Construction of Cd(II) compounds with a chelating ligand 2,2′-dipyridiylamine (Hdpa): Anion effect, catalytic activities and luminescence

Article abstract of DOI:10.1016/j.poly.2009.10.024

Six new structures of Cd(II) complexes containing Hdpa ligands have been determined. With chloride and bromide, Cd(II) ions produce halide-bridged dinuclear units 1 and 2 while CdI₂ produces mononuclear unit 3 without halide-bridging. Cd(II) ions produce mono-Hdpa complex 4 with chelating benzoate, di-Hdpa complex 5 with coordinating NO₃^- anion, and tri-Hdpa complexes 6 and 7 with non-coordinating ClO₄^- and BF₄^- anions. One-, two-, or three-dimensional structures of Cd(II)-Hdpa complexes can be produced by hydrogen bonding interactions and π-π interactions. The compounds 4, 5, and 6 catalyzed efficiently the transesterification of a variety of esters with methanol, while 1, 2, 3 and 7 have displayed a very slow conversion. The transesterification reactivity shown by the catalyst 6 is very efficient and the best among the compounds 1-7. In addition, all compounds 1-7 and ligand (Hdpa) have shown the similar luminescent properties at λ_max = 352 nm which suggest that their emissions seem to be attributed to the π-π* intraligand fluorescence.

Full text of DOI:10.1016/j.poly.2009.10.024

Polyhedron 29 (2010) 773–786
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Construction of Cd(II) compounds with a chelating ligand 2,20-dipyridiylamine
(Hdpa): Anion effect, catalytic activities and luminescence
Byeong Kwon Park a, Geun Hee Eom a, Soo Hyun Kim a, Han Kwak a, Seung Man Yoo a, Yu Jin Lee a,
b,
b
Cheal Kim a, , Sung-Jin Kim , Youngmee Kim
*
*
a Department of Fine Chemistry, Eco-Product and Materials Education Center, Seoul National University of Technology, Seoul 139-743, Republic of Korea
b Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Six new structures of Cd(II) complexes containing Hdpa ligands have been determined. With chloride and
bromide, Cd(II) ions produce halide-bridged dinuclear units 1 and 2 while CdI2 produces mononuclear
unit 3 without halide-bridging. Cd(II) ions produce mono-Hdpa complex 4 with chelating benzoate, di-
Received 30 September 2009
Accepted 26 October 2009
Available online 29 October 2009
ꢀ
Hdpa complex 5 with coordinating NO3 anion, and tri-Hdpa complexes 6 and 7 with non-coordinating
ꢀ
ꢀ
ClO4 and BF4 anions. One-, two-, or three-dimensional structures of Cd(II)–Hdpa complexes can be pro-
duced by hydrogen bonding interactions and interactions. The compounds 4, 5, and 6 catalyzed effi-
Keywords:
2,20-Dipyridylamine
Anion effect
Transesterification
Luminescence
Cd(II) complexes
p–p
ciently the transesterification of a variety of esters with methanol, while 1, 2, 3 and 7 have displayed a
very slow conversion. The transesterification reactivity shown by the catalyst 6 is very efficient and
the best among the compounds 1 –7. In addition, all compounds 1–7 and ligand (Hdpa) have shown
the similar luminescent properties at kmax = 352 nm which suggest that their emissions seem to be attrib-
uted to the p–p* intraligand fluorescence.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
complexes containing Hdpa have shown, surprisingly, unusual
heterogeneous catalytic activities on transesterification reaction
of esters [30,31].
Construction of coordination networks [1–6] by self-assembly
process has been affected by the hydrogen bonds [7–16],
p–p
As a part of our continued interests in the syntheses, structures,
and reactivities of coordination complexes with chelating Hdpa li-
gands, and with the aim to fully understand the anion effect on
construction of metal complexes in order to find efficient catalysts
to mediate various catalytic reactions that could be carried out un-
der mild reaction conditions, we employed cadmium salts with dif-
ferent counter-anions (halides, benzoate, nitrate [32], perchlorate,
and tetrafluoroborate) to develop new Cd(II) complexes. Here we
report the structures of several Cd(II) complexes with Hdpa, and
compare them with Zn(II) complexes, and examine their catalytic
activities and luminescence.
stacking [17], and anion effect [18–23] as well as ligand design
[24] and coordination numbers [25,26]. Among them, anion effect
has been realized as a very important role on the self-assembled
construction when anions can be coordinated to the metal
centers. In recent years, we and others have shown that 2,20-
dipyridylamine(Hdpa) as a chelating ligand mostly formed mono-
nuclear Zn(II) complexes (zinc salts used; (Zn(NO3)2, Zn(CN)2,
Zn(O2CCH3)2, Zn(O2CC6H5)2, Zn(ClO4)2, Zn(BF4)2, ZnCl2, ZnBr2,
ZnI2, and Zn(CF3SO3)2)) [27–31], and then these Zn(II) complexes
can be used as building blocks for one- or two-dimensional struc-
tures through weak hydrogen bonding and p–p interactions. With
sulfate anion, the chelating ligand 2,20-dipyridylamine(Hdpa),
unexpectedly, forms a one-dimensional chain compound [30].
These results demonstrated that both anion effect and inter-
molecular hydrogen bonds are very important roles for formation
of crystal structures in Zn(II)–Hdpa system. Some of Zn(II)
2. Experimental
2.1. Materials
2,20-Dipyridylamine (Hdpa), methanol, ethanol, acetone, isopro-
pyl ether, methylene chloride, para-substituted phenyl acetate,
para-substituted phenyl benzoate, methyl acetate, methyl benzo-
ate, ammonium benzoate, and cadmium salts were purchased from
Aldrich and were used as received. 4-Fluorophenyl acetate and 4-
nitrophenyl benzoate were obtained from Lancaster.
* Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim), tel.:
+82 2 3277 2350; fax: +82 2 3277 3419 (S.-J. Kim).
E-mail addresses: chealkim@snut.ac.kr (C. Kim), sjkim@ewha.ac.kr (S.-J. Kim).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.10.024

