Copper(II) solvatochromic complexes [Cu(acac)(N^N)(ligand)]BPh4 with various axial ligands. Correlation between coordination geometries and d–d transition energies (acac = acetylacetonato, N^N = 1,10-phenanthoroline, 2,2′-bipyridyl)

A series of copper(II) solvatochromic complexes [Cu(acac)(N^N)(ligand)]BPh4 (acac = acetylacetonato; N^N = 1,10-phenanthoroline (1), 2,2′-bipyridyl (2); ligand = HMPA, pyridine, DMSO, DMF, MeOH, acetone, and MeCN) have been synthesized and their coordination geometries were crystallographically investigated. The solvent-coordinated cations, adopting a five-coordinate square-pyramidal structure, formed head-to-tail dimers via π⋯π interactions. Solid-state absorption studies revealed that their d–d transition energies are correlated with the donor number of the axial ligands. A linear correlation was found between the d–d transition energies and the Cu–O (axial ligands) distances in the solid-state, revealing the role of the coordination environment on the d–d transition energies in the copper(II) solvatochromic complexes.

Graphical abstractThis study has revealed that the d-d transition energies of a series of solvatochromic complexes [Cu(acac)(N^N)(ligand)]BPh4 (acac = Acetylacetonato, N^N = 1,10-Phenanthoroline, 2,2’-Bipyridyl, ligand = HMPA, DMSO, DMF, MeOH, and acetone) are closely correlated with their Cu−O (axial ligands) distances in the solid state, which are further correlated with the donor number of the ligand.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The syntheses and crystal structures of [Cu(acac)(N^N)(ligand)]BPh4 are reported. ► The d–d transition energies are correlated with their Cu–O (axial ligands) distances. ► The d–d transition energies are correlated with the donor number of the ligand.