Four metal-organic networks based on benzene-1,4-dioxyacetic acid and dipyrido[3,2-a:2′,3′-c]phenazine ligand

Article abstract of DOI:10.1016/j.ica.2009.12.056

Four structurally diverse complexes, [Cd(dppz)(bdoa)]_n (1), [Zn(dppz)(bdoa)(H₂O)]_n (2), [Fe(dppz)₂(bdoa)]_n·2nH₂O (3), and [Co₂(dppz)₂(bdoa)₂(H₂O)]_n·3nH₂O (4), where H₂bdoa = benzene-1,4-dioxyacetic acid and dppz = dipyrido[3,2-a:2′,3′-c]phenazine, have been hydrothermally synthesized. Compounds 1-4 feature chain structures. There exist π-π interactions in the structures of 1, 2 and 4. Two neighboring chains of 1 are linked through the π-π interactions into a double chain supramolecular structure. The chains of 2 and 4 are further extended by the π-π interactions to form 3D and 2D supramolecular structures, respectively. The structural differences among such complexes show that the transition metals have important influences on their structures. The photoluminescent property of complex 2 and the magnetic property of complex 4 have also been investigated.

Full text of DOI:10.1016/j.ica.2009.12.056

Inorganica Chimica Acta 363 (2010) 1359–1366
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Four metal–organic networks based on benzene-1,4-dioxyacetic acid
and dipyrido[3,2-a:20,30-c]phenazine ligand
b
b
b
Xiuying Li a, Chunbo Liu b,c, Guangbo Che b,c, , Xiangcheng Wang , Chunxiang Li , Yongsheng Yan ,
*
Qingfeng Guan a,
*
a School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China
b School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China
c Department of Chemistry, Jilin Normal University, Siping 136000, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 October 2009
Received in revised form 24 December 2009
Accepted 29 December 2009
Available online 6 January 2010
Four structurally diverse complexes, [Cd(dppz)(bdoa)]n (1), [Zn(dppz)(bdoa)(H2O)]n (2), [Fe(dppz)2(b-
doa)]nꢀ2nH2O (3), and [Co2(dppz)2(bdoa)2(H2O)]nꢀ3nH2O (4), where H2bdoa = benzene-1,4-dioxyacetic
acid and dppz = dipyrido[3,2-a:20,30-c]phenazine, have been hydrothermally synthesized. Compounds
1–4 feature chain structures. There exist
chains of 1 are linked through the
chains of 2 and 4 are further extended by the
p
–
p
interactions in the structures of 1, 2 and 4. Two neighboring
interactions into a double chain supramolecular structure. The
interactions to form 3D and 2D supramolecular struc-
p–p
p–p
Keywords:
Benzene-1,4-dioxyacetic acid
Dipyrido[3,2-a:20,30-c]phenazine
p–p Interactions
Transition metals
tures, respectively. The structural differences among such complexes show that the transition metals
have important influences on their structures. The photoluminescent property of complex 2 and the mag-
netic property of complex 4 have also been investigated.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
is that the –OCH2– group makes this ligand more flexible in com-
parison with the corresponding benzenedicarboxylate [3]. Herein,
In the area of crystal engineering, the deliberate control of
structure, property and function, is a long-term objective being
vigorously pursued by chemists [1–4]. In this regard, much
progress has been made on the design and synthesis of novel
coordination frameworks and the relationships between their
we report four novel complexes with different structures by vary-
ing the transition metals. The photoluminescent property of com-
plex 2 and the magnetic property of complex 4 have also been
studied.
structures and properties [5–10]. The
p–p interaction is one of
2. Experimental
the most powerful non-covalent intermolecular interactions for
directing the supramolecular architectures or influencing the phys-
ical properties of final products [11–14]. Therefore, the design of
versatile functional ligands which are capable of providing the
2.1. General
All reagents of analytical grade were purchased and used with-
out further purification. The neutral chelating ligand dppz was syn-
thesized according to the literature [19,20]. A Perkin–Elmer 240
elemental analyzer was used to collect microanalytical data. The
photoluminescent properties of the ligands and compounds were
measured on a Perkin–Elmer LS55 spectrometer.
p-conjugated system for organizing their complexes into extended
networks is quite desirable. 1,10-Phenanthroline derivatives such
as pyrazino[2,3-f][1,10]phenanthroline and 2-phenyl-1H-1,3,7,8,-
tetraaza-cyclopenta[l]- phenanthrene are good candidates for con-
struction of metal-organic supramolecular architectures through
p–p interactions. Up to now, the reports of this field are scarce
[15–18]. In this contribution, we selected dipyrido[3,2-a:20,30-
c]phenazine (dppz) as the neutral chelating ligands (Scheme 1).
Benzene-1,4-dioxyacetic acid (H2bdoa) was selected as organic
acid (Scheme 2). This ligand has rarely been used in the field of
crystal engineering and supramolecular chemistry to construct
coordination polymers. A potentially valuable feature of the ligand
2.2. Syntheses of the complexes
2.2.1. Synthesis of [Cd(dppz)(bdoa)]n (1)
A mixture of Cd(OH)2 (0.059 g, 0.40 mmol), H2bdoa (0.090 g,
0.40 mmol), dppz (0.113 g, 0.40 mmol), and water (8 mL) was stir-
red for 10 min in air. The mixture was transferred and sealed in a
Teflon reactor (15 mL) and heated at 160 °C for 3 days. After the
mixture had been cooled to room temperature at 10 °C/h, colorless
block crystals were obtained. Yield: 45% based on Cd(II). IR (KBr,
* Corresponding authors. Tel.: +86 0511 88790683 (G. Che).
E-mail address: guangbochejl@yahoo.com (G. Che).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.12.056

