Aminobenzylphosphonate functionalized polyoxometalates

Article abstract of DOI:10.1016/j.molstruc.2003.12.058

The phosphonic acid H₂O₃PCH₂C ₆H₄(NH₃)₂ has been obtained by acidic hydrolysis of the corresponding ester, and the functionalized (NH ₄)₂[Mo₅O₂₁(PCH₂C ₆H₄NH₃)₂] (1) POM was prepared by reaction of the phosphonic acid with a solution of molybdate. (1) was characterized by IR, ³¹P NMR and single-crystal X-ray diffraction analysis. Five MoO₆ octahedra are linked by edges and corners to form the {Mo₅O₂₁} ring from which two monoaminobenzylphosphonates are dangling. The phenyl groups of the organic branches orientate in the solid state to form π-π stacking. The molecular structure is stable in dmso solution on the basis of ³¹P NMR. Similarly, (NH₄)₂[Mo₅O₂₁(PCH ₂C₆H₃(NH₃)₂) ₂] 2 was obtained by reaction of diaminobenzylphosphonate with the {Mo₅O₂₁} inorganic core. IR, ³¹P NMR spectra confirm the structure of 2 is identical to that of 1.

Full text of DOI:10.1016/j.molstruc.2003.12.058

Journal of Molecular Structure 704 (2004) 59–62
www.elsevier.com/locate/molstruc
Aminobenzylphosphonate functionalized polyoxometalates
*
C.R. Mayer , J. Marrot, F. Secheresse
´
´
Institut Lavoisier, UMR CNRS 8637, Universite de Versailles Saint Quentin, 45 Avenue des Etats-Unis, 78035 Versailles, France
Received 13 November 2003; revised 18 December 2003; accepted 18 December 2003
Abstract
The phosphonic acid H2O3PCH2C6H4(NH3)2 has been obtained by acidic hydrolysis of the corresponding ester, and the functionalized
(NH4)2[Mo5O21(PCH2C6H4NH3)2] (1) POM was prepared by reaction of the phosphonic acid with a solution of molybdate. (1) was
characterized by IR, 31P NMR and single-crystal X-ray diffraction analysis. Five MoO6 octahedra are linked by edges and corners to form the
{Mo5O21} ring from which two monoaminobenzylphosphonates are dangling. The phenyl groups of the organic branches orientate in
the solid state to form p–p stacking. The molecular structure is stable in dmso solution on the basis of 31P NMR. Similarly, (NH4)2
[Mo5O21(PCH2C6H3(NH3)2)2] 2 was obtained by reaction of diaminobenzylphosphonate with the {Mo5O21} inorganic core. IR, 31P NMR
spectra confirm the structure of 2 is identical to that of 1.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Polyoxometalate; Hybrid; Molybdenum
1. Introduction
report on the functionalization of the [Mo5O21] core by
aminophosphonates. The presence of a single terminal
amino-group in 1 makes this compound a good candidate
for the condensation with aromatic monoketones, e.g.
diazafluoren-9-on while the presence of two terminal
amino groups in 2 will permit the condensation with metal
chelating diketones. Thus, these compounds are good
precursors for the synthesis of extended structures with
specific properties, luminescence (Ru-derivatives), magnet-
ism (Fe-derivatives) and others.
Polyoxometalates (POMs) form an important family of
metal–oxygen clusters studied for their structural variety
and for their implication in catalysis, medicine, and
materials science [1,2]. If the first POMs were reported
from a long time, the development of single-crystal X-ray
diffraction techniques together with the need of new
architectures active in oxidation have boosted the research
for novel POMs with different shapes and sizes.
The derivatization of polyoxoanions by grafting organic
groups to the surface of metal-oxo frameworks is an old
field that recently developed over different directions. One
is related to pharmaceutical applications [3], the functiona-
lized POM need to be water-soluble and stable at
physiological pH, another is the synthesis of POM based
materials. Many organic modified POMs have been reported
and this field has been recently reviewed [4]. Aminoacids
[5], phosphonates [6], phosphites [7] are the groups most
frequently grafted on the surface of POMs. Very recently,
[Mo5O21] derivatives have been structurally characterized
with covalently bound phosphonocarboxylates [8]. Here we
2. Experimental
2.1. Materials and methods
All the chemicals used were purchased from commercial
sources and used, unless otherwise specified, without further
purification. Infrared spectra (4000–200 cm21) were
recorded on a Nicolet Magna-550 FTIR spectrometer
using the technique of pressed KBr pellets. 31P NMR
spectra were obtained at room temperature in 5 mm o.d.
tubes on a Bruker AC 300 spectrometer equipped with a
QNP probehead at the frequency of 121.5 MHz. Chemical
shifts are given according to the IUPAC convention with
respect to 85% H3PO4.
*
Corresponding author. Tel.: þ33-1-39-25-43-97; fax: þ33-1-39-25-
43-81.
E-mail address: cmayer@chimie.uvsq.fr (C.R. Mayer).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2003.12.058