774
B.K. Park et al. / Polyhedron 29 (2010) 773–786
2.2. Instrumentation
43.0 mg (0.125 mmol) of CdBr2ꢁ4H2O and 2,20-dipyridylamine
ligand (42.8 mg, 0.25 mmol) were stirred in 10 mL methanol for
15 h at room temperature and carefully layered by 3 mL iso-
propyl ether. Suitable crystals of compound 2 for X-ray analysis
were obtained in 2 months. The yield was 35.0 mg (30.2%) for
compound 2. 1H NMR (DMSO, 300 MHz): d 9.67 (s, 1H, N–H)
Elemental analysis for carbon, nitrogen, and hydrogen was car-
ried out by using an EA1108 (Carlo Erba Instrument, Italy) in the
Organic Chemistry Research Center of Sogang University, Korea.
Product analysis for the transesterification reaction was per-
formed on either a Hewlett–Packard 5890 II Plus gas chromato-
graph interfaced with Hewlett–Packard Model 5989B mass
and
d 8.21, 7.68 and 6.86 (m, 8H, pyridyl-H). IR (KBr):
m
(cmꢀ1) = 3282(m), 3196(w), 1623(s), 1581(s), 1523(s), 1461(s),
spectrometer or
equipped with a FID detector using 30-m capillary column (Hew-
lett–Packard, HP-1, HP-5, and Ultra 2). The emission/excitation
spectra were recorded on
spectrometer.
a
Donam Systems 6200 gas chromatograph
1415(s), 1349(s), 1270(m), 1232(s), 1157(s), 1056 (m),
1005(s), 903(s), 874(w), 842(w), 768(s), 743(w), 718(w),
634(brm), 598(w), 529(s), 411(s). Anal. Calc. for C20H18Br4Cd2N6
(886.84), 2: C, 27.08; H, 2.05; N, 9.48. Found: C, 26.89; H, 2.13;
N, 9.41%.
a Perkin–Elmer LS45 fluorescence
45.8 mg (0.125 mmol) of CdI2 were dissolved in 4 mL methanol
and carefully layered by 4 mL methylene chloride solution of 2,20-
dipyridylamine ligand (42.8 mg, 0.25 mmol). Suitable crystals of
compound 3 for X-ray analysis were obtained in a month. The yield
was 23.1 mg (34.0%) for compound 3. 1H NMR (DMSO, 300 MHz): d
9.69 (s, 1H, N–H) and d 8.22, 7.66 and 6.87 (m, 8H, pyridyl-H). IR
2.3. Syntheses of [{Cd(Hdpa)Cl(H2O)}2(l-Cl)2] (1), [{Cd(Hdpa)Br}2(l-
Br)2] (2), and [{Cd(Hdpa)I2] (3)
28.5 mg (0.125 mmol) of CdCl2 hemipentahydrate were dis-
solved in 4 mL H2O and carefully layered by 4 mL acetone solution
of 2,20-dipyridylamine ligand (42.8 mg, 0.25 mmol). Suitable crys-
tals of compound 1 for X-ray analysis were obtained in 3 weeks.
The yield was 47.7 mg (64.0%) for compound 1. 1H NMR (DMSO,
300 MHz): d 9.70 (s, 1H, N–H) and d 8.23, 7.66 and 6.87 (m, 8H,
(KBr):
m
(cmꢀ1) = 3349(brs), 1630(s), 1583(s), 1523(s), 1480(s),
1377(s), 1270(m), 1226(s), 1159(s), 1059 (m), 1011(s), 908(m),
829(m), 770(s), 645(m), 607(w), 565(brm), 514(s), 409(s). Anal.
Calc. for C10H7CdI2N3 (535.39), 3: C, 22.43; H, 1.32; N, 7.85. Found:
C, 22.61; H, 1.33; N, 7.62%.
pyridyl-H). IR (KBr):
m
(cmꢀ1) = 3485(brm), 3308(brm), 3209(s),
3149(m), 1644(s), 1581(s), 1531(s), 1487(s), 1425(s), 1383(m),
1278(s), 1229(s), 1158(s), 1060(s), 1005(s), 909(s), 868(s),
832(m), 769(s), 696(m), 640(brm), 523(s). Anal. Calc. for
C20H22Cd2Cl4N6O2 (745.04), 1: C, 32.24; H, 2.98; N, 11.28. Found:
C, 32.47; H, 2.78; N, 11.20%.
2.4. Synthesis of [Cd(Hdpa)(O2CC6H5)2] (4)
38.6 mg (0.125 mmol) of Cd(NO3)2ꢁ4H2O and 34.8 mg
(0.25 mmol) of ammonium benzoate were dissolved in 4 mL
Table 1
Crystallographic data for compounds 1–7.
1
2
3
4
5a
6
7
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Space group
a (Å)
C20H22Cd2Cl4N6O2 C20H18Br4Cd2N6
C10H7CdI2N3
535.39
170(2)
0.71073
P21/c
13.342(3)
8.1330(16)
12.958(3)
90.00
103.08(3)
90.00
1369.6(5)
4
C24H19CdN3O4
525.82
170(2)
0.71073
P21/n
7.5480(15)
16.603(3)
17.683(3)
90.00
101.057(3)
90.00
2174.9(7)
4
C20H18CdN8O6
578.82
170(2)
0.71073
P21/c
8.6546(12)
16.497(2)
7.7313(11)
90.00
94.572(2)
90.00
1100.3(3)
2
C30H27CdCl2N9O8
824.91
293(2)
0.71073
P21/c
19.3572(12)
11.0908(7)
15.8297(9)
90.00
102.8440(10)
90.00
3313.4(3)
4
C30H27B2CdF8N9
799.63
293(2)
0.71073
P21/c
19.208(4)
10.969(2)
15.868(3)
90.00
102.65(3)
90.00
3262.1(11)
4
745.04
293(2)
0.71073
886.82
293(2)
0.71073
ꢀ
ꢀ
P1
P1
7.0014(19)
9.959(3)
10.386(3)
109.838(4)
98.966(4)
107.849(4)
620.5(3)
1
8.5690(10)
8.6892(11)
9.4616(12)
105.007(2)
110.066(2)
95.899(2)
624.74(13)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Density (calc.)
(Mg/m3)
Absorption
coefficient
1.994
2.357
2.596
1.606
1.747
1.654
1.628
2.175
8.188
6.080
1.040
1.049
0.885
0.753
(mmꢀ1
)
Crystal size (mm3) 0.10 ꢂ 0.05 ꢂ 0.05 0.10 ꢂ 0.08 ꢂ 0.08 0.35 ꢂ 0.10 ꢂ 0.10 0.20 ꢂ 0.15 ꢂ 0.15 0.15 ꢂ 0.05 ꢂ 0.03 0.10 ꢂ 0.08 ꢂ 0.06 0.25 ꢂ 0.10 ꢂ 0.10
Reflections
collected
3479
3513
7108
12 020
6023
18 080
17 926
Independent
reflections
2379 [0.0549]
2405 [0.1116]
2628 [0.0367]
4277 [0.0678]
2160 [0.0636]
6506 [0.0400]
6413 [0.0212]
[R(int)
]
Data/restraints/
parameters
2379/0/166
0.977
2405/1/149
0.854
2628/0/165
1.092
4277/0/294
0.858
2160/1/164
0.866
6506/3/458
0.913
6413/0/457
1.048
Goodness-of-fit
(GOF) on F2
Final R indices
R1 = 0.0355,
wR2 = 0.0845
R1 = 0.0542,
wR2 = 0.1155
R1 = 0.0702,
wR2 = 0.1186
R1 = 0.0430,
wR2 = 0.1199
R1 = 0.0484,
wR2 = 0.1240
R1 = 0.0299,
wR2 = 0.0582
R1 = 0.0400,
wR2 = 0.0593
R1 = 0.0322,
wR2 = 0.0703
R1 = 0.0468,
wR2 = 0.0719
R1 = 0.0399,
wR2 = 0.1012
R1 = 0.0603,
wR2 = 0.1054
R1 = 0.0416,
wR2 = 0.1180
R1 = 0.0485,
wR2 = 0.1242
[I > 2r(I)]
R indices (all data) R1 = 0.0389,
wR2 = 0.0852
Largest difference
in peak and
1.207 and ꢀ1.064 2.027 and ꢀ1.570 1.189 and ꢀ1.138 0.607 and ꢀ0.740
0.956 and ꢀ0.758 1.171 and ꢀ0.637 0.837 and ꢀ0.892
hole (e Åꢀ3
)
a
The crystal structure of 5 was re-determined, and all the parameters were similar to the results reported by Amma et al. [32].

