a new three-dimensional open-framework iron(iii) phosphate,

Our continued Of the many open-framework metal phosphate structures effort on the synthesis of iron phosphates enabled us to that are known, those of the transition metals are interest-

A new three-dimensional open-framework iron(III) phosphate,

[C N H ][Fe (HPO ) ]2 2 10 2 4 4

a

Advanced Materials Research Laboratory, 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

Accepted 3 January 2000

Abstract

A new open-framework iron(III) phosphate, I, [C N H ][Fe (HPO ) ] has been hydrothermally synthesized in the presence of2 2 10 2 4 4

ethylenediamine (en) The structure is built up from the vertex linkages between the FeO octahedra and the PO tetrahedra, strictly6 4

alternating, forming the three-dimensional architecture The linkages between the FeO6 and PO4 polyhedra gives rise to ladder-like

edge-shared chains, which are connected variously forming two types of channels The di-protonated en molecules occupy these channels.

3

Crystal data for I, [C N H ][Fe P O ]: a59.341(1), b58.892(1), c59.480(1) A, b 5117.6(1)8, V5698.1(1) A , space group P2 /n2 2 10 2 4 16

(No 13), Z52, M5557.7, Dcalc52.65 g cm , MoKa ( l50.71073 A), R 50.03, wR 50.08 and S51.10 Magnetic susceptibility studies1 2 indicate a predominantly antiferromagnetic interaction with T 530 K.N  2000 Elsevier Science Ltd All rights reserved.

Keywords: A inorganic compounds; magnetic materials; B chemical synthesis; C X-ray diffraction

gradual spin crossover behavior from the low- to the The area of open-framework materials continues to be of high-spin state as a function of temperature [14] This iron interest not only because of the variety of interesting phosphate also possessed large voids bound by 24-T atoms structures but also due to the potential applications in the (T5Fe, P) in addition to having infinite one-dimensional area of catalysis, sorption and separation processes [1–3] chains made of Fe–O / F–Fe linkage [14] Our continued

Of the many open-framework metal phosphate structures effort on the synthesis of iron phosphates enabled us to that are known, those of the transition metals are interest- discover a new three-dimensional iron phosphate, I,

ing as they provide a variety of coordination environments [C N H ][Fe (HPO ) ], possessing a narrow arrow-head2 2 10 2 4 4

as well as showing interesting magnetic behavior In the type of one-dimensional channel bound by 8-T atoms The last couple of years, a large number of open-framework structure-directing agent, ethylenediamine (en), sits in the

iron phosphate materials have been synthesized and char- middle of these channels In this paper, the synthesis and acterized with interesting physical properties [4–13] The structure of I is presented.

iron phosphate structures, in general, comprise a vertex

linkage between the Fe–O polyhedra and PO tetrahedra4

forming chain, layer and three-dimensional architectures

2 Experimental

Most of these materials have been synthesized

hydrother-2 mally in the presence of F ions, which also get

incorpo-The title compound was synthesized from a gel con-rated as part of the framework in many cases Our efforts

taining ethylenediamine (en) as the structure-directing

on the hydrothermal synthesis of the iron phosphates

agent In a typical synthesis, 0.464 g of FeCl –6H O and3 2 resulted in a variety of solids, some of which were already

0.169 g of MnCl –4H O was dispersed and dissolved in 32 2

ml of water To this, 0.7 ml of phosphoric acid (aq 85

wt.%) and 0.34 ml of en was added and stirred vigorously.

*Corresponding author Fax: 191-80-846-2766.

