Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO4(OH) (A = Na, K)

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 −51 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.