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X. Li et al. / Inorganica Chimica Acta 363 (2010) 1359–1366
O
N
O
N
N
N
N
NH2 NH2
N
N
N
dppz
Scheme 1. Structure of the dppz ligand.
COOH
O
Table 2
Selected bond distances (Å) and angles (o) for 1–4.
Complex 1
Cd–O(6)
Cd–O(2)
Cd–O(1)
Cd–N(1)
Cd–N(2)
2.369(11)
2.455(11)
2.616(10)
2.670(12)
2.717(10)
O(6)–Cd–O(2)
O(2)–Cd–O(1)
O(1)–Cd–N(1)
O(6)–Cd–N(1)
O(2)–Cd–N(1)
81.0(4)
50.8(4)
126.7(4)
85.1(4)
77.2(4)
O
HOOC
H bdoa
2
Scheme 2. Structure of the H2bdoa acid.
Complex 2
Zn–O(1W)
Zn–O(4)
Zn–O(1)
Zn–N(1)
Zn–N(2)
1.984(3)
2.020(2)
2.074(2)
2.110(3)
2.196(3)
O(1W)–Zn–O(4)
O(4)–Zn–N(2)
O(4)–Zn–O(1)
O(1W)–Zn–N(1)
O(4)–Zn–N(1)
91.61(13)
168.35(10)
93.04(10)
105.26(11)
91.70(10)
cmꢁ1): 3604 s, 3421 s, 3125 m, 2942 m, 2364 w, 1616 s, 1546 s,
1461 s, 1390 s, 1137 m, 1081 m, 939 w, 855 w, 742 s. Anal. Calc.
for C28H18CdN4O6: C, 54.34; H, 2.93; N, 9.05. Found: C, 54.44; H,
2.85; N, 9.12%.
Complex 3
Fe–O(1)
Fe–N(2)
Fe–N(1)
2.054(2)
2.253(3)
2.262(3)
N(2)A–Fe–N(1)
O(1)A–Fe–N(1)
O(1)–Fe–O(1)A
O(1)A–Fe–N(2)A
N(2)–Fe–N(1)
106.78(9)
86.44(9)
180.0
92.45(9)
73.22(9)
2.2.2. Synthesis of [Zn(dppz)(bdoa)(H2O)]n (2)
The preparation of 2 was similar to that of 1 except that ZnCO3
was used instead of Cd(OH)2. Colorless block crystals were ob-
tained in a 41% yield based on Zn(II). IR (KBr, cmꢁ1): 3357 s,
3104 s, 2357 w, 1626 s, 1476 s, 1358 s, 1148 m, 1073 m, 954 m,
834 m, 790 s, 700 s. Anal. Calc. for C28H20ZnN4O7: C, 57.01; H,
3.42; N, 9.50. Found: C, 57.15; H, 3.47; N, 9.43%.
Complex 4
Co(1)–O(11)
Co(1)–O(7)
Co(1)–O(1)
Co(1)–N(2)
Co(1)–O(4W)
Co(1)–N(1)
Co(2)–O(12)
Co(2)–O(8)
Co(2)–O(5)
Co(2)–N(5)
Co(2)–O(4W)
Co(2)–N(6)
2.0481(18)
2.1138(18)
2.1149(19)
2.124(2)
2.1483(19)
2.153(2)
2.0478(19)
2.0648(19)
2.105(2)
O(11)–Co(1)–O(1)
O(7)–Co(1)–O(4W)
O(7)–Co(1)–N(2)
