Syntheses, structures and photoluminescent properties of cadmium(II), silver(I) and copper(I) complexes with novel long chain tetradentate ligands

Article abstract of DOI:10.1039/b300479a

Two new coordination complexes [Cd(L1)Br₂ (1) and [Ag ₃(L1)₂](ClO₄)₃ (2) were obtained by assembly reactions of CdBr₂ and AgClO₄ with long chain tetradentate ligand 1,6-bis(4-imidazol-1′-ylmethylphenyl)-2,5-diazahexane (L1). X-Ray diffraction analyses reveal that complex 1 is composed of neutral 2D grid networks, which are further linked by N-H ...Br and C-H ...Br hydrogen bonds to produce a 3D framework. Complex 2 with four- and two-coordinated silver(I) atoms has a double-stranded wandering chain structure formed by Ag-N coordination, Ag ...Ag and π-π interactions. Complexes [Ag(L2)]NO₃ (3), [Cu(L2)]ClO₄ (4) and [Cu(L2)]BF ₄ (5), with a relatively rigid long chain Schiff base ligand 1,6-bis(4-imidazol-1′-ylmethylphenyl)-2,5-diaza-1,5-hexadiene (L2), exhibit infinite ID zigzag chain structures. The results show that the structure of the assemblies is predominated by the nature of organic ligands and the geometric requirements of metal ions. The photoluminescent properties of the synthesized complexes were studied in the solid state at room temperature. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b300479a

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Syntheses, structures and photoluminescent properties of
cadmium(II), silver(I) and copper(I) complexes with novel long
chain tetradentate ligands
Xing-Mei Ouyang,a De-Jun Liu,a Taka-aki Okamura,b Hong-Wei Bu,a Wei-Yin Sun,*a
Wen-Xia Tanga and Norikazu Ueyamab
a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry,
Nanjing University, Nanjing 210093, China
b Department of Macromolecular Science, Graduate School of Science, Osaka University,
Toyonaka, Osaka 560-0043, Japan
Received 13th January 2003, Accepted 17th March 2003
First published as an Advance Article on the web 28th March 2003
Two new coordination complexes [Cd(L1)Br2] (1) and [Ag3(L1)2](ClO4)3 (2) were obtained by assembly reactions
of CdBr2 and AgClO4 with long chain tetradentate ligand 1,6-bis(4-imidazol-1Ј-ylmethylphenyl)-2,5-diazahexane
(L1). X-Ray diffraction analyses reveal that complex 1 is composed of neutral 2D grid networks, which are further
linked by N–H ؒ ؒ ؒ Br and C–H ؒ ؒ ؒ Br hydrogen bonds to produce a 3D framework. Complex 2 with four- and
two-coordinated silver() atoms has a double-stranded wandering chain structure formed by Ag–N coordination,
Ag ؒ ؒ ؒ Ag and π–π interactions. Complexes [Ag(L2)]NO3 (3), [Cu(L2)]ClO4 (4) and [Cu(L2)]BF4 (5), with a relatively
rigid long chain Schiff base ligand 1,6-bis(4-imidazol-1Ј-ylmethylphenyl)-2,5-diaza-1,5-hexadiene (L2), exhibit
infinite 1D zigzag chain structures. The results show that the structure of the assemblies is predominated by the
nature of organic ligands and the geometric requirements of metal ions. The photoluminescent properties of
the synthesized complexes were studied in the solid state at room temperature.
crystal engineering of coordination polymeric networks based
on multidentate ligands represents a growing area of coordin-
Introduction
In recent years, many efforts have been devoted to the design
and synthesis of pre-organized ligands that are able to control
the geometric and steric properties of metal ions.1–3 Metal–
organic frameworks with fascinating topologies, e.g. rotaxanes,
catenanes, helicates and knots, and interesting one- (1D), two-
(2D) and three-dimensional (3D) structures have been achieved
by assembly reactions of metal salts with organic ligands, for
example macrocycles, tripodal ligands, and short bidentate
N-donor rigid ligands.4–8 Although it has been reported that
long flexible chain-like bidentate ligands have the ability to
form unique interwoven extended structural motifs such as poly-
catenanes, polyrotaxane, double helixes and other species,9–12 it
is not well studied that long chain flexible ligands are used to
construct coordination polymers without interpenetration
compared with the short rigid ligands like 4,4Ј-bipyridine. The
ation and supramolecular chemistry. We focused our attentions
on the assembly of metal ions with flexible multidentate ligands
since they can adopt diverse coordination modes according to
the different geometric requirements of the metal ions.13 To
further expand our work, we designed and synthesized new
long chain flexible tetradentate ligands 1,6-bis(4-imidazol-1Ј-
ylmethylphenyl)-2,5-diazahexane (L1) and 1,6-bis(4-imidazol-
1Ј-ylmethylphenyl)-2,5-diaza-1,5-hexadiene (L2) (Scheme 1). In
these ligands, there are several salient points: (a) unlike rigid
groups such as 2,2Ј-bipyridine or 1,10-phenanthroine, the
ethylenediamine unit in L1 and L2 can adopt different con-
formations, which have been observed in our previous works;13
(b) the introduced aromatic rings can offer possible π–π inter-
actions which may stabilize the frameworks; (c) apart from
pyridyl group often used as the terminal groups, imidazole is
Scheme 1
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
1836

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also a good choice as a N-donor ligand. All these features
provide the networking ability of L1 and L2 ligands.
in methanol was layered over the buffer layer. Single crystals
appeared after several days. Yield: 47%. Calc. elem. anal. for
C24H34N6Br2CdO3: C, 39.66; H, 4.72; N, 11.56. Found: C, 39.47;
H, 4.72; N, 11.48.
