Anion effects on construction of cadmium(II) compounds with a chelating ligand bis(2-pyridylmethyl)amine: Their photoluminescence and catalytic activities

Article abstract of DOI:10.1016/j.ica.2012.01.002

Four new structures of Cd^II complexes containing bis(2-pyridylmethyl)amine (bispicam) ligands have been determined. Chloride anions bridge two Cd^II ions to form a dinuclear complex [(Cd(bispicam)Cl)₂(μ₂-Cl₂)] (1), and bromide and iodide ions produce two halide-coordinated [Cd(bispicam)X₂] complexes (X = Cl for 2 and Br for 3). Nitrate anions produce both nitrate-coordinated [Cd(bispicam)₂(NO₃)]⁺ and simple [mer-Cd(bispicam)₂]²⁺ with three nitrate counter-anions (4). These results indicate that anion effects play very important roles for construction of crystal structures and geometrical isomerism. Moreover, the homogeneous catalyst [Cd(bispicam)₂] (ClO₄)₂ (5) catalyzed efficiently the transesterification of a variety of esters with methanol, while rest of the complexes have displayed very slow conversions. Furthermore, 1-5 showed the intense emissions at room temperature, which could be used as a good candidate for a potential hybrid inorganic-organic photoactive material.

Full text of DOI:10.1016/j.ica.2012.01.002

Inorganica Chimica Acta 387 (2012) 106–116
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Anion effects on construction of cadmium(II) compounds with a chelating
ligand bis(2-pyridylmethyl)amine: Their photoluminescence and catalytic activities
Geun Hee Eom a, Jin Hoon Kim a, Young Dan Jo a, Eun Young Kim a, Jeong Mi Bae a, Cheal Kim a,
,
⇑
Sung-Jin Kim b, Youngmee Kim b,
⇑
a Department of Fine Chemistry, Seoul National University of Science & 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
Four new structures of CdII complexes containing bis(2-pyridylmethyl)amine (bispicam) ligands have been
determined. Chloride anions bridge two CdII ions to form a dinuclear complex [(Cd(bispicam)Cl)2(
2-Cl2)]
Article history:
Received 5 October 2011
Received in revised form 2 January 2012
Accepted 3 January 2012
Available online 11 January 2012
l
(1), and bromide and iodide ions produce two halide-coordinated [Cd(bispicam)X2] complexes (X = Cl for 2
and Br for 3). Nitrate anions produce both nitrate-coordinated [Cd(bispicam)2(NO3)]+ and simple [mer-
Cd(bispicam)2]2+ with three nitrate counter-anions (4). These results indicate that anion effects play very
important roles for construction of crystal structures and geometrical isomerism. Moreover, the homoge-
neous catalyst [Cd(bispicam)2](ClO4)2 (5) catalyzed efficiently the transesterification of a variety of esters
with methanol, while rest of the complexes have displayed very slow conversions. Furthermore, 1–5
showed the intense emissions at room temperature, which could be used as a good candidate for a poten-
tial hybrid inorganic–organic photoactive material.
Keywords:
CdII complexes
Photoluminescence
Bis(2-pyridylmethyl)amine
Catalyst
Ó 2012 Elsevier B.V. All rights reserved.
Transesterification
1. Introduction
with Zn(NO3)2, typical [Zn(bispicam)2]2+ cation was obtained and
ꢀ
showed fac geometric isomer. With non-coordinating ClO4 and
Much interest has recently been focused on the self-assembly
process for construction of coordination networks [1–6] that has
been affected by the hydrogen bonds [7–13],
OTfꢀ anions, there were fac isomers and enantiomers [25].
Another chelating ligand, 2,20-dipyridylamine (Hdpa), showed to
form mononuclear ZnII complexes by the reaction with zinc salts
[26–30], and then these ZnII complexes could be used as building
blocks for construction of polymeric compounds through weak
non-classical C/N–Hꢁ ꢁ ꢁX and C/N–Hꢁ ꢁ ꢁO hydrogen bonding. In addi-
tion, we have shown six new structures of CdII complexes contain-
ing Hdpa ligands to study anion effects [31]. With chloride and
bromide, CdII ions produce halide-bridged dinuclear units while
CdI2 produces a mononuclear unit without halide-bridging. CdII ions
produce mono-Hdpa complex with chelating benzoate, di-Hdpa
p–p stacking [14],
and anions [15–19] as well as ligand design [20] and metal ions
[21,22]. Among them, anion effects play very important roles for
construction of crystal structures and geometrical isomerism
[23–26]. For examples, bis(2-pyridylmethyl)amine (bispicam), a
tridentate ligand with the two terminal N-donor coordination sites
(pyridyl) and the central N-donor site (amine), can coordinate to
metal ions to provide complexes of the general formulation
[M(bispicam)2]X2. For this type of complex system, there are three
potential geometric isomers (Scheme 1): facial isomer, meridional
isomer, and enantiomers [23,24]. In our previous study, several ZnII
complexes of the general formulation [Zn(bispicam)2]X2 (X = Clꢀ
ꢀ
complex with coordinating NO3 anion, and tri-Hdpa complexes
ꢀ
ꢀ
with non-coordinating ClO4 and BF4 anions. Three-dimensional
structures of CdII-Hdpa complexes can be produced by hydrogen
[23], Brꢀ [24], Iꢀ [24], NO3 [25], ClO4 [23] and OTfꢀ [25]) have
been obtained, and there were fac geometric isomers or enantio-
mers according to anions. With halides, [Zn(bispicam)2]2+ cations
bonding and
inter-molecular hydrogen bonds and
p–p
interactions. These results also indicate that both
interactions as well as an-
ꢀ
ꢀ
p–p
ion effects play very important roles in the construction of crystal
structures in both ZnII and CdII systems [31]. In addition, many of
all these complexes catalyzed efficiently the transesterification of
a variety of esters with methanol, and Zn complexes showed gener-
ally better reactivities than Cd complexes. Moreover, most of Zn and
Cd complexes, especially ones with d10 metal centers, showed the
luminescent properties.