E-mail address: raj@jncasr.ac.in (S Natarajan) To this solution, 0.2 ml of HF was added and the mixture 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 7 - 6

was stirred until homogeneous The final mixture, a thick solved by direct-methods using SHELXS-86 [15], which white gel, with a composition, 2FeCl –6H O–MnCl –3 2 2 readily established the heavy atom (Fe, P) sites and most

4H O–12H PO –6en –3HF–200H O,2 3 4 2 was transferred of the light atom (O, N and C) positions All the hydrogen onto a 7 ml PTFE-lined acid digestion bomb and heated at positions were located from difference Fourier maps and 1808C for 64 h The fill factor was |50% The resultant for the final refinement the hydrogens were placed product contained only colorless rods, suitable for single- geometrically and held in the riding mode The relevant crystal X-ray diffraction, and was filtered and washed details of the structure determination are presented in

2 thoroughly with deionized distilled water The pH of the Table 2 Full-matrix least-squares refinement on uF u

mixture did not show any appreciable change during the (atomic coordinates, anisotropic thermal parameters for the hydrothermal reaction and remained at 2.0 The initial non-hydrogen atoms of the framework, water and amine characterization was carried out using powder X-ray molecule) were carried out using the program SHELXTL-diffraction (XRD) and thermogravimetric analysis (TGA) PLUS [16] The final atomic coordinates along with the The powder XRD pattern indicated that the product is a thermal parameters for I is presented in Table 3 and the

new material; the pattern is entirely consistent with the bond distances and angles in Tables 4 and 5

structure determined using the single-crystal X-ray

diffrac-tion A least-squares fit of the powder XRD (CuKa) lines,

using the hkl indices generated from single-crystal X-ray 3 Results and discussion

data, gave the following cell: a59.333(1), b58.845(1),

˚

c59.447(1) A, b 5117.6(2)8, which is in excellent agree- The iron phosphate I, [C N H ][Fe (HPO ) ], was2 2 10 2 4 4

ment with that determined using the single-crystal XRD synthesized by hydrothermal methods in the presence of

Powder data for I, [C N H ][Fe (HPO ) ], are listed in2 2 10 2 4 4 structure-directing agent, en, and the structure determined

Table 1 EDAX analysis indicated that the final product did using the single-crystal X-ray diffraction method The not contain any Mn and the Fe–P ratio was 1:2, consistent synthesis, predominantly kinetically controlled, does not with the stoichiometry determined using the single-crystal show any correlation between the starting composition and

A suitable single crystal of I was carefully selected product indicates that there are subtle forces that control under a polarizing microscope Data collection was per- the crystallization during the synthesis The role of Mn in formed on a Siemens SMART diffractometer with a CCD the synthesis is not yet clear and our efforts to form the detector in the u range 2.29–23.288 The structure was title compound in the absence of Mn did not come to

2 fruition The role of F ions in the formation open-framework solids is well documented in the literature [17],

and we believe, in the present case, F ions act as a

X-ray powder data for I, [C N H ][Fe (HPO ) ]2 2 10 2 4 4

mineralizer and facilitate the formation of I, as the final

product did not contain any fluorine F ions acting as a

0 1 1 14.561 0.015 6.089 20.006 32.5 mineralizer in the synthesis of aluminum phosphates has

1 1 21 14.913 0.025 5.950 20.001 60.5

been known in the literature [18,19]

2 0 0 21.531 0.012 4.129 20.002 34.4

[C N H ][Fe (HPO ) ] is a new three-dimensional2 2 10 2 4 4

open-framework network structure made from

1 2 22 27.615 0.011 3.231 20.001 100 linked FeO6 octahedra and PO4 tetrahedra incorporating

1 0 23 28.628 0.093 3.128 20.001 7.2 di-protonated en molecules within its pores The

ric unit of I, consisting of 14 non-hydrogen atoms, is

2 1 1 29.921 20.031 2.983 0.003 29.7

presented in Fig 1 There are two crystallographically

1 1 23 30.400 0.093 2.949 20.009 8.6

independent iron and phosphorus atoms The Fe atoms

3 1 21 30.843 0.029 2.902 20.003 22.9

0 3 1 32.413 20.032 2.782 0.003 3.8 occupy special positions and have occupancy of 0.5 The

0 1 3 33.556 20.030 2.668 0.003 1.0 two distinct Fe atoms each make three Fe–O–P bonds to P

neighbors The Fe–O–P bonds angles are in the narrow

3 2 22 35.914 0.048 2.504 20.004 4.2

region 137.8–152.48 (Table 5) indicating that both the

2 3 22 37.824 20.014 2.378 0.000 1.9

FeO octahedra and PO tetrahedra are regular The Fe–O

˚

2 1 24 39.397 20.020 2.286 20.002 13.4 bond distances are in the range 1.967–2.092 A [(Fe(1)–

