[en] Cluster calculations have been performed for the electronic structure of Cu-O clusters. The influence of atomic displacements on the energy levels of the antibonding state has been investigated. Strong electron-phonon coupling quadratic in displacements was found. Within a simple model the Eliashberg theory was treated for quadratic coupling. Using the Krezin formula it could be shown that it is possible to explain the high T_c values in the framework of a quadratic electron phonon mechanism. The isotope effect was discussed