1581
spectro-photometers, respectively. 1H (300 MHz) NMR 1543, 1517, 1492, 1423, 1408, 1350, 1305, 1265, 1120,
spectra was acquired on a JEOL AL300 FT-NMR spec- 1095, 1068, 1025, 823, 773, 730.
trometer using tetramethylsilane (TMS) as an internal
reference. Room temperature magnetic susceptibility
measurements were performed on a Cahn–Faraday
balance using Hg[Co(SCN)4] as a calibrant.
2.1d [Cu3(4-impdpm)2(hfacac)4] (1): To a stirr-
ing ice cooled dichloromethane solution (50 mL)
of 4-impdpm (0.288 g, 0.001 mol), DDQ (0.228 g,
1.0 mmol) dissolved in benzene (30 mL) was added
drop-wise and stirred for an hour. A methanolic (20 mL)
2.1 Syntheses
solution of Cu(hfacac)2·2H2O (0.496 g, 0.001 mol) was
added to it and stirred for 20 min. The reaction mix-
2.1a 5-(4-imidazol-1-yl-phenyl)-dipyrromethane (4-
impdpm): To a flask containing pyrrole (19.34 g),
4-imidazol-1-yl-benzaldehyde (3.44 g, 0.02 mol) was
added and heated at 120◦C with stirring under inert
atmosphere for 24 h. After cooling to ambient tem-
perature it was concentrated to dryness under reduced
pressure and the crude product purified by column chro-
matography [alumina; ethylacetate: dichloromethane
(1 : 1)]. Yield: 38% (2.19 g). Anal. Calc. for C18H16N4:
C, 74.96; H, 5.60; N, 19.44%. Found: C, 75.29; H,
ture was evaporated to dryness and crude product puri-
fied by column chromatography (SiO2: CHCl3 with 1%
MeOH) to afford a red solid. Dichroic reddish-green
crystals of 1 were obtained from CH2Cl2/ hexane (1
: 1) solution. Yield: 30% (0.190 g). Anal. Calc. for
C36H26N8Cu: C, 68.18; H, 4.13; N, 17.67%. Found: C,
68.38; H, 4.30; N, 17.55%. ESI-MS (m/z) obs (calcd.):
634 [M+H]+ (634). IR (KBr pellet, cm−1): 2923, 1606,
1546, 1377, 1335, 1244, 1185, 1109, 1035, 995, 893,
809, 775, 727, 654. UV-Vis. (CH2Cl2, λmax nm; ε,
M−1cm−1): 496 (39880), 332 (15655), 300 (33852).
1
5.47; N, 19.52%. H NMR (CDCl3, δ ppm): 5.54 (s,
1H, meso-H), 5.92 (s, 2H, pyr-H), 6.18 (q, 2H, J =
3.0 Hz, pyr-H), 6.74 (s, 2H, pyr-H), 7.19–7.32 (m, 6H),
7.80 (s, 1H, imi-H), 8.04 (bs, 2H, NH). IR (KBr pellet,
cm−1): 3255, 3115, 2966, 1655, 1567, 1518, 1431,
1305, 1253, 1112, 1058, 819, 774, 724.
2.1e [Cu(4-nimpdpm)(acac)] (2): It was prepared
following the above procedure for 1 using 4-
nimpdpm (0.288 g, 0.001 mol) and Cu(acac)2 (0.288 g,
0.001 mol). Yield: 35% (0.172 g). Anal. Calc. for
C23H19N5O4Cu: C, 56.04; H, 3.88; N, 14.21%. Found:
C, 56.24; H, 4.00; N, 14.33%. ESI-MS (m/z) obs
(calcd.): 492 [M]+ (492). IR (KBr pellet, cm−1): 2906,
1582, 1550, 1406, 1392, 1378, 1336, 1244, 1206, 1178,
1118, 1080, 1028, 994, 892, 818, 770, 732, 654. UV-
Vis. (CH2Cl2, λmax nm; εM−1cm−1 ): 490 (39764), 320
(15770), 233 (21567).
2.1b 5-(4-(4-nitro-imidazol)-1-yl-phenyl)-dipyrromethane
(4-nimpdpm): It was prepared by following the above
procedure for 4-impdpm using 4-(4-nitro-imidazol-
1-yl)-benzaldehyde (4.34 g, 0.02 mol). Yield: 40%
(2.67 g). Anal. Calc. for C18H15N5O2: C, 64.84; H,
4.54; N, 21.01%. Found: C, 65.00; H, 4.62; N, 21.30%.
