Influence of metal to ligand molar ratios on the supramolecular structure formation of Cu(II) with diaminopropane and iodide: Synthesis, structure, spectroscopic and DFT studies

• Sub-molar ligand to metal ratios lead to different products.
• H-bonding interactions aid in stabilising sq. pyramidal Cu(II) against octahedral Cu(II), at lower ligand ratios.
• DFT and TD-DFT calculations support the experimental observations.
• Sub-molar ligand ratios offer promising strategy for obtaining novel solid state systems for material applications.

Two new copper(II) complexes with 1,3-diaminopropane and iodide, viz., [{Cu ((1,3-diaminopropane)2 I (I3))}] (1) and [{Cu ((1,3 diaminopropane)2(I)2)}] (2) have been synthesized under self assembly conditions and structurally characterised to observe the structural variations brought about by varying ligand molar ratios, towards studying the effect of external factors on supramolecular structure formation, with a long term goal of obtaining magnetic materials. Corresponding to the variation in metal to ligand molar ratios from one to two, totally different products are obtained whose gross structural features are entirely different. The formation of 1, is unpredicted under given synthetic conditions and hence is interesting. The formation of 2, is as generally expected for the reacting components under given conditions. In case of 1, the metal ion’s choice to adopt a square pyramidal geometry by coordinating to two ligand units and a coordinated iodide, even in the absence of sufficient moles of ligand, as in 2, is due to sub-molar ligand ratios complemented by weak hydrogen bonding interactions, operating between the ligand amino hydrogens and coordinated iodide and uncoordinated triiodide moiety. This approach of providing sub-molar amounts of ligand to the metal to satisfy its coordination requirements, appear to be a promising strategy towards obtaining novel solid systems of material relevance. Both the complexes are characterised structurally and spectroscopically. Further, both the structures were satisfactorily modelled by calculations based on Density Functional Theory (DFT), and their UV–visible spectra were analyzed in depth with the help of Time Dependent DFT (TD-DFT).

Two new copper(II) complexes with 1,3-diaminopropane and iodide, viz., [{Cu ((1,3-diaminopropane)2 I (I3)}] (1) and [{Cu s((1,3 diaminopropane)2(I)2}] (2) have been synthesized by the self assembly of the reacting components in 1:1:2 and 1:2:2 M ratios respectively and structurally characterised to observe the structural variations brought about by varying ligand molar ratios. The formation of 2 is as expected for the reacting components in the given molar ratios. The formation of 1 at lower molar ratios of the reacting components is assisted by weak and cumulative hydrogen bonding interactions templated by the triiodide unit which remains uncoordinated in the unit cell. The approach of providing sub-molar amounts of ligand to the metal to satisfy its coordination requirements appears to be a promising strategy towards obtaining novel solid systems having interesting solid state structures.Figure optionsDownload as PowerPoint slide