Synthesis, crystal structures, and third-order nonlinear optical properties of two novel complexes of H4edbbp with Zn(II), Cd(II)

Article abstract of DOI:10.1016/j.molstruc.2004.07.013

We synthesized a new organo-diphosphonic acid ligand H₂O ₃PCH(Ph)NH(CH₂)₂NH(Ph)CHPO₃H ₂ [ethane-1,2-diamino-N,N′-bis(benzyl phosphonic)acid, H ₄edbbp] and its two complexes [NH₃CH(CH ₃)CH₂NH₃]₂M₂(edbbp) ₂·H₂O [M=Zn(II) (1), Cd(II) (2)] in this paper. The complexes 1-2 were structurally characterized by means of X-ray single crystal diffraction. The central ion (M=Zn or Cd) has a distorted square-pyramidal coordination environment by three oxygen atoms from phosphonate units and two nitrogen atoms of H₄edbbp. The fundamental structural units [M ₂(edbbp)₂]^4- are linked by extensive intermolecular hydrogen bonds between 1,2-propyldiamine cations and phosphonate oxygen atoms, forming a one-dimensional chain structure. The third-order nonlinear optical (NLO) properties of 2 were determined by Z-scan techniques. NLO refractive index n₂, χ⁽³⁾ of 2's, and hyperpolarizability γ values were calculated to be 1.31×10 ^-17 m² W^-1, 3.19×10^-11 and 8.57×10^-30 esu, respectively. The results indicate that complex 2 exhibits very strong NLO absorption and self-focusing effects.

Full text of DOI:10.1016/j.molstruc.2004.07.013

Journal of Molecular Structure 707 (2004) 153–160
www.elsevier.com/locate/molstruc
Synthesis, crystal structures, and third-order nonlinear optical properties
of two novel complexes of H4edbbp with Zn(II), Cd(II)
*
Yao-Ting Fan , Dong-Xu Xue, Gang Li, Hong-Wei Hou, Chen-Xia Du, Hui-Jie Lu
Department of Chemistry, Zhengzhou University, Zhengzhou 450052, China
Received 10 February 2004; revised 30 June 2004; accepted 8 July 2004
Available online 2 September 2004
Abstract
We synthesized a new organo-diphosphonic acid ligand H2O3PCH(Ph)NH(CH2)2NH(Ph)CHPO3H2 [ethane-1,2-diamino-N,N0-bis(benzyl
phosphonic)acid, H4edbbp] and its two complexes [NH3CH(CH3)CH2NH3]2M2(edbbp)2$H2O [MZZn(II) (1), Cd(II) (2)] in this paper.
The complexes 1–2 were structurally characterized by means of X-ray single crystal diffraction. The central ion (MZZn or Cd) has a
distorted square-pyramidal coordination environment by three oxygen atoms from phosphonate units and two nitrogen atoms of H4edbbp.
The fundamental structural units [M2(edbbp)2]4K are linked by extensive intermolecular hydrogen bonds between 1,2-propyldiamine
cations and phosphonate oxygen atoms, forming a one-dimensional chain structure. The third-order nonlinear optical (NLO) properties
of 2 were determined by Z-scan techniques. NLO refractive index n2, c(3) of 2’s, and hyperpolarizability g values were calculated to be
1.31!10K17 m2 WK1, 3.19!10K11 and 8.57!10K30 esu, respectively. The results indicate that complex 2 exhibits very strong NLO
absorption and self-focusing effects.
q 2004 Published by Elsevier B.V.
Keywords: Metal–organodiphosphonate complex; Synthesis; Crystal structures; Third-order NLO properties
1. Introduction
[(VO)(H2O){O3PCH2NH(C2H4)2NHCH2PO3}] of ligand
N,N0-piperazinebis-(methylenephosphonic acid) [3b]. Till
now, people’s research interest focuses on the design and
synthesis of novel metal diphosphonate complexes with
optimal magnetic properties, and do not give many efforts
toward the study of their nonlinear optical (NLO) proper-
ties, especially the third-order NLO refractive properties.
The design and synthesis of novel compounds with more
perfect optical nonlinearities represent an active research
field in modern chemistry and material science. This may be
due to that the third-order NLO materials can be used for a
number of photonic applications, such as optical signal
processing, optical communication, optical computing,
optical limiting effect, etc. [4].