B.K. Park et al. / Polyhedron 29 (2010) 773–786
775
H2O and carefully layered by a mixture solution (2 mL acetone,
2.5. Synthesis of [Cd(Hdpa)2(NO3)2] (5)
1 mL ethanol, and 1 mL methanol) of 2,20-dipyridylamine ligand
(42.8 mg, 0.25 mmol). Suitable crystals of compound 4 for X-
Complex 5 has been synthesized and its structure was reported
previously [32], but we re-synthesized, re-collected data and re-
determined the structure.
ray analysis were obtained in
3 weeks. The yield was
22.8 mg (34.7%) for compound 4. 1H NMR (DMSO, 300 MHz):
d 9.68 (s, 1H, N–H), d 7.96 and 7.42 (m, 10H, benzoate-H),
38.6 mg (0.125 mmol) of Cd(NO3)2ꢁ4H2O were dissolved in 4 mL
methanol and carefully layered by acetone solution of 2,20-dipyri-
dylamine ligand (42.8 mg, 0.25 mmol). Suitable crystals of com-
pound 5 for X-ray analysis were obtained in a week. The yield
was 43.9 mg (60.6%) for compound 5. 1H NMR (DMSO, 300 MHz):
d 9.67 (s, 1H, N–H) and d 8.20, 7.65 and 6.86 (m, 8H, pyridyl-H).
and
m
d
8.21, 7.70 and 6.86 (m, 8H, pyridyl-H). IR (KBr):
3213(w), 3069(w), 1647(s), 1596(s),
(cmꢀ1) = 3321(w),
1538(s), 1484(s), 1397(s), 1233(m), 1163(m), 854(m), 772(s),
731(s), 685(m), 520(w), 432(w). Anal. Calc. for C24H19CdN3O4
(525.82), 4: C, 54.82; H, 3.65; N, 8.00. Found: C, 54.65; H,
3.83; N, 8.22%.
IR (KBr):
m
(cmꢀ1) = 3305(s), 3202(m), 1629(s), 1580(s), 1527(s),
Scheme 1. Structures according to anions.

776
B.K. Park et al. / Polyhedron 29 (2010) 773–786
1479(s), 1328(brs), 1270(m), 1236(s), 1161(s), 1051(m), 882(m),
819(w), 773(s), 639(m), 527(m), 418(m). Anal. Calc. for
1032(w), 766(s), 526(w). Anal. Calc. for C30H27B2CdF8N9 (799.63),
7: C, 45.06; H, 3.41; N, 15.77. Found: C, 44.93; H, 3.32; N, 16.01%.
C20H18CdN8O6 (578.82), 5: C, 41.50; H, 3.14; N, 19.36. Found: C,
41.32; H, 3.10; N, 19.51%.
2.7. Catalytic activity of compounds 1–7
Catalytic
transesterification
reaction
conditions:
Esters
2.6. Syntheses of [Cd(Hdpa)3(ClO4)2] (6) and [Cd(Hdpa)3(BF4)2] (7)
(0.05 mmol) were dissolved in methanol (1 mL), and the catalyst
(1.0 mg, 1.34 ꢂ 10ꢀ3 mmol for 1, 1.0 mg, 1.13 ꢂ 10ꢀ3 mmol for 2,
1.0 mg, 1.87 ꢂ 10ꢀ3 mmol for 3, 1.0 mg, 1.90 ꢂ 10ꢀ3 mmol for 4,
1.0 mg, 1.73 ꢂ 10ꢀ3 mmol for 5, 1.0 mg, 1.21 ꢂ 10ꢀ3 mmol for 6,
and 1.0 mg, 1.25 ꢂ 10ꢀ3 mmol for 7) was added and shaken at
room temperature (450 rpm). Reaction conversion was monitored
by GC/mass analysis of 20 lL aliquots withdrawn periodically from
the reaction mixture. All reactions were run at least three times
and the average conversion yields are presented.
38.9 mg (0.125 mmol) of Cd(ClO4)2ꢁH2O were dissolved in 4 mL
H2O and carefully layered by 4 mL acetone solution of 2,20-dipyri-
dylamine ligand (42.8 mg, 0.25 mmol). Suitable crystals of
compound 6 for X-ray analysis were obtained in 2 months. The
yield was 18.5 mg (27.0%) for compound 6. 1H NMR (DMSO,
300 MHz): d 9.67 (s, 1H, N–H) and d 8.21, 7.67 and 6.86 (m, 8H,
pyridyl-H). IR (KBr):
m
(cmꢀ1) = 3340(brs), 3148(w), 1631(s),
1582(s), 1530(s), 1472(s), 1434(w), 1419(w), 1355(s), 1273(w),
1233(s), 1161(m), 1094(brs), 1000(m), 903(w), 770(s), 621(s),
527(m), 415(w). Anal. Calc. for C30H27CdCl2N9O8 (824.91), 6: C,
43.68; H, 3.31; N, 15.29. Found: C, 43.82; H, 3.52; N, 15.21%.
35.8 mg (0.125 mmol) of Cd(BF4)2 45% solution in water and
2,20-dipyridylamine ligand (42.8 mg, 0.25 mmol) were stirred in
10 mL methanol for 15 h at room temperature and carefully lay-
ered by 16 mL isopropyl ether. Suitable crystals of compound 7
for X-ray analysis were obtained in a week. The yield was
13.8 mg (17.0%) for compound 7. 1H NMR (DMSO, 300 MHz): d
9.73 (s, 1H, N–H) and d 8.21, 7.67 and 6.88 (m, 8H, pyridyl-H). IR
2.8. X-ray crystallography
The diffraction data for compounds 1–7 were collected on a Bru-
ker SMART AXS diffractometer equipped with a monochromator in
the Mo Ka (k = 0.71073 Å) incident beam. The crystal was mounted
on a glass fiber. The CCD data were integrated and scaled using the
Bruker-SAINT software package, and the structure was solved and
refined using SHEXTL V6.12 [33]. Hydrogen atoms were located in
the calculated positions. The crystallographic data for compounds
1–7 are listed in Table 1.
(KBr):
1435(m), 1419(w), 1352(m), 1232(m), 1160(m), 1083(s),
m
(cmꢀ1) = 3294(m), 1631(s), 1582(s), 1530(m), 1476(s),
Fig. 1. (a) Structure of [{Cd(Hdpa)(OH2)(Cl)}2(l-Cl)2] (1) with 50% ellipsoid. All hydrogen atoms are omitted for clarity. (b) Two-Dimensional structure derived by inter- and
intra-hydrogen bonds.

