From cyclic amines and acetonitrile to amidine zinc(ii) complexes

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• Zinc complexes with organic ligands are vital in catalysis and materials science.
• Understanding ligand exchange and complex formation is key to designing new functional materials.
• Quinaldinate and cyclic amines offer diverse coordination possibilities.

Purpose of the Study:

• To synthesize and characterize novel zinc(II) complexes using quinaldinate and secondary cyclic amines.
• To investigate the reactivity of piperidine, pyrrolidine, and morpholine with [Zn(quin)2(H2O)].
• To explore the formation of amidine ligands and their coordination to zinc.

Main Methods:

• Reaction of [Zn(quin)2(H2O)] with piperidine, pyrrolidine, or morpholine in acetonitrile.
• Isolation and characterization of resulting zinc complexes using various analytical techniques.
• Density Functional Theory (DFT) calculations to assess the stability of different isomers.

Main Results:

• Multiple anionic, neutral, and amidine-containing zinc complexes were synthesized.
• Piperidine and pyrrolidine reacted with acetonitrile to form amidines, which then coordinated to zinc.
• Morpholine degraded to ammonia at elevated temperatures, yielding only simple amine complexes.
• Two polymorphs of pyroamH[Zn(quin)3] were identified with different coordination environments.
• DFT calculations indicated that the six-coordinate [Zn(quin)3]- isomer is more stable.

Conclusions:

• The choice of cyclic amine significantly influences the outcome of reactions with zinc quinaldinate.
• Amidine formation is a viable pathway for synthesizing novel zinc complexes.
• Morpholine's thermal instability limits its use in these reactions.
• Polymorphism and coordination isomerism in zinc quinaldinate complexes can be influenced by crystal packing and electronic factors.