ꢀ
have only fac geometric isomer. With coordinating NO3 anion, a
nitrate-coordinated ZnII complex of the formulation [Zn(bispi-
cam)(NO3)2] was obtained, and when the benzoate was applied
⇑
Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim), tel.:
+82 2 3277 3589; fax: +82 2 3277 2384 (Y. Kim).
E-mail addresses: chealkim@seoultech.ac.kr (C. Kim), ymeekim@ewha.ac.kr
(Y. Kim).
To further investigate anion and metal effects on construction
of a variety of metal complexes containing chelating bispicam
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2012.01.002

G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
107
Herein we report the synthesis, crystal structures, catalytic
reactivities, and photoluminescence of four new Cd-containing
compounds formed by the reaction of the chelating bispicam
ligand and four different cadmium salts.
2. Experimental section
2.1. Materials
Methanol, diisopropyl ether, DMF, diethyl ether, methylene
chloride, 2,20-dipicolylamine, 4-nitrophenyl acetate, phenyl ace-
tate, 4-methylphenyl acetate, 4-nitrophenyl benzoate, phenyl ben-
zoate, 4-chlorophenyl benzoate, 4-methylphenyl benzoate, vinyl
acetate, methyl acetate, methyl benzoate, cadmium chloride, cad-
mium bromide, cadmium iodide, cadmium nitrate, and cadmium
perchlorate were purchased from Aldrich and were used as re-
ceived. Nitrophenyl benzoate was obtained from Lancaster.
2.2. Instrumentation
Elemental analysis for carbon, nitrogen, and hydrogen was car-
ried out by using a vario MACRO (Elemental Analysensysteme, Ger-
many) in the Laboratory Center of Seoul National University of
Science and Technology, Korea. IR spectra were measured on a
BIO RAD FTS 135 spectrometer as KBr pellets. 1H NMR spectra were
recorded on a Varian Mercury 400 spectrometer. Product analysis
for the transesterification reaction was performed on either a Hew-
lett–Packard 5890 II Plus gas chromatograph interfaced with Hew-
lett–Packard Model 5989B mass spectrometer or a Donam Systems
6200 gas chromatograph equipped with a FID detector using 30-m
capillary column (Hewlett.Packard, HP-1, HP-5, and Ultra 2). The
emission/excitation spectra were recorded on a Perkin Elmer
LS45 fluorescence spectrometer.
Scheme 1. Three potential geometric isomers of [M(bispicam)2]2+
.
ligands, and to find efficient catalysts to mediate catalytic transe-
sterification reactions and CdII-bispicam complexes with photolu-
minescence properties, therefore, CdII salts containing several
anions (Clꢀ, Brꢀ, Iꢀ, NO3ꢀ, and ClOꢀ4 [23]) have been applied to
this system.
2.3. Synthesis of [(Cd(bispicam)Cl)2(l2-Cl2)] (1)
35.9 mg (0.125 mmol) of CdCl2 was dissolved in 1 mL solution
MeOH/H2O (9:1) and added by 1 mL solution MeOH/H2O (9:1) of
2,20-dipicolylamine (56.8 mg, 0.25 mmol). Then, on the top of the
Table 1
Crystallographic data for compounds 1–5.
1
2
3
4
5a
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Space group
a (Å)
C25H30Cd2Cl4N6O
797.15
170(2)
0.71073
C2/c
33.458(2)
9.2278(6)
23.5759(16)
90.00
126.0330(10)
90.00
C12H10Br2CdN3
468.45
293(2)
0.71073
P21/n
8.6592(10)
27.482(3)
13.0114(16)
90.00
108.676(2)
90.00
C12H10CdI2N3
562.43
170(2)
0.71073
P21/c
8.8825(6)
28.850(2)
12.9269(10)
90.00
109.2470(10)
90.00
C48H52Cd2N16O12
1269.86
170(2)
0.71073
P1
8.5600(8)
9.8294(9)
15.9871(15)
86.052(2)
78.8910(10)
84.738(2)
1312.6(2)
1
C24H26CdCl2N6O8
709.81
293(2)
0.71073
C2/c
20.667(2)
10.9233(11)
13.9589(15)
90.00
114.488(2)
90.00
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
5886.2(7)
8
2933.3(6)
8
3127.5(4)
8
2867.7(5)
4
Z
Density (calc.) (Mg/m3)
Absorption coeff. (mmꢀ1
Crystal size (mm)
Reflections collected
Independent reflections
1.799
1.839
2.122
6.923
2.389
5.332
1.606
0.887
1.644
1.005
)
0.25 ꢂ 0.10 ꢂ 0.05
0.20 ꢂ 0.08 ꢂ 0.08
0.15 ꢂ 0.05 ꢂ 0.03
0.15 ꢂ 0.15 ꢂ 0.13
0.15 ꢂ 0.13 ꢂ 0.13
15999
16240
17329
7346
7783
5793 [R(int) = 0.0463]
5793/0/346
0.979
5720 [R(int) = 0.1138]
5720/0/325
0.816
6121 [R(int) = 0.0831]
6121/0/325
0.980
6014 [R(int) = 0.0301]
6014/3/703
1.025
2804 [R(int) = 0.0330]
2804/0/186
0.952
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0260,
wR2 = 0.0630
R1 = 0.0301,
wR2 = 0.0636
0.684 and ꢀ0.842
R1 = 0.0463,
wR2 = 0.1036
R1 = 0.0829,
wR2 = 0.1081
0.962 and ꢀ0.924
R1 = 0.0390,
wR2 = 0.0978
R1 = 0.0478,
wR2 = 0.1000
1.534 and ꢀ2.063
R1 = 0.0373,
wR2 = 0.0996
R1 = 0.0385,
wR2 = 0.1001
1.007 and ꢀ1.726
R1 = 0.0365,
wR2 = 0.0945
R1 = 0.0446,
wR2 = 0.0964
0.529 and ꢀ0.824
Largest difference in peak and hole
(e Åꢀ3
)
a
See Ref. [23].

