  The structure and the magnetic properties of layered Li3Cu2SbO6 are
investigated by powder X-ray diffraction, static susceptibility, and electron
spin resonance studies up to 330 GHz. The XRD data experimentally verify the
space group C2/m with halved unit cell volume in contrast to previously
reported C2/c. In addition, the data show significant Li/Cu-intersite exchange.
Static magnetic susceptibility and ESR measurements show two magnetic
contributions, i.e. quasi-free spins at low-temperature and a spin-gapped
magnetic subsystem, with about half of the spins being associated to each
subsystem. The data suggest ferromagnetic-antiferromagnetic alternating chains
with JFM = -285 K and JAFM = 160 K with a significant amount of Li-defects in
the chains. The results are discussed in the scenario of fragmented 1D S = 1
AFM chains with a rather high defect concentration of about 17% and associated
S = 1/2 edge states of the resulting finite Haldane chains.
