  We report nuclear magnetic resonance (NMR) studies in the antiferromagnetic
state of the quasi-two-dimensional (CuBr)LaNb2O7. The NMR spectra at zero
magnetic field and 4.2 K indicate a unique Cu and Br sites with an internal
field of 5.7 T (at Cu) and 16.4 T (at Br), confirming a magnetic order. For the
large internal field at the Br sites to be compatible with the collinear
antiferromagnetic order observed by neutron diffraction experiments (N. Oba et
al., J. Phys. Soc. Jpn. 75, (2006) 113601), the Br atoms must move
significantly off the center of the square of the Cu sublattice so that the Br
nuclei couple predominantly to two parallel Cu moments. While invalidating the
frustrated J1-J2 model defined on a C4-symmetric square lattice, our results
are compatible with the structural model proposed for (CuCl)LaNb2O7 by Yoshida
et al. (J. Phys. Soc. Jpn. 76 (2007) 104703).
