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

International Journal of Inorganic Materials 2 (2000) 217–223 A new three-dimensional open-framework iron(III) phosphate, [C N H ][Fe (HPO ) ] 2210 2 44 a,b a, * Amitava Choudhury , Srinivasan Natarajan 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 of 2210 2 44 ethylenediamine (en). The structure is built up from the vertex linkages between the FeO octahedra and the PO tetrahedra, strictly 64 alternating, forming the three-dimensional architecture. The linkages between the FeO and PO polyhedra gives rise to ladder-like 64 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 P 2 /n 2 2 10 2 4 16 23 ˚ (No. 13), Z52, M5557.7, D 52.65 g cm , MoKa ( l 50.71073 A), R 50.03, wR 50.08 and S51.10. Magnetic susceptibility studies calc 1 2 indicate a predominantly antiferromagnetic interaction with T 530 K.  2000 Elsevier Science Ltd. All rights reserved. N Keywords : A. inorganic compounds; magnetic materials; B. chemical synthesis; C. X-ray diffraction 1. Introduction known. A special case is iron fluro-phosphate, exhibiting a 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-head 2210 2 44 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 tetrahedra 4 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 and 32 resulted in a variety of solids, some of which were already 0.169 g of MnCl –4H O was dispersed and dissolved in 3 22 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. PII: S1466-6049(00)00007-6 218 A . Choudhury , S . Natarajan / International Journal of Inorganic Materials 2 (2000) 217 – 223 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 – readily established the heavy atom (Fe, P) sites and most 32 2 4H O–12H PO –6en–3HF–200H O, was transferred of the light atom (O, N and C) positions. All the hydrogen 234 2 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 ) ], was 2210 2 44 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 in structure-directing agent, en, and the structure determined 2210 2 44 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 studies. the final solid product. The absence of Mn in the final 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], Table 1 2 and we believe, in the present case, F ions act as a X-ray powder data for I, [C N H ][Fe (HPO ) ] 2210 2 44 mineralizer and facilitate the formation of I, as the final abc hkl 2 u D(2 u ) d D(d) I 2 obs calc rel 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 1121 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-dimensional 2210 2 44 2122 24.318 0.000 3.660 0.000 3.4 open-framework network structure made from vertex- 1 2 1 27.228 20.018 3.273 0.002 5.8 1222 27.615 0.011 3.231 20.001 100 linked FeO octahedra and PO tetrahedra incorporating 64 1023 28.628 0.093 3.128 20.001 7.2 di-protonated en molecules within its pores. The asymmet- 0 2 2 29.280 20.052 3.045 0.005 4.3 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 1123 30.400 0.093 2.949 20.009 8.6 independent iron and phosphorus atoms. The Fe atoms 3121 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 1 2 2 34.678 0.020 2.588 20.001 5.6 neighbors. The Fe–O–P bonds angles are in the narrow 3222 35.914 0.048 2.504 20.004 4.2 region 137.8–152.48 (Table 5) indicating that both the 2322 37.824 20.014 2.378 0.000 1.9 FeO octahedra and PO tetrahedra are regular. The Fe–O 2024 37.970 20.056 2.366 0.004 3.2 64 ˚ 2124 39.397 20.020 2.286 20.002 13.4 bond distances are in the range 1.967–2.092 A [(Fe(1)– 2323 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 av. av. 1 3 3 49.789 0.059 1.833 20.002 5.7 bond angle