Synthesis and Structure of a One-Dimensional Aluminum Phosphate,[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�

Srinivasan Natarajana,b,*, Wilhelm Kleinb, Jürgen Nussb, Leo van Wüllenb, and Martin Jansenb,*a Bangalore/India, Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research

b Stuttgart, Max-Planck-Institut für Festkörperforschung

Received September 6th, 2002.

Abstract. A one-dimensional aluminum phosphate,[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�, has been synthe-sized hydrothermally in the presence of N-(2-Aminoethyl-)1,3-di-aminopropane (AEDAP) and its structure determined by singlecrystal X-ray diffraction. Crystal data: space group � Pbca(no. 61), a � 16.850(2), b � 8.832(1), c � 17.688(4) A, V �

2632.4(2) A3, Z � 8, R1 � 0.0389 [5663 observed reflections withI > 2σ(I)]. The structure consists of anionic 1

�[Al(PO4)2]3� chainsbuilt up from AlO4 and PO4 tetrahedra, in which all the AlO4 verti-

Synthese und Struktur des eindimensionalen Aluminiumphosphats[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�

Inhaltsübersicht.Ein eindimensionales Aluminiumphosphat,[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�, wurde in Anwesen-heit von N-(2-Aminoethyl-)1,3-diaminopropan (AEDAP) hydro-thermal dargestellt. Die Kristallstruktur [Pbca, a � 16.850(2), b �

8.832(1), c � 17.688(4) A, V � 2632.4(2) A3, Z � 8, R1 � 0.0389,5663 beobachtete Reflexe mit I > 2σ(I)] wurde mittels Einkristall-röntgenstrukturanalyse bestimmt. In der Kristallstruktur sindAlO4- und PO4-Tetraeder über Ecken zu anionischen

Introduction

Aluminum phosphates with three-dimensional structures(AlPO4-n with n representing a particular structure type)were discovered by Wilson and others in the 1980s [1�4].Since then, much effort has been directed toward the syn-thesis and structural characterization of novel but AlPO4-nrelated materials. Structurally, most AlPO4-n phases are ex-

* Prof. Dr. S. NatarajanFramework Solids LaboratoryChemistry and Physics of Materials UnitJawaharlal Nehru Centre for Advanced Scientific ResearchJakkur P.O., Bangalore 560 064IndiaE-mail: raj@jncasr.ac.in

Prof. Dr. Martin JansenMax-Planck-Institut für FestkörperforschungHeisenbergstrasse 1, D-70569, StuttgartGermanyPhone: �49-0711-689-1500Fax: �49-0711-689-1502E-mail: m.jansen@fkf.mpg.de

Z. Anorg. Allg. Chem. 2003, 629, 339�343 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 0044�2313/03/629/339�343 $ 20.00�.50/0 339

ces are shared and each PO4 tetrahedron possesses two terminalP�O linkages. The cations, which balances the negative charge ofthe chains, are located in between the chains and interact with theoxygen atoms through strong N�H···O hydrogen bonds. Ad-ditional characterization of the compound by powder XRD andMAS-NMR has also been performed and described.

Keywords: Aluminum phosphate; One-dimensional chain structure;Crystal structure; NMR spectroscopy

1�[Al(PO4)2]3�-Ketten entlang der b-Achse verknüpft. Die AlO4-Te-traeder sind über sämtliche Ecken verknüpft, die PO4-Tetraeder ha-ben zwei endständige P�O-Bindungen. Die Ketten sind hexagonalgepackt und mit den dazwischenliegenden Kationen über starkeN�H···O-Wasserstoffbrücken verbunden. Zusätzlich wurde dieSubstanz durch Röntgenbeugung an Pulvern und durch MAS-NMR charakterisiert.

clusively formed of AlO4 and PO4 tetrahedral primarybuilding units, although AlO5 and AlO6 units have alsobeen observed [5�8]. In addition to the three-dimensionalaluminum phosphates, a number of AlPO4’s have been pre-pared with varying Al/P ratios possessing two- [9�12] andone-dimensional [13�15] structures. These compounds canbe synthesized utilizing the hydrothermal chemistry routein the presence of an organic amine molecule. The organicamines are incorporated in the interchains, interlayers, andchannels or cage voids, playing templating and charge-ba-lancing roles [16�18]. In spite of the large number of struc-tures known in the family of open-framework solids [19],new structures are continuously being discovered. Thus, inthe one-dimensional aluminum phosphates, new compo-sitions [H3N(CH2)3NH3][Al(PO4)(HPO4)] [15], Na4Al-(PO4)2OH [20], [C6H12NH2][AlP2O5(OH)3F] [21] have beenencountered in recent years.

