One-dimensional Cd metal string complex: Synthesis, structural and thermal properties of [(HPy)3(Cd3Cl9)] ∞

Article abstract of DOI:10.1016/j.ica.2005.10.054

The cadmium metal string complex of [(HPy)₃(Cd ₃Cl₉)]_∞ (Py = pyridine) was prepared. Its structural and thermal properties were also investigated. Its existing form in gas phase has been elucidated by density functional calculations. The crystal structure consists of protonation pyridine cations and infinite one-dimensional chains of [Cd₃Cl₉]^3- anions. Each Cd atom is octahedrally surround by bridged chlorine atoms, giving rise to polymeric chain along the a-axis. The pyridinium lie in the middle of the chain to balance the charge. The DFT study indicates that the HOMO orbital of optimized structure is mainly localized on the middle six chloride ions and the LUMO is delocalized. Differential thermal gravimetric analysis shows there is no presence of any structural phase transitions.

Full text of DOI:10.1016/j.ica.2005.10.054

Inorganica Chimica Acta 359 (2006) 1473–1477
www.elsevier.com/locate/ica
One-dimensional Cd metal string complex: Synthesis, structural
and thermal properties of [(HPy)3(Cd3Cl9)]1
*
Fang Fang Jian , Pu Su Zhao, Qing Xiang Wang, Ying Li
New Materials and Function Coordination Chemistry Laboratory, Qingdao University of Science and Technology, Qingdao 266042, PR China
Received 6 September 2005; received in revised form 22 October 2005; accepted 25 October 2005
Available online 15 December 2005
Abstract
The cadmium metal string complex of [(HPy)3(Cd3Cl9)] (Py = pyridine) was prepared. Its structural and thermal properties were
1
also investigated. Its existing form in gas phase has been elucidated by density functional calculations. The crystal structure consists
of protonation pyridine cations and infinite one-dimensional chains of [Cd3Cl9]3ꢀ anions. Each Cd atom is octahedrally surround by
bridged chlorine atoms, giving rise to polymeric chain along the a-axis. The pyridinium lie in the middle of the chain to balance the
charge. The DFT study indicates that the HOMO orbital of optimized structure is mainly localized on the middle six chloride ions
and the LUMO is delocalized. Differential thermal gravimetric analysis shows there is no presence of any structural phase transitions.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Cd metal string; Pyridinium chloride; TG; DFT
1. Introduction
When we reacted CdCl2 with pyridine in the presence of
hydrochloric acid, an unexpected a novel one-dimensional
The metal string complexes are highly interesting in the
fundamental study of metal–metal interaction [1–4] and in
their potential application as molecular metal wires. Some
metal string complexes have been synthesized successfully
[5] by using oligo-a-pyridylamine ligands, etc. There has
been an increasing interest in the coordination chemistry
of cadmium in recent years due to the increased recognition
of its role in biological organisms [6,7], as well as in molec-
ular-based materials [8–10]. In the quest for molecular-
based materials with interesting properties, much attention
has been given to one-, two- and three-dimensional
extended solids which involve cadmium [11]. The Cd2+
ion, being a d10, exhibits a variety of coordination numbers
and geometries. These enable the generation of a great vari-
ety of structures, such as one-dimensional linear chains [12],
ribbon-like structures [13] and two-dimensional layer [14].
Cd string complex, [(HPy)3(Cd3Cl9)] along with its single
1
crystal suitable for X-ray diffraction were obtained. Also,
we repeated this experiment and got this novel Cd string
complex in high yield. In order to verify whether the com-
plex [(HPy)3(Cd3Cl9)] forms Cd–Cd metal string in gas
1
phase or not, density functional theory (DFT) method
was used to optimize the geometry of this complex at
B3LYP/ Lanl2DZ level in terms of disk space and com-
puter time. Herein, we describe the synthesis, thermogravi-
metry, elemental analysis, single crystal X-ray structure
analysis and the DFT study of the new complex
[(HPy)3(Cd3Cl9)] .
1
2. Experimental
2.1. General remarks
All chemicals were obtained from a commercial source
and used without further purification. The C, H and N
analyses were carried out with a Perkin–Elmer 1400C
*
Corresponding author. Tel.: +86 532 84023606; fax: +86 532
84023606.
E-mail address: ffj2003@163169.net (F.F. Jian).
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.10.054

