Co-ordination bond properties in phthalocyaninatometal(II) complexes. Part 1. Stereochemistry and bond properties in bis(4-methylpyridine)-phthalocyaninatometal(II)–4-methylpyridine (1/2)(metal = cobalt or iron)

Abstract

A comparison between the vibrational properties and stereochemistry of [Co(pc)(4Me-py)₂] and [Fe(pc)-(4Me-py)₂][pc = phthalocyaninato(2 –), 4Me-py = 4-methylpyridine] is carried out by using far-i.r. spectroscopy and X-ray diffractometry. The crystals of the two complexes, based on the packing of [M(pc)(4Me-py)₂] adducts and solvated 4Me-py molecules, are isostructural and their orthorhombic unit cells (space group Pbca) have the following parameters: M = Co, a= 10.395(1), b= 25.069(3), c= 17.992(2)Å, 1 503 unique observed reflections, final R 0.061; M = Fe, a= 10.315(1), b= 25.006(3), c= 17.876(2)Å; 2 950 unique observed reflections, final R 0.063. All the findings lead to the conclusion that structural results and bond properties are strictly related in these complexes. The vibrational M–N(pc) parameters are much more affected than the corresponding structural parameters by differences in the electronic structures of cobalt and iron. In the case of axial M–N(4Me-py), however, the bond length depends strongly on the metal and its value (2.322 Å for M = Co and 2.040 Å for Fe) is a clear indication of the localization of the unpaired electron in the d_z² orbital of the cobalt complex. The importance of d_π→π*(pc) back donation is shown by the significant difference between the average values of the ‘internal’ and external C–N bond lengths in the macrocycle.