A metal-organic coordination polymer based on 1,2-bis(diphenylphosphino)ethane dioxide: Synthesis, crystal structure and fluorescence of [ZnI2{Ph2P(O)-CH2CH2-P(O)Ph2}]n

Article abstract of DOI:10.1016/j.inoche.2009.03.019

A zinc coordination polymer, [ZnI₂{Ph₂P(O)-CH₂CH₂-P(O)Ph₂}]_n (1), has been prepared, which features a one-dimensional concavo-convex chain with alternative ZnI₂ and 1,2-bis(diphe

Full text of DOI:10.1016/j.inoche.2009.03.019

Inorganic Chemistry Communications 12 (2009) 481–483
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A metal-organic coordination polymer based on
1,2-bis(diphenylphosphino)ethane dioxide: Synthesis, crystal structure and
fluorescence of [ZnI2{Ph2P(O)-CH2CH2-P(O)Ph2}]n
a
a
a,
Xiaoqing Liu a,b, Xiao-Juan Yang a, , Peiju Yang , Yanyan Liu , Biao Wu
*
*
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
b Graduate School of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A zinc coordination polymer, [ZnI2{Ph2P(O)-CH2CH2-P(O)Ph2}]n (1), has been prepared, which features a
one-dimensional concavo-convex chain with alternative ZnI2 and 1,2-bis(diphenylphosphino)ethane
dioxide (dppeO2) moieties. The dppeO2 ligand adopts the bridging coordination mode between two zinc
atoms.
Received 26 December 2008
Accepted 31 March 2009
Available online 7 April 2009
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Coordination polymer
Crystal structure
Zinc(II)
1,2-Bis(diphenylphosphino)ethane dioxide
The coordination chemistry of phosphine oxides R3P(O) with
transition metals [1–6], lanthanides [7–9] and actinides [10–12]
has been extensively studied in the past decades. In particular,
phosphine oxides have been used in solvent extraction and separa-
tion processes of the oxophilic lanthanide metal ions. The dimeric
bis(phosphine oxides), e.g. Ph2P(O)(CH2)2P(O)Ph2, have three dif-
ferent coordination modes: the most common chelating bidentate
fashion (g2-O, O0), the bridging mode between two metal centers
complex 1 was obtained as a colorless material by slow diffusion
of ZnI2 in aqueous ethanolic solution with dppeO2 in dichloro-
methane at room temperature (Scheme 1) [24]. It can also be pre-
pared by reaction of ZnI2 with dppe followed by oxidation in air or
by H2O2. The polymer 1 is slightly soluble in DMSO and is insoluble
in other common organic solvents such as diethyl ether, tetrahy-
drofuran and ethanol.
Single crystal X-ray analysis [25] revealed that compound 1
consists of one-dimensional concavo-convex chains with
alternative ZnI2 and dppeO2 units along the c-direction (Fig. 1a).
The zinc(II) center is coordinated by two oxygen atoms of two
dppeO2 ligands and two iodine atoms in a slightly distorted tetra-
hedral geometry with bond angles ranging from 106.94(6)° to
118.55(2)°. There are two halves of dppeO2 ligand, one zinc atom
and two iodine atoms in the asymmetric unit, with the remaining
parts being generated by a crystallographic inversion center at the
mid-point of the C–C bond of the ethylene group. The ligand
dppeO2 is coordinated in the bridging bidentate fashion, which is
similar to that in the dinuclear zinc complex anion
[Cl3ZnO:(Ph)2PCH2CH2P(Ph)2:OZnCl3]2ꢀ [13]. Such linear coordina-
tion polymers of transition metals bridged by bis(phosphine oxide)
are relatively rare in the literature, and only a few complexes of
bis(phosphine oxide) have previously been reported to form poly-
meric structure, e.g. [CuCl2(dppeO2)]n [15], and [CoCl2(dppeO2)]n
[26]. The chains are further packed parallel to each other in the
bc plane (Fig. 1b).
(l g
2-O, O0) [13], and the monodentate one ( 1-O) [14]. Therefore,
complexes of such ligands can exhibit richer structural topologies
than the mono phosphine oxides. Actually, there are some exam-
ples of metal complexes with different structures based on these
bis(phosphine oxide) ligands, such as coordination polymers [15–
18], macrocyclic compounds [19] and cage molecules [20]. The
use of zinc ion to assemble with bis-phosphine oxide ligands is
of interest because zinc atom with the d10 electron configuration
can produce a diversity of complexes that may find potential appli-
cations in photoluminescent and second-order nonlinear optical
(NLO) materials [21,22]. However, these areas have been relatively
less explored [13]. Herein we report the synthesis, crystal structure
and fluorescence properties of a zinc coordination polymer con-
structed with 1,2-bis(diphenylphosphino)ethane dioxide, dppeO2,
[ZnI2{Ph2P(O)-CH2CH2-P(O)Ph2}]n (1).
The ligand dppe [23] and its oxidized derivative dppeO2 [16]
were synthesized according to the reported methods. The zinc
The Zn–O distances in 1 (1.958(2) and 1.964(2) Å) are slightly
* Corresponding authors. Tel./fax: +86 931 4968286.
E-mail addresses: yangxj@lzb.ac.cn (X.-J. Yang), wubiao@lzb.ac.cn (B. Wu).
shorter than that in the [Cl3ZnO:(Ph)2PCH2CH2P(Ph)2:OZnCl3]2ꢀ
1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2009.03.019

