  We report on a detailed single crystal x-ray diffraction study of the
unconventional spin-Peierls compound TiOCl. The intermediate phase of TiOCl is
characterized by an incommensurate modulation which is virtually identical to
that recently found in the homologue compound TiOBr. The first order phase
transition between the spin-Peierls ground state and the incommensurate phase
reveals the same kind of thermal hysteresis in both, its crystal structure and
magnetic susceptibility. A weak, but significant magnetic field effect is found
for this phase transition with a field induced shift of the transition
temperature of Delta Tc1= -0.13 K for an applied field of B=10 T along the
chain direction. The field induced changes of the incommensurate crystal
structure are compatible with a scenario of competing intra- and inter-chain
interactions.