B.K. Park et al. / Polyhedron 29 (2010) 773–786
777
can be used as building blocks for one-, two-, or three-dimensional
structures through weak hydrogen bonding and interactions.
3. Results and discussion
p–p
To further investigate anion effects for the corresponding Cd(II)
complexes containing Hdpa ligands, various anions (halides, ben-
Hdpa has been used as a chelating ligand to mostly form mono-
nuclear Zn(II) complexes [27–31], and then these Zn(II) complexes
Table 2
Selected bond distances for compounds 1–7.
1
Cd(1)–N(3)
2.316(4)
Cd(1)–N(1)
2.333(4)
Cd(1)–O(1)
Cd(1)–Cl(2)
Cl(2)–Cd(1)#1
2.400(4)
Cd(1)–Cl(1)
Cd(1)–Cl(2)#1
2.6186(13)
2.6261(13)
2.6209(12)
2.6262(13)
80.90(12)
93.11(14)
94.21(9)
169.77(9)
82.68(10)
94.72(9)
N(3)–Cd(1)–N(1)
N(1)–Cd(1)–O(1)
N(1)–Cd(1)–Cl(1)
N(3)–Cd(1)–Cl(2)
O(1)–Cd(1)–Cl(2)
N(3)–Cd(1)–Cl(2)#1
O(1)–Cd(1)–Cl(2)#1
Cl(2)–Cd(1)–Cl(2)#1
N(3)–Cd(1)–O(1)
N(3)–Cd(1)–Cl(1)
O(1)–Cd(1)–Cl(1)
N(1)–Cd(1)–Cl(2)
Cl(1)–Cd(1)–Cl(2)
N(1)–Cd(1)–Cl(2)#1
Cl(1)–Cd(1)–Cl(2)#1
Cd(1)–Cl(2)–Cd(1)#1
87.63(13)
101.41(9)
169.16(10)
96.32(9)
88.58(4)
173.75(8)
91.02(4)
92.78(3)
82.20(12)
87.22(3)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, ꢀy + 1, ꢀz + 1
2
Cd(1)–N(3)
2.284(7)
Cd(1)–N(1)
2.307(7)
Cd(1)–Br(2)
Cd(1)–Br(1)
2.5349(11)
2.7729(11)
82.3(2)
103.16(16)
152.29(16)
138.69(17)
108.62(4)
Cd(1)–Br(1)#1
Br(1)–Cd(1)#1
2.7635(11)
2.7634(11)
112.58(17)
90.92(17)
104.25(4)
85.79(17)
81.72(3)
N(3)–Cd(1)–N(1)
N(1)–Cd(1)–Br(2)
N(1)–Cd(1)–Br(1)#1
N(3)–Cd(1)–Br(1)
Br(2)–Cd(1)–Br(1)
N(3)–Cd(1)–Br(2)
N(3)–Cd(1)–Br(1)#1
Br(2)–Cd(1)–Br(1)#1
N(1)–Cd(1)–Br(1)
Br(1)#1–Cd(1)–Br(1)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, ꢀy + 1, ꢀz + 1
3
N(1)–Cd(1)
2.260(6)
N(3)–Cd(1)
2.259(6)
Cd(1)–I(2)
2.6900(8)
84.2(3)
115.49(14)
113.23(14)
Cd(1)–I(1)
2.6956(8)
110.95(15)
113.61(15)
115.48(3)
N(3)–Cd(1)–N(1)
N(1)–Cd(1)–I(2)
N(1)–Cd(1)–I(1)
N(3)–Cd(1)–I(2)
N(3)–Cd(1)–I(1)
I(2)–Cd(1)–I(1)
4
Cd(1)–O(11)
Cd(1)–N(1)
Cd(1)–O(22)
Cd(1)–C(11)
O(11)–Cd(1)–N(3)
N(3)–Cd(1)–N(1)
N(3)–Cd(1)–O(21)
O(11)–Cd(1)–O(22)
N(1)–Cd(1)–O(22)
O(11)–Cd(1)–O(12)
N(1)–Cd(1)–O(12)
O(22)–Cd(1)–O(12)
2.2448(19)
2.280(2)
2.3886(19)
2.671(3)
103.27(7)
82.66(8)
100.30(7)
93.86(7)
154.91(7)
55.93(6)
96.28(7)
94.09(7)
Cd(1)–N(3)
Cd(1)–O(21)
Cd(1)–O(12)
Cd(1)–C(21)
O(11)–Cd(1)–N(1)
O(11)–Cd(1)–O(21)
N(1)–Cd(1)–O(21)
N(3)–Cd(1)–O(22)
O(21)–Cd(1)–O(22)
N(3)–Cd(1)–O(12)
O(21)–Cd(1)–O(12)
2.274(2)
2.3216(19)
2.4421(18)
2.696(3)
110.86(7)
143.39(7)
99.56(7)
96.15(7)
55.83(7)
157.45(7)
102.08(6)
6
Cd(1)–N(31)
2.302(3)
Cd(1)–N(11)
2.319(3)
Cd(1)–N(21)
2.341(3)
Cd(1)–N(33)
2.360(3)
Cd(1)–N(23)
2.365(3)
Cd(1)–N(13)
2.373(3)
N(31)–Cd(1)–N(11)
N(11)–Cd(1)–N(21)
N(11)–Cd(1)–N(33)
N(31)–Cd(1)–N(23)
N(21)–Cd(1)–N(23)
N(31)–Cd(1)–N(13)
N(21)–Cd(1)–N(13)
N(23)–Cd(1)–N(13)
92.98(12)
93.14(12)
93.55(12)
95.38(12)
79.49(12)
95.31(11)
88.96(11)
87.87(12)
N(31)–Cd(1)–N(21)
N(31)–Cd(1)–N(33)
N(21)–Cd(1)–N(33)
N(11)–Cd(1)–N(23)
N(33)–Cd(1)–N(23)
N(11)–Cd(1)–N(13)
N(33)–Cd(1)–N(13)
173.23(11)
77.81(11)
98.90(11)
162.79(12)
102.90(12)
76.38(12)
167.62(12)
7
Cd(1)–N(33)
2.307(3)
Cd(1)–N(21)
2.316(3)
Cd(1)–N(11)
2.342(3)
Cd(1)–N(13)
2.359(3)
Cd(1)–N(31)
2.365(3)
Cd(1)–N(23)
2.374(3)
N(33)–Cd(1)–N(21)
N(21)–Cd(1)–N(11)
N(21)–Cd(1)–N(13)
N(33)–Cd(1)–N(31)
N(11)–Cd(1)–N(31)
N(33)–Cd(1)–N(23)
N(11)–Cd(1)–N(23)
N(31)–Cd(1)–N(23)
92.33(10)
92.80(10)
162.30(10)
77.54(10)
98.63(10)
94.75(10)
89.79(10)
167.92(10)
N(33)–Cd(1)–N(11)
N(33)–Cd(1)–N(13)
N(11)–Cd(1)–N(13)
N(21)–Cd(1)–N(31)
N(13)–Cd(1)–N(31)
N(21)–Cd(1)–N(23)
N(13)–Cd(1)–N(23)
173.82(9)
96.06(10)
79.95(10)
94.32(11)
102.69(11)
76.54(11)
87.23(10)