N(2)–Co(1)–N(1)
O(4W)–Co(1)–N(1)
O(1)–Co(1)–N(1)
O(8)–Co(2)–O(5)
O(5)–Co(2)–N(6)
O(12)–Co(2)–O(4W)
O(4W)–Co(2)–N(6)
O(12)–Co(2)–N(5)
O(5)–Co(2)–N(5)
178.96(8)
94.73(7)
91.54(7)
77.16(8)
97.67(8)
93.66(8)
177.01(9)
92.06(9)
93.29(7)
99.72(8)
89.37(8)
89.98(8)
2.2.3. Synthesis of [Fe(dppz)2(bdoa)]nꢀ2nH2O (3)
The preparation of 3 was similar to that of 1 except that FeCl2
was used instead of Cd(OH)2. Red block crystals were obtained in
a 27% yield based on Fe(II). IR (KBr, cmꢁ1): 3479 s, 3119 s, 1626 s,
1574 s, 1526 m, 1504 m, 1439 m, 1342 s, 1248 m, 1111 m,
1095 m, 1032 w, 953 m, 768 s, 733 s, 656 m. Anal. Calc. for
C23H16Fe0.50N4O4: C, 62.74; H, 3.66; N, 12.72. Found: C, 62.61; H,
3.64; N, 12.81%.
2.125(2)
2.1246(18)
2.150(2)
Symmetry code for A: ꢁx + 2, ꢁy + 2, ꢁz.
Table 1
Crystallographic data for compounds 1–4.
Compound
1
2
3
4
Formula
C28H18CdN4O6
618.86
C28H20ZnN4O7
589.85
C23H16Fe0.50N4O4
440.32
C56H40Co2N8O16
1198.82
P21/c
0.26 ꢂ 0.16 ꢂ 0.15
20.0618(14)
13.1722(9)
21.1529(15)
90
111.5340(10)
90
5199.7(6)
4
0.720
1.033
Formula mass
Space group
Crystal size (mm)
a (Å)
b (Å)
c (Å)
ꢀ
ꢀ
ꢀ
P1
P1
P1
0.15 ꢂ 0.10 ꢂ 0.09
8.5900(17)
12.220(2)
12.960(3)
109.23(5)
100.10(4)
96.42(3)
1243.4(4)
2
0.931
0.18 ꢂ 0.15 ꢂ 0.10
9.5276(14)
11.3497(17)
11.9147(18)
101.551(2)
92.166(2)
93.645(2)
1258.1(3)
2
0.21 ꢂ 0.17 ꢂ 0.11
8.1485(16)
9.9529(19)
12.467(2)
110.590(2)
96.225(4)
95.175(2)
931.9(3)
a
(°)
b (°)
c
(°)
V (Å3)
Z
2
V (mmꢁ1
)
1.033
0.848
0.478
1.021
Goodness-of-fit (GOF) on F2
1.074
Reflections collected/unique
10 787/4883
1.653
1.99–26.09
0.0705, 0.2007
0.0885, 0.2214
10 906/4938
1.557
2.14–26.09
0.0437, 0.0572
0.0942, 0.0681
8092/3667
1.569
2.21–26.07
0.0524, 0.1155
0.0899, 0.1351
44 016/10 331
1.531
2.18–26.14
0.0402, 0.1030
0.0611, 0.1144
Dcalc (Mg mꢁ3
h Range (°)
)
R (I > 2r(I))
R (all data)

