Target syntheses of saturated Keggin polyoxometalate-based extended solids

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Inorganica Chimica Acta 358 (2005) 3701–3710

Target syntheses of saturated Kegginpolyoxometalate-based extended solids

Xiaojun Gu a, Jun Peng a,*, Zhenyu Shi a, Yanhui Chen a, Zhangang Han a, Enbo Wang a,Jianfang Ma a, Ninghai Hu b

a Institute of Polyoxometalate Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun, 130024, PR Chinab Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun, 130022, PR China

Received 24 February 2005; received in revised form 9 June 2005; accepted 16 June 2005Available online 1 August 2005

Abstract

By the approach of target synthesis, three infinitely extended hybrid compounds based on the saturated Keggin polyoxoanionshave been synthesized under hydrothermal conditions: f½CoðphenÞ2�2½SiMo8

VIMo4VO40ðVIVOÞ2�gf½CoðphenÞ2ðH2OÞ�2½SiMo8-

VIMo4VO40ðVIVOÞ2�g � 3H2O ð1Þ, f½CoðphenÞ2�2½GeMo8

VIMo4VO40ðVIVOÞ2�gf½CoðphenÞ2ðH2OÞ�2½GeMo8

VIMo4VO40ðVIVOÞ2�g�

4.8H2O ð2Þand ½NiðphenÞ2�½SiMo10VIMo2

VO40ðVIVOÞ2� � 2trea � 2H2O ð3Þ (phen = 1,10-phenanthroline, trea = triethylamine). Theisostructural compounds 1 and 2 belong to the monoclinic space group P21/c and both contain neutral 2D layers and discrete poly-oxometalate clusters decorated by transitional metal complexes. They represent an important example of the family of intercalatedsolids, in which both the 2D layers and the intercalated molecules are polyoxometalates with covalently linked transitional metalcomplex fragments. Compound 3, crystallizing in the monoclinic space group C2/c, consists of 1D zigzag chains constructed fromalternating ½SiMo10

VIMo2VO40ðVIVOÞ2�

2� polyoxoanions and [Ni(phen)2]2+ fragments. More interestingly, these three compounds

are constructed directly from saturated polyoxometalates, in which the intact skeletons of Keggin clusters are maintained underhydrothermal conditions. Variable-temperature magnetic susceptibility measurements of compounds 1 and 2 reveal the featureof antiferromagnetic exchange interaction in these compounds.� 2005 Elsevier B.V. All rights reserved.

Keywords: Target synthesis; Keggin polyoxometalate; Hydrothermal synthesis; Intercalation; Magnetic properties

1. Introduction

In the past decades, organic–inorganic hybrid mate-rials have received considerable attention in the solidstate materials chemistry, due to their diverse structuralflexibility and potential applications in molecularabsorption, biology, catalysis, photochemistry and elec-tromagnetism [1]. An attractive challenge in this field isthe design and synthesis of novel solid materials based

0020-1693/$ - see front matter � 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2005.06.002

* Corresponding author.E-mail addresses: [email protected], [email protected]

(J. Peng).

on polyoxometalates (POMs) [2]. One strategy hasbeen well developed and widely adopted, namely, theuse of the well-defined conditions which lead to theformation of POM building blocks in situ. Zubietaet al. [2d,3] have reported large numbers of organic–inorganic hybrid materials constructed from POMs un-der hydrothermal conditions. Muller et al. [2b,4] havesynthesized giant mixed-valence POMs. Another strat-egy, the direct use of pre-defined building blocks whosestructural integrity will be maintained in final products,has also been exploited. This strategy may provide arational way to not only target synthesis, but alsofine-tuning properties of materials on the molecularlevel. Peng et al. [5] have reported organoimido

mailto:[email protected], &emailxl2;

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3702 X. Gu et al. / Inorganica Chimica Acta 358 (2005) 3701–3710

derivatives of hexamolybdates. Pope et al. [6] have re-ported functionalized polyoxotungstates from lacunarypolyoxoanions.

Saturated Keggin polyoxoanions, for tailor makingnew solid materials with multidimensional frameworkstructures, are valuable building blocks, convenientand reliable. If they can be assembled into the prede-termined structures, meanwhile maintaining their struc-tural integrity throughout the construction process, thepossibility to control framework structure of KegginPOM-based solid materials with highly specific andcooperative functions will be improved. But severalfactors hinder their direct use as precursors: they arepredominantly characterized by octahedra with short‘‘terminal’’ bonds that tend to result in ‘‘closed’’ dis-crete structures; they are difficult to dissolve in organicsolvents; the maintenance of POM skeletons is some-times difficult due to rigorous reactive conditions.Although some effective strategies have been exploitedto solve them, for example, the approach of increasingthe surface charge density to activate the terminaloxygen atoms [2c,7], to maintain intact POM skeletonsunder hydrothermal conditions remains a greatchallenge.