60
C.R. Mayer et al. / Journal of Molecular Structure 704 (2004) 59–62
Fig. 1. Molecular structure of (NH4)2[Mo5O21(PCH2C6H4NH3)2] (1). The Mo5O21 central core is represented by co-ordination polyhedra, the organic branches
as ball-and-stick models.
2.2. Syntheses of (NH2)2C6H3CH2PO3H2, and
NH2C6H4CH2PO3H2
the mother solution was maintained at room temperature
for several hours. Yield: 0.8 g (66%). {1H}–31P NMR
(121.5 MHz, DMSO-d6, H3PO4): d ¼ 28:0 ppm,
The synthesis of the precursor ortho-4,5-(NH2)2C6H3-
CH2PO3Et2 will be described elsewhere [9]. Ortho-4,5-
(NH2)2C6H3CH2PO3Et2 (1 g, 3.9 mmol) was dissolved in
12 M HCl (30 ml) and the resulting acidic solution was
stirred at reflux for 3 h. Then, the expected 2HCl–(NH2)2-
C6H3CH2PO3H2 phosphonic acid was recovered after
evaporation of the solution under vacuum (EtOH is formed
and eliminated) and triturating the solid with acetonitrile
and ether. Yield: 0.85 g (79%). 31P NMR (121.5 MHz,
DMSO-d6, H3PO4): d ¼26.3 ppm. For HCl–NH2C6H4-
CH2PO3H2, the experimental procedure was similar except
that the starting material was NH2C6H4CH2PO3Et2 (1 g,
4.1 mmol) instead of ortho-4,5-(NH2)2C6H3CH2PO3Et2.
Yield: 0.90 g (98%). 31P NMR (121.5 MHz, DMSO-d6,
H3PO4): d ¼21.2 ppm.
(2JPH ¼ 19 Hz, t). IR (KBr): n ¼ 1145; 1095 (s), 1041 (s),
~
981 (s), 927 (vs), 905 (vs), 683 (vs) cm21
.
2.5. Single crystal X-ray diffraction
Single crystal X-ray data for 1 (NH4)2[Mo5O15{(O3-
PCH2C6H4NH3)2}] were collected at 293 K on a SMART
˚
CCD diffractometer using Mo Ka radiation (0.71073 A).
The structure was solved by direct methods SHELX-TL
[10]. The absorption correction was based on multiple and
symmetry-equivalent reflections in the data set using the
SADABS program [11] based on the method of Blessing
[12]. Crystal data: orthorhombic, space group Pbcn (no 60),
˚
˚
˚
a ¼ 19:4598ð5Þ A, b ¼ 9:8265ð2Þ A, c ¼ 16:8835ð2Þ A,
V ¼ 3228:49ð11Þ A , Z ¼ 4; rcalc ¼ 2:395 g cm23. The
3
˚
structure, refined on F2; converged for 4399 unique
reflections and 228 parameters to give R1 ¼ 0:0534
2.3. Synthesis of (NH4)2[Mo5O21(PCH2C6H4NH3)2]
((NH4)2-1)
Table 1
˚
Selected bond lengths [A] for 1
After Na2MoO4·2H2O (1.21 g, 5 mmol) and HCl–NH2-
C6H4CH2PO3H2 (0.38 g, 2 mmol) were dissolved in 70 ml
H2O, HCl (2 ml, 3 M) was added drop wise while the
mixture was stirred for 30 min at reflux. Then, NH4Cl
(0.22 g in 2 ml) was added and the solution was stirred for
15 min. A colorless crystalline solid was obtained after the
mother solution was kept at room temperature overnight.
Yield: 1.05 g (86%). {1H}–31P NMR (121.5 MHz, DMSO-
d6, H3PO4): d ¼ 23:0 ppm, (2JPH ¼ 18 Hz, t). IR (KBr):
Mo(1)–O(1)
Mo(1)–O(2)
Mo(1)–O(3)
Mo(1)–O(4)
Mo(1)–O(5)
Mo(1)–O(6)
Mo(2)–O(7)
Mo(2)–O(8)
Mo(2)–O(9)
Mo(2)–O(4)
Mo(2)–O(6)
Mo(2)–O(10)
Mo(3)–O(11)
Mo(3)–O(9)
Mo(3)–O(10)
P(1)–O(5)
1.705(5)
1.714(5)
1.9033(18)
1.973(4)
2.286(5)
2.346(4)
1.679(6)
1.713(5)
1.919(5)
1.964(4)
2.195(4)
2.389(5)
1.712(6)
1.924(5)
2.311(5)
1.503(5)
1.536(5)
1.556(4)
n ¼ 1149 (w), 1100 (s), 1046 (s), 976 (s), 911 (vs), 687
~
(vs) cm21
.
2.4. Synthesis of [Mo5O21(PCH2C6H3(NH3)2)2] (2)
After dissolution of a mixture of Na2MoO4·2H2O
(1.21 g, 5 mmol) and 2HCl–(NH2)2C6H3CH2PO3H2
(0.41 g, 2 mmol) in 70 ml H2O, HCl (2 ml, 3 M) was
added dropwise and the mixture was stirred over 30 min at
reflux. A brown crystalline powder was obtained after
P(1)–O(10)
P(1)–O(6)
Symmetry transformations used to generate equivalent atoms:
#1 2x,y, 2 z þ 3/2 #2 -x þ 1, 2 y, 2 z.

