Unbridged Au(II)-Au(II) bonds are theoretically allowed

The bonding in the unbridged closed-shell Au(II)-Au(II) dimers X4Au2(C5H5N)(2), X = H, F-I and CF3, is analyzed and the short Au-Au bonds around 250 pm are reproduced by a novel 6s6p(z)5d(xy) hybridization.