A new class of solvatochromic material: Geometrically unsaturated Ni (II) complexes

A series of Ni(II) double stranded binuclear complexes were synthesized upon treating the Ni(II) salts with series of diamino-bis-pyridine ligands, L1H2–L4H2 in 1:1 stiochiometric ratio. The Ni(II) centers existing in octahedral geometry, four of the coordination sites are occupied by two ligand strands, while the remaining two sites are occupied by solvent molecules in each metal centers. The Ni(II) complexes 1a–4a and 1b–4b are binuclear in nature with ClO4 and PF6 counter ions. The crystal structure obtained for complex 1b ascertains the solvent coordination. Solvatochromism though a well established phenomena, such observation is reported first time in the present manuscript in the area of helicate chemistry. Thus the manuscript elicits the solvatochromic property of geometrically unsaturated helicates, by appropriately tuning the d-d transition, adapting suitable solvents.

Graphical abstractThe series of binuclear double stranded coordinatively unsaturated Ni (II) helicates possessing labile/vacant sites with various ligand strands are synthesized. Color being fascinating area of research, this work opens-up a rich area of compounds, which gives options to design and develop new solvatochromic material with wide flexibility for systematic fine tuning of d-d transitions to achieve desired colors. Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of Dinuclear Ni(II) helicates. ► Series of coordinatively unsaturated double helicates exhibits solvatochromism. ► The change in solvents and the change in color has been successfully demonstrated. ► The novel helicates provides desired colors upon tuning the d-d transitions.