778
B.K. Park et al. / Polyhedron 29 (2010) 773–786
zoate, nitrate, perchlorate, and tetrafluoroborate) have been
adopted in this system. For each anion, different structures have
been obtained in both Zn(II) and Cd(II) systems as shown in
Scheme 1. Halide anions can be used as bridging ligands in Cd(II)
system while they were used for Zn(II) ions as simple coordinating
ligands. For halide ligands, smaller Zn(II) ion prefers tetrahedral
geometry, but depending on the size of the halide ions, the coordi-
nation on Cd(II) ion changes from octahedral in 1 to trigonal bipy-
ramidal in 2 and tetrahedral in 3. Compounds 1 and 2 form dimeric
compounds by halide bridges, and hydrogen bond interactions
provide two- and three-dimensional structures. In addition, the
bridging capability decreases from chloride down to iodide as de-
scribed below. Benzoate anions were used as chelating ligands in
both Zn(II) and Cd(II) systems with very similar structures. Nitrate
anions were used as chelating ligands for Zn(II) ions, in contrast
they can be used simple O-donor coordinating ligands for Cd(II)
ions. Its structure was reported previously [32]. For non-coordinat-
that both inter-molecular hydrogen bonds and p–p interactions as
well as anion effects play also very important roles in the construc-
tion of crystal structures in Cd(II) system. In addition, the bigger
size of a Cd(II) ion compared to that of a Zn(II) ion gives variety
of structures, and it makes that halides can act as bridging ligands
to form a dinuclear Cd(II) complex.
3.1. Crystal structures of compounds containing cadmium halides and
Hdpa ligands, [{Cd(Hdpa)Cl(H2O)}2(l-Cl)2] (1), [{Cd(Hdpa)Br}2(l-
Br)2] (2), and [{Cd(Hdpa)I2] (3)
Reactions of CdX2 (X = Clꢀ, Brꢀ, Iꢀ) yield the structures of
[{Cd(Hdpa)Cl(H2O)}2( -Cl)2] (1), [{Cd(Hdpa)Br}2( -Br)2] (2), and
l
l
[{Cd(Hdpa)I2] (3). Chloride and bromide act as both a simple
coordinating ligand and a bridging ligand to form halide-bridged
dinuclear compounds 1 and 2 (Scheme 1). Bridging ability of ha-
lides decreases from chlorides down to iodides. Iodide acts as a
simple coordinating ligand to form a mononuclear compound 3,
but the molecules are packed alternatively. Depending on the size
of the halide ions the coordination changes from octahedral in 1
to square pyramidal in 2 and tetrahedral in 3.
In compound 1, an asymmetric unit consists of a Cd atom, a
Hdpa ligand, a chloride, a water and a bridging chloride, and
whole dinuclear molecule has been generated through the inver-
sion center in the middle of the molecule (Fig. 1a). The geometry
ꢀ
ꢀ
ing ClO4 and BF4 anions, Cd(II) produces the same cation com-
plexes containing three chelating Hdpa ligands with octahedral
environments, but previous Zn(II) complexes showed different
structures in those anions. Both anions for Cd(II) ions occupy
empty positions between metal cations for charge balances. One-
, two-, and three-dimensional structures of Cd(II)–Hdpa complexes
can be produced by hydrogen bonding interactions and p–p inter-
actions as shown in Zn(II)–Hdpa complexes. These results confirm
Table 3
Hydrogen bonds for compounds 1–7.
D–Hꢁ ꢁ ꢁA
d(D–H)
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
\(DHA)
Compound 1
C(7)–H(7)ꢁ ꢁ ꢁCl(1)#2
O(1)–H(1B)ꢁ ꢁ ꢁCl(1)#1
O(1)–H(1A)ꢁ ꢁ ꢁCl(1)#3
0.93
0.83(6)
0.68(6)
2.84
2.57(7)
2.52(6)
3.635(5)
3.361(4)
3.191(5)
144.6
162(5)
174(7)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, ꢀy + 1, ꢀz + 1; #2 ꢀx + 2, ꢀy + 2, ꢀz + 2; #3 x ꢀ 1, y, z
Compound 2
C(10)–H(10)ꢁ ꢁ ꢁBr(2)#2
N(2)–H(2N)ꢁ ꢁ ꢁBr(1)#3
C(2)–H(2)ꢁ ꢁ ꢁBr(1)#4
C(10)–H(10)ꢁ ꢁ ꢁBr(1)#1
0.93
0.830(2)
0.93
3.07
2.82(5)
2.98
3.761(9)
3.584(8)
3.863(10)
3.504(9)
132.6
154(10)
158.5
0.93
2.94
120.3
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, ꢀy + 1, ꢀz + 1; #2 ꢀx + 1, ꢀy, ꢀz + 1; #3 ꢀx, ꢀy + 1, ꢀz + 1; #4 ꢀx, ꢀy + 1, ꢀz
Compound 4
C(16)–H(16)ꢁ ꢁ ꢁO(12)#1
C(23)–H(23)ꢁ ꢁ ꢁO(11)#2
N(2)–H(2N)ꢁ ꢁ ꢁO(21)#3
0.95
0.95
0.75(2)
2.46
2.33
2.22(3)
3.370(4)
3.259(4)
2.954(3)
160.8
164.1
165(3)
Symmetry transformations used to generate equivalent atoms: #1 x + 1, y, z; #2 x ꢀ 1, y, z; #3 ꢀx + 1, ꢀy + 2, ꢀz
Compound 5
N(2)–H(2N)ꢁ ꢁ ꢁO(2)#2
0.859(2)
2.250(14)
3.058(4)
157(3)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx, ꢀy, ꢀz; #2 x, ꢀy + 1/2, z + 1/2
Compound 6
N(32)–H(32N)ꢁ ꢁ ꢁO(13)#1
N(12)–H(12N)ꢁ ꢁ ꢁO(22)#2
N(22)–H(22N)ꢁ ꢁ ꢁO(24)#3
0.830(2)
0.830(2)
0.830(2)
2.128(16)
2.330(8)
2.198(9)
2.914(6)
3.153(5)
3.015(5)
158(4)
171(4)
168(4)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, y ꢀ 1/2, ꢀz + 1/2; #2 ꢀx, y ꢀ 1/2, ꢀz + 1/2; #3 x, yꢀ1, z
Compound 7
C(17)–H(17)ꢁ ꢁ ꢁF(14)
0.93
0.93
0.93
0.93
0.93
0.93
0.86
0.93
0.93
0.93
0.86
0.93
0.93
2.32
2.73
2.48
2.48
2.58
2.54
2.35
2.52
2.56
2.62
2.02
2.75
2.46
3.119(8)
3.614(9)
3.243(9)
3.268(10)
3.260(9)
3.418(7)
3.024(5)
3.306(5)
3.460(9)
3.292(10)
2.868(10)
3.368(10)
3.379(5)
143.1
159.6
138.8
142.8
130.4
157.2
135.3
142.0
162.3
130.0
166.7
124.5
171.3
C(14)–H(14)ꢁ ꢁ ꢁF(12)
C(13)–H(13)ꢁ ꢁ ꢁF(12)#1
C(29)–H(29)ꢁ ꢁ ꢁF(23)#2
C(28)–H(28)ꢁ ꢁ ꢁF(12)#3
C(27)–H(27)ꢁ ꢁ ꢁF(13)#4
N(22)–H(22A)ꢁ ꢁ ꢁF(11)#4
C(24)–H(24)ꢁ ꢁ ꢁF(11)#4
C(32)–H(32)ꢁ ꢁ ꢁF(23)#5
C(33)–H(33)ꢁ ꢁ ꢁF(22)#5
N(32)–H(32A)ꢁ ꢁ ꢁF(22)#6
C(37)–H(37)ꢁ ꢁ ꢁF(22)#6
C(37)–H(37)ꢁ ꢁ ꢁF(21)#6
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, ꢀy + 1, ꢀz + 1; #2 x, y, z ꢀ 1; #3 x, ꢀy + 3/2, z ꢀ 1/2; #4 ꢀx + 1, y ꢀ 1/2, ꢀz + 1/2; #5 x, ꢀy + 1/
2, z ꢀ 1/2; #6 ꢀx, ꢀy + 1, ꢀz + 1

