  Indirect exchange interaction between itinerant electrons and nano-structures
with non-trivial geometrical configurations manifests a plethora of unexpected
results. These configurations can be realized either in quantum dots with
several potential valleys or in real complex molecules with strong
correlations. Here we demonstrate that the Kondo effect may be suppressed under
certain conditions in triple quantum dots with mirror symmetry at odd electron
occupation. First, we show that the indirect exchange has ferromagnetic sign in
the ground state of triple quantum dot in a two-terminal cross geometry for
electron occupation N=3. Second, we show that for electron occupation N=1 in
three-terminal fork geometry the zero-bias anomaly in the tunnel conductance is
absent (despite the presence of Kondo screening) due to special symmetry of the
dot wave function.