1H NMR (CDCl3, δ ppm): 5.46 (s, 1H, meso-H), 5.89
(s, 2H, pyr-H), 6.18 (s, 2H, pyr-H), 6.70 (s, 2H, pyr-H),
7.35-7.40 (m, 4H), 7.71 (s, 1H, imi-H), 8.04 (bs, 2H,
NH), 8.06 (s, 1H, imi-H). IR (KBr pellet, cm−1): 3248,
3124, 2968, 1678, 1610, 1590, 1542, 1514, 1490, 1426,
1406, 1350, 1304, 1268, 1122, 1092, 1068, 1024, 822,
774, 732.
2.1f [Cu(4-nimpdpm)(hfacac)] (3): It was synthe-
sized adopting the above procedure for 1 using 4-
nimpdpm and Cu(hfacac)2·2H2O. Yield: 28% (0.168 g).
Anal. Calc. for: C, 46.00; H, 2.18; N, 11.65%. Found: C,
45.88; H, 2.32; N, 11.79%. ESI-MS (m/z) obs (calcd.):
600 [M]+, (600). IR (KBr pellet, cm−1): 2923, 1648,

Heteroleptic copper(II) dipyrrinato complexes
821
1552, 1456, 1408, 1378, 1340, 1302, 1248, 1212, 1146, 3. Results and discussion
1114, 1064, 1034, 1000, 964, 890, 818, 778, 672.
UV-Vis. (CH2Cl2, λmax nm; εM−1cm−1 ): 491 (32945),
3.1 Synthesis
318 (17354), 230 (22142).
The aldehydes
4-imidazol-1-yl-benzaldehyde,
4-(4-nitro-imidazol-1-yl)-benzaldehyde,
and
4-
benzimidazol-1-yl-benzaldehyde were prepared by
the reaction of 4-fluorobenzaldehyde with imidazole,
4-nitroimidazole and benzimidazole, respectively
following literature procedure with slight modifica-
tions (see Supplementary Information).33 Conden-
sation of the respective aldehydes with pyrrole in
the presence of catalytic amounts of TFA (0.1 mM)
afforded 5-(4-imidazol-1-yl-phenyl)-dipyrromethane,
5-(4-nitro-imidazol)-1-yl-phenyl)-dipyrromethane
and 5-(4-benzimidazol-1-yl-phenyl)-dipyrromethane
in reasonably good yields.28 Although, the synthe-
sis of 5-(4-imidazol-1-yl-phenyl)-dipyrromethane
has already been reported22 we prepared this com-
pound adopting a different method. The synthesis of
dipyrrins were achieved by oxidation of respective
dipyrromethanes using DDQ in a mixture of benzene
and dichloromethane.28,37 A simple route for the syn-
thesis of dipyrromethanes and corresponding dipyrrins
is depicted in scheme 1. The dipyrrinato complexes
1–5 were obtained in good yield by in situ reaction of
dipyrrins with metal precursors (scheme 2a, b).
The reaction of Cu(hfacac)2·2H2O with 4-
impdpm (1:1 molar ratio) gave a trinuclear complex
[Cu3(hfacac)4(4-impdpm)2] 1, while mononuclear com-
plexes [Cu(acac)(4-nimpdpm)] 2, and [Cu(hfacac)(4-
nimpdpm)] 3 were obtained from the reactions
of Cu(acac)2/Cu(hfacac)2·2H2O with 4-nimpdpm
under analogous conditions. On the other hand, 4-
bzimpdpm reacted with Cu(acac)2/Cu(hfacac)2 to
afford 1D polymers [{Cu(4-bimpdpm)(acac)}n] 4 and
[{Cu(4-bimpdpm)(hfacac)}n] 5. The complexes 1–5
are air-stable, crystalline solids, soluble in common
organic solvents viz., dichloromethane, chloroform,
acetone, acetonitrile, dimethylsulphoxide, dimethylfor-
mamide and insoluble in water, methanol, diethyl ether,
petroleum ether, n-hexane, benzene and toluene. The
characterization of dipyrromethanes and complexes
1–5 have been achieved by satisfactory elemental analy-
ses, and spectral (IR, mass, electronic absorption and
emission) studies.
