Double-salt formation in crystal structures containing [Co(en)₃]Cl₃

Area of Science:

• Inorganic Chemistry
• Crystallography
• Coordination Chemistry

Background:

• The parent compound, tris(ethane-1,2-diamine-κ2N,N')cobalt(III) trichloride tetrahydrate ([Co(en)3]Cl3·4H2O), serves as a reference for structural comparison.
• Double salts involving cobalt(III) complexes with alkali metals and ammonium ions are explored.

Purpose of the Study:

• To determine the crystal structures of three novel racemic double salts of [Co(en)3]Cl3.
• To compare the structural features of these double salts with the parent compound.
• To re-examine the structure of a chiral derivative at cryogenic temperatures.

Main Methods:

• Single-crystal X-ray diffraction was employed to determine the structures.
• Crystallographic data were collected and analyzed for four related compounds.
• Structural comparisons were made based on determined unit-cell parameters and atomic coordinates.

Main Results:

• Three racemic double salts, [Co(en)3]2[Na(H2O)6]Cl7, [Co(en)3]2[K(H2O)6]Cl7, and (NH4)[Co(en)3]2Cl7·6H2O, were structurally characterized.
• All four compounds, including the parent [Co(en)3]Cl3·4H2O, crystallize in the trigonal space group P-3c1.
• The double salts exhibit a modest increase in unit-cell volume compared to the parent compound.
• The structure of the chiral derivative [Λ-Co(en)3]2[Na(H2O)6]Cl7 was redetermined at 120 K, resolving previously noted disorder.

Conclusions:

• The study highlights structural similarities among the investigated cobalt(III) double salts and the parent compound.
• The crystallographic data confirm the trigonal P-3c1 space group for all studied compounds.
• The findings provide insights into the packing and structural variations in double salts of tris(ethane-1,2-diamine)cobalt(III) complexes.