is in the range 81.9–176.38, which is in 5121 52.246 20.031 1.750 0.001 6.5 agreement with those observed earlier in many of the 2424 57.014 0.017 1.616 20.001 8.9 open-framework iron phosphate structures [4–13]. The two 2325 57.839 20.083 1.592 0.002 3.3 a distinct phosphorus atoms in I are tetrahedrally coordi- 2 u 22 u . obs calc. b nated by oxygens and both of them make three P–O–Fe d 2d . obs calc. c 1003I/I . bonds with the remaining P–O vertex being ‘terminal’. max A . Choudhury , S . Natarajan / International Journal of Inorganic Materials 2 (2000) 217 – 223 219 Table 2 Crystal data and structure refinement parameters for I, [C N H ][Fe (HPO ) ] 2210 2 44 Empirical formula Fe P O C N H 2 4 16 2 2 14 Crystal system Monoclinic Space group P 2 /n (No. 13) Crystal size (mm) 0.2030.2030.28 ˚ a (A) 9.341(1) ˚ b (A) 8.892(1) ˚ c (A) 9.480(1) b (8) 117.6(1) 3 ˚ Volume (A ) 698.1(1) Z 2 Formula mass 557.7 23 r (g cm ) 2.65 calc ˚ l (MoKa) (A) 0.71073 21 m (mm ) 2.64 u range (8) 2.29–23.28 Total data collected 2879 Index ranges 210#h#10, 29#k#8, 210#l#9 Unique data 1010 Observed data [ s .2 s (I)] 914 R 0.02 merg. 2 Refinement method Full-matrix least-squares on uF u a R indices [I.2 s (I)] R 50.03; wR 50.08 12 R indices (all data) R 50.03; wR 50.08 12 Goodness of fit (S) 1.10 No. of variables 119 23 ˚ Largest difference map peak and hole (e A ) 0.734 and 20.687 a22 2 22 W5 1/[ s (F ) 1 (0.0466P) 1 1.7021P] where P 5 [F 1 2F ]/3. OOC ˚ 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) 51.537 A; (P(2)–O) 51.534 A] and the average valence sum calculations [21] indicated that the valence av. av. 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 octahedra 2210 2 44 6 ˚ O(8)51.586 A are formally terminal –OH groups. Termi- and PO tetrahedra sharing vertices. The vertex linking 4 nal hydroxyl groups, for example, in H PO –0.5H O and polyhedra form 4-membered rings made up of [Fe P O ] 34 2 22 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 2 3 a ˚ eters [A 310 ] for I, [C N H ][Fe (HPO ) ] Selected bond lengths in I, [C N H ][Fe (HPO ) ] 2210 2 44 2210 2 44 a ˚˚ Atom xy zU(eq) Moiety Distance (A) Moiety Distance (A) Fe(1) 2500 8818(1) 2500 7(1) Fe(1)–O(1) 2.016(3) Fe(2)–O(4) 1.987(3) Fe(2) 2500 3958(1) 7500 7(1) Fe(1)–O(2) 1.995(2) Fe(2)–O(5) 1.967(3) P(1) 3370(1) 1003(1) 5669(1) 7(1) Fe(1)–O(3) 2.048(2) Fe(2)–O(6) 2.092(3) [1 [2 P(2) 1376(1) 6586(1) 4676(1) 7(1) Fe(1)–O(1) 2.016(3) Fe(2)–O(4) 1.987(3) [1 [2 O(1) 97(3) 8546(3) 1181(3) 13(1) Fe(1)–O(2) 1.995(2) Fe(2)–O(5) 1.967(3) [1 [2 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 O(4) 2445(3) 5485(3) 5945(3) 14(1) P(1)–O(3) 1.533(3) P(2)–O(4) 1.514(3) [5 O(5) 141(3) 4124(3) 6613(3) 12(1) P(1)–O(6) 1.538(3) P(2)–O(5) 1.516(3) O(6) 2375(3) 2252(3) 5927(3) 12(1) P(1)–O(7) 1.568(3) P(2)–O(8) 1.586(3) O(7) 3462(3) 2390(3) 6722(3) 14(1) O(8) 801(3) 7833(3) 5499(3) 18(1) Organic moiety [1 N(1) 4442(4) 2983(4) 3073(4) 16(1) N(1)–C(1) 1.496(5) C(1)–C(1) 1.519(8) C(1) 3331(5) 4114(4) 3218(3) 13(1) a 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 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; I , j 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. 