Two Novel Chiral Inorganic–Organic Hybrid Materials Containing Preyssler and Wells–Dawson Heteropolyoxometallates with Valine (val), Glycine (gly), and Proline (pro) Amino acids:

ORI GIN AL PA PER

Two Novel Chiral Inorganic–Organic Hybrid MaterialsContaining Preyssler and Wells–DawsonHeteropolyoxometallates with Valine (val), Glycine(gly), and Proline (pro) Amino acids:(Hval)2(Hgly)(H3O)6K5[Na(H2O)P5W30O110]�19.5H2Oand (Hpro)6[P2W18O62]�8H2O

Hossein Eshtiagh-Hosseini • Masoud Mirzaei

Received: 13 November 2011 / Published online: 4 January 2012

� Springer Science+Business Media, LLC 2012

Abstract Two novel chiral organic–inorganic hybrid materials based on two impor-

tant heteropolyoxometallate namely Preyssler and Wells–Dawson anions, (Hval)2

(Hgly)(H3O)6K5[Na(H2O)P5W30O110]�19.5H2O (1) and (Hpro)6[P2W18O62]�8H2O (2),

were prepared and characterized by elemental analysis, X-ray diffraction, and infrared

spectroscopy. The mixed amino acid as cations, Preyssler and Wells–Dawson as

anions held together into a 3D-network through hydrogen-bonding interactions. The

most unique structural features of 1 and 2 are their 3D-inorganic infinite tunnel-like

framework. It results a weak van der Waals interlayer interaction. This provides a

desirable condition to use its potential as a host in a host–guest complex. The chirallity

for these two crystal structures, with the space group P21 has been observed. The

electrostatic forces and hydrogen bonding, keep these ‘‘adducts’’ stable in the solid

state.

Keywords Polyoxometallates � Preyssler � Wells-Dawson � Amino acids �Hybrid materials � Hydrogen bonding � Layered compounds

Introduction

Polyoxometallates (POMs), as a large family of metal–oxygen clusters, have been

viewed as ideal inorganic building blocks for the construction of larger clusters, or

multidimensional extended inorganic–organic hybrid materials. They exhibit a wide

Electronic supplementary material The online version of this article (doi:10.1007/s10876-011-0434-y)

contains supplementary material, which is available to authorized users.

H. Eshtiagh-Hosseini � M. Mirzaei (&)

Department of Chemistry, Ferdowsi University of Mashhad, 917791436 Mashhad, Iran

e-mail: [email protected]

H. Eshtiagh-Hosseini

e-mail: [email protected]

123

J Clust Sci (2012) 23:345–355

DOI 10.1007/s10876-011-0434-y

http://dx.doi.org/10.1007/s10876-011-0434-y

variety of robust structural motifs of different sizes and topologies [1]. Historically

POMs include the compounds known as ‘‘heteropoly acids’’. They have been

investigated for well over a century. No other class of compounds, inorganic or

organic, displays more versatility with respect to electronic and molecular

structures, properties and applications. Currently this field attracts wide academic

and industrial attention, with respect to catalysis, medicine (antiviral and anti-

retroviral activity), multifunctional materials and chemical analysis [2–6]. The

organic–inorganic hybrid materials have generated much interest in the field of

synthetically specialized materials. They exhibit remarkable characteristics in their

electrical, magnetic and optical properties [7–14]. These include compounds with

Keggin-type POMs and radical cations, derived from electron rich molecules, like

tetrathiafulvalene [15–19], decamethylferrocene [20] and porphyrins [21], as well as

salt-like compounds with several types of cationic organic species. They derived

from substituted amides [22], aromatic amines [23], and others [24]. Among organic

species, amino acids have important role in the structure of proteins and ordinary

antimicrobial and antibacterial. Therefore a growing interest observed in the

synthesis of POMs-amino acid hybrids. In these cases, POMs anions may act as

electron-accepting species; leading to unique features [25]. Pro is the only amino

acid, with an aliphatic ring that comprises both the ‘‘main’’ and the ‘‘side-chain’’ in

proteins. It is unique because, it forms a peptide bond; and covalently bonded

hydrogen no longer exists. So, it is not expected to occur as a a-helix or b-strand

proteins [15]. Nevertheless, Pro is found in the middle of a-helices. This has been

explained by the existence of a non-conventional C–H��O hydrogen bond involving

the ring C–H groups. It is interesting that the above mentioned characteristic,

normally found in naturally occurring systems, has been observed in an ‘‘artificial’’

