Two-dimensional square grid of neutral phosphonate ligands and eight-coordinated metal ions

Article abstract of DOI:10.1016/j.inoche.2008.07.005

Two dimensional coordination polymer [CdL₂(NO₃)₂]_n (where L = 4,4′-bis(dimethylphosphonomethyl)biphenyl) has been achieved. The crystal structure and molecular composition are measured using elemental analysis a

Full text of DOI:10.1016/j.inoche.2008.07.005

Inorganic Chemistry Communications 11 (2008) 1224–1226
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Two-dimensional square grid of neutral phosphonate ligands and
eight-coordinated metal ions
*
Xiang-Dong Zhang , Chun-Hua Ge, Xiao-Yan Zhang, Chun-Yue Shi, Cui He, Jing Yin
College of Chemistry, Liaoning University, Shenyang 110036, China
a r t i c l e i n f o
a b s t r a c t
Two dimensional coordination polymer [CdL2(NO3)2]n (where L = 4,40-bis(dimethylphosphonometh-
yl)biphenyl) has been achieved. The crystal structure and molecular composition are measured using ele-
mental analysis and X-ray crystal structure. Two-dimensional square grid was formed by semi-rigid
phosphonate ligands bridge metals, in which the metals adopt rare eight-coordinated geometry. Weak
C–Hꢀ ꢀ ꢀO hydrogen bonds which between coordinated nitrate anion and methyl group of phosphonate
ligands link two dimensional grids generating three dimensional supramolecular networks without
interpenetration.
Article history:
Received 28 April 2008
Accepted 2 July 2008
Available online 18 July 2008
Keywords:
Phosphonate ligand
C–Hꢀ ꢀ ꢀO hydrogen bond
Eight-coordinated geometry
Cadmium complex
Ó 2008 Elsevier B.V. All rights reserved.
Phosphate are widely used for syntheses materials in fileds of
microporosity, sorption, catalytic property, etc. [1–2]. Phosphonate
can be regarded as phosphor-containing organic compounds which
derived from the archetype of corresponding inorganic acid. They
are particularly intriguing because the metal-organic frameworks
(MOFs) of phosphonate represent an important group of complex
which has great interest in structural and topological diversity as
well as potential application in functional materials [3–4]. In fact,
phosphonate mentioned in documents can be classified into two
types. One is alkyl or aryl substituted phosphate, the other is phos-
phonate ester (Scheme 1). A tidal flow in the before expressive re-
search has been put forward in the past decade [5–13]. It is well
worth noting that phosphonate bearing additional functional
groups, such as crown ethers, amines, and carboxylic groups have
attracted much attention. There are few cases concerning the com-
plexes of phosphonate ester, though the results of existing research
show that the related complexes have demonstrated varied inter-
est [14–16]. The reasons of this situation are varied. One may be
the lack of this type of ligand, the other may be their poor ability
in coordination. Recently, an interesting open-framework Cd(II)
tetraphosphonate has been reported which was obtained by
hydrothermal synthesis from 1,2,4,5-tetrakis[(diethoxyphospho-
no)methyl]benzene and hydrated cadmium [17]. Herein, we intro-
duce the synthesis, structural characterization of complexes with
novel phosphonate ester ligand of 4,40-bis(dimethylphosphonom-
ethyl)biphenyl (Scheme 2). The ligand has rigid biphenyl group
and flexible methylene group, which make the molecule can be
used as semi-rigid building block.
The complex, [CdL2(NO3)2]n (1) (L = 4,40-bis(dimethylphospho-
nomethyl) biphenyl [18]) was readily achieved by reaction of the
ligand with hydrated nitrate in water–ethanol solvent [19]. Yellow
crystals of the complex were obtained directly by evaporation the
reaction solution. The crystal structures were determined by X-ray
crystallography [20].
Cd2+ ions in 1 are eight coordinated with eight oxygen atoms
from four different organic ligands and two bidentate coordinated
nitrate anions as shown in Fig. 1. The coordination polyhedron is a
distorted dodecahedron with a Cd2+ ion center. The bond lengths of
Cd–O(2.277(3) Å) which oxygen atoms are from phosphonate li-
gands are within normal range. The two oxygen atoms of the
bidentate nitrate anion which bind to the Cd centre are very sym-
metrical with Cd–O distance (2.611(5) Å). Though the bond length
is obviously longer than those what have been found for eight
coordinated Cd2+ complexes [21–23], is still less than the sum of
the van der Waals radii (2.90 Å). The longer bond length may sug-
gest the comparatively weak interaction between nitrate and me-
tal ions. Every phosphonate ligand is bridging two metal atoms
with the Cdꢀ ꢀ ꢀCd separation of 18.150 Å. Four phosphonate ligands
and four Cd2+ ions form 4-membered square with Cdꢀ ꢀ ꢀCdꢀ ꢀ ꢀCd an-
gle of 90.00 °. Cd2+ ions in square are co-planar without deviation.
Torsion angle of the Cd2+ ions is 0.00 °. By extending the squares,
two dimensional grids are formed (Fig. 2a). Phosphonate ligands
are crosswise arranged (Fig. 2b). For every metal ion, two ligands
are above and other two ligands are below the ions plane. Weak in-
ter-molecular C–Hꢀ ꢀ ꢀO hydrogen bonds (C(9)ꢀ ꢀ ꢀO(5) 3.246(8) Å,
C(9)-H(9B)ꢀ ꢀ ꢀO(5)144 °, symmetry code: x,1/2ꢁy,1/4ꢁz) link these
two dimensional grids to form three dimensional networks. Every
two grids form a double-layer structure and are further staggered
linked in an A–B–A–B fashion (Fig. 3).
* Corresponding author.
E-mail address: xdzhang@lnu.edu.cn (X.-D. Zhang).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2008.07.005

