Journal of Solid State Chemistry 173 (2003) 101–108 A new vanadium(III) fluorophosphate with ferromagnetic interactions, (NH 4 )[V(PO 4 )F] Estibaliz Alda, a Begon˜a Baza´n, b Jose´ L. Mesa, a Jose´ L. Pizarro, b Marı´a I. Arriortua, b and Teo´filo Rojo a, a Departamento de Quı´ mica Inorga´nica, Facultad de Ciencias, Universidad del Paı´ s Vasco, Apdo. 644, E-48080 Bilbao, Spain b Departamento de Mineralogı´ a-Petrologı´ a, Facultad de Ciencias, Universidad del Paı´ s Vasco, Apdo. 644, E-48080 Bilbao, Spain Received 23 October 2002; received in revised form 10 January 2003; accepted 31 January 2003 Abstract A new vanadium(III) phosphate, (NH 4 )[V(PO 4 )F], has been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure has been solved from X-ray single crystal data. The compound crystallizes in the Pnna orthorhombic space group, with the unit-cell parameters a ¼ 12:982ð2Þ; b ¼ 10:608ð1Þ; c ¼ 6:4789ð6Þ A ˚ and Z ¼ 8: The final R factors were R 1 ¼ 0:077 [all data] and wR 2 ¼ 0:068: The crystal structure consists of a three-dimensional framework formed by VO 4 F 2 octahedra and tetrahedral (PO 4 ) 3 phosphate anions. The vanadium(III) cations from the VO 4 F 2 octahedra are linked through the fluorine atoms giving rise to zig-zag chains. The ammonium cations are located in the cavities of the structure compensating the anionic charge of the [V(PO 4 )F]  inorganic skeleton. The IR spectrum shows the characteristic bands of the phosphate anion. The diffuse reflectance spectroscopy allowed us to calculate the Dq and Racah parameters. The values are Dq ¼ 1540; B ¼ 505 and C ¼ 2460cm 1 . Magnetic measurements indicate the existence of weak ferromagnetic interactions. r 2003 Elsevier Science (USA). All rights reserved. Keywords: Hydrothermal synthesis; V(III) phosphates; Crystal structure; Ferromagnetism 1. Introduction The research on phosphate materials with new open frameworks is currently in progress due to their potential applications in catalysis, gas separation, ion exchangers [1,2]. The study of phosphates of transition elements with low oxidation states has received great interest in recent years. The great ability of the phosphate frameworks to stabilize reduced oxidation states is a consequence of the relatively high charge in the (PO 4 ) 3 tetrahedral that favours the formation of anionic frameworks with a high degree of mechanical, chemical and thermal stability. The vanadium phos- phate systems are of interest for their different structural, catalytic and magnetic characteristics. V–O– P materials containing PO 4 , HPO 4 ,H 2 PO 4 or P 2 O 7 tetrahedra [3], and the vanadium metal in different oxidation states are now known [4]. It is worth mentioning, the vanadyl phosphate phases which shown a rich intercalation chemistry, with the possible conver- sion to porous materials [5]. Furthermore, the vanadyl pyrophosphate is today used as catalyst for the oxidation of butane to maleic anhydride [6]. In the last years, both organically templated and inorganic–organic hybrid vanadium phases with open frameworks have been reported [1]. The organically templated compounds were synthesized from soft hydrothermal conditions using alkyldiamines as struc- tural directing agents. In this way, mixed valence vanadium compounds with the ethylenediammonium [7] and pyperazinium [8] cations acting as counterions of the inorganic open-skeleton are known. Fluoropho- sphate compounds belonging to these kinds of com- pounds with vanadium(IV) and vanadium(V) cations have been recently reported [9,10]. Furthermore, inor- ganic–organic hybrid vanadium phosphates with a directly coordinated organonitrogen ligand such as the 2,2 0 -bipyridine or the 2,2 0 :6 0 ,2 00 -terpyridne are also known [11]. Up to day, few vanadium(III) phosphates have been synthesized and studied. A rubidium vanadium(III)  Corresponding author. Fax: +34-944648500. E-mail address: qiproapt@lg.ehu.es (T. Rojo). 0022-4596/03/$-see front matter r 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0022-4596(03)00098-7