Capped polyoxometalates, represented by early re-ported bicapped polyoxoanion [PMo12O40(VO)2]

5� [8],are proved to be very useful building blocks to constructmulti-dimensional extended solid materials. However,almost all the reported examples of this family were gen-erated in situ from simple inorganic components underhydrothermal reactions [9]. To our knowledge, no ex-tended solid materials formed directly from saturatedKeggin POMs under hydrothermal conditions havebeen reported.

On the basis of the aforementioned points, we haveattempted to synthesize saturated Keggin POM-basedextended solids, in which the intact skeletons of thepolyoxoanions are maintained. In this paper, we reportthe hydrothermal syntheses, crystal structures and mag-netic properties of three new compounds, f½CoðphenÞ2�2-½SiMo8

VIMo4VO40ðVIVOÞ2�gf½CoðphenÞ2ðH2OÞ�2½SiMo8-

VIMo4VO40ðVIVOÞ2�g � 3H2O ð1Þ, f½CoðphenÞ2�2½GeMo8-

VIMo4VO40ðVIVOÞ2�gf½CoðphenÞ2ðH2OÞ�2½GeMo8

VIMo4-VO40ðVIVOÞ2�g � 4.8H2O ð2Þ and ½NiðphenÞ2�½SiMo10-VIMo2

VO40ðVIVOÞ2� � 2trea � 2H2O ð3Þ (phen = 1,10-phenanthroline, trea = triethylamine). Isostructuralcompounds 1 and 2 are intercalated compounds, inwhich the discrete POM clusters decorated by transitionmetal complexes are embedded between neutral layers.Compound 3 exhibits a 1D zigzag chainlike structure,in which ½SiMo10


2� polyoxoanionsare connected by [Ni(phen)2]

2+ fragments. Unlike thosepreviously reported POM-based compounds, thesethree compounds are constructed directly from satu-rated Keggin polyoxoanions under hydrothermalconditions.

2. Experimental

2.1. Materials and general methods

All chemicals purchased were of reagent grade andused without further purification. H4[SiMo12O40] Æ x-H2O and H4[GeMo12O40] Æ xH2O were prepared accord-ing to the literature method [10]. All syntheses werecarried out in 18 ml Teflon-lined autoclaves underautogenous pressure. The reaction vessels were filledto approximately 60% volume capacity. Elemental anal-yses (C, H and N) were performed on a Perkin–Elmer2400 CHN Elemental Analyzer. Co, Ni, Mo and V weredetermined by a Leaman inductively coupled plasma(ICP) spectrometer. The IR spectra of 1, 2 and3 wererecorded in the range of 400–4000 cm�1 on an AlphaCentaurt FT/IR spectrophotometer using a KBr pellet.XPS analysis was performed on a VG ESCALAB MKII spectrometer with a Mg Ka (1253.6 eV) achromaticX-ray source. The vacuum inside the analysis chamberwas maintained at 6.2 · 10�6 Pa during analysis. TheESR spectrum was recorded on a Japanese JES–FE3AX spectrometer at room temperature. The TGanalysis was performed on a Perkin–Elmer TGA7instrument in flowing N2 with a heating rate of 10 �Cmin�1. X-ray power diffraction patterns were recordedon a Siemens D5005 diffractometer with Cu Ka(k = 1.5418 A) radiation. The magnetic susceptibilitymeasurements for 1 and 2 were carried out using aQuantum Design MPMS-XL SQUID magnetometerat 1000G. Diamagnetic corrections were estimated fromPascal�s constants [11].

2.2. Syntheses

2.2.1. {[Co(phen)2]2[SiMo8VIMo4

VO40(VIVO)2]}

{[Co(phen)2(H2O)]2 [SiMo8VIMo4

VO40-(VIVO)2]} Æ

3H2O (1)The starting materials, H4[SiMo12O40] Æ xH2O (0.5

mmol), Co(NO3)2 Æ 6H2O (0.5 mmol), NH4VO3 (1.0mmol), phen (0.5 mmol), trea (2.0 mmol) and H2O(9.0 ml), in a molar ration 1:1:2:1:4:1000 were mixed.The resulting suspension was stirred for 1 h, sealed inan 18 ml Teflon-lined reactor and heated at 160 �Cfor five days. Then the autoclave was cooled at5 �C/h to room temperature. Black block crystals of1 were isolated in 40% yield (based on molybdenum),along with a small amount of unidentified brownpowder. Anal. Calc. for C96H74Co4Mo24N16O89Si2V4

(5673.87): C, 20.30; H, 1.30; N, 3.95; Co, 4.16; Mo,40.61; V, 3.60. Found: C, 20.37; H, 1.27; N, 3.91;Co, 4.28; Mo, 40.25; V, 3.53%. IR (cm�1): 1628(m),1519(m), 1455(w), 1427(s), 1145(w), 956(m), 897(s),844(m), 794(s), 724(m).

