a layered aluminum phosphate,

The layered structure of I has Al both in trigonal bi-pyramidal and octahedral coordinations and the polyhedra are so connected as to give rise to 3-membered Al P rings and infinite Al–O

A layered aluminum phosphate, [C N H ][Al (OH) H O(PO ) ]H O,2 2 10 2 2 2 4 2 2

by the amine phosphate route

a

Chemistry and Physics of Materials Unit , Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India

b

Solid State and Structural Chemistry Unit , Indian Institute of Science, Bangalore 560 012, India

Received 13 December 1999; accepted 27 December 1999

Abstract

A layered aluminum phosphate, I, [C N H ][Al (OH) H O(PO ) ]H O, with Al:P ratio of 1:1 has been prepared using a novel2 2 10 2 2 2 4 2 2

31

synthetic route wherein the amine phosphate, [C N H ][HPO ], was reacted with Al2 2 10 4 ions under hydrothermal conditions I crystallizes

˚

in the triclinic space group P(21) (No 2); a56.614(1), b59.918(1), c510.381(1) A, a 5115.3(1), b590.2(1), g590.8(1)8; V5615.6(2)

˚

A ; Z52, Dcalc52.029 g cm ; m (MoKa)50.565 mm The final R50.07 and wR 50.17 and S51.15 have been obtained for 1982

parameters The layered structure of I has Al both in trigonal bi-pyramidal and octahedral coordinations and the polyhedra are so

connected as to give rise to 3-membered Al P rings and infinite Al–O(H)–Al linkages The structure is closely related to the mineral2 tancoite  2000 Elsevier Science Ltd All rights reserved.

Keywords: Inorganic compounds; Layered compounds; Chemical synthesis; X-ray diffraction

reaction with metal ions [11] We were interested in Aluminophosphates (AlPO’s) occupy a prominent posi- whether AlPO’s can be prepared using the reaction of

31 tion amongst the open-framework materials Since the an amine phosphate with Al ions We have been able early seminal work of Flanigen et al on the synthesis of to obtain the aluminophosphate, I, [C N H ]2 2 10 AlPO’s with microporosity [1], there has been intense [Al (OH) H O(PO ) ]H O, possessing a layered archi-2 2 2 4 2 2 research activity on these and related materials resulting in tecture, by the reaction of ethylenediamine–phosphate with

31 the discovery of a variety of metal phosphates with novel Al ions I is made up of AlO trigonal bi-pyramids and5

topologies [2] Aluminophosphates generally consist of AlO6 octahedra which are vertex-linked with PO4 tetra-vertex linkages between the AlO4 and PO4 tetrahedra, hedra The connectivity between these units results in forming 1-, 2- and 3-dimensionally extended structures In 3-membered rings of two Al and one P atom, and infinite some of the AlPO’s, the aluminum atoms have trigonal Al–O(H)–Al linkages

bipyramidal and octahedral coordination [3–9], high

2 coordination for aluminum often being stabilized by F or

2

OH species present in Al–OH / F–Al bridges [3–6] 2 Experimental

Infinite 1-dimensional Al–O–Al chains of the type found

in the mineral tancoite [4] also occur in certain cases The Compound I, was synthesized under hydrothermal

con-aluminophosphates are generally prepared hydrothermally ditions by the reaction of aluminum hydroxide with

in the presence of structure-directing amines It has been ethylenediamine–phosphate, [C N H ][HPO ],2 2 10 4 (EN– found recently that amine phosphates, which often occur as PHOS) EN–PHOS was synthesized by reacting ethyl-by-products in hydrothermal synthesis [10,11], may act as enediamine (en) with phosphoric acid in butan-2-ol and intermediates in the formation of open-framework metal characterized using single-crystal X-ray diffraction The

lattice parameters and the structure obtained agreed with that reported in the literature [12] In a typical synthesis,

*Corresponding author.

E-mail address: cnrrao@jncasr.ac.in (C.N.R Rao) 0.1960 g of hydrated aluminum oxide (55 mass% Al O ,2 3 1466-6049 / 00 / $ – see front matter  2000 Elsevier Science Ltd All rights reserved.

