Ionothermal Synthesis of Metal Oxalatophosphonates with a
Three-Dimensional Framework Structure: Na
2
M
3
(C
2
O
4
)
3
(CH
3
PO
3
H)
2
(M )
Fe
II
and Mn
II
)
Chun-Po Tsao,
†
Chyi-Yang Sheu,
†
Ninh Nguyen,
‡
and Kwang-Hwa Lii*
,†,§
Department of Chemistry, National Central UniVersity, Chungli, Taiwan 320, Republic of China,
Laboratoire CRISMAT, UMR CNRS 6508, ENSICAEN et UniVersite ´ de Caen, 14050 Caen Cedex,
France, and Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 115,
Republic of China
Received March 8, 2006
Two isostructural transition-metal oxalatophosphonates, Na
2
M
3
(C
2
O
4
)
3
(CH
3
PO
3
H)
2
(M ) Fe
II
and Mn
II
), have been
synthesized by using a low-melting-point eutectic mixture of choline chloride and malonic acid as a solvent and
characterized by single-crystal X-ray diffraction and
57
Fe Mo ¨ ssbauer spectroscopy. The 3D framework structure
consists of a corner-sharing octahedral trimer that is linked with other trimers through two distinct oxalate ligands
with unusual linkage types, phosphonate tetrahedra, and H bonds to form infinite channels along the [101] direction
where the Na
+
cations are located. They are the first examples for the use of an ionic liquid as a solvent in the
synthesis of metal oxalatophosphonates. Crystal data for the Fe compound follow: monoclinic, P2
1
/n (No. 14), a
) 5.8063(1) Å, b ) 10.3867(3) Å, c ) 14.8094(4) Å, ) 96.926(1)°, and Z ) 2. Crystal data for the Mn
compound are the same as those for the Fe compound except a ) 5.8734(9) Å, b ) 10.557(2) Å, c ) 14.863(2)
Å, and ) 96.691(2)°.
Introduction
Many research activities have focused on the synthesis of
organic-inorganic hybrid compounds by incorporating or-
ganic ligands in the structures of metal phosphates. A large
number of metal oxalatophosphates of transition metals and
main-group elements have been reported.
1
However, very
few reports in the literature illustrate the use of oxalate anions
forming part of the structure along with the phosphonate
groups, although the chemistry of metal phosphonates has
been extensively studied for many years. Sn
2
(O
3
PCH
3
)(C
2
O
4
)
and Sn
4
(O
3
PCH
2
CH
2
CO
2
)
2
(C
2
O
4
) are the first members of
metal oxalatophosphonates.
2,3
The former has a 2D layer
structure, and the latter adopts a 3D framework structure that
consists of two different bifunctional linkers, phosphono-
propionate and oxalate anions. Several lanthanide oxalate-
aminophosphonate hybrids with 3D framework structures
were also synthesized.
4
Recently, we reported the first
organically templated metal oxalatophosphonate, (C
3
H
12
N
2
)
0.5
-
[Ga
3
(C
2
O
4
)(CH
3
PO
3
)
4
]‚0.5H
2
O, with a layer structure.
5
All
of these oxalatophosphonates were synthesized in aqueous
solutions under mild hydrothermal conditions.
Recently, there were reports on the preparation of coor-
dination polymers and aluminophosphates by using ionic
liquid dialkylimidazolium salts or a low-melting-point eu-
tectic mixture of choline chloride and urea.
6-10
The ionic
liquids can not only act as solvents but also provide the
* To whom correspondence should be addressed. E-mail:
liikh@cc.ncu.edu.tw.
†
National Central University.
‡
ENSICAEN et Universite ´ de Caen.
§
Academia Sinica.
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Inorg. Chem. 2006, 45, 6361-6364
10.1021/ic0603959 CCC: $33.50 © 2006 American Chemical Society Inorganic Chemistry, Vol. 45, No. 16, 2006 6361
Published on Web 07/14/2006