Crystal structures of Zn(cyclam)I₂ (second monoclinic polymorph) and Zn(cyclam)I(I₃)

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Crystal Engineering

Background:

• Macrocyclic ligands like cyclam (C₁₀H₂₄N₄) are crucial in coordination chemistry.
• Zinc(II) complexes with halide ligands offer insights into metal-ligand interactions.
• Understanding crystal packing and hydrogen bonding is key to designing functional materials.

Purpose of the Study:

• To synthesize and characterize two novel zinc(II) iodide complexes with cyclam.
• To investigate the structural differences and bonding patterns in these complexes.
• To explore the role of iodide anions in crystal network formation.

Main Methods:

• Single-crystal X-ray diffraction to determine the molecular and crystal structures.
• Analysis of bond lengths, coordination geometry, and hydrogen bonding networks.
• Conformational analysis of the cyclam ligand.

Main Results:

• Two distinct zinc(II) complexes, [ZnI(C₁₀H₂₄N₄)]I (I) and [ZnI(C₁₀H₂₄N₄)]I₃ (II), were characterized.
• Complex I features a five-coordinate zinc(II) with one coordinated iodide and one counter-ion iodide.
• Complex II exhibits a disordered five-coordinate zinc(II) center and triiodide counter-ions, forming 1D chains and 2D sheets.
• The cyclam ligand adopts the stable trans-III conformation in both compounds.
• Compound I forms 2D networks via N-H···I hydrogen bonds, while Compound II shows limited hydrogen bonding.

Conclusions:

• The coordination environment and counter-ion type significantly influence the crystal structure of zinc(II)-cyclam iodide complexes.
• Hydrogen bonding plays a critical role in the supramolecular assembly of Compound I.
• Compound II demonstrates a different packing motif driven by metal-centered disorder and polyiodide interactions.