Synthesis and Molecular Structures of Cu II 15‐Metallacrown‐5 Complexes with Encapsulated Ca II , Pr III and Nd III Ions

Three complexes [Ca(ClO 4 )(H 2 O)Cu 5 (o‐picHA‐2H) 5 (H 2 O)]ClO 4 ( 1 ), [Pr(NO 3 ) 2 (py)Cu 5 (o‐picHA‐2H) 5 (py) 5 ]ClO 4 ( 2 ), and [Nd(NO 3 )(H 2 O)(py)Cu 5 (o‐picHA‐2H) 5 (py) 5 ](ClO 4 ) 2 · 5py ( 3 ) ( o ‐picHA = 2‐picolinehydroxamic acid) were synthesized in order to retrace structural trends caused by the change of the ionic radius of the central metal ion as well as to assess the effect of the axial ligands on the arrangement of metallacrowns. The complexes were characterized by elemental analysis, ESI‐mass spectrometry, IR spectroscopy, and single‐crystal X‐ray analysis. The heterometallic complexes have 15‐MC‐5 molecular topology with Ca II or Ln III ion in the center of the metallamacrocyclic cavity. The Ca–O and Ln –O bond lengths follow the trend of changes of the corresponding metal ionic radii. While the Ca II complex cation (without axial ligands) in 1 is almost flat, the Ln III containing cations in 2 and 3 have a “partially opened umbrella“ environment.