2.1g [{Cu(4-bimpdpm)(acac)}n] (4): This com-
pound was prepared following the above procedure for
1 using 4-bimpdpm and Cu(acac)2 in 1:1 molar ratio.
Yield: 33% (0.232 g). Anal. Calc. for C28H25N5O2Cu2:
C, 56.94, H, 4.27; N, 11.86%. Found: C,56.78; H,
4.23; N, 11.79%. ESI-MS (m/z) obs (calcd.): 498 [M]+
(498). IR (KBr pellet, cm−1): 2925, 1649, 1550, 1450,
1406, 1376, 1340, 1305, 1246, 1213, 1146, 1113, 1065,
1034, 1003, 965, 895, 816, 778, 675. UV-Vis. (CH2Cl2,
λmax nm; εM−1cm−1): 496 (22 245), 298 (19180), 231
(18605).
2.1h [{Cu(4-bimpdpm)(hfacac)}n]
(5): It
was
prepared following the above procedure for 1
using 4-bimpdpm and Cu(hfacac)2·.2H2O in 1:1
molar ratio. Yield: 28% (0.168 g). Anal. Calc. for
C28H19Cu2F6N5O2: C, 48.14; H, 2.74; N, 10.03%.
Found: C, 48.16; H, 2.72; N, 10.04%. ESI-MS
(m/z) obs (calcd.): 606 [M+H]+ (606). IR (KBr pellet,
cm−1): 2926, 1646, 1555, 1525, 1460, 1408, 1382,
1342, 1257, 1209, 1147, 1114, 1032, 1036, 1000, 799,
744, 672. UV-Vis. (CH2Cl2, λmax nm; εM−1cm−1): 502
(12592), 468 (25092), 340 (09536), 232 (17698).
2.2 X-ray crystallography
Preliminary data on the space group and unit cell
dimensions as well as intensity data for 1 and 3
were collected on OXFORD DIFFRACTION X
CALIBUR-S and for 4 on a Bruker APEX II with
Mo-Kα radiation (λ = 0.71073 Å). The structures
were solved by direct methods and refined using
SHELX-97.35 Non-hydrogen atoms were refined
with anisotropic thermal parameters. All the hydro-
gen atoms were geometrically fixed and refined
using a riding model. Computer program PLATON
was used for analysing the interaction and stack-
ing distances.36 CCDC-789391 (1), 789392 (3) and
832184 (4) contains supplementary crystallographic
data for this paper. It can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html
3.2 Spectral studies
(or from CCDC, 12 Union Road, Cambridge The infra red spectral data of 1–5 is summarized in
CB21EZ, UK; Fax: + 44-1223-336033; E-mail: experimental section alongwith other characterization
deposit@ccdc.cam.ac.uk).
data of the complexes. IR spectra of the complexes

822
Rakesh Kumar Gupta et al.
N
HN
NH HN
CHO
H
DDQ
TFA
+
N
H
R
R
R
N
N
N
R =
NO2
,
HN
HN
,
N
H
Scheme 1. Synthesis of dipyrrins.
under study displayed bands at ∼1546 cm−1 assignable at 340 and 233 nm. Intense low-energy transitions in
to νC=Npyr. Alongwith νC=Npyr vibrations 1, 3 and 5 the spectra of respective complexes have been assigned
exhibited bands due to νC=Ohfacac at ∼1648 cm−1. Simi- to charge-transfer processes associated with dipyrrin
larly, the complexes containing acac (2 and 5) displayed ligands25–28 and bands in the region ∼ 230–340 nm
bands at ∼1588 cm−1 assignable to νC=Oacac
.