(synthesized) compound [5]. Relatively few Preyssler and Wells–Dawson types

POMs, bearing amino acid ensembles, have been reported, so far there are too many

papers concerning exhibited antibacterial and antiviral properties including the

Keggin type POMs H3[(PO4)M12O36]�nH2O [26, 27]. Another pertinent example, a

new 3D structure has been synthesized by Chinese chemists [28]. The synthesis of

this chiral 3D open framework could open the door for analogous structures based

on POM anions with potential applications in medicine.

So, in the present study and in continuation of our previous reports [5, 8–14], we

describe the syntheses, and X-ray crystal structures of two chiral organic–inorganic

hybrid materials based on Preyssler and Wells–Dawson-types POMs including

monoprotonated valine, glycine, and proline amino acids.

Experimental

Synthesis of (Hval)2(Hgly)(H3O)6K5[Na(H2O)P5W30O110] �19.5H2O (1)

Chemical reagents were obtained from commercial suppliers and used after further

purification. Solvents were used as received or were distilled prior to use. The

synthetic routes for the preparation of K12.5Na1.5[Na(H2O)P5W30O110]�35H2O is

essentially the same reported by the Alizadeh et al. [4]. A column with 50 9 1 cm,

346 H. Eshtiagh-Hosseini, M. Mirzaei

123

Dowex 50WX8, in the H? form was used to prepare Preyssler heteropolyacid [4].

Pre-synthesized K5H9[Na(H2O)P5W30O110]�45H2O (0.25 g, 0.03 mmol) was dis-

solved in 10 mL hot water. Then 10 mL HCl solution of valine (0.03 g, 0.30 mmol)

and glycine (0.02 g, 0.30 mmol) was added. The resulting cloudy solution was

warmed to approximately 80 �C and stirred for 24 h, then filtered. The filtrate was

kept for 2 days at ambient conditions, giving green prism crystals of 1 in about 40%

yield (based on W). The weight loss of sample in autoclave after 5 h gave the

number of waters of hydration. Anal. Calcd. for 1: C, 1.70; H, 1.03; N, 0.50. Found:

C, 1.73; H, 1.00; N, 0.62. %. IR (KBr pellet, cm-1): 3360(m), 1674(m), 1568(m),

1250(m), 1166(m), 1082(m), 1022(m), 938(s), 913(s), 787(s), 653(s).

Synthesis of (Hpro)6[P2W18O62]�8H2O (2)

The Wells–Dawson acid (H6P2W18O62 aq.) was synthesized according to the

Dreschel method from alpha and beta isomer mixture of K6P2W18O62�10H2O. The

Wells–Dawson acid was obtained from treatment of an aqueous solution of

K6P2W18O62�10H2O salt, with ether and concentrated HCl (37%) solution. The acid

Table 1 The summary of crystal data and structural refinement parameters for 1 and 2

1 2

Empirical formula C12H87K5 N3NaO141.50P5W30 C30H76N6O82P2W18

Formula weight 8426.69 5204.21

Temperature/K 100(2) 100(2)

Wavelength/A 0.71073 0.71073

Crystal system Monoclinic Monoclinic

Space group P21 Z = 2 P21 Z = 2

Unit cell dimensions a = 17.9100(15) A a = 14.2153(4) A

b = 21.8653(18) A b = 21.1563(6) A

c = 18.0306(15) A c = 14.7503(4) A

b = 106.053(2)� b = 101.444(1)�Absorption coefficient/mm-1 25.65 23.864

F(000) 7426 4632

h range for data collection 1.42 to 29.00� 1.41 to 32.00�Index ranges -24 B h B 24, -21 B h B 21,

