Structural diversity in heteroleptic dipyrrinato copper(II) complexes

Abstract

Synthesis and characterization of the heteroleptic dipyrrinato complexes [Cu₂ (2-pcdpm)₂ (acac)₂] (1), [Cu₂ (2-pcdpm)₂ (hfacac)₂] (2), [Cu₃ (4-OHdpm)₂ (acac)₄] (3), [Cu₃ (4-OHdpm)₂ (hfacac)₄] (4), [Cu₂ (3-OHdpm)(acac)₃] (5), [Cu₂ (3-OHdpm)(hfacac)₃] (6), [Cu(2-OHdpm)(acac)] (7) and [Cu(2-OHdpm)(hfacac)] (8) (acac = acetylacetone; hfacac = hexafluoroacetylacetone; 2-pcdpm = 4-(2-methoxypyridyl)phenyldipyrromethene; 3-pcdpm = 4-(3-methoxypyridyl)phenyldipyrromethene; 4-pcdpm = 4-(4-methoxypyridyl)phenyldipyrromethene; 4-/3-/2-OHdpm = 4-/3-/(2-hydroxyphenyl)dipyrromethene) have been described. The complexes 1–8 have been characterized by elemental analyses, ESI-MS, IR, UV–Vis, EPR and electrochemical (CV and DPV) studies. Electronic absorption spectra of 1–8 clearly suggested that position of the absorption bands depend on the nuclearity and coordination geometry about the copper(II) centres. Structures of 1, 2, 3 and 7 have been determined by X-ray single crystal analyses. The spectral and structural studies revealed that copper(II) in 1 and 2 adopted square pyramidal geometry, whereas in 7 a square planar geometry. On the other hand in trinuclear complex 3 one copper(II) adopted square planar, while other two square pyramidal geometry. In their cyclic voltammograms, 1–6 exhibited an irreversible oxidation and two reduction waves whereas 7 and 8 displayed one oxidation and reduction wave. Variable temperature magnetic susceptibility measurements suggested paramagnetic nature of the complexes 1–3. The X-ray photoelectron spectroscopic (XPS) studies indicated that copper(II) centres in complex 3 are present in two different coordination environments. Room temperature EPR studies on 1–8 (g_|| > g_⊥ > 2.003) suggested a typical d⁹ copper(II) with unpaired electron lying in a d_x2-y2 orbital.