We describe here the synthesis, structural characterization
and luminescent properties of coordination polymers, [Cd-
(L1)Br2] (1), [Ag3(L1)2](ClO4)3 (2), [Ag(L2)]NO3 (3), [Cu(L2)]-
ClO4 (4) and [Cu(L2)]BF4 (5) obtained by reactions of L1 with
CdBr2, AgClO4 and L2 with AgNO3, [Cu(CH3CN)4]ClO4 and
[Cu(CH3CN)4]BF4, respectively.
Preparation of [Ag3(L1)2](ClO4)3 (2)
All procedures for synthesis and measurements of the silver()
complex were performed in the dark. The compound was pre-
pared by layering method. A buffer layer of solution (10 ml) of
CHCl3 and methanol (3 : 1) was carefully layered over a CHCl3
solution of L1 (40.0 mg, 0.1 mmol). Then a methanol solution
of AgClO4 (20.8 mg, 0.1 mmol) in methanol was layered over
the buffer layer. Single crystals were obtained after several
weeks. Yield: 70%. Calc. elem. anal. for C48H56N12Ag3Cl3O12: C,
40.52; H, 3.97; N, 11.81. Found: C, 40.71; H, 3.92; N, 11.90.
Experimental
All commercially available chemicals are of reagent grade and
used as received without further purification. 4Ј-Formylbenzyl-
1-imidazole was prepared according to the literature method.14
Solvents were purified according to standard methods. Ele-
mental analyses for C, H and N were made on a Perkin-Elmer
240C elemental analyzer at the Analysis Center of Nanjing
University. 1H NMR spectra were measured on a Bruker
DRX500 MHz NMR spectrometer at room temperature. The
UV-vis spectral measurements were carried out on a Perkin-
Elmer Lambda 35 UV-VIS spectrophotometer. The lumin-
escent spectra for the solid samples were recorded at room
temperature on a Hitachi 850 fluorescence spectrophotometer.
A SLM 48000 DSCF fluorescence spectrometer was used to
perform the lifetime measurements.
Preparation of [Ag(L2)](NO3) (3)
The title complex was obtained similarly to complex 1 by using
L2 and AgNO3 instead of L1 and CdBr2ؒ4H2O, respectively.
Yield: 65%. Calc. elem. anal. for C24H24N7AgO3: C, 50.90; H,
4.27; N, 17.31. Found: C, 50.98; H, 4.29; N, 17.35.
Preparation of [Cu(L2)](ClO4) (4)
All procedures for synthesis of copper() complex were carried
out under an argon atmosphere. Solid L2 (39.6 mg, 0.1 mmol)
was added to a degassed acetonitrile solution (5 ml) of
[Cu(CH3CN)4]ClO4 (32.7 mg, 0.1 mmol) to give a yellowish
solution. Yellow single crystals suitable for X-ray diffraction
were obtained in 56% yield by slow diffusion of diethyl ether
into the reaction solution for several days. Calc. elem. anal. for
C24H24ClCuN6O4: C, 51.52; H, 4.32; N, 15.02. Found: C, 51.51;
H, 4.41; N, 15.04.
Caution: perchlorate salts of metal complexes with organic lig-
ands are potentially explosive and should be handled with care.
Preparation of 1,6-bis(4-imidazol-1Ј-ylmethylphenyl)-2,5-diaza-
1,5-hexadiene (L2)
A solution of 4Ј-formylbenzyl-1-imidazole (2.6 g, 13.7 mmol)
in 130 ml of CH3CN was added dropwise to 0.50 ml (7.5 mmol)
of ethylenediamine in 140 ml of CH3CN over 4 h at room
temperature with stirring and then, further stirred for 24 h. The
mixture was subsequently concentrated in vacuo to ca. 30 ml
and then allowed to stand at Ϫ18 ЊC overnight. The resulting
yellow precipitate was collected by filtration, washed with
diethyl ether and dried in vacuo to give L2 (2.1 g, 76%). Mp
Preparation of [Cu(L2)](BF4) (5)
The title complex was obtained similarly to complex 4 by using
[Cu(CH3CN)4]BF4 instead of [Cu(CH3CN)4]ClO4. Yield: 52%.
Calc. elem. anal. for C24H24BCuF4N6: C, 52.71; H, 4.42; N,
15.37. Found: C, 52.58; H, 4.60; N, 15.42.
1
151–152 ЊC. H NMR [500 MHz, (CD3)2SO]: δ 8.28 (s, 2H,
–CH᎐N–), 7.67 (d, 4H, Ph), 7.58 (s, 2H, imidazole), 7.24 (d, 4H,
᎐
Ph), 7.03 (s, 2H, imidazole), 6.96 (s, 2H, imidazole), 5.18 (s, 4H,
–CH2Ph–), 3.89 (s, 4H, –CH2CH2–). Calc. elem. anal. for
C24H24N6: C, 72.70; H, 6.10; N, 21.20. Found: C, 72.58; H, 6.19;
N, 21.15.