In this work, we describe the synthesis and crystal struc-ture of a new one-dimensional aluminum phosphate,[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�, based onAlO4 and PO4 tetrahedra. Though aluminum phosphatechains with Al:P ratio of 1:2 have been encountered before

S. Natarajan, W. Klein, J. Nuss, L. v. Wüllen, M. Jansen

[13�15], to our knowledge, this is the first time this chainhas been identified in the presence of a triamine, N-(2-amino-ethyl-)1,3-diaminopropane (AEDAP). In the previously re-ported AlPO4 with Al:P ratio of 1:2 strong P�O···HO�Pintra-chain hydrogen bonds have been observed. In the pre-sent compound, there are neither P�O···HO�P intra-chainhydrogen bonds nor inter-chain hydrogen bonds have beenobserved.

Experimental

Synthesis

The title compound was synthesized under hydrothermal con-ditions. Aluminum isopropoxide (1g, 99.99 %) was dispersed in8.8 ml of distilled water. Phosphoric acid (0.7 ml, ACS reagent85 wt.%) was added to the above followed by the addition ofAEDAP (0.92 ml, 97 %). All the chemicals were obtained fromAldrich and were used without further purification. The mixturewith the composition, Al(iPr)3 : 2.7 H3PO4 : 1.5 AEDAP : 100H2O, was stirred at room temperature, transferred into a 23-mlPTFE-lined stainless-steel autoclave (Parr, USA) and heated at150 °C for 3 days. The initial pH was about 3.5 and the final pHdid not show appreciable change. The resulting product containedlarge quantity of rod-like single crystals, was vacuum filtered anddried under ambient conditions. An EDAX analysis indicated aAl:P ratio of 1:2. The powder XRD pattern of the powdered crys-tals indicated that the products were new materials; the patternswere entirely consistent with the structures determined using thesingle-crystal X-ray diffraction. Powder X-ray data for[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3� are presented inTable 1.

Table 1 X-ray powder data for [NH3(CH2)2NH2(CH2)3NH3]3�

1�[Al(PO4)2]3�

h k l d(obs) I (rel) h k l d(obs) I (rel)

0 0 2 8.844(2) 9.77 1 2 3 3.459(2) 28.62 0 0 8.425(1) 59.6 3 2 1 3.407(2) 26.91 0 2 7.831(1) 43.9 2 2 3 3.259(3) 18.12 1 0 6.096(2) 10.1 3 2 2 3.232(1) 29.61 1 2 5.859(2) 17.2 4 1 3 3.195(3) 7.12 1 2 5.019(2) 52.1 0 2 4 3.125(2) 16.23 0 2 4.741(2) 31.4 1 2 4 3.072(3) 9.20 0 4 4.221(1) 19.6 4 2 0 3.048(1) 17.60 2 0 4.416(1) 10.2 4 2 1 3.004(2) 23.30 2 1 4.285(1) 11.5 0 0 6 2.948(1) 5.31 0 4 4.277(2) 10.5 1 3 1 2.862(2) 15.22 1 3 4.238(1) 100 2 3 1 2.746(2) 10.54 0 0 4.213(2) 21 6 1 0 2,676(3) 17.12 0 4 3.916(2) 10.1 6 1 1 2.646(2) 7.92 2 0 3.911(2) 15.3 2 2 5 2.624(2) 5.11 1 4 3.850(1) 21.2 2 3 3 2.514(2) 7.61 2 2 3.847(2) 42.9 4 2 4 2.510(1) 7.24 1 0 3.802(2) 13.2 3 3 4 2.246(1) 17.73 1 3 3.694(1) 7.2 5 0 6 2.219(2) 6.42 1 4 3.579(2) 11.1 2 3 5 2.185(4) 11.72 2 2 3.577(1) 13 5 3 3 2.075(2) 7.14 1 2 3.493(1) 64.4 8 1 0 2.049(2) 7.1