108
G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
Table 2
reaction solution was carefully layered by 6 mL diethyl ether solu-
tion. Suitable crystals of compound 1 for X-ray analysis were ob-
tained in a few days. The yield was 16.0 mg (32.1%). 1H NMR
(DMSO, 400 MHz): d 7.45–8.65 (m, 16H, aromatic-H), d 4.50–4.55
Selected bond lengths (Å) and angles (°) for compounds 1–5.
1
Cd(1)–N(13)
Cd(1)–N(11)
Cd(1)–Cl(2)
Cd(2)–N(21)
Cd(2)–N(22)
Cd(2)–Cl(2)
Cd(1)–Cl(2)–Cd(2)
Cl(1)–Cd(1)–Cl(2)
Cl(2)–Cd(1)–Cl(3)
Cl(4)–Cd(2)–Cl(3)
2.352(2)
2.417(2)
2.5751(7)
2.339(2)
2.414(2)
2.6730(7)
90.59(2)
97.17(2)
89.93(2)
105.18(2)
Cd(1)–N(12)
Cd(1)–Cl(1)
Cd(1)–Cl(3)
Cd(2)–N(23)
Cd(2)–Cl(4)
Cd(2)–Cl(3)
Cd(1)–Cl(3)–Cd(2)
Cl(1)–Cd(1)–Cl(3)
Cl(4)–Cd(2)–Cl(2)
Cl(2)–Cd(2)–Cl(3)
2.413(2)
2.5251(7)
2.6722(7)
2.395(2)
2.4983(7)
2.6758(7)
88.46(2)
96.15(2)
99.55(2)
87.80(2)
(br, 2H, N–H), and
m
d
4.00–4.10 (br, 8H, CH2). IR (KBr):
(cmꢀ1) = 3257(brs, N–H), 1601(s), 1574(w), 1480(m), 1440(s),
1311(w), 1156(w), 1098(w), 1051(w), 1017(w), 985(w), 914(w),
881(w), 762(s), 637(w), 483(w). Anal. Calc. for C25H30Cd2Cl4N6O
(797.15), 1: C, 37.67; H, 3.79; N, 10.54. Found: C, 37.35; H, 3.89;
N, 10.26%.
2.4. Synthesis of [Cd(bispicam)X2] (X = Br for 2, I for 3)
2
Br(11)–Cd(1)
Br(21)–Cd(2)
Cd(1)–N(11)
Cd(1)–N(12)
2.5890(10)
2.6162(10)
2.319(6)
Br(12)–Cd(1)
Br(22)–Cd(2)
Cd(1)–N(13)
2.5757(11)
2.5616(10)
2.328(6)
43.9 mg (0.125 mmol) of CdBr2 was dissolved in 1 mL DMF and
added by 1 mL DMF solution of 2,20-dipicolylamine (56.8 mg,
0.25 mmol). Then, on the top of the reaction solution was carefully
layered by 6 mL diethyl ether solution. Suitable crystals of com-
pound 2 for X-ray analysis were obtained in a week. The yield
was 18.0 mg (30.7%). 1H NMR (DMSO, 400 MHz): d 7.45–8.15 (m,
8H, aromatic-H), d 4.55–4.65 (br, 1H, N–H), and d 4.00 4.15 (br,
2.397(10)
Cd(2)–N(23)
Cd(2)–N(22)
Br(22)–Cd(2)–Br(21)
2.332(6)
2.397(13)
113.60(4)
Cd(2)–N(21)
Br(12)–Cd(1)–Br(11)
2.339(6)
112.99(4)
3
Cd(1)–N(11)
Cd(1)–N(12)
Cd(1)–I(12)
Cd(2)–N(21)
2.339(5)
2.423(12)
2.8111(7)
2.351(5)
Cd(1)–N(13)
Cd(1)–I(11)
Cd(2)–N(23)
Cd(2)–N(22)
Cd(2)–I(22)
2.348(5)
2.7427(6)
2.340(5)
2.360(12)
2.7660(7)
114.35(2)
4H, CH2). IR (KBr):
m
(cmꢀ1) = 3206(brs, N–H), 1602(s), 1573(w),
1483(m), 1442(s), 1287(m), 1155(w), 1097(m), 1049(w),
1017(m), 988(w), 776(s), 640(w). Anal. Calc. for C12H10Br2CdN3
(468.45), 2: C, 30.77; H, 2.15; N, 8.97. Found: C, 30.97; H, 1.87;
N, 8.71%.