2 3 23 42.534 0.032 2.127 0.001 1.0 O) 52.019 A; (Fe(2)–O)˚ 52.015 A] and the O–Fe–O˚

bond angle is in the range 81.9–176.38, which is in

5 1 21 52.246 20.031 1.750 0.001 6.5

agreement with those observed earlier in many of the

2 4 24 57.014 0.017 1.616 20.001 8.9

open-framework iron phosphate structures [4–13] The two

2 3 25 57.839 20.083 1.592 0.002 3.3

coordi-obs calc.

obs calc.

c

Table 2

Crystal data and structure refinement parameters for I, [C N H ][Fe (HPO ) ]2 2 10 2 4 4

˚

˚

˚

3

˚

23

˚

21

2

a

23

˚

Largest difference map peak and hole (e A ) 0.734 and 20.687

W 5 1 / [s (F ) 1 (0.0466P) 1 1.7021P] where P 5 [F 1 2F ] / 3.O O C

˚

The P–O distances are in the range 1.508–1.586 A [(P(1)– in agreement with those reported earlier [4–13] Bond

O)av.51.537 A; (P(2)–O)av.51.534 A] and the average valence sum calculations [21] indicated that the valence O–P–O bond angles are 109.58 and 109.48, respectively, states of the Fe, P and O are 13, 15 and –2, respectively, for P(1) and P(2) Of the eight O atoms, six are bonded in agreement with the framework formula

with two Fe atoms and one P atom The remaining two The three-dimensional framework of I,

˚

oxygens with distances P(1)–O(7)51.568 A and P(2)– [C N H ][Fe (HPO ) ], is built up from FeO octahedra2 2 10 2 4 4 6

˚

O(8)51.586 A are formally terminal –OH groups Termi- and PO4 tetrahedra sharing vertices The vertex linking nal hydroxyl groups, for example, in H PO –0.5H O and3 4 2 polyhedra form 4-membered rings made up of [Fe P O ]2 2 4 a-zirconium phosphate have distances of 1.551 and 1.558 units and are connected edge-wise forming ladder-like

˚

A, respectively [20] The above geometrical parameters are chains The ladder-like chains are connected together by

Table 3

4

Atomic coordinates [310 ] and equivalent isotropic displacement param- Table 4

˚

eters [A 310 ] for I, [C N H ][Fe (HPO ) ]2 2 10 2 4 4 Selected bond lengths in I, [C N H ][Fe (HPO ) ]2 2 10 2 4 4

P(1) 3370(1) 1003(1) 5669(1) 7(1) Fe(1)–O(3) 2.048(2) Fe(2)–O(6) 2.092(3)

P(2) 1376(1) 6586(1) 4676(1) 7(1) Fe(1)–O(1) 2.016(3) Fe(2)–O(4) 1.987(3)

O(2) 2422(3) 7326(3) 4034(3) 11(1) Fe(1)–O(3) 2.048(2) Fe(2)–O(6) 2.092(3)

[3 O(3) 2519(3) 10557(3) 1092(3) 11(1) P(1)–O(1) 1.508(3) P(2)–O(2) 1.519(3)

[4

[5

O(7) 3462(3) 2390(3) 6722(3) 14(1)

O(8) 801(3) 7833(3) 5499(3) 18(1) Organic moiety

[1

Symmetry transformations used to generate atoms:[1, 2 x 1 1 / 2, y,

a

U(eq) is defined as one-third of the trace of the orthogonalized U I , j 2 z 1 1 / 2; [2, 2 x 1 1 / 2, y, 2 z 1 3 / 2; [3, x 1 1 / 2, 2 y 1 1, z 1 1 / 2;

tensor. [4, 2 x 1 1 / 2, y 2 1, 2 z 1 1 / 2; [5, 2 x, 2 y 1 1, 2 z 1 1.

