  We consider the simplest example of lattice frustration in the 1/4-filled
band, a one-dimensional chain with next-nearest neighbor interactions. For this
zigzag ladder with electron-electron as well as electron-phonon interactions we
present numerical results for ground state as well as thermodynamic properties.
In this system the ground state bond distortion pattern is independent of
electron-electron interaction strength. The spin gap in the ground state of the
zigzag ladder increases with the degree of frustration. Unlike in
one-dimension, where the spin-gap and charge ordering transitions can be
distinct, we show that in the ladder they occur simultaneously. We discuss spin
gap and charge ordering transitions in 1/4-filled materials with one, two, or
three dimensional crystal structures. We show empirically that regardless of
dimensionality the occurrence of simultaneous or distinct charge and magnetic
transitions can be correlated with the ground state bond distortion pattern.