X.-D. Zhang et al. / Inorganic Chemistry Communications 11 (2008) 1224–1226
1225
O-
OR
(Ar or R)
P
P
(Ar or R)
O
O
O-
OR
phosphonate ester
substituted phosphate
Scheme 1.
H
C
H
OMe
OMe
P
H
C
H
Fig. 3. View of the stacking grids along c direction.
P
O
O
OMe
OMe
Scheme 2.
Fig. 1. (a) ORTEP drawing of 1 with hydro gen atoms omitted for clarity (30% thermal ellipsoids probability). (b) The coordination polyhedron about Cd. Selected bond length
(Å) and (°): Cd(1)–O(1) 2.277(3), Cd(1)–O(4) 2.611(5), P(1)–O(1) 1.463(3), P(1)–O(2) 1.524(5), P(1)–O(3) 1.529(6), P(1)–C(1) 1.781(5), N(1)–O(5) 1.225(6), N(1)–O(4) 1.235(4),
O(1)–Cd(1)–O(1A) 91.69(3), O(1)–Cd(1)–O(1B) 160.23(17), O(1)–Cd(1)–O(1C) 91.69(3), O(1)–Cd(1)–O(4A,C) 80.82(11), O(1)–Cd(1)–O(4C) 123.77(11), O(1)–Cd(1)–O(4A)
81.12(11), O(1)–Cd(1)–O(4A) 76.00(12), O(4)–Cd(1)–O(4C) 47.78(16), O(1)–Cd(1)–O(4C) 76.00(12), O(1)–P(1)–O(2) 113.2(2), O(1)–P(1)–O(3) 114.2(2), O(2)–P(1)–O(3)
103.5(5), O(1)–P(1)–C(1) 116.4(2), O(2)–P(1)–C(1) 106.1(3), O(3)–P(1)–C(1) 102.1(4), P(1)–O(1)–Cd(1) 145.4(2). Symmetry transformations used to generate equivalent
atoms: (A) ꢁy + 1, x, ꢁz + 1; (B)ꢁx + 1, ꢁy + 1, z, (C) ꢁx, y + 1, ꢁz + 1.
Fig. 2. (a) View of the two dimensional grid along c direction. (b) A schematic showing the arrangement of phosphonate ligands.