Cd(2)–I(21)
I(22)–Cd(2)–I(21)
2.7774(6)
110.18(2)
I(11)–Cd(1)–I(12)
4
46.2 mg (0.125 mmol) of CdI2 was dissolved in 1 mL MeOH and
added by 1 mL MeOH solution of 2,20-dipicolylamine (56.8 mg,
0.25 mmol). Then, on the top of the reaction solution was carefully
layered by 6 mL methylene chloride solution. Suitable crystals of
compound 3 for X-ray analysis were obtained in a few days. The
yield was 20.0 mg (28.4%). 1H NMR (DMSO, 400 MHz): d 7.51–
8.67 (m, 8H, aromatic-H), d 4.60–4.70 (br, 1H, N–H), and d 4.00–
Cd(1)–N(23)
Cd(1)–N(21)
Cd(1)–N(22)
Cd(2)–N(33)
Cd(2)–N(42)
Cd(2)–N(43)
Cd(2)–N(41)
2.342(7)
2.356(6)
2.376(6)
2.330(7)
2.370(6)
2.409(6)
2.591(5)
99.0(2)
89.52(19)
70.5(2)
72.0(2)
71.8(2)
90.7(2)
105.9(2)
99.0(2)
92.7(2)
71.2(2)
148.31(19)
81.7(2)
113.00(19)
81.4(2)
132.22(19)
87.6(2)
69.83(19)
72.60(19)
Cd(1)–N(11)
Cd(1)–N(12)
Cd(1)–N(13)
Cd(2)–N(31)
Cd(2)–N(32)
Cd(2)–O(11)
2.347(5)
2.360(7)
2.379(6)
2.358(6)
2.402(5)
2.452(5)
N(23)–Cd(1)–N(11)
N(11)–Cd(1)–N(21)
N(11)–Cd(1)–N(12)
N(23)–Cd(1)–N(22)
N(21)–Cd(1)–N(22)
N(23)–Cd(1)–N(13)
N(21)–Cd(1)–N(13)
N(22)–Cd(1)–N(13)
N(33)–Cd(2)–N(42)
N(33)–Cd(2)–N(32)
N(42)–Cd(2)–N(32)
N(31)–Cd(2)–N(43)
N(32)–Cd(2)–N(43)
N(31)–Cd(2)–O(11)
N(32)–Cd(2)–O(11)
N(33)–Cd(2)–N(41)
N(42)–Cd(2)–N(41)
N(43)–Cd(2)–N(41)
N(23)–Cd(1)–N(21)
N(23)–Cd(1)–N(12)
N(21)–Cd(1)–N(12)
N(11)–Cd(1)–N(22)
N(12)–Cd(1)–N(22)
N(11)–Cd(1)–N(13)
N(12)–Cd(1)–N(13)
N(33)–Cd(2)–N(31)
N(31)–Cd(2)–N(42)
N(31)–Cd(2)–N(32)
N(33)–Cd(2)–N(43)
N(42)–Cd(2)–N(43)
N(33)–Cd(2)–O(11)
N(42)–Cd(2)–O(11)
N(43)–Cd(2)–O(11)
N(31)–Cd(2)–N(41)
N(32)–Cd(2)–N(41)
142.1(2)
112.5(2)
105.2(2)
120.4(2)
168.2(2)
140.5(2)
70.5(2)
118.7(3)
139.4(2)
71.1(2)
158.5(2)
72.90(19)
90.3(2)
72.82(19)
100.2(2)
131.53(19)
82.08(18)
4.20 (br, 4H, CH2). IR (KBr): m
(cmꢀ1) = 3226(brm, N–H), 1601(s),
1573(w), 1480(m), 1440(s), 1284(m), 1153(w), 1097(m),
1048(w), 1015(m), 988(w), 773(s), 728(w), 640(w), 484(w). Anal.
Calc. for C12H10CdI2N3 (562.43), 3: C, 25.63; H, 1.79; N, 7.47. Found:
C, 25.72; H, 1.52; N, 7.23%.
2.5. Synthesis of [Cd(bispicam)2][Cd(bispicam)2(NO3)](NO3)3 (4)
39.3 mg (0.125 mmol) of Cd(NO3)2 was dissolved in 1 mL meth-
anol and added by 1 mL methanol solution of 2,20-dipicolylamine
(56.8 mg, 0.25 mmol). Then, on the top of the reaction solution
was carefully layered by 6 mL diisopropyl ether solution. Suitable
crystals of compound 4 for X-ray analysis were obtained in a few
days. The yield was 20.0 mg (25.2%). 1H NMR (DMSO, 400 MHz):
d 7.35–8.05 (m, 32H, aromatic-H), d 5.10–5.20 (br, 4H, N–H), and
5
d 4.10–4.30 (br, 16H, CH2). IR (KBr):
m
(cmꢀ1) = 3201(brs, N–H),
Cd(1)–N(3)#1
Cd(1)–N(2)#1
Cd(1)–N(1)#1
2.338(3)
2.340(3)
2.375(3)
Cd(1)–N(3)
Cd(1)–N(2)
Cd(1)–N(1)
N(3)#1–Cd(1)–N(2)#1
N(3)#1–Cd(1)–N(2)
N(2)#1–Cd(1)–N(2)
N(3)–Cd(1)–N(1)#1
N(2)–Cd(1)–N(1)#1
N(3)–Cd(1)–N(1)
N(2)–Cd(1)–N(1)
2.338(3)
2.340(3)
2.375(3)
73.91(11)
147.75(11)
133.08(16)
90.31(11)
96.45(10)
111.00(11)
71.63(10)
2917(w), 1603(m), 1573(w), 1484(w), 1441(m), 1384(s),
1151(w), 1097(w), 1052(w), 1014(w), 913(w), 829(w), 763(m),
637(w), 488(w). Anal. Calc. for C48H52Cd2N16O12(1269.86), 4: C,
45.40; H, 4.13; N, 17.65. Found: C, 45.14; H, 4.32; N, 17.30%.
N(3)#1–Cd(1)–N(3)
N(3)–Cd(1)–N(2)#1
N(3)–Cd(1)–N(2)
N(3)#1–Cd(1)–N(1)#1
N(2)#1–Cd(1)–N(1)#1
N(3)#1–Cd(1)–N(1)
N(2)#1–Cd(1)–N(1)
N(1)#1–Cd(1)–N(1)
88.87(15)
147.75(11)
73.91(11)
111.00(11)
71.63(10)
90.31(11)
96.45(10)
150.48(15)
2.6. Catalytic activity of compounds 1–5
Catalytic reaction conditions: Ester (0.05 mmol) was dissolved
in methanol (1 mL), and the compounds 1–5 (1.0 mg, 1.25 ꢂ
10ꢀ3 mmol for 1, 1.0 mg, 2.14 ꢂ 10 mmol for 2, 1.0 mg,
1.78 ꢂ 10 mmol for 3, 1.0 mg, 0.79 ꢂ 10 mmol for 4, and 1.0 mg,
1.41 ꢂ 10ꢀ3 mmol for 5) were added and shaken at 50 °C
(450 rpm). Reaction conversion was monitored by GC/Mass analy-
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, y, ꢀz + 3/
2.