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F.F. Jian et al. / Inorganica Chimica Acta 359 (2006) 1473–1477
analyzer. Thermal gravity (TG) and Differential thermal
gravimetric analysis (DTG) were recorded on an SDT
2980 simultaneously for the samples of ca. 10 mg under a
nitrogen atmosphere (150 mL/min) in the temperature
range from 20 to 800 °C, with a heating rate of 10 °C/min.
cally refined. The hydrogen atom positions were fixed geo-
metrically at calculation distances and allowed to ride on
the parent carbon atoms. The molecular graphics were
plotted using SHELXTL. Crystallographic data for the com-
plex 1: formula C15H28Cd3Cl9N3; Mr = 896.57; crystal sys-
˚
tem orthorhombic, space group Ima2, a = 40.697(8) A,
˚
˚
2.2. Synthesis of complex 1
b = 7.369(2) A, c = 17.680(3) A, V = 5301.9(2); Z = 8,
Dc = 2.246, l = 3.302; F(000) = 3408; h/2h scan mode
1.00 6 h 6 27.56. 7832 collection reflections, 2839 indepen-
dent (Rint = 0.0504), 277 refined parameters with I P 2r(I),
R1 = 0.0519, wR2 = 0.1361, and GOF = 0.950.
The warm CdCl2 aqueous solution (50 ml, 30%) was
added drop-wise in pyridine (10 ml) with stirring. The
white precipitates were formed, filtered and completely dis-
solved by excess 6 N HCl solution, and then, added benzoic
acid acetonitrile solution. The above light yellow solution
was filtered and the filtrate was left to stand undisturbed.
Upon slow evaporation at room temperature, a yellow
rectangle shaped crystals formed after several weeks. The
crystals were separated by filtration, then collected and
dried. The yield is 82% and elemental analysis: Calc. for
C15H18Cd3Cl9N3: C, 20.07; H, 2.007; N, 4.684. Found: C,
19.86; H, 1.993; N, 4.691%.
2.4. Computational methods
The ab initio quantum chemical calculations were per-
formed with GAUSSIAN 03 program [17]. Density functional
calculations were all self-consistent Kohn–Sham calcula-
tions using the B3LYP density functional and the effective
core potentials of Hay and Wadt with a double-f valence
basis set (Lanl2DZ) were used [18]. All calculations were
performed on DELL PE 2650 server using the default con-
vergence criteria.
2.3. X-ray crystallographic study
The diffraction data were collected on a four-cycle
CAD4 diffractometer with graphite monochromatic Mo
Ka(k = 0.71073 A, T = 293 K) radiation. Empirical
absorption correction was carried out by using the SADABS
program [15]. The structures were solved by direct methods
and refined by least squares on F 2obs by using the SHELXTL
[16] software package. All non-H atoms were anisotropi-
3. Results and discussion
˚
The metal–wire complex 1, [(HPy)3(Cd3Cl9)] , was
obtained by reaction of CdCl2 and Py in the 6 N HCl solu-
tion. The crystal structure reveals the complex 1 consists of
1
3ꢀ
one-dimensional inorganic chains of ½Cd3Cl9ꢁ1 anions
and protonation pyridine cations. Fig. 1 shows a perspec-
Fig. 1. Molecular structure of [(HPy)3(Cd3Cl9)] with the atomic numbering scheme.
1