X-Ray crystal structure determinations
The data collections for complexes 1–5 were carried out on a
Rigaku RAXIS-RAPID Imaging Plate diffractometer using
graphite-monochromated Mo–Kα radiation (λ = 0.7107 Å) at
200 K. The structures were solved by direct method with
SIR92,15 and expanded using Fourier techniques.16 The absorp-
tion correction for all complexes was carried out by multi-scan
method. All data were refined anisotropically by the full-matrix
least-squares method on F 2 for non-hydrogen atoms. The
hydrogen atoms were generated geometrically. In complex 5, the
tetrafluoroborate anion is disordered. The atoms F2, F3 and F4
are located at two positions with site occupancy factors (s.o.f.)
of 0.617(13) and 0.383(13), respectively. All calculations were
carried out on SGI workstation using the teXsan crystallo-
graphic software package of Molecular Structure corpor-
ation.17 Details of the crystal parameters, data collection and
refinement for complexes 1–5 are summarized in Table 1, and
selected bond lengths and angles with their estimated standard
deviations are given in Table 2.
Preparation of 1,6-bis(4-imidazol-1Ј-ylmethylphenyl)-2,5-
diazahexane (L1)
2.1 g (5.3 mmol) of ligand L2 was dissolved in 150 ml MeOH.
Excess NaBH4 (1.0 g, 26.5 mmol) was added to the solution
with stirring at room temperature. After the addition of the
NaBH4 was completed, the reaction solution was continuously
stirred for 12 h and then evaporated to dryness, 20 ml H2O and
120 ml of CH2Cl2 were added to the mixture to extract the
product. The organic phase was separated, dried over Na2SO4
and evaporated to dryness under reduced pressure. After the
addition of diethyl ether, the white precipitate was obtained.
The product was recrystallized from MeOH (1.8 g, 88%).
1
Mp 117–119 ЊC. H NMR (500 MHz, D2O): δ 7.68 (s, 2H,
imidazole), 7.23 (d, 4H, Ph), 7.17 (d, 4H, Ph), 7.04 (s, 2H,
imidazole), 6.93 (s, 2H, imidazole), 5.13 (s, 4H, –CH2Ph–), 3.77
(s, 4H, –CH2NH–), 2.80 (s, 4H, –CH2CH2–). Calc. elem. anal.
for C24H28N6: C, 71.97; H, 7.05; N, 20.98. Found: C, 71.71; H,
7.30; N, 20.99.
CCDC reference numbers 201027–201031.
See http://www.rsc.org/suppdata/dt/b3/b300479a/ for crystal-
lographic data in CIF or other electronic format.
Preparation of [Cd(L1)Br2] (1)
Results and discussion
The title compound was prepared by layering method. A buffer
layer of solution (10 ml) of methanol and water (3 : 1) was
carefully layered over an aqueous solution of CdBr2ؒ4H2O
(34.4 mg, 0.1 mmol). Then a solution of L1 (40.0 mg, 0.1 mmol)
Crystal structure of [Cd(L1)Br2] (1)
Reaction of L1 with cadmium() bromide gives precipitate
immediately which may suggest polymeric species formed. Thus
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
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Table 1 Crystallographic data for complexes 1, 2, 3, 4 and 5
Complex
1
2
3
4
5
Empirical formula
Formula weight
Crystal system
Space group
C24H28Br2CdN6
672.74
Monoclinic
P21/c
C48H56Ag3Cl3N12O12
1423.01
C24H24AgN7O3
566.37
Monoclinic
C2/c
C24H24ClCuN6O4
559.48
Monoclinic
P21/c
C24H24BCuF4N6
546.84
Monoclinic
P21/c
Triclinic
¯
P1
a/Å
b/Å
c/Å
α/Њ
10.504(7)
11.790(7)
21.347(14)
90.00
97.46(3)
90.00
8.879(7)
9.997(12)
35.53(3)
94.69(9)
90.38(7)
115.90(8)
2824(5)
2
15.8499(4)
9.4345(4)
16.5889(6)
90.00
103.7920(10)
90.00
13.7180(7)
10.1127(7)
19.0653(10)
90.00
108.971(3)
90.00
13.70(2)
9.979(16)
19.23(4)
90.00
109.56(15)
90.00
β/Њ
γ/Њ
V/Å3
2621(3)
4
2409.11(15)
4
2501.2(3)
4
2478(8)
4
Z
T /K
200
3.905
200
1.241
200
0.878
200
1.023
200
0.936
µ/mmϪ1
Unique reflections
Observed reflections
Rint
R [I >2σ(I )]
wR [I >2σ(I )]
5876
3521
0.0821
0.0370
0.0528a
12802
7554
0.0578
0.0525
0.1303b
2755
2429
0.0256
5701
2025
0.0575
5647
2255
0.1550
0.0558
0.0996e
0.0310
0.0419
0.0740c
0.0606d
a w = 1/[σ2(F0)2 ϩ (0.0204P)2], where P = (F0 ϩ 2Fc2)/3. b w = 1/[σ2 (F0)2 ϩ (0.0799P)2], where P = (F0 ϩ 2Fc2)/3. c w = 1/[σ2 (F0)2 ϩ (0.0396P)2 ϩ
2
2
2.5281P], where P = (F02 ϩ 2Fc2)/3. d w = 1/[σ2(F0)2 ϩ (0.0217P)2], where P = (F02 ϩ 2Fc2)/3. e w = 1/[σ2 (F0)2 ϩ (0.0420P)2], where P = (F02 ϩ 2Fc2)/3.
