A Unique Asymmetric [Mn$rm{^{II}_{3}}$] Triple-Stranded Helicate from a Symmetric Pentadentate Ligand Financial support by the European Union, under contract HPMF-CT-1999-00113 (Marie Curie Fellowship to G.A.), the WFMO (J.R.), and the CW-NOW (A.L.S.) is thankfully acknowledged