International Journal of Inorganic Materials 2 (2000) 217–223 A new three-dimensional open-framework iron(III) phosphate, [C N H ][Fe (HPO ) ] 2 2 10 2 4 4 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 2 2 10 2 4 4 ethylenediamine (en). The structure is built up from the vertex linkages between the FeO octahedra and the PO tetrahedra, strictly 6 4 alternating, forming the three-dimensional architecture. The linkages between the FeO and PO polyhedra gives rise to ladder-like 6 4 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 / n 2 2 10 2 4 16 23 ˚ (No. 13), Z52, M5557.7, D 52.65 g cm , MoKa ( l50.71073 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 2 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 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 3 2 resulted in a variety of solids, some of which were already 0.169 g of MnCl –4H O was dispersed and dissolved in 3 2 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. PII: S1466-6049(00)00007-6