-29 B k B 29, -31 B k B 31,

-24 B l B 24 -21 B l B 21

Reflections collected/Unique 81134/35382 [R(int) = 0.0658] 107535/30049 [R(int) = 0.0498]

Completeness to h 98.8% (to h = 29.00�) 99.7% (to h = 32.00�)

Refinement method Full-matrix least-squares on F2 Full-matrix least-squares on F2

Data/restraints/parameters 35382/22/986 30049/1/1243

Goodness-of-fit on F2 1.025 1.024

Final R indices [I [ 2r(I)] R1 = 0.0612,

wR2 = 0.1371

R1 = 0.0290,

wR2 = 0.0575

Largest diff. peak and hole 4.100 and -1.945 e.A-3 2.938 and -2.151 e.A-3

Two Novel Chiral Inorganic–Organic Hybrid Materials Containing Preyssler 347

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formed an addition compound with the ether, which separated from the solution.

The remaining solution was placed in a vacuum-desiccator for crystallization

[29]. The H6P2W18O62�nH2O as a precursor was prepared according to the literature

[28]. The HCl solution containing proline (0.11 g, 1.0 mmol) was added to solution

of H6P2W18O62�15H2O (0.50 g, ca. 0.1 mmol) in distilled H2O (20.0 cm3) at room

temperature with stirring. The resulting solution was heated at 80 �C with

continuous stirring. The obtained solid was dissolved in acetonitrile–water (1:1,

volume ratio) then DMF (2.0 cm3) was added with stirring. The solution was filtered

and the filtrate allowed evaporating slowly at ambient temperature in the dim light

position. After a few days, colourless prism crystals of 2 suitable for X-ray single-

crystal diffraction were obtained in about 30% yield (based on W). The weight loss

of sample in autoclave after 5 h gave the number of waters of hydration. Anal.

Calcd. for 2: C, 6.91; H, 1.46; N, 1.61. Found: C, 6.84; H, 1.40; N, 1.72. %. IR (KBr

pellet, cm-1): 3450(m), 1724(m), 1634(m), 1465(m), 1235(m), 1166(m), 1090(s),

1082(m), 1022(m), 959(m), 912(s), 781(s).

Investigation Techniques

The title materials have been characterized by elemental analysis, single crystal

X-ray diffraction, and IR spectroscopy.

Elemental Analysis

Elemental analyses were performed on a Thermo Finnigan Flash-1112EA

microanalyzer.

IR Spectroscopy

The infrared spectra were recorded on a Buck-500 scientific spectrometer using KBr

discs.

Fig. 1 Structure of the Preyssler unit [Na(H2O)P5W30O110]14- in hybrid 1 (left), and the Wells–Dawsonunit [P2W18O62]6- in hybrid 2 (right) for an ORTEP representation with the atom labeling scheme shownat 50% thermal probability


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X-ray Diffraction

Experimental parameters pertaining to single crystal X-ray analysis of the title hybrids are

given in Table 1. Selected bond lengths and hydrogen-bonding geometry (A) for 1 and 2are displayed in Tables 1S–4S. Data were collected on a Bruker SMART APEX II

CCD area detector diffractometer with graphite monochromated Mo Ka radiation

(k = 0.71073 A). The final unit cell was determined from 6764 reflections for 1 and 9374

reflections for 2 in the range of 2.32\h\30.43 and 2.22\h\34.40, respectively.