B.K. Park et al. / Polyhedron 29 (2010) 773–786
779
around the Cd(II) ion is distorted octahedral constructed by two N
atoms of the chelating Hdpa ligand, a simple coordinating chlo-
ride, a bridging chloride, and an O atom of water. Hdpa ligand
is a little bent with the angle between two pyridyl rings of
8.21°. The Cd–Npyridyl bond distances are 2.316(4) and
2.333(4) Å which are typical and the Cd–Owater bond distance is
2.400(4) Å (Table 2). The Cd–Cl and Cd–Clbridge distances are
2.6186(13) and 2.6261(13) Å, respectively. Intra- and inter-molec-
ular hydrogen bonds between a water hydrogen atom and a
chloro atom (O–Hꢁ ꢁ ꢁCl) produce rectangular rings to form an 1-
D chain, and inter-molecular hydrogen bonds between 1-D chains
(C–Hꢁ ꢁ ꢁCl) form a 2-D sheet (Fig. 1b and Table 3). In the dinuclear
unit in 1, the Cd–Cl–Cd angle is 92.78(3)°, and the Cdꢁ ꢁ ꢁCd dis-
tance is 3.799(15) Å.
bromide, and a simple coordinating bromide occupying an apical
position. Hdpa ligand is a little bent with the angle between two
pyridyl rings of 13.76°. The Cd–Npyridyl bond distances are
2.284(7) and 2.307(7) Å which are typical (Table 2). The Cd–Br dis-
tance is 2.5349(11) Å which is much shorter than the Cd–Brbridge
distances (2.7635(11) and 2.7729(11) Å). This implies that the
bridging character of the bromide is weaker than that of the
chloride. Intra- and inter-molecular hydrogen bonding interactions
between bridging bromides and hydrogen atoms (C/N–H) produce
2-D sheets, and inter-molecular hydrogen bonds between simple
bromides and carbon hydrogen atoms form
a 3-D network
(Fig. 2b and Table 3). In the dinuclear unit in 2, the Cd–Br–Cd angle
is 98.28(3)°, and the Cdꢁ ꢁ ꢁCd distance is 4.187(7) Å which is much
longer than that in the chloride-bridged compound 1.
Compound 2 also shows bromide-bridged dinuclear Cd(II) units,
but differently a Cd(II) unit contains one Hdpa, a bromide, and no
water ligand (Fig. 2a). The geometry around Cd(II) ion is distorted
square pyramidal constructed by two N atoms of Hdpa, a bridging
In compound 3, it is recognized that the bridging character of
the iodide is much weaker than those of the chloride and the
bromide. The Cd(II) atom and the amine nitrogen atom (N2)
are disordered in two sites with occupancies of 77% and 23%.
Fig. 2. (a) Structure of [{Cd(Hdpa)Br}2(l-Br)2] (2) with 50% ellipsoid. (b) Three-Dimensional structure derived by non-classical hydrogen bonds between Br atoms and pyridyl
hydrogen atoms and amine hydrogen atoms.

780
B.K. Park et al. / Polyhedron 29 (2010) 773–786
Fig. 3. (a) Structure of [{Cd(Hdpa)I2] (3) with 50% ellipsoid. (b) Packing diagram along the a axis.
Fig. 4. (a) Structure of [Cd(Hdpa)(O2CC6H5)2] (4) with 50% ellipsoid. (b) One-dimensional structure derived by hydrogen bond interactions and
p–p interactions between
pyridyl rings.