X. Li et al. / Inorganica Chimica Acta 363 (2010) 1359–1366
1361
Fig. 1. (a) The coordination environment of the Cd(II) center in compound 1. (b) The 1D chain structure. (c) The supramolecular chain formed through
interactions. Symmetry codes: (A) x + 1, ꢁ1 + y, z; (B) x, y + 1, z.
p
–p
stacking
2.2.4. Synthesis of [Co2(dppz)2(bdoa)2(H2O)]nꢀ3nH2O (4)
2.3. X-ray crystallography
The preparation of 4 was similar to that of 1 except that CoCO3
was used instead of Cd(OH)2. Purple block crystals were obtained
in a 33% yield based on Co(II). IR (KBr, cmꢁ1): 3566 s, 3447 s,
3268 s, 2939 m, 2327 w, 1805 w, 1551 s, 1416 s, 1267 s, 1193 m,
1133 m, 999 m, 864 m, 789 s, 730 s, 625 w. Anal. Calc. for C56H38Co2-
N8O16: C, 56.20; H, 3.20; N, 9.36. Found: C, 56.26; H, 3.15; N, 9.51%.
Diffraction data for complexes 1–4 were recorded on a Bruker-
AXS Smart CCD diffractometer, using a scan technique with Mo
radiation (k = 0.71073 Å) at 293(2) K. All the structures were
x
Ka
solved by direct method of SHELXS-97 [21] and refined by full-matrix
least-squares techniques using the SHELXL-97 [22] program.