P I I : S 1 4 6 6 - 6 0 4 9 ( 0 0 ) 0 0 0 0 3 - 9

45 mass% H O) was dispersed in 4.5 ml of water To this,2 1 An EDAX analysis indicated an Al / P ratio of 1.0, in 0.1985 g of EN–PHOS was added and stirred vigorously agreement with single-crystal structure

The final mixture, with a composition 2Al(OH) –1EN–3 A suitable colorless single crystal (0.0430.1230.12 PHOS–200H O, was transferred onto a 7-ml PTFE-lined2 mm) was carefully selected under a polarizing microscope acid digestion bomb and heated at 1108C for 65 h The pH and glued to the tip of a glass fiber Crystal structure during the reaction changed from 6.0 to 10.5, indicating determination by X-ray diffraction was performed on a that the part of the phosphoric acid from the amine Siemens Smart-CCD diffractometer equipped with a nor-phosphate (EN–PHOS) has been consumed during the mal focus, 2.4-kW sealed tube X-ray source (MoKa

˚

reaction The resulting product, consisting of large color- radiation, l50.71073 A) operating at 50 kV and 40 mA A less single-crystalline platelets, was filtered off and dried at hemisphere of intensity data was collected at room

tem-ambient temperature Initial characterization of I was perature in 1321 frames with v scans (width of 0.308 and carried out using powder X-ray diffraction (XRD) and an exposure time of 20 s per frame) The final unit cell thermogravimetric analysis (TGA) The powder X-ray constants were determined using a least-squares fit of 1611 diffraction (XRD) pattern of the powdered single crystals reflections in the u range 2.17–23.298 A total of 2611 indicated that the product was a new material; the pattern reflections were collected and were merged to give 1750 was entirely consistent with the structure determined using unique reflections (R 50.03), of which 1225 were consid-int

single-crystal X-ray diffraction A least-squares fit of the ered to be observed for I.2s(I ) Pertinent experimental powder XRD (CuKa) lines, using the hkl indices garnered details for the structure determinations are presented in from single-crystal X-ray data, gave the following cell: Table 2

˚

b590.14(1), g590.71(1)8, in good agreement with that using SHELXS-86 [13] and difference Fourier syntheses

determined using single-crystal XRD Powder data for I, An empirical absorption correction based on symmetry-[C N H ][Al (OH) H O(PO ) ]H O, is listed in Table2 2 10 2 2 2 4 2 2 equivalent reflections was applied using SADABS program

[14] Other effects, such as absorption by the glass fiber, were simultaneously corrected The systematic absences in Table 1

the absorption corrected data indicated a triclinic space Powder X-ray diffraction pattern of I, [C N H ] 2 2 10

group P(-1) Though the cell looked pseudo-monoclinic we

[Al (OH) H O(PO ) ]H O 2 2 2 4 2 2

have not been able to get a satisfactory solution in any

monoclinic space groups and the successful completion of

0 0 1 9.434 9.433 0.001 9.374 100 the refinement validates the choice of the space group The

1 0 1 16.482 16.488 20.006 5.378 24.35

structure solution using SHELXS-86 gave the positions for

1 1 21 17.018 17.009 0.008 5.210 16.61

most of the heavy atoms (Al, P and O) and enabled us to

0 2 21 17.915 17.913 0.002 4.951 4.88

locate the other non-hydrogen positions from the

differ-0 0 2 18.962 18.931 0.030 4.680 2.22

0 2 0 19.817 19.805 0.011 4.480 3.14 ence Fourier maps All the hydrogen positions were also

0 2 22 20.772 20.747 0.025 4.276 19.75 located subsequently from the difference Fourier maps For

1 21 2 21.863 21.877 20.014 4.065 8.47

the final refinement the hydrogen atoms were place

1 0 2 23.328 23.367 20.040 3.813 1.87

geometrically and then held in the riding mode

Full-1 2 22 24.870 24.858 0.012 3.580 0.31

2 matrix least-squares structure refinement on uF u (atomic

0 2 1 25.447 25.427 0.020 3.500 15.44

0 2 23 26.918 26.908 0.010 3.312 24.76 coordinates and anisotropic thermal parameters of

non-1 21 22 28.221 28.247 20.026 3.162 5.59 hydrogen atoms, isotropic thermal parameters for all the

2 1 0 28.979 28.960 0.019 3.081 9.95

hydrogen atoms) was carried out using the

SHELXTL-1 2 23 30.207 30.201 0.006 2.959 14.40

PLUS package of programs [15] The final refinement

2 21 21 31.528 31.528 20.001 2.838 12.20

parameters obtained are: R 50.07, wR 50.17 and S51.15.