Fig. 1 (a) The coordination environment around the cadmium() atom in [Cd(L1)Br2] (1); hydrogen atoms were omitted for clarity. (b) The 2D grid
network structure of 1; a π–π stacking interaction is indicated by a dotted line. (c) The 2D sheet consists of rhombohedral grids and only the
cadmium() atoms are presented. (d) The 3D structure of 1 linked by hydrogen bonds between the adjacent sheets.
the complex was prepared by layering method. The polymeric
structure of 1 was confirmed by X-ray single crystal struc-
ture determination. The coordination environment around the
Cd() atom is exhibited in Fig. 1a along with the atom
numbering scheme. Each Cd() atom is six-coordinated with a
distorted octahedral geometry by two bromide atoms at axial
positions [Cd(1)–Br(1), 2.8167(19) Å; Cd(1)–Br(2), 2.7500(19)
Å; Br(1)–Cd(1)–Br(2), 175.083(16)Њ, Table 2] and four nitrogen
atoms at the equatorial plane [Cd(1)–N, 2.291(3) ∼ 2.430(3) Å ],
two of which are from one ethylenediamine unit of one L1
ligand and two from imidazole N atoms of other two L1
ligands. Thus each Cd() atom links three L1 ligands and in
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
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Table 2 Selected bond distances (Å) and angles (Њ) for 1, 2, 3, 4 and 5a
[Cd(L1)Br2] (1)
Cd(1)–N(1)
Cd(1)–N(22)i
Cd(1)–Br(1)
2.400(3)
2.291(3)
2.8167(19)
Cd(1)–N(2)
Cd(1)–N(12)ii
Cd(1)–Br(2)
2.430(3)
2.371(3)
2.7500(19)
N(22)i–Cd(1)–N(12)ii
N(22)i–Cd(1)–N(1)
N(12)ii –Cd(1)–N(1)
N(22)i–Cd(1)–Br(2)
N(1)–Cd(1)–Br(2)
N(22)i–Cd(1)–Br(1)
N(1)–Cd(1)–Br(1)
Br(1)–Cd(1)–Br(2)
95.41(11)
104.41(11)
160.04(10)
92.81(8)
86.99(7)
90.60(8)
N(22)i–Cd(1)–N(2)
N(12)ii–Cd(1)–N(2)
N(1)–Cd(1)–N(2)
N(12)ii–Cd(1)–Br(2)
N(2)–Cd(1)–Br(2)
N(12)ii–Cd(1)–Br(1)
N(2)–Cd(1)–Br(1)
173.14(10)
84.72(11)
75.90(10)
89.68(8)
94.05(8)
86.47(8)
82.56(8)
95.59(7)
175.083(16)
[Ag3(L1)2](ClO4)3 (2)
Ag(1)–N(1)
Ag(1)–N(3)
Ag(2)–N(102)
Ag(3)–N(202)
Ag(2)–Ag(2)iii
2.461(5)
2.332(4)
2.100(5)
2.113(5)
3.081(3)
Ag(1)–N(2)
Ag(1)–N(4)
Ag(2)–N(402)
Ag(3)–N(302)
Ag(3)–Ag(3)iv
2.317(5)
2.423(6)
2.103(5)
2.119(5)
3.054(4)
N(2)–Ag(1)–N(3)
N(3)–Ag(1)–N(4)
N(3)–Ag(1)–N(1)
N(102)–Ag(2)–N(402)
N(402)–Ag(2)–Ag(2)iii
N(202)–Ag(3)–Ag(3)iv
139.24(15)
77.85(17)
133.40(15)
169.8(2)
90.07(15)
113.62(16)
N(2)–Ag(1)–N(4)
N(2)–Ag(1)–N(1)
123.34(16)
75.70(16)
110.70(17)
99.40(15)
168.68(18)
77.37(16)
N(4)–Ag(1)–N(1)
N(102)–Ag(2)–Ag(2)iii
N(202)–Ag(3)–N(302)
N(302)–Ag(3)–Ag(3)iv
[Ag(L2)](NO3) (3)
Ag(1)–N(12)
2.295(2)
Ag(1)–N(1)
2.352(2)
N(12)–Ag (1)–N(12)v
N(12)v–Ag (1)–N(1)
88.54(12)
127.90(8)
N(12)–Ag (1)–N(1)
N(1)–Ag (1)–N(1)v
120.87(8)
76.16(11)
[Cu(L2)](ClO4) (4)
Cu(1)–N(1)
1.984(3)
2.014(3)
Cu(1)–N(12)iii
Cu(1)–N(2)
2.001(3)
2.335(3)
Cu(1)–N(22)vi
N(1)–Cu(1)–N(12)iii
N(12)iii–Cu(1)–N(22)vi
N(12)iii–Cu(1)–N(2)
133.18(12)
105.79(11)
107.16(11)
N(1)–Cu(1)–N(22)vi
N(1)–Cu(1)–N(2)
N(22)vi–Cu(1)–N(2)
112.70(11)
82.30(11)
112.11(12)
[Cu(L2)](BF4) (5)
Cu(1)–N(1)
Cu(1)–N(22)
1.986(4)
2.000(5)
Cu(1)–N(12)
Cu(1)–N(2)
1.996(4)
2.318(5)
N(1)–Cu(1)–N(12)
N(12)–Cu(1)–N(22)
N(12)–Cu(1)–N(2)
132.85(17)
105.67(18)
107.7(2)
N(1)–Cu(1)–N(22)
N(1)–Cu(1)–N(2)
N(22)–Cu(1)–N(2)
112.55(17)
82.16(18)
112.75(18)
a Symmetry codes: (i) x, Ϫy ϩ 1.5, z ϩ 0.5; (ii) x, y ϩ 1, z; (iii) Ϫx ϩ 1, Ϫy, Ϫz ϩ 1; (iv) Ϫx ϩ 1, Ϫy, Ϫz Ϫ 1; (v) Ϫx, y, Ϫz ϩ 0.5; (vi) Ϫx ϩ 2, Ϫy,
Ϫz ϩ 1.
