A new spin-1/2 quasi-one-dimensional antiferromagnet KCuMoO4(OH) is prepared by the hydrothermal method. The crystal structures of KCuMoO4(OH) and the already-known Na-analogue NaCuMoO4(OH) are isotypic, comprising chains of Cu2+ ions in edge-sharing CuO4(OH)2 octahedra. Despite the structural similarity, their magnetic properties are quite different because of the different arrangements of dx2-y2 orbitals carrying spins. For NaCuMoO4(OH), dx2-y2 orbitals are linked by superexchange couplings via two bridging oxide ions, which gives a ferromagnetic nearest-neighbor interaction J1 of â51 K and an antiferromagnetic next-nearest-neighbor interaction J2 of 36 K in the chain. In contrast, a staggered dx2-y2 orbital arrangement in KCuMoO4(OH) results in superexchange couplings via only one bridging oxide ion, which makes J1 antiferromagnetic as large as 238 K and J2 negligible. This comparison between the two isotypic compounds demonstrates an important role of orbital arrangements in determining the magnetic properties of cuprates.
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