  We report the crystal structure, magnetization measurements, and
band-structure calculations for the spin-1/2 quantum magnet CaCu2(SeO3)2Cl2.
The magnetic behavior of this compound is well reproduced by a uniform spin-1/2
chain model with the nearest-neighbor exchange of about 133 K. Due to the
peculiar crystal structure, spin chains run in the direction almost
perpendicular to the structural chains. We find an exotic regime of frustrated
interchain couplings owing to two inequivalent exchanges of 10 K each. Peculiar
superexchange paths grant an opportunity to investigate bond-randomness effects
under partial Cl-Br substitution.
