Synthesis, crystal structure, and magnetic properties of K4Mn3(HPO4)4(H2PO4)2

A new layered compound, K4Mn3(HPO4)(4)(H2PO4)(2) (1), has been synthesized under hydrothermal conditions. It crystallizes in the monoclinic space group P2(1)/n with a=8.874(2)angstrom, b=6.554(1)angstrom, c=18.075(4)angstrom, and beta=93.39(3)degrees. The structure consists of zigzag [Mn3O14](n) chains of edge-sharing MnO6 octahedrons and MnO7 pentagonal bi-pyramids, which form layers Of formula [Mn-3(HPO4)(4)(H2PO4)(2)](4-) in the ab plane via H2PO4 and HPO4 units with vertex-sharing. Potassium ions lie between these layers. Magnetic measurements indicate Curie-Weiss behavior above 6 K for 1. A Heisenberg model, with alternating exchange interactions J(1)J(1)J(2)... within the chain and exchange interactions J(3)J(3)... between the chains, is proposed to describe the magnetic behavior. (C) 2009 Elsevier Masson SAS. All rights reserved.