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Fig. 2. (a) The coordination environment of the Zn(II) center in compound 2. (b) The 1D chain structure. (c) The 3D supramolecular structure formed through
interactions. Symmetry codes: (A) ꢁx, ꢁy ꢁ 1, ꢁz; (B) ꢁxꢁ1, ꢁy, 1 ꢁ z.
p–p stacking

X. Li et al. / Inorganica Chimica Acta 363 (2010) 1359–1366
1363
Fig. 3. (a) The coordination environment of the Fe(II) center in compound 3. (b) The 1D chain structure. Symmetry codes: (A) 2 ꢁ x, ꢁy + 2, ꢁz; (B) 3 ꢁ x, 1 ꢁ y, ꢁz; (c) ꢁ1 + x,
1 + y, z.
Non-hydrogen atoms were refined with anisotropic temperature
parameters, and hydrogen atoms of the ligands were refined as
rigid groups. The H atoms of two lattice water molecules in
compound 4 could not be positioned reliably. Other H atoms of
water molecules were located from difference Fourier maps.
Further details for structural analysis are summarized in Table 1.
Selected bond distances and angles for compounds 1–4 are shown
in Table 2.
3.1.2. Structure description of [Zn(dppz)(bdoa)(H2O)]n (2)
As shown in Fig. 2a, the Zn atom of 2 is five-coordinated by two
nitrogen atoms from one dppz ligand, two carboxylate oxygen
atoms from two different bdoa anions, and one water molecule.
The Zn–O (1.984(3)–2.074(2) Å) and Zn–N (2.110(3)–2.196(3) Å)
bond lengths are all within the normal ranges [24,25]. Each bdoa
anion coordinates to two Zn atoms with its bis-monodentate car-
boxylate oxygen atoms, and the Zn atoms are bridged by bdoa an-
ions to form a chain (Fig. 2b). The dppz ligands are attached to the
Zn atoms, acting as a bidentate ligand. Unlike the structure of 1, the
dppz ligands in 2 are extended on two sides of the chain. As shown
in Fig. 2c, the dppz ligands from neighboring chains are well
matched with each other, and adjacent chains are linked through
3. Results and discussion
3.1. Description of crystal structures
p–p stacking interactions between two dppz rings (with the cen-
3.1.1. Structure description of [Cd(dppz)(bdoa)]n (1)
troid–centroid distance of 3.53 Å, face-to-face distance of 3.45 Å,
and dihedral of 4.04°), which extend the chains into a 3D supramo-
Single-crystal X-ray diffraction reveals that the structure of
compound 1 is a 1D chain. As shown in Fig. 1a, the cadmium ion
is five-coordinated in a distorted square-pyramidal environment
by two nitrogen atoms from one dppz ligand and three oxygen
atoms from two bdoa anions. The bond lengths of Cd–O
(2.369(11)–2.616(10) Å) and Cd–N1 (2.670(12) Å) are all within
the normal ranges; the bond length of Cd–N2 (2.717(10) Å) is a lit-
tle bit longer, but shorter than the van der Waals contact distance
for Cd–N of 3.17 Å [23]. Cd ions are bridged by bdoa anions to form
a 1D chain structure (Fig. 1b). As shown in Fig. 1c, there exist face-
lecular structure. It is believed that the very strong
p–p stacking
interactions play an important role in stabilizing the 1D chain
and the 3D supramolecular structure [26–28].
3.1.3. Structure description of [Fe(dppz)2(bdoa)]nꢀn2H2O (3)
As shown in Fig. 3a, Fe atom lies at an inversion center and is
six-coordinated by four nitrogen atoms from two dppz ligands,
and two carboxylate oxygen atoms from two bdoa anions. The dis-
tances of the Fe–O bond (2.054(2) Å) and Fe–N bonds (2.253(3)–
2.262(3) Å) are near to those of reported [29,30]. The Fe atoms
are bridged by bdoa molecules forming a 1D chain. The dppz
ligands are attached on both sides of the chains. Unlike the struc-
to-face p–p interactions between the dppz ring and phenyl ring of
bdoa anion of adjacent chain (with centroid-to-centroid distance of
3.56 Å, face-to-face distance of 3.38 Å, and dihedral of 4.09°),
resulting in a double chain structure of 1.
tures of 1 and 2, there exists no
p–p interaction in the structure.