Recently, the considerable attention of research activity
in the metal–organophosphonate chemistry has been
focused on the design and assembly of multifunctional
coordination compounds, because of their interesting
structures and potential applications in the fields of ion
exchange, catalyst, sensors, and nonlinear optics materials
[1]. The generation of these molecular architecture rests on
several factors: the performance of organic ligand, a species
of the metal ion, and the reaction conditions [2]. By careful
control of the synthesis conditions and the species of
organic ligand employed, a few diphosphonate compounds
with layered- or pillared-structure types have been reported
[3]. For example, Clearfield and co-workers have reported
the structure of layered compound [Cd2LCl(H2O)] (H3LZ
N-(phosphonomethyl)proline) [3a]. Haushalter and co-
Here our research interest focuses on new potential
third-order NLO materials. Considering organo-diphospho-
nic acid ligand and metal ion may make an important
contribution to optical nonlinearity of metal–organopho-
sphonate complexes, we synthesized a new organo-
diphosphonic acid ligand, H2O3PCH(Ph)NH(CH2)2-
NH(Ph)CHPO3H2 (ethane-1,2-diamino-N,N0-bis(benzyl
workers have described
a pillared-type complex
* Corresponding author. Tel./fax: C86-371-7766017.
E-mail address: yt.fan@zzu.edu.cn (Y.-T. Fan).
0022-2860/$ - see front matter q 2004 Published by Elsevier B.V.
doi:10.1016/j.molstruc.2004.07.013

154
Y.-T. Fan et al. / Journal of Molecular Structure 707 (2004) 153–160
phosphonic)acid) (H4edbbp), and its corresponding two
complexes [NH3CH(CH3)CH2NH3]2M2(edbbp)2$H2O
(MZZn(II) (1) and Cd(II) (2)). The crystal structures of
the two complexes were characterized by X-ray diffraction.
Moreover, the third-order NLO refractive property of
complex 2 was also measured by Z-scan techniques in
DMF solution. The calculated hyperpolarizability g value is
8.57!10K30 esu. The results indicate that complex 2
exhibits strong third-order NLO refractive properties.
Scheme 2.
pressure to give an acidified oil matter, distilled water
(60 ml) was then added, and the resultant solution was
stirred and refluxed for 1 h to give a white solid. The
compound may be purified from NaOH and HCl solution to
yield 24.1% white powder solid, m.p. 241–242 8C. IR
(KBr)/cmK1: 3423(–OH), 1626(NH), 1156(PaO), 1076
(–PO3), 785, 572(C6H5–); Anal. Calcd. for C16H22O6N2P2
(%): C, 48.0; H, 5.5; N, 7.0. Found (%): C, 47.5; H, 5.65; N,
6.95; 1H NMR (NaODCD2O): d 7.39(d, 10H), 3.71(t, 2H),
2.62(s, 4H).
2. Experimental
2.1. Materials and physical techniques
All chemicals were of reagent quality obtained from
commercial sources and used without further purification.
IR spectra were performed on a PE spectrophotometer
with KBr pellets in the region of 400–4000 cmK1. Carbon,
hydrogen and nitrogen analyses were carried out on a Carlo-
Erba 1106 elemental analyzer. 1H NMR spectra were
recorded at room temperature (RT) on a Bruker DPX-400
spectrometer.
The synthetic route of H4edbbp was shown in Scheme 2.
2.3. Preparation of
[NH3CH(CH3)CH2NH3]2Zn2(edbbp)2$20H2O (1)
A solution of Zn(NO3)2$6H2O (0.0130 g, 0.044 mmol)
in deionized water (4 ml) was added dropwise to a
solution of H4edbbp (0.0202 g, 0.051 mmol) in deionized
water (2 ml), and adjusted pHZ7 by 1,2-propyldiamine
aqueous solution. The mixed solution was then stirred for
30 min and filtered. The resulting solution was allowed to
stand at RT, colorless crystals suitable for X-ray single
crystal analysis were obtained over 24 h in 55% yield.
IR (KBr)/cmK1: 3411(OH), 1636(NH), 1051(–PO3), 703,
603(–C6H5).
2.2. Synthesis of ethane-1,2-diamino-N,N0-bis
(benzyl phosphonic)acid (H4edbbp)
The target compound H4edbbp was synthesized by two
step reaction in this paper. First of all, the benzaldehyde
ethylenediamino schiff base (Bded) was prepared as follows
(Scheme 1):
A mixture of benzaldehyde (0.24 mol) and ethylenedia-
mino (0.1 mol) in petroleum ether (30 ml) was refluxed for
3 h. The resulting solution was allowed to stand at RT in a
primrose solid powder. The compound was recrystallized
from petroleum ether to yield 90% primrose crystalline
powder, m.p. 60 8C. IR (KBr)/cmK1: 1550 (CaN),
1024(C–C), 710(C6H5–). Anal. Calcd. for C16H16N2 (%):
C, 81.36; H, 6.78; N, 11.86. Found (%): C, 80.95; H, 6.56;
N, 11.67.
