Trigonal prismatic metal complexes: a not so rare coordination geometry?

Area of Science:

• Coordination Chemistry
• Inorganic Chemistry
• Structural Chemistry

Background:

• Hexaamine macrobicyclic ligands are known to form stable metal complexes.
• Trigonal prismatic geometry is less common than octahedral or tetrahedral geometries in coordination chemistry.

Purpose of the Study:

• To determine the solid-state structures of two metal complexes featuring a specific hexaamine macrobicyclic ligand.
• To investigate the preferred coordination geometry of this ligand with various metal ions.
• To computationally validate the stability of the observed geometry.

Main Methods:

• Single-crystal X-ray diffraction was used to determine the solid-state structures.
• Theoretical calculations (e.g., density functional theory) were employed to assess geometric stability.

Main Results:

• The solid-state structures of two metal complexes were successfully determined.
• Both complexes exhibit an exact trigonal prismatic coordination geometry around the metal ion.
• Theoretical calculations indicate that trigonal prismatic geometry is the most stable configuration for d(0), d(10), and high-spin d(5) metal complexes with this ligand, provided M-N bond distances exceed approximately 2.35 Å.

Conclusions:

• The hexaamine macrobicyclic ligand enforces an exact trigonal prismatic geometry on metal ions in the solid state.
• This specific geometry is theoretically predicted to be highly stable for certain electronic configurations of metal ions coordinated by this ligand.