The data were integrated using the SAINT suite of software and corrected for the effects of

absorption using SADABS. The structure was solved by direct methods and refined

iteratively via full-matrix least-squares on Fo2 and difference Fourier analysis using the

SHELX-97 [30–33]. The H atoms in 1 were placed in calculated positions and refined in

riding model with fixed thermal parameters (Uiso(H) = 1.2Ueq(Ci) or 1.5Ueq(Cii, N or

O)), where Ueq(Ci, Cii, N or O) are the equivalent thermal parameters of the carbon

Fig. 2 The ORTEP representation of 1 with the atom labeling scheme shown at 50% displacementprobability level. The potassium cations show bridging role between adjacent Preyssler anions throughcoordinated oxygen atoms from Preyssler unit and amino acids


123

(Ci=CH and CH2–groups, Cii=CH3–groups), nitrogen and oxygen atoms, respectively, to

which corresponding H atoms are bonded. There is a high positive residual density of 4.10

eA3 near the W2 center (0.84 A) due to considerable absorption effects, which could not

be completely corrected. The hydrogen atoms attached to O and N atoms in 2 were found

in the difference Fourier synthesis. The H(C) atom positions were calculated. All the

Fig. 3 A crystal packing view of (Hval)2(Hgly)(H3O)6K5[Na(H2O)P5W30O110]�19.5H2O along thea-axis. The complex cations and H2O molecules of crystallization are omitted for further clarity (top).A fragment of the crystal packing of hybrid 1 showing the H-bonded network; the Preyssler moieties aredepicted as green circles (down)


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hydrogen atoms were refined in isotropic approximation within riding model with the

Uiso(H) parameters equal to 1.2 Ueq(Ci), 1.2 Ueq(Ni), 1.5 Ueq(Oi). Ueq(Xi) are the

equivalent thermal parameters of the atoms, to which corresponding H atoms are bonded.

Crystallographic data for the two structures have been deposited with the Cambridge

Crystallographic Data Centre, CCDC 663239 for hybrid 1 and CCDC 745422 for hybrid 2.

Copies of the data can be obtained free of charge on application to the Director, CCDC,

12 Union Road, Cambridge CB2 1EZ, UK (Fax: int.code ?(1223)336-033; e-mail for

inquiry: [email protected]; e-mail for deposition: [email protected]).

Results and Discussion

Single Crystal X-ray Analysis

Recently, the introduction of inorganic–organic hybrid methods in the field of

POMs has led to a plethora of extended crystalline materials, which are inaccessible

Fig. 4 Independent part of unit cell for hybrid 2. Thermal ellipsoids are drawn at 50% displacementprobability level


123


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or not easily obtainable under conventional crystallization conditions. Thus, we are

exploring the route for making such extended POM-based materials, using suitable

organic and bioorganic precursors, as starting materials. It is worth pointing out that

reaction between organic and inorganic fragments led to increase of chance of

obtaining crystals by the help of van der Waals interactions. As we know,

crystallization from organic compounds is not easily possible. Single crystal X-ray

structural analysis reveals that the crystal of 1 contains a polyoxoanion, two sodium

cations and 19.5 lattice water molecules. As shown in Fig. 1, the pre-synthesized

polyoxoanion consists of a Preyssler anion [Na(H2O)P5W30O110]14- accompanying

with five {K(O)8}?, supporting fragments, two [Hval]? and one [Hgly]? amino

acids and six [H3O]? complex cations 19.5 H2O molecules of crystallization. Each

[Na(H2O)P5W30O110]14- cluster acts as a poly-dentate ligand and coordinates to

five potassium ions through the terminal oxygen atoms of four equivalent tungsten

atoms from the two inner decatungsten planes. Each K atom is coordinated by seven

oxygen atoms from Preyssler anion with the average K–O distances of 3.43(2)–

2.66(3) A and one oxygen atom from the valine unit with the K–O distance of

2.71(3) A to finish its distorted bicapped trigonal prism coordination environment