220 A . Choudhury , S . Natarajan / International Journal of Inorganic Materials 2 (2000) 217 – 223 Table 5 a Selected bond angles in I, [C N H ][Fe (HPO ) ] 2210 2 44 Moiety Angle (8) Moiety Angle (8) [1 O(1)–Fe(1)–O(1) 166.2(2) O(5)–Fe(2)–O(4) 89.55(11) [2 O(2)–Fe(1)–O(1) 88.08(11) O(5)–Fe(2)–O(5) 171.4(2) [1 [2 O(2) –Fe(1)–O(2) 96.63(14) O(5) –Fe(2)–O(4) 84.55(11) [1 [2 O(2)–Fe(1)–O(1) 82.75(10) O(5)–Fe(2)–O(4) 84.55(11) [1 [2 [2 O(2) –Fe(1)–O(1) 82.75(10) O(5) –Fe(2)–O(4) 89.54(11) [1 [1 [2 O(2) –Fe(1)–O(1) 88.08(11) O(4)–Fe(2)–O(4) 93.8(2) [2 O(1)–Fe(1)–O(3) 91.68(10) O(5)–Fe(2)–O(6) 92.35(10) [1 [2 [2 O(1) –Fe(1)–O(3) 98.73(11) O(5) –Fe(2)–O(6) 93.93(10) [2 O(2)–Fe(1)–O(3) 172.54(10) O(4)–Fe(2)–O(6) 176.26(10) [1 O(2) –Fe(1)–O(3) 90.73(10) O(5)–Fe(2)–O(6) 93.91(10) [1 O(2)–Fe(1)–O(3) 90.73(10) O(4)–Fe(2)–O(6) 89.59(10) [1 [1 [2 [2 O(2) –Fe(1)–O(3) 172.54(10) O(4) –Fe(2)–O(6) 89.59(10) [1 [2 O(1)–Fe(1)–O(3) 98.74(11) O(5) –Fe(2)–O(6) 92.35(10) [1 [1 [2 O(1) –Fe(1)–O(3) 91.68(10) O(4) –Fe(2)–O(6) 176.26(10) [1 [2 O(3)–Fe(1)–O(3) 81.94(14) O(6) –Fe(2)–O(6) 87.07(14) [3 [4 [5 O(1) –P(1)–O(3) 112.3(2) O(4)–P(2)–O(5) 113.4(2) [3 O(1) –P(1)–O(6) 113.1(2) O(4)–P(2)–O(2) 106.8(2) [4 [5 O(3) –P(1)–O(6) 107.30(14) O(5) –P(2)–O(2) 113.1(2) [3 O(1) –P(1)–O(7) 105.6(2) O(4)–P(2)–O(8) 108.1(2) [4 [5 O(3) –P(1)–O(7) 109.36(14) O(5) –P(2)–O(8) 106.5(2) O(6)–P(1)–O(7) 109.16(14) O(2)–P(2)–O(8) 108.7(2) [6 P(1) –O(1)–Fe(1) 152.4(2) P(2)–O(2)–Fe(1) 145.8(2) [7 P(1) –O(3)–Fe(1) 137.8(2) P(2)–O(4)–Fe(2) 144.4(2) [5 P(1)–O(6)–Fe(2) 143.0(2) P(2) –O(5)–Fe(2) 139.3(2) Organic moiety [1 N(1)–C(1)–C(1) 112.5(3) 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 ) ], showing 2210 2 44 the ladder-like edge-shared chains and the connectivity between them. Fig. 1. ORTEP plot of I, [C N H ][Fe (HPO ) ]. Thermal ellipsoids are Note that the ladders are connected by another edge-shared ladder in a 2210 2 44 given at 50% probability. horizontal direction. A . Choudhury , S . Natarajan / International Journal of Inorganic Materials 2 (2000) 217 – 223 221 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 the 2210 2 44 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. 2210 2 44 222 A . Choudhury , S . Natarajan / International Journal of Inorganic Materials 2 (2000) 217 – 223 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 N 2 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 ) ]. 2210 2 44 amine and the –OH group resulted in the collapse of the framework, leading to the formation of an amorphous rings, formed between the FeO octahedra and PO material (XRD). 64 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 inverse 2210 2 44 susceptibility with temperature. A . Choudhury , S . Natarajan / International Journal of Inorganic Materials 2 (2000) 217 – 223 223 Table 6 interest, help and encouragement. One of us (AC) thanks Important hydrogen bond interaction in I, [C N H ][Fe (HPO ) ] 2210 2 44 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) aa 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 neous catalysis, Berlin: VCH, 1997. attached to the nitrogen and the framework oxygens. The [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. Solid State Chem 1997;134:349. 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 1998;10:2434. 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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 ) ], has [15] Sheldrick GM. SHELXS-86, A program for the solution of crystal 2210 2 44 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 Chem 1994;111:18. 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 Acknowledgements 1996;8:2391. [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 . International Journal of Inorganic Materials 2 (2000) 217–223 A new three-dimensional open-framework iron(III) phosphate, [C N H ][Fe (HPO ) ] 2210 2 44 a, b a, * Amitava Choudhury , Srinivasan Natarajan a Advanced. Natarajan 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. 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