turn each L1 ligand connects three Cd() atoms to meet the
geometric requirement of the Cd() atom. Such a coordination
been reported in the biological system.18 For example, it has
been reported that the distance between the phenyl group of the
inhibitor Phe residue and the imidazole group of chymotrypsin
His57 is 3.75 Å indicating the presence of π–π stacking
interactions.18a
The 2D layers of complex 1 are packed in an –ABAB–
sequence and the Cd() atoms in one layer sit above or below
the grids of the adjacent layers (Fig. 1d). Consequently there
are no open channels in complex 1. Furthermore, the 2D layers
are linked by hydrogen bonds to generate a 3D structure. Two
bromide atoms, binding to one cadmium() atom, form a
N–H ؒ ؒ ؒ Br(1) hydrogen bond with one of the ethylenediamine
N–H from one adjacent layer and a C–H ؒ ؒ ؒ Br(2) one with an
imidazole C–H from another neighboring layer. The hydrogen
bonding data are summarized in Table 3.
mode gives complex
1 a neutral two-dimensional (2D)
rhombohedral grid network with (4,4) topology (Fig. 1b), in
which the cadmium() atoms are in the same plane. A simplified
2D network where only the Cd() atoms are presented is shown
in Fig. 1c. In each Cd4 rhombus, the Cd ؒ ؒ ؒ Cd edge distances
are 11.29
Å for Cd(1M) ؒ ؒ ؒ Cd(1O) and 11.79 Å for
Cd(1M) ؒ ؒ ؒ Cd(1D) (Fig. 1b), respectively. The internal angles
of the rhombus are 70.9 and 109.1Њ, respectively. In addition,
there are π–π interactions between the imidazole ring contain-
ing N(22F) and benzene ring containing C(11D) within each
Cd4 rhombus (Fig. 1b). The distance between the two ring cen-
troids is 3.51 Å and the dihedral angle is 3.3Њ. Such π-stacking
interactions between the imidazole ring and benzene ring have
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
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Table 3 Hydrogen bond data for the complexes 1, 2, 3, 4 and 5
Compound
D–H ؒ ؒ ؒ Aa
D ؒ ؒ ؒ A/Å
ЄD–H ؒ ؒ ؒ A/Њ
1
N(1)–H(1) ؒ ؒ ؒ Br(1)i
3.445(4)
3.639(5)
138
159
C(103)–H(25) ؒ ؒ ؒ Br(2)ii
2
N(2)–H(2) ؒ ؒ ؒ O(24)
N(3)–H(3) ؒ ؒ ؒ O(12)
3.125(7)
3.279(7)
3.080(10)
3.442(10)
3.400(9)
3.299(9)
3.445(10)
3.457(10)
3.265(14)
3.332(13)
3.229(10)
3.430(12)
145
149
142
158
142
153
164
158
132
149
144
153
N(4)–H(4) ؒ ؒ ؒ O(23)iii
C(13)–H(16) ؒ ؒ ؒ O(31)iv
C(27)–H(27) ؒ ؒ ؒ O(14)
C(32)–H(31) ؒ ؒ ؒ O(13)
C(37)–H(36) ؒ ؒ ؒ O(11)v
C(40)–H(37) ؒ ؒ ؒ O(24)iv
C(101)–H(45) ؒ ؒ ؒ O(33)
C(103)–H(47) ؒ ؒ ؒ O(31)iv
C(301)–H(51) ؒ ؒ ؒ O(14)v
C(402)–H(55) ؒ ؒ ؒ O(34)vi
3
C(10)–H(3) ؒ ؒ ؒ O(3)
3.354(7)
3.413(6)
3.477(13)
3.199(10)
3.361(8)
3.067(10)
3.330(9)
3.160(10)
141
156
161
149
148
137
137
130
C(13)–H(5) ؒ ؒ ؒ O(3)vii
C(17)–H(8) ؒ ؒ ؒ O(1)vii
C(17)–H(8) ؒ ؒ ؒ O(2)viii
C(101)–H(10) ؒ ؒ ؒ O(3)ix
C(101)–H(10) ؒ ؒ ؒ O(2)x
C(103)–H(12) ؒ ؒ ؒ O(2)xi
C(103)–H(12) ؒ ؒ ؒ O(1)xii
4
5
C(10)–H(5) ؒ ؒ ؒ O(4)xiii
C(101)–H(12) ؒ ؒ ؒ O(4)
C(27)–H(21) ؒ ؒ ؒ O(3)xiv
3.418(4)
3.337(5)
3.405(6)
164
150
148
C(10)–H(5) ؒ ؒ ؒ F(2)xv
C(17)–H(10) ؒ ؒ ؒ F(3)xvi
C(20)–H(12) ؒ ؒ ؒ F(4)xvii
C(27)–H(18) ؒ ؒ ؒ F(4)
C(101)–H(19) ؒ ؒ ؒ F(2)xvi
C(203)–H(24) ؒ ؒ ؒ F(1)xviii
3.358(10)
3.486(12)
3.304(11)
3.399(12)
3.350(11)
142
166
164
137
158
148
3.350(9)
a Symmetry codes: (i) Ϫx, 1 Ϫ y, 1 Ϫ z; (ii) 1 Ϫ x, Ϫ0.5 ϩ y, 1.5 Ϫ z; (iii) 1 ϩ x, 1 ϩ y, z; (iv) x, 1 ϩ y, z; (v) Ϫ1 ϩ x, Ϫ1 ϩ y, z; (vi) 1 Ϫ x, Ϫy, 1 Ϫ z;
(vii) x, Ϫ1 ϩ y, z; (viii) 0.5 Ϫ x, 0.5 Ϫ y, 1 Ϫ z; (ix) Ϫx, 1 Ϫ y, 1 Ϫ z; (x) Ϫ0.5 ϩ x, Ϫ0.5 ϩ y, z; (xi) Ϫx, Ϫ1 ϩ y, 0.5 Ϫ z; (xii) Ϫ0.5 ϩ x, 0.5 Ϫ y, Ϫ0.5
ϩ z; (xiii) x, 1 ϩ y, z; (xiv) 2 Ϫ x, Ϫy, 1 Ϫ z; (xv) x, Ϫ1 ϩ y, z; (xvi) 2 Ϫ x, 1 Ϫ y, Ϫz; (xvii) x, 0.5 Ϫ y, 0.5 ϩ z; (xviii) 1 Ϫ x, Ϫ0.5 ϩ y, Ϫ0.5 Ϫ z.