Least-squares fitted (LSQ) lattice parameters from all the observed reflections (CuKα):a � 16.845(1), b � 8.832(2), c � 17.688(2) A

Solid state nuclear magnetic resonance (NMR) experiments wereperformed on a Bruker DSX 400 operating at 9.4 T with resonancefrequencies of 104.3 MHz and 162 MHz for 27Al and 31P, respec-tively. Magic angle spinning (MAS) was performed at rotating fre-quencies of 20 kHz using a 2.5 mm rotor system. Chemical shifts

Z. Anorg. Allg. Chem. 2003, 629, 339�343340

are referenced relative to 1M aqueous Al(NO3)3 (27Al) and H3PO4

(85 wt.%) (31P).

Crystal structure determination

A suitable colorless single crystal was carefully selected un-der a polarizing microscope and crystal structure determi-nation by X-ray diffraction was performed on a BrukerSMART-APEXCCD diffractometer. A full-sphere of inten-sity data was collected at room temperature in 1800 frameswith ω scans (width of 0.30° and exposure time of 30 sper frame) in the 2θ range 4.6 to 70.0°. Pertinent experi-mental details for the structure determinations of[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�, are pre-sented in Table 2.

Table 2 Crystal data and structure refinement parameters for[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�

Empirical formula C5H18Al1N3O8P2

Formula weight 337.14Crystal system OrthorhombicSpace group Pbca (no. 61)Crystal size (mm) 0.08 x 0.08 x 0.20a/A 16.850(2)b/A 8.832(1)c/A 17.688(4)Volume/A3 2632.4(2)Z 8ρcalc/gcm�3 1.701µ/mm�1 0.437θ range 2.30�35.12Total data collected 39381Unique data 5663Refinement method Full-matrix least-squares on �F�2Rmerg 0.0274R indexes [I >2σ(I)] R1 � 0.0389,a) wR2 � 0.1089b)

R (all data) R1 � 0.0447, wR2 � 0.1133Goodness of fit (Sobs.) 1.05No. of variables 172Largest difference map 0.858 and �0.324peak and hole / eA�3

a) R1 � Σ �F0 �� �Fc� / Σ �F0 � ; b) wR2 � {Σ [w(F02�Fc

2)2] / Σ [w(F02)2]}1/2.

w � 1/[σ2(F0)2 � (aP)2 � bP], P � [max.(F02, 0) � 2(Fc)2]/3, where a �

0.0644 and b � 1.2287.

An absorption correction was applied using SADABSprogram [22]. The structure was solved by direct methodsusing SHELXTL-PLUS [23], which readily revealed all theheavy atom positions (Al, P and O) to enable the remainderof the non-hydrogen atoms to be located from differenceFourier maps and the refinements to proceed to R < 10 %.All the hydrogen positions were initially located in the dif-ference map and for the final refinement the hydrogenatoms were placed in geometrically ideal positions and re-fined in the riding model. The last cycles of refinement in-cluded atomic positions for all the atoms, anisotropic ther-mal parameters for all the non-hydrogen atoms and iso-tropic thermal parameters for all the hydrogen atoms. Full-matrix-least-squares structure refinements against �F�2 werecarried out using the SHELXTL-PLUS [23] package of

A One-Dimensional Aluminum Phosphate

Table 3 Atomic coordinates (·104) and equivalent isotropic dis-placement parameters (A·103) for the non-hydrogen atoms in[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�

Atom x y z U(eq)a)

