Synthesis, crystal structures and spectroscopic characterization of Co(II) bis(4,4′-bipyridine) with meso-porphyrins α,β,α,β-tetrakis(o-pivalamidophenyl) porphyrin (α,β,α,β-TpivPP) and tetraphenylporphyrin (TPP)

Abstract

The reaction of the starting materials [ Co II ( Porph )] (Porph = α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrin (TpivPP) and the meso-tetraphenylporphyrin (TPP)) with an excess of 4,4′-bipyridine in chlorobenzene leads to the creation of two cobalt(II) derivatives: [ Co II (α,β,α,β- TpivPP )(4,4′- bpy )2]· C 6 H 5 Cl · C 6 H 14(1) and [ Co II ( TPP )(4,4′- bpy )2]·2 bpy (2). These compounds have been characterized by UV-vis, IR, 1 H NMR and MALDI-TOF spectroscopy. The proton NMR spectra of (1) and (2) clearly indicated that these derivatives are paramagnetic while the UV-vis data confirmed creation of a new six-coordinated or penta-coordinated Co ( II )-meso-porphyrin complexes by displaying red shifted Soret bands. The determined X-ray structures of (1) and (2) show that in the solid state these species are considered as coordination polymers which consist of 1D chains of alternating [ Co II ( Porph )] and 4,4′-bipyridine molecules located at the axial positions of the cobalt(II) coordination sphere. The coordination geometry of Co ( II ) in (1) and (2) is octahedral; the porphyrin (TpivPP or TPP) acts as a tetradentate chelating ligand with four nitrogen atoms from the pyrrole moieties occupying the equatorial positions along the porphyrin core. The N -donor atoms of the 4,4′-bipyridine create the axial ligands. It is noteworthy that for complex (1) the starting porphyrin is the α,α,α,α-TpivPP atropisomer but the final coordination polymer contains the α,β,α,β-TpivPP conformer.