20–22,38 The have been assigned to the ligand centred intra-ligand
IR spectral data supported formation of the respective transitions.39,40 The complexes 1–3 are non-fluorescent
complexes.
at room temperature, while 4–5 display weak fluores-
The electronic absorption and emission spectra of cence.41 The non fluorescent behaviour of 1–3 can be
1–5 were acquired in dichloromethane and resulting ascribed to the MLCT (metal to ligand charge trans-
data is summarized in table 3. In its UV-vis. spec- fer) transitions from paramagnetic Cu(II) core to π-
tra, 1–4 displayed intense low energy transitions at chromophore of the respective ligands along with its
∼ 495, 492, 491 and 496 nm alongwith high energy intrinsic quenching nature.42 In contrast, weak fluores-
bands at ∼ 332, 300 (1), 320, 233 (2), 318, 230 (3), cence displayed by 4 (572 nm) and 5 (555 nm) may be
298, 230 (4). Complex 5 displayed low energy bands at attributed to the extended conjugation in 4-bimpdpm
502 and 468 nm, while high energy transitions appeared relative to 4-impdpm, which dominates over MLCT
N
HN
O
O
N
X
O
O
O
Cu
O
O
O
N
N
N
Cu(hfacac)2
Cu(acac)2
N
N
N
N
O
Cu
N
Cu
Cu
N
X
DCM / MeOH
O
O
DCM / MeOH
N
N
X = H,
= hfacac (1)
X
O
N
X = H, NO2
N
X
X = NO2
,
O = acac (2), hfacac (3)
O
(a)
CR3
R3C
O
R3C
CR3
N
O
O
Cu
N
O
N
Cu
N
HN
N
N
N
N
Cu(acac)2
or
Cu(hfacac)2
N
N
M
N
DCM/MeOH
N
N
Cu
N
N
N
O
O
R = H(4), F(5)
R3C
(b)
CR3
Scheme 2. Synthesis of complexes 1–5.

Heteroleptic copper(II) dipyrrinato complexes
823
transitions in copper (II) complexes. Stronger fluores- other through bridging dipyrrin ligand. The immedi-
cence of 5 in comparison to 4 may be related to the ate coordination geometry about Cu2 centre is octa-
presence of electron withdrawing hfacac as a co-ligand hedral and defined by four oxygen donors from two
instead of acac.
independent hfacac co-ligands and imidazolyl nitro-
gens from two different 4-impdpm ligands (figure 1).
On the other hand, Cu1/ Cu1_1 cetres displayed dis-
torted square-planar geometry defined by two oxygen
donors from hfacac, and the pyrrolyl nitrogens of the
4-impdpm. The Cu–N and Cu–O bond distances about
the square planar Cu(II) centres are in the range of
1.912–1.923 Å and 1.955–1.956 Å, respectively. The
N(O)–Cu–N(O) bond angles fall in the range of 90.12–
93.24◦ (table 2).20–22,38 The angle (ω) between CuO2
and CuN2 planes has been found to be 25.14◦, which
clearly suggested distortion from regular square planar
geometry. The Cu–N and Cu–O bond distances about
the octahedral Cu2 are slightly longer in comparison to
the square planar Cu(II) centres (table 2). The Cu–O
(hfacac) bonds distances are not identical, it shows one
short (Cu2-O3/Cu2-O3_3, 2.003 Å) and one long (Cu2-
O4/Cu2-O4_4, 2.259 Å) bond. The observed elongation
of the bond distances may be ascribed to the Jahn–Teller
distortion.
3.3 Magnetic measurements
The room temperature (28.2◦C) magnetic moment
(μef f ) of the complexes were found to be 2.12 (1), 2.18
(2), 2.13 (3), 1.98 (4) and 1.95 B.M (5). These fall in
the range for spin only value (1.70–2.20), suggesting
that the metal centre in these complexes contains one
unpaired electron and supported the formation of Cu(II)
complexes.
3.4 Description of the crystal structures
Structures of 1, 3 and 4 have been authenticated crys-
tallographically. Details about the data collection and
refinement are gathered in table 1. Selected geometri-
cal parameters are summarized in table 2 and crystal
structures depicted in figures 1, 2 and S6 (Support-
ing information figure S6). Heteroleptic trinuclear com-
plex 1 contains three copper centres bonded to each
Complex 3 crystallizes in monoclinic system with
P21/c space group. The immediate coordination geom-
etry about Cu(II) in this complex is distorted square
Table 1. Crystal data and structure refinement parameters for 1, 3 and 4.