2.4. Preparation of
[NH3CH(CH3)CH2NH3]2Cd2(edbbp)2$25H2O (2)
Complex 2 was prepared in a similar manner as that of
complex 1. Reaction of Cd(NO3)2$4H2O (0.0141 g,
0.046 mmol) with H4edbbp (0.0201 g, 0.051 mmol) in
aqueous solution gave complex 2. Colorless single crystals
suitable for X-ray single crystals analysis were obtained
over 24 h in 65% yield. IR (KBr)/cmK1: 3400(OH),
1636(NH), 1050(–PO3), 702, 591(–C6H5).
Thereafter, H4edbbp was synthesized according to the
synthetic route described below : a trimethyl phosphate
(0.1 mol) was added dropwise to a solution of Bded
(0.05 mol) in glacial acetic acid (100 ml), then the reaction
mixture was stirred at 80–85 8C for 3 h, and the solvent was
removed under reduced pressure to give an a viscous
orange-yellow oil matter, adding concentrated HCl (80 ml)
to above oil matter, and the mixture was stirred and refluxed
for about 3 h. Excess HCl are removed under reduced
2.5. Single-crystal X-ray diffraction
Crystal data and structure refinement for the two
complexes are summarized in Table 1. All measurements
were made on a Rigaku RAXIS-IV imaging plate with
˚
graphite monochromated Mo Ka radiation (lZ0.71073 A).
Colorless single crystals of complexes 1 (0.3!0.2!
0.2 mm), and 2 (0.3!0.3!0.2 mm) were selected and
mounted on a glass fiber. All data were collected at a
temperature of 195 K using the u–2q scan technique and
corrected for Lorenz-polarization effects. A correction for
secondary extinction was applied.
Scheme 1.

Y.-T. Fan et al. / Journal of Molecular Structure 707 (2004) 153–160
155
Table 1
Crystal data and structure refinement for complexes 1 and 2
Table 2
˚
Selected bond lengths (A) and angles (8) for complexes 1 and 2
Compounds
1
2
Compound 1
Zn(1)–O(7)
1.956(3)
Zn(2)–O(5)
1.952(3)
Formula
C38H100Zn2N8P4O32
1434.8
C38H110Cd2N8P4O37
1556.8
Zn(1)–O(1)
1.990(3)
Zn(2)–O(10)
1.980(3)
Fw
Zn(1)–O(4)
2.052(3)
Zn(2)–O(8)
2.060(3)
Temperature (K)
˚
Wavelength (A)
195
195
Zn(1)–N(2)
2.099(4)
Zn(2)–N(3)
2.136(4)
0.71073
0.30!0.20!0.20
Colorless
Monoclinic
P21/n
0.71073
Zn(1)–N(1)
2.220(3)
Zn(2)–N(4)
2.224(3)
Crystal sizes (mm)
Color
0.30!0.30!0.20
Colorless
Triclinic
O(7)–Zn(1)–O(1)
O(7)–Zn(1)–O(4)
O(1)–Zn(1)–O(4)
O(7)–Zn(1)–N(2)
O(1)–Zn(1)–N(2)
O(4)–Zn(1)–N(2)
O(7)–Zn(1)–N(1)
O(1)–Zn(1)–N(1)
O(4)–Zn(1)–N(1)
N(2)–Zn(1)–N(1)
109.14(12)
103.32(12)
95.73(12)
118.16(13)
131.13(14)
85.25(13)
94.92(12)
85.20(12)
160.26(13)
79.45(13)
O(5)–Zn(2)–O(10)
O(5)–Zn(2)–O(8)
O(10)–Zn(2)–O(8)
O(5)–Zn(2)–N(3)
O(10)–Zn(2)–N(3)
O(8)–Zn(2)–N(3)
O(5)–Zn(2)–N4)
O(10)–Zn(2)–N(4)
O(8)–Zn(2)–N(4)
N(3)–Zn(2)–N(4)
104.99(14)
105.33(12)
95.55(12)
110.59(14)
143.09(15)
84.47(12)
103.20(13)
83.96(13)
150.55(14)
78.80(13)
Crystal syst
Space group
˚
a (A)
˚
b (A)
˚
c (A)
P-1
14.745(2)
25.171(4)
17.675(3)
90
14.6705(15)
15.5102(15)
17.5653(17)
68.3310(10)
71.3930(10)
79.2560(10)
3509.6(6)
2
a (8)
b (8)
g (8)
102.335(2)
90
3
˚
V (A )
6408.9(16)
4
Compound 2
Cd(1)–O(3)#1
Cd(1)–O(4)
Z
Dc (mg mK3
)
1.394
1.481
2.198(3)
2.218(3)
2.247(3)
2.336(3)
2.369(3)
102.55(11)
Cd(2)–O(10)#2
Cd(2)–O(7)
Cd(2)–O(12)
Cd (2)–N(4)
Cd(2)–N(3)
O(10)#2–Cd(2)–
O(7)
2.189(4)
2.200(3)
2.272(3)
2.339(4)
2.365(3)
113.36(14)
Absorption coefficient
(mmK1
0.933
0. 788
Cd(1)–O(1)
)
Cd(1)–N(1)
F(000)
2744
1582
Cd(1)–N(2)
Reflections collected/
unique
26,136/11,263
14,439/12,023
O(3)#1–Cd(1)–O(4)
Data/restraints/par-
ameters
Goodness-of-fit on F2
R1, wR2a
11,263/0/831
12,023/0/875
O(3)#1–Cd(1)–O(1)
O(4)–Cd(1)–O(1)
O(3)#1–Cd(1)–N(1)
96.62(11)
O(10)#2–Cd(2)–
O(12)
96.81(11)
96.68(11)
135.04(11)
1.036
1.129
102.93.