2.7. Crystallography
sis of 20 lL aliquots withdrawn periodically from the reaction mix-
ture. All reactions were run at least three times and the average
conversion yields are presented. Yields were based on the forma-
tion of the products, methylacetate or methylbenzoate.
The diffraction data for all five compounds were collected on a
Bruker SMART AXS diffractometer equipped with a monochroma-
tor in the Mo K
a (k = 0.71073 Å) incident beam. The crystal was

G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
109
Scheme 2. Structures of CdII compounds containing bispicam ligands.
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 [32]. Hydrogen atoms were
located in the calculated positions. All hydrogen atoms except
hydrogen atoms of water molecules were located in the calculated
positions. The crystallographic data for compounds 1–5 are listed
in Table 1.
(Fig. 1(b)) and Table 3). In the dinuclear unit in 1, the Cd–Cl–Cd an-
gles are 88.46(2)° and 90.59(2)°, and the Cdꢁ ꢁ ꢁCd distance is
3.731(1) Å.
3.2. Crystal structures of Cd(bispicam)X2 (X = Br for 2, I for 3)
Not like chlorides with bridging ability, bromides and iodides
act as simple coordinating ligands in this system. A bispicam ligand
and two bromides or iodides coordinate to a CdII ion to form a dis-
torted trigonal bipyramidal environment, and the amine nitrogen
atom is disordered as shown in Fig. 2(a) for 2 and Fig. 3(a) for 3.
The Cd–N bond distances range from 2.296(13) to 2.427(18) Å
which are longer than those of the CdII-Hdpa system (2.259(6)–
2.307(7) Å) [31]. The Cd–Br distances range from 2.5616(10) to
2.6162(10) Å, and the Cd–I distances range from 2.7427(6) to
2.8111(7) Å (Table 2). The Br–Cd–Br angles are 112.99(4)° and
113.60(4)°, and the I–Cd–I angles are 110.18(2)° and 114.35(2)°.
There are C–Hꢁ ꢁ ꢁX (X = Br or I) hydrogen bonding interactions in
both compounds 2 and 3 (Table 3). The packing diagrams of both
compounds are shown in Figs. 2(b) and 3(b), respectively.
3. Results and discussion
In order to understand the anion effects on the construction of
crystal structures with the chelating bispicam ligand, we synthe-
sized four new compounds 1–4. The previously reported com-
pound 5 has been synthesized again to study anion effects for
the CdII-bispicam system [23]. All five structures including the pre-
viously reported 5 have been determined by X-ray crystallography.
Table 2 lists the selected bond distances and angles for 1–4. The
structures of all five CdII compounds containing bispicam ligands
are shown in Scheme 2.
3.1. Crystal structure of [(Cd(bispicam)Cl)2(l2-Cl2)] 1
3.3. Crystal structures of [Cd(bispicam)2][Cd(bispicam)2(NO3)](NO3)3
Chlorides act as both a simple coordinating ligand and a bridg-
ing ligand to form chloride-bridged dinuclear compound
(4)
1
(Fig. 1(a)). There is a methanol solvent molecule per a dinuclear
molecule. The geometry around the CdII ion is distorted octahedral
constructed by three N atoms of the chelating bispicam ligand, a
simple coordinating chloride, and two bridging chlorides. The
Cd–N bond distances range from 2.339(2) to 2.417(2) Å which
are a little longer than those of the CdII-Hdpa system (2.316(4)
and 2.333(4) Å) [31]. The Cd–Cl distances are 2.4983(7) and
2.5251(7) Å, which are shorter than the Cd–Clbridging distances
(2.5751(7)–2.6758(7) Å) (Table 2). The C–Hꢁ ꢁ ꢁCl intra-molecular
hydrogen bonding interactions and the O–Hꢁ ꢁ ꢁCl inter-molecular
hydrogen bonding interactions produce a polymeric structure
An asymmetric unit contains two independent CdII complex
cations: one is CdII coordinated by two bispicam ligands and the
other is CdII coordinated by two bispicam ligands and a nitrate
(Fig. 4(a)). There are three nitrate counter-anions to balance
charge. The nitrate coordinated CdII complex has seven-coordina-
tion geometry, and the other CdII complex has distorted octahedral
geometry. This octahedral Cd complex shows mer geometry that is
the only example for bispicam-containing Cd compounds. The in-
ter-molecular hydrogen bonding interactions provide a polymeric
compound (Fig. 4(b) and Table 3). The Cd–N bond distances range
from 2.330(7) to 2.591(5) Å which are longer than those of the

110
G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
Fig. 1. (a) Structure of 1. Displacement ellipsoids are shown at the 50% probability level. All hydrogen atoms and methanol solvent molecules were omitted for clarity. (b)
Polymeric structure derived by hydrogen bond interactions (green dotted lines). (For interpretation of the references to colour in this figure legend, the reader is referred to
the web version of this article.)