1
3
4
Empirical formula
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C56H30F24N8O8Cu3 C23H13F6N5O4Cu C21H17Cu1 N3O1
Triclinic
P-1
Monoclinic
P21/c
Orthorhombic
P21 21 21
15.6718(10)
17.1682(13)
18.6430(14)
64.257(7)
73.389(6)
79.259(6)
4318.4(5), 2
0.71073
29.8569(6)
11.2531(3)
6.6573(2)
90.00
95.222(2)
90.00
8.6919(13)
15.754(2)
16.664(3)
90.00
90.00
90.00
2281.9(6), 5
0.71073
α (deg)
β (deg)
γ (deg)
V (Å3), Z
2227.45(10), 4
0.71073
λ (Å)
Colour and habbit
T (K)
Reflns collected
Reflns/restraint/params
Orange, block
150(2)
32866
15170/0/1339
Red, thin-plate
150(2)
10536
3907/0/352
Red, needle
293(2)
14949
5596/0/310
Dcalcd (Mg m−3
)
1.834
1.240
0.810
1.792
1.076
1.032
1.450
0.990
1.054
μ(mm−1
GOF on F2
)
Final R indices I >2σ(I)a
R indices (all data)a
R1 = 0.0426
wR2 = 0.0872
R1 = 0.0922
R1 = 0.0282
wR2 = 0.0774
R1 = 0.0351
wR2 = 0.0790
R1 = 0.0516
wR2 = 0.1050
R1 = 0.0823
wR2 = 0.1297
ꢁ
ꢂ
ꢀ
ꢀ
ꢀ
ꢀ
1/2
a R1 = ꢁ Fo| − Fc ꢁ / |Fo|; R2 =
[w(Fo2 − Fc2)2] / [wFoa]
.

824
Rakesh Kumar Gupta et al.
Table 2. Selected bond lengths (Å) and angles (◦) for 1, 3 and 4.
Bond lengths
Bond angles
Complex 1
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu2–N4
Cu2–N4_4
Cu2–O3
Cu2–O3_3
Cu2–O4
1.912(3)
1.923(3)
1.956(3)
1.955(3)
1.982(3)
1.982(3)
2.003(3)
2.003(3)
2.259(3)
2.259(3)
N2–Cu1–N1
93.24(13)
90.12(11)
91.36(12)
158.81(14)
O2–Cu1–O1
O1–Cu1–N1
O1–Cu1–N2
N4–Cu2–N4_4 180.000(1)
O3–Cu2–N4
O3–Cu2–O4
O3–Cu2–O4_4
88.10(12)
87.89(12)
92.11(12)
O3–Cu2–O3_3 180.00(15)
Cu2–O4_4
ω 25.14
N2–Cu1–N1
Complex 3
Complex 4
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
N5–O3
1.935(17)
1.926(17)
1.954(14)
1.951(15)
1.235(2)
1.219(2)
92.95(7)
88.92(6)
89.78(7)
174.94(7)
O2–Cu1–O1
O1–Cu1–N1
O1–Cu1–N2
N5–O4
ω 7.91
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu1–N4
1.994(3)
1.959(3)
1.974(3)
1.951(3)
2.349(3)
N2–Cu1–N1
O2–Cu1–O1
O1–Cu1–N1
O1–Cu1–N2
O2–Cu1–N4
N2–Cu1–N4
O1–Cu–N4
N1–Cu1–N4
90.53(13)
90.14(13)
154.97(13)
177.86(13)
92.27(12)
89.60(13)
104.28(12)
100.66(12)
ω 25.09
ω = Angle between CuO2 and CuN2 planes
planer and completed by two oxygen (O1, O2) from longer in comparison to 1 having hfacac as an ancilla-
the co-ligand hfacac and two nitrogen donors (N1, ry ligand. The bond angles N1–Cu–N2, O1–Cu–O2
N2) from 4-nimpdpm in bis-chelating manner. The dis- are 92.95 and 88.92◦, respectively. The angle between
tortion from ideal square planar geometry has been CuO2 and CuN2 (ω) planes is 7.91◦, which further
estimated from interplanar angle (ω) between the suggested distortion from square planar geometry.
planes containing N(1)-Cu(1)-O(2) and N(2)-Cu(1)-
The polymeric complex 4 crystallized in orthorhom-
O(1) which falls to be 84.25◦. The Cu–N bond dis- bic system with P212121 space group. Asymmetric unit
tances are comparable to the Cu–N separations in other contains two Cu(II), one 4-bzimpdpm ligand and one
related systems.20–22,38 Further, the Cu–N distances are acac group. Two Cu(II) centres are separated by 4-
slightly smaller, while Cu–Ohfacac distances are slightly bzimpdpm spacer with a Cu· · · Cu distance of 13.88 Å.
