Anion-controlled geometrically different Cu(II) ion-based coordination polymers and green synthetic route for copper nanoparticles: a combined experimental and computational insight

<p>The Cu(II) ion-based polymeric complexes [Cu(2,2′-bpy).(N₃)₂]_n (<b>I</b>), [Cu₂(2,2′-bpy)₂.(N₃)₄]_n (<b>II</b>), and monomeric complex [Cu(2,2′-bpy).(NO₃)₂].5H₂O (<b>III</b>) have been synthesized with rigid (–N₃) and aromatic (2,2′-bpy = 2,2′-bipyridyl) ligand. The rigid azide group is responsible for the formation of 1-D extended structures in complexes <b>I</b> and <b>II</b> where as in the case of complex <b>III</b>, a monomeric complex is formed due to lack of a bridging group like –N₃, resulting in limitation in dimensionality. The thermal stability of the 1-D complexes is comparatively higher than monomeric complex <b>III</b>. Hirshfeld surface analysis has also been applied to investigate other weak interactions and compared with the results from single-crystal X-ray data. Due to the presence of paramagnetic metal centers and long metal···metal distances in complexes <b>I</b> and <b>II</b> and presence of lattice water molecules in complex <b>III</b>, decrease in luminescence intensities have been observed. To attain further insights into the aforementioned interesting species, some chemical concepts such as highest occupied molecular orbital–lowest unoccupied molecular orbital gap, electronic chemical potential, chemical hardness, and electrophilicity index, identified as a derivative of electronic energy, have also been emphasized employing the quantum chemical calculations in the framework of the density functional theory method using the M06-2X/ 6-31G** level of study. Further, these complexes have been used to synthesize copper nanoparticles by applying a green synthetic route.