(10)
O(7)–Cd(2)–O(12)
0.1688, 0.2098
1.395, K0.863
0.0801, 0.1680
1.586, K1.331
Drmax and Drmin
K3
134.63(12)
O(10)#2–Cd(2)–
N(4)
˚
(e A
)
a
1=2
2
R1ZSjjFojKjFcjj=SjFoj; wR2ZfSwðjFojKjFojÞ =SwFo2g
:
O(4)–Cd(1)–N(1)
O(1)–Cd(1)–N(1)
O(3)#1–Cd(1)–N(2)
122.45(12)
79.98 (10)
107.33(11)
O(7)–Cd(2)–N(4)
O(12)–Cd(2)–N(4)
O(10)#2–Cd(2)–
N(3)
111.54(14)
80.02(11)
108.05(13)
The two structures were solved by direct methods and
expanded using the Fourier technique. All the non-hydrogen
atoms were refined using anisotropic thermal parameters.
Hydrogen atoms were included but not refined. The final
cycle of full-matrix least-squares refinement was based on
11,263 observed reflections and 831 variable parameters for
complex 1, and 12,023 observed reflections and 875
variable parameters for complex 2. All calculations were
performed using the SHELX-97 crystallographic software
package [5]. Selected bond lengths and bond angles of
complexes 1–2 are listed in Table 2. Primary intermolecular
hydrogen bonds are given in Table 3.
O(4)–Cd(1)–N(2)
O(1)–Cd(1)–N(2)
N(1)–Cd(1)–N(2)
80.57(11)
154.54(11)
77.10(11)
O(7)–Cd(2)–N(3)
O(12)–Cd(2)–N(3)
N(4)–Cd(2)–N(3)
81.12(11)
153.83(14)
76.68(12)
Symmetry transformations used to generate equivalent atoms: #1Kx,
KyC1, KzC1; #2 KxK1, KyC2, Kz.
the reaction of benzylidenediphenylamine with dimethyl
phosphate at 130–140 8C without the presence of solvent
[7]. However, the desired compound H4edbbp was not
obtained according to the literature [7]. Here we synthesized
target ligand H4edbbp by two step reaction under relatively
mild conditions. Furthermore, H4edbbp could also be
prepared by one-pot reaction of trimethyl phosphate with
benzaldehyde and ethylenediamine in glacial acetic acid at
80–85 8C directly. Its synthetic route is as follows
(Scheme 3):
2.6. Nonlinear optical measurements
A DMF solution for complex 2 was placed in a 1-mm
quartz cuvette for NLO measurements. The NLO properties
were determined by procedures described in previous
literature [6].
Trimethyl phosphate, which was used as a starting
material, directly reacted with benzaldehyde and ethylene-
diamine in glacial acetic acid at 80–85 8C, to afford
H4edbbp. Compared with two step reaction, the synthetic
route in one-pot reaction is simple and more effective for
preparation of H4edbbp. The ligand was insoluble in neutral
water and common organic solvents, such as MeOH, EtOH,
MeCN, THF, DMSO and DMF, but only soluble in aqueous
alkali solution.