Figure 1. Crystal structure of 1 (hydrogen atoms omitted for clarity).

Heteroleptic copper(II) dipyrrinato complexes
825
(a)
(b)
Figure 2. Crystal structure of 3 (a) and 4 (b) hydrogen atoms omitted for clarity.
A 1D linear polymeric chain is constructed upon 4. Conclusion
extending the asymmetric unit. The copper (II) cen-
tres in the polymeric chain adopted distorted square
pyramidal geometry defined by two oxygen donors
from acac, two nitrogens from 4-bzimpdpm and the
meso-benzimidazoyl nitrogen. Three Cu(II) centres in
1D polymeric chain oriented in such a way that
it generats isosceles triangle with side distances of
13.192 × 13.192 × 15.754 Å. The interplanar angle (ω)
between plane containing N(1)-Cu(1)-O(1) and N(2)-
Cu(1)-O(2) is 89.05◦, which is very close to the ideal
angle of 90◦. It strongly suggested that the donor sites
[N(1), N(2), O(1) and O(2)] lie in the same plane.
The Cu–N bond distances are comparable to the val-
ues reported in literature.20–22,38 The Cu–N (benzimi-
dazolyl) bond distances are 2.349 Å. The Cu–N and
Cu–O bond distances are relatively longer than those in
1 and 2. The bite angles N1–Cu–N2, O2–Cu1–O1, O2–
Cu1–N4, N2–Cu1–N4, O1–Cu1–N1, and O1–Cu1–N2
suggested slightly distorted square pyramidal geometry
about the Cu(II) centre (table 2).
Through this contribution we have presented three
novel meso-substituted dipyrrin ligands, and hete-
roleptic
[Cu(4-nimpdpm)(acac)],
complexes
[Cu3(4-impdpm)2(hfacac)4],
[Cu(4-nimpdpm)(hfacac)],
[{Cu(4-bimpdpm)(acac)}n], and [{Cu(4-bimpdpm)-
(hfacac)}n], based on it. The Cu(II) complexes impart
acetylacetonato (acac) and hexafluoroacetylaceto-
nato (hfacac) groups as ancillary ligands. It has been
observed that proper functionalization of heteroditopic
dipyrrins can lead to a variety of extended architectures
upon interaction with Cu(acac)2 and Cu(hfacac)2·H2O.
Further, it has been demonstrated that the meso-
substituent influences optical properties of the resulting
complexes. This approach seems promising for the
development of novel heteroleptic complexes.
Supplementary materials
X-ray crystallographic files in CIF format. Prepara-
tion of aldehydes, ESI-MS of 1–5 and some interest-
ing motifs resulting from weak interactions in 1, 3
and 4 are given as electronic supplementary informa-
tion. Helical 1D chain structure of 4 (S6), UV-vis and
fluorescence spectra of 1–5 (S10) and table for photo-
physical properties of 1–5 (table S1). For details, see
3.5 Supramolecular assemblies through weak
interactions
The weak interaction studies revealed the presence of www.ias.ac.in/chemsci website.
various types of weak interactions leading to interest-
ing motifs. Complex 1 displayed C–H· · · O (3.615 Å)
Acknowledgements
and C–H· · · π (3.57–3.74 Å) interactions leading to
formation a bi-layer structural motif (figure S7). The
outer layer of this motif consists of hfacac fragments,
wherein molecules have anti-parallel arrangement. In
complex 3, C–F· · · π (3.14 Å), C–H· · · π (3.61 Å),
π · · · π (3.29–3.37 Å) interactions lead to ladd-
er like motif (figure S8), while C–H· · · O (2.89 Å),
C–H· · · N (3.10 Å) and C–H· · · π (3.48 Å) interactions
in 4 are involved in the creation of independent infinite
1D polymer (figure S9).
We thank the Council of Scientific and Industrial
Research (CSIR), New Delhi for financial support
through the scheme 01(2361)/10/EMR-II and for
awarding JRF (09/013(0210)/-2009-EMR-I) to RKG.
We are also thankful to In-charge, National Single Cryst-
al X-ray Diffraction Laboratory, Indian Institute of
Technology, Powai, Mumbai and Indian Institute of
Technology, Kanpur for extending single crystal X-ray
facilities.

826
Rakesh Kumar Gupta et al.
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