X. Gu et al. / Inorganica Chimica Acta 358 (2005) 3701–3710 3703

2.2.2. {[Co(phen)2]2[GeMo8VIMo4

VO40(VIVO)2]}

{[Co(phen)2(H2O)]2[GeMo8VIMo4

VO40(VIVO)2]} Æ

4.8H2O (2)The synthetic method, here was similar to that used

for the preparation of 1 except that H4[SiMo12O40] Æ x-H2O was replaced by H4[GeMo12O40] Æ xH2O. Blackblock crystals suitable for X-ray analysis were obtainedin 43% yield. Anal. Calc. for C96H77.6Co4Ge2Mo24-N16O90.8V4 (5795.36): C, 19.88; H, 1.34; N, 3.87; Co,4.07; Mo, 39.76; V, 3.52. Found: C, 20.01; H, 1.31; N,3.80; Co, 4.17; Mo, 39.46; V, 3.44%. IR (cm�1):1636(m), 1513(w), 1430(m), 1092(m), 955(s), 875(w),806(m), 720(w).

2.2.3. [Ni(phen)2][SiMo10VIMo2

VO40(VIVO)2] Æ 2trea Æ

2H2O (3)The method is the same as 1, with the starting materi-

als H4[SiMo12O40] Æ xH2O (0.25 mmol), Ni(NO3)2 Æ6H2O (0.25 mmol), NH4VO3 (0.5 mmol), phen (0.25mmol), trea (1.0 mmol) and H2O (9 ml) in a molar ration1:1:2:1:4:2000. Black block crystals of 3 were filtered,washed with water, and dried (yield 80%, based onmolybdenum). Anal. Calc. for C36H50Mo12N6NiO44SiV2

(2610.78): C, 16.55; H, 1.92; N, 3.22; Ni, 2.26; Mo, 44.12;V, 3.91. Found: C, 16.64; H, 2.01; N, 3.15; Ni, 2.31; Mo,43.98; V, 3.98%. IR (cm�1): 1626(w), 1586(m), 1519(w),1456(m), 1426(s) 1147(w), 982(w), 956(s), 898(s),844(w), 794(s), 752(m).

2.3. X-ray crystallography

Crystal data for 1 and 2 were collected at 293 K onBruker SMART-CCD diffractormeter (graphite mono-

Table 1Crystal data and structure refinement of 1, 2 and 3

Complex 1 2

Empirical formula C96H74Co4Mo24N16O89Si2V4 C9

Formula weight 5673.87 57T (K) 293 29Crystal system monoclinic moSpace group P21/c P2a (A) 21.8202(15) 21b (A) 16.5372(11) 16c (A) 21.2228(15) 21b (�) 100.3940(10) 10V (A3) 7532.5(9) 75Z 2 2k (A) 0.71073 0.7Dc (Mg m�1) 2.498 2.5l (mm�1) 2.703 3.0F(000) 5404 55Crystal size (mm) 0.31 · 0.19 · 0.16 0.2Reflection collected 26286 38Independent reflections 14714 13Absorption correction empirical emRefinement method full-matrix least-squares on F2 fulR1, wR2 [I > 2r(I)] 0.0618, 0.1419 0.0R1, wR2 (all data) 0.0942, 0.1539 0.0

chromated Mo Ka radiation: k = 0.71073 A). Crystaldata for3 were collected at 293 K on Rigaku R-AXISRAPID IP diffractometer (graphite monochromatedMo Ka radiation: k = 0.71073 A). The three structureswere solved by the directed methods and refined byfull-matrix least-squares on F2 using the SHELXTL crystal-lographic software package [12]. All the non-hydrogenatoms were refined anisotropically. The hydrogen atomswere located from difference Fourier maps. X-ray datafor 1, 2 and 3 are listed in Table 1.

3. Results and discussion

3.1. Syntheses

Hydrothermal synthesis has been proved a powerfulmethod for the construction of organic–inorganic hy-brid materials [13]. Therefore, the introduction ofhydrothermal techniques and direct use of saturatedKeggin POM as building blocks may produce a largenumber of novel organic–inorganic hybrid materials.However, pre-synthesized saturated Keggin POM skele-tons are difficult to maintain in constructing extendedsolids under hydrothermal conditions, depending uponthe reaction conditions, such as starting materials, tem-perature, pH, filling volume and stoichiometry. Experi-ments demonstrated that among these factors, organicreductant species were crucial for maintaining the intactskeleton of pre-synthesized saturated Keggin polyoxoa-nions. If their reductibility was strong, the skeleton ofpre-synthesized Keggin cluster may incline to decom-pose and re-assemble into a new Keggin cluster with a

3

6H77.6Co4Mo24N16O90.8Ge2V4 C36H50Mo12N6NiO44SiV2

95.36 2610.783 293noclinic monoclinic

1/c C2/c.8169(9) 23.738(3).5716(7) 12.8470(8).2571(9) 25.506(2)0.2430(10) 116.213(3)62.8(5) 6978.4(11)

41073 0.7107345 2.48568 2.71028 50083 · 0.22 · 0.17 0.42 · 0.22 · 0.20326 24747219 7504pirical empiricall-matrix least-squares on F2 full-matrix least-squares on F2