3. Results and discussion
3.1. Syntheses
Green and co-workers reported previously the synthesis
of aromatic aminophosphonic acid NH2CH(Ph)PO3H2 by

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Y.-T. Fan et al. / Journal of Molecular Structure 707 (2004) 153–160
Table 3
Primary intermolecular hydrogen bonds for complexes 1 and 2
D–H
d(D–H) d(H/A) :DHA d(D/A)
A
Complex 1
N8–H8E
0.910
0.910
1.922
1.785
2.035
2.128
1.955
1.800
151.84
173.34
140.36
138.31
152.64
166.15
2.758
2.690
2.797
2.872
2.795
2.692
O2 [KxC5/2,
yK1/2,
KzC3/2]
O3 [KxC3/2,
yK1/2,
N6–H6B
KzC3/2]
O5 [KxC1/2,
yK1/2,
N5–H5D 0.910
KzC3/2]
O7 [KxC5/2,
yK1/2,
KzC3/2]
O11 [KxC1/
2, yK1/2,
KzC3/2]
O12 [KxC3/
2, yK1/2,
KzC3/2]
N8–H8C
N5–H5C
0.910
0.910
Fig. 1. The dimeric structural unit of [NH3CH(CH3)CH2NH3]2Zn2
(edbbp)2$20H2O.
MeOH, EtOH, MeCN, THF and DMF. Single crystals
suitable for X-ray crystallography for these compounds
were collected by slow evaporation of their aqueous
solution at RT.
N7–H7D 0.910
Complex 2
N5–H5B
N5–H5C
0.910
0.910
1.884
1.923
166.75
153.24
2.777
2.766
O6
3.2. Crystal structure of
[NH3(CH)CH3CH2NH3]2Zn2(II)(edbbp)2$20H2O(1)
O5 [KxK1,
KyC1,
KzC1]
O6
N6–H6B
N6–H6C
0.910
0.910
1.806
1.888
164.23
161.21
2.693
2.765
Complex 1 crystallizes in monoclinic with space group
of P21/n. The asymmetric unit consists of two Zn atoms, two
equivalent edbbp4K, two protonated 1,2-propyldiamine
cations, and 20 water molecules. Fig. 1 shows the structure
unit of complex 1 with atomic numbering, the water
molecules and protonated 1,2-propyldiamino cation are
omitted for clarity. Each Zn ion is five-coordinate bonding
to three oxygen atoms come from phosphonate units and
two nitrogen atoms from the ligand. The Zn–O and Zn–N
O3 [Kx,
KyC1,
KzC1]
O9
N8–H8D 0.910
N7–H7D 0.910
1.730
1.938
176.16
148.03
2.639
2.752
O11 [xC1,
y, z]
The complexes 1–2 were prepared by the reaction of
transition metal ions (MZZn(II), Cd(II)) with H4edbbp in
the presence of 1,2-propyldiamine in aqueous solution.
Herein, 1,2-propyldiamine was employed as a template
agent of the reaction. Although several inorganic or organic
alkalies, such as sodium hydroxide, methylamine, ethyle-
nediamine, and piperazine were also used as template agents
of the reaction, the corresponding complexes were not
obtained under the same experimental conditions. Our
experimental results reveals that 1,2-propyldiamine can be
used as an optimum directing structure agent in the
preparation of the complexes [NH3CH(CH3)CH2NH3]2-
M2(II)(edbbp)2$H2O (MZZn(II), Cd(II)).
˚
distances range from 1.952(3) to 2.060(3) A and from
˚
2.099(4) to 2.224(3) A, respectively, which are close to that
of the reported zinc diphosphonate compounds previously
[9]. The equatorial plane of Zn(1) is defined by O(1), N(1),
N(2), O(4) atoms with the largest deviation of Zn(1) at
˚
0.4550 A. The apical position is occupied by one phosho-
honate oxygen atom O(7) from the neighbouring edbbp. The
geometry around the Zn(1) atom can be best described as
severely distorted square-pyramidal coordination sphere,
with equatorial angles in the range 85.21(14)–160.76(14)8,
and an axial angle O(7)–Zn(1)–O(1) of 109.14(12)8. The
geometry around the Zn(2) is very similar to that of Zn(1),
and the Zn(2) atom is pulled out of this plane defined by the
four chelating atoms N(3), N(4), O(10), and O(8) at
Complexes 1, 2 are unstable in the air. When they were
removed from their mother liquors, they soon become
amorphous under atmospheric condition. They are not
soluble in water and common organic solvents, such as
˚
0.4443 A.
Both phosphonate groups of H4edbbp are completely
deprotonated, two NH2– groups of 1,2-propyldiamine are
2H– protonated, thus each edbbp carries four negative
charges and [Zn2(edbbp)2]4K unit are needed to balance the
four positive charges of two protonated 1,2-propyldiamines.
Each edbbp as tetradentate ligand chelates one Zn(II) ion and
bridges another Zn(II) ion via O atom of a phosphonate group
forming six five-membered rings and one eight-membered
Scheme 3.