F.F. Jian et al. / Inorganica Chimica Acta 359 (2006) 1473–1477
1475
Table 1
Selected bond lengths (A) and angles (°) for complex [(HPy)3(Cd3Cl9)]
features in the structure of [(HPy)3(Cd3Cl9)] as shown
1
˚
1
in Fig. 1. First, all the cadmium atoms are collinear. The
angles of Cd–Cd–Cd are close 180° (178.78(3)°,
178.25(6)° and 179.87(7)°, respectively). Three cadmium
atoms with the bridged chlorine atoms are coplanar,
respectively. The dihedral angles among these planar are
56.78° for P1 [Cd(1)–Cd(2)–Cd(3)–Cl(2)–Cl(4)–Cl(9)–
Cl(11)] with P2 [Cd(1)–Cd(2)–Cd(3)–Cl(5)–Cl(8)], 61.59°
for P1 with P3 [Cd(1)–Cd(2)–Cd(3)– Cl(6)–Cl(7)–Cl(10)],
and 61.63° for P2 with P3, respectively. Second, the Cd–
Cd(1)–Cl(3)
Cd(1)–Cl(4)
Cd(1)–Cl(5)
Cd(2)–Cl(8)
Cd(2)–Cl(7)
Cd(2)–Cl(6)
Cd(3)–Cl(8)
Cd(3)–Cl(11)
2.615(4)
2.647(4)
2.664(4)
2.630(4)
2.646(5)
2.647(5)
2.634(5)
2.644(4)
Cd(3)–Cl(9)
Cd(1)–Cd(2)
Cd(2)–Cd(3)
C(1)–C(2)
C(1)–N(1)
C(6)–C(5)
2.656(4)
3.3956(17)
3.3969(16)
1.28(4)
1.35(3)
1.30(4)
C(10)–N(6)
N(1)–N(2)
1.34(5)
1.43(3)
Cl(1)–Cd(1)–Cl(2)
Cl(6)–Cd(1)–Cl(4)
Cl(1)–Cd(1)–Cl(5)
Cl(3)–Cd(1)–Cl(4)
Cl(1)–Cd(1)–Cl(6)
Cl(7)–Cd(2)–Cl(9)
Cl(8)–Cd(2)–Cl(7)
Cl(6)–Cd(2)–Cl(9)
Cl(4)–Cd(2)–Cl(7)
Cl(7)–Cd(2)–Cl(6)
Cl(10)–Cd(3)–Cl(7)
Cl(10)–Cd(3)–Cl(8)
Cl(7)–Cd(3)–Cl(8)
Cl(10)–Cd(3)–Cl(11)
Cl(7)–Cd(3)–Cl(11)
81.35(15)
82.70(14)
96.05(15)
98.62(9)
Cl(8)–Cd(3)–Cl(11)
Cl(10)–Cd(3)–Cl(9)
Cl(7)–Cd(3)–Cl(9)
Cl(8)–Cd(3)–Cl(9)
Cl(11)–Cd(3)–Cl(9)
Cd(2)–Cl(4)–Cd(1)
Cd(1)–Cl(5)–Cd(2)
Cd(1)–Cl(6)–Cd(2)
Cd(3)–Cl(7)–Cd(2)
Cd(2)–Cl(8)–Cd(3)
Cd(3)–Cl(9)–Cd(2)
C(2)–C(1)–N(1)
96.06(11)
97.65(13)
82.24(12)
84.74(14)
179.17(18)
80.64(14)
78.82(11)
79.95(16)
80.01(16)
80.39(14)
79.08(13)
125.0(17)
111.8(14)
118.6(17)
178.02(6)
˚
Cd distances of 3.389(2), 3.393(2) and 3.395(2) A are much
shorter than those reported in other one-dimensional cad-
mium polymers bridged by chlorine atoms (average
177.75(10)
81.64(13)
83.19(13)
96.49(15)
98.37(16)
177.55(13)
179.51(14)
97.21(14)
83.26(14)
82.45(11)
97.66(14)
˚
ꢂ4.14 A) [20–22]. Although the Cd–Cd distances in this
complex are larger than the interatomic distance in bulk
˚
Cd (2.98 A) [23], they are still shorter than the 115% total
˚
sum of Cd metal radius (3.427 A). So we think there exist
the Cd–Cd metal bond [24,25]. Third, the protonation pyr-
idine cations on each side of the inorganic chain are
arranged in the zig-zag configuration. The pyridinium rings
are slightly twisted. The dihedral angles between the planes
of pyridinium rings are 9.02°, 16.53° and 19.57°, respec-
tively. There are some intermolecular hydrogen bonds in
the lattice. The N(1) atoms of pyridinium moieties is
involved in N–Hꢃ ꢃ ꢃCl intermolecular hydrogen bonds with
the coordinated Cl(6) atom. The Nꢃ ꢃ ꢃCl distances are
C(1)–N(1)–N(2)
C(2)–C(3)–C(4)
Cd(1)–Cd(2)–Cd(3)
tive view of the complex 1 with atomic numbering scheme,
and Table 1 lists the selected bond distances and angles of
3ꢀ
˚
complex 1. In the ½Cd3Cl9ꢁ1 moiety, each Cd(II) atom is
3.5888(2) A. The crystal packing is stabilized by those
octahedrally surrounded by six bridging chlorine atoms,
giving rise to polymeric chains along the a-axis. The
organic pyridinium groups which approximately parallel
to each other lie in the middle of the inorganic chains to
balance the charge (see Fig. 2). There is a little deformation
in three repeated pyridinium rings. The bond distances and
angles in pyridine ring are compared with those previously
found in other pyridine compound [19]. The Cd–Cl dis-
hydrogen bonds.
In order to investigate the existing form of the complex 1
in gas-phase, the structure of the molecular polynuclear
metal–wire is calculated for a hypothetical infinite one-
dimensional metal–wire created by extending the length
of the linear metal complex. In view of linear structure of
the metal complex, a model metal–wire is constructed with
[Cd3Cl12]ꢀ6 taken from the crystal structure of the
˚
tances are 2.604(4)–2.668(4) A, which are nearly equal to
[(HPy)3(Cd3Cl9)] as the repeat unit. The molecular struc-
1
the values for the similar octahedral one-dimensional chlo-
rocadmate(II) compounds [12,13]. The bond angles of Cd–
Cl–Cd bridges are from 79.3(1)° to 81.3(1)°, which are
much smaller than those in one-dimensional cadmium
polymer bridged by chlorine atoms [20]. There are several
ture of this model is then optimized. The results indicate
that the optimized bond lengths of Cd–Cl fall in the range
˚
˚
of 2.8558–2.9899 A and the Cd–Cd distance is 4.1407 A,
which are all much longer than those in the crystal struc-
ture. Maybe, in the crystal structure, the crystal field and
Fig. 2. View along the a-axis. Hydrogen atoms were omitted for clarity.