867 0.1797 0.0498, 0.1196841 0.1788 0.0783, 0.1296

Fig. 1. Structure of f½CoðphenÞ2�2½SiMo8VIMo4

VO40ðVIVOÞ2�gf½CoðphenÞ2ðH2OÞ�2½SiMo8VIMo4

VO40ðVIVOÞ2�g � 3H2O ð1Þ. Only parts of atoms arelabeled, and all H atoms, water molecules and some C atoms are omitted for clarity.


different composition [14]. By doing many trials, wefound that trea was a good candidate. In addition, thesaturated polyoxoanion surface is populated by weaklybasic oxygen atoms, and therefore is relatively non-reac-tive towards further graft or polymerization. Increase ofthe surface charge density by introducing lower-valencemetals can activate the surface oxygen atoms of poly-oxoanion and make covalent graft or polymerizationof POM with ease [15]. In the reaction system, vanadatewas used for this purpose. We ever attempted to synthe-size POM-based extended solids under similar reactionconditions without vanadate, but only obtained a non-extended solid [Co(phen)3]2[SiMo12O40] Æ 0.5H2O,1 inwhich the discrete polyoxoanion cluster [SiMo12O40]

4�

and metal complexes [Co(phen)3]2+ were connected

through supramolecular interactions.

3.2. Structural descriptions

3.2.1. {[Co(phen)2]2[SiMo8VIMo4

VO40(VIVO)2]}

{[Co(phen)2(H2O)]2 [SiMo8VIMo4

VO40(VIVO)2]} Æ

3H2O (1)X-ray structure analysis reveals that 1 is an interca-

lated compound, in which the discrete POM clustersdecorated by transition metal complexes are embeddedbetween neutral layers. As shown in Fig. 1, there are

1 Crystal data for [Co(phen)3]2[SiMo12O40] Æ 0.5H2O: monoclinic, Cc;a = 19.688(4) A, b = 18.143(3) A, c = 24.918(5) A, b = 101.095(4) �,V = 8734(3) A3, Z = 4.

two crystallographically independent POM clusters,one decorated by two [Co(phen)2(H2O)]2+ fragments,to form ½CoðphenÞ2ðH2OÞ�2½SiMo8


(see the right one in Fig. 1) and the other decorated byfour [Co(phen)2]

2+ units, to form ½CoðphenÞ2�2½SiMo8-VIMo4

VO40ðVIVOÞ2� (see the left one in Fig. 1). Theformer is a discrete cluster, in which ½SiMo8

VIMo4-VO40ðVIVOÞ2�

4� polyoxoanion coordinates to two[Co-(phen)2]

2+ by providing two oxygen atoms fromopposite {VO} groups. The latter forms the layer struc-ture. The polyoxoanion ½SiMo8


4� inthe latter acts as a tetradentate ligand, providing twooxygen atoms from opposite {VO} groups and the othertwo oxygen atoms from opposite {MoO} groups tocoordinate four [Co(phen)2]

2+ fragments. The polyoxo-anion ½SiMo8


4� has a bicappedKeggin structure, which can be best described as onea-Keggin core of [SiMo12O40]

6� capped by two{VO}2+ units. A {VO} group covers four bridging oxy-gen atoms from corner-sharing adjacent Mo3O13 trime-tallic clusters to form a vanadium cap. The othervanadium cap is located in the opposite site. The struc-ture of the polyoxoanion is similar to that of the discreteanions [SiMo14O44]

4� [16] and ½PMo6VMo6

VIO40

ðVIVOÞ2�5� generated in situ from Na2MoO4 Æ 2H2O,

VOSO4 Æ 3H2O, H3PO4 and (C2H5)3N Æ HCl underhydrothermal conditions [8]. The SiO4 tetrahedron inthe center of the polyoxoanion cage is disordered, whichis a common phenomenon in the Keggin polyoxoanionstructure. Both the valence sum calculations [17] andXPS spectra show that all vanadium atoms are in the

Fig. 2. View of the 2D layer on the bc-plane in 1 and 2.


+4 oxidation state, while four molybdenum atoms are inthe +5 oxidation state, which confirms the molecularformula of 1. Selected bond lengths and angles are col-lected in Table 2.

There are two crystallographically unique cobalt cen-ters in 1. One Co center is coordinated by four nitrogenatoms from two phen ligands with an average Co–Nbond length of 2.118(4) A, one oxygen atom from the½SiMo8


4� polyoxoanion and a termi-nal water ligand with Co–OW bond length of 2.144(5) A,to form a discrete POM cluster ½CoðphenÞ2ðH2OÞ�2-½SiMo8

VIMo4VO40ðVIVOÞ2�. The other Co center is coor-

dinated by four nitrogen atoms from two phen ligandswith an average Co–N bond length of 2.109(5) A, andtwo oxygen atoms from adjacent polyoxoanions, toform a neutral 2D layer along the bc-plane (see Fig. 2).

An interesting feature of 1 is that the discrete POMclusters decorated by transition metal complexes inter-calates between neutral 2D layers, as shown in Fig.3(a). The distance between the adjacent 2D layers isabout 17 A. Fig. 3(b) illustrates this structural feature.

