Spacer length dependent architectural diversity in bis-dipyrrin copper(II) complexes

Abstract

A series of copper(ii) complexes (1-9 and 3′) derived from bis-dipyrrin ligands (L1-L9 and L3′) with diverse spacer lengths [-(CH2)n-] have been described. Structural diversities in these complexes have been explicitly established by spectral and structural studies on these and a closely related nickel(ii) complex (3′′). All the ligands and complexes have been thoroughly characterized by spectroscopic studies (ESI-MS, IR, 1H, 13C NMR, UV/vis) and structures of 2, 3′, 3′′, 6, 8 and 9 were determined by X-ray single crystal analyses. It has been unambiguously established that ligands with n ≤ 6 gave heteroleptic binuclear (1-5), while those with n ≥ 7 yielded homoleptic mononuclear (6-9) bis-dipyrrinato complexes. Spectral and structural studies revealed distorted square planar (1-5) and distorted tetrahedral geometries (6-9) about the copper(ii) centre in these complexes which has further been evidenced by EPR and electrochemical studies. Structural differences based on the odd and even number of methylene spacers in these complexes have been supported by DFT studies. A line between the syn- and anti-conformations of the complexes has been drawn on the basis of a limiting spacer length. © The Royal Society of Chemistry.