2 22 1 32.437 32.416 0.022 2.760 2.13 The final difference Fourier had a minimum and maximum

23

1 3 0 33.073 33.085 20.013 2.708 3.35 of –0.744 and 1.033 e A˚ , respectively Details for the

1 23 3 34.185 34.145 0.040 2.623 4.78

final refinements are given in Table 2 The final atomic

0 1 24 35.216 35.191 0.026 2.548 1.03

coordinates, bond distances and bond angles are presented

1 22 22 35.632 35.615 0.018 2.520 0.84

in Tables 3–5

1 21 23 36.703 36.723 20.020 2.448 2.18

1 1 3 37.031 37.027 0.004 2.428 3.61

1 24 2 38.658 38.689 20.031 2.329 1.79

2 0 23 39.552 39.537 0.015 2.278 4.14

3 Results and discussion

1 0 4 40.961 40.971 20.010 2.203 2.80

0 2 3 41.734 41.707 0.026 2.164 4.12

The asymmetric unit, presented in Fig 1, contains 20

3 2 0 46.241 46.221 0.020 1.963 3.20

1 21 5 47.180 47.211 20.031 1.926 1.27 non-hydrogen independent atoms out of which 15 belong

1 5 23 48.607 48.637 20.030 1.873 2.04 to the ‘framework’ (two Al, two P and 11 O atoms) and

3 0 23 50.484 50.515 20.031 1.808 1.30

five to the guest (two N, two C atoms and one water

Table 2

Crystal data and structure refinement parameters for I, [C N H ][Al (OH) H O(PO ) ]H O2 2 10 2 2 2 4 2 2

˚

˚

˚

3

˚

23

˚

21

2

a

R indexes [I.2s(I )] R50.07; R 50.017w

23

˚

w 5 1 / [s (F ) 1 (0.1220P) 1 0.8633P], P 5 (F 1 2(F ) ] / 3.O O C

molecule) The two aluminum atoms in I are five- and 1.787–1.873 A (av 1.827 A) Both the Al(1) and Al(2) six-coordinated by their O atom neighbors Al(1), which is form connections with two distinct P atoms neighbors with

at the center of an octahedron has Al–O distances in the an average Al–O–P bond angle of 140.88, and have two

range 1.834–2.203 A (av 1.917 A) and Al(2) with a Al–O– Al linkages In addition, Al(1) possesses a terminal trigonal bipyramidal coordination has Al–O distances of Al–O bond The O–Al–O bond angles are in the range

83.5–178.08 (av O–Al(1)–O5106.5 and O–Al(2)–O5

4

Atomic coordinates [310 ] and equivalent isotropic displacement param-3 make three P–O–Al bonds and possess one terminal P–O

˚

eters [A310 ] for I, [C N H ][Al (OH) H O(PO ) ]H O2 2 10 2 2 2 4 2 2

a

Selected bond distances in I, [C N H ][Al (OH) H O(PO ) ]H O2 2 10 2 2 2 4 2 2

Al(2) 21706(3) 2726(2) 4576(2) 21(1) Moiety Distance (A) Moiety Distance (A)

Al(1)–O(1) 1.835(5) Al(2)–O(4) 1.800(5)

Al(1)–O(2) 1.834(5) Al(2)–O(5) 1.811(5)

Al(1)–O(3) 1.843(5) Al(2)–O(7) 1.787(5)

Al(1)–O(4) 1.885(5) Al(2)–O(8) 1.865(5)

Al(1)–O(5) 1.901(5) Al(2)–O(9) 1.873(5)

Al(1)–O(6) 2.203(6) P(2)–O(1) 1.543(5)

P(1)–O(3) 1.522(5) P(2)–O(2) 1.532(5)

P(1)–O(7) 1.541(5) P(2)–O(8) 1.539(5)

P(1)–O(9) 1.543(5) P(2)–O(11) 1.519(5)

P(1)–O(10) 1.517(5)

O(10) 693(7) 5873(5) 8567(5) 29(1) Organic moiety

O(11) 5511(7) 21248(5) 1318(5) 30(1) N(1)–C(1) 1.474(9) N(2)–C(2) 1.483(9)

O(100) 874(9) 8006(7) 2244(6) 53(2) C(1)–C(1) 1.534(14) C(2)–C(2) 1.494(14)

–x 11, 2y, 2z 11.

x 11, y, z.

