Crystal structure and magnetism in the S = 1/2 spin dimer compound NaCu(2)VP(2)O(10)

The crystal structure of the spin dimer magnet NaCu(2)VP(2)O(10) was determined using single-crystal X-ray diffraction and electron diffraction. NaCu(2)VP(2)O(10) displayed a non-centrosymmetric orthorhombic C222(1) structure with a = 6.13860 (10) Å, b = 14.4846 (3) Å and c = 8.2392 (2) Å. The layered structure comprised CuO(4) plaquettes, VO(6) octahedra and PO(4) tetrahedra. A pair of CuO(4) plaquettes formed Cu(2)O(6) 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 NaCu(2)VP(2)O(10) 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, NaCu(2)VP(2)O(10) was assumed to be an alternating chain system with a singlet ground state of dimer origin. The V(5+) ions in the VO(6) 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 d (0) transition metals.