Crystal structure of [Ag3(L1)2](ClO4)3 (2)
the same two-coordinated silver() atom, however, to form a 2D
network.19 Such a difference between the topologies of complex
2 and [Ag3(L3)2](NO3)3ؒH2O is considered to be attributed to
the difference of the length and the flexible degree of the lig-
ands L1 and L3. It is noteworthy that, in addition to the Ag–N
coordination interactions, there are Ag ؒ ؒ ؒ Ag interactions
since the distances of Ag(2)–Ag(2A) and Ag(3)–Ag(3B) (atom
numbering shown in Fig. 2b) are 3.081(3) and 3.054(4) Å,
respectively, close to the 3.089(1) Å observed in the complex
[Ag(bpp)](CF3SO3) [bpp = 1,3-bis(4-pyridyl)propane],20 and
shorter than the 3.179(1) Å observed in the reported complex
[Ag3(py-hep)2](ClO4)3ؒ0.5CH3CN [py-hep = 1,7-bis(4Ј-pyridyl)-
2,6-diazaheptane].21 Furthermore, each pair of two imidazole
rings binding to Ag(2) and Ag(2A) atoms, are nearly parallel
with a dihedral angle of 7.6Њ and separated by a centroid–cen-
troid distance of 3.62 Å, indicating the presence of π–π stacking
interactions.22 However, such π–π stacking interactions between
two imidazole rings binding to the Ag(3) and Ag(3B) atoms are
much weaker since the corresponding dihedral angle and dis-
In contrast to the usual six-coordinated Cd() atom, the Ag()
atom can adopt different coordination numbers from two to
five according to its surrounding environments. When the
ligand L1 reacted with Ag() salt, for example AgClO4, instead
of CdBr2, a new coordination polymer 2 was obtained and
its structure was determined by X-ray crystallography. The
coordination mode in complex 2 was found to be remarkably
different from that in complex 1. As depicted in Fig. 2, the
silver() atoms in 2 have two different coordination environ-
ments. The Ag(1) with a distorted tetrahedral geometry is
coordinated by four ethylenediamine N atoms from two L1
ligands resulting a double-stranded helicate, similar to the pre-
vious reported silver() complexes with di-Schiff base ligands
1,2-bis(4Ј-pyridylmethyleneamino)ethane (L3) and 1,2-bis(3Ј-
pyridylmethyleneamino)ethane (L4).19 The four-coordinated
Ag(1) has N–Ag(1)–N bond angles ranging from 75.70(16) to
139.24(15)Њ and an average Ag(1)–N bond length of 2.383(8) Å
as listed in Table 2. Similar Ag–N bond lengths have been
reported for silver() complex with the same AgN4 binding site,
for example [Ag(L5)]NO3 [L5 = 1,6-bis(4Ј-pyridyl)-2,5-diaza-
hexane] has an average Ag–N bond length of 2.360(3) Å.13 In
addition to the four-coordinated silver() atoms, the N(102)–
Ag(2)–N(40D) angle of 169.8(2)Њ and N(20F)–Ag(3)–N(302)
angle of 168.68(18)Њ indicate that the Ag(2) and Ag(3) atoms
have near linear coordination geometry as shown in Fig. 2b.
The double-stranded helicates are linked through the coordin-
ation of these two-coordinated Ag() atoms with the terminal
imidazole groups of L1 ligands to generate an infinite 1D wan-
dering chain structure (Fig. 2b). In the reported complex with
the L3 ligand, [Ag3(L3)2](NO3)3ؒH2O, the helicates are linked by
Ϫ
tance are 24.4Њ and 3.92 Å, respectively. In complex 2, the ClO4
anions are located in the vacancy of the 1D chains and held
there by nine C–H ؒ ؒ ؒ O and three N–H ؒ ؒ ؒ O hydrogen bonds
Ϫ
between the ClO4 anions and cationic chains (Fig. 2c and
Table 3).
Crystal structures of [Ag(L2)](NO3) (3), [Cu(L2)](ClO4) (4) and
[Cu(L2)](BF4) (5)
To further investigate the effect of the nature of organic ligands
on the assembly, we prepared a long chain Schiff base ligand L2
by reducing the flexibility of the ligand L1 and reactions of
L2 with Ag() and Cu() salts were carried out.