CdII-Hdpa system (2.315(3) and 2.320(3) Å), and Cd–Onitrate dis-
tance is 2.452(5) Å similar to that of the CdII-Hdpa system
(2.497(3) Å) (Table 2) [31].
systems as shown in Scheme 3. Halide anions can be used as bridg-
ing ligands in both CdII-Hdpa and CdII-bispicam systems. For CdII-
Hdpa system, depending on the size of the halide ions, the coordi-
nation on CdII ion changes from octahedral in chloride to trigonal
bipyramidal in bromide and tetrahedral in iodide. For CdII-bispi-
cam system, only chlorides can show bridging capability, and big-
ger bromides and iodides simply coordinate to CdII ions to form
mononuclear CdII complexes as shown in Scheme 3. In both sys-
tems, the bridging capability decreases from chloride down to io-
dide. Nitrate anions were used as simple O-donor coordinating
ligands for CdII-Hdpa system. In CdII-bispicam system, two inde-
pendent CdII-bispicam complexes were observed: one is nitrate-
coordinated Cd(bispicam)2 complex with a free nitrate, and the
other is simple [CdII(bispicam)2]+ cation complex with two free ni-
trates. CdII ion is big enough to produce a seven-coordinated
complex as well as six-coordinated (octahedral) complex. For
When the chelating bispicam ligands react with various ZnII
salts (Clꢀ [23], Brꢀ [24], Iꢀ [24], NO3 [25], ClO4 [23] and OTfꢀ
[25]), complexes of the general formulation [Zn(bispicam)2]X2
have been obtained, and there were fac geometric isomers or enan-
tiomers according to anions. In contrast to ZnII system, with CdII
salts, various structures (chloride bridged dinuclear, distorted
square pyramidal, distorted octahedral and seven-coordinated
mononuclear complexes) were observed according to the change
of the anions (Scheme 2).
ꢀ
ꢀ
Hdpa has also been used as a chelating ligand to form various
CdII complexes [31], and then those CdII complexes can be com-
pared to corresponding CdII complexes containing bispicam li-
gands. For both chelating Hdpa and bispicam ligands, various
anions (halides, nitrate, and perchlorate) have been adopted. For
each anion, different structures have been obtained in both
ꢀ
non-coordinating ClO4 anions, both Hdpa and bispicam ligands
produce the cation complexes containing three chelating Hdpa

G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
111
Table 3
ligands and two chelating bispicam ligands, respectively, with
Hydrogen bonds for compounds 1–5 (Å and °).
octahedral environments. The perchlorate anions occupy empty
positions between cation complexes for charge balances.
D–Hꢁ ꢁ ꢁA
d(D–H)
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
<(DHA)
1
C(23)–H(23)ꢁ ꢁ ꢁCl(4)#1
N(12)–H(12A)ꢁ ꢁ ꢁCl(3)#2
O(1S)–H(1S)ꢁ ꢁ ꢁCl(4)
C(11)–H(11)ꢁ ꢁ ꢁCl(2)
C(27)–H(27B)ꢁ ꢁ ꢁCl(3)
N(22)–H(22A)ꢁ ꢁ ꢁCl(1)
0.95
0.93
0.84
0.95
0.99
0.93
2.79
2.57
2.33
2.85
2.87
2.67
3.557(3)
3.453(2)
3.164(2)
3.504(3)
3.510(3)
3.524(2)
137.8
159.7
174.4
126.9
123.4
153.4
3.4. Photoluminescence property
Luminescent compounds are of great current interest because of
their various applications in chemical sensors, photochemistry,
and electroluminescent display [33]. In addition, coordination
polymers containing cadmium and zinc exhibit photoluminescent
properties [33,34]. Therefore, the luminescent properties of com-
pounds 1–5 have been investigated. The photoluminescent spectra
of compounds 1–5 have been measured in the solid state at room
temperature and that of bispicam ligand was measured in the li-
quid state. Emissions of compounds 1–5 were observed at
421 nm (kex = 354 nm) for 1, 421 nm (kex = 357 nm) for 2, 420 nm
(kex = 357 nm) for 3, 397 nm (kex = 355 nm) for 4, and 423 nm
(kex = 357 nm) for 5, respectively (Fig. 5), while ligand 2,20-dipicol-
ylamine showed an emission at 424 nm (kex = 350 nm). The emis-
sions for the complexes (Fig. 5) except for 4 can be tentatively
assigned to the intraligand transition of 2,20-dipicolylamine ligand,
since the similar emission was observed for the ligand. The emis-
sion band of complex 4 are blue-shifted compared to the corre-
sponding ligand, which indicates that the emission peak of 4
may be due to the metal-to-ligand charge transfer (MLCT) and/or
ligand-to-metal charge transfer (LMCT). In addition, it is notewor-
thy that 1–5 showed the intense emissions at room temperature,
suggesting that they may be a good candidate for a potential hy-
brid inorganic–organic photoactive material [35].
