  Recent X-ray analysis and NMR- experiments have shown that alpha'- NaV2O5 is
not a conventional spin-Peierls (SP) compound because above the transition at
33K it is in a homogeneous mixed valent (MV) state and atomic spin chains do
not exist. Furthermore, thermal expansion experiments have identified the
existence of a double phase transition. We present a theoretical model which
qualitatively explains these observations. We derive an effective Hamiltonian
for the insulating state which describes the transitions as primary charge
order leading to linear spin chains in b- direction and a secondary SP-
transition. We show that this scenario explains in a natural way the anomalous
BCS-ratio observed in alpha'- NaV2O5.