Al(1) 2536(1) 4159(1) 1331(1) 14(1)P(1) 1635(1) 6650(1) 2329(1) 15(1)P(2) 1399(1) 1701(1) 610(1) 14(1)O(1) 742(1) 6596(1) 2349(1) 31(1)O(2) 1973(1) 6508(1) 3118(1) 33(1)O(3) 1915(1) 5343(1) 1824(1) 37(1)O(4) 1920(1) 8138(1) 1971(1) 44(1)O(5) 1137(1) 1677(1) �209(1) 27(1)O(6) 1996(1) 3018(1) 727(1) 30(1)O(7) 1859(1) 222(1) 751(1) 36(1)O(8) 716(1) 1841(2) 1151(1) 39(1)N(1) 845(1) 8622(1) �701(1) 24(1)C(1) 992(1) 7452(2) �115(1) 30(1)C(2) 937(1) 5848(2) �429(1) 28(1)C(3) 1668(1) 5419(1) �886(1) 24(1)N(2) 1632(1) 3845(1) �1189(1) 20(1)C(4) 1030(1) 3602(1) �1790(1) 24(1)C(5) 1035(1) 1937(2) �1981(1) 30(1)N(3) 474(1) 1565(1) �2592(1) 21(1)

a) U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

Table 4 Selected bond distances/A and angles/° in[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�

Atom Distance Atom Distance

P(1)�O(1) 1.5059(10) [1.304] P(2)�O(8) 1.5026(11) [1.315]P(1)�O(2) 1.5123(11) [1.281] Σ(P�O) [4.937]P(1)�O(3) 1.5335(10) [1.210] Al(1)�O(3) 1.7120(10) [0.780]P(1)�O(4) 1.5335(11) [1.203] Al(1)�O(4)#1 1.7183(11) [0.767]Σ(P�O) [4.998] Al(1)�O(7)#2 1.7202(10) [0.763]P(2)�O(5) 1.5143(9) [1.274] Al(1)�O(6) 1.7332(10) [0.767]P(2)�O(6) 1.5512(10) [1.153] Σ(Al�O) [3.07]P(2)�O(7) 1.5385(10) [1.194]

Angle Amplitude, Angle Amplitude,deg deg

O(1)�P(1)�O(2) 110.63(7) O(5)�P(2)�O(8) 112.75(7)O(1)�P(1)�O(3) 107.30(7) O(6)�P(2)�O(8) 110.51(6)O(2)�P(1)�O(3) 111.02(7) O(7)�P(2)�O(8) 110.65(8)O(1)�P(1)�O(4) 110.44(7) O(3)�Al(1)�O(4)#1 108.15(7)O(2)�P(1)�O(4) 109.44(8) O(3)�Al(1)�O(7)#2 109.82(6)O(3)�P(1)�O(4) 107.95(7) O(4)#1�Al(1)�O(7)#2 111.32(7)O(5)�P(2)�O(6) 109.05(6) O(3)�Al(1)�O(6) 110.37(6)O(5)�P(2)�O(7) 106.83(6) O(4)#1�Al(1)�O(6) 112.07(6)O(6)�P(2)�O(7) 106.80(7) O(7)#2�Al(1)�O(6) 105.11(6)

Values in brackets are the bond valences. Their sum SVB appears in boldtype at the end of the list of the distances around every cations. Symmetrytransformations used to generate equivalent atoms:#1 �x�1/2, y�1/2, z; #2 �x�1/2, y�1/2, z

programs. The final atomic coordinates, bond distances andangles are given in Tables 3 and 4.

Results and Discussion

The asymmetric unit contains 19 non-hydrogen atoms asshown in Figure 1, of which 11 belong to the aluminumphosphate chain and 8 belong to the organic amine mo-lecule. In the asymmetric unit, there are two independentP atoms and one Al atom. The Al atom is tetrahedrallycoordinated by four oxygen atom neighbours with averageAl�O distance of 1.721 A, with an average O�Al�O bond

Z. Anorg. Allg. Chem. 2003, 629, 339�343 341

Fig. 1 Asymmetric unit of [NH3(CH2)2NH2(CH2)3NH3]3�

1�[Al(PO4)2]3�. The thermal ellipsoids are given at 50 % probability.

Fig. 2 Structure of [NH3(CH2)2NH2(CH2)3NH3]3� 1�[Al(PO4)2]3�

in the bc plane showing two different chains. The amine moleculesoccupy inter-chain spaces.

angles of 109.5°. These values are in good agreement withmany of the earlier reported structures of the aluminumphosphates [1�15]. Each P-atom is also tetrahedrally coor-dinated to four O atoms with average P�O distance of1.523 A. Each P has two O-atoms bonded to aluminumatoms and possesses two terminal linkages. The terminalP�O distances are in the range 1.503�1.514, indicatingthat they have multiple-bond character and are comparablewith those in, for example, H3PO4·0.5H2O (1.495 A) [24].The multiple-bond nature of the P�O bonds is also re-flected in the O�P�O angle (110.6°, 112.7°). The net nega-tive charge of �3 is then balanced by the presence of onecompletely protonated AEDAP molecule. This assignmentis also consistent with bond-valence sum calculations [25].Selected bond distances and angles are presented in Table 4.