482
X. Liu et al. / Inorganic Chemistry Communications 12 (2009) 481–483
P(Ph)2:O}]n (147.8(4)° and 138.7(4)°, respectively) [26] and the
cyclic dimer [CoCl2{O:(Ph)2PCH2CH2P(Ph)2:O}]2 (148.0(2)° and
138.9(2)°, respectively) [19]. This has been attributed to the orien-
tation of the phenyl rings relative to the ZnI2 units [26]. The bridg-
ing dppeO2 ligands preserve their anti-conformation of the oxygen
donor atoms, while in the chelating mode they should adopt the
syn conformation. The corresponding dihedral angle between
O@P–Cꢁ ꢁ ꢁC–P@O planes is 0° (due to the crystallographically im-
posed symmetry) for the antiparallel (anti) alignments of the
P@O groups in complex 1.
P
P
O
O
+
ZnI2
I
O
O
P
P
Zn
I
n
IR spectrum of 1 shows a distinct absorption at 1148 cmꢀ1 due
to the P@O stretching, which is particularly affected by the coordi-
nation, as the frequency is significantly red-shifted with respect to
Scheme 1.
the free ligand (m
P@O = 1180 cmꢀ1) [29]. This agrees fairly well with
anion (2.009 Å) [13], while the P@O distances (1.494(2) and
1.506(9) Å) fall in the normal range for complexes with similar
bis(phosphine oxide) ligands, e.g. [CuCl2(dppeO2)]n (P@O:
1.497(2) Å) [15], and [Cl3ZnO:(Ph)2PCH2CH2P(Ph)2:OZnCl3]2ꢀ
(P@O: 1.520 Å) [13]. The average P–C(sp3) and P–C(sp2) distances
of 1.804 and 1.792 Å, respectively, in compound 1 compare well
to those in [CuCl2(dppeO2)]n (1.809 and 1.797 Å, respectively)
[15], but is obviously shorter than that of the non-oxidized bis(ter-
tiaryphosphine) compounds such as [Hg(CN)2{P(C6H5)2CH2}2]n (P–
C: 1.825(2) Å) [27] or [Cu(dppe)(NO3)(CH3CN)]n (P–C: 1.840(3) Å)
[28], indicating that the oxidation of the P atom can influence
the P–C bond lengths. Interestingly, the Zn(1)–O(1)–P(1) bond an-
gle in compound 1 (148.8(2)°) is significantly larger than the corre-
sponding P(2)–O(2)–Zn(1) angle (132.4(1)°), which exactly
parallels the behavior previously noted for Co–O–P angles in the
two halves of the linear polymer [CoCl2{O:(Ph)2PCH2CH2-
the coordination of the phosphoryl oxygen atom to zinc, and has
also been observed previously for other coordinated phosphine
oxides [29–31].
The fluorescence properties of the ligand and complex 1 have
been studied. Free dppeO2 molecule in the solid state displayed
an emission band centered at about 375 nm when excited at
294 nm, while compound 1 showed an emission at 374 nm and
two weak, broad emission peaks at around 477 nm and 510 nm,
respectively, upon excitation at 332 nm (Fig. 2). The peak at
374 nm can be assigned to the intraligand fluorescent emission.
Since no emission bands for the dppeO2 ligand were observed in
the region 450–550 nm, the longer wavelength fluorescence bands
of 1 may be ascribed to the ligand-to-metal charge transfer (LMCT)
between Zn(II) centers and dppeO2 upon formation of the coordi-
nation polymer [32,33].
Fig. 1. (a) The one-dimensional chain of 1; (b) Packing diagram of 1 showing the parallel chains in the bc plane. Selected bond lengths (Å) and bond angles (°): Zn1–O1
1.958(2), Zn1–O2 1.964(2), C26–C26a 1.534(5), O1–P1 1.494(2), O2–P2 1.506(9), Zn1–I1 2.582(4), Zn1–I2 2.556(4), C7–P1 1.805(3), C26–P2 1.804(3), O1–Zn1–O2 100.6(9),
O1–Zn1–I2 108.9(7), O2–Zn1–I2 109.8(6), O1–Zn1–I1 110.3(7), O2–Zn1–I1 106.9(6), I2–Zn1–I1 118.5(6), P1–O1–Zn1 148.8(5), P2–O2–Zn1 132.4(2), O1–P1–C7 112.9(3), O2–
P2–C26 111.9(2). Symmetry transformation used to generate equivalent atoms: ꢀx + 1, ꢀy + 2, ꢀz + 1.