Y.-T. Fan et al. / Journal of Molecular Structure 707 (2004) 153–160
157
Fig. 2. One-dimensional chain structure of [NH3CH(CH3)CH2NH3]2Zn2 (edbbp)2$20H2O.
ring. The arrangement of the eight-membered ring
(Zn1–O4–P2–O5–Zn2–O8–P3–O7) is very similar to that
in complex Zn(O3PCH2CH2NH2) described by Bujoli et al.
[10]. In edbbp, two {CPO3} moieties coordinate with zinc
atoms by two different mode, one of them acts as
a monodentate mode, the another adopts bidentate fashion
bridging Zn(1) and Zn(2) atoms.
The [Zn2(edbbp)2]4K units are linked by extensive
intermolecular hydrogen bonds between 1,2-propyldiamine
cations and phosphonate oxygen atoms, forming a one-
dimensional chain structure with various voids (Fig. 2).
These voids are created by six and 14-membered rings. The
six-membered ring contains N8A, O2A, P1A, O1A, Zn1A,
O7A atoms, whereas, the 14-membered ring is composed of
atoms C36A, C37A, N7A, O12B, P4B, O11B, N5A, C33A,
C34A, N6A, O3A, P1A, O2A, N8A. The short N–O
distances indicate very strong mutual electrostatic
in Fig. 3, the complex 1 shows an open-network
supramolecular structure.
3.3. Crystal structure of
[NH3(CH)CH3CH2NH3]2Cd2(II)(edbbp)2$25H2O (2)
The structure of complex 2 crystallizes in the triclinic
space group P-1. The asymmetric structural unit consists of
two Cd atoms, two equivalent edbbp, two protonated
1,2-propyl-diamine cations, and 25 water molecules.
An ORTER view of the dimeric unit of complex 2 is
shown in Fig. 4. The geometry of complex 2 is similar to
that of complex 1. Each Cd ion is at a five-coordinated
geometry in which three oxygen atoms come from
phosphonate units and two nitrogen atoms from the ligand,
forming distorted square-pyramidal coordination geometry.
˚
The Cd–O distances are in the range of 2.189(3)–2.272(3) A
and Cd–N distances are in the range of 2.336(4)–
˚
2.369(3) A, comparable to those of other cadmium dipho-
˚
interactions: N(5)/O(5)Z2.797 A, N(5)/O(11)Z
˚
˚
˚
2.795 A, N(6)/O(3)Z2.690 A, N(7)/O(12)Z2.692 A,
˚
˚
N(8)/O(2)Z2.758 A, N(8)/O(7)Z2.872 A. In addition,
the crystal lattice of complex 1 contains a lot of water
molecules (about 20 water molecules per formula unit
[Zn2(edbbp)2]4K), which fill the spaces between the chains,
forming extensive hydrogen bonds with phosphonate
oxygen atoms or neighbouring water molecules. As shown
sphonate complexes [11]. In complex 2, 1,2-propyldiamine
cations serve not only as charge compensating counter ions
but as bridging functions for [Cd2(edbbp)2]4K units. As can
be seen from Fig. 5, there exist two types of one-
dimensional chain by means of extensive intermolecular
Fig. 3. The crystal packing viewing of NH3CH(CH3)CH2NH3]2Zn2
Fig. 4. The dimeric structural unit of complex 2 [NH3CH(CH3)CH2NH3]2-
Cd2 (edbbp)2$25H2O.
(edbbp)2$20H2O along the a axis.

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Y.-T. Fan et al. / Journal of Molecular Structure 707 (2004) 153–160
Fig. 5. Two one-dimensional chain structures of [NH3CH(CH3)CH2NH3]2Cd2(edbbp)2$25H2O: (a) formed by four strong intermolecular hydrogen bonds;
(b) formed by two mutual hydrogen bonds.
hydrogen bonds between 1,2-propyldiamine cations and
phosphonate oxygen atoms. One chain is constructed
through four strong intermolecular hydrogen bonds
the great steric hindrance of Ph group play an essential role
in blocking the assembly of metal diphosphonates into
extended structures. Another distinguished structural fea-
ture of metal–edbbp complexes is that there are a large
number of lattice water molecules filling the space between
chains, which is caused by the electrostatics between the
organo-amine cations and the edbbp anions. The hydrogen
bonds that hold the crystalline framework are relatively
weak, and removal of the guest water molecules from the
channels is accompanied by collapse of the structure.
˚
˚
(N5/-O6Z2.777 A, N5/O5Z2.766 A, N6/O3Z
˚
˚
2.765 A and N6/O6Z2.693 A) (Fig. 5(a)). The other
involves only two mutual hydrogen bonds (N8/O9Z
˚
˚
2.639 A and N7/O11Z2.752 A) (Fig. 5(b)). The lattice
water molecules are not coordinated to the Cd(II) ions, but
form strong hydrogen bonds with phosphonate oxygen
atoms or neighbouring water molecules. The large number
of water molecules play an essential role in stabilizing the
crystal lattice by filling space between chains through
extensive hydrogen bonds.