2x, 2y11, 2z11.

x 21, y, z.

Ueq is defined as one third of the trace of the orthogonalized U ij 2x, 2y, 2z.

f

Table 5

a

Selected bond angles in I, [C N H ][Al (OH) H O(PO ) ]H O2 2 10 2 2 2 4 2 2

a

O(2) –Al(1)–O(1) 95.2(2) O(5)–Al(2)–O(9) 89.0(2)

O(2) –Al(1)–O(3) 90.6(2) O(8) –Al(2)–O(9) 177.6(2)

a

O(2) –Al(1)–O(4) 95.0(2) O(10)–P(1)–O(3) 109.7(3)

O(1)–Al(1)–O(3) 174.1(2) O(10)–P(1)–O(7) 108.6(3)

O(1)–Al(1)–O(4) 88.6(2) O(3)–P(1)–O(7) 107.4(3)

O(3)–Al(1)–O(4) 89.5(2) O(10)–P(1)–O(9) 111.5(3)

O(2) –Al(1)–O(5) 97.9(2) O(3)–P(1)–O(9) 110.4(3)

b

O(1)–Al(1)–O(5) 92.4(2) O(7)–P(1)–O(9) 109.2(3)

b

O(3)–Al(1)–O(5) 88.2(2) O(11)–P(2)–O(2) 109.5(3)

b

O(4)–Al(1)–O(5) 167.0(2) O(11)–P(2)–O(8) 108.8(3)

a

O(2) –Al(1)–O(6) 178.0(2) O(2)–P(2)–O(8) 108.5(3)

O(1)–Al(1)–O(6) 86.1(2) O(11)–P(2)–O(1) 110.5(3)

O(2)–Al(1)–O(6) 88.1(2) O(2)–P(2)–O(1) 111.0(3)

O(4)–Al(1)–O(6) 83.5(2) O(8)–P(2)–O(1) 108.5(2)

b

O(5) –Al(1)–O(6) 83.6(2) P(2)–O(1)–Al(1) 133.5(3)

O(7) –Al(2)–O(4) 122.2(3) P(2)–O(2)–Al(1) 145.7(3)

c

O(7) –Al(2)–O(5) 115.4(2) P(1)–O(3)–Al(1) 140.3(3)

O(4)–Al(2)–O(5) 122.3(3) P(2)–O(4)–Al(1) 143.5(3)

O(7) –Al(2)–O(8) 87.4(2) Al(2)–O(5)–Al(1) 137.5(3)

O(4)–Al(2)–O(8) 89.6(2) P(1)–O(7)–Al(2) 144.9(3)

O(5)–Al(2)–O(8) 89.7(2) P(2)–O(8)–Al(2) 134.8(3)

c

O(7) –Al(2)–O(9) 91.3(2) P(1)–O(9)–Al(2) 137.4(3)

O(4)–Al(2)–O(9) 92.7(2)

Organic moiety

N(2)–C(2)–C(2) 110.4(7) N(1)–C(1)–C(1) 109.7(7)

a

2x 11, 2y, 2z11.

b

x 11, y, z.

c

2x, 2y11, 2z11.

d

x 21, y, z.

e

f

˚

bond The P–O distances are in the range 1.517–1.543 A arranged such that the Al–O–P bonds follow a sinusoidal

˚

(av P(1)–O51.531 and P(2)–O51.533 A) The O–P–O curve with the equitorial position being occupied by the bond angles are in the range 107.4–111.58 (av.5109.58) Al–O(H)–Al 1-dimensional chain, as shown in Fig 2(a) Assuming the normal valences of Al, P and O (13, 15 Two such units are joined together via a 4-membered ring and –2), the framework stoichiometry of Al P O2 2 11 has a in Fig 2(b) The connectivity between these units gives charge of 25 Assuming the extra-framework ethyl- rise to a layer arrangement along the ab plane with a

enediamine molecule is doubly protonated, we still require 6-membered aperture within the layer, as shown in Fig three ‘framework’ protons for charge-balancing purposes 2(c) Thus in I, within each layer, 3-, 4- and 6- membered