The chain structure is constructed from strictly alternat-ing AlO4 and PO4 tetrahedral units connected through their

S. Natarajan, W. Klein, J. Nuss, L. v. Wüllen, M. Jansen

Fig. 3 Polyhedral connectivity of [NH3(CH2)2NH2(CH2)3NH3]3�

1�[Al(PO4)2]3� in the ac plane showing the view down the chainaxis. Note that the chains are packed in a hexagonal arrangement.

Table 5 Important hydrogen bond interactions in[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�

N�H···O D-H (A) H···A (A) D···A (A) D�H···A (°)

N(1)�H(1)···O(5) 0.89 2.00 2.878(2) 168N(1)�H(2)···O(8) 0.89 1.89 2.777(2) 172N(1)�H(3)···O(2) 0.89 1.94 2.827(3) 176N(2)�H(10)···O(2) 0.90 1.79 2.671(2) 167N(2)�H(11)···O(5) 0.90 1.84 2.714(4) 165N(3)�H(16)···O(1) 0.89 1.96 2.830(2) 164N(3)�H(17)···O(8) 0.89 1.78 2.661(3) 172N(3)�H(18)···O(1) 0.89 1.87 2.650(4) 146

vertices. The connectivity between the tetrahedra gives riseto Al2P2O4 4-membered rings, which are linked throughtheir corners for the one-dimensional chain, in the bc plane,as shown in Figure 2. Looking down the chain axis, in theac plane, we find that there is no direct interaction betweenthe chains. The arrangement of individual chains resemblea hexagonal packing of rods (Fig. 3). The organic aminemolecule occupies space in between the chains and interactswith the oxygen atoms through N�H···O hydrogen bonds.Thus, strong hydrogen bonds are present in[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�, as evi-denced by the short N�O distances (2.65�2.88 A) andnearly linear N�H···O angles (av. 166°). The important hy-drogen bond interactions are listed in Table 5.

The 27Al MAS and 31P MAS NMR spectra of[NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�, are shownin Figure 4. The 27Al NMR spectrum reveals a single signalat 39.1 ppm. A fit using standard Bruker WINFIT softwareproduces an isotropic chemical shift value of δiso �

Z. Anorg. Allg. Chem. 2003, 629, 339�343342

Fig. 4 27Al MAS-NMR spectra (a) and 31P MAS-NMR spectra(b) for [NH3(CH2)2NH2(CH2)3NH3]3� 1

�[Al(PO4)2]3�.

41.4 ppm and a quadrupolar coupling constant of CQ �1.8 MHz for the signal at 39.1 ppm, values typical of Altetrahedrally coordinated by oxygen. The 31P MAS spec-trum indicates the presence of two distinct phosphoroussites�in accordance with the crystal structurerefinement�with chemical shifts of δiso � 10.3 ppm andδiso � 15.8 ppm.

This aluminum phosphate chain structure is differentfrom that of [Et3NH]�[Al(HPO4)2]� [13], in which the ter-minal P�O linkages (P�O and P�OH) form intra-chainhydrogen bonds. It follows that the number of the hydrogenatoms on each of the chain unit depends on the bulkinessof the template: the larger the template, the more hydrogenatoms on the inorganic chain. In the present case, the linearAEDAP molecule is relatively small compared to the bulkytriethylamine molecule, rendering the Al(PO4)2 chain with-out any terminal hydrogen atoms.

Acknowledgments. SN thanks Council of Scientific and IndustrialResearch (CSIR), Government of India, for the award of a researchgrant. SN also thanks the Royal Society of Chemistry for the travelsupport under the Travel Grant for International Authors programand the Max-Planck-Gesellschaft for financial support.

A One-Dimensional Aluminum Phosphate

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