Table 2Selected bond lengths (A) and angles (�) for 1

Mo(1)–O(22) 1.668(6) Mo(8)–O(39) 1.671(7)Mo(1)–O(1) 2.483(11) Mo(8)–O(26) 2.379(1)Mo(1)–O(5) 1.903(8) Mo(8)–O(27) 1.779(9)Mo(1)–O(6) 1.929(8) V(1)–O(17) 1.920(7)Mo(1)–O(15) 1.904(8) V(1)–O(13) 1.931(7)Mo(1)–O(12) 1.936(8) V(1)–O(21) 1.936(7)Mo(2)–O(9) 1.635(7) V(1)–O(18) 1.640(7)Mo(2)–O(2) 2.392(12) V(1)–O(23) 1.913(7)Mo(2)–O(7) 1.913(8) V(2)–O(45) 1.925(7)Mo(2)–O(8) 1.937(7) V(2)–O(46) 1.934(7)Mo(2)–O(14) 1.935(8) V(2)–O(41) 1.942(8)Mo(2)–O(16) 1.931(7) V(2)–O(42) 1.653(6)Mo(3)–O(3) 2.482(11) V(2)–O(44) 1.919(7)Mo(3)–O(20) 1.642(7) Si(2)–O(29) 1.597(1)Mo(3)–O(5) 1.808(8) Si(2)–O(24) 1.622(1)Mo(3)–O(16) 1.825(8) Si(2)–O(6) 1.693(1)Mo(3)–O(21) 2.051(7) Si(2)–O(25) 1.584(1)Mo(3)–O(13) 2.051(7) Si(1)–O(1) 1.619(1)Mo(8)–O(30) 1.803(9) Si(1)–O(2) 1.622(1)Mo(8)–O(41) 2.025(8) Si(1)–O(4) 1.704(1)Mo(8)–O(45) 2.050(7) Si(1)–O(3) 1.615(1)

O(22)–Mo(1)–O(5) 104.4(4) O(39)–Mo(8)–O(29) 155.3(4)O(22)–Mo(1)–O(6) 102.4(4) O(18)–V(1)–O(13) 114.4(4)O(5)–Mo(1)–O(15) 89.1(4) O(18)–V(1)–O(21) 116.9(3)O(5)–Mo(1)–O(6) 86.8(3) O(13)–V(1)–O(21) 79.9(3)O(22)–Mo(1)–O(1) 97.5(4) O(17)–V(1)–O(13) 131.7(4)O(5)–Mo(1)–O(12) 158.0(5) O(23)–V(1)–O(13) 80.4(3)O(9)–Mo(2)–O(7) 101.7(5) O(42)–V(2)–O(41) 114.0(4)O(9)–Mo(2)–O(8) 100.7(4) O(42)–V(2)–O(44) 112.0(4)O(7)–Mo(2)–O(8) 86.6(3) O(45)–V(2)–O(46) 80.2(3)O(7)–Mo(2)–O(16) 89.0(4) O(45)–V(2)–O(41) 79.4(3)O(16)–Mo(2)–O(2) 93.6(4) O(44)–V(2)–O(45) 132.0(4)O(16)–Mo(2)–O(8) 157.6(4) O(1)–Si(1)–O(3) 110.4(6)O(39)–Mo(8)–O(41) 99.0(4) O(2)–Si(1)–O(3) 113.6(6)O(39)–Mo(8)–O(45) 97.9(3) O(1)–Si(1)–O(2) 110.2(6)O(27)–Mo(8)–O(45) 91.4(3) O(1)–Si(1)–O(4) 108.7(6)

Compound 1 represents an interesting example ofPOM-based extended frameworks in which both the2D layers and the intercalated molecules are polyoxoa-nions with covalently linked transitional metal complexfragments.

3.2.2. {[Co(phen)2]2[GeMo8VI Mo4

VO40(VIVO)2]}

{[Co(phen)2(H2O)]2[GeMo8VIMo4

VO40(VIVO)2]} Æ

4.8H2O (2)The compound 2 is isostructural with 1, except that Si

atom is replaced by Ge atom. The Mo–Oand V–Obondlengths [Mo–Ot(Ot = terminal oxygen atom) 1.632(2)–1.669(2) A, Mo–Ob (Ob = bridge oxygen atom)1.791(6)–2.083(9) A, Mo–Oc (Oc = center oxygen atom)2.327(9)–2.498(8) A, V–Ot 1.633(3)–1.637(4), A V–Ob

1.905(5)–1.940(6) A] are comparable with those in 1

[Mo–Ot 1.635(0)–1.671(0) A, Mo–Ob 1.779(4)–2.051(4)A, Mo–Oc2.379(4)–2.516(2) A, V–Ot 1.640(2)–1.652(9),A V–Ob 1.912 (7)–1.942(2) A]. The GeO4 tetrahedronis also disordered. The Ge–O distances are in the rangeof 1.693(0)–1.829(7) A and the O–Ge–O angles in therange of 106.4(6)–115.0(6)�. Selected bond lengths andangles are collected in Table 3.