From the Fourier maps, a single framework proton posi- apertures are present [Fig 2(a)–(c)] The protons associ-tions for O(4) and O(5) and two for O(6) can be located ated with the –OH group and water molecules protrude Since O(4) and O(5) link with two aluminum atoms, the into the 6-membered apertures, as shown in Fig 3 The linkages must be Al–O(H)–Al The O(6) is terminal being layered architecture of I along the [010] direction is shown

part of a water molecule, and does not contribute to the in Fig 4 As can be seen, the layers interact strongly with total charge of the framework No framework proton the structure-directing amine, a diprotonated en, which positions, however, are found for the terminal P–O bonds forms a continuous chain in between the inorganic sheets The above assignments are in agreement with the bond- Structural stabilization by the hydrogen bond interac-valence sum calculations [16] The various geometrical tions between the amine and the framework, in lower

parameters observed in I agree with those observed earlier dimensional solids, is well known In I, there are strong

The basic building unit in I is a 3-membered ring of the amine and the framework oxygens Additionally, the formed by the bonding between the Al(1)O (OH)(H O),4 2 water molecule also participates in hydrogen bonding The Al(2)O (OH) and PO units The 3-membered rings are4 4 observation of a majority of the N–H O angles around

Fig 2 (a) Structure of I showing the 3-membered rings and the sinusoidal nature of the Al–O–P bonding Note that the Al–O–Al linkages are at the

equitorial position (dotted lines) (b) Structure showing the linkages between the 3-membered ring chains Note that the linkages are via a 4-membered ring

forming a 6-membered aperture (c) Polyhedral view of the layer in I.

Fig 3 Structure of I along the ab plane Note that the hydrogens protrude into the 6-membered aperture.

1608 indicates that the hydrogen bond interactions are tancoite [4] In both these structures, Al–O(H)–Al

1-nearly perfect The hydrogen bond interactions in I are dimensional chains are connected by two phosphate

27

A Al MAS-NMR study of I, indicates two signals, one such chains The structure of I is even more closely related

at 6 ppm and the other at 26.196 ppm The former is that to the layered AlPO structure of Simon et al [5], where

of the octahedral Al and the latter is that of penta- zig-zag chains of Al–O(H) / F–Al chains are linked by coordinated Al (Fig 5) These assignments are consistent phosphate groups forming layers with 3- and 6-membered with that observed earlier [17] We have not, however, rings In all these structures, Al is exclusively present in observed any signals corresponding to tetrahedral Al, in the octahedral coordination The Al–O–Al chains and the confirmation of the single-crystal structure relative positions of the phosphate tetrahedra grafted on it

The structure of I is unique in the sense that it is the first present a variety of AlPO compositions 0.5,Al / P,2.0 layered AlPO formed by 5- and 6- coordinated Al, the The structures of Attfield et al [3] and Simon et al [5] layers themselves being composed of 3-, 4- and 6-mem- represent two extremes in such a family I, with the Al / P

bered apertures It is to be noted that layered aluminophos- ratio of 1.0 is at the middle of the range The Al:P ratio of phates generally contain 4-, 6-, 8- and 12-membered 1.0 present in I is rather unusual in layered AlPO’s [18], apertures [18,19] It is instructive to compare I with the although it is commonly observed in 3-dimensional

struc-structure of AlPO’s reported in the literature Thus, I is tures [2,6]

comparable to the 1-dimensional chain AlPO structure of Thermogravimetric analysis showed two mass losses Attfield et al [3] and the naturally occurring mineral followed by a broad tail The mass loss at 2008C of 16.1%

Fig 4 Structure of I along the ac plane showing the position of the amine and the layers Note that the amine molecules form a chain Hydrogens of the

amine molecules are not shown for clarity Dotted lines represent the various possible hydrogen bond interactions.

