Hydrothermal synthesis, structure and magnetic properties of a one-dimensional iron arsenate, â?? 1[NH 3(CH2)2NH(CH2)2NH 3][Fe2F4(HAsO4)2]

A novel one-dimensional iron arsenate, â?? 1[NH3(CH2)2NH-(CH2) 2NH3][Fe2F4(HAsO4) 2], built up exclusively from SBU-4 units (two octahedral units sharing an edge and connected through two tetrahedra) with Fe3+ ions in the high-spin state has been synthesized by hydrothermal methods. Structure elucidation reveals that the compound is a two-leg ladder with very weak antiferromagnetic exchanges along the chains. The magnetic susceptibility data show activated behaviour at T = 14 K, suggesting a finite spin gap between the nonmagnetic ground state and the excited triplet state. We have estimated the exchange parameters theoretically based on the S = 5/2 Majumdar-Ghosh model with frustrations and dimerisations. Although the magnetic gap is quite small, this is the first example, to the best of our knowledge, where the rungs with two S = 5/2 spins form strong singlet dimers. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.