B.K. Park et al. / Polyhedron 29 (2010) 773–786
781
Considering only 77% Cd(II) ion, the structure of 3 is a di-iodide
mononuclear complex as shown in Fig. 3a. The diagram down to
the a axis shows that di-iodide complexes are packed alterna-
tively (Fig. 3b). The geometry around Cd(II) ion can be described
distorted tetrahedral constructed by two N atoms of Hdpa and
two simple coordinating iodides. Hdpa ligand is a little bent with
the angle between two pyridyl rings of 5.12°. The Cd–Npyridyl
bond distances are 2.260(6) and 2.259(6) Å which are typical
(Table 2). The Cd–I distances are 2.6956(8) and 2.6900(8) Å.
interactions (Table 3) and
p
–
p
interactions between pyridyl rings
(C6ꢁ ꢁ ꢁN1i 3.751(5), C7ꢁ ꢁ ꢁC1i 3.686(5), C8ꢁ ꢁ ꢁC2i 3.758(3), C9ꢁ ꢁ ꢁC3i
3.848(3), C10ꢁ ꢁ ꢁC4i 3.866(3) Å, symmetry operation i = (1 ꢀ x,
2 ꢀ y, ꢀz)) (Fig. 4b). Two pyridyl rings are somewhat tilted with
the angle of 9.57°.
3.3. Crystal structure of compound [Cd(Hdpa)2(NO3)2] (5)
Its structure was reported previously [32], but we re-collected
data and re-determined the structure to fully understand the role
of hydrogen bonds to form a 2-D sheet.
3.2. Crystal structure of compound [Cd(Hdpa)(O2CC6H5)2] (4)
An inversion center on a Cd(II) ion produces a whole molecule
[Cd(Hdpa)2(NO3)2]. Two Hdpa ligands and two nitrate ligands
coordinate to a Cd(II) ion to form a distorted octahedral environ-
ment [34,35]. There are hydrogen bonds between an amine
hydrogen atom and a nitrate oxygen atom (N–Hꢁ ꢁ ꢁO–Nnitrate) to
form a 2-D sheet (Fig. 5 and Table 3). In the 2-D structure, the
Cdꢁ ꢁ ꢁCd distances are 7.731(1) and 9.109(1) Å.
With chelating benzoate anions, Cd(II) produces a mononuclear
[Cd(Hdpa)(O2CC6H5)2] unit 4 whose structure is very similar to the
corresponding Zn(II) complex with the similar cell dimension
(Fig. 4a) [31]. The Cd–Obenzoate distances range from 2.2448(19)
to 2.4421(18) Å, and the Cd–Npyridyl distances are 2.280(2) and
2.274(2) Å (Table 2). There are inter-molecular hydrogen bond
Fig. 5. Two-Dimensional structure of 5 derived by hydrogen bonds between amine hydrogen atoms and nitrate oxygen atoms.

782
B.K. Park et al. / Polyhedron 29 (2010) 773–786
3.4. Crystal structures of compounds [Cd(Hdpa)3(ClO4)2] (6) and
[Cd(Hdpa)3(BF4)2] (7)
11.90°, 29.56°, and 31.95° for 6 and 10.46°, 29.64°, and 32.02° for
7. There are hydrogen bonds in 6 between amine nitrogen atoms
and perchlorate oxygen atoms (N–Hꢁ ꢁ ꢁOperchlorate
) to form a
ꢀ
With non-coordinating ligands ClO4 and BF4ꢀ, Cd(II) produces
three-dimensional structure (Fig. 6b and Table 3). There are also
non-classical N–Hꢁ ꢁ ꢁF and C–Hꢁ ꢁ ꢁF hydrogen bonds in 7 to form a
three-dimensional structure (Fig. 7b and Table 3).
mononuclear complexes containing (tri-Hdpa)-chelated Cd(II) and
two anions for charge balance (Fig. 6a for 6 and Fig. 7a for 7). The
Cd–Npyridyl distances range from 2.302(3) to 2.373(3) Å for 6 and
from 2.307(3) to 2.374(3) Å for 7 (Table 2). Two pyridyl rings in
three chelating Hdpa ligands of both 6 and 7 are all bent with
Fig. 6. (a) Structure of [Cd(Hdpa)3(ClO4)2] (6) with 50% ellipsoid. (b) Three-
dimensional structure derived by hydrogen bonds between amine hydrogen atoms
and perchlorate oxygen atoms.
Fig. 7. (a) Structure of [Cd(Hdpa)3(BF4)2] (7) with 50% ellipsoid. (b) Three-
dimensional structure derived by hydrogen bonds between amine and pyridyl
hydrogen atoms and tetrafluoroborate fluorine atoms.

B.K. Park et al. / Polyhedron 29 (2010) 773–786
783
Scheme 2. Structures of seven compounds containing chelating Hdpa ligands as transesterification catalysts.
Table 4
Transesterification of esters by methanol in the presence of compounds 4–6 at 50 °C.a
Entry
Substrate
4 (time/days)b
5 (time/days)b
6 (time/days)b
1
2
3
4
5
6
7
8
4-Nitrophenyl acetate
Phenyl acetate
4-Methylphenyl acetate
4-Nitrophenyl benzoatec
4-Chlorophenyl benzoate
Phenyl benzoate
0.5
4
35
2
4
4
0.38
1
44
4
2
2
0.25
0.92
13
4
1
2
4-Methylphenyl benzoate
Vinyl acetate
6
0.21
2
0.25
1
0.17
a
All esters were completely converted to the corresponding products, methyl acetate and methyl benzoate. Reaction conditions: esters; 0.05 mmol, catalyst; 1.0 mg,
1.90 ꢂ 10ꢀ3 mmol for 4, 1.0 mg, 1.73 ꢂ 10ꢀ3 mmol for 5, 1.0 mg, 1.21 ꢂ 10ꢀ3 mmol for 6, solvent; methanol (1 mL). See Section 2 for the detailed reaction conditions.
b
Time necessary for the complete conversion of substrate to product.
The solvent was a mixture of CH3OH/CH2Cl2 (1/1) because of low solubility of substrate in CH3OH.
c
3.5. Homogeneous catalytic activities of compounds 1–7
As part of our efforts to develop transesterification catalysts
based on metal ions that are not redox-active, we have previously
reported that Zn(Hdpa)X2 (X = NO3ꢀ, SO4
,
ꢀO2C6H5, Clꢀ, Brꢀ, and
2ꢀ
Iꢀ) could carry out the catalytic transesterification of a range of es-
ters with methanol at room temperature under the mild conditions
[30,31]. In addition, we have recently shown for the first time that
Cd-containing
polymers
[Cd2(O2CPh)4(4,40-bpy)2]n
and
[Cd(O2CPh)2(bpa)1.5 n
]
(4,40-bpy = 4,4-bipyridine, bpa = 1,2-bis(pyr-
idyl)ethane and ꢀO2CPh = benzoate) catalyzed efficiently the
transesterification reactions of a series of esters in spite of being
well known as an inert metal [34,35]. This experience led us to test
the transesterification with the compounds 1–7 (see Scheme 2 for
structures of seven compounds as transesterification catalysts).
Thus, the compounds 1–7 were treated with phenyl acetate and
methanol at 50 °C under the neutral conditions (Eq. (1)).
Scheme 3.