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F.F. Jian et al. / Inorganica Chimica Acta 359 (2006) 1473–1477
ꢀ6
Fig. 3. The HOMO and LUMO orbital of the [Cd3Cl12
]
.
Fig. 4. TG/DTG curves of compound [(HPy)3(Cd3Cl9)]
.
1
close packing of the molecules in the solid state make the
bond distances shorter around the Cd cations. The HOMO
orbital (Fig. 3) of this hypothetical metal–wire is mainly
localized on the middle six chloride ions and is mainly
made of the p orbitals of the chloride ions. The LUMO
is delocalized among all of the atoms of the [Cd3Cl12]ꢀ6
anion, and mainly constitutes of the s,d orbitals of Cd2+
and s,p orbitals of twelve chloride ions. The energy gap
between the HOMO and the LUMO is 5.14 eV .This model
shows that in gas-phase, the complex 1 is not a real metal–
wire and can not serve as a conducting wire.
sional metal–wire in the solid state. According to the TG
and DTG curves, we found that complex 1 has good ther-
mal stability, and it decomposes at about 214 °C. The
B3LYP/Lanl2DZ calculations show that the Cd–Cd dis-
tances are much longer than those in the solid state and
the energy gap between the HOMO and the LUMO is
5.14 eV, which indicate that complex 1 is not a conducting
wire in gas-phase.
Acknowledgement
The TG/DTG curves of the complex 1 are presented in
Fig. 4. Thermogravimetric analysis of the complex 1
reveals that there are mainly two steps of weight loss,
and the decomposition events mainly take place at 214.1
and 579.3 °C, respectively. On the base of weight changes,
the first process of the weight loss (37.86%) corresponds to
the loss of three pyridinium chloride [(C5H5N) Æ HCl; Calc.
38.64%], with two endothermic peaks; the residual weight
of 62.36% suggests that the residue may be Cd3Cl6 (Calc.
61.36%). Finally, the second event of the weight loss may
be related to the sublimation of Cd3Cl6, also with an endo-
thermic phenomenon.
The authors thank Natural Science Foundation of
Shandong Province (No. Y2002B06).
Appendix A. Supplementary data
Anisotropic displacement parameters, H-atom coordi-
nates and isotropic displacement parameters, structure
factor tables, and full bond length and bond angle data
are available from the authors on request. Crystallo-
graphic data for the structural analysis have been depos-
ited with the Cambridge Crystallographic Data Centre,
CCDC No. 276483. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre
(CCDC), 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 0 1223 336033; email: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.ica.2005.
10.054.
4. Conclusions
The synthesis and structural characterization of a novel
metal–wire complex 1 has been established. The crystal
structure has revealed that complex 1 forms one-dimen-

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[16] G.M. Sheldrick, SHELXTL97, Program for Crystal Structure refine-
ment, University of Gottingen, Germany, 1997.
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