1226
X.-D. Zhang et al. / Inorganic Chemistry Communications 11 (2008) 1224–1226
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
100
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.inoche.2008.
07.005.
80
60
40
20
0
References
1
[1] A. Clearfield, G.D. Smith, Inorg. Chem. 8 (1969) 431.
[2] D.M. Poojary, B. Shpeizer, A. Clearfield, J. Chem. Soc. Dalton Trans. (1995)
111.
[3] J.-G. Mao, Coord. Chem. Rev. 251 (2007) 1493.
[4] E. Matczak-Jon, V. Videnova-Adrabin´ ska, Coord. Chem. Rev. 249 (2005)
2458.
[5] K.D. Demadis, P. Lykoudis, R.G. Raptis, G. Mezei, Cryst. Growth. Des. 6 (2006)
1064.
L
[6] L.A. Vermeulen, R.Z. Fateen, P.D. Robinson, Inorg. Chem. 41 (2002) 310.
[7] J.-G. Mao, A. Clearfield, Inorg. Chem. 41 (2002) 2319.
[8] J.-G. Mao, Z. Wang, A. Clearfield, Inorg. Chem. 41 (2002) 2334.
[9] J.-G. Mao, Z. Wang, A. Clearfield, Inorg. Chem. 41 (2002) 3713.
[10] E. Barouda, K.D. Demadis, S.R. Freeman, F. Jones, M.I. Ogden, Cryst. Growth Des.
7 (2007) 321.
0
100
200
300
400
500
600
700
800
900
Temperature,oC
Fig. 4. TG curves for complex and ligand.
[11] Y.-S. Ma, T.-W. Wang, Y.-Z. Li, L.-M. Zheng, Inorg. Chim. Acta 360 (2007)
4117.
[12] J. Li, L. Meng, Z.-G. Sun, Z.-M. Liu, Y. Zhao, J. Zhang, Y.-Y. Zhu, X. Lu, L. Liu, N.
Zhang, Inorg. Chem. Comm. 11 (2008) 211.
[13] A.P.A. Demšar, J. Pinkas, M. Necas, Inorg. Chem. Comm. 11 (2008) 5.
[14] K. Raghuraman, N. Pillarsetty, K.R. Prabhu, K.K. Katti, K.V. Katti, Inorg. Chim.
Acta 357 (2004) 2933.
The UV–Vis spectra of the complex were recorded in solid state.
The absorption in the region of 230 and 300 nm with the kmax at
258 nm is due to
p–p transition for the ligand. The excitation
and emission maxima for the complex in DMF solution were ob-
served 320 and 626 nm with the excitation peak at 290 nm.
The TG curve for L shows that the organic compound melts at
204 °C, and then mainly decomposes in the temperature range of
204.3–403.8 °C (Fig. 4). Thermal gravimetric experiment shows
that when 1 was heated there is no obviously weight loss up to
178.4 °C and then undergoes three major stages of weight loss.
The first weight loss occurs over 178.4–205.3 °C. The value of the
weight loss at this stage (14.3%) indicates partial loss of small mol-
ecules. The second stage is in the temperature range of 205.3–
397.6 °C (weight loss 19.6%) and the third stage follows in the tem-
perature range of 397.6–579.1 °C (weight loss 10.1%). On the basis
of the decomposition of L, it is believed that the last two stages cor-
respond to the thermal decomposition of ligand in complex.
[15] J. Fawcett, A. W.G. Platt, S. Vickers, Polyhedron 22 (2003) 1431.
[16] P. Młynarz, A. Czernicka, A. Rydzewska, G. Schroeder, P. Kafarski, J. Mol. Struct.
875 (2008) 130.
[17] N. Stock, N. Guillou, J. Senker, G. Férey, T. Bein, Z. Anorg. Allg. Chem. 631 (2005)
575.
[18] The ligand was used as purchased from Shenyang Research Institute of
Chemical Industry (China) without further purification.
[19] Synthesis of the cadmium complex: Hydrated cadmium nitrate (0.1 mmol) in
water (10 mL) was mixed with L (0.1 mmol) in ethanol (5 mL). After the
resulting mixture had been refluxed for 4 h, a drop of hydrochloric acid was
added and further 4 h of reflux was performed. The solution was filtered.
Through slow evaporation of the solvent, Yellow crystals were suitable for
single crystal X-ray structure analysis which obtained within several weeks,
yield 53%. Anal. Calc. for C36 H48 CdN2 O18 P4: C, 41.85; H, 4.68; N, 2.71. Found:
C, 41.49; H, 5.10; N, 2.33.
[20] Crystal data for C36 H48 CdN2 O18 P4: M = 1033.04, Tetragonal, I ꢀ4 2d, a =
12.8343(5), b = 12.8343(5), c = 26.381(2) Å,
Z = 4, Dc = 1.579 g/cm3, R1 = 0.0437, wR2 = 0.1041 (I > 2
wR2 = 0.1062 (for all data). The diffraction data were collected with a Bruker
Smart Apex CCD area detector with graphite-monochromatized Mo
a = b = c
= 90.00 , V = 4345.5(4) Å3,
r(I)); R1 = 0.0468,
Acknowledgement
Ka
radiation (k = 0.71073 Å). The structure was solved by direct methods using
SHELXS-97 and refined by fullmatrix least-squares fitting on F2. Hydrogen
atoms were added theoretically.
This work was supported by the Doctoral Fund of Liaoning Uni-
versity and the Project for Innovation Team of Liaoning Province,
China (No. 2007T052).
[21] J. Pons, J. García-Antón, R. Jiménez, X. Solans, M. Font-Bardia, J. Ros, Inorg.
Chem. Commun. 10 (2007) 1554.
[22] H.-S. Wang, W. Shi, J. Xia, H.-B. Song, H.-G. Wang, P. Cheng, Inorg. Chem.
Commun. 10 (2007) 856.
[23] A. Michaelides, C.D. Papadimitriou, J.C. Plakatouras, S. Skoulika, P.G. Veltsistas,
Polyhedron 23 (2004) 2587.
Appendix A. Supplementary material
CCDC 683435 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The