C.R. Mayer et al. / Journal of Molecular Structure 704 (2004) 59–62
61
Fig. 2. View of the packing of (NH4)2[Mo5O21(PCH2C6H4NH3)2] showing the p–p stacking of the phenyl groups.
and wR2 ¼ 0:1082: Hydrogen atoms have been stereoche-
the Mo5-ring. These orientations are probably imposed by
the strong p–p interactions that exist between the phenyl
rings of adjacent polyoxoanions as revealed by the stacking
in the solid state, see Fig. 2. This orientation is possible by
the free rotation of the organic chains around the two PO3
tripods anchored to the Mo5 inorganic ring. Each polyanion
is balanced in the lattice by two ammonium cations.
˚
mically placed using constraints (C–H, 0.93 A, N–H,
˚
0.89 A). Crystallographic data for the structure reported in
this paper have been deposited with the Cambridge
Crystallographic Data Centre, on quoting the deposit
number CCDC 223192. Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road,
Cambridge, CB21EZ, UK (fax: þ44-1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk).
3.2. Lattice arrangement
Within an isolated anion, the two organic branches
decorating the inorganic rings are antiparallel. In a branch,
the terminal NH3 group interacts via hydrogen bonds with
three oxygen atoms of the closest inorganic ring of a
neighbouring anion as represented in Fig. 3. The related
3. Results and discussion
3.1. Molecular structure
The complete structure of (NH4)2-1 is formed of isolated
[Mo5O15{(O3PCH2C6H4NH3)2}]22 anions and two NHþ4
cations. The molecular structure of (NH4)2[Mo5O15{(O3
PCH2C6H4NH3)2}] is represented in Fig. 1. The inorganic
core of [Mo5O15{(O3PCH2C6H4NH3)2}]22 consists of a
ring of five distorted MoO6 octahedra linked through four
edge-sharing and one corner-sharing junctions. Three types
of Mo–O distances are observed within the inorganic ring,
˚
short terminal MoyO bonds (1.679–1.714 A), long terminal
˚
bonds trans to the MoyO groups (2.195–2.389 A) and
˚
Mo–O–Mo bridges (1.919–1.973 A), see Table 1. The
{Mo5O21} core was first observed in molybdophosphates
[7] and more recently in molybdophosphonates [6,7],
in peptides [5] and very recently in molybdophosphono-
carboxylates [8].
In 1, two pending aminobenzylphosphonate ligands are
attached on opposite sides of the ring by the two PO3
groups. The terminal amino group of each branch is
unambiguously protonated. The two organic branches
are oriented in almost perpendicular directions relative to
Fig. 3. View of the packing of (NH4)2[Mo5O21(PCH2C6H4NH3)2]
illustrating the hydrogen bonding scheme.