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
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Fig. 2 (a) A perspective view of double-stranded helicate motif in the structure of [Ag3(L1)2](ClO4)3 (2). (b) The 1D infinite wandering chain with
Ag ؒ ؒ ؒ Ag interactions. (c) The packing diagram of 2 with hydrogen bonds indicated by dashed lines.
When the ligand L2 reacts with silver() nitrate, a novel
coordination complex [Ag(L2)](NO3) (3) was obtained. The
crystallographic analysis reveals that complex 3 is composed
of an infinite 1D cationic chain, which is different from that
of complex 2 (Scheme 2). The coordination environment of
silver() atom is shown in Fig. 3a with the atom numbering
scheme. Each silver() atom is coordinated by two nitrogen
atoms of an ethylenediimine unit from one L2 ligand and two
imidazole nitrogen atoms from other two L2 ligands. Thus the
coordination geometry of the Ag() atom is distorted tetra-
hedral with the average Ag(1)–N bond length 2.323(1) Å and
N–Ag(1)–N bond angles ranging from 76.14(8) to 128.1(2)Њ.
Therefore, complex 3 shows an infinite 1D zigzag chain struc-
ture (Fig. 3b). The coordination mode of silver() atoms in 3 is
same as the one in the previous reported complex [Ag(L5)]-
NO3,13 that exhibited an infinite 1D hinged chain structure. The
L5 has a “Z” shape in this hinged chain due to the flexibility of
L5 while the shape of L2 in 3 is “U”. The formation 1D zigzag
chain of 3 is attributed to the long chain structure of L2. The
NO3Ϫ anions occupy the voids among the chains through eight
C–H ؒ ؒ ؒ O hydrogen bonds as shown in Fig. 3c and Table 3.
To investigate the influence of metal ion and anion on the
structures of assembly product, reactions of L2 with copper()
salts with different anions were carried out, and complexes 4
and 5 were obtained, since the copper() is usually four-
coordinated with tetrahedral geometry. The results of crystal-
lographic analyses indicate that the complexes 4 and 5
crystallize in the same monoclinic space group P21/c as listed in
Table 1. It is clear that the two compounds are isomorphous
and isostructural, which implies that the anions have no obvi-
ous influence on the structure of these complexes. In the
reported complexes with the flexible ligand L5, it has been
demonstrated that the anions play an important role in deter-
mining the structure of complexes.13 In both complexes 4 and 5,
each copper() atom is coordinated by two nitrogen atoms from
Scheme 2
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
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Fig. 3 (a) A part of the cationic structure of [Ag(L2)]NO3 (3); hydrogen atoms were omitted for clarity. (b) An infinite zigzag chain structure in 3.
(c) The packing diagram of 3 with hydrogen bonds indicated by dashed lines.
a diimine unit of one L2 ligand and two imidazole nitrogen
atoms from other two L2 ligands (Fig. 4). This coordination
mode in 4 and 5 is very similar to that of complex 3. However,
there is difference between the structures of complexes 3 and 4
(as well as 5). The two benzene ring planes of one L2 ligand
in complex 3 are almost parallel each other since the dihedral
angle between them is 3.6Њ and the Ag(1A) ؒ ؒ ؒ Ag(1B) (Fig. 3a)
non-bonded distance is 16.59 Å, while the corresponding
dihedral angle and Cu(1A) ؒ ؒ ؒ Cu(1B)distance are 98.0Њ and
13.72 Å in complex 4, and 98.3Њ and 13.70 Å in complex 5,
respectively. This means that the complexes 4 and 5 are com-
pressed zigzag chains compared with that of complex 3. There-
fore, the metal ions with the same coordination geometry react
with relatively rigid ligand L2 to form complexes with same
topology but subtle difference in their structures as observed in
complexes 3 and 4 (as well as 5). The anions of 4 are located in
the voids of the chains and held there by C–H ؒ ؒ ؒ O hydrogen
bonds as shown in Fig. 4c and Table 3.
at 485 nm, τ = 4.23 ns) under the same conditions as illustrated
in Fig. 5. Thus, the emission observed in complex 1 is tentatively
assigned to the intraligand fluorescence. In the case of complex
2, a blue shifted photoluminescence with the maximum emis-
sion at 464 nm (τ = 1.54 ns) and weaker intensity compared with
those of 1 and L1 was observed. It is rare that silver() com-
plexes can emit photoluminescence at room temperature.23–25
The photoluminescent property of complex 2 may be attributed
to the Ag–N coordination and Ag ؒ ؒ ؒ Ag interactions as
mentioned above, which is same as in the reported complex
[Ag3(py-hep)2](ClO4)3ؒ0.5CH3CN.21 The UV-vis spectra of the
complexes and ligands were measured in the solid state at room
temperature. The complexes 1 and 2 show high-energy band
around 250 nm, which can be readily assigned to the intraligand
π–π* transitions of the ligands, since similar band around
250 nm was also observed for L1.