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Fig. 4. (a) The coordination environment of the Co(II) center in compound 4. (b) Polyhedral representation of the 1D chain structure of 4. (c) The
supramolecular layer formed through
stacking interactions. Symmetry codes: (A) ꢁx, ꢁy + 2, ꢁz; (B) x, ꢁy + 1.5, 0.5 + z.
p–p interactions. (d) The 2D
p–p

X. Li et al. / Inorganica Chimica Acta 363 (2010) 1359–1366
1365
ꢁ1
Fig. 5. Solid-state photoluminescent spectrum of 2 at room temperature.
Fig. 6. Plots of the temperature dependence of
triangles) for compound 4.
vmT (open squares) and vm (open
The lattice water molecule is hydrogen-bonded to carboxylate oxy-
gen atom, stabilizing the chain structure of 3.
toluminescent emission of 2 may be attributed to the intraligand
fluorescent emissions of dppz [8,34].
3.1.4. Structure description of [Co2(dppz)2(bdoa)2(H2O)]nꢀ3nH2O (4)
As shown in Fig. 4a, the structure of 4 contains two kinds of
unique Co atoms. Both Co1 and Co2 are six-coordinated by three
oxygen atoms from three bdoa anions (Co–O 2.0478(19)–
3.3. Magnetic property
The temperature-dependent magnetic susceptibility data of
compound 4 has been measured for polycrystalline samples at an
applied magnetic field of 1000 Oe in the temperature range of 2–
2.1149(19) Å), one
l2-H2O (Co–O4W 2.1246(18)–2.1483(19) Å)
and two N atom from dppz ligand (Co–N 2.124(2)–2.153(2) Å).
Two carboxylate groups of bdoa anion adopt bis-monodentate
mode, and coordinate with Co1 and Co2, respectively. The rest of
300 K (Fig. 6). For 4, the
(5.55 B), which is consistent with the expected value (3.75
cm3 molꢁ1 K, 5.48 B) of two isolated S = 3/2 spin-only CoII ions
(g = 2.0). Upon cooling, the values of mT keep smoothly decreasing
v K
mT value at 300 K is 3.85 cm3 molꢁ1
l
l
bdoa anion displays a
l-4 bis-bidentate coordination mode. The
v
Co centers are connected by
l
2-H2O and bdoa anions to form a
in 300–2.0 K range, indicating an overall antiferromagnetic cou-
pling in compound 4 [35,36]. The magnetic can be well fit to Cur-
ie–Weiss law with C = 4.03 cm3 molꢁ1 K, h = ꢁ16.88 K. The
negative h value further confirms the presence of antiferromag-
netic interaction in 4.
dinuclear cobalt–oxygen cluster. The cobalt–oxygen clusters are
connected through bdoa anions to form a 1D chain (Fig. 4b). There
exist two types of p–p interactions among adjacent layers: one is
between dppz ligands (with the centroid–centroid distance of
3.91 Å, face-to-face distance of 3.35 Å, and dihedral of 3.39°), and
another is between dppz ligand and bdoa anion (with the cen-
troid–centroid distance of 3.57 Å, face-to-face distance of 3.40 Å,
and dihedral of 7.47°, Fig. 4c). The chains of 4 are connected by
4. Conclusions
Four complexes with dppz and H2bdoa ligands have been
hydrothermally synthesized under similar synthetic conditions.
The complexes form 1D polymeric structure, and three of which
the two kinds of
layer (Fig. 4d). Obviously, the
p
–
p
interactions to form a 2D supramolecular
p–p
stacking interactions play an
important role in the formation and stabilization of the 2D supra-
molecular structure of 4 [26–28]. In addition, the intramolecular
and intermolecular O–HꢀꢀꢀO hydrogen bonds involving the water
molecules and the carboxylic groups of bdoa anions further stabi-
lize the 2D framework (O4W–H4WBꢀꢀꢀO1: 0.868(18), 2.263(18),
and 2.898(3) Å, 130(2)°; O4W–H4WBꢀꢀꢀO2: 0.868(18), 1.73(2),
and 2.578(3) Å, 164(3)°; O4W–H4WAꢀꢀꢀO6: 0.838(17), 1.738(18),
and 2.554(3) Å, 164(3)°; O3W–H3WBꢀꢀꢀO5: 0.922(19), 2.29(2),
and 3.214(5) Å, 177(6)°, symmetry code: x, y – 1, z + 1).
connected by p–p interactions to form supramolecular structures.
The luminescent property of compound 2 demonstrates that it may
be good candidates for luminescent materials. The magnetic study
shows the presence of antiferromagnetic interaction in 4. Further
research on rational design and construction of related compounds
with interesting supramolecular structures as well as physical
properties is currently underway in our laboratory.
Acknowledgements
3.2. Photoluminescent property
This work was financially supported by the Postdoctoral Foun-
dation of Jiangsu Province (No. 0801010B) and the Natural Science
Foundation Project of Jiangsu University (No. 09JDG001) of China.
The solid-state photoluminescent spectrum of compound 2 is
depicted in Fig. 5. Compound 2 exhibit emissions at about
539 nm (kex = 360 nm). In order to understand the nature of this
emission band, the photoluminescence properties of free ligands
dppz and H2dboa were studied. The main emission peak of dppz
Appendix A. Supplementary material
*
is at 444 nm, which may be attributed to the
p
?
p
transition
CCDC 751617, 751618, 751619 and 751620 contain the
supplementary crystallographic data for [Cd(dppz)(bdoa)]n,
[Zn(dppz)(bdoa)(H2O)]n, [Fe(dppz)2(bdoa)]nꢀ2nH2O, and [Co2-
(dppz)2(bdoa)2(H2O)]nꢀ3nH2O. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
[16]. The dicarboxylate ligands H2dboa (kem = 380 nm) can also ex-
hibit fluorescence at room temperature. The emission bands can be
p
* ? n transition as previously reported [31–33].
Compared with the photoluminescent spectra, the emission spec-
assigned to the
tra of 2 are obviously similar to that of dppz. Thus, the green pho-
www.ccdc.cam.ac.uk/data_request/cif.
Supplementary
data

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X. Li et al. / Inorganica Chimica Acta 363 (2010) 1359–1366
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