3.2.3. [Ni(phen)2][SiMo10VIMo2

VO40(VIVO)2] Æ

2trea Æ 2H2O (3)The single crystal structure analysis shows that 3 con-

sists of 1D zigzag chains, trea and water molecules. Thefundamental unit of the 1D chain is shown in Fig. 4. It isconstructed from [Ni(phen)2]

2+ fragment and polyoxo-anion ½SiMo10


2�, which, to ourknowledge, has not been reported previously. The struc-ture of the polyoxoanion ½SiMo10


2�

is similar to that of ½SiMo8VIMo4

VO40ðVIVOÞ2� in 1,but the difference is that two MoV exist in each bicappedKeggin polyoxoanion in 3. The Si–O distances are in therange of 1.605(7)–1.697(8) A and the O–Si–O angles in

Fig. 3. (a) View of the intercalated frameworks of 1 and 2, showing the 2D layers intercalated by discrete polyoxometalate clusters. All C, Hatoms and water molecules are omitted for clarity. (b) Schematic representation of the intercalated frameworks. The 2D square grids represent theneutral 2D layers ½CoðphenÞ2�2½SiMo8

VIMo4VO40ðVIVOÞ2� and the ellipsoids represent the discrete POM clusters ½CoðphenÞ2ðH2OÞ�2-

½SiMo8VIMo4

VO40ðVIVOÞ2�.


the range of 105.3(4)–112.9(4)�. The distances of Mo–Obonds are divided into three groups: Mo–Oc, 2.368(8)–2.500(8) A; Mo–Ob, 1.796(6)–2.023(6) A and Mo–Ot,1.632(5)–1.659(5) A. The V–O distances are dividedinto two groups: V–Ob, 1.924(6)–1.948(6) A and V–Ot,1.618(4) A. Selected bond lengths and angles arecollected in Table 4. Each Ni atom is coordinated byfour nitrogen atoms from two phen ligands with anaverage Ni-N bond length of 2.075(5) A and two oxygenatoms from two {VO} groups of adjacent½SiMo10


2� polyoxoanions with Ni–O bond length of 2.043(5) A, to complete its distortedoctahedral coordination.

It is noteworthy that a 1D zigzag chain with alternatepolyoxoanion and cation is formed through V–Ot–Ni–Ot–V links along the c-axis (see Fig. 5). Adjacent 1D zig-zag chains construct 2D supramolecular framework viahydrogen bond interactions. Trea and water moleculesoccupy the space between the chains.

To confirm the purity of the product, X-ray powderdiffraction was measured. Typical powder X-ray datawith the simulated one are presented in Fig. S1. It indi-cates that the pattern of 3 is consistent with the structuredetermined by the single-crystal X-ray diffraction.

It is noteworthy that among the twelve terminal oxy-gen atoms (Ot) in a saturated Keggin polyoxoanion,


Mo(1)–O(12) 1.653(1) Mo(8)–O(31) 2.050(1)Mo(1)–O(23) 1.808(1) Mo(8)–O(37) 2.053(1)Mo(1)–O(21) 1.819(1) Mo(8)–O(24) 2.394(2)Mo(1)–O(16) 2.034(1) Mo(8)–O(30) 1.792(1)Mo(1)–O(10) 2.039(1) V(1)–O(17) 1.633(3)Mo(1)–O(4) 2.351(2) V(1)–O(10) 1.910(0)Mo(5)–O(18) 1.666(1) V(1)–O(9) 1.918(6)Mo(5)–O(22) 1.8894(1) V(1)–O(15) 1.940(6)Mo(5)–O(5) 1.933(1) V(1)–O(16) 1.905(5)Mo(5)–O(21) 1.938(1) V(2)–O(38) 1.637(4)Mo(5)–O(7) 1.945(1) V(2)–O(35) 1.911(3)Mo(5)–O(4) 2.349(2) V(2)–O(31) 1.928(3)Mo(5)–O(2) 2.429(2) V(2)–O(37) 1.915(3)Mo(7)–O(28) 1.659(1) V(2)–O(46) 1.940(2)Mo(7)–O(41) 1.933(1) Ge(2)–O(25) 1.693(2)Mo(7)–O(30) 1.946(1) Ge(2)–O(26) 1.722(2)Mo(7)–O(45) 1.933(1) Ge(2)–O(24) 1.714(2)Mo(7)–O(29) 1.942(1) Ge(2)–O(27) 1.830(2)Mo(7)–O(24) 2.329(2) Ge(1)–O(1) 1.714(2)Mo(7)–O(25) 2.368(2) Ge(1)–O(2) 1.736(2)Mo(8)–O(34) 1.659(1) Ge(1)–O(4) 1.797(2)Mo(8)–O(43) 1.817(1) Ge(1)–O(3) 1.745(2)

