Temperature influence on supramolecular structure formation. Synthesis, structure, spectral and DFT studies of Cu(II)–azide systems with symmetric diamines

Three new Cu(II) complexes, viz. [{Cu2((1,3-diaminopropane)2(N3)4}2] (1), [Cu((1,3-diaminopropane)2(N3)2] (2) and [Cu(en)2(N3)2] (3), with symmetric amines and azide ligands have been synthesized under self-assembly conditions and structurally characterized, towards understanding the influence of temperature in directing the final structure formation. Interestingly, temperature plays a decisive role in the final structure formation, leading to the formation of a tetramer 1 at low temperature (LT) and a monomer 2 at room temperature (RT) in the case of the Cu(II)–1,3-diaminopropane–N3 system. However, such a temperature influence has not been observed in the case where ethylene diamine is a ligand. Irrespective of the crystallization temperature, the Cu(II)–en–azide system always affords compound 3 only. The stability of both 1 and 2 is further confirmed by Single Point Energy calculations, which corroborate the experimental observations.

Three new Cu(II) complexes, viz. [{Cu2((1,3-diaminopropane)2(N3)4}2] (1), [Cu((1,3-diaminopropane)2(N3)2] (2) and [Cu(en)2(N3)2] (3), with symmetric amines and azide ligands have been synthesized under self-assembly conditions and structurally characterized, towards understanding the influence of temperature in directing the final structure formation. Interestingly, such an influence is reflected in the formation of tetramer 1 at low temperature (LT) and a monomer 2 at room temperature (RT) in the case of 1,3-diaminopropane as a ligand. However, on changing the ligand from 1,3-diaminopropane to ethylene diamine, the product is unaffected by temperature, as reflected by the formation of only 3 at all temperatures. SPE calculations confirm that 1 is the thermodynamically favored product, while 2 is kinetically favored at RT, which corroborate the experimental observations. The crystal system of 3 is interesting as it provides the first example of an uncoordinated azide acting as a counter ion, so far unreported for Cu(II) azide systems. These uncoordinated azide units hold the polymeric chains formed by octahedrally coordinated monomeric Cu centers, connected through single end to end azide units through hydrogen bonding interactions, leading to a 2D framework.Figure optionsDownload as PowerPoint slide