(Table 1S). In addition, there are two kinds of amino acid, distributed around the

quarterly linked [Na(H2O)P5W30O110]14- cluster in 1, which is hydrogen bonded to

bridging oxo-groups of Preyssler cluster as well as lattice water molecules (see

Table 2S). Interestingly, the potassium ions link the [Na(H2O)P5W30O110]14-

cluster into a 2D network (Fig. 2). All such 2D layers are arranged in an ABAB…sequence. The interlayer separation is approximately 3.191–5.473 A which is

occupied by lattice water molecules (Fig. 3). The crystal structure of (Hpro)6

[P2W18O62]�8H2O (Fig. 4) consists of [P2W18O62]6- Wells–Dawson anions units

linked together by [Hpro]? ions through electrostatic interactions. The ratio of anion

to proline is 1:6. The protonated prolines in the structure, by the acidic hydrogens of

H6[P2W18O62], function as cations and balance the charge. The proline and Wells–

Dawson structures bond distances and angles have standard values, thus we only

report the second one bond lengths data (Table 3S). In addition to intermolecular

interactions between them, there are intramolecular interactions, which force the

carboxylate group of one proline in the opposite direction (with respect to

the pentagonal ring to which they are attached) of the carboxylate group of the

neighboring proline. This spatial orientation is indicated by the torsion angles:

C(5C)–C(1C)–N(1C)–C(4C) = 134.24�, C(5B)–C(1B)–N(1B)–C(4B) = 128.12�,

C(5A)–C(1A)–N(1A)–C(4A) = 132.40�, C(5D)–C(1D)–N(1D)–C(4D) = 137.60�,

C(5F)–C(1F)–N(1F)–C(4F) = 148.80�, and C(5E)–C(1E)–N(1E)–C(4E) = 147.93�.

Hpro? ions are excellent hydrogen-bond donors and at the same time provide counter-

charges [5, 9]. The hydrogen bonds between Hpro? ions and crystallization water

molecules led to a suitable hole, which polyoxoanions are located in it (Table 4S;

Fig. 5 Fragment of crystal packing (projection along c crystal axis, hydrogen atoms are omitted forclarity). The cations and solvate water molecules take part in forming of complicated three-dimensionalH-bonded network (top). A fragment of the crystal packing of hybrid 2 illustrating the H-bonding networkresulting in a columnar architecture; Wells–Dawson moieties are not shown (down)

b


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Fig. 5). Electrostatic forces, van der Waals force and a lot of hydrogen bonds exist

between these networks. A careful survey of the structure indicates that water

molecules link the anionic and cationic fragments to each other with hydrogen

bonds, that is, the water molecules act as a ‘‘glue’’ to assemble the supramolecular

structure [34].

Conclusions

As a coating of the viral particles made up of proteins and the proved antiviral and

anticancer properties of polyoxometallates [35], there is a growing interest in the

synthesis of polyoxometallates-protein compounds. In this regards, chemical

reactions of amino acids, as the building blocks of proteins, with polyoxometallates,

is the focus of attention. In this communication, to better understanding of the

interactions between proteins and polyoxometallates, compounds resulting from

chemical reactions of tungstoheteropolyanions, having Preyssler and Wells–Dawson

structures with amino acids i.e., glycine, proline, valine were prepared and studied.

The spectral and crystallographically data confirm the structure of compounds 1 and

2. They show that all kinds of oxygen atoms in the structure of heteropolyanions

interact with the hydrogen atoms in amino acids and water molecules. In these

compounds, amino acids, as the positive moieties along with the polyoxoanions led

to pseudo organic–inorganic hybrid materials. Since the solution phase of the

hybrids are stable, making them a viable candidate for application as homogeneous

catalysis. There may be potential pharmaceutical benefits that expected to be

explored.

Acknowledgment The authors wish to thank to the Ferdowsi University of Mashhad for financial

support of this article (Grant No. 17897/2).

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Documents

Two Novel Chiral Inorganic–Organic Hybrid Materials Containing Preyssler and Wells–Dawson Heteropolyoxometallates with Valine (val), Glycine (gly), and Proline (pro) Amino acids: