Crystal structure and magnetism in the = 1/2 spin dimer compound NaCuVPO.

The crystal structure of the spin dimer magnet NaCuVPO was determined using single-crystal X-ray diffraction and electron diffraction. NaCuVPO displayed a non-centrosymmetric orthorhombic 222 structure with = 6.13860 (10) Å, = 14.4846 (3) Å and = 8.2392 (2) Å. The layered structure comprised CuO plaquettes, VO octahedra and PO tetrahedra. A pair of CuO plaquettes formed CuO structural dimers through edge sharing. The Cu-Cu network formed a distorted puckered-layer structure with pseudo-one-dimensional characteristics. Maximum magnetic susceptibility was observed at ∼60 K and NaCuVPO became non-magnetic upon further cooling. The spin gap between the spin-singlet non-magnetic ground state and triplet excited state was estimated to be 43.4 K. Thus, NaCuVPO was assumed to be an alternating chain system with a singlet ground state of dimer origin. The V ions in the VO octahedra showed large off-centre displacements along the [110] direction in the primitive perovskite structure, which were attributed to the pseudo-Jahn-Teller distortion of transition metals.