X. Liu et al. / Inorganic Chemistry Communications 12 (2009) 481–483
483
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solution (5 ml) of ZnI2 (23.9 mg, 0.075 mmol) over a solution of ligand dppeO2
(30 mg, 0.075 mmol) in 5 ml dichloromethane. After a couple of days, X-ray
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cmꢀ1): 3052 w, 2901 w, 1482 m, 1434 s, 1399 m, 1311 w, 1275 w, 1180 m,
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474 s.
In conclusion, we report a novel metal-organic coordination
polymer of Zn(II) with the bis(phosphine oxide) ligand dppeO2.
The compound features a 1D concavo-convex chain where the
dppeO2 ligand coordinates in the bridging bidentate fashion. The
solid-state fluorescence of the polymer has been investigated,
which showed a ligand-based emission along with two weak bands
of the LMCT process.
[25] Crystal data for 1: C26H24I2O2P2Zn (749.56), Crystal system: triclinic, Space
ꢀ
group P1, a = 8.9254(5)°, b = 11.7200(8)°, c = 15.182(1)°,
a
= 69.243(3)°,
= 73.663(3)°, V = 1420.2(2) Å3, Z = 2, Dcalc = 1.753 g cmꢀ3
= 3.171 mmꢀ1, T = 293(2) K, 8753 reflections collected, 6065
(I)]. Diffraction
data were collected on a Bruker SMART APEX II diffractometer with graphite-
monochromated Mo K radiation (k = 0.71073 Å). An empirical absorption
b = 88.554(3)°,
F(0 0 0) = 724,
c
,
l
Acknowledgement
independent (Rint = 0.0116), R1 = 0.0255, wR2 = 0.0706 [I > 2
r
This work was supported by the ‘‘Bairen Jihua” program of Chi-
nese Academy of Sciences.
a
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included in idealized positions with thermal parameters equivalent to 1.2
times those of the atom to which they were attached.
Appendix A. Supplementary material
CCDC 725492 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via 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.inoche.2009.03.019.
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