  We report on the emergence of antiferromagnetic spin chains from
two-dimensionally aligned spins on the anisotropic triangular lattice (ATL) in
the insulating calcium rhenium oxychloride Ca3ReO5Cl2. The compound contains
Re6+ ions each with one unpaired electron in the dxy orbital, which are
arranged to form a spin-1/2 ATL with J'/J ~ 0.32 and J = 41 K, where J and J'
are magnetic interactions in and between the chains, respectively. In spite of
the apparent two dimensionality, we observe clear evidence of a gapless spin
liquid that is characteristic of the spin-1/2 Heisenberg chain. This
one-dimensionalization must be caused by geometrical frustration: growing
antiferromagnetic correlations in every chain effectively cancel out
inter-chain zigzag couplings at low temperature. Ca3ReO5Cl2 provides us with a
detailed insight into the interesting physics of the ATL antiferromagnet,
especially via comparison with the typical ATL compound Cs2CuCl4.