Table 5

a

Selected bond angles in I, [C N H ][Fe (HPO ) ]2 2 10 2 4 4

[1

[2

[2

[2

[1

[1

[3

[3

[6

[7

[5

Organic moiety

[1

a

Symmetry transformations used to generate atoms:[1, 2 x 1 1 / 2, y, 2 z 1 1 / 2; [2, 2 x 1 1 / 2, y, 2 z 1 3 / 2; [3, x 1 1 / 2, 2 y 1 1, z 1 1 / 2; [4,

2 x 1 1 / 2, y 2 1, 2 z 1 1 / 2; [5, 2 x, 2 y 1 1, 2 z 1 1; [6, x 2 1 / 2, 2 y 1 1, z 2 1 / 2; [7, 2 x 1 1 / 2, y 1 1, 2 z 1 1 / 2.

another edge-shared ladder in a direction perpendicular to

the plane of the chains as shown in Fig 2 It is to be noted

that 4-membered rings have been hypothesized as the

fundamental building units in aluminum and other metal

phosphates [22,23] The observation of such 4-membered

Fig 2 The basic building unit in I, [C N H ][Fe (HPO ) ], showing2 2 10 2 4 4

the ladder-like edge-shared chains and the connectivity between them.

Fig 1 ORTEP plot of I, [C N H ][Fe (HPO ) ] Thermal ellipsoids are2 2 10 2 4 4 Note that the ladders are connected by another edge-shared ladder in a

Fig 3 Structure of I, [C N H ][Fe (HPO ) ], along the [1 0 1] direction Note that the amine molecules sit in one and the –OH group protrude into the2 2 10 2 4 4

other creating hydrophobic and hydrophilic channels Hydrogens of the amine molecule are not given for clarity.

Fig 4 Structure of I, [C N H ][Fe (HPO ) ], along the a axis The amine molecules are not given for clarity.

directing amine molecules sits in the middle of one of the channels with the terminal –OH groups of the phosphates protrude into the another as shown in Fig 3 The formation

of two types of channels, one hydrophobic and another hydrophilic, is noteworthy Along the [1 0 0] direction, the connectivity gives rise to narrow arrowhead-type

one-dimensional channels, as shown in Fig 4 Thus, I, possess

two distinct channels

Thermogravimetric analysis of I was carried out in N2

atmosphere from room temperature to 7008C using a

21 heating rate of 108C min , as shown in Fig 5 The result shows two mass losses, a sharp one and a second rather broad one The first mass loss of about 12% occurring in the region 350–3808C corresponds to the loss of the amine and some adsorbed water (calc 11.1%) and the second mass loss of 8% in the region 400–7008C corresponds to the loss of the –OH group (calc 6.5%) The loss of the

Fig 5 Thermogravimetric analysis of I, [C N H ][Fe (HPO ) ].2 2 10 2 4 4

amine and the –OH group resulted in the collapse of the framework, leading to the formation of an amorphous rings, formed between the FeO6 octahedra and PO4 material (XRD)

tetrahedra (Fig 2), is crucial as they constitute the majority The structure of I possesses strong hydrogen bond

of the building blocks in I The ladder-like chains are interactions between the amine and the framework The connected in such a way forming 8-membered one-dimen- presence of two terminal –OH groups also ensured that sional channels along the [1 0 1] direction The structure- there are intra-framework hydrogen bond interactions in I.

Fig 6 The variation of magnetic susceptibility as a function of temperature in I, [C N H ][Fe (HPO ) ] Inset shows the variation of inverse2 2 10 2 4 4

susceptibility with temperature.