The luminescent spectra of complexes 3 and 4 as well as
ligand L2 in the solid state at room temperature are shown in
Fig. 6. Complex 3 exhibits an intense broad photoluminescence
with maximum emission at ca. 462 nm (τ = 1.36 ns) upon excit-
ation at 394 nm, which is near to the maximum emission at
459 nm (τ = 1.56 ns) of the free ligand L2 under the same
conditions. Therefore the luminescence observed in 3 is attrib-
uted to the intraligand luminescent emission. In contrast to the
very similar emission maximum and lifetime of complex 3 and
L2, complex 2 showed blue-shifted emission with short lifetime
Photoluminescent properties of complexes 1–4
The photoluminescent properties of the synthesized complexes
were studied in the solid state at room temperature. 2D grid
network complex 1 exhibits a broad blue-fluorescent emission
around 480 nm (lifetime τ = 3.15 ns) upon excitation at 394 nm,
which is quite similar to that of ligand L1 (emission maximum
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
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Fig. 4 (a) The coordination environment around the copper() atom in [Cu(L2)]ClO4 (4); hydrogen atoms were omitted for clarity. (b) An infinite
zigzag chain structure in 4. (c) The crystal packing diagram of 4 with hydrogen bonds indicated by dashed lines.
Fig. 6 The emission spectra of (a) ligand L2, (b) complex 3,
(c) complex 4 in the solid state at room temperature, λexc = 394 nm for
L2 and 3 and λexc = 250 nm for 4.
Fig. 5 The emission spectra of (a) ligand L1, (b) complex 1 and
(c) complex 2 in the solid state at room temperature, λexc = 394 nm.
D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
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compared with those of ligand L1 as mentioned above. Such
differences in maximum emission and lifetime between complex
2 and L1 may probably be caused by Ag ؒ ؒ ؒ Ag interactions in
2, since no such interactions were found in 3 as revealed by
crystal structure analyses. It has been suggested that Ag ؒ ؒ ؒ Ag
interactions may have impact on the emissions.26
in complex 2 is very different from that in complex 3. In com-
plex 2, the silver() atoms have two types, namely, four- and two-
coordinate, while the complex 3 only contains four-coordinated
silver() atoms. The results are assigned to the different flexi-
bility of long chain ligands L1 and L2 and demonstrate the
important role of the nature of ligand on the assembly.
In the emission spectrum of complex 4 (Fig. 6c), a weak
photoluminescence with maximum emission at ca. 574 nm was
observed upon excitation at 250 nm. Similar photolumines-
cence has been reported for the 2D layered Cu() coordination
polymer with maximum emission at ca. 580 nm (ca. τ = 1.06 ns,
λex = 250 nm).27 The UV-vis spectrum of complex 4 exhibits a
low-energy band at ca. 402 nm in the solid state, which corre-
sponds to the metal-to-ligand charge transfer (MLCT).28 How-
ever, the metal center d to s orbital transition could not be
completely ruled out.27 It is well known that low-energy emis-
sions of [Cu(NN)2]ϩ (NN = 2,9-disubstituted-1,10-phenanthro-
line) systems are usually assigned to the metal-to-ligand d–π*
charge transfer (MLCT) and hence the observed luminescence
of 4 can be ascribed to the MLCT emission similar to the
reported Cu() complexes.29–31
During the past decades, the photoluminescence properties
of copper() complexes, especially with 2,9-disubstituted-1,10-
phenanthroline ligands, have been extensively examined.29 The
results showed that the emission behavior of these Cu() com-
plexes, e.g. emission wavelength, excited state lifetime, is quite
changeable depending on the chemical nature, size, and pos-
ition of substituents and distortions of the structure. To inhibit
the flattening distortion of the excited state, bulky substituents
in the ligands were introduced, and as a result, fluorescent
properties of their Cu() complexes were improved.29 On the
other hand, McMillin et al. reported the luminescent property
of a bis(phenanthroline)copper() complex without such steric
substituents in the solid state.31a The observation of this lumin-
escence is ascribed to the small flattening distortion probably
due to the packing interactions in the crystal, which prevent
further distortion in the photoexcited state. Compared with
these [Cu(NN)2]ϩ complexes, the coordination polymer 4, in
which the coordinated N atoms are of mixed types (two imino
Ns and two imidazole Ns), shows both flattening and rocking
distortions in the solid.32 The flattening distortion is demon-
strated by a dihedral angle of 98.7Њ between the planes defined
by Cu(1), N(1), N(2) and by Cu(1), N(12A), N(22B) (Fig. 4a),
and the rocking distortion is reflected by a long Cu(1)–N(2)
bond length [2.335(3) Å] compared with other three bonds
(Table 2) and an approximately pyramidal coordination geom-
etry around the copper() atom. Such distortions in the crystal
are probably induced by crystal packing interactions that
may also oppose further distortion in the excited state,31a and
as a consequence the coordination polymer 4 shows a weak,
short-lived emission (ca. τ = 1.7 ns) in the solid.
Acknowledgements
This work was supported by National Natural Science Found-
ation of China (Grant No. 20231020).
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Conclusion
The present study shows that the reactions of new long-chain
ligands L1 and L2 with various metal salts can afford a variety
of fascinating self-assembled polymeric frameworks. The dif-
ference between ligands L1 and L2 is that the former is more
flexible than the latter. Flexible ligand L1 can adjust its con-
formations to fit with the geometrical needs of transition metal
ions. In complex 1, ligand L1 adopts the compressed W-shape
to give a 2D rhombic grid network when it reacted with
cadmium() bromide. In the reaction with Ag() salt, long-chain
ligand L1 adopts conformations of U- and W-shapes to meet
the geometric need of four-coordinated and two-coordinated
Ag() atoms to form an infinite wandering 1D chain in complex
2 (Scheme 2). The relatively rigid ligand L2 only adopts a
U-shape conformation in complexes 3, 4 and 5 and its com-
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2). On the other hand, the coordination mode of silver() atoms
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D a l t o n T r a n s . , 2 0 0 3 , 1 8 3 6 – 1 8 4 5
1845