corresponded to the loss of the inter-layer water molecules sample heated in oxygen at 6008C showed it to be

as well as part of the amine and the next mass loss at amorphous

3508C of 10.6% corresponded to the further loss of the The presence of 5- and 6-coordinated Al in I, may be

amine and the bound water molecule The total mass loss the result of the novel method of synthesis employed in the during the first two steps (26.7%) agrees with the calcu- current study It is possible that the amine phosphate is not lated mass loss of 26.1% The broad mass loss of 10.9% in only the source for both the amine and phosphorus, but the region 475–5508C corresponds to the loss of the –OH also acts as a complex template species in situ The amine groups (calc 9.4%) The powder diffraction pattern of a phosphate can be considered an ion-pair, possibly

occur-ring in an associated form in solution Such a situation would favor the formation of novel architecture Further work is currently under way to evaluate the role of amine Table 6

phosphates in the synthesis of AlPO’s and other related Selected hydrogen bond interactions in I, [C N H ] 2 2 10

phases

[Al (OH) H O(PO ) ]H O 2 2 2 4 2 2

˚

Moiety Distance (A) Moiety Angle (8)

O(3)–H(1) 2.457(2) O(3)–H(1)–N(1) 142.2(1)

O(10)–H(1) 2.150(1) O(10)–H(1)–N(1) 147.1(2)

Acknowledgements

O(11)–H(2) 1.889(2) O(11)–H(2)–N(1) 169.9(2)

O(10)–H(3) 1.849(2) O(10)–H(3)–N(1) 172.3(3)

The authors thank Mr S Neeraj for his help in NMR O(10)–H(6) 1.972(3) O(10)–H(6)–N(2) 163.8(4)

O(8)–H(7) 2.056(2) O(8)–H(7)–N(2) 162.9(1) measurements A.C thanks the Council of Scientific and O(11)–H(8) 1.856(1) O(11)–H(8)–N(2) 159.5(2) Industrial Research (CSIR), Government of India, for the O(100)–H(9) 2.588(1) O(100)–H(9)–C(2) 131.1(1)

support of a research fellowship

Fig 5 Al MAS-NMR signals in (a) 7 kHz, and (b) 5.3 kHz, showing the position of octahedral and penta-coordinated Al atoms; *, represents the spinning side-bands.

[10] Chippindale AM, Cowley AR J Chem Soc, Dalton Trans

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Chem Soc 1982;104:1146. [12] Averbuch-Pouchot MT, Durif A. Acta Crystallogr, Sect C [2] Loiseau T, Ferey G, Cheetham AK Angew Chem Int Ed 1987;43:1894.

1999;38:3268. [13] Sheldrick GM SHELXS-86 A program for the solution of crystal [3] Attfield MP, Morris RE, Burshtein I, Campana CF, Cheetham AK J structures, Gottingen, Germany: University of Gottingen, 1986.¨ ¨ Solid State Chem 1995;118:412. [14] Sheldrick GM SADABS: Siemens area detector absorption correc-[4] Ramik RA, Sturman BD, Dunn PJ, Poverennykh AS Can Mineral tion program, Gottingen, Germany: University of Gottingen, 1994.¨ ¨ 1980;18:185. [15] Sheldrick GM SHELXTL-PLUS program for crystal structure [5] Simon N, Guillou N, Loiseau T, Taulelle F, Ferey G J Solid State solution and refinement, Gottingen, Germany: University of Gotting-¨ ¨

[6] Natarajan S, Gabriel J-CP, Cheetham AK Chem Commun [16] Brown ID, Aldermatt D Acta Crystallogr, Sect B 1984;41:244. 1996;:1416. [17] Quartararo J, Guelton M, Rigole M, Amoureux J-P, Ferenandez C, [7] Chippindale AM, Powell AV, Bull LM, Jones RH, Thomas JM, Grimblot J J Mater Chem 1999;9:2646, and references therein. Cheetham AK, Huo Q, Xu R J Solid State Chem 1992;96:199. [18] Zhou B, Yu J, Li J, Xu Y, Xu W, Qiu S, Xu R Chem Mater [8] Li L, Wu L, Chen J, Xu R Acta Crystallogr, Sect C 1991;47:246 1999;11:1094, and references therein.

[9] Neeraj S, Natarajan S, Rao CNR Chem Mater 1999;11:1390, and [19] Williams ID, Gao Q, Chen J, Ngai L-Y, Lin Z, Xu R Chem