O(12)–Mo(1)–O(21) 102.1(8) O(30)–Mo(8)–O(37) 89.7(5)O(12)–Mo(1)–O(10) 99.7(6) O(17)–V(1)–O(16) 113.5(5)O(12)–Mo(1)–O(16) 99.1(5) O(17)–V(1)–O(10) 115.1(6)O(16)–Mo(1)–O(21) 156.0(6) O(16)–V(1)–O(10) 79.4(5)O(12)–Mo(1)–O(4) 154.8(6) O(16)–V(1)–O(15) 130.5(5)O(23)–Mo(1)–O(10) 154.9(6) O(17)–V(1)–O(15) 116.0(5)O(18)–Mo(5)–O(22) 98.3(7) O(38)–V(2)–O(37) 113.4(8)O(18)–Mo(5)–O(5) 103.3(7) O(38)–V(2)–O(35) 115.8(7)O(22)–Mo(5)–O(5) 89.3(7) O(38)–V(2)–O(31) 113.9(6)O(18)–Mo(5)–O(21) 103.0(7) O(37)–V(2)–O(31) 81.1(5)O(22)–Mo(5)–O(21) 158.7(8) O(37)–V(2)–O(35) 130.6(6)O(18)–Mo(5)–O(4) 159.3(6) O(1)–Ge(1)–O(3) 113.9(8)O(34)–Mo(8)–O(24) 156.01(6) O(1)–Ge(1)–O(4) 107.9(8)O(34)–Mo(8)–O(31) 97.7(6) O(3)–Ge(1)–O(4) 107.3(9)O(30)–Mo(8)–O(31) 156.7(7) O(2)–Ge(1)–O(4)#1 109.0(7)


Mo(1)–O(17) 1.632(5) V–O(20) 1.618(6)Mo(1)–O(22) 1.813(6) V–O(10) 1.931(6)Mo(1)–O(10) 2.034(6) V–O(12) 1.948(6)Mo(1)–O(21) 1.796(6) V–O(9) 1.924(6)Mo(1)–O(12) 2.026(6) V–O(13)#1 1.938(6)Mo(1)–O(4) 2.397(8) Ni–N1 2.075(5)Mo(3)–O(8) 1.885(6) Ni–N2 2.075(5)Mo(3)–O(23) 1.938(7) Ni–O(20) 2.043(5)Mo(3)–O(1) 2.368(8) Si–O(1) 1.697(8)Mo(3)–O(18) 1.651(5) Si–O(2) 1.623(8)Mo(3)–O(6) 1.890(6) Si–O(3) 1.605(7)Mo(3)–O(3)#1 2.472(8) Si–O(4) 1.614(8)

O(17)–Mo(1)–O(21) 101.7(4) O(6)–Mo(3)–O(23) 87.9(3)O(21)–Mo(1)–O(22) 97.1(3) O(1)–Mo(3)–O(8) 96.7(3)O(21)–Mo(1)–O(12) 156.8(3) O(20)–V–O(12) 113.1(3)O(22)–Mo(1)–O(4) 65.0(3) O(20)–V–O(9) 115.1(3)O(10)–Mo(1)–O(4) 92.1(3) O(10)–V–O(12) 79.4(2)O(17)–Mo(1)–O(12) 98.3(3) O(20)–V–O(13)#1 116.5(3)O(21)–Mo(1)–O(4) 99.3(4) O(3)–Si–O(4)#1 110.2(4)O(18)–Mo(3)–O(8) 101.0(3) O(2)–Si–O(4) 112.9(4)O(18)–Mo(3)–O(6) 102.2(4) O(4)–Si–O(1)# 107.1(4)O(8)–Mo(3)–O(23) 157.4(4) O(2)#1–Si–O(1) 105.3(4)O(6)–Mo(3)–O(1) 63.0(3) O(20)–Ni–N(2) 94.1(2)


shown in Scheme S1, the formation of 1D structure ofPOM derivatives disqualifies eight Ot as ligands for fur-ther coordination owing to the hindrance of the adjacentbridging oxygen atoms decorated by {VO} groups, likethe case in 3. The formation of 2D structure of POM

Fig. 4. Structure of ½NiðphenÞ2�½SiMo10VIMo2

VO40ðVIVOÞ2�ðtreaÞ2ðH2OÞ2 ð3molecules are omitted for clarity.

derivatives uses two more Ot, like the case in 1 and 2.We speculate that 3D structure of POM derivativescan be constructed, if the remaining two Ot can be usedto bridge metal complexes. The possibility is now beingtestified.

3.3. Spectroscopic properties

In the IR spectra (see Fig. S2), characteristic vibra-tion modes of the Keggin polyoxoanions are observedfor m(Mo@Ot), m(M–Ob–M), and m(M–Oc–M) (M = Vor Mo) at 956, 897, 844, 794 cm�1, 1; 955, 875, 806cm�1, 2 and 957, 898, 845, 793 cm�1, 3. The character-istic absorption bands of phen ligand occur at 1628,1583, 1519, 1455, 1427 cm�1, 1; 1636, 1513, 1430cm�1, 2; and 1626, 1586, 1519, 1456, 1426 cm�1, 3.The XPS spectra (see Fig. S3) give a peak at 516.2 eV,

Þ. Only parts of atoms are labeled, and all H atoms, trea and water

Fig. 5. View of 1D zigzag chain of 3 along the c-axis.