Table 6 interest, help and encouragement One of us (AC) thanks

Important hydrogen bond interaction in I, [C N H ][Fe (HPO ) ]2 2 10 2 4 4 the Council of Scientific and Industrial Research (CSIR),

˚

Moiety Distance (A) Moiety Angle (8) Government of India, for the award of a research

fellow-ship

O(3)–H(1) 2.157(1) O(3)–H(1)–N(1) 137.7(1)

O(8)–H(3) 2.560(1) O(8)–H(3)–N(1) 142.6(1)

O(2)–H(3) 2.080(1) O(2)–H(3)–N(1) 169.2(1)

O(7)–H(10) 1.978(3) O(7)–H(10)–O(8) 148.6(1)

N(1)–H(20) 2.181(2) N(1)–H(20)–O(7) 162.4(1)

References

O(4)–H(4) 2.548(2) O(4)–H(4)–C(1) 133.5(1)

a

Intra-framework.

[1] Meier WH, Olson DH Atlas of zeolite structure types, London: Butterworth–Heinemann, 1992.

¨ [2] Ertl G, Knozinger H, Weitkamp J, editors, Handbook of heteroge-The predominant interactions are between the hydrogens

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[3] Cheetham AK, Loiseau T, Ferey G Angew Chem Int Ed

˚

strongest interactions are: O(2) H(3)52.080 A and 1999;38:3268.

˚

O(2) H(3)–N(1)5169.28; N(1) H(20)52.181 A; [4] Cavellec M, Riou D, Ferey G J Solid State Chem 1994;112:441. N(1) H(20)–O(7)5162.48 The complete list of hydro- [5] Cavellec M, Riou D, Greneche J-M, Ferey G Zeolites 1996;17:252.

[6] Cavellec M, Egger C, Linares J, Nogues M, Varret F, Ferey G J

gen bond interactions observed in I is presented in Table 6.

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Magnetic susceptibility of I as a function of temperature

[7] Cavellec MR, Greneche J-M, Riou D, Ferey G Chem Mater was measured in the temperature range 20–300 K using a

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T 530 K The magnetic behavior above the orderingN [9] DeBord JRD, Reiff WM, Warren CJ, Haushalter RC, Zubieta J.

Chem Mater 1994;1997:9.

temperature follows the Curie–Weiss behavior with u 284.p

[10] DeBord JRD, Reiff WM, Haushalter RC, Zubieta J J Solid State The meff calculated from the Curie–Weiss law shows that

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Chem 1999;144:163.

[12] Lethbridge ZAD, Lightfoot P, Morris RE, Wragg DS, Wright PA,

˚

Kvick A, Vaughan G Solid State Chem 1999;142:455.

4 Conclusions

[13] Choudhury A, Natarajan S Proc Ind Natl Acad (Chem Sci) 1999;111:627.

The hydrothermal synthesis and single-crystal structure [14] Choudhury A, Natarajan S, Rao CNR Chem Commun 1999:1305.

of a new iron(III) phosphate, [C N H ][Fe (HPO ) ], has2 2 10 2 4 4 [15] Sheldrick GM SHELXS-86, A program for the solution of crystal been accomplished The structure possesses and is primari- structures, Gottingen, Germany: University of Gottingen, 1986 ¨ ¨

[16] Sheldrick GM SHELXTL-PLUS program for crystal structure

ly made up of 4-membered ladder-like chains connected to

solution and refinement, Gottingen, Germany: University of Gotting-form two distinct channels along the [1 0 1] and [1 0 0]

en, 1993.

directions The di-protonated amine molecules are located [17] Ferey G J Flour Chem 1995;72:187.

2 within these channels The absence of both F and Mn [18] Natarajan S, Gabriel JC-P, Cheetham AK J Chem Soc, Chem

ions in I indicates that our understanding of the formation Commun 1996:1415.

[19] Chippindale AM, Natarajan S, Thomas JM, Jones RH J Solid State

of these solids is poor and further research is needed to get

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better control over the synthesis of such phases

[20] Troup JM, Clearfield A Inorg Chem 1977;16:3311.

[21] Brown ID, Altermatt D Acta Crystallogr, Sect B 1985;41:244 [22] Oliver S, Kuperman A, Lough A, Ozin GA Chem Mater

[23] Oliver S, Kuperman A, Ozin GA Angew Chem Int Ed 1998;37:46. The authors thank Prof C.N.R Rao FRS, for his keen