Intermediate (S = 1) spin state in five-coordinate cobalt(iii): Magnetic properties of N-o-hydroxy-benzamido-meso-tetraphenylporphyrin cobalt(iii), Co(N-NCO(o-O)C6H4-tpp)

Abstract

The crystal structures of paramagnetic N-o-oxido-benzimido-meso-tetraphenylporphyrinato (-κ⁴,N¹,N²,N³,N⁵,κO²)cobalt(III) [Co(N-NCO(o-O)C₆H₄-tpp); 2] (S = 1) and diamagnetic N-o-oxido-benzimido-meso-tetraphenylporphyrinato (-κ⁴,N¹,N²,N³,N⁵,κO²) gallium(III) chloroform·methanol solvate [Ga(N-NCO(o-O)C₆H₄-tpp)·0.5CHCl₃·MeOH; 3·0.5CHCl₃·MeOH] (S = 0) were determined. The coordination sphere around Co(III) in 2 [or Ga(III) in 3·0.5CHCl₃·MeOH] is described as five-coordinate distorted trigonal bipyramid (DTBP) with O(1), N(1) and N(3) [or O(2), N(1), N(3)] lying in the equatorial plane for 2 [or 3·0.5CHCl₃·MeOH]. The magnitude of axial (D) zero-field splitting (ZFS) for the Co(III) (S = 1) in 2 was determined as approximately 107 cm⁻¹ by paramagnetic susceptibility measurements. The compound (2) reacts in donor solvent such as pyridine to form six-coordinate diamagnetic species of the type Co(N-NCO(o-O)C₆H₄-tpp)(py) (4), whose ¹H NMR spectra can be interpreted as for Co(III) in an octahedral environment.