  We consider the effect of the nearest neighbour copper-oxygen repulsion, V,
when coupled to the charge transfer resonances Cu2+ to Cu3+ and Cu2+ to Cu+ in
the high temperature cuprate superconductors. This is done by deriving
effective low energy Hamiltonians correct to second order in the copper-oxygen
hybridisation. Only hole doping is considered. When Cu2+ to Cu3+ fluctuations
dominate we derive an effective one-band model of `Zhang-Rice' singlets with a
nearest neighbour repulsion between these singlets. When Cu2+ to Cu+
fluctuations dominate we find rich and complex behaviour. For large V we show
that clusters of charge are more stable than isolated charges. On the other
hand, for small V the Hamiltonian contains both weak attractive and repulsive
two body potentials. Calculations on clusters indicate that the attractive
potentials have the same correlations as the more dominate `single particle'
terms suggesting the possibility of `s' wave pairing.