784
B.K. Park et al. / Polyhedron 29 (2010) 773–786
O
O
acylating agent and, expectedly, converted efficiently to the prod-
uct methyl acetate within 0.17–0.25 day by 4, 5, and 6 (entry 8).
Though we do not know, at this moment, about the exact reac-
tive species and the reaction mechanism for the transesterification
reaction by the catalysts, we are able to propose the possible
transesterification reaction mechanism based on the structure of
the complexes 4, 5, and 6. With 4 and 5 having the labile ligands
catalysts
HOCH3
..
OCCH3
CH3COCH3
+
OH +
ð1Þ
This reaction produced quantitatively the corresponding product
methyl acetate within 0.9–20 days, while a control reaction carried
out in absence of the complexes showed trace amounts of the con-
version of the ester to the product in the same time period. Com-
plexes 4, 5, and 6 have shown efficient catalytic reactivities (0.92–
4 days; see Table 4), while 1, 2, 3 and 7 has displayed a very slow
conversion (12–20 days; data not shown). Importantly, the transe-
sterification reactivity shown by the catalyst 6 are very efficient
and the best among the catalytic efficiencies reported previously
with Cd-containing compounds, to our best knowledge [36]. In
addition, the catalytic reactivity of 6 is comparable to those of Zn
catalysts which are well known as the efficient catalysts for the
transesterification reactions [30,31,34–36].
Once having established that 4 –6 represents an excellent
catalyst for the tansesterification reaction of phenyl acetate with
methanol, we have investigated the transesterification of various
p-substituted phenyl acetates and benzoates with them. The
substrates with the electron-withdrawing substituents have
undergone faster transesterification (entries 1, 4 and 6), while
those with the electron-donating ones have shown slow reaction
(entries 3 and 7).
ꢀ
NO3 and benzoate, respectively, the plausible mechanism shown
in Scheme 3, based on our previous proposed mechanism [30]. The
substrate phenyl acetate substitutes an anion (NO3ꢀ) to give the
adduct (Hdpa)2Cd(NO3)(Sub). Then, the nucleophile methanol
would attack the carbon atom of carbonyl moiety of the adduct
to produce the product methyl acetate.
With 6 having no labile ligand, we can presume that there is no
direct interaction between the substrate ester and cadmium ion of
the complex as Lewis acid, since it is saturated with three Hdpa li-
gands. Therefore, we propose that the hydrogen atom of amine N–
H moiety in the complex can do the acid-catalyzed transesterifica-
tion, as we have previously proposed with the Zn complexes of
bis(2-pyridylmethyl)amine ligands [42]. Thus, this acidic hydrogen
Table 5
Emission data for complexes 1–7 and ligand (Hdpa) at room temperature.
Compound
Excitation (k/nm)
Emission (kmax /nm)
Ligand (Hdpa)
314
315
315
315
315
315
314
314
352
354
353
354
354
352
350
351
1
2
3
4
5
6
7
In a certain case, transesterification of esters with alcohol can-
not achieve high conversions because of the reversibility of the
reaction. To solve this problem, therefore, we have used an enol es-
ter as an acylating agent, since the resultant enolate is converted to
an aldehyde or ketone that is unable to participate in the reverse
reaction [37–41]. In this work, vinyl acetate was used as the
Scheme 4.

B.K. Park et al. / Polyhedron 29 (2010) 773–786
785
Fig. 8. Emission spectra of complexes 1–7 and ligand (Hdpa) at room temperature.
interacts with the oxygen atom of carbonyl of ester, resulting in
that the carbonyl is more electrophilic. Then, the resultant acti-
vated carbonyl could be easily attacked by methanol to produce
the product methyl ester as shown in Scheme 4. Further explora-
tions into the uses of this catalyst family in organic transforma-
tions as well as mechanistic investigations are ongoing.
Cd(II) ions produce mono-Hdpa complex
benzoate, di-Hdpa complex 5 with coordinating NO3 anion,
4
with chelating
ꢀ
ꢀ
and tri-Hdpa complexes 6 and 7 with non-coordinating ClO4
ꢀ
and BF4 anions. One-, two-, or three-dimensional structures of
Cd(II)–Hdpa complexes can be produced by hydrogen bonding
and
p
–
p
interactions. These results indicate that both inter-molec-
interactions as well as anion effects
ular hydrogen bonds and
p–p
play very important roles in the construction of crystal structures
3.6. Luminescent study
in Cd(II)–Hdpa system.
We have also shown that the homogeneous catalysts 4, 5, and 6
catalyzed efficiently the transesterification of a variety of esters
with methanol, while 1, 2, 3 and 7 have displayed very slow con-
version. Importantly, the transesterification reaction catalyzed by
the catalyst 6 is the best among the catalytic systems reported pre-
viously in Cd-containing coordination compounds, to our best
knowledge. This result offers the opportunity to use many Cd-con-
taining complexes reported to date as a potential catalyst for the
transesterification reactions. In addition, the luminescent proper-
ties of compounds 1–7 have been investigated at room tempera-
ture, and the emissions for the complexes were found to be
similar to that of the free ligand (kmax = 352 nm), suggesting that
Luminescent compounds are of great current interest because of
their various applications in chemical sensors, photochemistry,
and electroluminescent display [43]. The luminescent properties
of compounds 1–7 have been investigated. The photoluminescent
spectra of compounds 1–7 and Hdpa ligand have been measured
at room temperature, and the wavelengths of the emission maxi-
mums and excitations are listed in Table 5 for compounds 1–7
and Hdpa ligand. The emissions for the complexes (Fig. 8) were
found to be similar to that of the free ligand ((kmax = 352 nm). Upon
complexation, the emissions of the complexes are not shifted com-
pared to the free ligand. Therefore, the emissions of 1–7 seem to be
attributed to the p–p* intraligand fluorescence [27,44,45]. In addi-
the emissions of 1–7 seem to be attributed to the p–p* intraligand
fluorescence.
tion, the enhancement of luminescence in 1, 2 and 5–7 may be
attributed to the ligation of ligand to the metal center, which effec-
tively increases the rigidity and reduces the loss of energy by radi-
ationless decay. These observations indicate that they may be
excellent candidates for potential photoactive materials [46].
Supplementary data
4. Conclusion
CCDC 737385, 737386, 737387, 737388, 737389 and 737390
contain the supplementary crystallographic data for 1, 2, 3, 4, 6
and 7. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.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.
We have shown six new structures of Cd(II) complexes contain-
ing Hdpa ligands to study anion effects. With chloride and bro-
mide, Cd(II) ions produce halide-bridged dinuclear units 1 and 2
while CdI2 produces mononuclear unit 3 without halide-bridging.

786
B.K. Park et al. / Polyhedron 29 (2010) 773–786
[23] L.C. Gianfranco, G. Ciani, D.M. Proserpio, S. Rizzato, CrystEngCommun 5 (2003)
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man resource development Project”, the Korean Science & Engi-
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