3.4. NLO properties
It is generally accepted that the protonation of the
phosphonate oxygens may block the assembly of the metal
diphosphonate into higher dimensionalities [12]. In this
study, although two phosphonate groups of H4edbbp are
fully deprotonated and there are six phosphonate oxygen
atoms as potential chelating groups, only three of them are
coordinated to the center ions. The remaining three
phosphonate oxygen atoms are only involved in extensive
hydrogen bonding network with 1,2-propyldiamine cations
as well as with lattice water molecules. In the molecular
structure of edbbp, the additional –Ph group attached to the
methylene of edbbp provides not only a steric hindrance but
also a possible hydrophobic environment. It is argued that
Till date, several groups have studied the NLO properties
of some metal–organophosphonate compounds [13], but
these investigations were focused on second order NLO
properties, third-order NLO properties of these compounds
are lacking.
The NLO properties of complexes 1 and 2 were
measured as described in the literature [4b] except that
the concentration was 1.3!10K3 mol dmK3 for complex 1
or 6.2!10K3 mol dmK3 for complex 2 in a DMF solution.
We found that complex 2 possesses strong NLO refractive
effects, but complex 1 has no NLO refractive under
the same condition. Fig. 6 depicts NLO refractive proper-
ties of complex 2. The data are assessed by dividing

Y.-T. Fan et al. / Journal of Molecular Structure 707 (2004) 153–160
159
complexes, such as [Hg2(OAc)4(4-BPFA)2(CH3OH)2],
[Cd2(OAc)4(4-BPFA)2] [4c]. This result shows that
complex 2 owns strong third-order optical nonlinearity.
To the best of our knowledge, complex 2 is the first
example with third-order NLO properties in the reported
metal–organophosphonate compounds. We believe that
our exploration may provide a useful guide to the design
of metal organo-diphosphonic complexes with third-order
NLO materials.
4. Supporting information available
Crystallographic data in CIF format. CCDC-225313(1)
and -225314(2) contain the supplementary crystallographic
data for this paper. This material is available free of charge
via the Internet at www.ccdc.cam.ac.uk/conts/retrieving.
html [or from the Cambridge Crystallographic Data Center,
12 Union Road, Cambridge CB2 1EZ, UK. Fax: C44-1223-
336033; E-mail: deposit@ccdc.cam.ac.uk]
Fig. 6. The data were assessed by dividing the normalized Z-scan data
obtained under the closed aperture configuration by the normalized Z-scan
data obtained under the open aperture configuration. The self-focusing
effects of complex 2 in 6.2!10K3 mol dmK3 DMF solution at 532 nm.
the normalized Z-scan data obtained under the open
aperture configuration. The third-order NLO refractive
index n2 can be derived by Eq. (1)
la0
n2 Z
DTVKP
(1)
0:812pIð1 KeKa L
Þ
Acknowledgements
0
where DTVKP is the difference between normalized
transmittance values at valley and peak portion. I is
the peak irradiation intensity at focus (4.2!1012 W/m2), a0
is the linear absorption coefficient, L is the sample
thickness (1 mm in this study), and l is the wavelength
of the laser (532 nm). Fig. 6 shows the NLO refractive
effects of complex 2. The DTVKP and a0 values of the
compound are 0.243 and 1.60 cmK1, respectively. The data
show that the compound has the positive sign for the
refractive nonlinearity, which gives rise to self-focusing
behavior. The calculated refractive index n2 value is
The authors acknowledge the financial support of the
National Natural Science Foundation of China (No.
20171040) and the China National Key Basic Research
Special Funds (No. 2003CD214500).
Appendix. Supplementary material
Supplementary data associated with this article canbe found,
in the online version, at doi:10.1016/j.molstruc.2004.07.013
1.31!10K17 m2 WK1
.