2
C(210)–H(210)ꢁ ꢁ ꢁBr(12)#1
3
C(110)–H(110)ꢁ ꢁ ꢁI(22)#1
4
0.93
0.95
2.81
3.03
3.681(10)
3.886(8)
156.6
151.1
C(210)–H(210)ꢁ ꢁ ꢁO(13)#1
C(110)–H(110)ꢁ ꢁ ꢁO(33)#2
C(49)–H(49)ꢁ ꢁ ꢁO(12)#3
C(27)–H(27B)ꢁ ꢁ ꢁO(41)
C(412)–H(412)ꢁ ꢁ ꢁO(23)
C(312)–H(312)ꢁ ꢁ ꢁO(32)#4
C(311)–H(311)ꢁ ꢁ ꢁO(43)
C(212)–H(212)ꢁ ꢁ ꢁO(33)#5
C(212)–H(212)ꢁ ꢁ ꢁO(31)#5
C(42)–H(42)ꢁ ꢁ ꢁO(13)#6
C(37)–H(37B)ꢁ ꢁ ꢁO(13)#1
C(31)–H(31)ꢁ ꢁ ꢁO(22)#4
C(29)–H(29)ꢁ ꢁ ꢁO(32)
0.95
0.95
0.95
0.99
0.95
0.95
0.95
0.95
0.95
0.95
0.99
0.95
0.95
0.95
0.95
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.48
2.51
2.58
2.38
2.48
2.43
2.45
2.43
2.50
2.53
2.57
2.55
2.40
2.47
2.45
2.36
2.38
2.46
2.24
2.22
2.24
2.02
3.415(10)
3.371(10)
3.147(10)
3.341(10)
3.360(11)
3.175(10)
3.160(11)
3.372(10)
3.189(10)
3.259(9)
3.552(9)
3.484(13)
3.352(12)
3.408(9)
3.379(10)
3.191(10)
3.097(8)
3.295(9)
3.030(9)
3.053(9)
3.035(8)
2.934(8)
167.1
150.4
118.7
162.3
154.6
134.9
131.1
174.0
129.2
133.8
170.0
166.9
174.9
169.0
165.4
148.2
133.4
149.0
142.9
149.3
143.0
168.2
C(23)–H(23)ꢁ ꢁ ꢁO(13)#7
C(13)–H(13)ꢁ ꢁ ꢁO(21)#8
N(42)–H(42A)ꢁ ꢁ ꢁO(32)#4
N(42)–H(42A)ꢁ ꢁ ꢁO(31)#4
N(32)–H(32A)ꢁ ꢁ ꢁO(23)
N(32)–H(32A)ꢁ ꢁ ꢁO(22)
N(22)–H(22A)ꢁ ꢁ ꢁO(43)#1
N(22)–H(22A)ꢁ ꢁ ꢁO(42)#1
N(12)–H(12A)ꢁ ꢁ ꢁO(33)#5
3.5. Catalytic transesterification reactions by the compounds 1–5
We have previously reported that Zn(Hdpa)X2 (X = Clꢀ, Brꢀ, Iꢀ,
ꢀO2CC6H5, NO3ꢀ, and SO42ꢀ) and Zn(bispicam)2Y2 (Y = Clꢀ, Brꢀ, Iꢀ,
NO3ꢀ, ClO4ꢀ, and OTfꢀ) complexes could carry out the catalytic
transesterification of a range of esters with methanol at room tem-
perature under the mild conditions [24,25,29,30]. Moreover, we
have recently shown that [Cd(Hdpa)1–3]Z2 (Z = Clꢀ, Brꢀ, Iꢀ,
ꢀO2CC6H5, NO3ꢀ, ClO4ꢀ, and BF4ꢀ) could also catalyzed the transe-
sterification reactions of a series of esters in spite of being well
known as an inert metal [31]. In order to compare the reactivity
of the complexes containing Zn ion and Cd ion, therefore, we have
examined the transesterification reaction with the compounds 1–
5. Thus, the compounds 1–5 were treated with phenyl acetate
and methanol at 50 °C under the neutral conditions (Eq. (1)). This
reaction produced quantitatively the corresponding product
methyl acetate.1
5
C(6)–H(6B)ꢁ ꢁ ꢁO(3)#2
C(6)–H(6A)ꢁ ꢁ ꢁO(2)
C(3)–H(3)ꢁ ꢁ ꢁO(2)#3
N(2)–H(2A)ꢁ ꢁ ꢁO(1)
0.97
0.97
0.93
0.91
2.51
2.55
2.53
2.13
3.335(5)
3.255(6)
3.367(6)
3.033(4)
143.1
129.6
150.5
171.1
Symmetry transformations used to generate equivalent atoms of 1: #1 x, y + 1, z; #2
ꢀx + 1/2, ꢀy + 1/2, ꢀz + 1.
Symmetry transformations used to generate equivalent atoms of 2: #1 x ꢀ 3/2,
ꢀy + 3/2, z + 1/2.
Symmetry transformations used to generate equivalent atoms of 3: #1 ꢀx + 2,
ꢀy + 2, ꢀz + 1.
Symmetry transformations used to generate equivalent atoms of 4: #1 x ꢀ 1, y, z;
#2 x ꢀ 1, y ꢀ 1, z; #3 x, y + 1, z; #4 x + 1, y, z; #5 x, y ꢀ 1, z; #6 x ꢀ 1, y + 1, z; #7
x ꢀ 1, y, z ꢀ 1; #8 x + 1, y ꢀ 1, z ꢀ 1.
Symmetry transformations used to generate equivalent atoms of 5: #1 ꢀx + 1, y,
ꢀz + 3/2; #2 x, ꢀy + 2, z + 1/2; #3 ꢀx + 1, ꢀy + 2, ꢀz + 2.
O
O
catalysts 1-5
CH3COCH3
HOCH3
..
O2N
OCCH3
O2N
ð1Þ
+
OH +
Compound 5 has shown a moderate catalytic reactivity (6 days; see
Table 4), while rest of the complexes have displayed very slow con-
versions (17–30 days; data not shown). The catalytic reactivity of 5
is three times slower than that of the corresponding Zn complexes
[23], confirming the fact that the second period transition metals
are less labile for the substitution reaction. Moreover, 5 showed six
times slower activity than the corresponding Cd complexes contain-
ing Hdpa ligand [31]. This difference might be explained by the elec-
tron density of metal center. Cadmium ion center of 5 would be more
electron-rich than that of [Cd(Hdpa)3](ClO4)2 complex, because the
electron-rich central-amine of the ligand bispicam in 5 coordinates
to the Cd center, while the central amine of Hdpa in [Cd(Hdpa)3](-
ClO4)2 is not involved in the coordination sphere. Therefore, 5 having
more electron-rich Cd center might show slower catalytic reactivity
1
A control reaction carried out in absence of the complexes showed trace amounts
of the conversion of the ester to the product in the same time period.