1; 516.2 eV, 3, attributed to V4+ [18], two overlappedpeaks at 232.1 eV, 231.4 eV, 1; 232.4 eV, 231.5 eV, 3,attributed to Mo6+ and Mo5+ [19], respectively. Allthese results further confirm the structure analysis.

3.4. Thermogravimetric analyses

The thermogravimetric analyses (TGA) of 1, 2 and 3

show two steps of weight loss (see Fig. S4). TGA curvefor 1 shows an initial weight loss of 1.71% (calc. 1.59%)from 80 �C to 230 �C corresponding to the removal oflattice water and ligand water molecules, while theweight loss at 230–4500 �C, 24.82% (calc. 25.39%) is as-cribed to decomposition of phen ligands. The TGA for 2is very similar to that of 1. The first weight loss at 70–200 �C is 2.21% (calc. 2.11%), in correspondence withthe loss of lattice water and ligand water molecules,and the second weight loss at 200–550 �C, 24.71% (calc.24.85%), is ascribed to decomposition of phen ligands.However, for 3, the first weight loss is 9.24% (calc.9.12%) in the temperature range 65–480 �C, contributedto the release of the crystal water and trea molecules.The second weight loss at 480–590 �C is ascribed todecomposition of phen ligands, 12.98% (calc. 13.79%).

Fig. 6. Temperature dependence of vmT for

These results also support the chemical compositionsof 1, 2 and 3.

3.5. Magnetic properties

The variable temperature magnetic susceptibilities of1 and 2 were measured from 300 to 2 K and the vmT ver-sus T is plotted in Fig. 6 (where vm is the molar magneticsusceptibility). The vmT value for 1 is 12.28 emu Kmol�1

at 300 K and 5.77 emu K mol�1 at 2 K, respectively. ThevmT value at 300 K is lower than that estimated for fourVIV (S = 1/2), eight MoV (S = 1/2) and four CoII (S = 3/2), by assuming g � 2.0 for VIV and MoV, and g � 2.65for CoII (17.7 emu K mol�1). Generally, in the hetero-polymolybdoblues, the introduced electrons are stronglypaired for giving diamagnetic substances. As mentionedabove, the lower value may be due to strongly pairedMoV. The vmT versus T plot shows antiferromagnetic ex-change interaction with the feature of the spin–orbit cou-pling for CoII. The magnetic behaviors of 1 obeys theCurie–Weiss law with C = 12.3 cm3 K mol�1 andh = �9.5 K. ESR measurement was carried out at roomtemperature for 1. A signal at g = 1.9684 attributed toVIV with the typical eight-line pattern due to hyperfine

compounds 1 between 2 and 300 K.


coupling with 51V (I = 7/2) was observed, showing thatunpaired electron in VIV is localized at room tempera-ture. No observable ESR signals of CoII and MoV wereobtained (see Fig. S5).

The magnetic property of 2 is slightly different fromthat of 1, with vmT value of 14.40 emu K mol�1 at300 K and 10.15 emu K mol�1 at 2 K, C = 14.1 cm3

K mol�1 and h = �12.1 K.We failed to fit the data according to the Brillouin

function, and unfortunately other trials did not get sat-isfying results as well. So the magnetic behavior of thethree solid hybrids is not yet perfectly understood atthe moment.

4. Conclusions

In this paper, three novel extended solids based onsaturated Keggin polyoxoanions were synthesized underhydrothermal conditions. The successful design and syn-theses of the three compounds not only confirm that tar-get syntheses of saturated Keggin POM-based extendedsolids can be carried out under hydrothermal conditionsby rational tune of the reaction, but also provide a valu-able clue to hydrothermal reaction mechanism for theformation of capped Keggin POM-based compoundsin situ, that is, Keggin polyoxoanions may form previ-ously and then the surface oxygen atoms are activatedto make capping of V atoms feasible under particularsynthetic conditions. Molecular design and assemblyof 3D saturated Keggin POM-based extended solidsby this route are underway.

Acknowledgments

This work was financially supported by the NationalNatural Science Foundation of China (20271001). Weare grateful for the measurements of magnetic suscepti-bility and for helpful discussions provided by Prof.Coronado and Prof. Gomez Garcıa of the Institute ofMolecular Materials, Department of Inorganic Chemis-try, University of Valencia, Spain.

Appendix A. Supplementary data

CCDC-236762 (1), -252508 (2) and -236763 (3) con-tain the supplementary crystallographic data for this pa-per. These data can be obtained free of charge atwww.ccdc.cam.ac.uk/conts/retrieving.html [or from theCambridge Crystallographic Data Center, 12 UnionRoad, Cambridge CB2 1EZ, UK; fax: (internet.) +441223 336 033; e-mail: [email protected]]. Supple-mentary data associated with this article can be found,in the online version, at doi:10.1016/j.ica.2005.06.002.

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Target syntheses of saturated Keggin polyoxometalate-based extended solids

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