In accordance with the n2 value, the effective third-
order NLO susceptibility c(3) value can be calculated by
References
c
(3)Zcn20n2/80p, where c is speed of light in a vacuum, n0
[1] (a) O.R. Evans, H.L. Ngo, W. Lin, J. Am. Chem. Soc. 123 (2001)
10395;
is the linear refractive index of the sample (w1.43), and
n2 is the third-order nonlinear refractive index. Thus, the
calculated c(3) value is 3.19!10K11 esu. The correspond-
ing modulus of the hyperpolarizability value g is obtained
from jgjZc(3)/NF4, where N is the number density of
complex 2 in the sample (in cmK3) (NZ10K3!CNA, C is
the molar concentration of the compound in a DMF
solution, NA is the Avagadro constant); F4Z3 is the local
field correction factor. The calculated g value of complex
2 is 8.57!10K30 esu. The g value is similar to that of the
reported 3D supramolecule compound [Zn(TIPT)Cl2]$
2CH3OH [4a], several orders of magnitude larger
than those of the reported ferrocenyl complexes, such as
NiL2 , PdL2 (L2ZFcC(CH3)ZN2HCS2CH2C6H5), and
(b) B. Zhang, A. Clearfield, J. Am. Chem. Soc. 119 (1997) 2751;
(c) A. Clearfield, C.Y. Ortiz-Avila, ACS Symp. Ser. 449 (1992) 178.
(d) Ch.X. Du, D.X. Xue, X.N. Cheng, Y.T. Fan, H.W. Hou, H.J. Lu,
Chin. J. Inorg. Chem. 20 (2004) submitted for publication.
[2] A. Distler, D.L. Lohse, S.C. Sevov, J. Chem. Soc., Dalton Trans.
1999; 1805.
[3] (a) B.P. Yang, J.G. Mao, Y.Q. Sun, H.H. Zhao, A. Clearfield, Eur.
J. Inorg. Chem. 2003 (2003) 4211;
(b) V. Soghomonian, R. Diaz, R.C. Haushalter, C.J. O’Connor,
J. Zubieta, Inorg. Chem. 34 (1995) 4460;
(c) V. Soghomonian, Q. Chem, R.C. Haushalter, Angew. Chem. Int.
Ed. Engl. 34 (1995) 223;
´
(d) F. Serpaggi, G. Ferey, Inorg. Chem. 38 (1999) 4741;
(e) D.M. Poojary, B. Zhang, A. Clearfield, J. Am. Chem. Soc. 119
(1997) 12550;
´
(f) G. Alberti, S.M. Mascaros, R. Vivani, J. Am. Chem. Soc. 120
2
2
[Ag(L)2](NO3)$(MeOH)$(EtOH), [HgI2(L)] {LZ1,2-bis
[(ferrocen-1-ylmethylene)amino]ethane [4b], but smaller
than that of several reported ferrocenyl organometallics
(1998) 9291.
[4] (a) Y.T. Fan, G. Li, Z.F. Li, H.W. Hou, H.R. Mao, J. Mol. Struct. 693
(2004) 217;

160
Y.-T. Fan et al. / Journal of Molecular Structure 707 (2004) 153–160
(b) H.W. Hou, G. Li, Y.L. Song, Y.T. Fan, Y. Zhu, L. Zhu, Eur.
[7] D. Green, G. Patel, S. Elgendy, J.A. Baban, G. Claesonl, V.V. Kakkar,
J. Dedman, Tetrahedron 50 (1994) 5099.
J. Inorg. Chem. 2003 (2003) 2325;
(c) G. Li, Y.L. Song, H.W. Hou, L.K. Li, Y.T. Fan, Y. Zhu,
X.R. Meng, L.W. Mi, Inorg. Chem. 42 (2003) 913;
(d) C. Zhang, Y.L. Song, Y. Xu, H.K. Fun, G.Y. Fang, Y.X. Wang,
X.Q. Xin, J. Chem. Soc., Dalton Trans. 2000; 2823.
[8] N. Palta, B.V. Rao, S.N. Dubey, D.M. Puri, Indian J. Chem. 23A
(1984) 397.
[9] D.M. Poojary, B. Zhang, A. Clearfield, J. Am. Chem. Soc. 119 (1997)
12550.
[5] G.M. Sheldrick, SHELX-97 Program for the Solution and
¨
Refinement of Crystal Structures, University of Gottingen,
[10] D. Drumel, P. Janvier, D. Deniaud, B. Bujoli, J. Chem. Soc., Chem.
Commun. 1995; 1051.
Germany, 1997.
[11] C.V.K. Sharma, A. Clearfield, J. Am. Chem. Soc. 122 (2000) 1558.
[12] L.M. Zheng, H.H. Song, C.Y. Duan, X.Q. Xin, Inorg. Chem. 38
(1999) 5061.
[6] (a) M. Sheik-Bahae, A.A. Said, T.H. Wei, D.J. Hagan, E.W. Van
Stryland, IEEE J. Quantum Electron. 26 (1990) 760;
(b) H.W. Hou, X.Q. Xin, J. Liu, M.Q. Chen, S. Shi, J. Chem. Soc.,
Dalton. Trans. 1994; 3211.
[13] P. Ayyapppan, O.R. Evans, Y. Cui, K.A. Wheeler, W. Lin, Inorg.
Chem. 41 (2002) 4978.