112
G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
Fig. 2. (a) Structure of 2. Displacement ellipsoids are shown at the 50% probability level. The disordered amine N atom is shown. The C–Hꢁ ꢁ ꢁBr hydrogen bond interaction
(green dotted lines) is shown. All hydrogen atoms except a hydrogen bonding atom were omitted for clarity. (b) Packing diagram of 2. (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
than the corresponding [Cd(Hdpa)3](ClO4)2 having more electron-
deficient Cd center.
complexes with Hdpa ligand [29–31]. These results suggest that
5 could be used to carry out efficient transesterification reaction
of phenyl benzoates, which are known as difficult substrates. Vinyl
acetate, which is widely used as a precursor for ester synthesis
[24,25,29–31], was also converted efficiently to the product methyl
acetate within 0.4 days by the catalyst (entry 8).
Based on the structure of 4 containing both seven-coordinated
CdII complex and octahedral CdII complex, we are able to propose
a possible reaction mechanism for 5-catalyzed transesterification.
Though 5 has the saturated structure without a labile ligand, the se-
ven-coordination on CdII suggests that the substrate ester might
coordinate to cadmium ion of the complex acting as Lewis acid.
Therefore, the Cd center interacts with the oxygen atom of carbonyl
As 5 showed the moderate catalytic reactivity for the transeste-
rification reaction of phenyl acetate with methanol, we have inves-
tigated the transesterification of various p-substituted phenyl
acetates and benzoates with it (Table 4). The substrates with the
electron-withdrawing substituents have undergone faster transe-
sterification (entries 1 and 4), while those with the electron-donat-
ing ones have shown slow reaction (entries 3 and 7). It is
worthwhile to note that in the presence of 5, p-substituted phenyl
benzoates have undergone 2–10 times faster transesterification
reactions than p-substituted phenyl acetates, unlike the transeste-
rification reaction results previously shown in zinc and cadmium

G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
113
Fig. 3. (a) Structure of 3. Displacement ellipsoids are shown at the 50% probability level. The disordered amine N atom is shown. The C–Hꢁ ꢁ ꢁI hydrogen bond interaction
(green dotted lines) is shown. All hydrogen atoms except a hydrogen bonding atom were omitted for clarity. (b) Packing diagram of 3. (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
of ester, making the carbonyl more electrophilic. Then, the nucleo-
phile methanol could attack the resulting activated carbonyl group
to produce the product methyl ester as shown in Scheme 4.
Moreover, as shown in Table 4, the fact that the substrates with
the electron-withdrawing substituents have undergone faster
transesterification, suggests that the second step in Scheme 4, the

114
G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
Fig. 4. (a) Structure of 4. Displacement ellipsoids are shown at the 30% probability level. All hydrogen atoms and nitrate counter-anions were omitted for clarity. (b) The
hydrogen bond interactions in a unit cell (green dotted lines). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of
this article.)
attack of the nucleophile methanol into the resulting activated car-
bonyl group, is the rate-determining step. If the first step is the
rate-determining step, the presence of the electron-withdrawing
groups on the phenyl ring of substrate would destabilize the first
reaction intermediate, resulting in slower transesterification
reactions.
There is another possible mechanism that cannot be ruled out.
The hydrogen atom of amine N–H moiety in the complex 5 acts as
the general-acid catalyst as previously proposed [24,25], because
the hydrogen atom could be acidic by coordinating of nitrogen of
N–H to cadmium ion (Scheme 5). As 5 has the saturated structure
without a labile ligand, we presume that the substrate ester does
not coordinate to zinc ion of the complex acting as Lewis acid, unlike
the former proposed mechanism. Therefore, we propose that this
acidic hydrogen interacts with the oxygen atom of carbonyl of ester,
making the carbonyl more electrophilic. As proposed in the former
mechanism (Scheme 4), then, the nucleophile methanol could at-
tack the resulting activated carbonyl group to produce the product
methyl ester. More detailed mechanistic studies to figure out the
reaction mechanism are in progress in our laboratory.
4. Conclusions
Four new structures of CdII complexes containing bispicam
ligands have been determined. For chloride, chloride bridging
dinuclear complex [(Cd(bispicam)Cl)2(l2-Cl2)] with octahedral

G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
115
Scheme 3. Structures of CdII complexes containing Hdpa or bispicam ligands according to anions.
Table 4
Transesterification of esters by methanol in the presence of compound 5 at 50 °C.a
Entry
Substrate
5
(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
3
6
8
0.3
2
0.6
4
0.4
4-Methylphenyl benzoate
Vinyl acetate
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, 1.41 ꢂ 10ꢀ3 mmol for 5, 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
c
substrate in CH3OH.
Fig. 5. Emission spectra of complexes 1–5 and ligand (bispicam) at room
temperature.
three nitrate counter-anions were obtained. These results indicate
that anion effects play very important roles for construction of
crystal structures and geometrical isomerism. We have also shown
that the homogeneous catalyst [Cd(bispicam)2](ClO4)2 (5) cata-
lyzed efficiently the transesterification of a variety of esters with
geometry was obtained. For bromide and iodide, two halide-coor-
dinated [Cd(bispicam)X2] complexes with trigonal bipyramidal
geometry were obtained. For nitrate, both a nitrate-coordinated
[Cd(bispicam)2(NO3)]+ and a simple [mer-Cd(bispicam)2]2+ with

116
G.H. Eom et al. / Inorganica Chimica Acta 387 (2012) 106–116
and Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Education, Sci-
ence and Technology (2011-0008018), and RP-Grant 2011 of Ewha
Womans University is gratefully acknowledged.
Appendix A. Supplementary material
CCDC 806245, 806244, 806246, 806243 and 806242 contains
the supplementary crystallographic data for 1, 2, 3, 4 and 5. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via http://www.ccdc.cam.ac.uk/data_request/
cif. Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.ica.2012.01.002.
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Scheme 5. Another possible mechanism with the saturated complex 5.
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Financial support from Korean Science & Engineering Founda-
tion (2009-0074066), Converging Research Center Program through
the National Research Foundation of Korea (NRF) funded by the
Ministry of Education, Science and Technology (2011K000675),