62
C.R. Mayer et al. / Journal of Molecular Structure 704 (2004) 59–62
Table 2
˚
Hydrogen bonds 1 [A and deg.]
observed as only features, illustrating the stability of 1 and 2
in DMSO, see Fig. 4. These chemical shifts are quite
comparable to the value d ¼ 22 ppm observed for the
related molybdophosphonocarboxylates [8].
D–H· · ·A
d(D–H) d(H· · ·A) d(D· · ·A)
,(DHA)
IR spectra of 1 and 2 are similar and clearly reflect the co-
ordination of the organic chains to the central {Mo5O21}
group, see Fig. 5. The bands located about 1000 cm21 are
characteristic of the PO3 group and are very sensitive to
symmetry. Thus, they represent a very good probe for the
mode of bonding of this group with the polyoxometalate
core, the three bands observed in this region for 1 and 2 are
in agreement with a local C3v symmetry. The bands at 980,
920 and 905 cm21 are unambiguously attributed to MoyO
groups while the band at 680 cm21 corresponds to Mo–O
bridges [6].
N(1)–H(1C)· · ·O(11)#3 0.89
1.96
2.28
2.18
2.847(10) 174.7
2.797(9) 116.9
3.014(10) 156.3
N(1)–H(1D)· · ·O(7)#4
N(1)–H(1E)· · ·O(5)#6
0.89
0.89
Symmetry transformations used to generate equivalent atoms: #1
2x,y, 2 z þ 3/2 #2 2x þ 1, 2 y, 2 z #3 x þ 1/2,y þ 1/2, 2 z þ 3/2 #4
2x þ 1/2, 2 y þ 3/2,z 2 1/2 #5 2x þ 1,y þ 1, 2 z þ 1/2 #6
x þ 1/2,y 2 1/2,z.
-
References
[1] M.T. Pope, Heteropoly and Isopoly Oxometalates, Springer, Berlin,
1983.
[2] (a) in: M.T. Pope, A. Mu¨ller (Eds.), Polyoxometalate Chemistry:
From Topology via Self-Assembly to Applications, Kluwer,
Dordrecht, 2001.
Fig. 4. {1H}–31P NMR of [Mo5O21(PCH2C6H3(NH3)2)2] (2).
(b) in: C. Hill (Ed.), Thematic issue on Polyoxometalates, Chemical
Review, 1998, p. 98.
´
(c) A. Dolbecq, F. Secheresse, Adv. Inorg. Chem., 53, 2002, pp. 1.
[3] S. Sarafianos, U. Kortz, M.T. Pope, M. Modak, J. Biochem. 319
(1996) 619.
[4] C. Sanchez, G.J. de Soler-Illia, F. Ribot, T. Lalot, C.R. Mayer, V.
Cabuil, Chem. Mater. 13 (2001) 3061.
[5] (a) M. Inoue, T. Yamase, Bull. Soc. Jpn 68 (1995) 3055.
(b) T. Yamase, M. Inoue, H. Naruke, K. Fukaya, Chem. Lett. 7 (1999)
563.
(c) U. Kortz, M.G. Savelieff, F.Y. Abou Ghali, L.M. Khalil, S.A.
Maalouf, D.I. Sinno, Angew. Chem. Int. Ed. Engl. 41 (2002) 4070.
[6] (a) W. Kwak, M.T. Pope, T.F. Scully, J. Am. Chem. Soc. 97 (1975)
5735.
¨
(b) L. Petterson, I. Andersson, L.-O. Ohman, Acta Chem. Scand. A39
(1985) 53.
¨
(c) L. Pettersson, I. Andersson, L.O. Ohman, Inorg. Chem. 25 (1986)
4726.
(d) A. Yagasaki, I. Andersson, L. Pettersson, Inorg. Chem. 26 (1987)
3926.
(e) U. Kortz, J. Vaissermann, R. Thouvenot, P. Gouzerh, Inorg. Chem.
42 (2003) 1135.
[7] (a) T. Ozeki, H. Ichida, H. Sasaki, Bull. Chem. Soc. Jpn 61 (1988)
4455.
Fig. 5. IR spectra of (NH4)2[Mo5O21(PCH2C6H4NH3)2] (1) (upper) and of
[Mo5O21(PCH2C6H3(NH3)2)2] (2) (lower).
(b) D.D. Lyxell, R. Strandberg, Acta Crystallogr. C44 (1988) 1535.
(c) J.K. Stalick, C.O. Quicksall, Inorg. Chem. 15 (1976) 1577.
[8] U. Kortz, C. Marquer, R. Thouvenot, M. Nierlich, Inorg. Chem. 42
(2003) 1158.
N-H· · ·O distances are given in Table 2. This hydrogen-
bonding scheme probably reinforces the orientation of the
phenyl rings engaged in p–p stacking.
´ ´
[9] C. R. Mayer, M. Herve, F. Secheresse, Tet. Lett., Manuscript in
preparation.
[10] (a) G.M. Sheldrick, Acta Crystallogr. A 46 (1990) 467.
(b) M. Sheldrick, SHELX-TL Version 5.03, Software Package for the
Crystal Structure Determination Siemens Analytical X-ray Instrument
Division Madison, WI, 1994.
3.3. Spectroscopies
The solid state structures of 1 and 2 are maintained in
dmso solution as confirmed by 31P-NMR spectra carried out
on solutions of re-dissolved solids. Triplets with a chemical
[11] G. M. Sheldrick, SADABS: program for scaling and correction of area
¨
detector data, University of Gottingen, Germany, 1997.
2
[12] R. Blessing, Acta Crystallogr. A 51 (1995) 33.
shift of 23 ppm ð JPH ¼ 18Þ for 1 and 28 ppm for 2 are